shall afterwards shew it to be very probable, that the like accidents
happen even to the Air it self.

Further, as these solutions and tinctures do alter the nature of these
fluid bodies, as to their aptness to propagate a motion or impulse through
them, even so does the particles of the Air, Water, and other fluid bodies,
and of Glass, Crystal, &c. which are commixt with this bulk of the _Æther_
alter the motion of the propagated pulse of light; that is, where these
more bulkie particles are more plentifull, and consequently a lesser
quantity of the _Æther_ between them to be mov'd, there the motion must
necessarily be the swifter, though not so robust, which will produce those
effects, which I have (I hope) with some probability, ascribed to it in the
digression about Colours, at the end of the _Observations_ on
_Muscovy-glass._

Now, that other Stones, and those which have the closest and hardest
textures, and seem (as far as we are able to discover with our eyes, though
help'd with the best _Microscopes_) freest from pores, are yet
notwithstanding replenish'd with them, an Instance or two will, I suppose,
make more probable.

A very solid and unflaw'd piece of cleer white _Marble_, if it be well
polish'd and glaz'd, has so curiously smooth a surface, that the best and
most polish'd surface of any wrought-glass, seems not to the naked eye, nor
through a _Microscope_, to be more smooth, and less porous. And yet, that
this hard close body is replenish'd with abundance of pores, I think these
following Experiments will sufficiently prove.

The first is, That if you take such a piece, and for a pretty while boyl it
in Turpentine and Oyl of Turpentine, you shall find that the stone will be