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and hung down about the centre of the room. Myself and several others were at this time inclofed in the ftove, without experiencing any oppreffive or painful fenfation of heat, proportioned to the degree pointed out by the thermometer. Every metallic about us foon became very hot.

II. My friend Mr. Park, an ingenious furgeon of this place, went into the stove heated to 202°. After ten minutes I found the pulfe quickened to 120. And to determine the increase of the animal heat, another thermometer was handed to him, in which the quick filver already ftood at 98°; but it rofe only to 99%, whether the bulb of the thermometer was inclofed in the palms of the hands, or received into the mouth *. The natural state of this gentleman's pulfe is about 65.

III. Another gentleman went through the fame experiment in the fame circumstances, and with the fame effects.

IV. One of the porters to the Hofpital, a healthy young man, and the pulfe 75, was inclofed in the ftove when the quick filver flood at 210°; and he remained there, with little inconvenience, for 20 minutes. The pulfe, now 164, and the animal heat, determined by another thermometer as in the former experiments, was 1011.

V. A young gentleman of a delicate and irritable habit, whofe natural pulfe is about 80, remained in the ftove ten minutes when heated to 224°. The pulfe rose

The fcake of the thermometer, which was fufpended by the ftring about the middle of the room, was of metal; this was the only one I could then procure, on which the degrees ran fo high as to give any scope for the experiThe fcale of the other thermometer, which was employed for afcertaining the variations in the animal heat, was of ivory.

ment.

to

to 145, and the animal heat to 102°. This gentleman, who had been frequently in the ftove during the courfe of the day, found himfelf feeble, and difpofed to break out into fweats for 24 hours after the experiment.

VI. Two fmall tin veffels, containing each the white of an egg, were put into the flove heated to 224°. One of them was placed on a wooden feat near the wall, and the other fufpended by a firing about the middle of the love. After ten minutes, they began to coagulate; but the coagulation was fenfibly quicker and firmer in that which was fufpended, than in that which was placed on the wooden feat. The progress of the coagulation was as follows: it was firft formed on the fides, and gradually extended itself; the whole of the bottom was next coagulated; and last of all the middle part of the top.

the end of another hour it was ftill fluid, except on the edges where it was thinneft; and here it was ftill transparent; a fufficient proof, that it was dried, not coagulated.

VII. Part of the fhell of an egg was peeled away, leaving only the film which furrounds the white; and part of the white being drawn out, the film funk fo as to form a - little cup. This cup was filled with fome of the albumen ovi, which was confequently detached as much as poffible from every thing but the contact of the air and of the film which formed the cup. The lower part of the egg stood upon fome light tow in a common galiipot, and was placed on the wooden feat in the ftove. The quick filver in the thermometer ftill continued at 224°. After remaining in the ftove, for an hour, the lower part of the egg, which was covered with the fhell, was firmly coagulated; but that which was in the little cup was fluid and tranfparent. At

VIII. A piece of bees wax, placed in the fame fituation with the albumen ovi of the preceding experiment, and expofed to the fame degree of heat in the stove, began to melt in five minutes: another piece fufpended by a ftring, and a third piece put into the tin veffel and fufpended, began likewife to liquify in five minutes.

Obfervations.

That heated air fhould have fuch a speedy and powerful effect in quickening the pulfe, while the animal heat is little altered from its natural ftandard; that the human body fhould fo eafily bear to be furrounded with air heated to 224°; that the albumen ovi, which begins to coagulate in water at 150°, fhould remain fluid in 224°; and that the fame albumen ovi, ftill placed in air heated to 224°, thould coagulate, if in contact either with tin or its own shell, are facts as fingular as they are difficult of explanation. From the different effects of heated air on the pulfe and the heat of the body, do we not difcover the fallacy of that theory of animal heat which has been adopted by Boerhaave and other celebrated phyñologists? They fuppofe that animal heat is produced by the attrition of the globules of the circulating fluids against the fides of the containing veffels; but in feveral of the preceding experiments, the circulation was amazingly quickened, with little increase of the animal heat. But whence is it that the human body G 3

can

can bear, without immediate injury, to be furrounded with air heated to 224? And whence is it, that the albumen ovi does not coagulate in this degree of heat? Is it that fire as it paffes into fome bodies becomes latent, agreeable to a doctrine which has for fome time been taught at Edinburgh by Profeffor BLACK? Or does fire become fixed and quiefcent, according to a fimilar fyftem adopted by Dr. Franklin * ? Air we know exifts either in a fixed or elaftic fate; and fire may in like manner exift in bodies, either in a latent, fixed, and quiefcent; or in a fenfible, fluid, and active state. Agreeable to this idea, the bees wax receives the fire in an active ftate, and diffolves; while the human body and the albumen ovi, receiving the fire in a latent ftate, are little altered in their temperature. Let each of these, however, be put in contact with a different body, tin for inftance; and though the heat of the air continues the fame, yet the fire no longer enters in a latent ftate, but with all its fenfible and active powers; for the albumen ovi fufpended in a tin veffel foon coagulates; and the human body, covered with the fame metal, would quickly experience an intolerable and deftructive degree of heat. Or are the above phænomena more fatisfactorily explained, by confidering different bodies as poffeffing different conducting powers; fome being rong, others weak conductors of fire? All thofe bodies then which are weak conductors of fire from air, may be placed in air, without receiving the

