44 



THE RADIATIONS OF IGNITED BODIES. [MEMOIR I. 



Table of the Intensity of Radiant Heat emitted by Platinum at Dif- 

 ferent Temperatures. 



lar deviations of the needle as expressing the force of 

 the thermo-electric current, or, in other words, as being 

 proportional to the temperatures. This hypothesis, it is 

 known, is admissible. 



It therefore appears that if the quantity of heat radi- 

 ated by platinum at 980 be taken as unity, it will have 

 increased at 1440 to 2.5, at 1900 to 7.8, and at 2360 

 to 17.8, nearly. The rate of increase is, therefore, very 

 rapid. Further, it may be remarked, as illustrative of 

 the same fact, that the quantity of heat radiated by a 

 mass of platinum in passing from 1000 to 1300 is near- 

 ly equal to the amount it gives out in passing from com- 

 mon temperatures up to 1000. 



I cannot here express myself with too much emphasis 

 on the remarkable analogy between light and heat which 

 these experiments reveal. The march of the phenomena 

 in all their leading points is the same in both cases. The 

 rapid increase of effect as the temperature rises is com- 

 mon to both. 



It is not to be forgotten, however, that in the case of 

 light we necessarily measure its effects by an apparatus 

 which possesses special peculiarities. The eye is insen- 



