and the Mode of its Communication. 345 
In one of the preceding experiments, it cooled through the 
given interval in 39^ minutes, and in the other in 39^ minutes ; 
but, in this experiment, it took up only 38! minutes, in cooling 
through it, as we have just seen. 
Supposing now, (what appears to me to be not improbable,) 
that all, or very nearly all, the heat lost by the instrument No. 5 
passed off in rays through the air, we can ascertain what part of 
the heat lost by the instrument No. 6, was communicated to the 
air which came into contact with its surface. 
Putting the total quantity of heat lost by each of the instru- 
ments, in cooling through the given interval, = 10000; as we 
have just seen that a quantity of heat = 13 96, passes through the 
covered sides of each of these instruments in 39^ minutes, the 
quantities so lost in this experiment must have been as follows. 
By the instrument No. 5, in 384- minutes, = 1081 ; by No. 6, in 
37|- minutes, = 1046 ; and, deducting these quantities so lost 
(through the covered sides of the instruments) from the total 
quantity lost by each, (= 10000,) we shall find out how much 
heat passed off through the bottom of each of the instruments. 
For the instrument No. 5, it is 10000 — 1.081 = 9199, 
And for - - No. 6, 10000 — 1.046 == 9954. 
If now the whole of the heat lost through the bottom of the in- 
strument No. 5, passed off through the air in rays, as there is no 
reason to suppose that a less quantity passed offin the same time, 
in the same way, through the bottom of the instrument No. 6, it 
appears, that this last mentioned instrument must* have lost, by 
radiation, or in rays which passed through the air, a quantity of 
heat = 9597. 
For it is 38^ minutes to 9919, as 37 J minutes to 9597. 
MDCCCIV.* U 
