tnote: _Trace the nice lines of form_, l. 125. When the
idea of solidity is excited 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 world.

Now, as the whole universe with all its parts possesses a
certain form or figure, if any part of it moves, that form or
figure of the whole is varied. Hence, as motion is no other
than a perpetual variation of figure, our idea of motion is
also a real resemblance of the motion that produced it.

Hence arises the certainty of the mathematical sciences, as
they explain these properties of bodies, which are exactly
resembled by our ideas of them, whilst we are obliged to
collect almost all our other knowledge from experiment; that
is, by observing the effects exerted by one body upon
another.]

"Slow could the tangent organ wander o'er
The rock-built mountain, and the winding shore;
No apt ideas could the pigmy mite,
Or embryon emmet to the touch excite;
But as each mass the solar ray reflects,
The eye's clear glass the transient beams collects;
Bends to their focal point the rays that swerve,
And paints the living image on the nerve.
So in some village-barn, or festive hall
The spheric lens illumes the whiten'd wall; 140
O'er the bright field successive figures fleet,
And motley shadows dance along the sheet.--
Symbol of solid forms is colour'd light,
And the mute language of the touch is sight.

[Footnote: _The mute language of the touch_, l. 144. Our eyes
observe a difference of colour, or of shade, in the
prominences and depressions of objects, and that those shades
uniformly vary when the sense of touch observes any
variation. Hence when the retina becomes stimulated by
colours or shades of light in a certain form, as in a
circular spot, we know by e