in various Substances. 455 



In the last experiment (No. 30), the result of which 

 was so very extraordinary, the instrument was cooled to 

 o in thawing ice, after which it was plunged suddenly 

 into boiling water, where it remained till the inclosed 

 thermometer had acquired the Heat of 70, which took 

 up no less than 2459 seconds, or above 40 minutes ; 

 and it had remained in the boiling water full a minute 

 and a half before the mercury in the thermometer showed 

 the least sign of rising. Having at length been put in- 

 to motion, it rose very rapidly 40 or 50 degrees, after 

 which its motion gradually abating became so slow, that 

 it took up 1585 seconds, or something more than 26 

 minutes, in rising from 60 to 70, though the tempera- 

 ture of the medium in which it was placed during the 

 whole of this time was very nearly 80; the mercury in 

 the barometer standing but little short of 27 Paris 

 inches. 



All the different substances which I had yet made use 

 of in these experiments for surrounding or covering the 

 bulb of the thermometer, fluids excepted, had, in a 

 greater or in a less degree confined the Heat, or pre- 

 vented its passing into or out of the thermometer so 

 rapidly as it would have done, had there been nothing 

 but air in the glass globe, in the center of which the 

 bulb of the thermometer was suspended. But the great 

 question is, how, or in what manner, they produced this 

 effect ? 



And first, it was not in consequence of their own non- 

 conducting powers, simply considered ; for if, instead 

 of being only bad conductors of Heat, we suppose 

 them to have been totally impervious to Heat, their 

 volumes or solid contents were so exceedingly small in 

 proportion to the capacity of the globe in which they 



