Take a stick of Glass of a considerable length, and fit it so between the two ends or screws of a Lath, that it may but just easily turn, and that the very ends of it may be just toucht and susteined thereby; then applying the flame of the Candle to the middle of it, and heating it hot, you will presently find the Glass to stick very fast on those points, and not without much difficulty to be convertible on them, before that by removing the flame for a while from it, it be suffered to cool, and when you will find it as easie to be turned round as at the first.

From all which Experiments it is very evident, that all those Bodies, and particularly Glass, suffers an Expansion by Heat, and that a very considerable one, whilst they are in a state of Fusion.  For Fluidity, as I elsewhere mention, being nothing but an effect of very strong and quick shaking motion, whereby the parts are, as it were, loosened from each other, and consequently leave an interjacent space or vacuity; it follows, that all those shaken Particles must necessarily take up much more room then when they were at rest, and lay quietly upon each other.  And this is further confirmed by a Pot of boyling Alabaster, which will manifestly rise a sixth or eighth part higher in the Pot, whilst it is boyling, then it will remain at, both before and after it be boyled.  The reason of which odd Phaenomenon (to hint it here only by the way) is this, that there is in the curious powder of Alabaster, and other calcining Stones, a certain watery substance, which is so fixt and included with the solid Particles, that till the heat be very considerable they will not fly away; but after the heat is increased to such a degree, they break out every way in vapours, and thereby so shake and loosen the small corpusles of the Powder from each other, that they become perfectly of the nature of a fluid body, and one may move a stick to and fro through it, and stir it as easily as water, and the vapours burst and break out in bubbles just as in boyling water, and the like; whereas, both before those watery parts are flying away, and after they are quite gone; that is, before and after it have done boyling, all those effects cease, and a stick is as difficultly moved to and fro in it as in sand, or the like.  Which Explication I could easily prove, had I time; but this is not a fit place for it.

To proceed therefore, I say, that the dropping of this expanded Body into cold Water, does make the parts of the Glass suffer a double contraction:  The first is, of those parts which are neer the Surface of the Drop.  For Cold, as I said before, contracting Bodies, that is, by the abatement of the agitating faculty the parts falling neerer together; the parts next adjoyning to the Water must needs lose much of their motion, and impart it to the Ambient-water (which the Ebullition and commotion of it manifests) and thereby become a solid and hard crust, whilst the