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CH. IX]
COMBINED PROJECTION
293
apparatus. This tube has a set screw in the side to hold the post at any desired level (fig. is8F). In order to be able to perfect the centering of the apparatus, the screw holes in the flanges are made larger than the screws so that by loosening the screws the flange can be shifted slightly from side to side. If necessary one can use washers to increase the size of the screw heads, so that the holes in the flange can be quite large.
§ 431. Wooden shields for holding objectives, etc. — For holding projection objectives of low power, shields of thin board (i to
FIGURE 158?. SECTIONAL VIEW OF A RAILING FLANGE AND SOCKET.
/ The flange in section. The screw holes are made large for centering. 5 The set screw to hold the post in place.
p Post extending down into the socket. It is held at any desired height by the set screw (s).
sc Socket for receiving the post or stem of any piece of apparatus.
1^2 cm., y£ in. thick) can be used, and a post or stem of iron made from a bolt by hammering out the end in the form of a fan (fig. 1 58 A). To aid in centering, the screw holes in this post should also be larger than the screws.
MICROSCOPE AND LANTERN-SLIDE PROJECTION COMBINED
§ 432. With an outfit of the lathe-bed type (fig. 138), it is very simple to change from lantern-slide to micro-projection and the reverse. All that is necessary is to put the lantern-slide carrier next the condenser, and the lantern-slide projection objective on its block in position. The stage and the microscope must be set off the track on the table. The only difficulty is that the second element of the condenser for the micro-projection is of too short a focus for most lantern-slide projection. This can be overcome in