Light, as well as a more robust that causes Heat, may be argued from the
celerity wherewith the bodyes are dissolv'd.

Next, it must be a _Vibrative motion_. And for this the newly mention'd
_Diamond_ affords us a good argument; since if the motion of the parts did
not return, the Diamond must after many rubbings decay and be wasted: but
we have no reason to suspect the latter, especially if we consider the
exceeding difficulty that is found in cutting or wearing away a Diamond.
And a Circular motion of the parts is much more improbable, since, if that
were granted, and they be suppos'd irregular and Angular parts, I see not
how the parts of the Diamond should hold so firmly together, or remain in
the same sensible dimensions, which yet they do. Next, if they be
_Globular_, and mov'd only with a _turbinated_ motion, I know not any cause
that can impress that motion upon the _pellucid medium_, which yet is done.
Thirdly, any other _irregular_ motion of the parts one amongst another,
must necessarily make the body of a fluid consistence, from which it is far
enough. It must therefore be a _Vibrating_ motion.

And Thirdly, That it is a very _short-vibrating motion_, I think the
instances drawn from the shining of Diamonds will also make probable. For a
Diamond being the hardest body we yet know in the World, and consequently
the least apt to yield or bend, must consequently also have its
_vibrations_ exceeding short.

And these, I think, are the three principal proprieties of a motion,
requisite to produce the effect call'd Light in the Object.

The next thing we are to consider, is the way or manner of the _trajection_
of this motion through the interpos'd pellucid body to the eye: And here it
will be easily granted,