44 Dr. Darwin’s frigorific Experiments 
the atmofphere, I have, at different times, endeavoured to fub- 
jecl it to experiment. 
i. When Dr. Hutton of Edinburgh, and Mr. Edge- 
worth of Edgeworthtown in Ireland, were with me about 
twelve or fourteen years ago, the following experiment, which 
had been propofed by one of the company, was carefully 
made, The blaft from an air-gun was repeatedly thrown on 
the bulb of a thermometer, and it uniformly funk it about two 
degrees. The thermometer was firmly fixed again ft a wall, 
and the air-gun, after being charged, w T as left for an hour in 
its vicinity, that it might previoufly lofe the heat acquired in 
the aft of charging ; the air was then difeharged in a conti- 
nued ftream on the bulb of the thermometer, and the event 
fhewed, that the air at the time of its expanfion attracted or 
abforbed heat from the mercury of the thermometer. 
In March 1785, by the afliftance of Mr. Fox and Mr. 
Strutt, of Derby, a thermometer was fixed in a wooden 
tube, and fo applied to the receiver of an air-gun, that, on dif- 
charging the air by means of a ferew prefling on the valve 
of the receiver, a continued ftream of air, at the very time of 
its expanfion, palled over the bulb of the thermometer. This 
experiment was four times repeated in the prefence of many 
obfervers, and uniformly funk the thermometer from five to 
feven degrees. During the time of condenfing the air into the 
receiver, there was a great difference in the heat, as perceived 
by the hand, at the two ends of the condenfing lyringe ; that 
next the air-globe was almoft painful to the touch ; and the 
globe itfelf became hotter than could have been expefled from 
its contact with the fvringe. Add to this, that in exploding t 
an air-gun, the ftream of air always becomes vifible, which is 
owing to the cold then produced precipitating the vapour it 
contained ; 
