on the Subject of Heat. 203 



texture, and may be equally distributed through the 

 whole space occupied by it, as raw silk, for example; 

 or it may be coarser and have larger interstices, as, 

 for example, a covering consisting of bits of stout 

 sewing-thread, or one consisting of ravellings of cloth. 



If heat really passed through the substances of which 

 the covering is made, and if the efficiency of such a 

 covering in restraining the same depended solely on the 

 greater or less difficulty which the heat meets in passing 

 through the solid parts of the covering, in that case 

 the warmth of a covering would be, c<eteris paribus, the 

 same as that of the raw materials employed in its con- 

 struction. It is evident, however, from the foregoing 

 experiments, as well as from those to be detailed here- 

 after, that heat is not propagated in any such manner. 



In one of my previous experiments I had endeav- 

 oured to determine the warmth of 16 grains of raw 

 silk, which I had distributed equally in a certain space 

 about the bulb of a thermometer. I now repeated this 

 experiment twice, but with this difference : the first 

 time I surrounded the bulb of the thermometer with 

 1 6 grains of a sort of lint made from a piece of 

 white taffety ; the second time with 16 grains of white 

 sewing-silk, cut into small pieces, two inches long. The 

 results of these experiments are recorded in the fol- 

 lowing table. My apparatus was warmed in boiling 

 water, and then cooled in a mixture of water and 

 pounded ice. 



