RADIATION 69 



obscure radiation, until at the end it is fully 440 times 

 what it was at the beginning. 



What has been here proved true of the totality of the 

 ultra-red rays is true for each of them singly. Placing 

 our linear thermo-electric pile in any part of the ultra-red 

 spectrum, it may be proved that a ray once emitted con- 

 tinues to be emitted with increased energy as the temper- 

 ature is augmented. The platinum spiral, so often referred 

 to, being raised to whiteness by an electric current, a bril- 

 liant spectrum was formed from its light. A linear thermo- 

 electric pile was placed in the region of obscure rays be- 

 yond the red, and by diminishing the current the spiral 

 was reduced to a low temperature. It was then caused to 

 pass through various degrees of darkness and incandes- 

 cence, with the following results: 



Appearance Energy of 



of spiral obscure rays 



Dark 1 



Dark •••..6 



Faint red 10 



DuUred 13 



Eed . . r 18 



Full red 27 



Orange ,, 60 



Yellow 93 



White 122 



Here, as in the former case, the dark and bright radia- 

 tions reached their maximum together; as the one aug- 

 mented, the other augmented, until at last the energy of 

 the obscure rays of the particular refrangibility here 

 chosen became 122 times what it was at first. To reach 

 a white heat the wire has to pass through all the stages 

 of invisible radiation, but in its most brilliant condition 



