OF THE PROPAGATION OF HEAT IN 

 VARIOUS SUBSTANCES. 



CHAPTER I. 



An Account of the' Instruments that were prepared for mak- 

 ing the proposed Experiments. — A Thermometer is con- 

 structed whose Bulb is surrounded by a Torricellian 

 Vacuum. — Heat is found to pass in a Torricellian Vac- 

 uum with greater Difficulty than in Air. — Relative con- 

 ducting Powers of a Torricellian Vacuum and of Air with 

 regard to Heat determined by Experiment. — Relative con- 

 ducting Powers of dry Air and of moist Air. — Relative 

 conducting Powers of Air of different Degrees of Density. 

 — Relative conducting Powers of Mercury ; Water ; 

 Air ; and a Torricellian Vacuum. 



EXAMINING the conducting power of air, and of 

 various other fluid and solid bodies, with regard to 

 Heat, I was led to examine the conducting power of the 

 Torricellian vacuum. From the striking analogy between 

 the electric fluid and Heat respecting their conductors 

 and non-conductors (having found that bodies, in 

 general, which are conductors of the electric fluid, are 

 likewise good conductors of Heat, and, on the contrary, 

 that electric bodies, or such as are bad conductors of the 

 electric fluid, are likewise bad conductors of Heat), I 

 was led to imagine that the Torricellian vacuum, which 



