Here is a piece of glass [producing a piece of plate-glass about two inches square]--(I shall want this afterwards to look to and examine its internal condition)--and here is some of the same sort of glass differing only in its power of cohesion, because while yet melted it has been dropped into cold water [exhibiting a “Prince Rupert’s drop”.[10] (fig. 13)]; and if I take one of these little tear-like pieces and break off ever so little from the point, the whole will at once burst and fall to pieces. I will now break off a piece of this. [The Lecturer nipped off a small piece from the end of one of the Rupert’s drops, whereupon the whole immediately fell to pieces.] There! you see the solid glass has suddenly become powder--and more than that, it has knocked a hole in the glass vessel in which it was held. I can shew the effect better in this bottle of water; and it is very likely the whole bottle will go. [A 6-oz. vial was filled with water, and a Rupert’s drop placed in it, with the point of the tail just projecting out; upon breaking the tip off, the drop burst, and the shock being transmitted through the water to the sides of the bottle, shattered the latter to pieces.] Here is another form of the same kind of experiment. I have here some more glass which has not been annealed [showing some thick glass vessels[11] (fig. 14)], and if I take one of these glass vessels and drop a piece of pounded glass into it (or I will take some of these small pieces of rock crystal--they have the advantage of being harder than glass), and so make the least scratch upon the inside, the whole bottle will break to pieces,--it cannot hold together. [The Lecturer here dropped a small fragment of rock crystal into one of these glass vessels, when the bottom immediately came out and fell upon the plate.] There! it goes through, just as it would through a sieve. [Illustration: Fig. 13. and Fig. 14.]