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from hard earth, and ftony fubftances. That fingular fofiil, called Afbeftos, most evidently grows from an earthy root. Thofe productions, named BrainStones, have all their radical parts by which they grow from fubmarine rocks. Pyrites, or fire-ftones, exhibit the root from which they fhoot upwards in curious forms and configurations; and even many common pebbles have the moft evident figns of a root or radical part from whence the fubftance of the ftone gradually proceeded. Metals, too, in their purest forms, actually prefent us with arborefcent vegetations: thus we find real fprigs and branchery of maffy and malleable copper in the mines. All kinds of metals grow in their proper earths or ores; and filver, in particular, difcovers as perfect a vegetation, in branches and leaves, as even fern: gold grows in grains of different fizes; tin is frequently found in the form of pebbles; and iron in that of very large ftones of the pebble kind. The copperas-ftone evidently grows from a root; as well as that called the Starry Waxen Vein, which exhibits, when broke, a moft curious irradiation in the form of a ftar. Numberlefs other inftances might be adduced, to prove the existence of this univerfal power of vegetation, in and through all parts of the earth, and the

various bodies it contains.

The third great principle in nature, viz. an univerfal plaftic power, is what, in the beginning, gave birth to the beautiful order and frame of the mundane fyftem, which we every where behold; and to that regularity, diftribution, and distinction, obferved to be permanent, and at all times uniformly the fame, amongst all the myriads of different kinds and fpecies of beings and bodies found therein. This power impreffes on matter thofe general marks and characteristic forms, fhapes, traits, and lineaments, by which bodies are distinguished into their primary kinds and claffes, and which ever continue the fame. Thus earth, fand, gravel, clay, loam, &c. are in all parts of the world of the fame unchangeable form and nature. Stones, flints, pebbles, flate, marble,marcafites, and metals, are

conftantly the fame in every part of the globe. Spars, cryftals, and precious ftones, are invariably the fame for ever. Skins,fhells, feathers, &c are always the fame for the fame animals. All matter, while it retains it's original form, will conftitute the fame kind of body. If the form of a fcollop-fhell be impreffed upon the fubftance of hard stone, it will make a fcollop-ftone, though not a fcollop-fhell: and many fuch forms of fhells we find every where exifting in mere earth, fand, loam, pebbles, the hardest rocks, and on the highest mountains. But the perfect impreffion of a cockle-fhell in the middle of a fmall pebble, fcarce half an inch wide, and of the very fame matter with the pebble, is an infallible proof that it was folely the effect of this plaftic power. That this power forms fhells at land the fame as thofe in the fea when it has the fame materials to work upon, is evident from numberless small fhells conftantly formed from the spray of the fea, at the distance of a mile from that element; and though they are deftroyed every year by the ploughing of the ground, they are yet as conftantly regenerated. In many parts of the earth, fhells are formed in beds without the leaft admixture of earth be tween them. Some hard ftones confift of nothing but fhells throughout. Lumps of foft moift fand, in a fandpit, appear with the lineaments of cockle-thells more or less vifible; while by the touch only they would crumble to powder. Not only the impreffions of thells, but of plants and animals of many forts, are found in all parts of the earth: the figures of the fern and the fish may as well be ftamped in stone as in the fubftance of a plant or animal. We find nature, as it were, fportive with this power, fometimes in prefenting us with the figures of many forts of fhells, animals, &c. which were never feen, or known to exift in any part of the world. The most remarkable inftance of this kind is the ferpentftone, coiled up in folds like a serpent or fnake, from the smallest fize to the enormous one of two feet in diameter, both in foft sarth, and in the hardest flone.

PHILOSOPHICAL

PHILOSOPHICAL TRANSACTIONS. EXPERIMENTS ON THE POWER OF

mode of it's operation, is fo obfcure and incomprehenfible.

It appears to be accumulated in an

ANIMALS TO PRODUCE COLD, immenfe quantity in the fun and

WHEN PLACED IN CERTAIN CIRCUMSTANCES. BY ADAIR CRAWFORD, MD: COMMUNICATED BY SIR JOSEPH BANKS, BART. PRIS.

IN

N the following paper I fhall lay before the Society the refult of Tome experiments, which I made in the courfe of the fummer 1780, on the power that animals, when placed in certain circumstances, poffefs, of producing cold, having premifed a few remarks on the progreffive improve ments which have been made in the knowledge of heat in general.

