rse. Respecting the harmonies of sound I
must hereafter speak.

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) whe