2097. Hartley's rough plate-glass is strongly recommended by Dr. Lindley. 'This kind of glass,' he observes, 'is made of the same materials as the sheet-glass, but by a very different process. Instead of being, in the first instance, blown into the form of a cylinder, or 'muff,' then slit and flattened�a difficult process, incapable of making it level or free from large irregular lenses,�rough plate is at once rolled into plates, and left with an irregular granulated surface, which breaks, and bends, and separates the rays of light as they pass through it, thus rendering their concentration, and the burning consequent upon it, impossible. (Gard. Chron. for 1849, p. 115.) Another advantage of this kind of glass is that it does not require shading.
