lOi Count Rumford's Experiments. [Book II. 



contact of their parts * j hence the excefllve flownefs 

 with which heat is communicated to bodies of a rare 

 and fpcngy texture. Thus flannel, wool, and feathers, 

 are confidered as warm coverings, not becaufe they 

 pofiefs more heat in themfeJves (for they ferve to pre- 

 ferve any cold body in a cool ilate better than other 

 fubftances) but becaufe they prevent the efcape of the 

 animal heat from our bodies. It is a well-known 

 fact, that ice is generally kept in ice-houfcs in ftraw 

 or wool, thofe fubftances, from the rarity of their parts, 

 preventing the entrance of the matter of heat. On 

 the fame principle the ground is kept warm by fnow, 

 that fubftance being of a foft and fpongy texture. It 

 is true, it will not keep the ground warmer than the 

 -freezing point; but that is warm, when compared 

 with the intenfe cold which is occafionally experienced 

 in moft'northern climates. 



An ingenious and accurate experimentalifl has lately 

 endeavoured to eftimate the conducting power of dif- 

 ferent bodies. The conducting power of mercury he 

 found to be to that of water as i,coo to 313. Hence 

 it is plain why mercury appears fo much hotter or fo 

 much colder to the touch than water, at a time when 

 they are evidently of the fame temperature by the ther- 

 mometer. Common air is a much better conductor 

 than the Torricellian vacuum f ; its conducting power, 



* This is proved by an eafy experiment:- If a cube and a 

 fphere of the fame metal are put upon a plane intenfely healed, 

 the heat will flow fader into the^cube ; and if the fame bodies are 

 previoufly heated, and expofed on a cold plane, the cube will ccol 

 fooneit. 



f Made by filling a tube, clofed at the top, with mercury, and 

 emptying the upper part of the tube by immernng the lower in a 

 veflel filled with the fame fluid, as is the cafe in the common ba~ 

 rometers. This is the moil perfeft vacuum we can make. 



compared 



