and the Mode of its Communication. 87 



Min. Sec. Seconds. 



Of the vessel suspended over ice, . . 33 15=1995 

 Of the other vessel, . . . . 3930=2370 



x is therefore tojy, as 1995 to 2370; consequently, 



x = '-Sr = 0.841 77 y; 



And, substituting for x its value = 0.84177^, the 

 quantities of heat which passed off through the bottoms 

 of the two vessels, in the experiment in question (No. 

 30), must have been = a 0.84177 y for the vessel 

 which was suspended over ice, and = a y fort he 

 other vessel. 



And, asjy is greater than 0.84177 jy, consequently^ 

 0.84177 y is greater than a jy, or the quantity of heat 

 which passed off through the bottom of the vessel which 

 was cooled the most rapidly was greater than that 

 which passed off through the bottom of the other vessel ; 

 and hence we perceive that the effect produced by the 

 frigorific rays from the cold surface, in the experiments 

 in question, was greater than it appeared to be at first 

 sight, when it was estimated by the times of cooling. 



To determine exactly how much the cooling was ac- 

 celerated by the presence of the cold body, it is neces- 

 sary to find out how much heat actually passed off 

 through the bottoms of the two vessels, in the experi- 

 ments in question. This we will endeavour to do by 

 comparing the results of those experiments with the re- 

 sults of some other experiments of a similar nature. 



In the experiment No. 28, a cylindrical vessel of thin 

 sheet brass, 4 inches in diameter, and 4 inches in height, 

 covered with gold-beater's skin painted black with In- 

 dian ink, being filled with hot water and exposed to 

 cool in the air of a large quiet room, cooled from the 

 point of 50 degrees to that of 40 degrees above the 

 temperature of the air of the room in 23 \ minutes. 



