of the whole problem, and of every thing that has been said and done in the way of experiment and conjecture, we are afraid we must leave it where we found it. The malleability of glass is still a secret. [Footnote 12: Ibn Abd Alhakim.] DESCRIPTION OF A GLASS-HOUSE. Dismissing history and theory, we will now step into the glass-house itself, where the practical work of converting sand into goblets, vases, mirrors, and window-panes is going forward with a celerity and accuracy of hand and head that can not fail to excite wonder and admiration. As the whole agency employed is that of heat, the interior of the manufactory consists of furnaces specially constructed for the progressive processes to which the material is subjected before it is sent out perfected for use. Look round this extensive area, where you see numbers of men in their shirt-sleeves, with aprons before them, and various implements in their hands, which they exercise with extraordinary rapidity, and you will soon understand how the glittering wonders of glass are produced. Of these furnaces there are three kinds, the first called the calcar, the second the working furnace, and the third the annealing oven, or _lier_. The calcar, built in the form of an oven, is used for the calcination of the materials, preliminary to their fusion and vitrification. This process is of the utmost importance: it expels all moisture and carbonic acid gas, the presence of which would hazard the destruction of the glass-pots in the subsequent stages of the manufacture, while it effects a chemical union between the salt, sand, and metallic oxides, which is essential to prevent the alkali from fusing and volatilizing, and to insure the vitrification of the sand in the heat of the working furnace, to which the whole of the materials are to be afterwards submitted.