But because I have not yet acquired sufficient knowledge of all
the matters of which I should desire to treat in these two last
parts, and do not know whether I shall ever have sufficient leisure
to finish them, I will here subjoin a few things regarding the
objects of our senses, that I may not, for the sake of the latter,
delay too long the publication of the former parts, or of what may
be desiderated in them, which I might have reserved for explanation
in those others: for I have hitherto described this earth, and
generally the whole visible world, as if it were merely a machine in
which there was nothing at all to consider except the figures and
motions of its parts, whereas our senses present to us many other
things, for example colours, smells, sounds, and the like, of which,
if I did not speak at all, it would be thought I had omitted the
explication of the majority of the objects that are in nature.
CLXXXIX. What perception (SENSUS) is, and how we perceive.
We must know, therefore, that although the human soul is united to
the whole body, it has, nevertheless, its principal seat in the
brain, where alone it not only understands and imagines, but also
perceives; and this by the medium of the nerves, which are extended
like threads from the brain to all the other members, with which
they are so connected that we can hardly touch any one of them
without moving the extremities of some of the nerves spread over it;
and this motion passes to the other extremities of those nerves
which are collected in the brain round the seat of the soul,
[Footnote: *** FOOTNOTE NOT VISIBLE IN PAGE IMAGE (#98, Text p 195)]
as I have already explained with sufficient minuteness in the fourth
chapter of the Dioptrics.
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