BENJAMIN THOMPSON, COUNT RUMFORD 37 



occasion, as usual, to pay a few compliments to Divine Providence 

 for so arranging it that cold air shall contain less moisture than 

 warm. 



He exhausted the air from the space surrounding the ther- 

 mometer in one of these double-walled apparatus by fastening 

 the bulb on the upper end of a barometer tube, and discovered 

 that through such a Torricellian vacuum heat passes with greater 

 difficulty than through the air. It was by means of this double- 

 walled vacuum apparatus, silvered on the internal surfaces as 

 recommended by Rumford, to prevent the radiation of heat, that 

 Professor Dewar a hundred years later was enabled to experiment 

 with liquified air and hydrogen in the Royal Institution which 

 Rumford founded. Bottles, jacketed with a vacuum as Rumford 

 suggested, are now in use to provide automobilists with hot and 

 cold drinks. 



In the same way he tested the relative conductivity for heat of 

 a layer of fur, wool, silk, cotton, linen and many other substances, 

 and found that heat does not pass from particle to particle of the 

 air (conduction), but by currents (convection), and that such 

 fibrous bodies as cloth and fur are poor conductors of heat, be- 

 cause the air in their interstices is prevented from circulating. 

 Recent researches on adsorption have proved that he was right 

 in the importance he attached to the "cast" or layer of air which 

 is held so firmly to the surface of the fibers that it is very difficult 

 to remove. He applies the principle he had discovered in the 

 explanation of why bears and wolves have thicker fur on their 

 backs than on their bellies, and how the snow protects the ground. 



By exposing dry cloths, fur and down on china plates in a damp 

 cellar and then reweighing them, he determined the quality of 

 moisture they absorbed from the atmosphere, and, finding that 

 wool absorbed most, he determined to wear flannel next to the 

 skin in all seasons and climates; a deduction of doubtful validity. 



The important researches he conducted on convection owed 

 their origin to the fact that he was brought up in "the Great Pie 

 Belt." Like other New England boys he was much struck with 

 the length of time it took for an apple-pie to get cool enough to eat. 



