and
very slow in recollecting them; for if I now think of the tangible idea of
a cube, that is, if I think of its figure, and of the solidity of every
part of that figure, I must conceive myself as passing my fingers over it,
and seem in some measure to feel the idea, as I formerly did the
impression, at the ends of them, and am thus very slow in distinctly
recollecting it.

When a body compresses any part of our sense of touch, what happens? First,
this part of our sensorium undergoes a mechanical compression, which is
termed a stimulus; secondly, an idea, or contraction of a part of the organ
of sense is excited; thirdly, a motion of the central parts, or of the
whole sensorium, which is termed sensation, is produced; and these three
constitute the perception of solidity.

2. _Of Figure, Motion, Time, Place, Space, Number._

No one will deny, that the medulla of the brain and nerves has a certain
figure; which, as it is diffused through nearly the whole of the body, must
have nearly the figure of that body. Now it follows, that the spirit of
animation, or living principle, as it occupies this medulla, and no other
part, (which is evinced by a great variety of cruel experiments on living
animals,) it follows, that this spirit of animation has also the same
figure as the medulla above described. I appeal to common sense! the spirit
of animation acts, Where does it act? It acts wherever there is the medulla
above mentioned; and that whether the limb is yet joined to a living
animal, or whether it be recently detached from it; as the heart of a viper
or frog will renew its contractions, when pricked with a pin, for many
minutes of time after its exsection from the body.--Does it act any where
else?--No; then it certainly exists in this part of space, and no where
else; that is, it hath figure; namely, the figure of the nervous system,
which is nearly the figure of the body. When the idea of solidity is
excited, as above explained, a part of the extensive organ of touch is
compressed by some external body, and this part of the sensorium so
compressed exactly resembles _in figure_ the figure of the body that
compressed it. Hence, when we acquire the idea of solidity, we acquire at
the same time the idea of FIGURE; and this idea of figure, or motion of _a
part_ of the organ of touch, exactly resembles _in its figure_ the figure
of the body that occasions it; and thus exactly acquaints us with this
property of the external