VOL. LXXI.J PHILOSOPHICAL TRANSACTIONS. 1^9 



mates, the laws which nature observes in the heating and cooling of bodies, the 

 melting, the vaporific, and shining points, and the degrees of heat in the 

 animal, the mineral, and the vegetable kingdoms, were accurately determined. 

 In consequence of the attention that was paid to this subject, many curious 

 questions arose, which have long exercised the ingenuity of philosophers. That 

 property of heat by which it is capable of expanding the densest and hardest 

 bodies ; its power in producing fluidity ; its tendency to an equilibrium ; and the 

 causes of its various distribution throughout the different substances in nature, 

 have become the objects of philosophical inquiry. It was observed, that some 

 bodies on exposure to heat, become red and luminous, but are incapable of pro- 

 ducing flame, or of maintaining fire : that, on the contrary, others, by the ap- 

 lication of fire, and the contact of fresh air, kindle into flame, and continue to 

 emit light and heat, apparently from a source within themselves, till they are 

 consumed. Hence arose the questions concerning the pabulum of fire, the use 

 of the air in inflammation, and the distinction of bodies into combustible and 

 incombustible. 



From the first dawnings of philosophy it must have been perceived, that most 

 animals have a higher temperature than the medium in which they live ; and that 

 a constant succession of fresh air is necessary to the support of animal life. The 

 causes of these phenomena have afforded matter for much speculation in ancient 

 as well as modern times : but the discovery that animals have, in certain circum- 

 stances, the power of keeping themselves at a lower temperature than the sur- 

 rounding medium, was reserved for the industry of the present age. This dis- 

 covery seems originally to have arisen from observations on the heat of the 

 human body in warm climates. It was mentioned by governor Ellis in 1758; 

 it was taught by Dr. Cullen before the year 17(35 ; and at length it was com- 

 pletely established by the experiments of Dr. Fordyce in heated rooms, which 

 were laid before the Society in 1774. 



In the course of these experiments the doctor remained in a moist air heated 

 to 130° for the space of 15 minutes, during which time the thermometer under 

 his tongue stood at 100°, his pulse made 139 beats in a minute, his respiration 

 was but little affected, and streams of water ran down over his whole body, pro- 

 ceeding from the condensation of vapour, as evidently appeared from a similar 

 condensation on the side of a Florentine flask that had been filled with water at 

 100°. He found however, that he could bear a much greater degree of heat 

 when the air was dry. In this situation, he frequently supported, naked, for a 

 considerable time, without much inconvenience, the heat of 260°, his body pre- 

 serving very nearly its proper temperature, being never raised more than 2° 

 above the natural standard. 



Various opinions have been entertained with regard to the causes of the facts 



