If you take up a small quantity of melted glass with a tube, (the bowl
of a common tobacco pipe will do,) and let a drop fall into a vessel of
water, it will chill and condense with a fine spiral tail, which being
broken, the whole substance will burst with a loud explosion, without
injury either to the party that holds it, or him that breaks it; but if
the _thick_ end is struck even with a hammer, it will not break.