to be regarded as primitives--and from their interblending, seven,
as recorded by Newton, and shown in the accompanying wood cut.
These rays being absorbed, or reflected differently by various bodies,
give to nature the charm of color. Thus to the eve is given the pleasure
we derive in looking upon the green fields and forests, the enumerable
varieties of flowers, the glowing ruby, jasper, topaz, amethist, and emerald,
the brilliant diamond, and all the rich and varied hues of nature,
both animate and inanimate.
[hipho_3.gif]

Now, if we allow this prismatic spectrum (b. fig. 3.) to fall upon
any surface (as at c.) prepared with a sensitive photographic compound,
we shall find that the chemical effect produced bears no relation
to the intensity of the light of any particular colored ray,
but that, on the contrary, it is dispersed over the largest portion
of the spectrum, being most energetic in the least luminous rays,
and ever active over an extensive space, where no traces of light
can be detected. Fig. 4, will give the student a better idea
of this principle. It is a copy of the kind of impression
which the spectrum, spoken of, would make on a piece of paper
covered with a very sensitive photographic preparation.
The white space a. corresponds with the most luminous, or yellow ray,
(5, fig. 3) over limits of which all chemical change is prevented.
A similar action is also produced by the lower end of the red ray c;
but in the upper portion, however we find a decided change
(as at d). The most active chemical change, you will percieve,
is produced by the rays above the yellow a; viz. 4, 3, 2 and 1
(as at b) the green (4) being the least active, and the blue
(3) and violet (1) rays the most so, the action still continuing
far beyond the point b which is the end of the luminous image.