[ Pobierz całość w formacie PDF ]
divine revelation, as if the power of our thought extended beyond what God has in reality made; but likewise
still more if we persuaded ourselves that all things were created by God for us only, or if we merely supposed
that we could comprehend by the power of our intellect the ends which God proposed to himself in creating
the universe.
III. In what sense it may be said that all things were created for the sake of man.
For although, as far as regards morals, it may be a pious thought to believe that God made all things for us,
seeing we may thus be incited to greater gratitude and love toward him; and although it is even in some sense
true, because there is no created thing of which we cannot make some use, if it be only that of exercising our
mind in considering it, and honouring God on account of it, it is yet by no means probable that all things were
created for us in this way that God had no other end in their creation; and this supposition would be plainly
ridiculous and inept in physical reasoning, for we do not doubt but that many things exist, or formerly existed
and have now ceased to be, which were never seen or known by man, and were never of use to him.
PART IV. OF THE EARTH.
CLXXXVIII. Of what is to be borrowed from disquisitions on animals and man to advance the knowledge
of material objects.
I should add nothing farther to this the Fourth Part of the Principles of Philosophy, did I purpose carrying out
my original design of writing a Fifth and Sixth Part, the one treating of things possessed of life, that is,
animals and plants, and the other of man. 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
PART IV. OF THE EARTH. 34
The Principles of Philosophy
IMAGE (#98, Text p 195)] as I have already explained with sufficient minuteness in the fourth chapter of the
Dioptrics. But the movements which are thus excited in the brain by the nerves variously affect the soul or
mind, which is intimately conjoined with the brain, according to the diversity of the motions themselves. And
the diverse affections of the mind or thoughts that immediately arise from these motions, are called
perceptions of the senses (SENSUUM PERCEPTIONES), or, as we commonly speak, sensations (SENSUS).
CXC. Of the distinction of the senses; and, first, of the internal, that is, of the affections of the mind
(passions), and the natural appetites.
The varieties of these sensations depend, firstly, on the diversity of the nerves themselves, and, secondly, of
the movements that are made in each nerve. We have not, however, as many different senses as there are
nerves. We can distinguish but seven principal classes of nerves, of which two belong to the internal, and the
other five to the external senses. The nerves which extend to the stomach, the oesophagus, the fauces, and the
other internal parts that are subservient to our natural wants, constitute one of our internal senses. This is
called the natural appetite (APPETITUS NATURALIS). The other internal sense, which embraces all the
emotions (COMMOTIONES) of the mind or passions, and affections, as joy, sadness, love, hate, and the like,
depends upon the nerves which extend to the heart and the parts about the heart, and are exceedingly small;
for, by way of example, when the blood happens to be pure and well tempered, so that it dilates in the heart
more readily and strongly than usual, this so enlarges and moves the small nerves scattered around the
orifices, that there is thence a corresponding movement in the brain, which affects the mind with a certain
natural feeling of joy; and as often as these same nerves are moved in the same way, although this is by other
causes, they excite in our mind the same feeling (sensus, sentiment). Thus, the imagination of the enjoyment
of a good does not contain in itself the feeling of joy, but it causes the animal spirits to pass from the brain to
the muscles in which these nerves are inserted; and thus dilating the orifices of the heart, it also causes these
small nerves to move in the way appointed by nature to afford the sensation of joy. Thus, when we receive
news, the mind first of all judges of it, and if the news be good, it rejoices with that intellectual joy
(GAUDIUM INTELLECTUALE) which is independent of any emotion (COMMOTIO) of the body, and
which the Stoics did not deny to their wise man [although they supposed him exempt from all passion]. But
as soon as this joy passes from the understanding to the imagination, the spirits flow from the brain to the
muscles that are about the heart, and there excite the motion of the small nerves, by means of which another
motion is caused in the brain, which affects the mind with the sensation of animal joy (LAETITIA
ANIMALIS). On the same principle, when the blood is so thick that it flows but sparingly into the ventricles
of the heart, and is not there sufficiently dilated, it excites in the same nerves a motion quite different from
[ Pobierz całość w formacie PDF ]