NOTE I.—METEORS.

THERE seem to be three concentric strata of our incumbent atmosphere; in which, or between them, are produced four kinds of meteors; lightning, shooting stars, fire-balls, and northern lights. First, the lower region of air, or that which is dense enough to resist, by the adhesion of its particles, the descent of condensed vapour, or clouds, which may extend from one to three or four miles high. In this region the common lightning is produced from the accumulation or defect of electric matter in those floating fields of vapour, either in respect to each other, or in respect to the earth beneath them, or the dissolved vapour above them, which is constantly varying both with the change of the form of the clouds, which thus evolve a greater or less surface; and also with their ever-changing degree of condensation. As the lightning is thus produced in dense air, it proceeds but a short course, on account of the greater resistance which it encounters, is attended with a loud explosion, and appears with a red light.

2. The second region of the atmosphere I suppose to be that which has too little tenacity to support condensed vapour, or clouds; but which yet contains invisible vapour, or water in aerial solution. This aerial solution of water differs from that dissolved in the matter of heat, as it is supported by its adhesion to the particles of air, and is not precipitated by cold. In this stratum it seems probable that the meteors called shooting stars are pro­duced; and that they consist of electric sparks, or lightning, passing from one region to another of these invisible fields of aero-aqueous solution. The height of these shooting stars has not yet been ascertained by sufficient ob­servation. Dr. Blagden thinks their situation is lower down in the atmos­phere than that of fire-balls, which he conjectures from their swift apparent motion, and ascribes their smallness to the more minute division of the elec­tric matter of which they are supposed to consist, owing to the greater re­sistance of the denser medium through which they pass, than that in which the fire-balls exist. Mr. Brydone observed that the shooting stars appeared [Page 136] to him to be as high in the atmosphere, when he was near the summit of Mount Etna, as they do when observed from the plain. Phil. Trans. vol. LXIII.

As the stratum of air in which shooting stars are supposed to exist, is much rarer than that in which lightning resides, and yet much denser than that in which fire-balls are produced, they will be attracted at a greater distance than the former, and at a less than the latter. From this rarity of the air, so small a sound will be produced by their explosion, as not to reach the lower parts of the atmosphere; their quantity of light, from their greater distance, being small, is never seen through dense air at all, and thence does not appear red, like lightning or fire-balls. There are no apparent clouds to emit or to attract them, because the constituent parts of these aero-aque­ous regions may possess an abundance or deficiency of electric matter, and yet be in perfect reciprocal solution. And, lastly, their apparent train of light is probably owing only to a continuance of their impression on the eye; as when a fire stick is whirled in the dark it gives the appearance of a complete circle of fire: for these white trains of shooting stars quickly va­nish, and do not seem to set any thing on fire in their passage, as seems to happen in the transit of fire-balls.

3. The second region or stratum of air terminates, I suppose, where the twilight ceases to be refracted, that is, where the air is 3000 times rarer than at the surface of the earth and where it seems probable that the com­mon air ends, and is surrounded by an atmosphere of inflammable gas ten­fold rarer than itself. In this region I believe fire-balls sometimes to pass, and at other times the northern lights to exist. One of these fire-balls, or draco volans, was observed by Dr. Pringle, and many others, on Nov. 26, 1758, which was afterwards estimated to have been a mile and a half in circum­ference, to have been about one hundred miles high, and to have moved towards the north with a velocity of near thirty miles in a second of time. This meteor had a real tail many miles long, which threw off sparks in its course, and the whole exploded, with a sound like distant thunder. Phil. Trans. vol. LI.

Dr. Blagden has related the history of another large meteor, or fire-ball, which was seen the 18th August, 1783, with many ingenious observa­tions and conjectures. This was estimated to be between 60 and 70 miles high, and to travel 1000 miles at the rate of about twenty miles in a second. This fire-ball had likewise a real train of light lest behind it in its passage, which varied in colour, and, in some part of its course, gave off sparks or explosions where it had been brightest; and a dusky red streak remained visible perhaps a minute. Phil. Trans. vol. LXXIV.

These fire-balls differ from lightning, and from shooting stars, in many re­markable circumstances; as their very great bulk, being a mile and a half in diameter; their travelling 1000 miles nearly horizontally; their throwing off sparks in their passage; and changing colours from bright blue to dusky red; and leaving a train of fire behind them, continuing about a minute. They differ from the northern lights in not being dissused, but passing from one point of the heavens to another in a defined line; and this in a region [Page 137] above the crepuscular atmosphere, where the air is 3000 times rarer than at the surface of the earth. There has not yet been even a conjecture which can account for these appearances!—One I shall therefore hazard; which, if it does not inform, may amuse the reader.

In the note on l. 123, it was shewn that there is probably a supernatant stratum of inflammable gas or hydrogene, over the common atmosphere; and whose density at the surface where they meet, must be at least ten times less than that upon which it swims; like chemical ether floating upon water, and perhaps without any real contact. 1. In this region, where the aerial atmosphere terminates, and the inflammable one begins, the quantity of tenacity or resistance must be almost inconceivable; in which a ball of elec­tricity might pass 1000 miles with greater ease than through a thousandth part of an inch of glass. 2. Such a ball of electricity passing between in­flammable and common air, would set fire to them in a line as it passed along; which would differ in colour according to the greater proportionate commixture of the two airs; and from the same cause there might occur greater degrees of inflammation, or branches of fire, in some parts of its course.

As these fire-balls travel in a defined line, it is pretty evident from the known laws of electricity, that they must be attracted; and as they are a mile or more in diameter, they must be emitted from a large surface of electric matter; because large nobs give larger sparks, less diffused, and more brightly luminous, than less ones or points, and resist more forcibly the emission of the electric matter. What is there in nature can attract them at so great a distance as 1000 miles, and so forceibly as to detach an electric spark of a mile diameter? Can volcanos, at the time of their eruptions, have this effect, as they are generally attended with lightning? Future observa­tions must discover these secret operations of nature! As a stream of com­mon air is carried along with the passage of electric aura from one body to another, it is easy to conceive, that the common air and the inflamma­ble air between which the fire-ball is supposed to pass, will be partially in­termixed by being thus agitated, and so far as it becomes intermixed it will take fire, and produce the linear flame and branching sparks above described. In this circumstance of their being attracted, and thence passing in a defined line, the fire-balls seem to differ from the coruscations of the aurora borealis, or northern lights, which probably take place in the same region of the at­mosphere; where the common air exists in extreme tenuity, and is covered by a still rarer sphere of inflammable gas, ten times lighter than itself.

As the electric streams, which constitute these northern lights, seem to be repelled or radiated from an accumulation of that fluid in the north, and not attracted like the fire-balls; this accounts for the diffusion of their light, as well as the silence of their passage; while their variety of colours, and the permanency of them, and even the breadth of them in different places, may depend on their sitting on fire the mixture of inflammable and common air through which they pass; as seems to happen in the transit of the fire-balls.

It was observed by Dr. Priestley, that the electric shock taken through in­flammable air was red, in common air it is blueish; to these circumstances [Page 138] perhaps some of the colours of the northern lights may bear analogy; though the density of the medium through which light is seen must principally vary its colour, as is well explained by Mr. Morgan. Phil. Trans. Vol. LXXV. Hence lightning is red when seen through a dark cloud, or near the horizon; because the more refrangible rays cannot permeate so dense a medium. But the shooting stars consist of white light, as they are generally seen on clear nights, and nearly [...]; in other situations their light is probably too faint to come to us. But as in some remarkable appearances of the northern lights, as in March, 1716, all the prismatic colours were seen quickly to suc­ceed each other, these appear to have been owing to real combustion; as the density of the interposed medium could not be supposed to change so fre­quently; and therefore these colours must have been owing to different de­grees of heat, according to Mr. Morgan's theory of combustion. In Smith's Optics, p. 69. the prismatic colours, and optical deceptions of the northern lights, are described by Mr. Cotes.

The Torricellian vacuum, if perfectly free from air, is said, by Mr. Mor­gan and others, to be a perfect non-conductor. This circumstance there­fore would preclude the electric streams from rising above the atmosphere. But as Mr. Morgan did not try to pass an electric shock through a vacuum, and as air, or something containing air, surrounding the transit of electricity, may be necessary to the production of light, the conclusion may perhaps still be dubious. If, however, the streams of the northern lights were supposed to rise above our atmosphere, they would only be visible at each extremity of their course; where they emerge from, or are again immerged into the at­mosphere; but not in their journey through the vacuum; for the absence of electric light in a vacuum is sufficiently proved by the common experiment of shaking a barometer in the dark; the electricity, produced by the friction of the mercury in the glass at its top, is luminous if the barometer has a little air in it; but there is no light if the vacuum be complete.

The aurora borealis, or northern dawn, is very ingeniously accounted for by Dr. Franklin, on principles of electricity. He premises the following elec­tric phenomena: 1. That all new-fallen snow has much positive electricity standing on its surface. 2. That about twelve degrees of latitude round the poles are covered with a crust of eternal ice, which is impervious to the elec­tric fluid. 3. That the dense part of the atmosphere rises but a few miles high; and that in the rarer parts of it the electric fluid will pass to almost any distance.

Hence he supposes there must be a great accumulation of positive electric matter on the fresh-fallen snow in the polar regions; which, not being able to pass through the crust of ice into the earth, must rise into the rare air of the upper parts of our atmosphere, which will the least resist its passage; and passing towards the equator, descend again into the denser atmosphere, and thence into the earth in silent streams. And that many of the appearances attending these lights are optical deceptions, owing to the situation of the eye that beholds them; which makes all ascending parallel lines appear to converge to a point.

The idea, above explained in note on l. 123, of the existence of a sphere of [Page 139] inflammable gas over the aerial atmosphere, would much favour this theory of Dr. Franklin; because in that case the dense aerial atmosphere would rise a much less height in the polar regions, diminishing almost to nothing at the pole itself; and thus give an easier passage to the ascent of the electric fluid. And from the great difference in the specific gravity of the two airs, and the velocity of the earth's rotation, there must be a place between the poles and the equator, where the superior atmosphere of inflammable gas would termi­nate; which would account for these streams of the aurora borealis not appear­ing near the equator; add to this, that it is probable the electric fluid may be heavier than the magnetic one; and will thence, by the rotation of the earth's surface, ascend over the magnetic one by its centrifugal force; and may thus be induced to rise through the thin stratum of aerial atmosphere over the poles. See note on Canto II. l. 193. I shall have occasion again to mention this great accumulation of inflammable air over the poles; and to conjecture that these northern lights may be produced by the union of inflammable with common air, without the assistance of the electric spark to throw them into combustion.

The antiquity of the appearance of northern lights has been doubted; as none were recorded in our annals since the remarkable one on Nov. 14, 1574. till another remarkable one on March 6, 1716, and the three following nights, which was seen at the same time in Ireland, Russia, and Poland, extending near 30 degrees of longitude, and from about the 50th degree of latitude over almost all the north of Europe. There is, however, reason to believe them of remote antiquity, though inaccurately described; thus the fol­lowing curious passage from the book of Maccabees (B. II. c. v.) is such a description of them, as might probably be given by an ignorant and alarmed people. "Through all the city, for the space of almost forty days, there were seen horsemen running in the air, in cloth of gold, and armed with lances, like a band of soldiers; and troops of horsemen in array encountering and running one against another, with shaking of shields and multitude of pikes, and drawing of swords, and casting of darts, and glittering of golden ornaments and harness."

NOTE II.—PRIMARY COLOURS.

THE manner in which the rainbow is produced, was, in some measure, understood before Sir Isaac Newton had discovered his theory of colours. The first person who expressly shewed the rainbow to be formed by the reflection of the sun-beams from drops of falling rain, was Antonio de Do­minis. This was afterwards more fully and distinctly explained by Des Cartes. But what caused the diversity of its colours was not then under­stood; it was reserved for the immortal Newton to discover that the rays of light consisted of seven combined colours of different refrangibility, which [Page 140] could be separated at pleasure by a wedge of glass. Pemberton's View of Newton.

Sir Isaac Newton discovered that the prismatic spectrum was composed of seven colours, in the following proportions; violet 80, indigo 40, blue 60, green 60, yellow 48, orange 27, red 45. If all these colours be painted on a circular card, in the proportion above mentioned, and the card be rapidly whirled on its centre, they produce in the eye the sensation of white. And any one of these colours may be imitated by painting a card with the two colours which are contiguous to it, in the same proportions as in the spec­trum, and whirling them in the same manner.

My ingenious friend, Mr. Galton, of Birmingham, ascertained, in this manner, by a set of experiments, the following propositions; the truth of which he had preconceived from the above data.

1. Any colour [...] the prismatic spectrum may be imitated by a mixture of the two colours contiguous to it.

2. If any three successive colours in the prismatic spectrum are mixed, they compose only the second or middlemost colour.

3. If any four successive colours in the prismatic spectrum be mixed, a tint similar to a mixture of the second and third colours will be produced, but not precisely the same, because they are not in the same proportion.

4. If, beginning with any colour in the circular spectrum, you take of the second colour a quantity equal to the first, second, and third; and add to that the fifth colour, equal in quantity to the fourth, fifth, and sixth; and with these combine the seventh colour in the proportion it exists in the spectrum, white will be produced. Because the first, second, and third, compose only the second; and the fourth, fifth, and sixth, compose only the fifth; there­fore, if the seventh be added, the same effect is produced as if all the seven were employed.

5. Beginning with any colour in the circular spectrum, if you take a tint composed of a certain proportion of the second and third, (equal in quantity to the first, second, third, and fourth,) and add to this the sixth colour, equal in quantity to the fifth, sixth, and seventh, white will be produced.

From these curious experiments of Mr. Galton, many phenomena in the chemical changes of colours may probably become better understood; espe­cially if, as I suppose, the same theory must apply to transmitted colours, as to reflected ones. Thus it is well known, that if the glass of manganese, which is a tint probably composed of violet and indigo, be mixed in a cer­tain proportion with the glass of lead, which is yellow, that the mixture be­comes transparent. Now, from Mr. Galton's experiments, it appears, that in reflected colours such a mixture would produce white, that is, the same as if all the colours were reflected. And, therefore, in transmitted colours the same circumstances must produce transparency, that is, the same as if all the colours were transmitted. For the particles which constitute the glass of manganese will transmit red, violet, indigo, and blue; and those of the glass of lead will transmit orange, yellow, and green; hence all the pri­mary colours, by a mixture of these glasses, become transmitted, that is, the glass becomes transparent.

[Page 141] Mr. Galton has further observed, that five successive prismatic colours may be combined in such proportions as to produce but one colour, a cir­cumstance which might be of consequence in the art of painting. For if you begin at any part of the circular spectrum above described, and take the first, second, and third colours, in the proportions in which they exist in the spectrum; these will compose only the second colour, equal in quantity to the first, second, and third; add to these the third, fourth and fifth, in the proportion they exist in the spectrum, and these will produce the fourth colour, equal in quantity to the third, fourth, and fifth. Conse­quently this is precisely the same thing as mixing the second and fourth co­lours only; which mixture would only produce the third colour. There­fore, if you combine the first, second, fourth and fifth, in the proportions in which they exist in the spectrum, with double the quantity of the third colour, this third colour will be produced. It is probable that many of the unexpected changes in mixing colours on a painter's pallet, as well as in more fluid chemical mixtures, may depend on these principles rather than on a new arrangement or combination of their minute particles.

Mr. Galton further observes, that white may universally be produced by the combination of one prismatic colour, and a tint intermediate to two others. Which tint may be distinguished by a name compounded of the two colours to which it is intermediate. Thus white is produced by a mix­ture of red with blue-green. Of orange with indigo-blue. Of yellow with violet-indigo. Of green with red-violet. Of blue with orange-red. Of indigo with yellow-orange. Of violet with green-yellow. Which, he fur­ther remarks, exactly coincides with the theory and facts mentioned by Dr. Robert Darwin, of Shrewsbury, in his account of ocular spectra; who has shewn, that when one of these contrasted colours has been long viewed, a spectrum, or appearance of the other, becomes visible in the fatigued eye. Phil. Trans. vol. LXXVI. for the year 1786.

These experiments of Mr. Galton might much assist the copper-plate prin­ters of callicoes and papers in colours, as three colours, or more, might be produced by two copper-plates. Thus, suppose some yellow figures were put on by the first plate, and upon some parts of these yellow figures, and on other parts of the ground, blue was laid on by another copper-plate. The three colours of yellow, blue, and green, might be produced, as green leaves with yellow and blue flowers.

NOTE III.—COLOURED CLOUDS.

THE rays from the rising and setting sun are refracted by our spherical atmosphere; hence the most refrangible rays, as the violet, indigo, and blue, are reflected in greater quantities from the morning and evening skies; and [Page 142] the least refrangible ones, as red and orange, are last seen about the setting sun. Hence Mr. Beguelin observed, that the shadow of his finger on his pocket-book was much bluer in the morning and evening, when the shadow was about eight times as long as the body from which it was projected. Mr. Melville observes, that the blue rays being more refrangible, are bent down in the evenings by our atmosphere, while the red and orange, being less refrangible, continue to pass on, and tinge the morning and evening clouds with their colours. See Priestley's History of Light and Colours, p. 440. But as the particles of air, like those of water, are themselves blue, a blue shadow may be seen at all times of the day, though much more beautifully in the mornings and evenings, or by means of a candle in the middle of the day. For if a shadow on a piece of white paper is produced by placing your finger between the paper and a candle in the day light, the shadow will appear very blue; the yellow light of the candle upon the other parts of the paper apparently deepens the blue by its contrast, these colours being opposite to each other, as explained in note II.

Colours are produced from clouds or mists by refraction, as well as by reflection. In riding in the night over an unequal country, I observed a very beautiful coloured halo round the moon, whenever I was covered with a few feet of mist, as I ascended from the vallies, which ceased to appear when I rose above the mist. This I suppose was owing to the thinness of the stratum of mist in which I was immersed; had it been thicker, the co­lours refracted by the small drops, of which a fog consists, would not have passed through it down to my eye.

There is a bright spot seen on the cornea of the eye, when we face a win­dow, which is much attended to by portrait-painters; this is the light re­flected from the spherical surface of the polished cornea, and brought to a focus; if the observer is placed in this focus, he sees the image of the win­dow; if he is placed before or behind the focus, he only sees a luminous spot, which is more luminous, and of less extent, the nearer he approaches to the focus. The luminous appearance of the eyes of animals in the dusky corners of a room, or in holes in the earth, may arise, in some instances, from the same principle; viz. the reflection of the light from the spherical cornea, which will be coloured red or blue, in some degree, by the morn­ing, evening, or meridian light, or by the objects from which that light is previously reflected. In the cavern at Colebrook Dale, where the mineral far exsudes, the eyes of the horse which was drawing a cart from within towards the mouth of it, appeared like two balls of phosphorus, when he was above 100 yards off, and for a long time before any other part of the animal was visible. In this case I suspect the luminous appearance to have been owing to the light which had entered the eye, being reflected from the back surface of the vitreous humor, and thence emerging again in pa­rallel rays from the animal's eye, as it does from the back surface of the drops of the rainbow, and from the water-drops which lie, perhaps without contact, on cabbage-leaves, and have the brilliancy of quick-silver. This accounts for this luminous appearance being best seen in those animals which have large apertures in their iris, as in cats and horses, and is the only part [Page 143] visible in obscure places, because this is a better reflecting surface than any other part of the animal. If any of these emergent rays from the animal's eye can be supposed to have been reflected from the choroid coat, through the semi-transparent retina, this would account for the coloured glare of the eyes of dogs, or cats, and rabits, in dark corners.

NOTE IV.—COMETS.

THERE have been many theories invented to account for the tails of co­mets. Sir Isaac Newton thinks that they consist of rare vapours raised from the nucleus of the comet, and so rarefied by the sun's heat as to have their general gravitation diminished, and that they, in consequence, ascend oppo­site to the sun, and from thence reflect the rays of light. Dr. Halley com­pares the light of the tails of comets to the streams of the aurora borealis, and other electric effluvia. Phil. Trans. No. 347.

Dr. Hamilton observes, that the light of small stars is seen undiminished through both the light of the tails of comets, and of the aurora borealis, and has farther illustrated their electric analogy; and adds, that the tails of co­mets consist of a lucid self-shining substance, which has not the power of re­fracting or reflecting the rays of light. Essays.

The tail of the comet of 1744, at one time appeared to extend above 16 degrees from its body, and must have thence been above twenty-three mil­lions of miles long. And the comet of 1680, according to the calculations of Dr. Halley, on Nov. the 11th, was not above one semi-diameter of the earth, or less than 4000 miles to the northward of the way of the earth; at which time had the earth been in that part of its orbit, what might have been the consequence! No one would probably have survived to have re­gistered the tremendous effects.

The comet of 1531, 1607, and 1682, having returned in the year 1759, according to Dr. Halley's prediction in the Phil. Trans. for 1705, there seems no reason to doubt that all the other comets will return after their proper periods. Astronomers have in general acquiesced in the conjecture of Dr. Halley, that the comets of 1532, and 1661, are one and the same comet, from the similarity of the elements of their orbits, and were, there­fore, induced to expect its return to its perihelium in 1789. As this comet is liable to be disturbed, in its ascent from the sun, by the planets Jupiter and Saturn, Dr. Maskelyne expected its return to its perihelium in the be­ginning of the year 1789, or the latter end of the year 1788, and certainly some time before the 27th of April, 1789; which prediction has not been fulfilled. Phil. Trans. vol. LXXVI.

As the comets are small masses of matter, and pass in their perihelion very near the sun, and become invisible to us, on these accounts, in a short [Page 144] space of time, their number has not yet been ascertained, and will pro­bably increase with the improvement of our telescopes. M. Bode has gi­ven a table of 72 comets, whose orbits are already calculated; of these 60 pass within the earth's orbit, and only twelve without it; and most of them appear between the orbits of Venus and Mercury, or nearly midway between the sun and earth; from whence, and from the planes of their or­bits being inclined to that of the earth and other planets in all possible an­gles, they are believed to be less liable to interfere with, or injure each other. M. Bode afterwards inquires into the nearest approach it is possible for each of the known comets to make towards the earth's orbit. He finds that only three of them can come within a distance equal to two or three times the distance of the moon from it; and then adds the great improba­bility, that the earth should be in that dangerous point of its orbit, at the instant when a comet, which may have been absent some centuries, passes so rapidly past it. Histoire de I' Academ. Royal. Berlin. 1792.

NOTE V.—SUN's RAYS.

THE dispute among philosophers about phlogiston is not concerning the existence of an inflammable principle, but rather whether there be one or more inflammable principles. The disciples of Stahl, which till lately in­cluded the whole chemical world, believed in the identity of phlogiston in all bodies which would flame or calcine. The disciples of Lavoisier pay homage to a plurality of phlogistons, under the various names of charcoal, sulphur, metals, &c. Whatever will unite with pure air, and thence compose an acid, is esteemed, in this ingenious theory, to be a different kind of phlogistic or inflammable body. At the same time there remains a doubt whether these inflammable bodies, as metals, sulphur, charcoal, &c. may not be compounded of the same phlogiston along with some other material yet undiscovered, and thus an unity of phlogiston exist, as in the theory of Stahl, though very dif­ferently applied in the explication of chemical phenomena.

Some modern philosophers are of opinion, that the sun is the great fountain from which the earth and other planets derive all the phlogiston which they possess; and that this is formed by the combination of the solar rays with all opake bodies, but particularly with the leaves of vegetables, which they sup­pose to be organs adapted to absorb them. And that as animals receive their nourishment from vegetables, they also obtain, in a secondary manner, their phlogiston from the sun. And lastly, as great masses of the mineral kingdom, which have been found in the thin crust of the earth which human labour has penetrated, have evidently been formed from the recrements of animal and vegetable bodies, these also are supposed thus to have derived their phlogiston from the sun.

Another opinion concerning the sun's rays is, that they are not luminous [Page 145] till they arrive at our atmosphere; and that there uniting with some part of the air, they produce combustion, and light is emitted; and that an ethereal acid, yet undiscovered, is formed from this combustion.

The more probable opinion is, perhaps, that the sun is a phlogistic mass of matter, whose surface is in a state of combustion, which, like other burning bodies, emits light, with immense velocity, in all directions; that these rays of light act upon all opake bodies, and, combining with them, either displace or produce their elementary heat, and become chemically combined with the phlogistic part of them; for light is given out when phlogistic bo­dies unite with the oxygenous principle of the air, as in combustion, or in the reduction of metallic calxes; thus in presenting to the flame of a candle a letter-wafer (if it be coloured with red-lead) at the time the red-lead be­comes a metallic drop, a flash of light is perceived. Dr. Alexander Wilson very ingeniously endeavours to prove, that the sun is only in a state of com­bustion on its surface, and that the dark spots seen on the disk are excava­tions or caverns through the luminous crust, some of which are 4000 miles in diameter. Phil. Trans. 1774. Of this I shall have occasion to speak again.

NOTE VI.—CENTRAL FIRES.

M. DE MAIRAN, in a paper published in the Histoire de I' Academic de Sciences, 1765, has endeavoured to shew, that the earth receives but a small part of the heat which it possesses, from the sun's rays, but it is prin­cipally heated by fires within itself. He thinks the sun is the cause of the vicissitudes of our seasons of summer and winter, by a very small quantity of heat in addition to that already residing in the earth, which, by emana­tions from the centre to the circumference, renders the surface habitable, and without which, though the sun was constantly to illuminate two thirds of the globe at once, with a heat equal to that at the equator, it would soon become a mass of solid ice. His reasonings and calculations on this subject are too long and too intricate to be inserted here, but are equally curious and ingenious, and carry much conviction along with them.

The opinion that the centre of the earth consists of a large mass of burn­ing lava, has been espoused by Boyle, Boerhaave, and many other philo­sophers. Some of whom, considering its supposed effects on vegetation and the formation of minerals, have called it a second sun. There are many argu­ments in support of this opinion. 1. Because the power of the sun does not extend much beyond ten feet deep into the earth, all below being, in winter and summer, always of the same degree of heat, viz. 48, which being much warmer than the mildest frost, is supposed to be sustained by some in­ternal distant fire. Add to this, however, that from experiments made some [Page 146] years ago by Dr. Franklin, the spring-water at Philadelphia appeared to be of 52 of heat, which seems farther to confirm this opinion, since the climates in North-America are supposed to be colder than those of Europe under similar degrees of latitude. 2. M. De Luc, in going 1359 feet perpendicular into the mines of Hartz, on July the 5th, 1778, on a very fine day, found the air at the bottom a little warmer than at the top of the shaft. Phil. Trans. vol. LXIX. p. 488. In the mines in Hungary, which are 500 cu­bits deep, the heat becomes very troublesome when the miners get below 480 feet depth. Morinus de L [...]cis subter. p. 131. But as some other deep mines, as mentioned by Mr. Kirwan, are said to possess but the common heat of the earth; and as the crust of the globe, thus penetrated by human labour, is so thin compared with the whole, no certain deduction can be made from these facts on either side of the question. 3. The warm-springs in many parts of the earth, at great distance from any volcanos, seem to originate from the condensation of vapours arising from water which is boiled by sub­terraneous fires, and cooled again in their passage through a certain length of the colder soil; for the theory of chemical solution will not explain the equality of their heat at all seasons, and through so many centuries. See note on Fucus, in vol. II. See a letter on this subject in Mr. Pilkinton's View of Derbyshire, from Dr. Darwin. 4. From the situations of volcanos which are always found upon the summit of the highest mountains. For as these mountains have been lifted up, and lose several of their uppermost strata as they rise, the lowest strata of the earth yet known appear at the tops of the highest hills; and the beds of the volcanos upon these hills must, in consequence, belong to the lowest strata of the earth, consisting, perhaps, of granite or basaltes, which were produced before the existence of animal or vegetable bodies, and might constitute the original nucleus of the earth, which I have supposed to have been projected from the sun; hence the vol­canos themselves appear to be spiracula, or chimneys, belonging to great cen­tral fires. It is probably owing to the escape of the elastic vapours from these spiracula, that the modern earthquakes are of such small extent com­pared with those of remote antiquity, of which the vestiges remain all over the globe. 5. The great size and height of the continents, and the great size and depth of the South-sea, Atlantic, and other oceans, evince that the first earthquakes, which produce [...] these immense changes in the globe, must have been occasioned by central fires. 6. The very distant and expeditious communication of the shocks of some great earthquakes. The earthquake at Lisbon, in 1755, was perceived in Scotland, in the Peak of Derbyshire, and in many other distant parts of Europe. The percussions of it travelled with about the velocity of sound, viz. about thirteen miles in a minute. The earthquake in 1693 extended 2600 leagues. (Goldsmith's History.) These phenomena are easily explained if the central parts of the earth con­sist of a fluid lava, as a percussion on one part of such a fluid mass would be felt on other parts of its confining vault, like a stroke on a fluid contained in a bladder, which, however gentle on one side, is perceptible to the hand placed on the other; and the velocity with which such a concussion would travel, would be that of sound, or thirteen miles in a minute. For further [Page 147] information on this part of the subject, the reader is referred to Mr. Michel's excellent treatise on earthquakes in the Phil. Trans. vol. LI. 7. That there is a cavity at the centre of the earth is made probable by the late experi­ments on the attraction of mountains, by Mr. Maskelyne, who supposed, from other considerations, that the density of the earth near the surface should be five times less than its mean density. Phil. Trans. vol. LX [...]. p. 498. But found from the attraction of the mountain Schehallien, [...] probable, the mean density of the earth is but double that of the hill. [...]. p. 532. Hence, if the first supposition be well founded, there would appear to be a cavity at the centre of considerable magnitude, from whence the immense beds and mountains of lava, toadstone, basaltes, granite, &c. have been protruded. 8. The variation of the compass can only be accounted for by supposing the central parts of the earth to consist of a fluid mass, and that part of this fluid is iron, which, requiring a greater degree of heat to bring it into fusion than glass or other metals, remains a solid, and the vis inertae of this fluid mass, with the iron in it, occasions it to perform fewer revolutions than the crust of solid earth over it, and thus it is gradu­ally left behind, and the place where the floating iron resides is pointed to by the direct or retrograde motions of the magnetic needle. This seems to have been nearly the opinion of Dr. Halley and Mr. Euler.

