either be impossible for it
_afterwards_ to induce us to associate them with the presence of
tangible bodies distant and different from the eye: or, (_secondly_),
such an association would merely give birth to the abstract knowledge or
conclusion, that these bodies were in one place, while the sensations
suggesting them were felt to be associated with something in another
place; colour would not be seen--as it is--incarnated with body: or,
(_thirdly_), we should be compelled to postulate for the eye, as many
philosophers have done, in our opinion, most unwarrantably, "a faculty
of projection"[37] by which it might dissolve the association between
itself and its sensations, throwing off the latter in the form of
colours over the surface of things, and reversing the old Epicurean
doctrine that perception is kept up by the transit to the sensorium of
the ghosts or _simulacra_ of things,

Quae, quasi membranae, summo de corpore rerum,
Direptae, volitant ultro citroque per auras.[38]

It is difficult to say whether the hypothesis of "cast-off films" is
more absurd when we make the films come from things to us as spectral
effluxes, or go from us to them in the semblance of colours.

[37] We observe that even Mueller speaks of the "faculty of
projection" as if he sanctioned and adopted the hypothesis.--See
_Physiology_, vol. ii. p. 1167.

[38] Lucretius.

But according to the present view no such incomprehensible faculty, no
such crude and untenable hypothesis, is required. _Before_ the touch has
informed us that we have an eye, _before_ it has led us to associate any
thing visual with the eye, it has _already_ taught us to associate in
place the sensations of vision (colours) with the presence of tangible
objects which are not the eye. Therefore, when the touch discovers the
eye, and induces us to associate vision in some way with it, it cannot
be the particular sensations of vision called colours which it leads us
to associate with that organ; for these have been already associated
with something very different. If it be not colours, then what is it
that the touch compels us to associate with the eye? We answer that it
is the abstract _condition_ of impressions as the general law on which
all seeing depends, but as quite distinct from the particular visual
sensations apprehended in virtue of the observance of that law.

Nor is it at all difficult to understand how this general condition
comes t