possible colours; and their action is limited to the sifting of that
total--the appropriating or absorbing of some of its constituents,
and the rejecting of others. It will fix this subject in your minds if
I say, that it is the portion of light which they reject, and not that
which they appropriate or absorb, that gives bodies their colours.

Let us begin our experimental inquiries here by asking, What is the
meaning of blackness? Pass a black ribbon through the colours of the
spectrum; it quenches all of them. The meaning of blackness is thus
revealed--it is the result of the absorption of all the constituents
of solar light. Pass a red ribbon through the spectrum. In the red
light the ribbon is a vivid red. Why? Because the light that enters
the ribbon is not quenched or absorbed, but in great part sent back to
the eye. Place the same ribbon in the green of the spectrum; it is
black as jet. It absorbs the green light, and renders the space on
which that light falls a space of intense darkness. Place a green
ribbon in the green of the spectrum. It shines vividly with its proper
colour; transfer it to the red, it is black as jet. Here it absorbs
all the light that falls upon it, and offers mere darkness to the eye.

Thus, when white light is employed, the red sifts it by quenching the
green, and the green sifts it by quenching the red, both exhibiting
the residual colour. The process through which natural bodies acquire
their colours is therefore a _negative_ one. The colours are produced
by subtraction, not by addition. This red glass is red because it
destroys all the more refrangible rays of the spectrum. This blue
liquid is blue because it destroys all the less refrangible rays. Both
together are opaque because the light transmitted by the one is
quenched by the other. In this way, by the union of two transparent
substances, we obtain a combination as dark as pitch to solar light.