202 Historical Review of Experiments 



In order to determine what influence the density of 

 a covering or clothing of a given thickness exerted on 

 the warmth of this covering or on its power to confine 

 heat, I made three consecutive experiments with differ- 

 ent quantities of one and the same substance, namely, 

 with eider-down. For the first experiment I took 16 

 grains of this substance, for the second 32 grains, and 

 for the third 64 grains. In all cases I used the same 

 apparatus, so that the thickness of the covering always 

 remained the same. 



The results of these three experiments are contained 

 in the following table. 



Having convinced myself by these experiments that 

 the density of any covering or clothing exercises a very 

 considerable influence on its power to confine heat, 

 its thickness remaining the same, I now sought to dis- 

 cover what effect the internal structure or constitution 

 of the covering has on this power, its mean density and 

 its thickness remaining the same. 



By the expression internal structure I mean the state 

 of division, whether fine or coarse, of the substance of 

 which the covering consists, in the space which it occu- 

 pies. This substance may be very fine and of delicate 