NOTE VII.—ELEMENTARY HEAT.

A CERTAIN quantity of heat seems to be combined with all bodies, be­sides the sensible quantity which gravitates like the electric fluid amongst them. This combined heat, or latent heat, of Dr. Black, when set at li­berty of fermentation, inflammation, crystallization, freezing, or other che­mical attractions producing new combination, passes as a fluid element into the surrounding bodies. And by thawing, diffusion of neutral salts in wa­ter, melting, and other chemical solutions, a portion of heat is attracted from the bodies in vicinity, and enters into or becomes combined with the new solutions.

Hence a combination of metals with acids, of essential oils and acids, of al­cohol and water, of acids and water, give out heat; whilst a solution of snow in water or in acids, and of neutral salts in water, attract heat from the surrounding bodies. So the acid of nitre mixed with oil of cloves unites with it, and produces a most violent flame; the same acid of nitre poured on snow instantly dissolves it, and produces the greatest degree of cold yet known, by which, at Petersburgh, quick-silver was first frozen in 1760.

Water may be cooled below 32 degrees without being frozen, if it be placed on a solid floor, and secured from agitation; but when thus cooled below the freezing point, the least agitation turns part of it suddenly into ice, and [Page 148] when this sudden freezing takes place, a thermometer placed in it instantly ri­ses, as some heat is given out in the act of congelation, and the ice is thus left with the same sensible degree of cold as the water had possessed before it was agitated, but is, nevertheless, now combined with less latent heat.

A cubic inch of water thus cooled down to 32 degrees, mixed with an equal quantity of boiling water at 212 degrees, will cool it to the middle number between these two, or to 132. But a cubic inch of ice, whose sen­sible cold also is but 32▪ mixed with an equal quantity of boiling water, will cool it six times as much as the cubic inch of cold water above-men­tioned, as the ice not only gains its share of the sensible or gravitating heat of the boiling water, but attracts to itself also, and combines with the quan­tity of latent heat which it had lost at the time of its congelation.

So boiling water will acquire but 212 degrees of heat under the common pressure of the atmosphere, but the steam raised from it by its expansion, or by its solution in the atmosphere, combines with and carries away a prodi­gious quantity of heat, which it again parts with on its condensation, as is seen in common distillation, where the large quantity of water in the worm tub is so soon heated. Hence the evaporation of ether on a thermometer soon sinks the mercury below freezing▪ and hence a warmth of the air in winter frequently succeeds a shower.

When the matter of heat, or calorique, is set at liberty from its combina­tions, as by inflammation, it passes into the surrounding bodies, which pos­sess different capacities of acquiring their share of the loose or sensible heat; thus a pint measure of cold water at 48 degrees, mixed with a pint of boil­ing water at 212 degrees, will cool it to the degree between these two numbers, or to 154 degrees, but it requires two pint measures of quick-silver at 48 degrees of heat, to cool one pint of water as above. These and other curious experiment [...] are adduced by Dr. Black, to evince the existence of combined or latent heat in bodies, as has been explained by some of his pu­pils, and well illustrated by Dr. Crawford. The world has long been in expectation of an account of his discoveries on this subject by the celebrated author himself.

As this doctrine of elementary heat in its fluid and combined state is not yet universally received, I shall here add two arguments in support of it, drawn from different sources, viz. from the heat given out or absorbed by the mechanical condensation or expansion of the air, and perhaps of other bodies, and from the analogy of the various phenomena of heat with those of electricity.

I. It a thermometer be placed in the receiver of an air-pump, and the air hastily exhausted, the thermometer will sink some degrees, and the glass be­come steamy: the same occurs in hastily admitting a part of the air again. This I suppose to be produced by the expansion of part of the air, both dur­ing the exhaustion and re-admission of it; and that the air so expanded be­comes capable of attracting from the bodies in its vicinity a part of their heat, hence the vapours contained in it, and the glass receiver, are for a time colder, and the steam is precipitated. That the air thus parts with its moisture from the cold occasioned [...] its rarefaction, and not simply by the [Page 149] rarefaction itself, is evident, because, in a minute or two, the same rare­fied air will again take up the dew deposited on the receiver; and because water will evaporate sooner in rare than in dense air.

There is a curious phenomenon, similar to this, observed in the fountain of Hiero, constructed on a large scale at the Chemnicensian mines in Hungary. In this machine, the air in a large vessel is compressed by a column of wa­ter 260 feet high, a stop-cock is then opened, and as the air issues out with great vehemence, and thus becomes immediately greatly expanded, so much cold is produced, that the moisture from this stream of air is precipitated in the form of snow, and ice is formed, adhering to the nosel of the cock. This remarkable circumstance is described at large, with a plate of the ma­chine, in Phil. Trans. vol. LII. for 1761.

The following experiment is related by Dr. Darwin, in the Phil. Trans. vol. LXXVIII. Having charged an air-gun as forcibly as he well could, the air-cell and syringe became exceedingly hot, much more so than could be ascribed to the friction in working it; it was then left about half an hour to cool down the temperature of the air, and a thermometer having been previously fixed against a wall, the air was discharged in a continual stream on its bulb, and it sunk many degrees. From these three experi­ments of the steam in the exhausted receiver being deposited and re-absorb­ed, when a part of the air is exhausted or re-admitted, and the snow pro­duced by the fountain of Hiero, and the extraordinary heat given out in charging, and the cold produced in discharging an air-gun, there is reason to conclude, that when air is mechanically compressed, the elementary fluid heat is pressed out of it, and that when it is mechanically expanded the same fluid heat is re-absorbed from the common mass.

It is probable all other bodies as well as air attract heat from their neigh­bours when they are mechanically expanded, and give it out when they are mechanically condensed. Thus when a vibration of the particles of hard bodies is excited by friction or by percussion, these particles mutually recede from and approach each other reciprocally; at the times of their recession from each other, the body becomes enlarged in bulk, and is then in a con­dition to attract heat from those in its vicinity with great and sudden power, at the times of their approach to each other this heat is again given out; but the bodies in contact having in the mean while received the heat they had thus lost, from other bodies behind them, do not so suddenly or so sor­cibly re-absorb the heat again from the body in vibration; hence it remains on its surface like the electric fluid on a rubbed glass globe, and for the same reason▪ because there is no good conductor to take it up again. Hence at every vibration more and more heat is acquired, and stands loose upon the surface, as in filing metals, or rubbing glass tubes, and thus a smith, with a few strokes on a nail on his anvil, can make it hot enough to light a brim­stone match; and hence in striking flint and steel together, heat enough is produced to vitrify the parts thus strucken off, the quantity of which heat is again probably increased by the new chemical combination.

II. The analogy between the phenomena of the electric fluid and of heat, furnishes another argument in support of the existence of heat as a gravitat­ing [Page 150] fluid. 1. They are both accumulated by friction on the excited body. 2. They are propagated easily or with difficulty along the same classes of bodies; with ease by metals, with less ease by water, and with difficulty by resins, bees-wax, silk, air, and glass. Thus glass canes, or canes of sealing­wax, may be melted by a blow-pipe, or a candle, within a quarter of an inch of the fingers which hold them, without any inconvenient heat, while a pin, or other metallic substance, applied to the flame of a candle, so rea­dily conducts the heat as immediately to burn the fingers. Hence clothes of silk keep the body warmer than clothes of linen of equal thickness, by confining the heat upon the body. And hence plains are so much warmer than the summits of mountains, by the greater density of the air confining the acquired heat upon them. 3. They both give out light in their passage through air, perhaps not in their passage through a vacuum. 4. They both of them fuse or vitrify metals. 5. Bodies, after being electrized, if they are mechanically extended, will receive a greater quantity of electricity, as in Dr. Franklin's experiment of the chain in the tankard; the same seems true in respect to heat, as explained above. 6. Both heat and electricity con­tribute to suspend steam in the atmosphere, by producing or increasing the repulsion of its particles. 7. They both gravitate, when they have been accumulated, till they find their equilibrium.

If we add to the above the many chemical experiments which receive an easy and elegant explanation from the supposed matter of heat, as employed in the works of Bergman and Lavoisier, I think we may reasonably allow of its existence as an element, occasionally combined with other bodies, and oc­casionally existing as a fluid, like the electric fluid gravitating amongst them, and that hence it may be propagated from the central fires of the earth to the whole mass, and contribute to preserve the mean heat of the earth, which, in this country, is about 48 degrees, but variable from the greater or less effect of the sun's heat in different climates, so well explained in Mr. Kirwan's Treatise on the temperature of different latitudes. 1787. Elmsly. London.

NOTE VIII.—MEMNON's LYRE.

THE gigantic statue of Memnon, in his temple at Thebes, had a lyre in his hands, which, many credible writers assure us, founded when the rising sun shone upon it. Some philosophers have supposed that the sun's light possesses a mechanical impulse, and that the founds above-mentioned might be thence produced. Mr. Michel constructed a very tender horizontal ba­lance, as related by Dr. Priestley in his history of light and colours, for this purpose, but some experiments, with this balance, which I saw made by the late Dr. Powel, who threw the focus of a large reflector on one extremity [Page 151] of it, were not conclusive either way, as the copper leaf of the balance ap­proached in one experiment and receded in another.

There are, however, methods by which either a rotative or alternating motion may be produced by very moderate degrees of heat. If a straight glass tube, such as are used for barometers, be suspended horizontally before a fire, like a roasting spit, it will revolve by intervals; for as glass is a bad conductor of heat, the side next the fire becomes heated sooner than the op­posite side, and the tube becomes bent into a bow, with the external part of the curve towards the fire; this curve then falls down, and produces a fourth part of a revolution of the glass tube, which thus revolves with intermediate pauses.

Another alternating motion I have seen produced by suspending a glass tube about eight inches long, with bulbs at each end, on a centre like a scale­beam. This curious machine is filled about one third part with purest spirit of wine, the other two thirds being a vacuum, and is called a pulse-glass: if it be placed on a box before the fire, so that either bulb, as it rises, may become shaded from the fire, and exposed to it when it descends, an alter­nate libration of it is produced. For spirit of wine in vacuo emits steam by a very small degree of heat, and this steam forces the spirit beneath it up into the upper bulb, which therefore descends. It is probable such a ma­chine, on a larger scale, might be of use to open the doors or windows of hot­houses or melon-frames, when the air within them should become too much heated, or might be employed in more important mechanical purposes.

On travelling through a hot summer's day in a chaise, with a box co­vered with leather on the fore-axle-tree, I observed, as the sun shone upon the black leather, the box began to open its lid, which, at noon, rose above a foot, and could not, without great force, be pressed down; and which gradually closed again as the sun declined in the evening. This, I suppose▪ might with still greater facility be applied to the purpose of opening melon­frames, or the sashes of hot-houses.

The statue of Memnon was overthrown and sawed in two by Cambyses, to discover its internal structure, and is said still to exist. See Savery's Let­ters on Egypt. The truncated statue is said, for many centuries, to have saluted the rising sun with cheerful tones, and the setting sun with melan­choly ones.

NOTE IX.—LUMINOUS INSECTS.

THERE are eighteen species of Lampyris, or glow-worm, according to Linnaeus, some of which are found in almost every part of the world. In many of the species the females have no wings, and are supposed to be discovered by the winged males by their shining in the night. They become much more lucid when they put themselves in motion, which would seem to in­dicate [Page 152] that their light is owing to their respiration; in which process it is probable phosphoric acid is produced by the combination of vital air with some part of the blood, and that light is given out through their transparent bodies, by this slow internal combustion.

There is a fire-fly, of the beetle kind, described in the Dict. Raisonné, un­der the name of Acudia, which is said to be two inches long, and inhabits the West-Indies and South-America; the natives use them instead of candles, putting from one to three of them under a glass. Madam Merian says, that at Surinam the light of this fly is so great, that she saw sufficiently well by one of them to paint and finish one of the figures of them in her work on insects. The largest and oldest of them are said to become four inches long, and to shine like a shooting star as they fly, and are thence called Lan­tern-bearers. The use of this light to the insect itself seems to be, that it may not fly against objects in the night; by which contrivance these insects are enabled to procure their sustenance either by night or day, as their wants may require, or their numerous enemies permit them; whereas some of our beetles have eyes adapted only to the night, and if they happen to come abroad too soon in the evening, are so dazzled that they fly against every thing in their way. See note on Phosphorus, No. X.

In some seas, as particularly about the coast of Malabar, as a ship floats along, it seems, during the night, to be surrounded with fire, and to leave a long tract of light behind it. Whenever the sea is gently agitated, it seems converted into little stars; every drop, as it breaks, emits light, like bodies electrified in the dark. Mr. Bomare says, that when he was at the port of Cettes, in Languedoc, and bathing with a companion in the sea, after a very hot day, they both appeared covered with fire after every im­mersion, and that laying his wet hand on the arm of his companion, who had not then dipped himself, the exact mark of his hand and fingers was seen in characters of fire. As numerous microscopic insects are found in this shining water, its light has been generally ascribed to them, though it seems probable that fish-slime, in hot countries, may become in such a state of incipient putrefaction, as to give light, especially when by agitation it is more exposed to the air; otherwise it is not easy to explain why agitation should be necessary to produce this marine light. See note on Phosphorus, No. X.

NOTE X.—PHOSPHORUS.

KUNKEL, a native of Hamburgh, was the first who discovered to the world the process for producing phosphorus, though Brandt and Boyle were likewise said to have previously had the art of making it. It was ob­tained from sal microcosmicum, by evaporation, in the form of an acid, but [Page 153] has since been found in other animal substances, as in the ashes of bones, and even in some vegetables, as in wheat flour. Keir's Chemical Dict. This phosphoric acid is, like all other acids, united with vital air, and requires to be treated with charcoal or phlogiston to deprive it of this air; it then be­comes a kind of animal sulphur, but of so inflammable a nature, that on the access of air it takes fire spontaneously, and, as it burns, becomes again united with vital air, and re-assumes its form of phosphoric acid.

As animal respiration seems to be a kind of slow combustion, in which it is probable that phosphoric acid is produced by the union of phosphorus with the vital air, so it is also probable that phosphoric acid is produced in the excretory or respiratory vessels of luminous insects, as the glow-worm and fire-fly, and some marine insects. From the same principle I suppose the light from putrid flesh, as from the heads of haddocks, and from putrid veal, and from rotten wood, in a certain state of their putrefaction, is produced, and phosphorus, thus slowly combined with air, is changed into phosphoric acid. The light from the Bolognian stone, and from calcined shells, and from white paper, and linen, after having been exposed for a time to the sun's light, seem to produce either the phosphoric or some other kind of acid, from the sulphurous or phlogistic matter which they contain. See note on Beccari's shells, l. 182.

There is another process seems similar to this slow combustion, and that is bleaching. By the warmth and light of the sun, the water sprinkled upon linen or cotton cloth seems to be decomposed (if we credit the theory of M. Lavoisier), and a part of the vital air thus set at liberty and uncombined, and not being in its elastic form, more easily dissolves the colouring or phlo­gistic matter of the cloth, and produces a new acid, which is itself colourless, or is washed out of the cloth by water. The new process of bleaching confirms a part of this theory, for by uniting much vital air to marine acid, by distilling it from manganese, on dipping the cloth to be bleached in wa­ter replete with this superaerated marine acid, the colouring matter disap­pears immediately, sooner indeed in cotton than in linen. See note XXXIV.

There is another process which, I suspect, bears analogy to these above­mentioned, and that is the rancidity of animal fat, as of bacon; if bacon be hung up in a warm kitchen, with much salt adhering on the outside of it, the fat part of it soon becomes yellow and rancid; if it be washed with much cold water after it has imbibed the salt, and just before it is hung up, I am well informed, that it will not become rancid, or in very slight degrees. In the former case I imagine the salt on the surface of the bacon attracts water during the cold of the night, which is evaporated during the day, and that in this evaporation a part of the water becomes decomposed, as in bleaching, and its vital air uniting with greater facility in its unelastic state with the animal fat, produces an acid, perhaps of the phosphoric kind, which being of a fixed nature, lies upon the bacon, giving it the yellow colour and rancid taste. It is remarkable that the superaerated marine acid does not bleach living animal substances, at least it did not whiten a part of my hand which I for some minutes exposed to it.

NOTE XI.—STEAM-ENGINE.

THE expansive force of steam was known in some degree to the ancients. Hero, of Alexandria, describes an application of it to produce a rotative mo­tion by the re-action of steam issuing from a sphere mounted upon an axis, through two small tubes bent into tangents, and issuing from the opposite sides of the equatorial diameter of the sphere; the sphere was supplied with steam by a pipe communicating with a pan of boiling water, and entering the sphere at one of its poles.

A French writer, about the year 1630, describes a method of raising wa­ter to the upper part of a house, by filling a chamber with steam, and suf­fering it to condense of itself; but it seems to have been mere theory, as his method was scarcely practible as he describes it. In 1655, the Marquis of Worcester mentions a method of raising water by fire, in his Century of Inventions, but he seems only to have availed himself of the expansive force, and not to have known the advantages arising from condensing the steam by an injection of cold water. This latter and most important improvement seems to have been made by Capt. Savery, some time prior to 1698, for in that year his patent for the use of that invention was confirmed by act of parliament. This gentleman appears to have been the first who reduced the machine to practice, and exhibited it in an useful form. This method consisted only in expelling the air from a vessel by steam, and condensing the steam by an injection of cold water, which making a vacuum, the pres­sure of the atmosphere forced the water to ascend into the steam-vessel through a pipe of 24 to 26 feet high, and by the admission of dense steam from the boiler, forcing the water in the steam-vessel to ascend to the height desired. This construction was defective, because it required very strong vessels to re­sist the force of the steam, and because an enormous quantity of steam was condensed by coming in contact with the cold water in the steam-vessel.

About, or soon after that time, M. Papin attempted a steam-engine on similar principles, but rather more defective in its construction.

The next improvement was made very soon afterwards by Messrs. New­comen and Cawley, of Dartmouth; it consisted in employing for the steam­vessel a hollow cylinder, shut at bottom and open at top, furnished with a piston sliding easily up and down in it, and made tight by oakum or hemp, and covered with water. This piston is suspended by chains from one end of a beam, moveable upon an axis in the middle of its length; to the other end of this beam are suspended the pump-rods.

The danger of bursting the vessels was avoided in this machine; as how­ever high the water was to be raised, it was not necessary to increase the density of the steam, but only to enlarge the diameter of the cylinder.

Another advantage was, that the cylinder, not being made so cold as in [Page 155] Savery's method, much less steam was lost in filling it after each con­densation.

The machine, however, still remained imperfect, for the cold water thrown into the cylinder acquired heat from the steam it condensed, and being in a vessel exhausted of air, it produced steam itself, which, in part, resisted the action of the atmosphere on the piston; were this remedied by throwing in more cold water, the destruction of steam in the next filling of the cylinder would be proportionally increased. It has therefore, in prac­tice, been found adviseable not to load these engines with columns of water weighing more than seven pounds for each square inch of the area of the piston. The bulk of water, when converted into steam, remained unknown, until Mr. J. Watt, then of Glasgow, in 1764, determined it to be about 1800 times more rare than water. It soon occurred to Mr. Watt, that a perfect engine would be that in which no steam should be condensed in fil­ling the cylinder, and in which the steam should be so perfectly cooled as to produce nearly a perfect vacuum.

Mr. Watt having ascertained the degree of heat in which water boiled in vacuo, and under progressive degrees of pressure, and instructed by Dr. Black's discovery of latent heat, having calculated the quantity of cold water necessary to condense certain quantities of steam so far as to produce the exhaustion required, he made a communication from the cylinder to a cold vessel previously exhausted of air and water, into which the steam rushed, by its elasticity, and became immediately condensed. He then adapted a cover to the cylinder, and admitted steam above the piston to press it down instead of air, and instead of applying water, he used oil or grease to fill the pores of the oakum, and to lubricate the cylinder.

He next applied a pump to extract the injection water, the condensed steam, and the air, from the condensing vessel, every stroke of the engine.

To prevent the cooling of the cylinder by the contact of the external air, he surrounded it with a case containing steam, which he again protected by a covering of matters which conduct heat slowly.

This construction presented an easy means of regulating the power of the engine, for the steam being the acting power, as the pipe which admits it from the boiler is more or less opened, a greater or smaller quantity can enter during the time of a stroke, and, consequently, the engine can act with exactly the necessary degree of energy.

Mr. Watt gained a patent for his engine in 1768, but the further prose­cution of his designs was delayed by other avocations till 1775, when, in conjunction with Mr. Boulton, of Soho, near Birmingham, numerous expe­riments were made, on a large scale, by their united ingenuity, and great improvements added to the machinery, and an act of parliament obtained for the prolongation of their patent for twenty-five years; they have, since that time, drained many of the deep mines in Cornwall, which, but for the happy union of such genius, must immediately have ceased to work. One of these engines works a pump of eighteen inches diameter, and upwards of 100 fathom, or 600 feet high, at the rate of ten to twelve strokes, of seven feet long each, in a minute, and that with one fifth part of the coals which [Page 156] a common engine would have taken to do the same work. The power of this engine may be easier comprehended by saying, that it raised a weight equal to 81,000 pounds, 80 feet high, in a minute, which is equal to the combined action of 200 good horses. In Newcomen's engine this would have required a cylinder of the enormous diameter of 120 inches, or ten feet; but as in this engine of Mr. Watt and Mr. Boulton the steam acts, and a vacuum is made, alternately above and below the piston, the power exerted is double to what the same cylinder would otherways produce, and is further augmented by an inequality in the length of the two ends of the lever.

These gentlemen have also, by other contrivances, applied their engines to the turning of mills for almost every purpose, of which that great pile of machinery, the Albion Mill, is a well known instance. Forges, slitting mills, and other great works, are erected where nature has furnished no running water, and future times may boast that this grand and useful engine was invented and perfected in our own country.

Since the above article went to the press, the Albion Mill is no more; it is supposed to have been set on fire by interested or malicious incendiaries, and is burnt to the ground. Whence London has lost the credit and the advantage of possessing the most powerful machine in the world.

NOTE XII.—FROST.

THE cause of the expansion of water during its conversion into ice, is not yet well ascertained; it was supposed to have been owing to the air being set at liberty in the act of congelation, which was before dissolved in the water, and the many air bubbles in ice were thought to countenance this opinion. But the great force with which ice expands during its congelation, so as to burst iron bombs and coehorns, according to the experiments of Major Williams, at Quebec, invalidates this idea of the cause of it, and may some time be brought into use as a means of breaking rocks in mining, or pro­jecting cannon-balls, or for other mechanical purposes, if the means of pro­ducing congelation should ever be discovered to be as easy as the means of producing combustion.

Mr. de Mairan attributes the increase of bulk of frozen water to the dif­ferent arrangement of the particles of it in crystallization, as they are con­stantly joined at an angle of 60 degrees, and must, by this disposition, he thinks, occupy a greater volume than if they were parallel. He found the augmentation of the water, during freezing, to amount to one-fourteenth, one-eighteenth, one-nineteenth, and when the water was previously purged of air, to only one-twenty-second part. He adds, that a piece of ice, which was at first only one-fourteenth part specifically lighter than water, on being exposed some days to the frost, became one-twelfth lighter than water. Hence [Page 157] he thinks ice, by being exposed to greater cold, still increases in volume, and to this attributes the bursting of ice in ponds, and on the glaciers. See Lewis's Commerce of Arts, p. 257, and the note on Muschus, in the second part of this work.

This expansion of ice well accounts for the greater mischief done by ver­nal frosts attended with moisture (as by hoar frosts), than by the dry frosts, called black frosts. Mr. Lawrence, in a letter to Mr. Bradley, complains that the dale-mist, attended with a frost, on May-day, had destroyed all his tender fruits; though there was a sharper frost the night before, without a mist, that did him no injury; and adds, that a garden not a stone's throw from his own, on a higher situation, being above the dale-mist, had re­ceived no damage. Bradley, vol. II. p. 232.

Mr. Hunter, by very curious experiments, discovered that the living principle in fish, in vegetables, and even in eggs and seeds, possesses a power of resisting congelation. Phil. Trans. There can be no doubt but that the exertions of animals to avoid the pain of cold, may produce in them a greater quantity of heat, at least for a time; but that vegetables, eggs, or seeds, should possess such a quality, is truly wonderful. Others have ima­gined that animals possess a power of preventing themselves from becoming much warmer than 98 degrees of heat, when immersed in an atmosphere above that degree of heat. It is true that the increased exhalation from their bodies will, in some measure, cool them, as much heat is carried off by the evaporation of fluids; but this is a chemical, not an animal process. The experiments made by those who continued many minutes in the air of a room heated so much above any natural atmospheric heat, do not seem conclusive, as they remained in it a less time than would have been neces­sary to have heated a mass of beef of the same magnitude; and the circula­tion of the blood in living animals, by perpetually bringing new supplies of fluid to the skin, would prevent the external surface from becoming hot much sooner than the whole mass. And, thirdly, there appears no power of animal bodies to produce cold in diseases, as in scarlet fever, in which the increased action of the vessels of the skin produces heat, and contributes to exhaust the animal power already to much weakened.

It has been thought by many that frosts meliorate the ground, and that they are in general salubrious to mankind. In respect to the former, it is now well known that ice or snow contains no nitrous particles, and though frost, by enlarging the bulk of moist clay, leaves it softer for a time after the thaw, yet as soon as the water exhales, the clay becomes as hard as before, being pressed together by the incumbent atmosphere, and by its self-attrac­tion, called setting by the potters. Add to this, that on the coasts of Africa, where frost is unknown, the fertility of the soil is almost beyond our con­ceptions of it. In respect to the general salubrity of frosty seasons, the bills of mortality are an evidence in the negative, as in long frosts many weakly and old people perish from debility occasioned by the cold, and many classes of birds, and other wild animals, are benumbed by the cold, or destroyed by the consequent scarcity of food, and many tender vegetables perish from the degree of cold.

[Page 158] I do not think it should be objected to this doctrine, that there are moist days, attended with a brisk cold wind, when no visible ice appears, and which are yet more disagreeable and destructive than frosty weather. For on these days the cold moisture which is deposited on the skin is there eva­porated, and thus produces a degree of cold perhaps greater than the milder frosts. Whence, even in such days, both the disagreeable sensations and in­salubrious effects belong to the cause above-mentioned, viz. the intensity of the cold. Add to this, that in these cold moist days, as we pass along, or as the wind blows upon us, a new sheet of cold water is, as it were, per­petually applied to us, and hangs upon our bodies. Now, as water is 800 times denser than air, and is a much better conductor of heat, we are starved with cold, like those who go into a cold bath, both by the great number of particles in contact with the skin, and their great facility of re­ceiving our heat.

