RADIATION. 191 



raised to whiteness by an electric current, a brilliant spec- 

 trum 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 

 various degrees of darkness and incandescence, with the 

 following results : 



Appearance Energy of 



of spiral obscure rays. 



Dark 1 



Dark 6 



Faint red 10 



Dull red 13 



Red 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 one hundred and twenty-two times what it was at 

 first. To reach a white heat the wire has to pass through 

 all the stages of invisible radiation, and in its most brilliant 

 condition it embraces, in an intensified form, the rays of all 

 those stages. 



And thus it is with all other kinds of matter, as far as 

 they have hitherto been examined. Coke, whether brought 

 to a white heat by the electric current, or by the oxyhydro- 

 gen jet, pours out invisible rays with augmented energy, 

 as its light is increased. The same is true of lime, bricks, 

 and other substances. It is true of all metals which are 

 capable of being heated to incandescence. It also holds 

 good for phosphorus burning in oxygen. Every gush of 

 dazzling light has associated with it a gush of invisible ra- 



