Other stones I have found so porous, that with the
_Microscope_ I could perceive several small winding holes, much like
Worm-holes, as I have noted in some kind of _Purbeck-stone_, by looking on
the surface of a piece newly flaw'd off, for if otherwise, the surface has
been long expos'd to the Air, or has been scraped with any tool, those
small caverns are fill'd with dust, and disappear.
And to confirm this _Conjecture_, yet further, I shall here insert an
excellent account, given into the _Royal Society_ by that Eminently Learned
Physician, Doctor _Goddard_, of an Experiment, not less instructive then
curious and accurate, made by himself on a very hard and seemingly close
stone call'd _Oculus Mundi_, as I find it preserv'd in the Records of that
Honourable Society.
A small stone of the kind, call'd by some Authours, _Oculus Mundi_,
being dry and cloudy, weigh'd 5-209/256 _Grains_.
The same put under water for a night, and somewhat more, became
transparent, and the superficies being wiped dry, weighed 6-3/256
_Grains_.
The difference between these two weights, 0-50/256 of a _Grain_.
The same Stone kept out of water one Day and becoming cloudy again
weighed, 5-225/256 _Graines_.
Which was more then the first weight, 0-16/256 of a _Grain_.
The same being kept two Days longer weighed, 5-202/256 _Graines_.
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