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RADIATION. 1 9 I

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.
1
Dark ..................................... 6
Faintred ............. ' ................... 1 O
Dullred .................................. 13
18
Fullred ............................ . ...... 27
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-

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