46 Inquiry concerning the Nature of Heat, 



No. 2, when its sides were exposed naked to the air, 

 and when they were covered with the different sub- 

 stances which appeared to facilitate the escape of the 

 heat. 



In the experiment No. n, when the sides of the in- 

 strument were made quite black by holding it over the 

 flame of a wax candle, the instrument cooled through 

 the standard interval of 10 degrees in 36^ minutes. 



In that time a quantity of heat = 1942 parts must 

 have passed off through the covered ends and neck of 

 the instrument; for, if a quantity = 2985 parts could 

 pass off that way in 55-! minutes, the quantity above 

 mentioned (= 1942 parts) must have escaped in 36^ 

 minutes. 



This quantity, = !94 2 parts, taken from the whole 

 quantity, = 10,000 parts, lost by the instrument in 

 cooling through the interval in question, leaves 8058 

 parts for the quantity which made its escape through 

 the sides of the instrument in the experiment in 

 question. 



Now, if a quantity of heat = 7015 parts, requires 

 55^- minutes to make its way through the naked sides 

 of the instrument (as we have just seen), it would 

 require 63 f minutes for the quantity in question, = 

 8058 parts, to pass off through the same surface. 



But, when that surface was blackened over the flame 

 of a candle, that quantity of heat passed off through it 

 in 36^ minutes. 



Hence it appears, that the velocity with v/hich heat is 

 given off from the naked surface of a heated metal ex- 

 posed to cool in the air, is to the velocity with which it 

 is given off by the same metal when its surface is black- 

 ened in the manner above described, as 36^ to 63!, or 



