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MANAGERS AND PROJECTIONISTS 859
while pressing it down on the lens, tighten the thumbscrews so that it will be held securely. The holder may then be replaced in the lamphouse and the wing nuts returned to their original position to lock the holder in place.
THE REFLECTOR may be placed in position in its holder by resting it on the two lower spring clips, tipping it backward and raising the upper clip until it permits the reflector to slip into place. The clips are adjustable and should be so set that the mirror will be held firmly.
CLEANING REFLECTOR AND LENS.— See page 831.
ELECTRICAL CONNECTIONS.— Those who supply you the lamp will have complete knowledge as to the proper rheostats and connections to be made for each installation. The positive lead of D C circuits must be connected to the front carbon — the one nearest the condenser — and the negative to the other. The two leads from the arc control are connected to the projector table switch, on its dead side — the side which is electrically dead when the switch is open.
ADJUSTMENTS.— Move the lamphouse backward or forward until the front face of the converging lens (condenser) is approximately thirteen (13) inches from the film when it is in position in the projector. NOTE: This distance will vary somewhat with varying focal lengths of the projection lens.
When this has been done, loosen the lock nut on the feed screw handle of the lamp and turn the feed screw handle until the carbon holders of the lamp are separated to the limit of their travel. Insert the smaller diameter carbon in the rear or negative carbon holder, and the larger one in the other (positive) holder. IMPORTANT: So place the carbons that there is exactly the same length of each between the carbon holders.
By means of the adjusting handle immediately to the right of the feed screw handle, adjust the lamp carriage, or bed, so that it is at the central point of its movement backward and forward. Then loosen the thumb screw on the side of the reflector carriage (on the side toward the arc control) and pull the entire reflector assembly toward the rear.
CARBON SIZES. — For twenty to twenty-five amperes the manufacturer recommends a combination of 8 millimeter (See page 400^) negative and a 12 millimeter positive. For fifteen to twenty amperes use 7 mm negative and 10 mm positive. The lamp is fitted with carbon holders for the larger sizes, since