other liquid, finally, is purple because it destroys the green
and the yellow, and allows the terminal colours of the spectrum to
pass unimpeded. From the blending of the blue and the red this
gorgeous purple is produced.

One step further for the sake of exactness. The light which falls upon
a body is divided into two portions, one of which is reflected from
the surface of the body; and this is of the same colour as the
incident light. If the incident light be white, the superficially
reflected light will also be white. Solar light, for example,
reflected from the surface of even a black body, is white. The
blackest camphine smoke in a dark room, through which a sunbeam passes
from an aperture in the window-shutter, renders the track of the beam
white, by the light scattered from the surfaces of the soot particles.
The moon appears to us as if

'Clothed in white samite, mystic, wonderful;'

but were it covered with the blackest velvet it would still hang as a
white orb in the heavens, shining upon our world substantially as it
does now.

Sec. 8. _Colours of Pigments as distinguished from Colours of Light_.

The second portion of the incident light enters the body, and upon its
treatment there the colour of the body depends. And here a moment may
properly be given to the analysis of the action of pigments upon
light. They are composed of fine particles mixed with a vehicle; but
how intimately soever the particles may be blended, they still remain
particles, separated, it may be, by exceedingly minute distances, but
still separated. To use the scientific phrase, they are not optically
continuous. Now, wherever optical continuity is ruptured we have
reflection of the incident light. It is the multitude of reflections
at the limiting surfaces of the particles that prevents light from
passing through snow, powdered glass, or common salt. The light here
is exhausted in echoes, not extinguished by true absorption. It is the
same kind of reflection that renders the thunder-cloud so impervious
to light. Such a cloud is composed of particles of water, mixed with
particles of air, both separately transparent, but practically opaque
when thus mixed together.

In the case of pigments, then, the light is _reflected_ at the
limiting surfaces of the particles, but it is in part _absorbed_
within the particles. The reflection is necessary to send the light
back to the eye; the absorption is necessary to give the body its