112 PHILOSOPHICAL TRANSACTIONS. [aNNO 1 786. 



that is, till they had acquired exactly the temperature of freezing water or melt- 

 ing ice ; and then taking them out of the ice I plunged them suddenly into a 

 large vessel of boiling water, and observed the time required for the mercury to 

 rise in the thermometers from J0° to 10°, from 0° to 80°, taking care to keep the 

 water constantly boiling during the whole of this time, and taking care also to 

 keep the instruments immersed to the same depth, that is, just so deep that the 

 point 0° of the inclosed thermometer was even with the surface of the water. 

 These experiments were repeated twice, with the utmost care ; and the following 

 table gives the result of them. 



It appears from these experiments, that the conducting power of air to that 

 of the Torricellian vacuum, under the circumstances described, is as 7-§-^ to 



4.8^ 



10-^^ inversely, or as 1000 to 702 nearly ; for the quantities of heat communi- 

 cated 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, .1 put the instruments into boiling water, and 

 let them remain there till they had acquired the temperature of the water, that 

 is, till the mercury in the inclosed thermometers stood at SO'' ; 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. 



