. 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 of spiral Energy of 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. 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 various degrees of darkness and incandescence,
with the following results:

Appearance of spiral Energy of 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 radiations reached
their maximum together; as the one augmented, 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 h