on tJie Subject of Heat. 



20 1 



always mixed the water with such a quantity of ice 

 that the temperature of this mixture remained con- 

 stant. 



Since in such experiments the thermometer bulb in 

 the middle of the glass globe was entirely surrounded 

 as well by the air contained in the globe as by the sub- 

 stances of which the covering consisted, I made a few 

 experiments to determine the time necessary for the 

 bulb of the thermometer to become cold again when the 

 globe contained nothing but air. I thus learned that 

 when the apparatus previously warmed in boiling water 

 was plunged into the mixture of cold water and pounded 

 ice, it required 576 seconds to cool from 70 to 10 

 Reaumur. 



The following table contains the results of several 

 experiments undertaken with a view to determine the 

 relative warmth of various substances such as are com- 

 monly used for clothing. 



I only remark, in addition, that I always determined 

 the amount of the substance by weight (16 grains stand- 

 ard weight), and endeavoured to distribute it as equally 

 as possible in the globe, and in such a manner that the 

 bulb of the thermometer was surrounded by it. 



