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228
Appendix
Another instrument I have made consists of a piece of glass inclined at a very acute
angle to the line of sight, and of a
Fig. 1 shows the simple apparatus which carries the prism and on which the photograph is mounted. The former
is set in a round box which can he rotated in the ring at the end of the arm and can be clamped when
adjusted. The arm can be rotated and can also be pulled out or in if desired, and clamped. The floor of the
instrument is overlaid with cork covered with black cloth, on which the components can easily be fixed by
drawing-pins. When using it, one portrait is pinned down and the other is moved near to it, overlapping its
margin if necessary, until the eye looking through the prism sees the required combination; then the second
portrait is pinned down also. It may now receive its register-marks from needles fixed in a hinged arm, and
this is a more generally applicable method than the plan with cross threads, already described, as any desired
feature—the nose, the ear, or the hand, may thus be selected for composite purposes. Let A, B, c, … , y z, be
the components. A is pinned down, and B, c, … y, z, are successfully combined with A, and registered. Then
before removing z, take away A and substitute any other of the already registered portraits, say a, by
combining it with z; lastly, remove z and substitute A by combining it with a, and register it. Fig. 2 shows
one of three similarly jointed arms, which clamp on to the vertical rod. Two of these carry a light frame
covered with cork and cloth, and the other carries Fig. 3, which is a frame having lenses of different powers
set into it, and on which, or on the third frame, a small mirror inclined at 450 may be laid. When a portrait
requires foreshortening it can be pinned on one of these frames and be inclined to the line of sight; when it is
smaller than its fellow it can be brought nearer to the eye and an appropriate lens interposed; when a right-
sided profile has to be combined with a left-handed one, it must be pinned on one of the frames and viewed
by reflection from the mirror in the other. The apparatus I have drawn is roughly made, and being chiefly of
wood is rather clumsy, but it acts well.
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