43^ Q/ M ie Propagation 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 Quantities 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- 

 periments 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 



