CHAPTER XVI. 

 RADIATION AND TEMPERATURE. 



Variation of Rate of Radiation with Temperature Newton's Law of Cooling 

 Dulong and Petit's Law- Rosetti's Law Stefan's Law Constants of Radia- 

 tion Radiation from Surfaces which Absorb Selectively Rate of Solar Radia- 

 tion Solar Constant Pouillet's Pyrheliometer Violle's Actinometer Lang- 

 ley's Researches Crova's Researches Effective Temperature of the Sun 

 Source of Solar Energy. 



Variation of Rate of Radiation with Temperature- When a 



body is in a constant temperature enclosure, at an excess e above the 

 temperature of the enclosure, it is radiating out at a rate depending on 



e e*e 



* Absolute Temperature 



FIG. 140a. 



its own temperature + e, but if its absorbing power is the same as when 

 it was at it is absorbing as much as it would radiate out at 6. For at 

 that temperature it would radiate out as much as it receives. Hence if 

 we represent its total radiation per second at any temperature t, by R, it 

 is losing energy by radiation at a rate 



If we could surround the body by an enclosure at the absolute zero 

 the enclosure would probably cease to radiate and we might put R, = 0. 

 The rate of cooling would then represent the total radiation per second 

 from the body at the temperature e. 



244 



