d, and water, and all other bodies, as much rarer as
he pleases, so that light may find a ready passage through transparent
substances(43)."

(43) Newton, Optics, Book II, Part III, Prop. viii.

Again: "The colours of bodies arise from the magnitude of the particles
that reflect them. Now, if we conceive these particles of bodies to
be so disposed among themselves, that the intervals, or empty spaces
between them, may be equal in magnitude to them all; and that these
particles may be composed of other particles much smaller, which have
as much empty space between them as equals all the magnitudes of these
smaller particles; and that in like manner these smaller particles are
again composed of others much smaller, all which together are equal to
all the pores, or empty spaces, between them; and so on perpetually
till you come to solid particles, such as have no pores, or empty spaces
within them: and if in any gross body there be, for instance, three such
degrees of particles, the least of which are solid; this body will
have seven times more pores than solid parts. But if there be four such
degrees of particles, the least of which are solid, the body will have
fifteen times more pores than solid parts. If there be five degrees, the
body will have one and thirty times more pores than solid parts. If six
degrees, the body will have sixty and three times more pores than solid
parts. And so on perpetually(44)."

(44) Ibid.

In the Queries annexed to the Optics, Newton further suggests an
opinion, that the rays of light are repelled by bodies without immediate
contact. He observes that:

"Where attraction ceases, there a repulsive virtue ought to succeed.
And that there is such a virtue, seems to follow from the reflexions and
inflexions of the rays of light. For the rays are repelled by bodies,
in both these cases, without the immediate contact of the reflecting or
inflecting body. It seems also to follow from the emission of light; the
ray, so soon as it is shaken off from a shining body by the vibrating
motion of the parts of the body, and gets beyond the reach of
attraction, being driven away with exceeding great velocity. For
that force, which is sufficient to turn it back in reflexion, may be
sufficient to emit it. It seems also to follow from the production of
air and vapour: the particles, when they are shaken off from bodies
by heat or fermentation, so soon as they are beyond the reach of the
att