VOL. LXXVIII.] PHILOSOPHICAL TRANSACTIONS. 373 



would attract or absorb heat from the bodies in their vicinity ; and that when 

 they were mechanically condensed, the fluid matter of heat would be pressed 

 out of them, and diffused among the adjacent bodies. As this principle might 

 possibly be extended to elastic solid bodies, as well as to fluid ones, and explain 

 the cause of the heat occasioned by percussion or friction, and by some chemi- 

 cal combinations, as well as the perpetual mutability of it in the atmosphere, I 

 have, at different times, endeavoured to subject it to experiment. 



1 . When Dr. Hutton of Edinburgh, and Mr. Edgeworth of Edgeworthtown 

 in Ireland, were with me about 12 or 14 years ago, the following experiment, 

 which had been proposed by one of the company, was carefully made. The 

 blast from an air-gun was repeatedly thrown on the bulb of a thermometer, and 

 it uniformly sunk it about '1 degrees. The thermometer was firmly fixed against 

 a wall, and the air-gun, after being charged, was left for an hour in its vicinity, 

 that it might previously lose the heat acquired in the act of charging ; the air 

 was then discharged in a continued stream on the bulb of the thermometer, and 

 the event showed, that the air at the time of its expansion attracted or absorbed 

 heat from the mercury of the thermometer. 



In March 1785, by the assistance of Mr. Fox and Mr. Strutt, of Derby, a 

 thermometer was fixed in a wooden tube, and so applied to the receiver of an 

 air-gun, that on discharging the air by means of a screw pressing on the valve 

 of the receiver, a continued stream of air, at the very time of its expansion, 

 passed over the bulb of the thermometer. This experiment was 4 times re- 

 peated in the presence of many observers, and uniformly sunk the thermometer 

 from 5 to 7 degrees. During the time of condensing the air into the receiver, 

 there was a great difference in the heat, as perceived by the hand, at the two 

 ends of the condensing syringe ; that next the air-globe was almost painful to 

 the touch ; and the globe itself became hotter than could have been expected 

 from its contact with the syringe. Add to this, that in exploding an air-gun, 

 the stream of air always becomes visible, which is owing to the cold then pro- 

 duced precipitating the vapour it contained ; and if this stream of air had pre- 

 viously been more condensed, or in greater quantity, so as not instantly to ac- 

 quire heat from the common atmosphere in its vicinity, it would probably have 

 fallen in snow, as in the fountain of Hiero, mentioned below. 



1. About 12 or 14 years ago, by the assistance of Mr. Waltire, a celebrated 

 itinerant teacher of philosophy, a thermometer was placed in the receiver of an 

 air-pump, and some time being allowed, that it might accurately adapt itself to 

 the heat of the receiver, the air was hastily exhausted ; during which the mer- 

 cury of the thermometer sunk 2 or 3 degrees, and after some minutes regained 

 its previous height. In November 17c>7> by the assistance of my very ingenious 

 friend Mr. Forester French, the above experiment was repeated ; but with this 



