52 Of the Management of Fire 



heat. All kinds of air, artificial as well as natural, and 

 in general all elastic fluids, steam not excepted, seem to 

 possess this property in as high a degree of perfection 

 as atmospheric air. 



That steam is not a conductor of heat I proved by 

 the following experiment : A large globular bottle being 

 provided, of very thin and very transparent glass, with a 

 narrow neck, and its bottom drawn inward so as to form 

 a hollow hemisphere about 6 inches in diameter ; this 

 bottle, which was about 8 inches in diameter externally, 

 being filled with cold water, was placed in a shallow dish, 

 or rather plate, about 10 inches in diameter, with a flat 

 bottom formed of very thin sheet brass, and raised upon 

 a tripod, and which contained a small quantity (about 

 & of an inch in dep'th) of water ; a spirit-lamp being 

 then placed under the middle of this plate, in a very few 

 minutes the water in the plate began to boil, and the 

 hollow formed by the bottom of the bottle was filled 

 with clouds of steam, which, after circulating in it with 

 surprising rapidity 4 or 5 minutes, and after forcing out 

 a good deal of air from under the bottle, began gradually 

 to clear up. At the end of 8 or 10 minutes (when, as I 

 supposed, the air remaining with the steam in the hol- 

 low cavity formed by the bottom of the bottle had ac- 

 quired nearly the same temperature as that of the steam) 

 these clouds totally disappeared ; and though the water 

 continued to boil with the utmost violence, the contents 

 of this hollow cavity became so perfectly invisible, and 

 so little appearance was there of steam, that had it not 

 been for the streams of water which were continually 

 running down its sides I should almost have been 

 tempted to doubt whether any steam was actually gen- 

 erated. 



