There is a fourth class of sensible things, having many intricate
varieties, which must now be distinguished. They are called by
the general name of colours, and are a flame which emanates from
every sort of body, and has particles corresponding to the sense
of sight. I have spoken already, in what has preceded, of the
causes which generate sight, and in this place it will be natural
and suitable to give a rational theory of colours.
Of the particles coming from other bodies which fall upon the
sight, some are smaller and some are larger, and some are equal
to the parts of the sight itself. Those which are equal are
imperceptible, and we call them transparent. The larger produce
contraction, the smaller dilation, in the sight, exercising a
power akin to that of hot and cold bodies on the flesh, or of
astringent bodies on the tongue, or of those heating bodies which
we termed pungent. White and black are similar effects of
contraction and dilation in another sphere, and for this reason
have a different appearance. Wherefore, we ought to term white
that which dilates the visual ray, and the opposite of this is
black. There is also a swifter motion of a different sort of fire
which strikes and dilates the ray of sight until it reaches the
eyes, forcing a way through their passages and melting them, and
eliciting from them a union of fire and water which we call
tears, being itself an opposite fire which comes to them from an
opposite direction—the inner fire flashes forth like lightning,
and the outer finds a way in and is extinguished in the moisture,
and all sorts of colours are generated by the mixture. This
affection is termed dazzling, and the object which produces it is
called bright and flashing. There is another sort of fire which
is intermediate, and which reaches and mingles with the moisture
of the eye without flashing; and in this, the fire mingling with
the ray of the moisture, produces a colour like blood, to which
we give the name of red. A bright hue mingled with red and white
gives the colour called auburn (Greek). The law of proportion,
however, according to which the several colours are formed, even
if a man knew he would be foolish in telling, for he could not
give any necessary reason, nor indeed any tolerable or probable
explanation of them. Again, red, when mingled with black and
white, becomes purple, but it becomes umber (Greek) when the
colours are burnt as well as mingled and the black is more
thoroughly mixed with them. Flame-colour (Greek) is produced by a
union of auburn and dun (Greek), and dun by an admixture of black
and white; pale yellow (Greek), by an admixture of white and
auburn. White and bright meeting, and falling upon a full black,