It may nevertheless be true, that snows of long duration, in our winters, may be less injurious to vegetation than great rains and shorter frosts, for two reasons. 1. Because great rains carry down many thousand pounds worth of the best part of the manure off the lands into the sea, whereas snow dissolves more gradually, and thence carries away less from the land. Any one may distinguish a snow-flood from a rain-flood by the transparency of the water. Hence hills or fields, with considerable inclination of surface, should be ploughed horizontally, that the furrows may stay the water from showers till it deposits its mud. 2. Snow protects vegetables from the seve­rity of the frost, since it is always in a state of thaw where it is in contact with the earth; as the earth's heat is about 48 degrees, and the heat of thawing snow is 32 degrees, the vegetables between them are kept in a de­gree of heat about 40, by which many of them are preserved. See note on Muschus, part II. of this work.

NOTE XIII.—ELECTRICITY.

NOTE XIV.—BUDS AND BULBS.

A TREE is, properly speaking, a family or swarm of buds, each bud be­ing an individual plant; for if one of these buds be torn or cut out, and planted in the earth, with a glass cup inverted over it, to prevent its exha­lation from being at first greater than its power of absorption, it will pro­duce a tree similar to its parent; each bud has a leaf, which is its lungs, ap­propriated to it, and the bark of the tree is a congeries of the roots of these individual buds; whence old hollow trees are often seen to have some branches flourish with vigour after the internal wood is almost entirely de­cayed and vanished. According to this idea, Linnaeus has observed, that trees and shrubs are roots above ground, for if a tree be inverted, leaves will grow from the root-part, and roots from the trunk-part. Phil. [...]ot. p. 39. Hence it appears that vegetables have two methods of propagating themselves, the oviparous as by seeds, and the viviparous as by their buds and bulbs; and that the individual plants, whether from seeds, or buds, or bulbs, are all annual productions, like many kinds of insects, as the silk-worm [Page 161] the parent perishing in the autumn after having produced an embryon, which lies in a torpid state during the winter, and is matured in the suc­ceeding summer. Hence Linnaeus names buds and bulbs the winter cra­dles of the plant, or hybernacula, and might have given the same term to seeds. In warm climates few plants produce buds, as the vegetable life can be completed in one summer, and hence the hybernacle is not wanted; in cold climates also some plants do not produce buds, as philadelphus, fran­gula, viburnum, ivy, heath, wood-nightshade, rue, geranium.

The bulbs of plants are another kind of winter cradle, or hybernacle, ad­hering to the descending trunk, and are found in the perennial herbaceous plants, which are too tender to bear the cold of the winter. The produc­tion of these subterraneous winter lodges, is not yet, perhaps, clearly under­stood; they have been distributed by Linnaeus, according to their forms, into scaly, solid, coated, and jointed bulbs, which, however, does not elucidate their manner of production. As the buds of trees may be truly esteemed individual annual plants, their roots constituting the bark of the trees, it follows, that these roots ( viz. of each individual bud) spread themselves over the last year's bark, making a new bark over the old one, and thence descending, cover with a new bark the old roots also in the same manner. A similar circumstance I suppose to happen in some herbaceous plants, that is, a new bark is annually produced over the old root, and thus, for some years at least, the old root or caudex increases in size, and puts up new stems. As these roots increase in size, the central part, I suppose, changes like the internal wood of a tree, and does not possess any vegetable life, and there­fore gives out no fibres or rootlets, and hence appears bitten off, as in vale­rian, plantain, and devil's-bit. And this decay of the central part of the root, I suppose, has given occasion to the belief of the root-fibres drawing down the bulb, so much insisted on by Mr. Milne, in his Botanical Dic­tionary, art. Bulb.

From the observations and drawings of various kinds, of bulbous roots, at different times of their growth, sent me by a young lady of nice observa­tion, it appears probable that all bulbous roots, properly so called, perish annually in this climate. Bradley, Miller, and the author of Spectacle de la Nature, observe that the tulip annually renews its bulb, for the stalk of the old flower is found under the old dry coat, but on the outside of the new bulb. This large new bulb is the flowering bulb; but besides this there are other small new bulbs produced between the coats of this large one, but from the same caudex (or circle from which the root-fibres spring); these small bulbs are leaf-bearing bulbs, and renew themselves annually, with in­creasing size, till they bear flowers.

Miss [...] favoured me with the following curious experiment: She took a small tulip-root out of the earth when the green leaves were suffi­ciently high to show the flower, and placed it in a glass of water; the leaves and flower soon withered, and the bulb became wrinkled and soft, but put out one small side bulb, and three bulbs beneath, descending an inch into the water by processes from the caudex; the old bulb in some weeks entirely decayed. On dissecting this monster, the middle descending bulb was found, [Page 162] by its process, to adhere to the caudex, and to the old flower-stem; and the side ones were separated from the flower-stem by a few shrivelled coats, but adhered to the caudex. Whence she concludes that these last were off­sets, or leaf-bulbs, which should have been seen between the coats of the new flower-bulb, if it had been left to grow in the earth, and that the mid­dle one would have been the new flower-bulb. In some years (perhaps in wet seasons) the florists are said to lose many of their tulip-roots by a simi­lar process, the new leaf-bulbs being produced beneath the old ones by an elongation of the caudex, without any new flower-bulbs.

By repeated dissections, she observes, that the leaf-bulbs, or off-sets of tulip, crocus, gladiolus, sritillary, are renewed in the same manner as the flowering-bulbs, contrary to the opinion of many writers; this new leaf-bulb is formed on the inside of the coats from whence the leaves grow, and is more or less advanced in size as the outer coats and leaves are more or less shrivelled. In examining tulip, i [...]ris, hyacinth, hare-bell, the new bulb was invariably found between the flower-stem and the base of the innermost leaf of those roots which had flowered, and inclosed by the base of the innermost leaf in those roots which had not flowered, in both cases adhering to the cau­dex or fleshy circle from which the root-fibres spring.

Hence it is probable that the bulbs of hyacinths are renewed annually, but that this is performed from the caudex within the old bulb, the outer coat of which does not so shrivel as in crocus and fritillary, and hence this change is not so apparent. But, I believe, as soon as the flower is advanced, the new bulbs may be seen on dissection; nor does the annual increase of the size of the root of cyclamen, and of aletris capensis, militate against this annual renewal of them, since the leaf-bulbs, or off-sets, as described above, are increased in size as they are annually renewed. See note on Orchis, and on Anthoxanthum, in Part II. of this work.

NOTE XV.—SOLAR VOLCANOS.

DR. ALEXANDER WILSON, Professor of Astronomy at Glasgow, published a paper in the Philosophical Transactions for 1774, demonstrating that the spots in the sun's disk are real cavities, excavations through the lu­minous material, which covers the other parts of the sun's surface. One of these cavities he found to be about 4000 miles deep, and many times as wide. Some objections were made to this doctrine by M. De la Lande, in the Memoirs of the French Academy for the year 1776, which, however, have been ably answered by professor Wilson in reply, in the Philos. Trans. for 1783. Keil observes, in his Astronomical Lectures, p. 44, "We fre­quently see spots in the sun which are larger and broader not only than Eu­rope or Africa, but which even equal, if they do not exceed, the surface of [Page 163] the whole terraqueous globe." Now that these cavities are made in the sun's body by a process of nature similar to our earthquakes, does not seem impro­bable on several accounts. 1. Because, from this discovery of Dr. Wilson, it appears that the internal parts of the sun are not in a state of inflammation or of ejecting light, like the external part or luminous ocean which covers it; and hence that a greater degree of heat or inflammation, and consequent expan­sion or explosion, may occasionally be produced in its internal or dark nucleus. 2. Because the solar spots or cavities are frequently increased or diminished in size. 3. New ones are often produced. 4. And old ones vanish. 5. Be­cause there are brighter or more luminous parts of the sun's disk, called fa­culae by Scheiner and Hevelius, which would seem to be volcanos in the sun, or, as Dr. Wilson calls them, "eructations of matter more luminous than that which covers the sun's surface." 6. To which may be added that all the planets added together, with their satellites, do not amount to more than one six hundred and fiftieth part of the mass of the sun, according to Sir Isaac Newton.

Now, if it could be supposed that the planets were originally thrown out of the sun by larger sun-quakes than those frequent ones which occasion these spots or excavations above-mentioned, what would happen? 1. Accord­ing to the observations and opinion of Mr. Herschel, the sun itself and all its planets are moving forwards round some other centre with an unknown velocity, which may be of opake matter, corresponding with the very ancient and general idea of a chaos. Whence, if a ponderous planet, as Saturn, could be supposed to be projected from the sun by an explosion, the motion of the sun itself might be at the same time disturbed in such a manner as to prevent the planet from falling again into it. 2. As the sun revolves round its own axis, its form must be that of an oblate spheroid like the earth, and therefore a body prejected from its surface perpendicularly upwards from that surface would not rise perpendicularly from the sun's centre, unless it happened to be projected exactly from either of its poles or from its equator. Whence it may not be necessary that a planet, if thus projected from the sun by explosion, should again fall into the sun. 3. They would part from the sun's surface with the velocity with which that surface was moving, and with the velocity acquired by the explosion, and would therefore move round the sun in the same direction in which the sun rotates on its axis, and perform eliptic or­bits. 4. All the planets would move the same way round the sun, from this first motion acquired at leaving its surface, but their orbits would be inclined to each other according to the distance of the part, where they were thrown out, from the sun's equator. Hence those which were ejected near the sun's equator would have orbits but little inclined to each other, as the primary pla­nets; the plain of all whose orbits are inclined but seven degrees and a half from each other. Others which were ejected near the sun's poles would have much more eccentric orbits, as they would partake so much less of the sun's rotatory motion at the time they parted from his surface, and would, therefore, be carried further from the sun by the velocity they had gained by the explosion which ejected them, and become comets. 5. They would all obey the same laws of motion in their revolutions round the sun; this has been determined by astro­nomers, [Page 164] who have demonstrated that they move through equal areas, in equal times. 6. As their annual periods would depend on the height they rose by the explosion, these would differ in them all. 7. As their diurnal revolu­tions would depend on one side of the exploded matter adhering more than the other at the time it was torn off by the explosion, these would also differ in the different planets, and not bear any proportion to their annual periods. Now, as all these circumstances coincide with the known laws of the plane­tary system, they serve to strenghten this conjecture.

This coincidence of such a variety of circumstances induced M. de Buffon to suppose that the planets were all struck off from the sun's surface by the impact of a large comet, such as approached so near the sun's disk, and with such amazing velocity, in the year 1680, and is expected to return in 2255. But Mr. Buffon did not recollect that these comets themselves are only planets with more eccentric orbits, and that therefore it must be asked, what had previously struck off these comets from the sun's body? 2. That if all these planets were struck off from the sun at the same time, they must have been so near as to have attracted each other and have formed one mass. 3. That we shall want new causes for separating the secondary planets from the primary ones, and must therefore look out for some other agent, as it does not appear how the impulse of a comet could have made one planet roll round another at the time they both of them were driven off from the surface of the sun.

If it should be asked, why new planets are not frequently ejected from the sun? it may be answered, that after many large earthquakes many vents are left for the elastic vapours to escape, and hence, by the present appear­ance of the surface of our earth, earthquakes, prodigiously larger than any recorded in history, have existed; the same circumstances may have affected the sun, on whose surface there are appearances of volcanos, as described above. Add to this, that some of the comets, and even the georgium sidus, may, for aught we know to the contrary, have been emitted from the sun in more modern days, and have been diverted from their course, and thus per­vented from returning into the sun, by their approach to some of the older planets, which is somewhat countenanced by the opinion several philosophers have maintained, that the quantity of matter of the sun has decreased. Dr. Halley observed, by comparing the proportion which the periodical time of the moon bore to that of the sun in former times, with the proportion be­tween them at present, that the moon is found to be somewhat accelerated in respect to the sun. Pemberton's View of Sir Isaac Newton, p. 247. And so large is the body of this mighty luminary, that all the planets thus thrown out of it would make scarce any perceptible diminution of it as mentioned above. The cavity mentioned above, as measured by Dr. Wilson, of 4000 miles in depth, not penetrating an hundredth part of the sun's semi-diame­ter; and yet as its width was many times greater than its depth, was large enough to contain a greater body than our terrestrial world.

I do not mean to conceal, that from the laws of gravity unsolded by Sir Isaac Newton, supposing the sun to be a sphere, and to have no progressive motion, and not liable itself to be disturbed by the supposed projection of [Page 165] the planets from it, that such planets must return into the sun. The late Rev. William Ludlam, of [...], whose genius never met with reward equal to its merits, in a letter to me, dated January, 1787, after having shewn, as mentioned above, that planets so projected from the sun would return to it, adds, ‘That a body as large as the moon so prejected, would disturb the motion of the earth in its orbit, is certain; but the calculation of such disturbing forces is difficult. The body in some circumstances might become a satellite, and both move round their common centre of gravity, and that centre be carried in an annual orbit round the sun.’

There are other circumstances which might have concurred at the time of such supposed explosions, which would render this idea not impossible. 1. The planets might be thrown out of the sun at the time the sun itself was rising from chaos, and be attracted by other suns in their vicinity rising at the same time out of chaos, which would prevent them from returning into the sun. 2. The new planet, in its course or ascent from the sun, might ex­plode and eject a satellite, or perhaps more than one, and thus, by its course being affected, might not return into the sun. 3. If more planets were ejected at the same time from the sun, they might attract and disturb each others course at the time they left the body of the sun, or very soon afterwards, when they would be so much nearer each other.

NOTE XVI.—CALCAREOUS EARTH.

FROM having observed that many of the highest mountains of the world consist of lime-stone replete with shells, and that these mountains bear the marks of having been lifted up by subterraneous fires from the interior parts of the globe; and as lime-stone replete with shells is found at the bottom of many of our deepest mines, some philosophers have concluded that the nu­cleus of the earth was for many ages covered with water, which was peo­pled with its adapted animals; that the shells and bones of these animals, in a long series of time, produced solid strata in the ocean surrounding the original nucleus.

These strata consist of the accumulated exuviae of shell-fish—the animals perished age after age, but their shells remained, and, in progression of time, produced the amazing quantities of lime-stone which almost cover the earth. Other marine animals, called coralloids, raised walls, and even mountains, by the congeries of their calcareous habitations; these perpendicular coral­line rocks make some parts of the southern ocean highly dangerous, as ap­pears in the journals of Capt. Cook. From contemplating the immense strata of lime-stone, both in respect to their extent and thickness, formed from these shells of animals, philosophers have been led to conclude, that much of the water of the sea has been converted into calcareous earth, by passing through their organs of digestion. The formation of calcareous earth [Page 166] seems more particularly to be an animal process, as the formation of clay be­longs to the vegetable economy; thus the shells of crabs, and other testaceous fish, are annually re-produced from the mucous membrane beneath them; the shells of eggs are first a mucous membrane, and the calculi of the kid­neys, and those found in all other parts of our system, which sometimes con­tain calcareous earth▪ seem to originate from inflamed membranes; the bones themselves consist of calcareous earth united with the phosphoric or animal acid, which may be separated by dissolving the ashes of calcined bones in the nitrous acid; the various secretions of animals, as their saliva and urine, abound likewise with calcareous earth, as appears by the incrustations about the teeth, and the sediments of urine. It is probable that animal mucus is a previous process towards the formation of calcareous earth; and that all the calcareous earth in the world, which is seen in lime-stones, marbles, spars, alabasters, marls (which make up the greatest part of the earth's crust, as far as it has yet been penetrated), have been formed originally by animal and vegetable bodies from the mass of water, and that by these means the solid part of the terraqueous globe has perpetually been in an increasing state, and the water perpetually in a decreasing one.

After the mountains of shells, and other recrements of aquatic animals, were elevated above the water, the upper heaps of them were gradually dis­solved by rains and dews, and oozing through, were either perfectly crystal­lized in smaller cavities, and formed calcareous spar, or were imperfectly crystallized on the roofs of larger cavities, and produced stalactites; or mix­ing with other undissolved shells beneath them, formed marbles, which were more or less crystallized and more or less pure; or, lastly, after being dis­solved, the water was exhaled from them in such a manner that the external parts became solid, and, forming an arch, prevented the internal parts from approaching each other so near as to become solid, and thus chalk was pro­duced. I have specimens of chalk formed a [...] the root of several stalactites, and in their central parts; and of other stalactites, which are hollow like quills, from a similar cause, viz. from the external part of the stalactite harden­ing first by its evaporation, and thus either attracting the internal dissolved particles to the crust, or preventing them from approaching each other so as to form a solid body. Of these I saw many hanging from the arched roof of a cellar under the high street in Edinburgh.

If this dissolved lime-stone met with vitriolic acid, it was converted into alabaster, parting at the same time with its fixable air. If it met with the fluor acid, it became fluor; if with the siliceous acid, flint; and when mixed with clay and sand, or either of them, acquires the name of marl. And under one or other of these forms, composes a great part of the solid globe of the earth.

Another mode in which lime-stone appears is in the form of round granu­lated particles, but slightly cohering together; of this kind a bed extends over Lincoln heath, perhaps twenty miles long by ten wide. The form of this calcareous sand, its angles having been rubbed off, and the flatness of its bed, evince that that part of the country was so formed under water, the particles of sand having thus been rounded, like all other rounded pebbles. [Page 167] This round form of calcareous sand, and of other larger pebbles, is produced under water, partly by their being more or less soluble in water, and hence the angular parts become dissolved; first, by their exposing a larger surface to the action of the menstruum; and, secondly, from their attrition against each other by the streams or tides, for a great length of time, successively, as they were collected, and, perhaps, when some of them had not acquired their hardest state.

This calcareous sand has generally been called ketton-stone, and believed to resemble the spawn of fish; it has acquired a form so much rounder than siliceous sand, from its being of so much softer a texture, and also much more soluble in water. There are other soft calcareous stones called tupha, which are deposited from water on mosses, as at Matlock, from which moss it is probable the water may receive something which induces it the readier to part with its earth.

In some lime-stones the living animals seem to have been buried, as well as their shells, during some great convulsion of nature. These shells contain a black coaly substance within them, in others some phlogiston or volatile alkali, from the bodies of the dead animals, remains mixed with the stone, which is then called liver-stone, as it emits a sulphurous smell on being struck; and there is a stratum about six inches thick extends a considerable way over the iron-ore at Wingerworth, near Chesterfield, in Derbyshire, which seems evidently to have been formed from the shells of fresh-water muscles.

There is, however, another source of calcareous earth besides the aquatic one above described, and that is from the recrements of land animals and vegetables, as found in marls, which consist of various mixtures of calcareous earth, sand, and clay, all of them, perhaps, principally from vegetable origin.

Dr. Hutton is of opinion, that the rocks of marble have been softened by fire into a fluid mass, which, he thinks, under immense pressure, might be done without the escape of their carbonic acid or fixed air. Edinb. Trans. vol. I. If this ingenious idea be allowed, it might account for the purity of some white marbles, as during their fluid state there might be time for their partial impurities, whether from the bodies of the animals which produced the shells, or from other extraneous matter, either to sublime to the upper­most part of the stratum, or to subside to the lowermost part of it. As a confirmation of this theory of Dr. Hutton's, it may be added, that some cal­careous stones are found mixed with lime, and have thence lost a part of their fixed air, or carbonic gas, as the bath-stone, and, on that account, hardens on being exposed to the air, and, mixed with sulphur, produces cal­careous liver of sulphur. Falconer on Bath-water, vol. I. p. 156 and p. 257. Mr. Monnet found lime in powder in the mountains of Auvergne, and sus­pected it of volcanic origin. Kirwan's Min. p. 22.

NOTE XVII.—MORASSES.

WHERE woods have repeatedly grown and perished, morasses are, in pro­cess of time, produced, and by their long roots, fill up the interstices till the whole becomes, for many yards deep, a mass of vegetation. This fact is cu­riously verified by an account given many years ago by the Earl of Cromar­tie, of which the following is a short abstract.

In the year 1651, the Earl of Cromartie, being then nineteen years of age, saw a plain in the parish of Lockburn covered over with a firm standing wood, which was so old that not only the trees had no green leaves upon them, but the bark was totally thrown off, which, he was there informed by the old countrymen, was the universal manner in which fir-woods termi­nated, and that in twenty or thirty years the trees would cast themselves up by the roots. About fifteen years after he had occasion to travel the same way, and observed that there was not a tree nor the appearance of a root of any of them; but in their place, the whole plain where the wood stood was covered with a flat green moss, or morass, and on asking the country people what was become of the wood, he was informed that no one had been at the trouble to carry it away, but that it had all been overturned by the wind, that the trees lay thick over each other, and that the moss or bog had overgrown the whole timber, which, they added, was occasioned by the moisture which came down from the high hills above it, and stagnated upon the plain, and that nobody could yet pass over it, which, however, his Lordship was so incautious as to attempt, and slipt up to the arm-pits. Be­fore the year 1699, that whole piece of ground was become a solid moss, wherein the peasants then dug turf or peat, which, however, was not yet of the best sort. Phil. Trans. No. 330. Abridg. vol. V. p. 272.

Morasses in great length of time undergo variety of changes, first by elu­triation, and afterwards by fermentation, and the consequent heat. 1. By water perpetually oozing through them the most soluble parts are first washed away, as the essential salts; these, together with the salts from animal recre­ments, are carried down the rivers into the sea, where all of them seem to decompose each other except the marine salt. Hence the ashes of peat con­tain little or no vegetable alkali, and are not used in the countries where peat constitutes the fuel of the lower people, for the purpose of washing linen. The second thing which is always seen oozing from morasses is iron in solution, which produces chalybeat springs, from whence depositions of ochre and variety of iron ores. The third elutriation seems to consist of ve­getable acid, which by means unknown appears to be converted into all other acids. 1. Into marine and nitrous acids as mentioned above. 2. Into vi­triolic acid, which is found in some morasses so plentifully as to preserve the bodies of animals from putrefaction which have been buried in them, and this acid, carried away by rain and dews, and meeting with calcareous earth, pro­duces [Page 169] gypsum or alabaster, with clay it produces alum, and, deprived of its vital air, produces sulphur. 3. Fluor acid, which being washed away, and meeting with calcareous earth, produces fluor or cubic spar. 4. The siliceous acid, which seems to have been disseminated in great quantity either by solu­tion in water or by solution in air, and appears to have produced the sand in the sea, uniting with calcareous earth, previously dissolved in that element, from which were afterwards formed some of the grit-stone rocks by means of a siliceous or calcareous cement. By its union with the calcareous earth of the morass, other strata of siliceous sand have been produced; and by the mixture of this with clay and lime arose the beds of marl.

In other circumstances, probably where less moisture has prevailed, mo­rasses seem to have undergone a fermentation, as other vegetable matter, new hay, for instance, is liable to do from the great quantity of sugar it con­tains. From the great heat thus produced in the lower parts of immense beds of morass, the phlogistic part, or oil, or asphaltum, becomes distilled, and rising into higher strata, becomes again condensed, forming coal-beds of greater or less purity according to their greater or less quantity of inflam­mable matter; at the same time the clay-beds become purer or less so, as the phlogistic part is more or less completely exhaled from them. Though coal and clay are frequently produced in this manner, yet I have no doubt, but that they are likewise often produced by elutriation; in situations on decli­vities the clay is washed away down into the valleys, and the phlogistic part or coal left behind; this circumstance is seen in many valleys near the beds of rivers, which are covered recently by a whitish impure clay, called wa­ter-clay. See note XIX. XX. and XXIII.

LORD CROMARTIE has furnished another curious observation on morasses in the paper above refered to. In a moss near the town of Eglin, in Murray, though there is no river or water which communicates with the moss, yet for three or four feet of depth in the moss there are little shell-fish resembling oysters, with living fish in them in great quantities, though no such fish are found in the adjacent rivers, nor even in the water pits in the moss, but only in the solid substance of the moss. This curious fact not only accounts for the shells sometimes found on the surface of coals, and in the clay above them, but also for a thin stratum of shells which sometimes exist over iron­ore.

NOTE XVIII.—IRON.

AS iron is formed near the surface of the earth, it becomes exposed to streams of water and of air more than most other metallic bodies, and thence becomes combined with oxygene, or vital air, and appears very frequently in its calciform state, as in variety of ochres. Manganese and zinc, and [Page 170] sometimes lead, are also found near the surface of the earth, and, on that ac­count, become combined with vital air, and are exhibited in their calciform state.

The avidity with which iron unites with oxygene, or vital air, in which process much heat is given out from the combining materials, is shewn by a curious experiment of M. Ingenhouz. A fine iron wire, twisted spirally, is fixed to a cork, on the point of the spire is fixed a match made of agaric, dipped in solution of nitre; the match is then ignited, and the wire with the cork put immediately into a bottle full of vital air, the match first burns vividly, and the iron soon takes fire, and consumes with brilliant sparks till it is reduced to small brittle globules, gaining an addition of about one third of its weight by its union with vital air. Annales de Chimie. Traité de Chimie, par Lavoisier, c. iii.

NOTE XIX.—FLINT.

NOTE XX.—CLAY.

THE philosophers who have attended to the formation of the earth, have acknowledged two great agents in producing the various changes which the terraqueous globe has undergone, and these are water and fire. Some of them have, perhaps, ascribed too much to one of these great agents of na­ture, and some to the other. They have generally agreed, that the strati­fication of materials could only be produced from sediments or precipita­tions, which were previously mixed or dissolved in the sea; and that what­ever effects were produced by fire, were performed afterwards.

There is, however, great difficulty in accounting for the universal strati­fication of the solid globe of the earth in this manner, since many of the materials, which appear in strata, could not have been suspended in water; as the nodules of flint in chalk-beds, the extensive beds of shells; and, lastly, the strata of coal, clay, sand, and iron-ore, which, in most coal-countries, lie from five to seven times alternately stratified over each other, and none of them are soluble in water. Add to this, if a solution of them, or a mixture of them in water, could be supposed, the cause of that solution must cease be­fore a precipitation could commence.

1. The great masses of lava, under the various names of granite, por­phyry, toad-stone, moor-stone, rag, and slate, which constitute the old world, may have acquired the old stratification, which some of them appear to possess, by their having been formed by successive eruptions of a fluid mass, which, at different periods of ancient time, arose from volcanic shafts and covered each other, the surface of the interior mass of lava would cool, and become solid, before the superincumbent stratum was poured over it; to the same cause may be ascribed their different compositions and textures, which are scarcely the same in any two parts of the world.

2. The stratifications of the great masses of lime-stone, which were produced from sea-shells, seem to have been formed by the different times at which the innumerable shells were produced and deposited. A colony of echini, or madrepores, or cornua ammonis, lived and perished in one period of time; in another, a new colony of either similar or different shells lived and died over the former ones, producing a stratum of more recent shells over a stratum of others which had begun to petrify, or to become marble; and thus, from unknown depths to what are now the summits of mountains, the lime-stone is disposed in strata of varying solidity and colour. These have afterwards undergone variety of changes by their solution and deposition from the water in which they were immersed, or from having been exposed to great heat under great pressure, according to the ingenious theory of Dr. Hutton. Edinb. Transact. vol. I. See Note XVI.

3. In most of the coal-countries of this island, there are from five to seven beds of coal stratified, with an equal number of beds, though of much greater [Page 183] thickness, of clay and sand-stone, and occasionally of iron-ores. In what manner to account for the stratification of these materials seems to be a problem of great difficulty. Philosophers have generally supposed that they have been arranged by the currents of the sea; but considering their insolubility in water, and their almost similar specific gravity, an accumula­tion of them in such distinct beds from this cause is altogether inconceivable, though some coal-countries bear marks of having been, at some time, im­mersed beneath the waves, and raised again by subterranean fires.

The higher and lower parts of morasses were necessarily produced at dif­ferent periods of time, see Note XVII. and would thus originally be formed in strata of different ages. For when an old wood perished, and produced a morass, many centuries would elapse before another wood could grow, and perish again, upon the same ground, which would thus produce a new stra­tum of morass over the other, differing, indeed, principally in its age, and, perhaps, as the timber might be different, in the proportion of its compo­nent parts.

