ON HEAT. 71 



with which ihe Oafs has honoured the three Memoirs I have 

 lately preferred, encourages me to communicate the conti- 

 nuation of my refearches. 



All philofophers are agreed in confidering glafs as one of Glafs is allowed 

 the worft conductors of heat which exifis; and when it i Cor ft conduct 

 propofed to confine the heat in a body of which the temitors. 

 perature has been railed, or to hinder its diffipafion as much 

 as poffible, care is taken to furround the heated body with 

 fubftances known to be bad conductors of ..heat. 



The refults of many of my experiments having led me to fuf- Bodies are not, 

 pea that the cooling' of bodies-, is not effected in the manner J robab ' y, « c . oole(i 



r ™ • by conducting 



which is generally fuppofed, I. made the following experi-off. 

 ment with the intention of clearing up this interefting part of 

 the fcience. .* 



I procured two bottles nearly cylindrical, of the fame formExp™™™* 1 

 and the fame dimenfions when meafured externally; one be- bottl^ahd a thin 

 ing of glafs and very thick, and the other of tin or tinned iron, one gf tin, 

 which was very thin. Each of them is three inches ten lines 

 in diameter very nearly, and five inches in height, and each 

 has a neck one inch three lines in diameter, and one inch two 

 lines in height. The glafs bottle weighs 13 ounces 1 gros 

 and J 8 grains poids de marc, and the other thin metallic vef- 

 fcl weighs only 5 ounces J gros and 65 grains. 



Having very exactly weighed the bottle of tinned iron, I were prepared, 

 found its exterior furface to be 54,462 inches, which give weighed, 

 0,21 142 of a line for the thicknefs of its fides, taking the fpe- 

 cific gravity of the metal at 7,8404. 



The mean thicknefs of Ihe tides of the glafs bottle is more and meafured. 

 than fix times as great, as may be ealily deduced from a calcu- 

 lation founded on the weight of the bottle, the quantity of its 

 furface, and the fpecific gravity of glafs. I 



Having filled thefe two bottles with boiling water, I hung They were filled, 

 them up by {lender firings in the midft of the tranquil air of a ™f ^^JS" 

 large chamber, at the height of five feet from the floor, and in the air. 

 at the diftance of four feet afunder. 



The temperature of the air of the chamber, which did not 

 vary a quarter of a degree during the whole time of the expe- 

 riment, was 9| degrees of Reaumur's fcale. 



An excellent mercurial thermometer, with a cylindrical 

 bulb, of four inches long and two lines and a half in diameter, 

 fufpended in the axjs of each of thefe bottles, indicated the 



temperature 



