John L. Gillerland, late of the Brooklyn Glass-Works, is remarkably skilful in mixing metal. He has succeeded in producing the most brilliant glass of refractory power, which is so difficult to obtain. A gold medal was awarded his glass, in face of European competition, at the Great International Exhibition in London, 1852. In making rich glass, the gaffer or foreman must understand the science of chemistry sufficiently well to mix and purify his materials in the best possible manner, removing all crude or foreign matter, and combining the proper substances into a homogeneous mass. Without this practical experience and knowledge, his glass, instead of being clear and brilliant, and of uniform color, will be dull, and of many hues or shades. It is important also that his personal character be such as to command the respect of the workmen. LENSES. Optical glasses have engaged the attention and investigation of scientific men for centuries. We read of the wonderful exploits of the burning lens of Archimedes, and find the remains of lenses thousands of years old in the ruins of Nineveh, Babylon, and Pompeii. They are of the utmost importance in the science of astronomy. The slow progress made in perfecting them shows the inherent difficulties that exist in obtaining glass of the required purity. One of these is the different specific gravities of the material used. Hence the lower part of a pot of melted glass is of greater specific gravity than the top, causing a tendency to cords or threads, an evil which science has yet to learn to overcome. Not even the large bounty offered by the English Government and the Board of Longitude has been successful in effecting any important improvement in this branch of manufacture. Munich enjoys the reputation of producing the best lenses, and consequently the finest telescopes. Sir Isaac Newton, Gregory, Dolland, Keir, and others adopted lenses made from flint- and from crown-glass, it being necessary to use both in the construction of achromatic telescopes, one possessing as small and the other as great dispersive powers relative to the mean refractive powers as can be procured. But the inherent defect of the lenses still remained. M. Macquer remarks, "The correction of this fault appears therefore to be very difficult." He had tried in vain to remove it by very long fusion and fierce fire. Others have found this by experience not to correct, but to augment the evil. Mr. Keir is of opinion that some new composition must be discovered, which, along with a sufficient refractive power, shall possess a greater uniformity of texture.