RADIATION. 53 



fall afterwards upon a thermo-electric pile. Placing 

 in front of the orifice an opaque solution of iodine, 

 the platinum was gradually raised from a low dark 

 heat to the fullest incandescence, with the following 

 results: 



Appearance Energy of 

 of spiral obscure radiation 



Dark 1 



Dark, but hotter 3 



Dark, but still hotter 5 



Dark, but still hotter 10 



.Feeble red 19 



Dull red 25 



Red 37 



Full red 62 



Orange 89 



Bright orange 144 



Yellow 202 



White 276 



Intense white 440 



Thus the augmentation of the electric current, 

 which raises the wire from its primitive dark condition 

 to an intense white heat, exalts at the same time the 

 energy of the 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. Plac- 

 ing our linear thermo-electric pile in any part of the 

 ultra-red spectrum, it may be proved that a ray once 

 emitted continues to be emitted with increased energy 

 as the temperature is augmented. The platinum spiral, 

 so often referred to, being raised to whiteness by an 

 electric current, a brilliant spectrum was formed from 

 its light. A linear thermo-electric pile was placed in 

 the region of obscure rays beyond the red, and by di- 

 minishing the current the spiral was reduced to a low 

 temperature. It was then caused to pass through vari- 



