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874 HANDBOOK OF PROJECTION FOR
regulation may be had with the adjusting screw. The motor and magnet are protected by a three-ampere cartridge fuse. Should the controller refuse to function, put in a new fuse. SPARE FUSES SHOULD BE KEPT ON HAND.
TO OPERATE BY HAND.— To feed the carbons by hand, merely cut out the controller by means of the toggle switch on its top.
THE RHEOSTAT.— With the rheostat supplied with the equipment you may use either 10, 15, 20 or 25 amperes, at will, but bear in mind the fact that 25 amperes D C will, if you have the equipment properly adjusted, supply screen illumination equal to that supplied by a 75 ampere D C regular arc with the old type arc. Provided the line voltage be not in excess of 110, the rheostat will deliver 10 amperes with both switches open, 15 when the switch marked 15 amperes is closed, 20 amperes when the 20 ampere switch is closed and 25 amperes when both the 15 and 20 ampere switches are closed. The statement of comparative illumination is the manufacturer's claim.
STEREOPTICON ATTACHMENT.— The stereopticon attachment consists of a metal box about 14 inches long by 6 inches square. This box is attached to the front left hand corner of the lamphouse, at about the center of the attachment box, by means of two ordinary iron hinges. Inside of this attachment box are two movable metal plates, one at either end, each carrying a mirror.
The mirror which faces the light source when the attachment is in use, is of metal, highly polished, and slightly convex. The other mirror is plain flat glass, about 4 inches wide by 6 inches long. These mirror holders are both adjustable. The convex mirror facing the light source is, by means of knurled thumbscrew on the side of the box, so adjusted that it reflects the light to the flat glass mirror at the other end of the attachment. The flat glass mirror is then adjusted, by means of two knurled thumb-screws, so that it reflects the light through a piano convex single lens condenser, held in front of the slide, and the.nce onward into the projection lens.
All this sounds quite complicated, but is really very simple. The attachment is placed permanently and locked in place by means of the hinges and a conveniently located latch. When it is desired to project motion pictures, the convex mirror is merely moved back against the end of the box, which leaves