MEMOIH I.] THE RADIATIONS OF IGNITED BODIES. 



41 



Table of the Intensity of Light emitted by Platinum at Different 



Temperatures. 



the Argand lamp at the moment of the extinction of the 

 shadow. 



In this table the first column gives the temperatures 

 under examination in Fahrenheit degrees; the second 

 and third the distances of the Argand lamp from the 

 screen in English inches, in two different sets of experi- 

 ments; the fourth the mean of the two; and the fifth 

 the corresponding intensity of the light. 



The results thus obtained proved that the increase in 

 the intensity of the light of the ignited platinum, though 

 slow at first, became very rapid as the temperature rose. 

 At 2590 the brilliancy of the light was more than 

 thirty-six times as great as it was at 1900. 



Thus, therefore, the theoretical anticipation founded 

 on the analogy of light and heat was completely veri- 

 fied, the emission of light by a self-luminous solid as its 

 temperature rises being in greater proportion than would 

 correspond to mere difference of temperature. 



To place this in a more striking point of view, I made 

 some corresponding experiments in relation to the heat 

 emitted. No one thus far had published results for high 

 temperatures, or had endeavored to establish through an 

 extensive scale the principle of Delaroche, that " the 

 quantity of heat which a hot body gives off in a given 

 time, by way of radiation to a cold body situated at a 



