auditory Nerves by the Tremors of the Air, and propagated through the
solid, pellucid and uniform Capillamenta of those Nerves into the place
of Sensation? And so of the other Senses.
_Qu._ 24. Is not Animal Motion perform'd by the Vibrations of this
Medium, excited in the Brain by the power of the Will, and propagated
from thence through the solid, pellucid and uniform Capillamenta of the
Nerves into the Muscles, for contracting and dilating them? I suppose
that the Capillamenta of the Nerves are each of them solid and uniform,
that the vibrating Motion of the thereal Medium may be propagated along
them from one end to the other uniformly, and without interruption: For
Obstructions in the Nerves create Palsies. And that they may be
sufficiently uniform, I suppose them to be pellucid when view'd singly,
tho' the Reflexions in their cylindrical Surfaces may make the whole
Nerve (composed of many Capillamenta) appear opake and white. For
opacity arises from reflecting Surfaces, such as may disturb and
interrupt the Motions of this Medium.
[Sidenote: _See the following Scheme, p. 356._]
_Qu._ 25. Are there not other original Properties of the Rays of Light,
besides those already described? An instance of another original
Property we have in the Refraction of Island Crystal, described first by
_Erasmus Bartholine_, and afterwards more exactly by _Hugenius_, in his
Book _De la Lumiere_. This Crystal is a pellucid fissile Stone, clear as
Water or Crystal of the Rock, and without Colour; enduring a red Heat
without losing its transparency, and in a very strong Heat calcining
without Fusion. Steep'd a Day or two in Water, it loses its natural
Polish. Being rubb'd on Cloth, it attracts pieces of Straws and other
light things, like Ambar or Glass; and with _Aqua fortis_ it makes an
Ebullition. It seems to be a sort of Talk, and is found in form of an
oblique Parallelopiped, with six parallelogram Sides and eight solid
Angles. The obtuse Angles of the Parallelograms are each of them 101
Degrees and 52 Minutes; the acute ones 78 Degrees and 8 Minutes. Two of
the solid Angles opposite to one another, as C and E, are compassed each
of them with three of these obtuse Angles, and each of the other six
with one obtuse and two acute ones. It cleaves easily in planes parallel
to any of its Sides, and not in any other Planes. It cleaves with a
glossy polite Surface not perfectly plane, but with some little
unevenness. It is easily scratch'd, and by reason of its softness it
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