This mirror was the special delight of the Shah of Persia during his visit of this year to Paris; and as I suppose the seven plate-glass manufactories which have grown up in my own beloved country under the benediction of the Protective Tariff, since a prohibitive duty was originally clapped on plate glass to encourage the one solitary establishment of the sort then existing in America, will give themselves up to producing something more stupendous still for the New York Exposition of 1892, I here set down its dimensions. It measures in height 7 metres 63 centimetres, and in width 4 metres 10 centimetres, giving it a superficial area of 34 metres 24 centimetres. It is 12 millimetres thick, and weighs 940 kilogrammes. This enormous glass was cast from a single crucible, containing 1,600 kilogrammes of vitreous matter. To have seen this operation would have been worth a very much longer journey than that from New York to St.-Gobain, for the colour and glow of such a mass of vitreous matter in fusion can only be matched by the evanescent hues of a crimson aurora on a fine night in the North, or by the intense lights which play over the surface of a stream of molten lava. At every stage in the operation the utmost skill and delicacy of handling are required to convert what might easily pass for a heap of rubbish swept together from a macadamised roadway into the smooth, glittering, lustrous plate which the French so picturesquely call a _glace_, and which indeed most nearly resembles the evenly frozen surface of a crystal lakelet. These sands, silicates, chalks, and carbonates--rough contributions from Oken's 'silent realm of the minerals'--are first crushed and mingled together by machines--one of the best of them, I was glad to hear, of American invention--then passed on into the great rectangular hall, in which they are shot into the crucibles of the melting furnaces and fused, mainly by gas, on a system invented and perfected by the late Dr. Siemens, I believe, who made such a stir a decade ago at Glasgow by his discourse on the storage of force before the British Association. The furnaces which, according to their varying capacity, now require from eight to ten tons of coal a day, consumed, before the development of the Siemens system, from sixteen to twenty tons. Twenty-four hours now suffice for the fusion and the casting of the glass, and if the casting were now to be conducted as ceremoniously as in the time of that fine old martinet M. Deslandes, M. Henrivaux would pass his life in a cocked hat, knee-breeches, peruke, embroidered coat, and sword, for the casting now takes place every day and at a fixed hour. None the less, rather the more, it is a work still of extreme nicety, one to be done by experts, who must be as cool as soldiers under fire. In a certain way and measure it is like ladling out the molten lava of Vesuvius and pressing it into slabs for a lady's toilette-table. The plates, once cast, must be smoothed and made even.