414 



Of the Propagation of Heat 



It appears from these experiments that the conduct- 

 ing power of air to that of the Torricellian vacuum, 

 under the circumstances described, is as yf-- to loH* 

 inversely, or as 1000 to 702 nearly; for, the quantities 

 of Heat communicated being equal, the intensity of the 

 communication is as the times inversely. 



In these experiments the Heat passed through the 

 surrounding medium into the bulb of the thermometer : 

 in order to reverse the experiment, and make the Heat 

 pass out of the thermometer, I put the instruments into 

 boiling water, and let them remain therein till they had 

 acquired the temperature of the water, that is to say, till 

 the mercury in the inclosed thermometers stood at 80; 

 and then, taking them out of the boiling water, I plunged 

 them suddenly into a mixture of water and pounded ice, 

 and moving them about continually in this mixture, I 

 observed the times employed in cooling as follows : 



