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American Hand Book of the Daguerrotype by S. D. (Samuel Dwight) Humphrey
page 92 of 162 (56%)
Light--Optics--Solar Spectrum--Decomposition of Light--Light, Heat,
and Actinism--Blue Paper and Color for the Walls of the Operating Room--
Proportions of Light, Heat, and Actinism composing a Sunbeam--
Refraction--Reflection--Lenses--Copying Spherical Aberration--
Chromatic Aberration.

It is advisable that persons engaging in the Daguerreotype art should have
at least a little knowledge of the general principles of light and optics.
It is not the author's design here to give a full treatise on these subjects,
but he only briefly refers to the matter, giving a few facts.

It has been well observed by an able writer, that it is impossible to trace
the path of a sunbeam through our atmosphere without feeling a desire
to know its nature, by what power it traverses the immensity of space,
and the various modifications it undergoes at the surfaces and interior
of terrestrial substances.

Light is white and colorless, as long as it does not come
in contact with matter. When in apposition with any body,
it suffers variable degrees of decomposition, resulting in color,
as by reflection, dispersion, refraction, and unequal absorption.

To Sir I. Newton the world is indebted for proving the compound
nature of a ray of white light emitted from the sun.
The object of this work is not to engage in an extended theory
upon the subject of light, but to recur only to some points
of more particular interest to the photographic operator.

The decomposition of a beam of light can be noticed by exposing
it to a prism. If, in a dark room, a beam of light be admitted
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