45 6 ^f ^^^^ Propagation of Heat 



were placed, that, had they had no effect whatever upon 

 the air filling their interstices, that air would have been 

 sufficient to have conducted all the Heat communicated 

 in less time than was actually taken up in the experi- 

 ment. 



The diameter of the globe being 1.6 inches, its con- 

 tents amounted to 2.14466 cubic inches; and the con- 

 tents of the bulb of the thermometer being only 0.087 11 

 of a cubic inch (its diameter being 0.55 of an inch), the 

 space between the bulb of the thermometer and the in- 

 ternal surface of the globe amounted to 2.14466 — 

 0.08711 = 2.05755 cubic inches; the whole of which 

 space was occupied by the substances by which the bulb 

 of the thermometer was surrounded in the experiments 

 in question. 



But though these substances occupied this space, they 

 were far from filling it ; by much the greater part of it 

 being filled by the air which occupied the interstices of 

 the substances in question. In the experiment No. 4, 

 this space was occupied by 16 grains of raw silk; and 

 as the specific gravity of raw silk Is to that of water as 

 1734 to 1000, the volume of this silk was equal to the 

 volume of 9.4422 grains of water; and as i cubic inch 

 of water weighs 253.185 grains, its volume was equal to 

 2l^^if 5 0" ^^^ 0*037294 of a cubic inch ; and, as the 

 space it occupied amounted to 2.05755 cubic inches, it 

 appears that the silk filled no more than about -^\ part 

 of the space in which It was confined, the rest of that 

 space being filled with air. 



In the experiment No. i, when the space between the 

 bulb of the thermometer and the glass globe, in the 

 center of which it was confined, was filled with nothing 

 but air, the time taken up by the thermometer In cool- 



