Fig. 106.
When thus finished from the hammer, the reflector is put into the apparatus shewn in [fig. 106], which is placed at the end of a long dark corridor. RR is a wooden frame fixed to the wall with projecting brackets at K, which carry the reflector, fixed at E, E, by means of screws, so as always to have a definite position with reference to the bracket B, which carries the lamp and its fountain f, so arranged that its flame may admit of perfect adjustment to the point which ought to be the focus of the reflector. For the purpose of this adjustment, S shews screws for raising and depressing the level of the burner; and the lines or marks M, M′ shewn at the sockets J being brought into line, regulate the position of the burner in the plane of the focus, after it has been raised to the level of that plane by means of the screws at S. The lamp being lighted and thus properly placed, its effect on the reflector’s surface is observed by some one stationed at a convenient distance; and if the whole surface appear luminous, the instrument is considered fit for polishing; but if any dark spaces be found in it, the whole reflector must be again carefully tested by means of the mould, and the defective parts remedied in the manner above described.
The next step is to turn over the edge of the reflector, so as to stiffen it. For this purpose it is placed in the matrix P′P′ ([fig. 107]), and the needle-point at V is adjusted by the screw at D, so as just to enter the small hole formerly drilled in the vertex of the reflector. The die-plate PP (which is worked by means of the arms AA, which turn the screw S) then descends and presses the edge over, which is finished with a finely polished tool C, revolving round the axis of the instrument, which coincides with the centre of the matrix and die. In order to ensure a steady vertical movement of the die-plate PP, cross-arms FF, which are provided with sockets HH, which slide over the rods GG, GG, are added to prevent any lateral shake or derangement. The whole frame is stiffened by the cross-head in which the screw S works.
Fig. 107.
Fig. 108.
Fig. 109.
