RADIATION. 53 



spiral and 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 follow- 

 ing results : 



Appearance Energy of 



of spiral obscure radiation 



Dark 1 



Dark, but hotter . 3 



Dark, but still hotter 

 Dark, but still hotter 

 Feeble red . 

 Dull red . 



5 

 10 

 19 

 25 



Bed 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. 

 Placing 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 

 diminishing the current the spiral was reduced to a low 

 temperature. It was then caused to pass through 



