72 ON HEAT. 



temperature of the contained water; and the time employed 

 in its cooling for every five degrees of Fahrenheit's thermo- 

 meter, was carefully obferved during eight hours. 



The glafs being confidered as a very bad conductor of heat, 



and the tides of the bottle being fo thick, who would not have 



expected that the water in this bottle would have been more 



ilowly cooled than that in the very thin bottle of tin. 



The glafs bottle The contrary however was the event ; the bottle of glafs 



quick aTtW vvas cooIed almoft twice as quickly as that of tin. 

 tin. While the water included in the bottle of tinned iron em- 



ployed 56 minutes to pafs through a certain interval of cooling, 

 namely through ten degrees, between the 50th and 40th de- 

 gree of the thermometer of Fahrenheit above the temperature 

 of the air of the chamber, the water in the glafs bottle em- 

 ployed only 30 minutes for the fame change. 

 Inference. It appears to me, that the refult of this experiment throws 



great light on the myfterious operation of the communication 

 of' heat. 

 Heat is not If we admit the hypothecs that hot bodies are cooled, not 



material fub- ^y lofing or acquiring fome material fubftance, but by the 

 itance. action of colder furrounding bodies, communicated by undu- 



lations or radiations excited in an etherial fluid, the refults of 

 this experiment may be- eaiily explained ; but if this hypo- 

 thecs be not adopted, I cannot explain them. 

 Bodies are not it might perhaps be fufpected that the air attached by a 

 furrounding air. G erta ' n attraction, but with unequal forces, to the furfaces of 

 the two bottles, might have been the caufe of this remarkable 

 difference in the time of their cooling ; but thofe who will take 

 the trouble to reflect attentively on the refults of the experi- 

 ments I have defcribed in a preceding memoir, which were 

 made with a view to clear up this point, with a metallic veilel 

 firfl naked, and afterwards with one, two, four and five coat- 

 ings of varnith, will be perfuaded that this caufe is not fuffi- 

 cient to explain the facts. 

 AH metallic vef- By a courfe of experiments made at Munich lafl year, of 

 famedi'fpofiUon which the. details are given in a Memoir fent to the Royal 

 to cool. Society of London *, I have found that a given quantity of 



hot water included in a metallic veflel of a given form and 

 capacity, always cools with the fame quicknefs in the air, 



* See our Journal, Vol. IX. p. 194. 



whatever 