The opinions of the ancients, refpecting the nature and properties of fire, confifted of bold conjectures, which feem rather to have been the offspring of a lively and vigorous imagination, than of a juft and correct judgment: their ideas on this fubject being evidently derived, not fo much from an accurate obfervation of facts, as from thofe fentiments of admiration and awe which many of the phænomena of fire are calculated to excite. Thus, this element was fuppofed, on the original formation of the univerfe, to have afcended to the highest place, and to have occupied the region of the heavens; it was conceived to be the principle which first communicated life and activity to the animal kingdom; it was confidered as conftituting the effence of inferior intellectual beings; and, by many of the ancient nations, it was reverenced as the Supreme Deity. Indeed, the profound veneration with which the element of fire was contemplated, for a long fucceffion of ages, by a great part of mankind, appears to be one of the most curious circumftances in the hiftory of ancient opinions.. To account for this, we may obferve, that there is no principle in nature, obvious to the fenfes, which produces fuch important effects in the material fyftem, and which, at the fame time, in the VOL. III,

fixed ftars, from whence it's beneficial influence feems to be continually dif fufed over the universe: it is the great inftrument by means of which the changes of the seasons are effected; the diverfity of climates is chiefly owing to the various proportions in which it is diftributed throughout the earth. If we add to this the mighty alterations which have been pro duced in human affairs by the introduction of artificial fire, by it's employment in the feparation of metals from their ores, and in the various arts which are fubfervient to the com= fort, the ornament, and the preservation of the fpecies, it will not ap pear furprizing that, in a rude and ignorant age, this wonderful principle fhould have been confidered as endued with life and intelligence, and that it should have become the object of religious veneration.

In the dark ages the alchymifts regarded pure fire as the refidence of the Deity: they conceived it to be uncreated and immense, and attributed to it's influence most of the phænomena of nature. Indeed, it is not wonderful that they should have affigned it a high rank in the fcale of being, as it was the great agent which they employed in the chymical analyfis of bodies, and was the inftrument of thofe difcoveries that attracted such universal admiration, and that enabled them fo fuc cefsfully to impofe upon the ignorance and credulity of the times.

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ment thofe motions are begun and fupported in the animal and vegetable kingdoms, which are essential to the production and prefervation of life; and that it is the great agent in thofe fucceffive combinations and decompofitions, by which all things on the furface of the earth, and probably throughout the univerfe, are kept in a continual fluctuation.

But though the utility of this branch of science was perceived, yet the progrefs that was made in the cultivation of it did not keep pace with the opinion which men entertained of it's importance. Our fenfes inform us, that heat has a real exiftence, but they give us no direct information with regard to it's nature and properties: it is endowed with fuch infinite fubtlety, that it has been called, by a very eminent philofopher, an occult quality; by fome it has even been confidered as an immaterial being. It is, therefore, with great difficulty, that it can be made the fubject of philofophical investigation; and hence the opinions of men concerning it have been fluctuating and various, and the words which exprefs it vague and ambiguous.

exploded, fince all were found to produce fimilar effects upon the thermometer. The increase and diminution of temperature in the different feafons and climates, the laws which nature obferves in the heating and cooling of bodies, the melting, the vaporific, and fhining points, and the degrees of heat in the animal, the mineral and the vegetable kingdoms, were accurately determined. In confequence of the attention that was paid to this fubject, many curious questions arofe, which have long exercifed the ingenuity of philofophers. That property of heat by which it is capable of expanding the denfeft and hardest bodies; it's power in producing fluidity; it's tendency to an equilibrium; and the causes of it's various diftribution throughout the different fubftances in nature, have become the objects of philofophical enquiry. It was observed, that fome bodies, on expofure to heat, become red and luminous, but are incapable of producing flame, or of maintaining fire: that, on the contrary, others, by the application of fire, and the contact of fresh air, kindle into flame, and continue to emit light and heat, apparently from a fource within themselves, till they are confumed. Hence arofe the queftions concerning the pabulum of fire, the ufe of the air in inflammation, and the diftinction of bodies into combustible and incombustible.

From the firft dawnings of philofophy it must have been perceived, that moft animals have a higher temperature than the medium in which they live; and that a conftant fucceffion of fresh air is neceffary to the fupport of animal life. The causes of

The first step that was taken with a view to the cultivation of this branch of fcience, was the conftruction of a machine for meafuring the variations of fenfible heat; obferving, that heat has the power of expanding bodies, and confidering the degree of expanfion as proportional to the increase of heat, philofophers have endea voured by means of the former to render the latter obvious to the fenfes. To this important invention, the -author of which cannot be diftin&tly traced, we are indebted for all the fucceeding improvements in the phi-thefe phænomena have afforded matlofophy of heat. By means of it men were enabled to establish a variety of interefting facts, and to bring fome of the moft obfcure and intricate phænomena of nature to the teit of experiment. The opinion, that the heats inherent in various heterogeneous fubftances differed from each other in kind, as well as in degree, was now

ter for much fpeculation in ancient as well as modern times: but the difcovery that animals have, in certain circumftances, the power of keeping themfelves at a lower temperature than the furrounding medium, was referved for the induitry of the prefent age.

