2817. Couper, J., and Richardson, W. H. July 11.
Making lenses; moulding; shaping. Lenses of the dioptric class, such as are used for ships masthead, side, and anchor lights, and for railway lights and analogous purposes, are formed with the several dioptric prisms B, C, D, Fig. 1, surrounding the central convex portion A of a gradually increasing thickness from the centre outwards.
Fig. 2 shows a vertical section of a mould for a lens having a segment greater than a semicircle. It is formed with a bed-plate H having at the centre an opening I to receive the lower part of the block J, and with the sides N, bearing against the flat sides of the block J, hinged to a vertical plate K fixed to the bed-plate. These sides are kept tight against the block by a catch S centered on one of the doors and engaging a square stud on the other. The cover P, formed with a central opening to allow the insertion or withdrawal of the hydraulic plunger Q, is also hinged to the vertical plate K and held down tightly upon the top of the block J by a catch U centered on the bed-plate. The glass having been poured into the mould the plunger Q is inserted so as to distribute it to all parts. As soon as the glass is set, the plunger Q is withdrawn and the upper portion of the mould opened up. The upper portions of the lens, which are left straight by the form of the plunger, are then bent to the required curvature by pressing inwards, by hand or mechanism, two strips of wood applied to projections at ends. A series of parallel lines, or a scale, is engraved on the top of the mould for indicating the curvature, or the glass may be bent over a wooden or other block inserted in the mould.
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