Considerable curiosity has been excited of late by a new invention, which has resulted from the investigations of a Frenchman. We have been told that tumblers and wine-glasses, and other glass utensils, could be so treated that they would never break; and experiments performed upon many samples of these glasses led one to suppose, that the object had been attained. There is no doubt whatever, that some who have had experience of what is termed toughened glass know, that in many cases very uncertain results are obtained in the resisting power of the glass to the action of a violent blow. Before, however, entering into some researches which I have made on the subject, it will be well to state what is the nature of the change which the toughening process produces in the glass, and this seems to be a fit place for this consideration, as the method of making, and the behaviour, of Prince Rupert's drops, have just been discussed. The physical properties of these Rupert's drops have been examined with great care by M. Victor de Luynes, and the results of his experiments have been communicated to the _SociA(C)tA(C) de Secours des Amis des Sciences_. For the purposes of this article, many of his experiments have been repeated, confirming in general his observations, and others have also been instituted. The toughness and hardness of these drops are remarkable; the thick pear-shaped portion will bear a sharp stroke with a hammer without breaking; nor can it be scratched with a diamond. To break the tapering thread or tail, as it may be conveniently called, requires considerable force. To find out what weight was required to do this, a series of experiments was performed, the results of which are given in the table following. The tail of a drop was placed over a small hole bored in the top of a table; a hook was then adjusted round a part of the tail which measured 19 on a Birmingham wire gauge; below the table and attached to this hook, a scale-pan was hung. This pan was then carefully loaded, all shock being avoided, until the thread was ruptured and the weight required to effect this was then noted: White Glass Rupert's Drops. Gauge. Strain. 19 16 lb. 0 oz. 19 15-1/2 " 0 " 19 16 " 0 " 19 (poor) 9-1/4 " 0 " Green Glass. Gauge. Strain. 19 18-3/4 " 0 " 19 (poor) 9 " 0 " 19 28 " 6 " 16 26-1/4 " 0 "