ense? Which I can only repeat from what is mentioned in Sect. XIV. 2. 2.
that if part of an organ of sense be stimulated into action, as of the
sense of touch, that part so stimulated into action must possess figure,
which must be similar to the figure of the body, which stimulates it.

Another previous prepossession of the mind, which may have rendered the
manner of our acquiring the knowledge of figure less intelligible, may have
arisen from the common opinion of the perceiving faculty residing in the
head; whereas our daily experience shews, that our perception (which
consists of an idea, and of the pleasure or pain it occasions) exists
principally in the organ of sense, which is stimulated into action; as
every one, who burns his finger in the candle, must be bold to deny.

When an ivory triangle is pressed on the palm of the hand, the figure of
the surface of the part of the organ of touch thus compressed is a
triangle, resembling in figure the figure of the external body, which
compresses it. The action of the stimulated fibres, which constitute the
idea of hardness and of figure, remains in this part of the sensorium,
which forms the sense of touch; but the sensorial motion, which constitutes
pleasure or pain, and which is excited in consequence of these fibrous
motions of the organ of sense, is propagated to the central parts of the
sensorium, or to the whole of it; though this generally occurs in less
degree of energy, than it exists in the stimulated organ of sense; as in
the instance above mentioned of burning a finger in the candle.

Some, who have espoused the doctrine of the immateriality of ideas, have
seriously doubted the existence of a material world, with which only our
senses acquaint us; and yet have assented to the existence of spirit, with
which our senses cannot acquaint us; and have finally allowed, that all our
knowledge is derived through the medium of our senses! They forget, that if
the spirit of animation had no properties in common with matter, it could
neither affect nor be affected by the material body. But the knowledge of
our own material existence being granted, which I suspect few rational
persons will seriously deny, the existence of a material external world
follows in course; as our perceptions, when we are awake and not insane,
are distinguished from those excited by sensation, as in our dreams, and
from those excited by volition or by association as in insanity and
reverie, by t