Now, if we suppose the lowermost stratum of a morass become ignited, like fermenting hay (after whatever could be carried away by solution in water was gone), what would happen? Certainly the inflammable part, the oil, sulphur, or bitumen, would burn away, and be evaporated in air; and the fixed parts would be left, as clay, lime, and iron; while some of the cal­careous earth would join with the siliceous acid, and produce sand; or with the argillaceous earth, and produce marl. Thence, after many centuries, another bed would take fire, but with less degree of ignition, and with a greater body of morass over it; what then would happen? The bitumen and sulphur would rise, and might become condensed under an impervious stra­tum, which might not be ignited, and there form coal of different purities, according to its degree of fluidity, which would permit some of the clay to subside through it into the place from which it was sublimed.

Some centuries afterwards another similar process might take place, and either thicken the coal-bed, or produce a new clay-bed, or marl, or sand, or deposit iron upon it, according to the concomitant circumstances above­mentioned.

I do not mean to contend, that a few masses of some materials may not have been rolled together by currents, when the mountains were much more elevated than at present, and, in consequence, the rivers broader and more rapid, and the storms of rain and wind greater both in quantity and force. Some gravel-beds may have been thus washed from the mountains; and some white clay washed from morasses into valleys beneath them; and some ochres of iron dissolved and again deposited by water; and some calcareous depositions from water (as the bank, for instance, on which stand the houses at Matlock-bath); but these are all of small extent or consequence compared to the primitive rocks of granite or porphyry which form the nucleus of the earth or to the immense strata of lime-stone which crust over the greatest part of this granite or porphyry; or, lastly, to the very extensive beds of clay, marl, sand-stone, coal, and iron, which were probably for many mil­lions of years the only parts of our continents and islands, which were then [Page 184] elevated above the level of the sea, and which, on that account, became covered with vegetation, and thence acquired their later or superincumbent strata, which constitute what some have termed the new world.

There is another source of clay, and that of the finest kind, from decom­posed granite; this is of a snowy white, and mixed with shining particles of mica; of this kind is an earth from the country of Cherokees. Other kinds are from less pure lavas; Mr. Ferber asserts that the sulphurous steams from Mount Vesuvius convert the lava into clay.

"The lavas of the ancient Solfatara volcano have been undoubtedly of a vitreous nature, and these appear at present argillaceous. Some fragments of this lava are but half, or at one side changed into clay, which either is viscid or ductile, or hard and stony. Clays, by fire, are deprived of their coherent quality, which cannot be restored to them by polverization, nor by humectation. But the sulphureous Solfatara steams restore it, as may be easily observed on the broken pots wherein they gather the sal ammoniac; though very well baked and burnt at Naples, they are mollified again by the acid steams into a viscid clay, which keeps the former fire-burnt colour." Travels in Italy. p. 156.

NOTE XXI.—ENAMELS.

THE fine bright purples or rose colours which we see on china cups, are not producible with any other material except gold; manganese indeed gives a purple, but of a very different kind.

In Europe, the application of gold to these purposes, appears to be of mo­dern invention. Cassius's discovery of the precipitate of gold by tin, and the use of that precipitate for colouring glass and enamels, are now gene­rally known; but though the precipitate with tin be more successful in pro­ducing the ruby glass, or the colourless glass, which becomes red by sub­sequent ignition, the tin probably contributing to prevent the gold from separating (which it is very liable to do during the fusion); yet, for ena­mels, the precipitates made by alkaline salts answer equally well, and give a finer red; the colour produced by the tin precipitate being a bluish purple, but with the others a rose red. I am informed that some of our best artists prefer aurum fulminans, mixing it, before it has become dry, with the white composition, or enamel flux; when once it is divided by the other matter, it is ground with great safety, and without the least danger of explosion, whether moist or dry. The colour is remarkably improved and brought forth by long grinding, which accordingly makes an essential circumstance in the process.

The precipitates of gold, and the colcothar, or other red preparations of iron, are called tender colours. The heat must be no greater than is just [Page 185] sufficient to make the enamel run upon the piece, for if greater, the colours will be destroyed or changed to a different kind. When the vitreous mattes has just become fluid, it seems as if the coloured matallic calx remained barely intermixed with it, like a coloured powder of exquisite tennity suspended in water; but by stronger fire the calx is dissolved, and metallic colours are altered by solution in glass, as well as in acids or alkalies.

The Saxon mines have, till very lately, almost exclusively supplied the rest of Europe with cobalt, or rather with its preparations, [...]affire and smalt, for the exportation of the ore itself is there a capital crime. Hungary, Spain, Sweden, and some other parts of the continent, are now said to afford, cobalts equal to the Saxon, and specimens have been discovered in our own island, both in Cornwall and in Scotland, but hitherto in no great quantity.

Calces of cobalt and of copper differ very materially from those above, mentioned in their application for colouring enamels. In those the calx has previously acquired the intended colour, a colour which hears a red heat, without injury, and all that remains in to fix it on the piece by a vitreous, flux. But the blue colour of cobalt, and the green or bluish green of cop­per, are produced by vitrification, that is, by solution in the glass, and a strong fire is necessary for their perfection. These calces, therefore, when mixed with the enamel flux, are melted in crucibles, once or oftener, and the deep coloured opake glass, thence resulting, is ground into impalpable pow­der, and used for enamel. One part of either of these calces is put to ten, sixteen, or twenty parts of the flux, according to the depth of colour required. The heat of the enamel-kiln is only a full red, such as is marked on Mr. Wedgwood's thermometer 6 degrees. It is therefore necessary that the flux be so adjusted as to melt in that low heat. The usual materials are flint or flint-glass, with a due proportion of red-led, or borax, or both, and some­times a little tin calx to give opacity.

Ka- [...]-lin is the name given by the Chinese to their porcelain clay, and pe-tun-tse to the other ingredient in their China ware. Specimens of both these have been brought into England, and found to agree in quality with some of our own materials. Kaolin is the very same with the clay called in Cornwall [...] and the petuntse is a granite similar to the Cornish moor-stone. There are differences, both in the Chinese petuntses, and the English moor-stones; all of them contain micaceous and quartzy particles, in greater or less quantity, along with feltspat, which last is the essential ingredient for the porcelain manufactory. The only injurious material com­monly found in them is iron, which discolours the ware in porportion to its quantity, and which our moor-stones are, perhaps, more frequently tainted with than the Chinese. Very fine porcelain has been made from English mate­rials, but the nature of the manufacture renders the process precarious and the profit hazardous; for the semi-vitrification, which constitutes porcelain, is necessarily accompanied with a degree of softness or semi-fusion, so that the vessels are liable to have their forms altered in the kiln, or to run toge­ther with any accidental augmentations of the fire.

NOTE XXII.—PORTLAND VASE.

THE celebrated funeral vase, long in possession of the Barberini family, and lately purchased by the Duke of Porland for a thousand guineas, is about ten inches high, and fix in diameter in the broadest part. The figures are of most exquisite workmanship in has relief, of white opake glass, raised on a ground of deep blue glass, which appears black, except when held against the light. Mr. Wedgwood is of opinion, from many circumstances, that the figures have been made by cutting away the external crust of white opake glass, in the manner the finest cameos have been produced, and that it must thence have been the labour of a great many years. Some antiqua­rians, have placed the time of its production many centuries before the chris­tian aera, as sculpture was said to have been declining, in respect to its ex­cellence, in the time of Alexander the Great. See an account of the Bar­berini, or Portland vase, by M. D'Hancarville, and by Mr. Wedgwood.

Many opinions and conjectures have been published concerning the figures on this celebrated vase. Having carefully examined one of Mr. Wedg­wood's beautiful copies of this wonderful production of art, I shall add one more conjecture to the number.

Mr. Wedgwood has well observed, that it does not seem probable that the Portland vase was purposely made for the ashes of any particular person deceased, because many years must have been necessary for its production. Hence it may be concluded, that the subject of its embellishments is not private history, but of a general nature. This subject appears to me to be well chosen, and the story to be finely told; and that it represents what in ancient times engaged the attention of philosophers, poets, and heroes; I mean a part of the Eleusinian mysteries.

These mysteries were invented in Egypt, and afterwards transferred to Greece, and flourished more particularly at Athens, which was, at the same time, the seat of the fine arts. They consisted of scenical exhibitions, re­presenting and inculcating the expectation of a future life after death, and, on this account, were encouraged by the government, in so much that the Athe­nian laws punished a discovery of their secrets with death. Dr. Warbur­ton has, with great learning and ingenuity, shewn, that the descent of AEneas into hell, described in the sixth Book of Virgil, is a poetical account of the representations of the future state in the Eleusinian mysteries. Divine Le­gation, vol. I. p. 210.

And though some writers have differed in opinion from Dr. Warburton on this subject, because Virgil has introduced some of his own heroes into the Elysian fields, as Deiphobus, Palinurus, and Dido, in the same manner as Homer had done before him; yet it is agreed, that the received notions about a future state were exhibited in these mysteries; and as these poets described those received notions, they may be said, as far as these religious doctrines were concerned, to have described the mysteries.

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[Page 187] Now, as these were emblematic exhibitions, they must have been as well adapted to the purposes of sculpture as of poetry, which, indeed, does not seem to have been uncommon, since one compartment of figures in the shield of AEneas represented the regions of Tartares. [...] Lib. X. The procession of torches, which, according to M. De. St. Croix, was exhibited in these mysteries, is still to be seen in basso relieve, discovered by Span and Wheler. Memoires fur le Mysaeres per De. St. Croix. 1784. And it is very probable that the beautiful gem representing the marriage of Cupid and Psyche, as described by Apuleus, was originally descriptive of another part of the exhibitions in these mysteries, though afterwards it became a common subject of ancient art. See Divine Legat. vol. I. p. 323. What subject could have been imagined so sublime for the [...] of a funeral urn, as the mortality of all things, and their resuscitation? Where could the designer be supplied with emblems for this purpose, before the Christian aera, but from the Eleusinian mysteries?

1. The exhibitions of the mysteries were of two kinds—these which the people were permitted to see, and those which were only shewn to the ini­tiated. Concerning the latter, Aristides calls them "the most shocking and most ravishing representations." And Stob [...]us asserts, that the initiation into the grand mysteries exactly resembles death. Divine Legat. vol. 1. p. 280, and p. 272. And Virgil, in his entrance to the shades below, amongst other things of terrible form, mentions death. AEn. VI. This part of the exhibition seems to be represented in one of the compartments of the Port­land vase.

Three figures of exquisite workmanship are placed by the side of a ruined column, whose capital is fallen off, and lies at their feet with other disjointed stones, they sit on loose piles of stone, beneath a tree, which has not the leaves of any evergreen of this climate, but may be supposed to be an elm, which Virgil places near the entrance of the infernal regions, and adds, that a dream was believed to dwell under every leaf to it. AEn. VI. l. 281. In the midst of this group reclines a female figure in a dying attitude, in which extreme languor is beautiful represented; in her hand is an inverted torch, an ancient emblem of extinguished life; the elbow of the same arm resting on a stone, supports her as she sinks, while the other hand is raised, and thrown over her drooping head, in some measure sustaining it, and gives, with great art, the idea of fainting lassitude. On the right of her sits a man, and on the left a woman, both supporting themselves on their arms, as people are liable to do when they are thinking intensely. Then have their backs towards the dying figure, yet with their faces turned towards her, as if seriously contemplating her situation, but without stretching out their hands to assist her.

This central figure, then, appears to me to be an hieroglyphic, or Eleusi­nian emblem of MORTAL LIFE, that is, the lethum, or death, mentioned by Virgil amongst the terrible things exhibited at the beginning of the myste­ries. The inverted torch shews the figure to be emblematic; if it had been designed to represent a real person in the act of dying, there had been no necessity for the expiring torch, as the dying figure alone would have been [Page 188] sufficiently intelligible;—it would have been as absurd as to have put an in­verted torch into the hand of a real person at the time of his expiring. Be­sides, if this figure had represented a real dying person, would not the other figures, or one of them at least, have stretched out a hand to support her, to have cased her fall among loose stones, or to have smoothed her pillow? These circumstances evince that the figure is an emblem, and, therefore, could not be a representation of the private history of any particular family [...] event.

The man and woman on each side of the dying figure must be considered as emblems, both from their similarity of situation and dress to the middle figure, and their being grouped along with it. These, I think, are hierogly­phic or Eleusinian emblems of HUMANKIND, with their backs toward the dy­ing figure of MORTAL LIFE, unwilling to associate with her, yet turning back their serious and attentive countenances, curious indeed to behold, yet sorry to contemplate their latter end. These figures bring strongly to one's mind the Adam and Eve of sacred writ, whom some have supposed to have been allegorical or hieroglyphic persons of Egyptian origin, but of more ancient date; amongst whom, I think, is Dr. Warburton. According to this opi­nion, Adam and Eve were the names of two hieroglyphic figures, represent­ing the early state of mankind; Abel was the name of an hieroglyphic fi­gure, representing the age of pasturage; and Cain, the name of another hie­roglyphic symbol, representing the age of agriculture; at which time the uses of iron were discovered. And as the people who cultivated the earth, and built houses, would increase in numbers much faster by their greater pro­duction of food, they would readily conquer or destroy the people who were sustained by pasturage, which was typified by Cain slaying Abel.

2. On the other compartment of this celebrated vase, is exhibited an em­blem of immortality, the representation of which was well known to con­stitute a very principal part of the shews at the Eleusinian mysteries, as Dr. Warburton has proved by variety of authority. The habitation of spi­rits or ghosts, after death, was supposed by the ancients to be placed beneath the earth, where Pluto reigned, and dispensed rewards or punishments. Hence the first figure in this group is of the MANES, or GHOST, who, hav­ing passed through an open portal, is descending into a dusky region, point­ing his toe with timid and unsteady step, feeling, as it were, his way in the gloom. This portal AEneas enters, which is described by Virgil,—patet arti janua Ditls, AEn. VI. l. 126; as well as the easy descent,—facilis de­scensus Averni. Ib. The darkness at the entrance to the shades is humor­ously described by Lucian. Div. Legat. vol. I. p. 241. And the horror of the gates of hell was, in the time of Homer, become a proverb. Achilles says to Ulysses, "I hate a lyar worse than the gates of hell;" the same ex­pression is used in Isaiah, ch. xxxviii. v. 10. The MANES, or GHOST, appears lingering and fearful, and wishes to drag after him a part of his mortal garment, which, however, adheres to the side of the portal through which he has passed. The beauty of this allegory would have been expressed by Mr. Pope, by "we feel the ruling passion strong in death."

A little lower down in the group, the manes, or ghost, is received by a [Page]

[Page 189] beautiful female, a symbol of IMMORTAL LIFE. This is evinced by her fondling between her knees a large and playful serpent, which, from its an­nually renewing its external skin, has, from great antiquity, even as early as the fable of Prometheus, been esteemed an emblem of renovated youth. The story of the serpent acquiring immortal life from the ass of Prome­theus, who carried it on his back, is told in Bacon's Works, vol. V. p. 462. quarto edit. Lond. 1778. For a similar purpose a serpent was wrapped round the large hieroglyphic egg in the temple of Dioscuri, as an emblem of the renewal of life from a state of death. Bryant's Mythology, vol. II. p. 359. sec. edit. On this account also the serpent was an attendant on AEsculapias, which seems to have been the name of the hieroglyphic figure of medicine. This serpent shews this figure to be an emblem, as the torch shewed the central figure of the other compartment to be an emblem; hence they agreeably correspond, and explain each other, one representing MOR­TAL LIFE, and the other IMMORTAL LIFE.

This emblematic figure of immortal life sits down with her feet towards the figure of Pluto, but, turning back her face towards the timid ghost, she stretches forth her hand, and, taking hold of his elbow, supports his totter­ing steps, as well as encourages him to advance, both which circumstances are thus, with wonderful ingenuity, brought to the eye. At the same time the spirit loosely lays his hand upon her arm, as one walking in the dark would naturally do for the greater certainty of following his conductress; while the general part of the symbol of IMMORTAL LIFE, being turned to­ward the figure of Pluto, shews that she is leading the phantom to his realms.

In the Pamphili gardens at Rome, Perseus, in assisting Andromeda to de­scend from the rock, takes hold of her elbow to steady or support her step, and she lays her hand loosely on his arm, as in this figure. Admir, Roman Antiq.

The figure of PLUTO can not be mistaken, as it is agreed by most of the writers who have mentioned this vase; his grisley heard, and his having one foot buried in the earth, denote the infernal monarch. He is placed at the lowest part of the group, and, resting his chin on his hand, and his arm upon his knee, receives the stranger-spirit with inquisitive attention. It was before observed, that when people think attentively, they naturally rest their bodies in some easy attitude, that more animal power may be employed on the thinking faculty. In this group of figures there is great art shewn in giving an idea of a descending plain, viz. from earth to Elysium, and yet all the figures are, in reality, on a horizontal one. This wonderful decep­tion is produced, first, by the descending step of the manes, or ghost; se­condly, by the arm of the sitting figure of Immortal Life being raised up to receive him as he descends; and, lastly, by Pluto having one foot sunk into the earth.

There is yet another figure which is concerned in conducting the manes, or ghost, to the realms of Pluto, and this is LOVE. He precedes the descend­ing spirit on expanded wings, lights him with his torch, and turning back his beautiful countenance, beckons him to advance. The ancient God of love [Page 190] was of much higher dignity than the modern Cupid. He was the first that came out of the great egg of night, (Hesiod. Theog. V. CXX. Briant's Mythol. vol. II. p. 348.) and is said to possess the keys of the sky, sea, and earth. As he, therefore, led the way into this life, he seems to constitute a proper emblem for leading the way to a future life. See Bacon's works, vol. I. p. 568. and vol. III. p. 582. quarto edit.

The introduction of Love into this part of the mysteries requires a little further explanation. The Psyche of the Egyptians was one of their most favourite emblems, and represented the soul, or a future life; it was origi­nally no other than the aurelia, or butterfly, but in after time, was repre­sented by a lovely female child, with the beautiful wings of that insect. The aurelia, after its first stage as an eruca or caterpillar, lies for a season in a manner dead, and is inclosed in a sort of coffin; in this state of darkness it remains all the winter; but, at the return of spring, it bursts its bonds and comes out with new life, and in the most beautiful attire. The Egyptians thought this a very proper picture of the soul of man, and of the immor­tality to which it aspired. But as this was all owing to divine Love, of which EROS was an emblem, we find this person frequently introduced as a concomitant of the soul in general, or Psyche. (Bryant's Mythol. vol. II. p. 386.) EROS, or divine Love, is for the same reason as proper attendant on the manes or soul after death, and much contributes to tell the story, that is, to shew that a soul or manes is designed by the descending figure. From this figure of Love, M. D'Hancarville imagines that Orpheus and Eurydice are typified under the figure of the manes, and immortal life as above de­scribed. It may be sufficient to answer, first, that Orpheus is always repre­sented with a lyre, of which there are prints of four different gems in Spence's Polymetis, and Virgil so describes him, AEn. VI. cytharâ fretus. And secondly, that it is absurd to suppose that Eurydice was fondling and playing with a serpent that had slain her. Add to this, that Love seems to have been an inhabitant of the infernal regions, as exhibited in the mysteries; for Claudian, who treats more openly of the Eleusinian mysteries, when they were held in less veneration, invokes the deities to disclose to him their secrets, and amongst other things, by what torch Love softens Pluto.

In this compartment there are two trees, whose branches spread over the figures; one of them has smoother leaves, like some evergreens, and might thence be supposed to have some allusion to immortality, but they may perhaps have been designed only as ornaments, or to relieve the figures, or because it was in groves, where these mysteries were originally celebrated. Thus Homer speaks of the woods of Proserpine, and mentions many trees in Tartarus, as presenting their fruits to Tantalus; Virgil speaks of the pleasant groves of Elysium; and in Spence's Polymetis there are prints of two ancient gems, one of Orpheus charming Cerberus with his lyre, and the other of Hercules binding him in a cord; each of them standing by a [Page]

[Page 191] tree. Polymet. p. 284. As, however, these trees have all different foliage so clearly marked by the artist, they may have had specific meanings in the exhibitions of the mysteries, which have not reached posterity: of this kind seem to have been the tree of knowledge of good and evil, and the tree of life, in sacred writ, both which must have been emblematic or allegorical. The masks hanging to the handles of the vase, seem to indicate that there is a concealed meaning in the figures besides their general appearance. And the priestess at the bottom, which I come now to describe, seems to shew this concealed meaning to be of the sacred or Eleusinian kind.

3. The figure on the bottom of the vase, is on a larger scale than the others, and less finely finished, and less elevated; and, as this bottom part was afterwards cemented to the upper part, it might be executed by ano­ther artist, for the sake of expedition; but there seems no reason to suppose that it was not originally designed for the upper part of it, as some have conjectured. As the mysteries of Ceres were celebrated by female priests, for Porphyrius says the ancients called, the priestesses of Ceres, Melissai, or bees, which were emblems of chastity, Div. Leg. vol. I. p. 235. and, as in his Satire against the sex, Juvenal says, that few women are worthy to be priestesses of Ceres, Sat. VI. the figure at the bottom of the vase would seem to represent a PRIESTESS, or HIEROPHANT, whose office it was to intro­duce the initiated, and point out to them, and explain the exhibitions in the mysteries, and to exclude the uninitiated, calling out to them, "Far, far retire, ye profane!" and to guard the secrets of the temple. Thus the in­troductory hymn sung by the hierophant, according to Eusebius, begins, "I will declare a secret to the initiated, but let the doors be shut against the profane." Div. Leg. vol. I. p. 177. The priestess or hierophant ap­pears in this figure, with a close hood, and dressed in linen, which sits close about her; except a light cloak, which flutters in the wind. Wool, as taken from slaughtered animals, was esteemed profane by the priests of Egypt, who were always dressed in linen. Apuleus, p. 64. Div. Leg. vol. 1. p. 318. Thus Eli made for Samuel a linen ephod. Samuel i. 3.

Secrecy was the foundation on which all mysteries rested; when publicly known, they ceased to be mysteries; hence a discovery of them was not only punished with death by the Athenian law, but in other countries a disgrace attended the breach of a solemn oath. The priestess, in the figure before us, has her finger pointing to her lips, as an emblem of silence. There is a figure of Harpocrates, who was of Egyptian origin, the same as Orus, with the lotus on his head, and with his finger pointing to his lips, not pressed upon them, in Bryant's Mythol. vol. II. p. 398. and another female figure standing on a lotus, as if just risen from the Nile, with her finger in the same attitude; these seem to have been representations or emblems of male and female priests of the secret mysteries. As these sorts of emblems were frequently changed by artists for their more elegant exhibition, it is possible the foliage over the head of this figure may bear some analogy to the lotus above-mentioned.

This figure of secrecy seems to be here placed, with great ingenuity, as a caution to the initiated, who might understand the meaning of the em­blems [Page 192] round the vase, not to divulge it. And this circumstance seems to account for there being no written explanation extant, and no tradition con­cerning these beautiful figures handed down to us along with them.

Another explanation of this figure, at the bottom of the vase, would seem to confirm the idea that the basso relievos round its sides are representations of a part of the mysteries; I mean that it is the head of ATIS. Lucian says that Atis was a young man of Phrygia, of uncommon beauty; that he dedi­cated a temple in Syria to Rhea, or Cybele, and first taught her mysteries to the Lydians, Phrygians, and Samothracians, which mysteries he brought from India. He was afterwards made an eunuch by Rhea, and lived like a woman, and assumed a feminine habit, and in that garb went over the world, teaching her ceremonies and mysteries. Dict. par M. Danet, art. Atis. As this figure is covered with clothes, while those on the sides of the vase are naked, and has a Phrygian cap on the head, and as the form and features are so soft, that it is difficult to say whether it be a male or female figure, there is reason to conclude, 1. That it has reference to some particular person of some particular country; 2. That this person is Atis, the first great hierophant, or teacher of mysteries, to whom M. De la Chausse says the figure itself bears a resemblance. Museo. Capitol. Tom. IV. p. 402.

In the Museum Etruscum, vol. 1. plate 96, there is the head of Atis with feminine features, clothed with a Phrygian cap, and rising from very broad foliage placed on a kind of term, supported by the paw of a lion. Goreus, in his explanation of the figure, says that it is placed on a lion's foot be­cause that animal was sacred to Cybele, and that it rises from very broad leaves, because after he became an eunuch, he determined to dwell in the groves. Thus the foliage, as well as the cap and feminine features, confirm the idea of this figure at the bottom of the vase, representing the head of Atis, the first great hierophant; and that the figures on the sides of the vase are emblems from the ancient mysteries.

I beg leave to add, that it does not appear to have been uncommon amongst the ancients, to put allegorical figures on funeral vases. In the Pamphili palace at Rome, there is an elaborate representation of Life and Death, on an ancient sarcophagus. In the first Prometheus is represented making man, and Minerva is placing a butterfly, or the soul, upon his head. In the other compartment, Love extinguishes his torch in the bosom of the dying figure, and is receiving the butterfly, or Psyche, from him, with a great number of complicated emblematic figures grouped in very bad taste. Admir. Roman Antiq.

NOTE XXIII.—COAL.

To elucidate the formation of coal-beds, I shall here describe a fountain of fossil tar, or petroleum, discovered lately near Colebrook Dale, in Shrop­shire, the particulars of which were sent me by Dr. Robert Darwin, of Shrewsbury.

About a mile and a half below the celebrated iron-bridge, constructed by the late Mr. Darby, near Colebrook Dale, on the east side of the river Severn, as the workmen, in October, 1786, were making a subterranean canal into the mountain, for the more easy acquisition and conveyance of the coals which lie under it, they found an oozing of liquid bitumen, or petro­leum; and as they proceeded further, cut through small cavities of different sizes, from which the bitumen issued. From ten to fifteen barrels of this fossil tar, each barrel containing thirty-two gallons, were at first collected in a day, which has since, however, gradually diminished in quantity, so that at present the product is about seven barrels in fourteen days.

The mountain into which this canal enters, consists of siliceous sand, in which, however, a few marine productions, apparently in their recent state, have been found, and are now in the possession of Mr. William Reynolds, of Ketly Bank. About three hundred yards from the entrance into the mountain, and about twenty-eight yards below the surface of it, the tar is found oozing from the sand-rock above, into the top and sides of the canal.

Beneath the level of this canal, a shaft has been sunk through a grey argillaceous substance, called, in this country, clunch, which is said to be a pretty certain indication of coal; beneath this lies a stratum of coal, about two or three inches thick, of an inferior kind, yielding little flame in burn­ing, and leaving much ashes; below this is a rock of a harder texture; and beneath this are found coals of an excellent quality; for the purpose of pro­curing which with greater facility, the canal, or horizontal aperture, is now making into the mountain. July, 1788.

Beneath these coals, in some places is found salt water; in other parts of the adjacent country, there are beds of iron-stone, which also contain some bitumen in a less fluid state, and which are about on a level with the new canal, into which the fossil tar oozes, as above described.

There are many interesting circumstances attending the situation and ac­companiments of this fountain of fossil tar, tending to develope the manner of its production. 1. As the canal passing into the mountain runs over the beds of coals, and under the reservoir of petroleum, it appears that a natural distillation of this fossil, in the bowels of the earth, must have taken place at some early period of the world, similar to the artificial distillation of coal, which has many years been carried on in this place on a smaller scale above ground. When this reservoir of petroleum was cut into, the slowness of its exsudation into the canal, was not only owing to its viscidity, but to the [Page 194] pressure of the atmosphere, or to the necessity there was that air should at the same time insinuate itself into the small cavities from which the petro­leum descended. The existence of such a distillation at some ancient time, is confirmed by the thin stratum of coal beneath the canal, (which covers the hard rock,) having been deprived of its fossil oil, so as to burn without flame, and thus to have become a natural cock, or fossil charcoal, while the petroleum distilled from it is found in the cavities of the rock above it.

There are appearances in other places, which favour this idea of the natu­ral distillation of petroleum: thus, at Matlock, in Derbyshire, a hard bitumen is found adhering to the spar in the clefts of the lime-rocks, in the form of round drops about the size of peas; which could, perhaps, only be deposited there in that form by sublimation.

2. The second deduction which offers itself is, that these beds of coal have been exposed to a considerable degree of beat, since the petroleum above could not be separated, as far as we know, by any other means, and that the good quality of the coals beneath the hard rock, was owing to the im­permeability of this rock to the bituminous vapour, and to its pressure being too great to permit its being removed by the elasticity of that vapour. Thus, from the degree of heat, the degree of pressure, and the permeability of the superincumbent strata, many of the phenomena attending coal-beds receive an easy explanation, which much accords with the ingenious theory of the earth by Dr. Hutton. Trans. of Edinb. vol. 1.

