formerly repleat with air (that has a very differing refraction, and
consequently is very reflective) which seems to be confirm'd by the second
Observable, namely, the increase of weight after keeping, and decrease upon
drying. And thirdly, seem'd yet more sensibly confirm'd by the multitude of
bubbles in the last Experiment.

We find also most Acid Salts very readily to dissolve and separate the
parts of this body one from another; which is yet a further Argument to
confirm the porousness of bodies, and will serve as such, to shew that even
Glass also has an abundance of pores in it, since there are several
liquors, that with long staying in a Glass, will so _Corrode_ and eat into
it, as at last, to make it pervious to the liquor it contain'd, of which I
have seen very many Instances.

Since therefore we find by other proofs, that many of those bodies which we
think the most solid ones, and appear so to our sight, have notwithstanding
abundance of those grosser kind of pores, which will admit several kinds of
liquors into them, why should we not believe that Glass, and all other
transparent bodies abound with them, since we have many other arguments,
besides the propagation of light, which seem to argue for it?

And whereas it may be objected, that the propagation of light is no
argument that there are those atomical pores in glass, since there are
_Hypotheses_ plausible enough to solve those _Phænomena_, by supposing the
pulse onely to be communicated through the transparent body.

To this I answer, that that _Hypothesis_ which the industrious _Mersennus_
has publish'd about the slower motion of the end of a Ray in a denser
_medium_, then in a more rare and thin, seems altogether unsufficient to
solve abundance of _Phænomena_, of which this is not the least