43^ Of the Pi^opagation of Heat 



In the further prosecution of these inquiries, I do 

 not mean to confine myself solely to the determining of 

 the conducting powers of Fluids ; on the contrary, 

 solids, and particularly such bodies as are made use of 

 for cloathing, will be principal subjects of my future ex- 

 periments. I have indeed already begun these researches, 

 and have made some progress in them ; but I forbear to 

 anticipate a matter which will be the subject of a future 

 communication. 



CHAPTER II. 



The relative Warmth of various Substances used in making 

 artificial Cloathing^ determined by Experiment. — Relative 

 Warmth of Coverings of the same Thickness^ and formed 

 of the same Substance^ but of different Densities. — Rela- 

 tive Warmth of Coverings formed of equal ^antities of 

 the same Substance^ disposed in different Ways. — Experi- 

 ments made with a View to determining how far the Power 

 which certain Bodies possess of confining Heat depends on 

 their chymical Properties. — Experiments with Charcoal 

 — with Lampblack — with Wood-ashes — Striking Ex- 

 perir/ients with Semen Lycopodii. — All these Experi- 

 ments indicate that the Air which occupies the Interstices 

 of Substances used in forming Coverings for confining Heat, 

 acts a very important Part in that Operation. — Those 

 Substances appear to prevent the Air from conducting the 

 Heat. — An Inquiry concerning the Manner in which this 

 is effected. — This Inquiry leads to a decisive Experiment 

 from the Result of which it appears that Air is a perfect 

 Non-conductor of Heat. — This Discovery affords the 