In some coal works, the fusion of the strata of coal has been so light, that there remains the appearance of ligneous sebres and the impression of leaves, as at Bovey, near Exeter, and even seeds of vegetables, of which I have had specimens from the collieries near Polesworth, in Warwickshire. In some, where the heat was not very intense, and the incumbent stratum not permeable to vapour, the fossil oil has only risen to the upper part of the coal-bed, and has rendered that much more inflammable than the lower parts of it, as in the collieries near Beaudesert, the seat of the Earl of Ux­bridge, in Staffordshire, where the upper stratum is a perfect cannel, or can­dle-coal, and the lower of an inferior quality. Over the coal-beds near Sir H. Harpur's house, in Derbyshire, a thin lamina of asphaltum is found in some places near the surface of the earth, which would seem to be from a distillation of petroleum from the coals below, the more fluid part of which had, in process of time, exhaled, or been consolidated by its absorption of air. In other coal-works the upper part of the stratum is of a worse kind than the lower one, as at Alfreton and Denbigh, in Derbyshire, owing to the superincumbent stratum having permitted the exhalation of a great part of the petroleum; whilst at Widdrington, in Northumberland, there is first a seam of coal about six inches thick of no value, which lies under about four fathom of clay; beneath this is a white free-stone, then a hard stone, which the workmen there call a whin, then two fathoms of clay, then ano­ther white stone, and under that a vein of coals three feet nine inches thick, of a similar nature to the Newcastle coal. Phil. Trans. Abridg. vol. VI. plate 2, p. 192. The similitude between the circumstances of this colliery, and of the coal beneath the fountain of tar above described, readers it [Page 195] highly probable, that this upper thin seam of coal has suffered a similar dis­tillation, and that the inflammable part of it had either been received into the clay above, in the form of sulphur, which, when burnt in the open air, would produce alum; or had been dissipated, for want of a receiver, where it could be condensed. The former opinion is, perhaps, in this case, more pro­bable, as in some other coal-beds, of which I have procured accounts, the surface of the coal beneath clunch or clay is of an inferior quality, as at West Hallum, in Nottinghamshire. The clunch probably from hence acquires its inflammable part, which, on calcination, becomes vitriolic acid. I ga­thered pieces of clunch, converted partially into alum, at a colliery near Bil­ston, where the ground was still on fire a few years ago.

The heat, which has thus pervaded the beds of morass, seems to have been the effect of the fermentation of their vegetable materials; as new hay sometimes takes fire, even in such very small masses, from the sugar it contains, and seems, hence, not to have been attended with any expulsion of lava, like the deeper craters of volcanos situated in the beds of granite.

3. The marine shells found in the loose sand-rock, above this reservoir of petroleum, and the coal-beds beneath it, together with the existence of sea­salt beneath these coals, prove that these coal-beds have been at the bottom of the sea, during some remote period of time, and were afterwards raised into their present situation by subterraneous expansions of vapour. This doc­trine is further supported by the marks of violence, which some coal-beds received at the time they were raised out of the sea, as in the colleries at Men­dip, in Somersetshire. In these are seven strata of coals, equitant upon each other, with beds of clay and stone intervening; amongst which clay are found shells and fern branches. In one part of this hill the strata are disjoined, and a quantity of heterogeneous substances fill up the chasm which disjoins them; on one side of this chasm the seven strata of coal are seen corresponding, in respect to their reciprocal thickness and goodness, with the seven strata on the other side of the cavity, except that they have been elevated several yards higher. Phil. Trans. No. 360. Abridg. vol. V. p. 237.

The cracks in the coal-bed near Ticknall, in Derbyshire, and in the sand­stone rock over it, in both of which specimens of lead-ore and spar are found, confirm this opinion of their having been forcibly raised up by sub­terraneous fires. Over the colliery at Brown-hills, near Lichfield, there is a stratum of gravel on the surface of the ground, which may be adduced as ano­ther proof to shew that those coals had some time been beneath the sea, or the bed of a river. Nevertheless, these arguments only apply to the collieries above-mentioned, which are few compared with those which bear no marks of having been immersed in the sea.

On the other hand, the production of coals from morasses, as described in note XX. is evinced from the vegetable matters frequently found in them, and in the strata over them; as fern-leaves in nodules of iron-ore, and from the bog-shells, or fresh water muscles, sometimes found over them, of both which I have what I believe to be specimens; and is further proved, from some parts of these beds being only in part transformed to coal; and the [Page 196] other part still retaining not only the form, but some of the properties of wood; specimens of which are not unfrequent in the cabinets of the curi­ous, procured from Loch Neigh, in Ireland, from Bovey, near Exeter, and other places; and from a famous cavern called the Temple of the Devil, near the town of Altorf, in Franconia, at the foot of a mountain covered with pine and savine, in which are found large coals resembling trees of ebony; which are so far mineralized as to be heavy and compact; and so to effloresce with pyrites in some parts as to crumble to pieces; yet from other parts white ashes are produced on calcination, from which fixed alkali is procured; which evinces their vegetable origin. (Dict. Raisonné, art. Charbon.) To these may be added another argument, from the oil which is distilled from coals, and which is analogous to vegetable oil, and does not exist in any bodies truly mineral. Keir's Chemical Dictionary, art. Bitumen.

Whence it would appear, that though most collieries, with their attendant strata of clay, sand-stone, and iron, were formed on the places where the vegetables grew, from which they had their origin; yet that other collec­tions of vegetable matter were washed down from eminences, by currents of waters, into the beds of rivers, or the neighbouring seas, and were there accumulated at different periods of time, and underwent a great degree of heat, from their fermentation, in the same manner as those beds of morass which had continued on the plains where they were produced. And that, by this fermentation, many of them had been raised from the ocean, with sand and sea-shells over them; and others from the beds of rivers, with ac­cumulations of gravel upon them.

4. For the purpose of bringing this history of the products of morasses more distinctly to the eye of the reader, I shall here subjoin two or three ac­counts of sinking or boring for coals, out of above twenty, which I have procured from various places, though the terms are not very intelligible, being the language of the overseers of coal-works.

1. Whitfield mine, near the Pottery, in Staffordshire. Soil 1 foot, brick­clay 3 feet, shale 4, metal which is hard brown, and falls in the weather, 42, coal 3, warrant clay 6, brown grit-stone 36, coal 3 ½, warrant clay 3 ½, bass and metal 53 ½, hard-stone 4, shaly bass 1 ½, coal 4, warrant clay depth unknown; in all about 55 yards.

2. Coal-mine at Alfreton, in Derbyshire. Soil and clay 7 feet, fragments of stone 9, bind 13, stone 6, bind 34, stone 5, bind 2, stone 2, bind 10, coal 1 ½, bind 1 ½, stone 37, bind 7, soft coal 3, bind 3, stone 20, bind 16, coal 7 ½, in all about 61 yards.

3. A basset coal-mine at Woolarton, in Nottinghamshire. Sand and gravel 6 feet, bind 21, stone 10, smut or effete coal 1, clunch 4, bind 21, stone 18, bind 18, stone-bind 15, soft coal 2, clunch and bind 21, coal 7; in all about 48 yards.

4. Coal-mine at West-Hallam, in Nottinghamshire. Soil and clay 7 feet, bind 48, smut 1 ½, clunch 4, bind 3, stone 2, bind 1, stone 1, bind 3, stone 1, bind 16, shale 2, bind 12, shale 3, clunch, stone, and a bed of cank, 54, soft coal 4, clay and dun 1, soft coal 4 ½ clunch and bind 21, coal 1, broad bind 26, hard coal 6; in all about 74 yards.

[Page 197] As these strata generally lie inclined, I suppose, parallel with the lime­stone on which they rest, the upper edges of them all come out to day, which is termed bassetting; when the whole mass was iginited by its fer­mentation, it is probable that the inflammable part of some strata might thus more easily escape than of others, in the form of vapour, as dews are known to slide between such strata in the production of springs; which ac­counts for some coal-beds being so much worse than others. See note XX.

From this account of the production of coals from morasses, it would ap­pear, that coal-beds are not to be expected beneath, masses of lime-stone. Nevertheless, I have been lately informed by my friend, Mr. Michel, of Thornhill, who, I hope, will soon favour the public with his geological investigations, that the beds of chalk are the uppermost of all the lime­stones; and that they rest on the granulated lime-stone, called ketton-stone; which, I suppose, is similar to that which covers the whole country from Leadenham to Sleaford, and from Sleaford to Lincoln; and that, thirdly, coal-delphs are frequently found beneath these two uppermost beds of lime­stone.

Now, as the beds of chalk, and of granulated lime-stone may have been formed by alluviation, on or beneath the shores of the sea, or in vallies of the land, it would seem, that some coal-countries, which, in the great com­motions of the earth, had been sunk beneath the water, were thus covered with alluvial lime-stone, as well as others with alluvial basaltes, or com­mon gravel-beds. Very extensive plains, which now consist of alluvial ma­terials, were, in the early times, covered with water, which has since di­minished, as the solid parts of the earth have increased. For the solid parts of the earth, consisting chiefly of animal and vegetable recrements, must have originally been formed or produced from the water, by animal and vegetable processes; and as the solid parts of the earth may be supposed to be thrice as heavy as water, it follows, that thrice the quantity of water must have vanished, compared with the quantity of earth thus produced. This may account for many immense beds of alluvial materials, as gravel, rounded sand, granulated lime-stone, and chalk, covering such extensive plains as Lincoln-heath, having become dry without the supposition of their having been again elevated from the ocean. At the same time we acquire the knowledge of one of the uses or final causes of the organized world, not indeed very flattering to our vanity; that it converts water into earth, forming islands and continents by its recrements or exuviae.

NOTE XXIV.—GRANITE.

THE lowest stratum of the earth which human labour has arrived to, is granite; and of this, likewise, consists the highest mountains of the world. It is known under variety of names, according to some difference in its ap­pearance [Page 198] of composition, but is now generally considered by philosophers as a species of lava; if it contains quartz, feltspat, and mica, in distinct crystals, it is called granite; which is found, in Cornwall, in rocks; and in loose stones in the gravel near Drayton, in Shropshire, in the road towards New­castle. If these parts of the composition be less distinct, or if only two of them be visible to the eye, it is termed porphyry, trap, whin-stone, moor­stone, slate. And if it appears in a regular angular form, it is called ba­saltes. The affinity of these bodies has lately been further well established by Dr. Beddoes, in the Phil. Trans. vol. LXXX.

These are all esteemed to have been volcanic productions, that have un­dergone different degrees of heat. It is well known, that in Papin's digester water may be made red-hot by confinement, and will then dissolve many bodies which otherwise are little or not at all acted upon by it. From hence it may be conceived, that under immense pressure of superincumbent materials, and by great heat, these masses of lava may have undergone a kind of aqueous solution, without any tendency to vitrifaction, and might thence have a power of ceystallization; whence all the varieties above-men­tioned, from the different proportion of the materials, or the different de­grees of heat they may have undergone in this aqueous solution. And that the uniformity of the mixture of the original earths, as of lime, argil, silex, magnesia, and barytes, which they contain, was owing to their boiling to­gether a longer or shorter time before their elevation into mountains. See note XIX. art. 8.

The seat of volcanos seems to be principally, if not entirely, in these strata of granite, as many of them are situated on granite mountains, and throw up, from time to time, sheets of lava, which run down over the pre­ceding strata, from the same origin; and in this they seem to differ from the heat which has separated the clay, coal, and sand, in morasses, which would appear to have risen from a kind of fermentation, and thus to have pervaded the whole mass, without any expuition of lava.

All the lavas from Vesuvius contain one fourth part of iron, (Kirwan's Min.) and all the five primitive earths, viz. calcareous, argillaceous, siliceous, barytic, and magnesian earths, which are also evidently produced now, daily, from the recrements of animal and vegetable bodies. What is to be thence concluded? Has the granite stratum, in very ancient times, been produced like the present calcareous and siliceous masses, according to the ingenious theory of Dr. Hutton, who says new continents are now forming at the bottom of the sea, to rise in their turn; and that thus the terraqueous globe has been, and will be, eternal? Or shall we suppose, that this internal heated mass of granite, which forms the nucleus of the earth, was a part of the body of the sun, before it was separated by an explosion? Or was the sun originally a planet, inhabited like ours, and a satellite to some other greater sun, which has long been extinguished by diffusion of its light, and around which the present sun continues to revolve, according to a conjec­ture of the celebrated Mr. Herschell, and which conveys to the mind a most sublime idea of the progressive and increasing excellence of the works of the Creator of all things?

[Page]

[Page 199] For the more easy comprehension of the facts and conjectures concern­ing the situation and production of the various strata of the earth, I shall here subjoin a supposed section of the globe, but without any attempt to give the proportions of the parts, or the number of them, but only their re­spective situation over each other, and a geological recapitulation.

NOTE XXV.—EVAPORATION.

1. THE atmosphere will dissolve a certain quantity of moisture, as a che­mical menstruum, even when it is much below the freezing point, as ap­pears from the diminution of ice suspended in frosty air; but a much greater quantity of water is evaporated, and suspended in the air, by means of heat, which is, perhaps, the universal cause of fluidity; for water is known to boil with less heat in vacuo, which is a proof that it will evaporate faster in va­cuo, [Page 201] and that the air, therefore, rather hinders than promotes its evapora­tion in higher degrees of heat. The quick evaporation occasioned in vacuo by a small degree of heat, is agreeably seen in what is termed a pulse-glass, which consists of an exhausted tube of glass, with a bulb at each end of it, and with about two thirds of the cavity filled with alkohol, in which the spirit is instantly seen to boil, by the heat of the finger-end applied on a bub­ble of steam in the lower bulb, and is condensed again in the upper bulb by the least conceivable comparative coldness.

2. Another circumstance, evincing that heat is the principal cause of eva­poration, is, that at the time of water being converted into steam, a great quantity of heat is taken away from the neighbouring bodies. If a ther­mometer be repeatedly dipped in ether, or in rectified spirit of wine, and exposed to a blast of air, to expedite the evaporation by perpetually remov­ing the saturated air from it, the thermometer will presently sink below freezing. This warmth, taken from the ambient bodies at the time of eva­poration by the steam, is again given out when the steam is condensed into water. Hence the water in a worm-tub, during distillation, so soon be­comes hot; and hence the warmth accompanying the descent of rain in cold weather.

3. The third circumstance, shewing that heat is the principal cause of evaporation, is, that some of the steam becomes again condensed when any part of the heat is withdrawn. Thus, when warmer south-west winds, re­plete with moisture, succeed the colder north-east winds, all bodies that are dense and substantial, as stone walls, brick floors, &c. absorb some of the heat from the passing air, and its moisture becomes precipitated on them; while the north-east winds become warmer on their arrival in this latitude, and are thence disposed to take up more moisture, and are termed drying winds.

4. Heat seems to be the principal cause of the solution of many other bo­dies, as common salt, or blue vitriol, dissolved in water, which, when ex­posed to severe cold, are precipitated, or carried, to the part of the water last frozen; this I observed in a phial filled with a solution of blue vitriol, which was frozen: the phial was burst, the ice thawed, and a blue column of cupreous vitriol was left standing upright on the bottom of the broken glass, as described in note XIX. art. 3.

II. Hence water may either be dissolved in air, and may then be called an aerial solution of water; or it may be dissolved in the fluid matter of heat, according to the theory of M. Lavoisier, and may then be called steam. In the former case, it is probable, there are many other vapours which may precipitate it, as marine acid gas, or fluor acid gas. So alkaline gas and acid gas, dissolved in air, precipitate each other; nitrous gas precipitates vi­tal air from its azote; and inflammable gas, mixed with vital air, ignited by an electric spark, either produces or precipitates the water in both of them. Are there any subtle exhalations, occasionally diffused in the atmos­phere, which may thus cause rain?

1. But as water is, perhaps, many hundred times more soluble in the fluid matter of heat than in air, I suppose the eduction of this heat, by [Page 202] whatever means it is occasioned, is the principal cause of devaporation. Thus, if a region of air is brought from a warmer climate, as the S. W. winds, it becomes cooled by its contact with the earth in this latitude, and parts with so much of its moisture as was dissolved in the quantity of calo­rique, or heat, which it now loses, but retains that part which was suspended by its attraction to the particles of air, or by aerial solution, even in the most severe frosts.

2. A second immediate cause of rain a stream of N. E. wind descend­ing from a superior current of air, and mixing with the warmer S. W. wind below; or the reverse of this, viz. a superior current of S. W. wind mixing with an inferior one of N. E. wind: in both th [...]se cases the whole heaven becomes instantly clouded, and the moisture contained in the S. W. current is precipitated. This cause of devaporation has been ingeniously explained by Dr. Hutton, in the Transact. of Edinburgh, vol. 1. and seems to arise from this circumstance; the particles of air of the N. E. wind educe part of the heat from the S. W. wind, and therefore the water which was dissolved by that quantity of beat is precipitated; all the other part of the water, which was suspended by its attraction to the particles of air, or dissolved in the remainder of the heat, continues unprecipitated.

3. A third method by which a region of air becomes cooled, and, in con­sequence, deposits much of its moisture, is from the mechanical expansion of air, when part of the pressure is taken off. In this case the expanded air becomes capable of receiving or attracting more of the matter of heat into its interstices; and the vapour, which was previously dissolved in this heat, is deposited, as is seen in the receiver of an air-pump, which becomes dewy, as the air within becomes expanded by the eduction of part of it. See note VII. Hence, when the mercury in the barometer sinks without a change of the wind, the air generally becomes colder. See note VII. on Elementa­ry Heat. And it is probably from the varying pressure of the incumbent air, that in summer days small black clouds are often thus suddenly produced, and again soon vanish. See a paper in Phil. Trans. vol. LXXVIII. en­titled Frigorific Experiments on the Mechanical Expansion of Air.

4. Another portion of atmospheric water may possibly be held in solution by the electric fluid, since, in thunder-storms, a precipitation of the water seems to be either the cause or the consequence of the eduction of the elec­tricity. But it appears more probable that the water is condensed into clouds by the eduction of its heat, and that then the surplus of electricity prevents their coalescence into larger drops, which immediately succeeds the departure of the lightning.

5. The immediate cause why the barometer sinks before rain, is, first, be­cause a region of warm air, brought to us in the place of the cold air which it had displaced, must weigh lighter, both specifically and absolutely, if the height of the warm atmosphere be supposed to be equal to that of the pre­ceding cold one. And, secondly, after the drops of rain begin to fall in any column of air, that column becomes lighter, the falling drops only adding to the pressure of the air in proportion to the resistance which they meet with in passing through that fluid.

[Page 203] If we could suppose water to be dissolved in air without heat, or in very low degrees of heat, I suppose the air would become heavier, as happens in many chemical solutions; but if water, dissolved in the matter of heat, or calorique be mixed with an aerial solution of water, there can be no doubt but an atmosphere consisting of such a mixture, must become lighter in pro­portion to the quantity of calorique. On the same circumstance depends the visible vapour produced from the breath of animals in cold weather, or from a boiling kettle; the particles of cold air with which it is mixed, steal a part of its heat, and become themselves raised in temperature; whence part of the water is precipitated in visible vapour, which if in great quan­tity, sinks to the ground; if in small quantity, and the surrounding air is not previously saturated, it spreads itself till it becomes again dissolved.

NOTE XXVI.—SPRINGS.

THE surface of the earth consists of strata, many of which were formed originally beneath the sea; the mountains were afterwards forced up by sub­terraneous fires, as appears from the fissures in the rocks of which they consist, the quantity of volcanic productions all over the world, and the numerous remains of craters of volcanos in mountainous countries. Hence the strata which compose the sides of mountains lie slanting downwards, and one or two, or more, of the external strata not reaching to the summit when the moun­tain was raised up, the second or third stratum, or a more inferior one, is there exposed to day; this may be well represented by forceably thrusting a blunt instrument through several sheets of paper; a bur will stand up with the lowermost sheet, standing highest in the centre of it. On this upper­most stratum, which is colder as it is more elevated, the dews are condensed in large quantities, and, sliding down, pass under the first, or second, or third stratum, which compose the sides of the hill, and either, form a morass below, or a weeping rock, by oozing out in numerous places, or many of these less currents meeting together, burst out in a more copious rill.

The summits of mountains are much colder than the plains in their vici­nity, owing to several causes; 1. Their being, in a manner, insulated or cut off from the common heat of the earth, which is always, of 48 degrees, and perpetually counteracts the effect of external cold beneath that degree. 2. From their surfaces being larger in proportion to their solid contents, and hence their heat more expeditiously carried away by the ever-moving atmos­phere. 3. The increasing rarity of the air as the mountain rises. All those bodies which conduct electricity well or ill, conduct the matter of heat like­wise well or ill. See note VII. Atmosphere air is a bad conductor of electricity, and thence confines it on the body where it is accumulated; but, when it is made very rare, as in the exhausted receiver, the electric aura [Page 204] passes away immediately to any distance. The same circumstance probably happens in respect to heat, which is thus kept, by the denser air on the plains, from escaping, but is dissipated on the hills, where the air is thinner. 4. As the currents of air rise up the sides of mountains, they become mecha­nically rarefied, the pressure of the incumbent column lessening as they ascend. Hence the expanding air absorbs heat from the mountain as it ascends, as explained in note VII. 5. There is another, and, perhaps, more powerful cause, I suspect, which may occasion the great cold on mountains, and in the higher parts of the atmosphere, and which has not yet been at­tended to; I mean that the fluid matter of heat may probably gravitate round the earth, and form an atmosphere on its surface, mixed with the aerial at­mosphere, which may diminish or become rarer, as it recedes from the earth [...] surface, in a greater proportion than the air diminishes.

6. The great condensation of moisture on the summits of hills has ano­ther cause, which is the dashing of moving clouds against them: in misty days this is often seen to have great effect on plains, where an eminent tree, by obstructing the mist as it moves along, shall have a much greater quantity of moisture drop from its leaves, than falls at the same time on the ground in its vicinity. Mr. White, in his History of Selborne, gives an account of a large tree so situated, from which a stream flowed, during a moving mist, so as to fill the cart-ruts in a lane otherwise not very moist; and ingeniously adds, that trees planted about ponds of stagnant water, contribute much, by these means, to supply the reservoir. The spherules which constitute a mist or cloud, are kept from uniting by so small a power, that a little agita­tion against the leaves of a tree, or the greater attraction of a flat moist sur­face, condenses or precipitates them.

If a leaf has its surface moistened, and particles of water separate from each other, as in a mist, be brought near the moistened surface of a leaf, each particle will be attracted more by that plain surface of water on the leaf, than it can be by the surrounding particles of the mist; because globules only at­tract each other in one point, whereas a plain attracts a globule by a greater extent of its surface.

The common cold springs are thus formed on elevated grounds by the condensed vapours, and hence are stronger when the nights are cold, after hot days, in spring, than even in the wet days of winter. For the warm atmosphere, during the day, has dissolved much more water than it can support in solution during the cold of the night, which is thus deposited in large quantities on the hills, and yet so gradually as to soak in between the strata of them, rather than to slide off over their surfaces, like showers of rain. The common heat of the internal parts of the earth is ascertained by springs which arise from strata of earth too deep to be affected by the heat of summer or the frosts of winter. Those, in this country, are of 48 degrees of heat; those about Philadelphia were said, by Dr. Franklin, to be 52; whether this variation is to be accounted for by the difference of the sun's heat on that country, according to the ingenious theory of Mr. Kir­wan, or to the vicinity of subterranean fires, is not yet, I think, decided. There are, however, subterraneous streams of water not exactly produced [Page 205] in this manner, as streams issuing from fissures in the earth, communicating with the craters of old volcanos: in the Peak of Derbyshire are many hol­lows, called swallows, where the land floods sink into the earth, and come out at some miles distant, as at Ilam, near Ashborne. See note on Fica, vol. II.

Other streams of cold water arise from beneath the snow on the Alps and Andes, and other high mountains, which is perpetually thawing at its un­der surface by the common heat of the earth, and gives rise to large rivers. For the origin of warm springs see note on Fucus, vol. II.

NOTE XXVII.—SHELL FISH.

THE armour of the Echinus, or Sea hedge-hog, consists generally of moveable spines; ( Linnoei System. Nat. vol. 1. p. 1102.) and, in that respect, resembles the armour of the land animal of the same name. The irregular protuberances on other sea-shells, as on some species of the Purpura, and Murex, serve them as a fortification against the attacks of their enemies.

It is said that this animal foresees tempestuous weather, and, sinking to the bottom of the sea, adheres firmly to sea-plants, or other bodies, by means of a substance which resembles the horns of snails. Above twelve hundred of these fillets have been counted, by which this animal fix [...] itself; and when afloat, it contracts these fillets between the basis of its points, the number of which often amounts to two thousand. Dict. Raisonné. art. Oursin. de mer.

There is a kind of Nautilus, called, by Linnaeus, Argonauta, whose shell has but one cell: of this animal Pliny affirms, that having exonerated its shell by throwing out the water, it swims upon the surface, extending a web of wonderful tenuity, and bending back two of its arms, and rowing with the rest, makes a sail, and, at length, receiving the water, dives again. Plin IX. 29. Linnaeus adds to his description of this animal, that like the Crab Diogenes, or Bernhard, it occupies a house not its own, as it is not connected to its shell, and is therefore foreign to it; who could have given credit to this if it had not been attested by so many who have, with their own eyes, seen this argonaut in the act of sailing? Syst. Nat. p. 1161.

The Nautilus, properly so named by Linnaeus, has a shell, consisting of many chambers, of which cups are made in the East with beautiful paint­ing and carying on the mother-pearl. The animal is said to inhabit only the uppermost or open chamber, which is larger than the rest; and that the rest remain empty, except that the pipe, or siphunculus, which communi­cates from one to the other of them, is filled with an appendage of the ani­mal, [Page 206] like a gut or string. Mr. Hook, in his Philos. Exper. p. 306, imagines this to be a dilatable or compressible tube, like the air bladders of fish, and that, by contracting or permitting it to expand, it renders its shell buoyant, or the contrary. See note on Ulva, vol. II.

The Pinna, or Sea-wing, is contained in a two-valve shell, weighing sometimes fifteen pounds, and emits a beard of fine long glossy silk-like fibres, by which it is suspended to the rocks twenty or thirty feet beneath the sur­face of the sea. In this situation it is so successfully attacked by the eight­footed Polypus, that the species, perhaps, could not exist but for the exer­tions of the Cancer Pinnotheris, who lives in the same shell as a guard and companion. Amoen. Acad. vol. II. p. 48. Lin. Syst. Nat. vol. I. p. 1159. and p. 1040.

The Pinnotheris, or Pinnophylax, is a small crab, naked, like Bernard the Hermit, but is furnished with good eyes, and lives in the same shell with the Pinna; when they want food the Pinna opens it shell, and sends its faithful ally to forage; but if the Cancer sees the Polypus, he returns sud­denly to the arms of his blind hostess, who, by closing the shell, avoids the fury of her enemy; otherwise, when it has procured a booty, it brings it to the opening of the shell, where it is admitted, and they divide the prey. This was observed by Haslequist, in his voyage to Palestine.

The Byssus of the ancients, according to Aristotle, was the beard of the Pinna above-mentioned, but seems to have been used by other writers indis­criminately for any spun material, which was esteemed finer or more valu­able than wool. Reaumur says, the threads of this Byssus are not less fine or less beautiful than the silk, as it is spun by the silk-worm; the Pinna on the coast of Italy and Provence (where it is fished up by iron-hooks fixed on long poles) is called the silk-worm of the sea. The stockings and gloves manufactured from it, are of exquisite fineness, but too warm for common wear, and are thence esteemed useful in rheumatism and gout. Dict. Rai­sonné. art. Pinne-marine. The warmth of the Byssus, like that of silk, is probably owing to their being bad conductors of heat, as well as of electricity. When these sibres are broken by violence, this animal, as well as the muscle, has the power to re-produce them like the common spiders, as was observ­ed by M. Adanson. As raw silk, and raw cobwebs, when swallowed, are liable to produce great sickness (as I am informed) it is probable, the part of muscles, which sometimes disagrees with the people who eat them, may be this silky web, by which they attach themselves to stones. The large kind of [...] contains some mother-pearl, of a reddish tinge, ac­cording to M. d'Argeuville. The substance sold under the name of Indian­weed, and used at the bottom of fish-lines, is probably a production of this kind; which, however, is scarcely to be distinguished by the eye from the tendons of a rat's tail, after they have been separated by putrefaction in water, and well cleaned and rubbed; a production, which I was once shewn as a great curiosity; it had the uppermost bone of the tail adhering to it; and was said to have been used as an ornament in a lady's hair.

