our Daguerreotype operators in their operating rooms and skylights,
in order to facilitate the operation in the camera. I fancy, however,
that this plan cannot be productive of as much good as thought by some,
from the fact, that the light falling upon the subject, and then reflected
into the camera, is, coming through colorless glass, not affected
by such rays as may be reflected from the walls of the operating room;
and even if it were so, I conceive that it would be injurious,
by destroying the harmony of shadows which might otherwise occur.)
The greatest amount of white light is at C; the yellow contains less
of the chemical power than any other portion of the solar spectrum.
It has been found that the most intense heat is at the extreme red, b.

Artificial lights differ in their color; the white light
of burning charcoal, which is the principal light from candles,
oil and gas, contains three rays--red, yellow, and blue.
The dazzling light emitted from lime intensely heated,
known as the Drummond light, gives the colors of the prism
almost as bright as the solar spectrum.

If we expose a prepared Daguerreotype plate or sensitive paper
to the solar spectrum, it will be observed that the luminous power
(the yellow) occupies but a small space compared with the influence
of heat and chemical power. R. Hunt, in his Researches on Light,
has presented the following remarks upon the accompanying illustration:

"If the linear measure, or the diameter of a circle which shall
include the luminous rays,

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