in variotts Substances. 



445 



Without stopping at present to draw any particular 

 conclusions from the results of these experiments, I 

 shall proceed to give an account of some others, which 

 will afford us a little further insight into the nature of 

 some of the circumstances upon which the warmth of 

 covering depends. 



Finding, by the last experiments, that the density of 

 the covering added so considerably to the warmth of it, 

 its thickness remaining the same, I was now desirous 

 of discovering how far the internal structure of it con- 

 tributed to render it more or less pervious to Heat, its 

 thickness and quantity of matter remaining the same. 

 By internal structure, I mean the disposition of the 

 parts of the substance which forms the covering ; thus 

 they may be extremely divided, or very fine, as raw silk 

 as spun by the worms, and they may be equally dis- 

 tributed through the whole space they occupy ; or they 

 may be coarser, or in larger masses, with larger inter- 

 stices, as the ravelings of cloth, or cuttings of thread. 



If Heat passed through the substances made use of 

 for covering, and if the warmth of the covering de- 

 pended solely upon the difficulty which the Heat meets 