NOTE XXVIII.—STURGEON.

THE Sturgeon, Acipenser, Strurio. Lin. Syst. Nat. vol. 1. p. 403. is a fish of great curiosity, as well as of great importance; his mouth is placed under the head, without teeth, like the opening of a purse, which he has the power to push suddenly out, or retract. Before this mouth, under the beak, or nose, hang four tendrils, some inches long, and which so resemble earth­worms, that at first sight they may be mistaken for them. This clumsy toothless fish is supposed, by this contrivance, to keep himself in good con­dition, the solidity of his flesh evidently shewing him to be a fish of prey. He is said to hide his large body amongst the weeds near the sea coast, or at the mouths of large rivers, only exposing his cirrhi, or tendrils, which small fish, or sea insects, mistaking for real worms, approach for plunder, and are sucked into the jaws of their enemy. He has been supposed by some to root into the soil at the bottom of the sea or rivers; but the cirrhi, or ten­drils above-mentioned, which hang from his snout over his mouth, must themselves be very inconvenient for this purpose, and, as it has no jaws, it evidently lives by suction, and, during its residence in the sea, a quantity of sea-insects are sound in its stomach.

The flesh was so valued in the time of the Emperor Severus, that it was brought to table by servants with coronets on their heads, and preceded by music, which might give rise to its being, in our country, presented by the Lord Mayor to the King. At present it is caught in the Danube, and the Wolga, the Don, and other large rivers, for various purposes. The skin makes the best covering for carriages; isinglass is prepared from parts of the skin; cavear from the spawn; and the flesh is pickled, or salted, and sent all over Europe.

NOTE XXIX.—OIL ON WATER.

THERE is reason to believe, that when oil is poured upon water, the two surfaces do not touch each other, but that the oil is suspended over the water by their mutual repulsion. This seems to be rendered probable by the following experiment: if one drop of oil be dropped on a bason of wa­ter, it will immediately diffuse itself over the whole, for there being no friction between the two surfaces. there is nothing to prevent its spreading itself by the gravity of the upper part of it, except its own tenacity, into a pellicle of the greatest tenuity. But if a second drop of oil be put upon [Page 208] the former, it does not spread itself, but remains in the form of a drop, as the other already occupied the whole surface of the bason; and there is friction in oil passing over oil though none in oil passing over water.

Hence, when oil is diffused on the surface of water, gentle breezes have no influence in raising waves upon it; for a small quantity of oil will cover a very great surface of water (I suppose a spoonful will diffuse itself over some acres), and the wind blowing upon this, carries it gradually forwards, and there being no friction between the two surfaces, the water is not af­fected. On which account oil has no effect in stilling the agitation of the water after the wind ceases, as was found by the experiments of Dr. Franklin.

This circumstance, lately brought into notice by Dr. Franklin, had been mentioned by Pliny, and is said to be in use by the divers for pearls, who, in windy weather, take down with them a little oil in their mouths, which they occasionally give out, when the inequality of the supernatant waves prevents them from seeing sufficiently distinctly for their purpose.

The wonderful tenuity with which oil can be spread upon water, is evinced by a few drops projected from a bridge, where the eye is properly placed over it, passing through all the prismatic colours as it diffuses itself. And also from another curious experiment of Dr. Franklin's: he cut a piece of cork to about the size of a letter-wafer, leaving a point standing off like a tangent, at one edge of the circle. This piece of cork was then dipped in oil, and thrown into a large pond of water, and as the oil flowed off at the point, the cork-wafer continued to revolve in a contrary direction for seve­ral minutes. The oil flowing off all that time at the pointed tangent, in coloured streams. In a small pond of water this experiment does not so well succeed, as the circulation of the cork stops as soon as the water be­comes covered with the pellicles of oil. See additional notes, No. XIII. and note on Fucus, vol. II.

The ease with which oil and water slide over each other, is agreeable seen if a phial be about half filled with equal parts of oil and water, and made to oscillate, suspended by a string; the upper surface of the oil, and the lower one of the water, will always keep smooth: but the agitation of the surfaces where the oil and water meet, is curious; for their specific gravi­ties being not very different, and their friction on each other nothing, the highest side of the water, as the phial descends in its oscillation, having, ac­quired a greater momentum than the lowest side (from its having descended further) would rise the highest on the ascending side of the oscillation, and thence pushes the then uppermost part of the water amongst the oil.

NOTE XXX.—SHIP-WORM.

THE Teredo, or ship-worm, has two calcareous jaws, hemispherical, flat before, and angular behind. The shell is taper, winding, penetrating ships and submarine wood, and was brought from India into Europe. Linnaei System. Nat. p. 1267. The Tarieres, or sea-worms, attack and erode ships with such fury, and in such numbers, as often greatly to endanger them. It is said that our vessels have not known this new enemy above fifty years; that they were brought from the sea about the Antilles, to our parts of the ocean, where they have increased prodigiously. They bore their passage in the direction of the fibres of the wood, which is their nourishment, and cannot return or pass obliquely, and thence when they come to a knot in the wood, or when two of them meet together, with their stony mouths, they perish for want of food.

In the years 1731 and 1732, the United Provinces were under a dreadful alarm concerning these insects, which had made great depredation on the piles which support the banks of Zealand; but it was happily discovered a few years afterwards, that these insects had totally abandoned that island (Dict. Raisonné, art. Vers Rongeurs), which might have been occasioned by their not being able to live in that latitude, when the winter was rather severer than usual.

NOTE XXXI.—MAELSTROM.

ON the coast of Norway there is an extensive vortex, or eddy, which lies between the islands of Moskoe and Moskenas, and is called Moskoestrom, or Maelstrom; it occupies some leagues in circumference, and is said to be very dangerous, and often destructive, to vessels navigating these seas. It is not easy to understand the existence of a constant descending stream, with­out supposing it must pass through a subterranean cavity, to some other part of the earth or ocean which may lie beneath its level; as the Mediterranean seems to lie beneath the level of the Atlantic ocean, which, therefore, con­stantly flows into it through the Straits; and the waters of the Gulph of Mexico lie much above the level of the sea about the Floridas, and farther northward, which gives rise to the Gulph-stream, as described in note on Cassia, in vol. II.

The Maelstrom is said to be still twice in about twenty-four hours, when the tide is up, and most violent at the opposite times of the day. This is [Page 210] not difficult to account for, since, when so much water is brought over the subterraneous passage, if such exists as completely to fill it, and stand many feet above it, less disturbance must appear on the surface. The Maelstrom is described in the Memoires of the Swedish Academy of Sciences, and Pon­topiddan's History of Norway, and in the Universal Museum for 1763, p. 131.

The reason why eddies of water become hollow in the middle is, because the water immediately over the centre of the well, or cavity, falls faster, having less friction to oppose its descent, than the water over the circumfe­rence or edges of the well. The circular motion, or gyration of eddies, de­pends on the obliquity of the course of the stream, or to the friction or op­position to it being greater on one side of the well than the other: I have observed in water passing through a hole in the bottom of a trough, which was always kept full, the gyration of the stream might be turned either way by increasing the opposition of one side of the eddy with one's finger, or by turning the spout, through which the water was introduced, a little more obliquely to the hole on one side or on the other. Lighter bodies are liable to be retained long in eddies of water, while those rather heavier than water, are soon thrown out beyond the circumference, by their acquired mo­mentum becoming greater than that of the water. Thus, if equal portions of oil and water be put into a phial, and, by means of a string, be whirled in a circle round the hand, the water will always keep at the greater dis­tance from the centre; whence, in the eddies formed in rivers during a flood, a person who endeavours to keep above water, or to swim, is liable to be detained in them, but on suffering himself to sink, or dive, he is said readily to escape. This circulation of water, in descending through a hole in a vessel, Dr. Franklin has ingeniously applied to the explanation of hur­ricanes, or eddies of air.

NOTE XXXII.—GLACIERS.

THE common heat of the interior parts of the earth being always 48 degrees, both in winter and summer, the snow which lies in contact with it is always in a thawing state. Hence, in ice-houses, the external part of the collection of ice is perpetually thawing, and thus preserves the internal part of it, so that it is necessary to lay up many tons for the preservation of one ton. Hence, in Italy, considerable rivers have their source from be­neath the eternal glaciers, or mountains of snow and ice.

In our country, when the air, in the course of a frost, continues a day or two at very near 32 degrees, the common heat of the earth thaws the ice on its surface, while the thermometer remains at the freezing point. This circumstance is often observable in the rimy mornings of spring; the ther­mometer [Page 211] shall continue at the freezing point, yet all the rime will vanish, except that which happens to lie on a bridge, a board, or on a cake of cow­dung, which, being thus, as it were, insulated or cut off from so free a com­munication with the common heat of the earth, by means of air under the bridge, or wood, or dung, which are bad conductors of heat, continues some time longer unthawed. Hence, when the ground is covered thick with snow, though the frost continues, and the sun does not shine, yet the snow is observed to decrease very sensibly. For the common heat of the earth melts the under surface of it, and the upper one evaporates by its solution in the air. The great evaporation of ice was observed by Mr. Boyle, which experiment I repeated some time ago. Having suspended a piece of ice by a wire, and weighed it with care, without touching it with my hand, I hung it out the whole of a clear frosty night, and found, in the morning, it had lost nearly a fifth of its weight. Mr. N. Wallerius has since observed, that ice, at the time of its congelation, evaporates faster than watèr in its fluid form; which may be accounted for from the heat given out at the in­stant of freezing; (Saussure's Essais sur Hygromet. p. 249.) but this effect is only momentary.

Thus the vegetables that are covered with snow are seldom injured; since, as they lie between the thawing snow, which has 32 degrees of heat, and the covered earth, which has 48, they are preserved in a degree of heat be­tween these, viz. in 40 degrees of heat. Whence the moss on which the rein­deer feed, in the northern latitudes, vegetates beneath the snow; (See note on Muschus, vol. II.) and hence many Lapland and Alpine plants perished through cold in the botanic garden at Upsal; for, in their native situations, though the cold is much more intense, yet at its very commencement they are covered deep with snow, which remains till late in the spring. For this fact see Amaenit. Academ. vol. 1. No. 48. In our climate such plants do well covered with dried fern, under which they will grow, and even flower, till the severe vernal frosts cease. For the increase of glaciers see note on Canto I. l. 529.

NOTE XXXIII.—WINDS.

THE theory of the winds is yet very imperfect, in part, perhaps, owing to the want of observations sufficiently numerous of the exact times and places where they begin and cease to blow, but chiefly to our yet imperfect knowledge of the means by which great regions of air are either suddenly produced or suddenly destroyed.

The air is perpetually subject to increase or diminution, from its com­bination with other bodies, or its evolution from them. The vital part of the air, called oxygene, is continually produced in this climate, from the [Page 212] perspiration of vegetables in the sunshine, and probably from the action of light on clouds, or on water, in tropical climates, where the sun has greater power, and may exert some yet unknown laws of luminous com­bination. Another part of the atmosphere, which is called azote, is perpe­tually set at liberty from animal and vegetable bodies by putrefaction or combustion, from many springs of water, from volatile alkali, and probably from fixed alkali, of which there is an exhaustless source in the water of the ocean. Both these component parts of the air are perpetually again diminished by their contact with the soil, which covers the surface of the earth, producing nitre, The oxygene is diminished in the production of all acids, of which the carbonic and muriatic exist in great abundance. The azote is diminished in the growth of animal bodies, of which it constitutes an important part, and in its combinations with many other natural pro­ductions.

They are both probably diminished, in immense quantities, by uniting with the inflammable air, which arises from the mud of rivers and lakes at some seasons, when the atmosphere is light; the oxygene of the air pro­ducing water, and the azote producing volatile alkali, by their combina­tions with this inflammable air. At other seasons of the year these prin­ciples may again change their combinations, and the atmospheric air be re­produced.

Mr. Lavoisier found that one pound of charcoal, in burning, consumed two pounds nine ounces of vital air, or oxygene. The consumption of vital air, in the process of making red-lead, may readily be reduced to cal­culation; a small barrel contains about twelve hundred weight of this com­modity; 1200 pounds of lead, by calcination, absorb about 144 pounds of vital air: now, as a cubic foot of water weighs 1000 averdupois ounces, and as vital air is above 800 times lighter than water, it follows, that every barrel of red-lead contains nearly 2000 cubic feet of vital air. If this can be performed in miniature in a small oven, what may not be done in the immense elaboratories of nature!

These great elaboratories of nature include almost all her fossil, as well as her animal and vegetable productions. Dr. Priestley obtained air of greater or less purity, both vital and azotic, from almost all the fossil sub­stances he subjected to experiment. Four ounce-weight of lava, from Ice­land, heated in an earthen retort, yielded twenty ounce-measures of air.

• 4 ounce-weight of lava gave 20 ounce-measures of air.
• 7 .......... basaltes ... 104 ........... air.
• 2 .......... toad-stone ... 40 ........... air.
• 1 ½ .......... granite ... 20 ........... air.
• 1 .......... elvain ... 30 ........... air.
• 7 .......... gypsum ... 230 ........... air.
• 4 .......... blue slate ... 230 ........... air.
• 4 .......... clay ... 20 ........... air.
• 4 .......... lime-stone spar ... 830 ........... air.
• 5 .......... lime-stone ... 1160 ........... air.
• [Page 213] 3 .......... chalk ... 630 ...........
• 3 ½ .......... white iron-ore ... 560 ...........
• 4 .......... dark iron-ore ... 410 ...........
• ½ .......... molybdena ... 25 ...........
• ¼ .......... stream tin ... 20 ...........
• 2 .......... steatites ... 40 ...........
• 2 .......... barytes ... 26 ...........
• 2 .......... black wad ... 80 ...........
• 4 .......... sand-stone ... 75 ...........
• 3 .......... coal ... 700 ...........

In this account the fixed air was previously extracted from the lime-stones by acids, and the heat applied was much less than was necessary to extract all the air from the bodies employed. Add to this the known quantities of air which are combined with the calciform ores, as the ochres of iron, man­ganese, calamy, grey ore of lead, and some idea may be formed of the great production of air in volcanic eruptions, as mentioned in note on Chunda, vol. II. and of the perpetual absorptions and evolutions of whole oceans of air from every part of the earth.

But there would seem to be an officina aeris, a shop where air is both manufactured and destroyed in the greatest abundance within the polar cir­cles, as will hereafter be spoken of. Can this be effected by some yet un­known law of the congelation of aqueous or saline fluids, which may set at liberty their combined heat, and convert a part both of the acid and alkali of sea-water into their component airs? Or, on the contrary, can the elec­tricity of the northern lights convert inflammable air and oxygene into wa­ter, whilst the great degree of cold at the poles unites the azote with some other base? Another officina aeris, or manufacture of air, would seem to exist within the tropics, or at the line, though in a much less quantity than at the poles, owing, perhaps, to the action of the sun's light on the moisture suspended in the air, as will also be spoken of hereafter; but in all other parts of the earth these absorptions and evolutions of air, in a greater or less de­gree, are perpetually going on in inconceivable abundance; increased, pro­bably, and diminished, at different seasons of the year, by the approach or retrocession of the sun's light: future discoveries must elucidate this part of the subject. To this should be added, that as heat and electricity, and per­haps magnetism, are known to displace air, that it is not impossible but that the increased or diminished quantities of these fluids diffused in the atmos­phere, may increase its weight as well as its bulk; since their specific attrac­tions, or affinities to matter, are very strong, they probably also possess ge­neral gravitation to the earth; a subject which wants further investigation. See note XXVI.

NOTE XXXIV.—VEGETABLE PERSPIRATION.

WHEN points or hairs are put into spring-water, as in the experiments of Sir B. Thompson, (Phil. Trans. LXXVII.) and exposed to the light of the sun, much air, which loosely adhered to the water, rises in bubbles, as explained in the note on Fucus, vol. II. A still greater quantity of air, and of a purer kind, is emitted by Dr. Priestley's green matter, and by vegeta­ble leaves growing in water in sunshine, according to Mr. Ingenhouz's ex­periments; both which I suspect to be owing to a decomposition of the wa­ter perspired by the plant; for the edge of a capillary tube of great tenuity may be considered as a circle of points, and as the oxygene, or principle of vital air, may be expanded into a gas by the sun's light, the hydrogene, or inflammable air, may be detained in the pores of the vegetable.

Hence plants growing in the shade are white, and become green by be­ing exposed to the sun's light; for their natural colour being blue, the ad­dition of hydrogene adds yellow to this blue, and tans them green. I sup­pose a similar circumstance takes place in animal bodies; their perspirable matter, as it escapes in the sunshine, becomes decomposed by the edges of their pores, as in vegetables, though in less quantity, as their perspiration is le [...]s, and by their hydrogene being retained the skin becomes tanned yel­low. In proof of this it must be observed, that both vegetable and animal substances become bleached white by the sun-beams when they are dead, as cabbage-stalks, bones, ivory, tallow, bees-wax, linen and cotton cloth; and hence, I suppose, the copper-coloured natives of sunny countries might become etiolated, or blanched, by being kept from their infancy in the dark, or removed, for a few generations, to more northerly climates.

It is probable that on a sunny morning much pure air becomes separated from the dew, by means of the points of vegetables, on which it adheres, [Page 228] and much inflammable air imbibed by the vegetable, or combined with it; and by the sun's light thus decomposing water, the effects of it in bleach­ing linen seems to depend (as described in note X.): the water is decom­posed by the light at the ends or points of the cotton or thread, and the vital air unites with the phlogistic or colouring matters of the cloth, and produces a new acid, which is either itself colourless, or washes out; at the same time the inflammable part of the water escapes. Hence there seems a reason why cotton bleaches so much sooner than linen, viz. because its fi­bres are three or four times shorter, and therefore protrude so many more points, which seem to facilitate the liberation of the vital air from the in­flammable part of the water.

Bees-wax becomes bleached by exposure to the sun and dews, in a simi­lar manner as metals become calcined or rusty, viz. by the water on their surface being decomposed; and hence the inflammable material, which caused the colour, becomes united with vital air, forming a new acid, and is washed away.

Oil, close stopped in a phial not full, and exposed long to the sun's light, becomes bleached, as I suppose, by the decomposition of the water it con­tains; the inflammable air rising above the surface, and the vital air unit­ing with the colouring matter of the oil. For it is remarkable, that by shutting up a phial of bleached oil in a dark drawer, it, in a little time, becomes coloured again.

The following experiment shews the power of light in separating vital air from another basis, viz. from azote. Mr. Scheele inverted a glass ves­sel, filled with colourless nitrous acid, into another glass, containing the same acid, and, on exposing them to the sun's light, the inverted glass be­came partly filled with pure air, and the acid, at the same time, became co­loured. Scheele, in Crell's Annal. 1786. But if the vessel of colourless nitrous acid be quite full, and stopped, so that no space is left for the air produced to expand itself into, no change of colour takes place. Priestley's Exp. VI. p. 344. See Keir's very excellent Chemical Dictionary, p. 99. new edition.

A sun-flower, three feet and a half high, according to the experiment of Dr. Hales, perspired two pints in one day (Vegetable Statics), which is many times as much, in proportion to its surface, as is perspired from the surface and lungs of animal bodies; it follows, that the vital air liberated from the surfaces of plants by the sunshine, must much exceed the quan­tity of it absorbed by their respiration, and that hence they improve the air in which they live during the light part of the day; and thus blanched ve­getables will sooner become tanned into green by the sun's light, than etiolated animal bodies will become tanned yellow by the same means.

It is hence evident, that the curious discovery of▪ Dr. Priestley, that his green vegetable matter, and other aquatic plants, gave out vital air when the sun shone upon them, and the leaves of other plants did the same when immersed in water, as observed by Mr. Ingenhouz, refer to the per­spiration of vegetables, not to their respiration. Because Dr. Priestley ob­served the pure air to come from both side of the leaves, and even from [Page 229] the stalks of a water-flag, whereas one side of the leaf only serves the office of lungs, and certainly not the stalks. Exper. on Air, vol. III. And thus, in respect to the circumstance in which plants and animals seemed the far­thest removed from each other, I mean in their supposed mode of respira­tion, by which one was believed to purify the air which the other had in­jured, they seem to differ only in degree, and the analogy between them remains unbroken.

Plants are said, by many writers, to grow much faster in the night than in the day, as is particularly observable in seedlings, at their rising out of the ground. This probably is a consequence of their sleep rather than of the absence of light; and in this, I suppose, they also resemble animal bodies.

NOTE XXXV.—VEGETABLE PLACENTATION.

AS buds are the viviparous offspring of vegetables, it becomes necessary that they should be furnished with placental vessels for their nourishment, till they acquire lungs, or leaves, for the purpose of elaborating the com­mon juices of the earth into nutriment. These vessels exist in bulbs and in seeds, and supply the young plant with a sweet juice, till it acquires leaves, as is seen in converting barley into malt, and appears from the sweet taste of onions and potatoes, when they begin to grow.

The placental vessels belonging to the buds of trees are placed about the roots of most, as the vine; so many roots are furnished with sweet or mealy matter, as fern-root, bryony, carrot, turnip, potatoe, or in the albur­num, or sap-wood, as in those trees which produce manna, which is depo­sited about the month of August, or in the joints of sugar-cane, and grasses; early in the spring the absorbent mouths of these vessels drink up moisture from the earth, with a saccharine matter lodged for that purpose during the preceding autumn, and push this nutritive fluid up the vessels of the al­burnum, to every individual bud, as is evinced by the experiments of Dr. Hales, and of Mr. Walker, in the Edinburgh Philosophical Trans. The for­mer observed, that the sap from the stump of a vine, which he had cut off in the beginning of April, arose twenty-one feet high, in tubes affixed to it for that purpose; but in a few weeks it ceased to bleed at all, and Dr. Walker marked the progress of the ascending sap, and found likewise that as soon as the leaves became expanded, the sap ceased to rise; the ascending juice of some trees is so copious and so sweet during the sap-season, that it is used to make wine, as the birch, betula, and sycamore, acer pseudo-platanus, and particularly the palm, and maple acer.

During this ascent of the sap-juice, each individual leaf-bud expands its new leaves, and shoots down new roots, covering, by their intermixture, the old bark with a new one; and as soon as these new roots (or bark) are capable of absorbing sufficient juices from the earth for the support of each [Page 230] bud, and the new leaves are capable of performing their office of exposing these juices to the influence of the air, the placental vessels cease to act, co­alesce, and are transformed from sap-wood, or alburnum, into inert wood, serving only for the support of the new tree, which grows over them.

Thus from the pith of the new bud of the horse-chesnut five vessels pass out through the circle of the placental vessels above described, and carry with them a minuter circle of those vessels; these five bundles of vessels unite after their exit, and form the foot-stalk or petiole of the new five-fin­gered leaf, to be spoken of hereafter. This structure is well seen by cutting off a leaf of the horse-chesnut(AEsculus Hippocastanum) in September, be­fore it falls, as the buds of this tree are so large that the flower may be seen in them with the naked eye.

After a time, perhaps about midsummer, another bundle of vessels pas­ses from the pith through the alburnum, or sap-vessels, in the bosom of each leaf, and unites, by the new bark, with the leaf, which becomes either a flower-bud or leaf-bud, to be expanded in the ensuing spring, for which purpose an apparatus of placental vessels is produced, with proper nutri­ment, during the progress of the summer and autumn; and thus the vege­table becomes annually increased, ten thousand buds often existing on one tree, according to the estimate of Linnaeus. Phil. Bot.

The vascular connection of vegetable buds with the leaves in whose bo­soms they are formed, is confirmed by the following experiment,(Oct. 20, 1781.) On the extremity of a young bud of the Mimosa (sensitive plant) a small drop of acid of vitriol was put, by means of a pen, and, after a few seconds, the leaf in whose axilla it dwelt closed, and opened no more, though the drop of vitriolic acid was so small as apparently only to injure the summit of the bud. Does not this seem to shew that the leaf and its bud have connecting vessels, though they arise at different times, and from different parts of the medulla, or pith? And, as it exists previously to it, that the leaf is the parent of the bud?

This placentation of vegetable buds is clearly evinced from the sweetness of the rising sap, and from its ceasing to rise as soon as the leaves are ex­panded, and thus completes the analogy between buds and bulbs. Nor need we wonder at the length of the umbilical cords of buds, since that must correspond with their situation on the tree, in the same manner as their lymphatics and arteries are proportionally elongated.

It does not appear probable that any umbilical artery attends these pla­cental absorbents, since, as there seems to be no system of veins in vegeta­bles to bring back the blood from the extremities of their arteries (except their pulmonary veins), there could not be any vegetable fluids to be re­turned to their placenta, which, in vegetables, seems to be simply an organ for nutrition, whereas the placenta of the animal foetus seems likewise to serve as a respiratory organ, like the gills of fishes.

NOTE XXXVI.—VEGETABLE CIRCULATION.

THE individuality of vegetable buds was spoken of before, and is con­firmed by the method of raising all kinds of trees, by Mr. Barnes. (Method of propagating Fruit Trees. 1759. Lond. Bladwin.) He cut a branch into as many pieces as there were buds or leaves upon it, and wiping the two wounded ends dry, he quickly applied to each a cement, previously warmed a little, which consisted principally of pitch, and planted there in the earth. The use of this cement I suppose to consist in its preventing the bud from bleeding to death, though the author ascribes it to its antiseptic quality.

These buds of plants, which are thus each an individual vegetable, in many circumstances resemble individual animals; but as animal bodies are detached from the earth, and move from place to place in search of food, and take that food at considerable intervals of time, and prepare it for their nourishment within their own bodies after it is taken, it is evident they must require many organs and powers which are not necessary to a stationary bud. As vegetables are immoveably fixed to the soil from whence they draw their nourishment ready prepared, and this uniformly, not at returning intervals, it follows, that in examining their anatome, we are not to look for muscles of locomotion, as arms and legs; nor for organs to receive and prepare their nourishment, as a stomach and bowels; nor for a reservoir for it after it is prepared, as a general system of veins, which, in locomotive animals, contains and returns the superfluous blood which is left after the various organs of secretion have been supplied, by which contrivance they are enabled to live a long time without new supplies of food.

The parts which we may expect to find in the anatome of vegetables, cor­respondent to those in the animal economy, are, [...]. A system of absorbent vessels, to imbibe the moisture of the earth similar to the lacteal vessels, as in the roots of plants; and another system of absorbents, similar to the lym­phatics of animal bodies, opening its mouths on the internal cells and ex­ternal surfaces of vegetables; and a third system of absorbent vessels, cor­respondent with those of the placentation of the animal foetus, 2. A pulmo­nary system, correspondent to the lungs or gills of quadrupeds and fish, by which the fluid absorbed by the lacteals and lymphatics may be exposed to the influence of the air: this is done by the green leaves of plants, those in the air resembling lungs, and those in the water resembling gills; and by the petals of flowers. 3. Arterial systems to convey the fluid thus elaborated to the various glands of the vegetable, for the purposes of its growth, nutrition, and various secretions. 4. The various glands which separate from the ve­getable blood the honey, wax, gum, resin, starch, sugar, essential oil, &c. 5. The organs adapted for their propagation or reproduction. 6. Muscles to perform several motions of their parts.

