And this, by
the by, minds me of the appearing magnitude of the _aperture_ of the
_iris_, or _pupil_ of the eye, which though it appear, and be therefore
judged very large, is yet not above a quarter of the bigness it appears of,
by the _lenticular_ refraction of the _Cornea_.
The cause of all which _Phaenomena_ I imagine to be no other then this,
That the Parts of the Glass being by the excessive heat of the fire kept
off and separated one from another, and thereby put into a kind of sluggish
fluid consistence, are suffered to drop off with that heat or agitation
remaining in them, into cold Water; by which means the outsides of the drop
are presently cool'd and _crusted_, and are thereby made of a loose
texture, because the parts of it have not time to settle themselves
leisurely together, and so to lie very close together: And the innermost
parts of the drop, retaining still much of their former heat and
agitations, remain of a loose texture also, and, according as the cold
strikes inwards from the bottom and sides, are quenched, as it were, and
made rigid in that very posture wherein the cold finds them. For the parts
of the _crust_ being already hardened, will not suffer the parts to shrink
any more from the outward Surface inward; and though it shrink a little by
reason of the small parcels of some Aerial substances dispersed through
the matter of the Glass, yet that is not neer so much as it appears (as I
just now hinted;) nor if it were, would it be sufficient for to consolidate
and condense the body of Glass into a _tuff_ and close _texture_, after it
had been so excessively rarified by the heat of the glass-Furnace.
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