heat of this medium. Hence the albumen ovi remains fluid in air heated to 224°. Hence likewife the frog, the lizard, the camelion, &c. retain their natural temperature, and feel cold to the touch, though perpetually furrounded with air hotter than their own bodies. Hence alfo, the human body keeps nearly its own temperature, in a ftove heated to 224° or may even pafs without injury into air heated to a much greater degree, according to the obfervations of DU HAMEL and TILLETT, published in the Memoirs of the Academy of Sciences +. On the other hand, all thofe bodies which are powerful conductors of fire from air, are influenced in proportion when furrounded with this medium. The bees wax melted from the mere contact of the air in experiment VIII; and in experiment VI. the albumen ovi was coagulated on the intervention of another body, which is a ftrong conductor of fire from air. But whether this method of reafoning on the natural caufe of thefe effects be juft or not, the final caufe is obvious, and is to be refolved into the wife and benevolent appointment of the Almighty. Man is happily fo framed, as to poffefs a power of keeping nearly the fame tenor of heat, in all the variations of the temperature of the air in fummer and winter, in hot and cold climates; and confequently changes his fituation on the furface of the globe, with much lefs inconvenience or injury, than he could otherwise have done. The fame power likewife happily adapts different animals to their

* Exper. and Obferv. p. 346. and 412.

† Memoirs pour 1761: And likewife our Volume for 1768. Second

Part, p. 91.

respective

respective destinations. The lizard and the camelion remain cool under the equator, while the whale and porpoile retain a degree of heat above that of the human body, though furrounded with the waters of the coldest Northern feas, and amidit mountains of ice in the neighbourhood of the Pole.

Should you think thefe experiments and obfervations on heated air of fufficient importance to be com. municated to the Royal Society, they are at your disposal.

I have the pleafure to find, that Dr. Priestley is profecuting his very ingenious inquiries on air. In a letter I lately received from him he informs me, that he has difcovered a fpecies of air, which will preferve animal life fix times longer than atmospheric air.

I remain with great esteem, &c.

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for a very different purpose; which was no other than to fatisfy myfelf, whether an animal could retain life after it was frozen, as had been confidently afferted both of fifh and fnakes. I mention this, to account for what might otherwife be attributed to negligence and inattention; namely, that lit tle nicety was used in measuring the precife degrees of the cold applied in thefe experiments. Accuracy in this particular was not aimed at, being of no confequence in the inquiry more immediately before me. The cold produced was firft by means of ice and fnow with fal ammoniac or fea falt, and was about 10 of Fahrenheit's thermometer. Then ice, fo cooled, was mixed with fpirit of nitre; but what degree of cold was thus produced I did not examine. This cold mixture was made in a tub furrounded with woollen cloths, and covered with the fame, to prevent the effects of the heat of the atmosphere upon the mixture itself, and to preferve, as much as poffible, a cold atmosphere within the vessel. The animal juices, the blood for example, freeze at 25°; fo that a in fuch an atmosphere.

fented to this learned Society, upon a power which animals feem to poffefs of generating cold, induced me to look over my notes of certain experiments and obfervations made in the year 1766, which indicate an oppofite power in animals; whereby they are capable of refifting any external cold while alive, by generating within themfelves a degree of heat fufficient to counteract it. Thefe experiments were not originally inftituted in view of the discovery, which in the event refulted from them, but

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'melted alfo; and this was repeated feveral times, till we grew tired, and at laft left them covered up in the yard, to freeze by the joint operation of the furrounding mix ture and the natural cold of the atmofphere. They were frozen at laft, after having exhaufted the whole powers of life in the production of heat. That this was really the cafe, could not be known, till I had completed that part of the experiment, for which the whole was begun; viz. the thawing of the animals. This was done very gradually; but the animals did not with flexibility recover life. While in this cold, they fhewed figns of great uneafnefs by their violent motions. In fome of thefe experiments, where 'air was made the conductor of the cold and heat, that the heat might be more readily carried off from the animal, a leaden veffel was ufed. It was fmall for the fame reafon; and as it was neceffary, for the animal's refpiration, that the mouth of the veffel fhould communicate with the open air, it was made pretty deep, that the cold of the atmosphere round the animal might not be diminished faft by the warmth of the open air, which would have fpoiled it as a conductor.

II. The fecond upon a dormouse. funk in the cold to its edge.

experiment was The veffel was mixture almoft The atmosphere

round the animal foon cooled; its breath froze as it came from the mouth; an hoar-froft gathered on its whiskers, and on all the infide of the veffel; and the external ends of the hair became covered with the fame. While this was going on, the animal fhewed figns of great uneafinefs: fometimes it would coil itself into a round form, to preferve its extremities, and confine its heat, but finding that ineffectual, it then endeavoured to make its efcape; its motions became lefs violent by the finking of the vital powers; and its feet were frozen; but we were not able to keep up the cold a fufficient time to freeze the whole animal, its hair being fuch a bad conductor of heat, that the confumption was not more than the animal powers were capable of fupporting t.

III. The third experiment was made upon another dormouse. From the failure of the laft experiment, I took care that the hair should not a fecond time be an ob. ftruction to the fuccefs of our experiment. I therefore firft wetted it all over, that the heat of the animal might be more inftantaneously carried off; and then it was put into the leaden veffel. The whole was put into the cold mixture as before. The animal foon gave figns of its feeling the cold, by repeated attempts to make its efcape. The breath, and the evaporating water from its body

This fhews, that cold, carried to a great degree, rather roufes the animal into action than depreffes it; but it would appear, from many circumstances and obfervations, that a certain degree of cold produces inactivity both in the living and fenfitive principle, which will be farther illustrated hereafter.

+ Thefe experiments were made in prefence of Dr. George Fordyce, and Dr. Ervin, teacher of Chemistry at Glasgow; the latter of whom came in accidentally in the middle of our operations.

were

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