XLIII. Experiments on Animals and Vegetables, with respect to the Power of producing Heat. By John Hunter, F. R. S.

P. 446.

Reprinted with additions, in Mr. John Hunter's Observations on Certain Parts of the Animal Economy.

By John

XLIV. A Comparison of the Heat of London and Edinburgh. Roebuck,* M. D., F. R. S., in a Letter to William Heberden, M. D., F. R. S. p. 459.

I delivered to you some time ago, a register of the thermometer at Hawkhill, * Dr. John Roebuck was born at Sheffield, in Yorkshire, in the year 1718; and he died in 1794, at 76 years of age, in Scotland, where for many years he had conducted several important manufactural concerns, of his own establishing, in iron, coal, and chemical productions. His father, being a manufacturer of Sheffield goods, had intended his son for the same occupation; but from the young man's promising genius, he was induced to give him a more liberal education and profession. After the common grammar school foundation at Sheffield, he was sent to Dr. Doddridge's academy at Northampton, where he pursued his studies with distinguished reputation. Hence Mr. R. was removed to the university of Edinburgh, where having gone through a regular course of studies and practice in physic and chemistry, he next spent some time at the university of Leyden, then in high reputation as a school of medicine. There, after the usual residence and course of trials, he obtained the degree of M. D., and returned to England about the end of the year 1743. Here Dr. R. first settled and practised as a physician at Birmingham; where he afterwards established a laboratory,

for 10 years; but as these observations were made at 8 o'clock in the morning and 4 in the afternoon, and yours at 8 o'clock in the morning and 2 in the afternoon, the corresponding years of the morning's observations only admit of a comparison. It appears by your register, that the mean heat at London for 9 years, from the end of 1763 to the end of 1772, at 8 o'clock in the morning, was 47°.4; and the mean heat at Hawkhill, during the same period of time, was 40°. The difference of which is only 1°.4. A difference much less than might be expected from the difference of latitude, and not sufficient to account why nonpareils, golden rennets, peaches, nectarines, and many kinds of grapes, generally come to maturity near London, and scarcely ever near Edinburgh, without the aid of artificial heat. Before proceeding further to perplex myse f with this difficulty, I procured from Hawkhill and from yourself the register of the thermometer for 3 years, at the same periods of time. And by these it appears, that the mean heat of London of these 3 years exceeded that of Edinburgh, by 4.5. And the mean heat of the 3 hottest months in London exceeded the mean heat of the same 3 at Edinburgh, by 5°.8. And the mean heat of these 3 summer months, at 2 o'clock in the afternoon in London, exceeded the mean heat of the same months, at the same hour, in Edinburgh, by 70.3; which sufficiently accounts why some fruit may come to maturity in one country and not in the other: and also why corn and grass, which vegetate for the manufacture of certain useful preparations in chemistry. Extending his practice and projects in this line, he next established a manufactory of oil of vitriol at Prestonpans, in Scotland, in the year 1749; after which he made that country his chief residence. Dr. R.'s chemical practice leading him to experiments on smelting iron stone, and preparing that metal, which he did by means of pitcoal, he was thus gradually induced to establish, at Carron, the greatest manufactory of iron in this country. Thus, by the force of his own genius and great exertions, he established three very large and profitable manufactories, the laboratory at Birmingham, the oil of vitriol works at Prestonpans, and the iron works at Carron, all which are still carried on with great emolument to the several proprietors. Unfortunately however for Dr. R. he was induced successively to relinquish each of these concerns, to employ his capital on the next in succession, and finally to that of a large concern in coal-mines, in which his whole fortune was sunk and lost; to the grievous embitterment of the latter years of his life.

From a man so deeply and so constantly engaged in the detail of active business, many literary compositions were not to be expected. It has been happily said that Dr. R. left behind him many works, but few writings. The great object he kept constantly in view, was to promote arts and manufactures, rather than to establish theories or hypotheses. The above paper, on the comparison of the heat of London and Edinburgh; with another, in these Transactions, of experiments on ignited bodies; and one in the Edinburgh Transactions, on the filling and ripening of corn, are all his essays that have been published, besides two political pamphlets. The paper on ignited bodies was occasioned by a report of some experiments made by the celebrated Buffon, from which he had inferred that matter is heavier when hot than when cold. But Dr. R.'s experiments, made with great accuracy before a committee of the R. §. at London, seem to refute that notion.-See a pretty large and circumstantial account of Dr. R.'s concerns in the Supplement to the Encyclopædia Britannica, from which the above particulars are extracted.

with a more temperate heat, but require longer continuance of it, may arrive at
maturity in both countries. The reason why the mean heat of London exceeds
that of Edinburgh, may arise principally from the difference of latitude. But
the reason why the excess is greater in proportion in the 3 hottest months of the
year, at the hottest time of the day, than in the winter months, arises from
Edinburgh's being situated nearer to the sea than London. We might speak
with more precision on this subject, if we had a register of the thermometer at
Moscow, which is nearly in the same latitude as Edinburgh; though it is well
known that the heat of summer is much more intense, and the cold of winter
much more severe, at Moscow, than at Edinburgh. The mean heat of springs
near Edinburgh seems to be 47°; and at London 51°. It is probable, that the
mean heat of good springs in any country is very nearly the mean heat of the
country. A faithful account of the heat of springs in different latitudes, and of
water taken from the same depth of the sea in different latitudes is yet wanted..