This discovery seems originally to

have arisen from obfervations on the heat of the human body in warm climates. It was mentioned by Governor Ellis in 1758; it was taught by Doctor Cullen before the year 1765; and at length it was compleatly eftablished by the experiments of Doctor Fordyce in heated rooms, which were laid before the Society in 1774•

In the course of thefe experiments, the doctor remained in a moist air heated to 130 degrees for the space of fifteen minutes, during which time the thermometer under his tongue ftood at 100 degrees, his pulfe made 139 beats in a minute, his refpiration was but little affected, and streams of water ran down over his whole body, proceeding from the condenfation of vapour, as evidently appeared from a fimilar condensation on the fide of a Florentine flask that had been filled with water at 100 degrees.

He found, however, that he could bear a much greater degree of heat when the air was dry. In this fituation, he frequently fupported, naked, for a confiderable time, without much inconvenience, the heat of 260 degrees, his body preferving very nearly it's proper temperature, being never raised more than 2 degrees above the natural ftandard.

Various opinions have been entertained with regard to the causes of the facts which were established by thefe experiments. Some have attributed the cold folely to evaporation, and have conceived that the fame degree of refrigeration would have been produced by an equal mafs of dead matter, containing an equal quantity of moisture. Others have affirmed, that the cold did not arife folely from this caufe; but have maintained, that it depended partly upon the energy of the vital principle, being greater than what would have been produced by an equal mass of inanimate matter.

The ingenious Doctor Munro, of Edinburgh, afcribes the cold in the above-mentioned experiments to the

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circulation of the blood, in confequence of which the warmer fluids are continually propelled from the furface towards the centre, where they are mixed with blood at a lower temperature; and hence the animal is flowly heated, in the fame manner as the water in a deep lake, during the winter, is flowly cooled, and not without a long continuance of frost congealed, no part of it becoming folid till the whole is brought down to the freezing point.

The following experiments were made with a view to determine with greater certainty the caufes of the refrigeration in the above inftances.

To discover whether the cold produced by a living animal, placed in air hotter than it's body, be not greater than what would be produced by an equal mass of inanimate matter, I took a living and a dead frog, equally moist, and of nearly the fame bulk, the former of which was at 67, the latter at 68 degrees, and laid them upon flannel in air which had been raised to 106 degrees. In the courfe of twenty-five minutes the order of heating was as follows*.

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*In the two following experiments the thermometers were placed in contact with the skin of the animals under the axillæ,

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911 91

89

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89 Thefe experiments prove, that live ing frogs have the faculty of refifting heat, or producing cold, when im merfed in warm water; and the experiments of Doctor Fordyce prove, that the human body has the fame power in a moift as well as in a dry air; it is therefore highly probable, that this power does not depend folely upon evaporation.

It may not be improper here to obferve, that healthy frogs, in an atmafphere above 70 degrees, keep themselves at a lower temperature than the external air, but are warmer internally than at the furface of their bodies; for when the air was 77 degrees, a frog was found to be 68, the thermometer being placed in contact with the skin; but when the thermometer was introduced into the ftomach, it rofe to 70%,

It may likewife be proper to mention, that an animal of the fame fpecies placed in water at 61, was found to be nearly 611 at the furface, and internally it was 661. Thefe obfervations are meant to extend only to frogs living in air or water at the common temperature of the atmofphere in fummer. They do not hold with respect to thofe animals, when plunged fuddenly into a warm medium, as in the preceding experiments,

To determine whether other animals also have the power of producing cold, when furrounded with water above the standard of their natural heat, a dog at 102 degrees was immerfed in water at 114, the thermo

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112 the refpiration having become very rapid. În thirteen minutes the dog was 108 degrees, water 112, the refpiration being ftill more rapid..

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In about half an hour the dog was 109 degrees, water 112; the animal was then in a very languid state.

Small quantities of blood being drawn from the femoral artery, and from a contiguous vein, the temperature did not feem to be much increafed above the natural ftandard, and the fenfible heat of the former appeared to be nearly the fame with that of the latter.

In this experiment a remarkable change was produced in the appearance of the venous blood: for it is well known that, in the natural state, the colour of the venous blood is a dark red, that of the arterial being light and florid; but after the animal, in the experiment in question, had been immersed in warm water for half an hour, the venous blood affumed very nearly the hue of the arterial, and resembled it so much in appearance, that it was difficult to diftinguish between them. It is proper to obferve, that the animal which was the fubject of this experiment, had been previously weakened by lofing a confiderable quantity of blood a few days before. When the experiment was repeated with dogs which had not fuffered a fimilar evacuation, the change in the colour of the venous blood was more gradual; but in every inftance in which the trial was made, and it was repeated fix times, the alteration was fo remarkable, that the blood which was taken in the warm bath could readily be diftinguished from that which had been taken from the fame vein

In the above experiment, the water, by the cold frogs and by the agitation which it fuffered during their immerfion, was reduced nearly to 91 degrees.

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