Democratic Sentinel, Volume 15, Number 43, Rensselaer, Jasper County, 13 November 1891 — HOW LENSES ARE MADE. [ARTICLE]

HOW LENSES ARE MADE.

The Art of lilamtfaoturing; Spectacles Reduced to a Science. The art of making spectacles, says the Popular Science Monthly, has been reduced to a science. The bit of glass to be formed into a lens is fastened by means of pitch to a small block of hard rubber so that it may be more readily handled. It is ground by being pressed against a rapidly revolving metal tool, whose curvature is ef}ual and opposite to that desired in the lens. This is known as the “rough tool” and is made of cast iron. It is mounted on a vertical spindle, and is kept moistened with emery and water. Several grades of emery are used in succession, changing from coarse to line as the grinding pnv ceeds. As a result of this process the glass has a rough surface and is nd longer transparent. It is now transferred to the “fine tool.” This is made of and has Its surface as true as possible. It is compared from time to time with a standard curve in order to insure accuracy. lirthis second grinding the abrading material is rouge (carefully calcined sulphate of iron). Finally the lens is polished by being pressed against a piece of cloth powdered with rouge and fastened to the rotating tool. The glass is now loosened

from its block, turned over, and the reverse side of the lens ground When this has been accomplished thr lens must be cut down to the propef shape for iihoiihting in the spectaclcframe. Itf‘ is - placed on a leather cushion and held firmly in position by a rubber-tjpped arm while a diamond glass-cutter passing around ar oval guide traces a similar oval of the glass below. t The superfluous glass outside tb< oval is removed by steel pincers, the rough edges are ground smooth on Scotch wheels, and the lens is ready for mounting. ‘ The glasses for small telescopes, microscopes, burning glasses and the like are gtoand in the same fashion. Honissty is th 3 bast policy, but insurance agents c sf(\ fom trying to force it on you