y, like the facility or
even pleasure with which we act with contrary muscles in yawning or
stretching after having been fatigued with a long previous exertion in
the contrary direction.

Hence where colours are required to be distinct, those which are
opposite to each other, should be brought into succession or vicinity;
as red and green, orange and blue, yellow and violet; but where
colours are required to intermix imperceptibly, or slide into each
other, these should not be chosen; as they might by contrast appear
too glaring or tawdry. These gradations and contrasts of colours have
been practically employed both by the painters of landscape, and by
the planters of ornamental gardens; though the theory of this part of
the pleasure derived from visible objects was not explained before the
publication of the paper on ocular spectra above mentioned; which is
reprinted at the end of the first part of Zoonomia, and has thrown
great light on the actions of the nerves of sense in consequence of
the stimulus of external bodies.

IV. _Association of agreeable sentiments with visible objects._

Besides the pleasure experienced simply by the perception of visible
objects, it has been already shown, that there is an additional
pleasure arising from the inspection of those, which possess novelty,
or some degree of it; a second additional pleasure from those, which
possess in some degree a repetition of their parts; and a third from
those, which possess a succession of particular colours, which either
contrast or slide into each other, and which we have termed melody of
colours.

We now step forward to the fourth source of the pleasures arising from
the contemplation of visible objects besides that simply of
perception, which consists in our previous association of some
agreeable sentiment with certain forms or combinations of them. These
four kinds of pleasure singly or in combination constitute what is
generally understood by the word Taste in respect to the visible
world; and by parity of reasoning it is probable, that the pleasurable
ideas received by the other senses, or which are associated with
language, may be traced to similar sources.

It has been shown by Bishop Berkeley in his ingenious essay on vision,
that the eye only acquaints us with the perception of light and
colours; and that our idea of the solidity of the bodies, which
reflect them, is learnt by the organ of touch: he therefore calls our
vision the l