I. The existence of that branch of the absorbent vessels of vegetables which resembles the lacteals of animal bodies, and imbibes their nutriment [Page 232] from the moist earth, is evinced by their growth so long as moisture is ap­plied to their roots, and their quickly withering when it is withdrawn,

Besides these absorbents in the roots of plants there are others, which open their mouths on the external surfaces of the bark and leaves, and on the in­ternal surfaces of all the cells, and between the bark and the alburnum, or sap-wood; the existence of these is shewn, because a leaf plucked off, and laid with its under side on water, will not wither so soon as if left in the dry air,—the same if the bark alone of a branch which is separated from a tree [...]e kept moist with water,—and, lastly, by moistening the alburnum or sap­wood alone of a branch detached from a tree, it will not so soon wither as if left in the dry air. By the following experiment these vessels were agree­ably visible by a common magnifying glass: I placed, in the summer of 1781, the foot-stalks of some large fig-leaves about an inch deep in a decoction of madder (rubia tinctorum) and others in a decoction of logwood (haematoxy­lum campechense), along with some sprigs cut off from a plant of picris; these plants were chosen because their blood is white; after some hours, and on the next day, on taking out either of these, and cutting off from its bottom about a quarter of an inch of the stalk, an internal circle of red points ap­peared, which were the ends of absorbent vessels, coloured red with the de­coction, while an external ring of arteries was seen to bleed out hastily a milky juice, and, at once, evinced both the absorbent and arterial system. These absorbent vessels have been called by Grew, and Malphigi, and some other philosophers, bronchi, and erroneously supposed to be air-vessels. It is probable that these vessels, when cut through, may effuse their fluids, and receive air, their sides being too stiff to collapse; since dry wood emits air­bubbles in the exhausted receiver in the same manner as moist wood.

The structure of these vegetable absorbents consists of a spiral line, and not of a vessel interrupted with valves like the animal lymphatics, since on breaking almost any tender leaf, and drawing out some of the fibres, which adhere longest, this spiral structure becomes visible, even to the naked eye, and distinctly so by the use of a common lens. See Grew, plate 51.

In such a structure it is easy to conceive how a vermicular or peristaltic motion of the vessel, beginning at the lowest part of it, each spiral ring successively contracting itself till it fills up the tube, must forcibly push for­wards its contents, as from the roots of vines in the bleeding season; and if this vermicular motion should begin at the upper end of the vessel, it is as easy to see how it must carry its contained fluid in a contrary direction. The retrograde motion of the vegetable absorbent vessels is shewn by cut­ting a forked branch from a tree, and immersing [...] part of one of the forks in water, which will, for many days, prevent the other from withering; or, it is shewn by planting a willow branch with the wrong end upwards. This structure, in some degree, obtains in the oesophagus, or throat of cows, who, by similar means, convey their food first downwards, and afterward upwards, by a retrograde motion of the annular muscles, or cartilages, for the purpose of a second mastication of it.

II. The fluids thus drank up by the vegetable absorbent vessels from the earth, or from the atmosphere, or from their own cells and interstices, are [Page 233] carried to the foot-stalk of every leaf, where the absorbents belonging to each leaf unite into branches, forming so many pulmonary arteries, and are thence dispersed to the extremities of the leaf, as may be seen in cutting away, slice after slice, the foot-stalk of a horse-chesnut in September, before the leaf falls. There is then a complete circulation in the leaf; a pulmonary vein receiving the blood from the extremities of each artery, on the upper side of the leaf, and joining again in the foot-stalk of the leaf, these veins produce so many arteries, or aortas, which disperse the new blood over the new bark, elongating its vessels, or producing its secretions; but as a reservoir of blend could not be wanted by a vegetable bud which takes in its nutriment at all times, I ima­gine there is no venous system, no veins, properly so called, which receive the blood which was to spare, and return it into the pulmonary or arterial system.

The want of a system of veins was countenanced by the following experi­ment: I cut off several stems of tall spurge (Euphorbia helioscopia) in au­tumn, about the centre of the plant, and observed tensold the quantity of milky juice ooze from the upper than from the lower extremity, which could hardly have happened if there had been a venous system of vessels to re­turn the blood from the roots to the leaves.

Thus the vegetable circulation, complete in the lungs, but, probably, in the other part of the system deficient, in respect to a system of returning veins, is carried forwards without a heart, like the circulation through the livers of animals, where the blood brought from the intestines and mesen­tery by one vein, is dispersed through the liver by the vena portarum, which assumes the office of an artery. See note XXXVII.

At the same time so minute are the vessels in the intertexture of the barks of plants, which belong to each individual bud, that a general circulation may possibly exist, though we have not yet been able to discover the venous part of it.

There is, however, another part of the circulation of vegetable juices vi­sible to the naked eye, and that is in the corol or petals of flowers, in which a part of the blood of the plant is exposed to the influence of the air and light in the same manner as in the foliage, as will be mentioned more at large in notes XXXVII and XXXIX.

These circulations of their respective fluids seem to be carried on in the vessels of plants precisely as in animal bodies, by their irritability to the stimulus of their adapted fluids, and not by any mechanical or chemical at­traction, for their absorbent vessels propel the juice upwards, which they drink up from the earth, with great violence; I suppose with much greater than is exerted by the lacteals of animals, probably owing to the greater minuteness of these vessels in vegetables, and the greater rigidity of their coats. Dr. Hales, in the spring season, cut off a vine near the ground, and, by fixing tubes on the remaining stump of it, found the sap to rise twenty­one feet in the tube, by the propulsive power of these absorbents of the roots of it▪ Veget. Stat. p. 102. Such a power cannot be produced by capil­lary attraction, as that could only raise a fluid nearly to the upper edge of the attracting cylinder, but not enable it to flow over that edge, and much [Page 234] less to rise at feet above it. What then can this power be owing to? Doubtless to the living activity of the absorbent vessels, and to their increas­ed vivacity, from the influence of the warmth of the spring succeeding the winter's cold, and their thence greater susceptibility to irritation from the juices which they absorb, resembling, in all circumstances, the action of the living vessels of animals.

NOTE XXXVII.—VEGETABLE RESPIRATION.

1. THERE have been various opinions concerning the use of the leaves of plants in the vegetable economy. Some have contended that they are perspiratory organs; this does not seem probable from an experiment of Dr. Hales. Veget. Stat. p. 30. He found, by cutting off branches of trees with apples on them, and taking off the leaves, that an apple exhaled about as much as two leaves, the surfaces of which were nearly equal to the apple; whence it would appear that apples have as good a claim to be termed per­spiratory organs as leaves. Others have believed them excretory organs of excrementitious juices; but as the vapour exhaled from vegetables has no taste, this idea is no more probable than the other; add to this, that in moist weather they do not appear to perspire or exhale at all.

The internal surface of the lungs or air-vessels in men, is said to be equal to the external surface of the whole body, or about fifteen square feet; on this surface the blood is exposed to the influence of the respired air, through the medium, however, of a thin pellicle; by this exposure to the air it has its colour changed from deep red to bright scarlet, and acquires something so necessary to the existence of life, that we can live scarcely a minute without this wonderful process.

The analogy between the leaves of plants and the lungs or gills of ani­mals, seems to embrace so many circumstances, that we can scarcely with­hold our assent to their performing similar offices.

I. The great surface of the leaves, compared to that of the trunk and branches of trees, is such, that it would seem to be an organ well adapted for the purpose of exposing the vegetable juices to the influence of the air; this, however, we shall see afterwards, is probably performed only by their upper surfaces; yet even in this case the surface of the leaves in ge­neral bears a greater proportion to the surface of the tree, than the lungs of animals to their external surfaces.

2. In the lungs of animals, the blood, after having been exposed to the air in the extremities of the pulmonary artery, is changed in colour from deep red to bright scarlet, and certainly in some of its essential properties; it is then collected by the pulmonary vein, and returned to the heart. To shew a si­milarity of circumstances in the leaves of plants, the following experiment was made, June 24, 1781. A stalk, with leaves and seed-vessels, of large [Page 235] spurge (Euphorbia helioscopia) had been several days placed in a decoction of madder (Rubia tinctorum), so that the lower part of the stem, and two of the undermost leaves, were immersed in it. After having washed the immersed leaves in clear water, I could readily discern the colour of the madder passing along the middle rib of each leaf. This red artery was beau­tifully visible both on the under and upper surface of the leaf; but on the upper side many red branches were seen going from it to the extremities of the leaf, which, on the other side, were not visible, except by looking through it against the light. On this under side a system of branching vessels, car­rying a pale milky fluid, were seen coming from the extremities of the leaf, and covering the whole under side of it, and joining into two large veins, one on each side of the red artery, in the middle rib of the leaf, and along with it descending to the foot-stalk or petiole. On flitting one of these leaves with sciffars, and having a common magnifying lens ready, the milky blood was seen oozing out of the returning veins on each side of the red ar­tery, in the middle rib, but none of the red fluid from the artery.

All these appearances were more easily seen in a leaf of picris treated in the same manner; for in this milky plant the stems and middle rib of the leaves are sometimes naturally coloured reddish, and hence the colour of the madder seemed to pass further into the ramifications of their leaf-arte­ries, and was there beautifully visible, with the returning branches of milky veins on each side.

3. From these experiments, the upper surface of the leaf appeared to be the immediate organ of respiration, because the coloured fluid was carried to the extremities of the leaf by vessels most conspicuous on the upper sur­face, and there changed into a milky fluid, which is the blood of the plant, and then returned, by concomitant veins, on the under surface, which were seen to ooze when divided with scissars, and which, in picris particularly, render the under surface of the leaves greatly whiter than the upper one.

4. As the upper surface of leaves constitutes the organ of respiration, on which the sap is exposed, in the terminations of arteries, beneath a thin pellicle, to the action of the atmosphere, these surfaces, in many plants, strongly repel moisture, as cabbage-leaves; whence the particles of rain ly­ing over their surfaces without touching them, as observed by Mr. Melville (Essays Literary and Philosoph. Edinburgh), have the appearance of globu­les of quick-silver. And hence leaves, laid with the upper surface on wa­ter, wither as soon as in the dry air, but continue green many days if placed with the under surfaces on water, as appears in the experiments of Mons. Bonnet (Usage des Feuilles). Hence some aquatic plants, as the water-lily (Nymphoea), have the lower sides of their leaves floating on the water, while the upper surfaces remain dry in the air.

5. As those insects which have many spiracula, or breathing apertures, as wasps and flies, are immediately suffocated by pouring oil upon them, I carefully covered with oil the surfaces of several leaves of Phlomis, of Portu­gal Laurel, and Balsams; and though it would not regularly adhere, I found them all die in a day or two.

Of aquatic leaves, see note on Trapa and on Fucus, in vol II. to which [Page 236] must be added, that many leaves are furnished with muscles about their foot-stalks, to turn their upper surfaces to the air or light, as Mimosa and Hedysarum gyrans. From all these analogies, I think there can be no doubt but that leaves of trees are their lungs, giving out a phlogistic material to the atmosphere, and absorbing oxygene or vital air.

6. The great use of light to vegetation would appear, from this theory, to be, by disengaging vital air from the water which they perspire, and thence to facilitate its union with their blood, exposed beneath the thin sur­face of their leaves; since, when pure air is thus applied, it is probable that it can be more readily absorbed. Hence, in the curious experiments of Dr. Priestley and Mr. Ingenhouz, some plants purified air less than others, that is, they perspired less in the sunshine; and Mr. Scheele found, that by put­ting peas into water which about half covered them, they converted the vital air into fixed air, or carbonic acid gas, in the same manner as in ani­mal respiration. See note XXXIV.

7. The circulation in the lungs or leaves of plants is very similar to that of fish. In fish, the blood, after having passed through their gills, does not return to the heart, as from the lungs of air-breathing animals, but the pulmonary vein, taking the structure of an artery, after having received the blood from the gills, which there gains a more florid colour, distributes it to the other parts of their bodies. The same structure occurs in the li­vers of fish, whence we see, in those animals, two circulations independent of the power of the heart, viz. that beginning at the termination of the veins of the gills, and branching through the muscles, and that which passes through the liver; both which are carried on by the action of those re­spective arteries and veins. Monro's Physiology of Fish, p. 19.

The course of the fluids in the roots, leaves, and buds of vegetables, seems to be performed in a manner similar to both these. First the absorbent vessels of the roots and surfaces unite at the foot-stalk of the leaf, and then, like the vena portarum, an artery commences without the intervention of a heart, and spreads the sap, in its numerous ramifications, on the upper surface of the leaf: here it changes its colour and properties, and becomes vegetable blood; and is again collected by a pulmonary vein on the under surface of the leaf. This vein, like that which receives the blood from the gills of fish, assumes the office and name of an artery, and, branching again, disperses the blood upward to the bud, from the foot-stalk of the leaf, and downward to the roots; where it is all expended in the various secretions, the nourishment and growth of the plant, as fast as it is prepared.

II. The organ of respiration already spoken of belongs particularly to the shoots or buds; but there is another pulmonary system, perhaps totally in­dependent of the green foliage, which belongs to the fructification only; I mean the corol or petals. In this there is an artery belonging to each pe­tal, which conveys the vegetable blood to its extremities, exposing it to the light and air under a delicate membrane, covering the internal surface of the petal, where it often changes its colour, as is beautifully seen in some party-coloured poppies; though it is probable some of the iridescent colours of flowers may be owing to the different degrees of tenuity of the exterior [Page 237] membrane of the leaf, refracting the light like soap-bubbles; the vegetable blood is then returned by correspondent vegetable veins, exactly as in the green foliage; for the purposes of the important secretions of honey, wax, the finer essential oil, and the prolific dust of the anthers.

1. The vascular structure of the corol, as above described, and which is visible to the naked eye, and its exposing the vegetable juices to the air and light during the day, evinces that it is a pulmonary organ.

2. As the gland which produce the prolific dust of the anthers, the honey, wax, and frequently some odoriferous essential oil, are generally attached to the corol, and always fall off, and perish with it, it is evident that the blood is elaborated or oxygenated in this pulmonary system, for the purpose of these important sercretions.

3. Many flowers, as the Colchicum, and Hamamelis, arise naked in au­tumn, no green leaves appearing till the ensuing spring; and many others put forth their flowers, and complete their impregnation, early in the spring, before the green foliage appears, as Mezerion, cherries, pears, which shews that these corols are the lungs belonging to the fructification.

4. This organ does not seem to have been necessary for the defence of the stamens and pistils, since the calyx of many flowers, as Tragopogon, performs this office; and, in many flowers, these petals themselves are so tender as to require being shut up in the calyx during the night; for what other use then can such an apparatus of vessels be designed?

5. In the Helleborus niger, Christmas-rose, after the seeds are grown to a certain size, the nectaries and stamens drop off, and the beautiful large white petals change their colour to a deep green, and gradually thus become a calyx, inclosing and defending the ripening seeds; hence it would seem that the white vessels of the corol served the office of exposing the blood to the action of the air, for the purposes of separating or producing the ho­ney, wax, and prolific dust; and when these were no longer wanted, that these vessels coalesced like the placental vessels of animals, after their birth, and thus ceased to perform that office, and lost, at the same time, their white colour. Why should they lose their white colour, unless they, at the same time, lost some other property besides that of defending the seed-ves­sel, which they still continue to defend?

6. From these observations I am led to doubt whether green leaves be ab­solutely necessary to the progress of the fruit-bud, after the last year's leaves are fallen off. The green leaves serve as lungs to the shoots, and foster the new buds in their bosoms, whether these buds be leaf-buds or fruit-buds; but in the early spring the fruit-buds expand their corols, which are their lungs, and seem no longer to require green leaves; hence the vine bears fruit at one joint without leaves, and puts out a leaf-bud at another joint without fruit. And, I suppose, the green leaves which rise out of the earth, in the spring, from the Colchicum, are for the purpose of producing the new bulb and its placenta, and not for the giving maturity to the seed. When currant or goosberry trees lose their leaves by the depredation of insects, the fruit still continues to be formed, though less sweet and less in size.

[Page 238] 7. From these facts it appears, that the flower-bud, after the corol falls off (which is its lungs), and the stamens and nectary along with it, becomes simply an uterus for the purpose of supplying the growing embryon with nourishment, together with a system of absorbent vessels, which bring the juices of the earth to the foot-stalk of the fruit, and which there changes into an artery, for the purpose of distributing the sap for the secretion of the saccharine, or farinaceous, or acescent materials, for the use of the em­beyon. At the same time as all the vessels of the different buds of trees inosculate or communicate with each other, the fruit becomes sweeter and larger when the green leaves continue on the tree, but the mature flowers themselves (the succeeding fruit not considered), perhaps suffer little injury from the green leaves being taken off, as some florists have observed.

8. That the vessels of different vegetable buds inosculate in various parts of their circulation, is rendered probable by the increased growth of one bud, when others in its vicinity are cut away; as it thus seems to receive the nourishment which was before divided amongst many.

NOTE XXXVIII.—VEGETABLES IMPREGNATION.

FROM the accurate experiments and observations of Spallanzani, it ap­pears, that in the Spartium Junceum, rush-broom, the very minute seeds were discerned in the pod at least twenty days before the flower is in full bloom, that is, twenty days before fecùndation. At this time also the pow­der of the anthers was visible, but glued fast to their summits. The seeds, however, at this time, and for ten days after the blossom had fallen off, ap­peared to consist of a gelatinous substance. On the eleventh day after the falling of the blossom, the seeds became heart-shape, with the basis attached by an appendage to the pod, and a white point at the apex; this white point was, on pressure, sound to be a cavity including a drop of liquor.

On the 25th day, the cavity, which at first appeared at the apex, was much enlarged, and still full of liquor; it also contained a very small semi­transparent body, of a yellowish colour, gelatinous, and fixed by its two op­posite ends to the sides of the cavity.

In a month the seed was much enlarged, and its shape changed from a heart to a kidney; the little body contained in the cavity was increased in bulk, and was less transparent and gelatinous, but there yet appeared no or­ganization.

On the 40th day, the cavity, now grown larger, was quite filled with the body, which was covered with a thin membrance; after this membrance was removed, the body appeared of a bright green, and was easily divided, by the point of a needle, into two portions, which manifestly formed the two lobes, and within these, attached to the lower part, the exceedingly small plantule was easily perceived.

[Page 239] The foregoing observations evince, 1. That the seeds exist in the ova­rium many days before fecundation. 2. That they remain for some time solid, and then a cavity, containing a liquid, is formed in them. 3. That after fecundation a body begins to appear within the cavity, fixed by two points to the sides, which, in process of time, proves to be two lobes contain­ing a plantule. 4. That the ripe seed consists of two lobes adhering to a plantule, and surrounded by a thin membrane, which is itself covered with a husk or cuticle. Spallanzani's Dissertations, vol. II. p. 253.

The analogy between seeds and eggs has long been observed, and is con­firmed by the mode of their production. The egg is known to be formed within the hen long before its impregnation. C. F. Wolf asserts, that the yolk of the egg is nourished by the vessels of the mother, and that it has from those its arterial and venous branches, but that after impregnation these vessels gradually become impervious and obliterated, and that new ones are produced from the foetus, and dispersed into the yolk. Haller's Physiolog. Tom. VIII. p. 94. The young seed, after fecundation, I sup­pose, is nourished in a similar manner, from the gelatinous liquor, which is previously deposited for that purpose; the uterus of the plant producing or secreting it into a reservoir or amnios, in which the embryon is lodged, and that the young embryon is furnished with vessels to absorb a part of it, as in the very early embryon in the animal uterus.

The spawn of frogs and of fish is delivered from the female before its im­pregnation. M. Bonnet says, that the male salamander darts his semen into the water, where it forms a little whitish cloud, which is afterwards received by the swoln anus of the female, and she is fecundated.—He adds, that marine plants approach near to these animals, as the male does not project a fine powder, but a liquor, which, in like manner, forms a little cloud in the water.—And further adds, who knows but the powder of the stamina of certain plants may make some impression on certain germs be­longing to the animal kingdom! Letter XLIII, to Spallanzani, Oeuvres Philos.

Spallanzani found that the seminal fluid of frogs and dogs, even when diluted with much water, retained its prolific quality. Whether this quality be simply a stimulus exciting the egg into animal action, which may be called a vivifying principle, or whether part of it be actually conjoined with the egg, is not yet determined, though the latter seems more probable, from the frequent resemblance of the foetus to the male parent. A con­junction, however, of both the male and female influence seems necessary for the purpose of reproduction throughout all organized nature, as well in hermaphrodite insects, microscopic animals, and polypi, and exists as well in the formation of the buds of vegetables, as in the production of their seeds, which is ingeniously conceived and explained by Linnaeus. After having compared the flower to the larva of a butterfly, consisting of petals instead of wings, calyxes instead of wing-sheaths, with the organs of reproduction; and having shewn the use of the farina in fecundating the egg or seed, he proceeds to explain the production of the bud. The calyx of a flower, he says, is an expansion of the outer bark; the petals proceed from the inner [Page 240] bark, or rind, the stamens from the alburnum, or woody circle, and the style from the pith. In the production and impregnation of the seed, a commix­ture of the secretions of the stamens and style are necessary; and for the pro­duction of a bud, he thinks the medulla, or pith, bursts its integuments, and mixes with the woody part, or alburnum, and these, forcing their passage through the rind and bark, constitute the bud, or viviparous progeny of the vegetable. System of Vegetables translated from Linnaeus, p. 8.

It has been supposed that the embryon vegetable, after fecundation, by its living activity, or stimulus exerted on the vessels of the parent plant, may produce the fruit or feed-lobes, as the animal foetus produces its pla­centa, and as vegetable buds may be supposed to produce their umbilical vessels or roots, down the bark of the tree. This, in respect to the produc­tion of the fruit surrounding the seeds of trees, has been assimilated to the gall-nuts or oak-leaves, and to the bedeguar on briars; but there is a power­ful objection to this doctrine, viz. that the fruit of figs, all which are female in this country, grow nearly as large without fecundation, and, therefore, the embryon has in them no self-living principle.

NOTE XXXIX.—VEGETABLE GLANDULATION.

THE glands of vegetables, which separate from their blood the mucilage, starch, or sugar, for the placentation or support of their seeds, bulbs, and buds; or those which deposit their bitter, acrid, or narcotic juices for their defence from depredations of insects or larger animals; or those which secrete resins or wax for their protection from moisture or frosts, consist of vessels too fine for the injection or absorption of coloured fluids, and have not, therefore, yet been exhibited to the inspection even of our glasses, and can, therefore, only be known by their effects; but one of the most curious and important of all vegetable secretions, that of honey, is apparent to our naked eyes, though, before the discoveries of Linnaeus, the nectary, or honey­gland, had not even acquired a name.

The odoriferous essential oils of several flowers seem to have been design­ed for their defence against the depredations of insects, while their beautiful colours were a necessary consequence of the size of the particles of their blood, or of the tenuity of the exterior membrane of the petal. The use of the prolific dust is now well ascertained; the wax which covers the an­thers prevents this dust from receiving moisture, which would make it burst prematurely, and thence prevent its application to the stigma, as some­times happens in moist years, and is the cause of deficient fecundation, both of our fields and orchards.

The universality of the production of honey in the vegetable world, and the very complicated apparatus which nature has constructed in many flow­ers, as well as the acrid or deleterious juices she has furnished those flowers [Page 241] with (as in the Aconite) to protect this honey from rain, and from the depredations of insects, seem to imply that this fluid is of very great im­portance in the vegetable economy; and also, that it was necessary to expose it to the open air previous to its re-absorption into the vegetable vessels.

In the animal system the lachrymal gland separates its fluid into the open air, for the purpose of moistening the eye; of this fluid, the part which does not exhale is absorbed by the puncta lachrymalia, and carried into the nostrils; but as this is not a nutritive fluid, the analogy goes no further than its secretion into the open air, and its re-absorption into the system; every other secreted fluid in the animal body is in part absorbed again into the system; even those which are esteemed excrementitious, as the urine and perspirable matter, of which the latter is secreted, like the honey, into the external air. That the honey is a nutritious fluid, perhaps the most so of any vegetable production, appears from its great similarity to sugar, and from its affording sustenance to such numbers of insects, which live upon it solely during summer, and lay it up for their winter provision. These proofs of its nutritive nature evince the necessity of its re-absorption into the vegetable system, for some useful purpose.

This purpose, however, has, as yet, escaped the researches of philosophi­cal botanists. M. Pontedera believes it designed to lubricate the vegetable uterus, and compares the horn-like nectaries of some flowers to the appen­dicle of the caecum intestinum of animals. (Antholog. p. 49.) Others have supposed, that the honey, when re-absorbed, might serve the purpose of the liquor amnii, or white of the egg, as a nutriment for the young embryon, or fecundated seed, in its early state of existence. But as the nectary is found equally general in male flowers as in female ones; and as the young embryon, or seed, grows before the petals and nectary are expanded and after they fall off; and, thirdly, as the nectary so soon falls off after the fecundation of the pistillum; these seem to be insurmountable objec­tions to both the above-mentioned opinions.

In this state of uncertainty, conjectures may be of use so far as they lead to further experiment and investigation. In many tribes of insects, as the silk-worm, and, perhaps, in all the moths and butterflies, the male and fe­male parents die as soon as the eggs are impregnated and excluded; the eggs remaining to be perfected and hatched at some future time. The same thing happens in regard to the male and female parts of flowers; the anthers and filaments, which constitute the male parts of the flower, and the stigma and style, which constitute the female parts of the flower, fall off, and die, as soon as the seeds are impregnated, and along with these the petals and nectary. Now, the moths and butterflies above-mentioned, as soon as they acquire the passion and the apparatus for the reproduction of their species, lose the power of seeding upon leaves as they did before, and become nourished by what?—by honey alone.

Hence we acquire a strong analogy for the use of the nectary, or secre­tion of honey in the vegetable economy, which is, that the male parts of flowers, and the female parts, as soon as they leave their soetus-state, ex­panding their petals (which constitute their lungs), become sensible to the [Page 242] passion, and gain the apparatus for the reproduction of their species, and are sed and nourished with honey, like the insects above described; and that hence the nectary begins its office of producing honey, and dies, or ceases to produce honey, at the same time with the birth and death of the stamens and the pistils; which, whether existing in the same or in different flowers, are separate and distinct animated beings.

Previous to this time, the anthers with their filaments, and the stigmas with their styles, are, in their foetus-state, sustained by their placental ves­sels, like the unexpanded leaf-bud, with the seeds existing in the vegetable womb, yet unimpregnated, and the dust, yet unripe, in the cells of the an­thers. After this period they expand their petals, which have been shewn above to constitute the lungs of the flower; the placental vessels, which be­fore nourished the anthers and the stigmas, coalesee, or cease to nourish them; and they now acquire blood more oxygenated by the air, obtain the passion and power of reproduction, are sensible to heat, and cold, and moisture, and to mechanic stimulus, and become, in reality, insects fed with honey, similar in every respect, except their being attached to the tree on which they were produced.

Some experiments I have made this summer, by cutting out the nectaries of several flowers of the aconites, before the petals were open, or had be­come much coloured: some of these flowers, near the summit of the plants, produced no seeds; others, lower down, produced seeds; but they were not sufficiently guarded from the farina of the flowers in their vicinity; nor have I had opportunity to try if these seeds would vegetate.

I am acquainted with a philosopher, who, contemplating this subject, thinks it not impossible, that the first insects were the anthers or stigmas of flowers; which had, by some means, loosed themselves from their parent plant, like the male flowers of Vallisneria; and that many other insects have gradually, in long process of time, been formed from these; some ac­quiring wings, others sins, and others claws, from their ceaseless efforts to procure their food, or to secure themselves from injury. He contends, that none of these changes are more incomprehensible than the transformation of tadpoles into frogs, and caterpillars into butterflies.

There are parts of animal bodies which do not require oxygenated blood for the purpose of their secretions, as the liver, which, for the production of bile, takes its blood from the mesenteric veins, after it must have lost the whole or a great part of its oxygenation, which it had acquired in its passage through the lungs. In like manner the pericarpium, or womb of the flower, continues to secrete its proper juices for the present nourish­ment of the newly animated embryon-seed; and the saccharine, acescent, or starchy matter of the fruit or seed-lobes, for its future growth, in the same manner as these things went on before fecundation; that is, without any circulation of juices in the petals, or production of honey in the nec­tary; these having perished, and fallen off, with the male and female ap­paratus for impregnation.

It is probable that the depredations of insects on this nutritious fluid, must be injurious to the products of vegetation, and would be much more so, [Page 243] but that the plants have either acquired means to desend their honey in part, or have learned to make more than is absolutely necessary for their own economy. In the same manner the honey-dew on trees is very inju­rious to them; in which disease the nutritive fluid, the vegetable sap-juice, seems to be exsuded by a retrograde motion of the cutaneous lymphatics, as in the sweating sickness of the last century. To prevent the depreda­tion of insects on honey, a wealthy man in Italy is said to have poisoned his neighbour's bees, perhaps by mixing arsenic with honey, against which there is a most flowery declamation in Quintilian, No. XIII. As the use of the wax is to preserve the dust of the anthers from moisture, which would prematurely burst them, the bees which collect this for the construc­tion of the combs or cells, must, on this account, also injure the vegetation of a country where they too much abound.

