and the Mode of its Communication. 93 



minutes ; but in this experiment it took up only 

 38 J minutes in cooling through it, as we have just seen. 



Supposing now (what appears to me to be not im- 

 probable) 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 instru- 

 ment 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 

 instruments in cooling through the given interval = 

 10,000, as we have just seen that a quantity of heat 

 = 1396 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 38^ minutes, = 1081 ; by 

 No. 6, in 37 J minutes, = 1046 ; and, deducting these 

 quantities so lost (through the covered sides of the in- 

 struments) from the total quantity lost by each (= 

 10,000), we shall find out how much heat passed off 

 through the bottom of each of the instruments. 



For the instrument No. 5 it is . 10,000 1081 = 9919 

 And for " No. 6 . 10,000 1046 = 9954 



If now the whole of the heat lost through the bot- 

 tom of the instrument No. 5 passed off through the air 

 in rays, as there is no reason to suppose that a less 

 quantity passed off in the same time, in the same way, 

 through the bottom of the instrument No. 6, it ap- 

 pears 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 J minutes to 9919 as 37 J minutes to 



9597- 