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Exper. The sweating-room of our public hospital at Liverpool, says Dr. D.,
which is nearly a cube of 9 feet, lighted from the top, was heated till the.
quicksilver stood at 224° on Fahrenheit's scale; above which the tube of the
thermometer would not admit the heat to be raised. The thermometer was,
suspended by a string fixed to the wooden frame of the sky-light, and hung
down about the centre of the room. Myself and several others were at this
time inclosed in the stove, without experiencing any oppressive or painful sensation
of heat, proportioned to the degree pointed out by the thermometer. Every
metallic about us soon become very hot. 2. My friend Mr. Park, a surgeon,
went into the stove heated to 202°. After 10 minutes, I found the pulse
quickened to 120°. And to determine the increase of the animal heat, another s

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thermometer was handed to him, in which the quicksilver already stood at 98°; but it rose only to 994, whether the bulb of the thermometer was inclosed in the palms of the hands, or received into the mouth.* The natural state of this gentleman's pulse is about 65. 3. Another gentleman went through the same experiment in the same circumstances, and with the same effects. 4. One of the porters to the hospital, a healthy young man, and the pulse 75, was inclosed in the stove when the quicksilver stood at 210°; and he remained there, with little inconvenience, for 20 minutes. The pulse, now 164, and the animal heat, determined by another thermometer as in the former experiments, was 101. 5. A young gentleman of a delicate and irritable habit, whose natural pulse is about 80, remained in the stove 10 minutes when heated to 224°. The pulse rose to 145, and the animal heat to 102°. This gentleman, who had been frequently in the stove during the course of the day, found himself feeble, and disposed to break out into sweats for 24 hours after the experiment. 6. Two small tin vessels, containing each the white of an egg, were put into the stove heated to 224°. One of them was placed on a wooden seat near the wall, and the other suspended by a string about the middle of the stove. After 10 minutes, they began to coagulate; but the coagulation sensibly quicker and firmer in that which was suspended, than in that which was placed on the wooden seat. The progress of the coagulation was as follows: it was first formed on the sides, and gradually extended itself; the whole of the bottom was next coagulated; and last of all the middle part of the top. 7. Part of the shell of an egg was peeled away, leaving only the film which surrounds the white; and part of the white being drawn out, the film sunk so as to form a little cup. This cup was filled with some of the albumen ovi, which was consequently detached as much as possible from every thing but the contact of the air and of the film which formed the cup. The lower part of the egg stood on some light tow in a common gallipot, and was placed on the wooden seat in the stove. The quicksilver in the thermometer still continued at 224°. After remaining in the stove for an hour, the lower part of the egg, which was covered with the shell, was firmly coagulated; but that which was in the little cup was fluid and transparent. At the end of another hour it was still fluid, except on the edges where it was thinnest; and here it was still transparent; a sufficient proof that it was dried, not coagulated. 8. A piece of bees wax, placed in the same situation with the albumen ovi of the preceding experiment, and exposed to the same degree of heat in the stove, began to melt in 5 minutes: another piece suspended by a string, and a 3d piece put into the tin vessel and suspended, began likewise to liquify in 5 minutes.

* The scale of the thermometer, which was suspended by the string about the middle of the 100m, was of metal; this was the only one I could then procure, on which the degrees ran so high as to give any scope to the experiment. The scale of the other thermometer, which was employed for ascertaining the variations in the animal heat, was of ivory-Orig.

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Observations.-That heated air should have such a speedy and powerful effect in quickening the pulse, while the animal heat is little altered from its natural standard; that the human body should so easily bear to be surrounded with air heated to 224°; that the albumen ovi, which begins to coagulate in water at 150°, should remain fluid in 224°; and that the same albumen ovi, still placed in air heated to 224°, should coagulate if in-contact either with tin or its own shell, are facts as singular as they are difficult of explanation. From the different effects of heated air on the pulse and the heat of the body, do we not discover the fallacy of that theory of animal heat which has been adopted by Boerhaave and other celebrated physiologists? They suppose that animal heat is produced by the attrition of the globules of the circulating fluids against the sides of the containing vessels; but in several of the preceding experiments, the circulation was amazingly quickened with little increase of the animal heat. But whence is it that the human body can bear without immediate injury, to be surrounded 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 passes into some bodies becomes latent, agreeable to a doctrine which has for some time been taught at Edinburgh by Professor Black? Or does fire become fixed and quiescent, according to a similar system adopted by Dr. Franklin ?* Air we know: exists either in a fixed or elastic state; and fire may in like manner exist in bodies, either in a latent, fixed, and quiescent; or in a sensible, fluid, and active state. Agreeable to this idea, the bees wax receives the fire in an active state, and dissolves; while the human body and the albumen ovi, receiving the fire in a latent state, are little altered in their temperature. Let each of these however be put in contact with a different body, tin for instance; and though the heat of the air continues the same, yet the fire no longer enters in a latent. state, but with all its sensible and active powers; for the albumen ovi suspended in a tin vessel soon coagulates; and the human body, covered with the same metal, would quickly experience an intolerable and destructive degree of heat. Or are the above phenomena more satisfactorily explained, by considering different bodies as possessing different conducting powers; some being strong, others weak conductors of fire? All those 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 likewise the frog, the lizard, the camelion, &c. retain their natural temperature, and feel cold to the touch, though perpetually surrounded with air hotter than their own bodies. Hence also, the human body keeps nearly its own temperature, in a stove heated to