and the Mode of its Communication. 139 
have been = a — x ; and that which passed off through the 
bottom of the other vessel, during the time of its cooling through 
the same interval, — a — y. 
But, as the velocities of the heat through the covered sides of 
both vessels must have been equal, the quantities of heat which 
passed off that way must have been as the times of cooling. 
The times of cooling in the last mentioned experiment, (No. 30,) 
were as follows : 
Min. Sec. Seconds. 
Of the vessel suspended over ice 33 15 = 1995 
Of the other vessel - - 39 30 — 2370 
x is therefore to y, as 1995 to 2370 ; 
consequently, x = = 0.841 jjy ; 
And, substituting for x, its value =±= 0.84177 y, 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: 
— 0.841 77^, for the vessel which was suspended over ice; and 
= a — y, for the other vessel. 
And, as y is greater than 0.841 jjy, consequently a~ 0.84177^7 
is greater than a — y, 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 pro- 
duced by the frigorific rays from the cold surface, in the expe- 
riments 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 tnuch the cooling was accelerated 
by the presence of the cold body, it is necessary to find out how 
much heat actually passed off through the bottoms of the two 
vessels, in the experiments in question. This we will endeavour 
T 2 