It is not easy to conjecture why it was necessary that this secretion of ho­ney should be exposed to the open air in the nectary, or honey-cup, for which purpose so great an apparatus for its defence from insects and from showers became necessary. This difficulty increases when we recollect that the sugar in the joints of grass, in the sugar-cane, and in the roots of beets, and in ripe fruits, is produced without exposure to the air.—On supposition of its serving for nutriment to the anthers and stigmas, it may thus acquire greater oxygenation, for the purpose of producing greater powers of sensi­bility, according to a doctrine lately advanced by a French philosopher, who has endeavoured to shew, that the oxygene, or base of vital air, is the constituent principle of our power of sensibility.

So caterpillars are fed upon the common juices of vegetables found in their leaves, till they acquire the organs of reproduction, and then they feed on honey; all, I believe, except the silk-worm, which, in this country, takes no nourishment after it becomes a butterfly. Thus also the maggot of the bee, according to the observations of Mr. Hunter, is fed with raw vegeta­ble matter, called bee-bread, which is collected from the anthers of flowers, and laid up in cells for that purpose, till the maggot becomes a winged bee, acquires greater sensibility, and is fed with honey. Phil. Trans. 1792. See Zoonomia, Sect. XIII. on vegetable animation.

From this provision of honey for the male and female parts of flowers, and from the provision of sugar, starch, oil, and mucilage, in the fruits, seed-cotyledons, roots, and buds of plants, laid up for the nutriment of the expanding foetus, not only a very numerous class of insects, but a great part of the larger animals procure their food, and thus enjoy life and plea­sure without producing pain to others; for these seeds or eggs, with the nutriment laid up in them, are not yet endued with sensitive life.

The secretions from various vegetable glands, hardened in the air, pro­duce gums, resins, and various kinds of saccharine, saponaceous, and wax­like substances, as the gum of cherry or plumb trees, gum tragacanth from the astragulus tragacantha, camphor from the laurus camphora, elemi from amyris elemifera, aneme from hymenoea courbaril, turpentine from pis­tacia terebinthus, balsam of Mecca from the buds of amyris opobalsamum, branches of which are placed in the temples of the East, on account of their [Page 244] fragrance; the wood is called xylobalsamum, and the fruit carpohalsamum; aloe from a plant of the same name, myrrh from a plant not yet described; the remarkably elastic resin is brought into Europe principally in the form of flasks, which look like black leather, and are wonderfully elastic, and not penetrable by water; rectified ether dissolves it; its inflexibility is increased by warmth, and destroyed by cold; the tree which yields this juice is the jatropha elastica; it grows in Guaiana and the neighbouring tracts of Ame­rica; its juice is said to resemble wax, in becoming soft by heat, but that it acquires no elasticity till that property is communicated to it by a secret art, after which it is poured into moulds, and well dried, and can no longer be rendered fluid by heat.—Mr. de la Borde, physician at Cayenne, has given this account. Manna is obtained at Naples from the fraxinus ornus, or manna-ash; it partly issues spontaneously, which is preferred, and partly exsudes from wounds made purposely in the month of August; many other plants yield manna more sparingly. Sugar is properly made from the sac­charum officinale, or sugar-ca [...]e, but is found in the roots of beet and many other plants; American wax is obtained from the myrica cerifera, candle-berry myrtle; the berries are boiled in water, and a green wax separates; with luke-warm water, the wax is yellow: the seeds of croton febiferum are lodged in tallow: there are many other vegetable exsudations used in the various arts of dyeing, varnishing, tanning, lacquering, and which supply the shop of the druggist with medicines and with poisons.

There is another analogy, which would seem to associate plants with ani­mals, and which, perhaps, belongs to this note on Glandulation; I mean the similarity of their digestive powers. In the roots of growing vegeta­bles, as in the process of making malt, the farinaceous part of the seed is converted into sugar by the vegetable power of digestion, in the same manner as the farinaceous matter of seeds is converted into sweet chyle by the animal digestion. The sap-juice which rises in the vernal months from the roots of trees, through the alburnum, or sap-wood, owes its sweetness, I suppose, to a similar digestive power of the absorbent sys­tem of the young buds. This exists in many vegetables in great abundance, as in vines, sycamore, birch, and most abundantly in the palm-tree (Isert's Voyage to Guinea), and seems to be a similar fluid in all plants, as chyle is similar in all animals.

Hence, as the digested food of vegetables consists principally of sugar, and from that is produced again their mucilage, starch, and oil, and since ani­mals are sustained by these vegetable productions, it would seem, that the sugar-making process carried on in vegetable vessels was the great source of life to all organized beings. And that, if our improved chemistry should ever discover the art of making sugar from fossile or aerial matter, without the assistance of vegetation, food for animals would then become as plentiful as water, and mankind might live upon the earth as thick as blades of grass, with no restraint to their numbers but the want of local room.

It would seem, that roots fixed in the earth, and leaves, innumerable, waving in the air, were necessary for the decomposition of water, and the conversion of it into [...] matter, which would have been not only [Page 245] cumberous, but totally incompatible with the locomotion of animal bodies. For how could a man or quadruped have carried on his head or back a forest of leaves, or have had long branching lacteal or absorbent vessels terminat­ing in the earth? Animals, therefore, subsist on vegetables; that is, they take the matter so far prepared, and have organs to prepare it further for the purposes of higher animation, and greater sensibility. In the same man­ner the apparatus of green leaves and long roots were [...]ound inconvenient for the more animated and sensitive parts of vegetable flowers; I mean the anthers and stigmas, which are, therefore, separate beings, endued with the passion and power of reproduction, with lungs of their own, and fed with honey, a food ready prepared by the long roots and green leaves of the plant, and presented to their absorbent mouths.

From this outline, a philosopher may catch a glimpse of the general eco­nomy of nature; and, like the mariner cast upon an unknown shore, who rejoiced when he saw the print of a human foot upon the sand, he may cry out with rapture, "A GOD DWELLS HERE."

NOTE 1.—METEORS.

THERE are four strata of the atmosphere, and four kinds of meteors. 1. Lightning is electric, exists in visible clouds, its short course, and red light. 2. Shooting stars exist in visible vapour, without found, white light, have no luminous trains. 3. Twilight; fire-balls move thirty miles in a second, and are about sixty miles high; have luminous trains, occasioned by an electric spark passing between the aerial and inflammable strata of the atmosphere, and mixing them and setting them on fire in its passage; attracted by volcanic eruptions; one thousand miles through such a medium resists less than the tenth of an inch of glass. 4. Northern lights not at­tracted to a point, but diffused; their colours; passage of electric fire in va­cuo dubious; Dr. Franklin's theory of northern lights countenaced in part by the supposition of a superior atmosphere of inflammable air; antiquity of their appearance; described in Maccabees.

NOTE II.—PRIMARY COLOURS.

THE rainbow was in part understood before Sir Isaac Newton; the seven colours were discovered by him; Mr. Galton's experiments on colours; manganese and lead produce colourless glass.

NOTE III.—COLOURED CLOUDS.

THE rays refracted by the convexity of the atmosphere; the particles of air and of water are blue; shadow by means of a candle in the day; halo round the moon in a sog; bright spot in the cornea of the eye; light from cat's eyes in the dark, from a horse's eyes in a cavern, coloured by the choroid coat within the eye.

NOTE IV.—COMETS.

TAILS of comets from rarified vapour, like northern lights, from elec­tricity; twenty millions of miles long; expected comet; 72 comets already described.

NOTE V.—SUN's RAYS.

DISPUTE about phlogiston; the sun the fountain from whence all phlo­giston is derived; its rays not luminous till they arrive at our atmosphere; light owing to their combustion with air, whence an unknown acid; the sun is on fire only on its surface; the dark spots on it are excavations through its luminous crust.

NOTE VI.—CENTRAL FIRES.

SUN's heat much less than that from the fire at the earth's centre; sun's heat penetrates but a few feet in summer; some mines are warm; warm springs owing to subterrancous fire; situations of volcanos on high moun­tains; original nucleus of the earth; deep vallies of the ocean; distant per­ception of earthquakes; great attraction of mountains; variation of the com­pass; countenance the existence of a cavity or fluid lava within the earth.

NOTE VII.—ELEMENTARY HEAT.

COMBINED and sensible heat; chemical combinations attract heat, solu­tions reject heat; ice cools boiling water six times as much as cold water cools it; cold produced by evaporation; heat by devaporation; capacities of bodies in respect to heat: 1. Existence of the matter of heat shewn from the mechanical condensation and rarefaction of air, from the steam produc­ed in exhausting a receiver, snow from rarified air, cold from discharging an air-gun, heat from vibration or friction; 2. Matter of heat analogous to the electric fluid in many circumstances, explains many chemical phenomena.

NOTE VIII.—MEMNON'S LYRE.

MECHANICAL impulse of light dubious; a glass tube laid horizontally before a fire revolves; pulse-glass suspended on a centre; black leather con­tracts in the sunshine; Memnon's statue broken by Cambyses.

NOTE IX.—LUMINOUS INSECTS.

EIGHTEEN species of glow-worm, their light owing to their respiration in transparent lungs; Acudia of Surinam gives light enough to read and draw by; use of its light to the insect; luminous sea-insects adhere to the skin of those who bathe in the ports of Languedoc; the light may arise from putrescent slime.

NOTE X.—PHOSPHORUS.

DISCOVERED by Kunkel, Brandt, and Boyle; produced in respiration, and by luminous insects, decayed wood, and calcined shells; bleaching a slow combustion in which the water is decomposed; rancidity of animal fat owing of the decomposition of water on its surface; aerated marine acid does not whiten or bleach the hand.

NOTE XI.—STEAM-ENGINE.

HERO of Alexandria first applied steam to machinery, next a French wri­ter in 1630, the Marquis of Worcester in 1655, Capt. Savery in 1689, [Page 249] Newcomen and Cawley added the piston; the improvements of Watt and Boulton; power of one of their large engines equal to two hundred horses.

NOTE XII.—FROST.

EXPANSION of water in freezing; injury done by vernal frosts; fish, eggs, seeds, resist congelation; animals do not resist the increase of heat; frosts do not meliorate the ground, nor are, in general, salubrious; damp air produces cold on the skin by evaporation; snow less pernicious to agriculture than heavy rains for two reasons.

NOTE XIII.—ELECTRICITY.

1. Points preferable to knobs for defence of buildings; why points emit the electric fluid; diffusion of oil on water; mountains are points on the earth's globe; do they produce ascending currents of air? 2. Fairy-rings ex­plained; advantage of paring and burning ground.

NOTE XIV.—BUDS and BULBS.

A TREE is a swarm of individual plants; vegetables are either oviparous or viviparous; are all annual productions like many kinds of insects; hy­bernacula; a new bark annually produced over the old one, in trees and in some herbaceous plants, whence their roots seem end-bitten; all bulbous roots perish annually; experiment on a tulip-root; both the leaf-bulbs and flower-bulbs are annually renewed.

NOTE XV.—SOLAR VOLCANOS.

THE spots in the sun are cavities, some of them four thousand miles deep, and many times as broad; internal parts of the sun are not in a state of combustion; volcanos visible in the sun; all the planets together are less than one six hundred and fiftieth part of the sun; planets were ejected from the sun by volcanos; many reasons shewing the probability of this hypo­thesis; Mr. Busson's hypothesis, that planets were struck off from the sun by comets; why no new planets are ejected from the sun; some comets, and the georgium sidus, may be of later date; sun's matter decreased; Mr. Ludlam's opinion, that it is possible the moon might be projected from the earth.

NOTE XVI.—CALCAREOUS EARTH.

HIGH mountains and deep mines replete with shells; the earth's nucleus covered with lime-stone; animals convert water into lime-stone; all the cal­careous earth in the world formed in animal and vegetable bodies; solid parts of the earth increase; the water decreases; tops of calcareous moun­tains dissolved; whence spar, marble, chalk, stalactites; whence alabaster, flour, flint, granulated lime-stone, from solution of their angles, and by at­trition; tupha deposited on moss; lime-stones from shells with animals in them; liver-stone from fresh-water muscles; calcareous earth from land-animals and vegetables, as marl; beds of marble softened by fire; whence Bath-stone contains lime as well as lime-stone.

NOTE XVII.—MORASSES.

THE production of morasses from fallen woods; account by the Earl Cro­martic of a new morass; morasses lose their salts by solution in water; then their iron; their vegetable acid is converted into marine, nitrous, and vi­triolic acid; whence gypsum, alum, sulphur; into fluor-acid, whence fluor; into siliceous acid, whence flint, the sand of the sea, and other strata of siliceous sand and marl; some morasses ferment like new hay, and, sublim­ing their phlogistic part, form coal-beds above and clay below, which are also produced by elutriation; shell-fish in some morasses, hence shells some­times found on coals, and over iron-stone.

NOTE XVIII.—IRON.

CALCIFORM ores; combustion of iron in vital air; steel from deprivation of vital air; welding; hardness; brittleness like Rupert's drops; specific levity; hardness and brittleness compared; steel tempered by its colours; modern production of iron, manganese, calamy; septaria of iron-stone ejected from volcanos; red-hot cannon-balls.

NOTE XIX.—FLINT.

1. Siliceous rocks from morasses; their cements. 2. Siliceous trees; coloured by iron or manganese; Peak-diamonds; Bristol-stones; flint in form of cal­careous spar; has been fluid without much heat; obtained from powdered quartz and flour-acid by Bergman and by Achard. 3. Agates and onyxes found in sand-rocks; of vegetable origin; have been in complete fusion; their concentric coloured circles not from superinduction, but from congela­tion; experiment of freezing a solution of the blue-vitriol; iron and manganese repelled in spheres, as the nodule of flint cooled; circular stains of marl in salt-mines; some flint nodules resemble knots of wood or roots. 4. Sand of the sea: its acid from morasses; its base from shells. Chert or petrosilex stra­tified in cooling; their colour and their acid from sea-animals; Labradore­stone from mother-pearl. 6. Flints in chalk-beds; their form, colour, and acid, from the flesh of sea-animals; some are hollow, and lined with crystals; contain iron; not produced by injection from without; coralloids converted to flint; French mill-stones; flints sometimes found in solid strata. 7. An­gles of sand destroyed by attrition and solution in steam; siliceous breccia ce­mented by solution in red-hot water. 8. Basaltes and granites are ancient lavas; basaltes raised by its congelation, not by subterraneous fire.

NOTE XX.—CLAY.

FIRE and water two great agents; stratification from precipitation; many stratified materials not soluble in water. 1. Stratification of lava from suc­cessive accumulation. 2. Stratifications of lime-stone from the different pe­riods of time in which the shells were deposited. 3. Stratifications of coal, and clay, and sand-stone, and iron-ores, not from currents of water, but from the production of morass-beds, at different periods of time; morass­beds become ignited; their bitumen and sulphur is sublimed, the clay, lime, and iron, remain; whence sand, marl, co [...]l, white clay in valleys, and gravel­beds, [Page 251] and some others, and some calcareous depositions, owing to alluvia­tion; clay from decomposed granite; from the lava of Vesuvius; from vi­treous lavas.

NOTE XXI.—ENAMELS.

ROSE-COLOUR and purple from gold; precipitates of gold by alkaline salt preferable to those by tin; aurum fulminans long ground; tender co­lours from gold or iron not dissolved, but suspended in the glass; cobalts▪ calces of cobalt and copper require a strong fire; Ka-o-lin and Pe-tun-tse the same as our own materials.

NOTE XXII.—PORTLAND VASE.

ITS figures do not allude to private history; they represent a part of the Eleusinian mysteries; marriage of Cupid and Psyche; procession of torches; the figures in one compartment represent MORTAL LIFE in the act of ex­piring, and HUMANKIND attending to her with concern; Adam and Eve hieroglyphic figures; Abel and Cain other hieroglyphic figures: on the other compartment is represented IMMORTAL LIFE; the Manes, or Ghost, descending into Elysium, is led on by DIVINE LOVE, and received by IMMOR­TAL LIFE, and conducted to Pluto; Trees of Life and Knowledge are em­blematical: the figure at the bottom is of Atis, the first great Hierophant, or teacher of mysteries.

NOTE XXIII.—COAL.

1. A FOUNTAIN of soffile tar in Shropshire; has been distilled from the coal-beds beneath, and condensed in the cavities of a sand-rock; the coal beneath is deprived of its bitumen in part; bitumen sublimed at Matlock, into cavities lined with spar. 2. Coal has been exposed to heat; woody fi­bres and vegetable seeds in coal at Bovey and Polesworth; upper part of coal-heds more bituminous at Beaudesert; thin stratum of asphaltum near Caulk; upper part of coal-bed worse at Alfreton; upper stratum of no va­lue at Widdington; alum at West-Hallum; at Bilston. 3. Coal at Coal­brook-Dale has been immersed in the sea, shewn by sea-shells; marks of vio­lence in the colliery at Mendip and at Ticknal; lead-ore and spar in coal- [...]eds; gravel over coal near Lichfield; coal produced from morasses, shewn by fern-leaves, and bog-shells, and muscle-shells; by some parts of coal be­ing still woody; from Loch Neagh, and Bovey, and the Temple of the De­vil; fixed alkali; oil.

NOTE XXIV.—GRANITE.

GRANITE the lowest stratum of the earth yet known; porphyry, trap, moor-stone, whin-stone, state, basaltes, all volcanic productions dissolved in red-hot water; volcanos in granite strata; differ from the heat of morasses from fermentation; the nucleus of the earth ejected from the sun; was the sun originally a planet? supposed section of the globe.

NOTE XXV.—EVAPORATION.

1. 1. SOLUTION of water in air; in the matter of heat; pulse-glass. 2. Heat is the principal cause of evaporation; thermometer cooled by evapo­ration of ether; heat given from steam to the worm-tub; warmth accom­panying rain. 3. Steam condensed on the education of heat; moisture on cold walls; south-west and north-east winds. 4. Solution of salt and of blue vitriol in the matter of heat. II. Other vapours may precipitate steam, and form rain. 1. Cold the principal cause of devaporation; hence the steam dis­solved in heat is precipitated, but that dissolved in air remains even in frosts; south-west wind. 2. North-east winds mixing with south-west winds produce rain; because the cold particles of air of the north-east acquire some of the matter of heat from the south-west winds. 3. Devapo [...]atio [...] from me­chanical expansion of air, as in the receiver of an air-pump; summer clouds appear and vanish; when the barometer sinks without change of wind, the weather becomes colder. 4. Solution of water in electric fluid dubious. 5. Barometer sinks from the lessened gravity of the air, and from the rain having less pressure as it falls; a mixture of a solution of water in calo­rique, with an aerial solution of water, is lighter than dry air; breath of ani­mals in cold weather, why condensed into visible vapour, and dissolved again.

NOTE XXVI.—SPRINGS.

LOWEST strata of the earth appear on the highest hills; springs from dews sliding between them; mountains are colder than plains; 1. From their being insulated in the air; 2. From their enlarged surface; 3. From the rarity of the air it becomes a better conductor of heat; 4. By the air on mountains being mechanically rarefied as it ascends; 5. Gravitation of the matter of heat; 6. The dashing of clouds against hills; of fogs against trees; springs stronger in hot days with cold nights; streams from subterranean caverns; from beneath the snow on the Alpa.

NOTE XXVII.—SHELL-FISH.

THE armour of the Echinus moveable; holds itself in storms to stones, by 1200 or 2000 strings: Nautilus rows and fails; renders its shell buoyant: Pinna and cancer; Byssus of the ancients was the beard of the Pinna; as fine as the silk is spun by the silk-worm; gloves made of it; the beard of mus­cles produces sickness; Indian-weed; tendons of rats' tails.

NOTE XXVIII.—STURGEON.

STURGEON's mouth like a purse; without teeth; tendrils like worms hang before his lips, which entice small fish and sea-insects, mistaking them for worms; his skin used for covering carriages; isinglass made from it; ca­viare from the spawn.

NOTE XXIX.—OIL ON WATER.

OIL and water do not touch; a second drop of oil will not diffuse itself on the preceding one; hence it stills the waves; divers for pearl carry oil in their mouths; oil on water produces prismatic colours; oiled cork circu­lates on water; a phial of oil and water made to oscillate.

NOTE XXX.—SHIP-WORM.

THE Teredo has calcareous jaws; a new enemy; they perish when they meet together in their ligneous canals; United Provinces alarmed for the piles of the banks of Zealand; were destroyed by a severe winter.

NOTE XXXI.—MAELSTROM.

A WHIRLPOOL on the coast of Norway, passes through a subterraneous cavity; less violent when the tide is up; eddies become hollow in the mid­dle; heavy bodies are thrown out by eddies; light ones retained; oil and water whirled in a phial; hurricanes explained.

NOTE XXXII.—GLACIERS.

SNOW in contact with the earth is in a state of thaw; ice-houses; ri­vers from beneath the snow; rime, in spring, vanishes by its contact with the earth; and snow by its evaporation and contact with the earth; moss vegetates beneath the snow; and Alpine plants perish at Upsal for want of snow.

NOTE XXXIII.—WINDS.

AIR is perpetually subject to increase and to diminution; Oxygene is per­petually produced from vegetables in the sunshine, and from clouds in the light, and from water; Azote is perpetually produced from animal and ve­getable putrefaction, or combustion; from springs of water; volatile alkali; fixed alkali; sea-water; they are both perpetually diminished by their con­tact with the soil, producing nitre; Oxygene is diminished in the produc­tion of all acids; Azote by the growth of animal bodies; charcoal in burn­ing consumes double its weight of pure air; every barrel of red-lead ab­sorbs 2000 cubic feet of vital air; air obtained from variety of substances by Dr. Priestley; Officina aeris in the polar circle, and at the line. South­west winds; their westerly direction from the less velocity of the earth's sur­face; the contrary in respect to north-east winds; South-west winds consist of regions of air from the south; and north-east winds of regions of air from the north; when the south-west prevails for weeks, and the barometer sinks to 28, what becomes of above one fifteenth part of the atmosphere? 1. It is not carried back by superior currents; 2. Not from its loss of moisture; [Page 254] 3. Not carried over the pole; 4. Not owing to atmospheric tides or moun­tains; 5. It is absorbed at the polar circle; hence south-west winds and rain; south-west sometimes cold. North-east winds consist of air from the north; cold by the evaporation of ice; are dry winds; 1. Not supplied by superior currents; 2. The whole atmosphere increased in quantity by air set at liberty from its combinations in the polar circles. South-east winds consist of north winds driven back. North-west winds consist of south-west winds driven back; north-west winds of America bring frost; owing to a vertical spiral eddy of air between the eastern coast and the Apalachian mountains; hence the greater cold of North-America. Trade-winds; air over the line always hotter than at the tropics; trade-winds gain their easterly direction from the greater velocity of the earth's surface at the line; not supplied by su­perior currents; supplied by decomposed water in the sun's great light; 1. Because there are no constant rains in the tract of the trade-winds; 2. Be­cause there is no condensible vapour above three or four miles high at the line. Monsoons and Toreadors: some places at the tropic become warmer when the sun is vertical than at the line; hence the air ascends, supplied on one side by the north-east winds, and on the other by the south-west; whence an ascending eddy or tornado, raising water from the sea, or sand from the desert, and [...] air diminished to the northward produces south-west winds [...] from heavier air above sinking through lighter air below, which rises [...]; hence trees are thrown down in a narrow line of twenty or forty yards broad, the sea rises like a cone, with great rain and lightning. Land and sea breezes; sea less heated than land; tropical islands more heated in the day than the sea, and are cooled more in the night. [...] irregular winds from other causes; only two original winds, north and south; different sounds of north-east and south-west winds; a Bear or Dragon in the arctic circle that swallows at times, and disem­bogues again, above one fifteenth part of the atmosphere; wind-instruments; recapitulation.

NOTE XXXIV.—VEGETABLE PERSPIRATION.

PURE air from Dr. Priestley's vegetable matter, and from vegetable leaves, owing to decomposition of water; the hydrogene retained by the vegetables; plants in the shade are tanned green by the sun's light; animal skins are tanned yellow by the retention of hydrogene; much pure air from dew on a sunny morning; bleaching, why sooner performed on cotton than linen; bees wax bleached; metals calcined by decomposition of water; oil bleached in the light becomes yellow again in the dark; nitrous acid co­loured by being exposed to the sun; vegetables perspire more than animals, hence in the sunshine they purify air more by their perspiration than they injure it by their respiration; they grow fastest in their sleep.

NOTE XXXV.—VEGETABLE PLACENTATION.

BUDS the viviparous offspring of vegetables; placentation in bulbs and feeds; placentation of buds in the roots, hence the rising of sap in the spring, as in vines, birch, which ceases as soon as the leaves expand; production of the leaf of Horse-chesnut, and of its new bud; oil of vitriol on the bud of Mimosa killed the leaf also; placentation shewn from the sweetness of the sap; no umbilical artery in vegetables.

NOTE XXXVI.—VEGETABLE CIRCULATION.

BUDS set in the ground will grow if prevented from bleeding to death by a cement; vegetables require no muscles of locomotion, no stomach or bow­els, no general system of veins; they have, 1. Three systems of absorbent vessels; 2. Two pulmonary systems; 3. Arterial systems; 4. Glands; 5. Organs of reproduction; 6. muscles. I. Absorbent system evinced by experi­ments by coloured absorptions in fig-tree and picris; called air-vessels erro­neously; spiral structure of absorbent vessels; retrograde motion of them like the throats of cows. II. Pulmonary arteries in the leaves; and pul­monary veins; no general system of veins shewn by experiment; no heart; the arteries act like the vena portarum of the liver; pulmonary system in the petals of flowers; circulation owing to living irritability; vegetable ab­sorption more powerful than animal, as in vines; not by capillary attraction.

NOTE XXXVII.—VEGETABLE RESPIRATION.

I. LEAVES not perspiratory organs, nor excretory ones; lungs of animals. 1. Great surfaces of leaves. 2. Vegetable blood changes colour in the leaves; experiment with spurge; with picris. 3. Upper surface of the leaf only acts as a respiratory organ. 4. Upper surface repels moisture; leaves laid on water. 5. Leaves killed by oil like insects; muscles at the foot-stalks of leaves. 6. Use of light to vegetable leaves; experiments of Priestley, Ingenhouz, and Scheele. 7. Vegetable circulation similar to that of fish. II. Another pulmonary system belongs to flowers; colours of flowers. 1. Vascular structure of the corol. 2. Glands producing honey, wax, &c. perish with the corol. 3. Many flowers have no green leaves attending them, as Colchicum. 4. Corols not for the defence of the stamens. 5. Co­rol of Helleborus Niger changes to a calyx. 6. Green leaves not necessary to the fruit-bud; green leaves of Colchicum belong to the new bulb, not to the flower. 7. Flower-bud after the corol falls is simply an uterus; mature flowers not injured by taking off the green leaves. 8. Inosculation of vege­table vessels.

NOTE XXXVIII.—VEGETABLE IMPREGNATION.

SEEDS in broom discovered twenty days before the flower opens; pro­gress of the seeds after impregnation; seeds exist before fecundation; analo­gy [Page 256] between seeds and eggs; progress of the egg within the hen; spawn of frogs and fishes; male Salamander; marine plants project a liquor, not a powder; seminal fluid diluted with water, if a stimulas only? Male and fe­male influence necessary in animals, insects, and vegetables, both in produc­tion of seeds and buds; does the embryon-seed produce the surrounding fruit, like insects in gall-nuts?

NOTE XXXIX.—VEGETABLE GLANDULATION.

VEGETABLE glands cannot be injected with coloured fluids; essential oil; wax; honey; nectary, its complicate apparatus; exposes the honey to the air like the lachrymal gland; honey is nutritious; the male and female parts of flowers copulate and die like moths and butterflies, and are fed like them with honey; anthers supposed to become insects; depredation of the honey and wax injurious to plants; honey-dew; honey oxygenated by expo­sure to air; necessary for the production of sensibility; the provision for the embryon plant of honey, sugar, starch, &c. supplies food to numerous clas­ses of animals; various vegetable secretions, as gum tragacanth, camphor, elemi, anime, turpentine, balsam of Mecca, aloe, myrrh, elastic resin, manna, sugar, wax, tallow, and many other concrete juices; vegetable digestion; chemical production of sugar would multiply mankind; economy of nature.