Motography (Jan-Jun 1913)

276 MOTOGRAPHY Vol. IX. No. 8 move a rod that acts on the safety shutter. A spring that acts on the revolving weights places a limit on the allowable shutter travel for any given speed, hence the rise of the weights is roughly proportional to the speed of the crank and spindle. To reduce the danger of having flame spread back into the feed reel, it is customary to enclose all of the film, except that immediately in front of the lens, in a fire-proof metal casing. A metallic tube, placed around the film issuing from the reels, smothers the flame before it travels more than an inch, with the result that only a few pictures are burned in the vicinity of the aperture. This, however, does not prevent possible interruption of the show, nor does it insure complete protection against the loss of the reel of film, for it is possible for the operator to neglect closing the access doors of the magazine. FEED AND TAKE-UP REELS. The reels upon which the film is wound are invariably encased in metal shields called "magazines," which are directly attached to the motion head. Circular doors ■ .«* i ■ ^N^W^'^M JK / fijt — UfcSfW j 7 -^P/^UiiiH If I;1 L 1 . f ?\;$ ii ru Fig. 16. — View in the Operating Booth of a Motion Picture Theater, With the Projector in the Foreground. At the Rear, One of the Operators is Rewinding a Film. located in the sides of the magazine allow the operator to insert and remove the reels of film. A spindle is provided on which the reel turns freely as the film is wound and unwound by the action of the feeding mechanism. The feed reel is simply a spool having two metal flanges about ten inches in diameter, and a core that is provided with a spring clip for holding the end of the film. Fig. 14, shows a reel of film ready for mounting in the projector. The take-up reel is the same as the feed, except that is is mechanically driven through a belt by the operating crank instead of by the pull of the intermittent feed mechanism. As the take-up reel receives the film from the feed reel, the roll of film becomes larger and larger in diameter, and therefore revolves more slowly than the feed reel from which the film is unwound. To compensate for this difference in speed, it is necessary to have the take-up reel slip in regard to the feed reel to prevent excessive strain on the delicate film. This is accomplished in some machines by means of friction discs attached to the reel drive adjusted so that it is possible to apply only enough power to turn the reel, and not enough to snap the film. In other machines the tension of the belt is adjusted so that it will slip when too much pull is exerted on the film. Since all friction devices wear in time and cause trouble by getting out of adjustment it would seem that a differential gear, such as used on spinning machinery, could be applied with advantage to the projector. The action of the differential insures constant tension on the strand at all times, and is not influenced by wear. REWINDING THE FILM. After the film has been projected, and is completely wound on the take-up reel, it is necessary to rewind it on the feed reel so that the pictures will again go through the projector in the proper order. If the film were fed into the machine directly from the take-up reel the pictures would appear reversed upon the screen. Rewinding may either be accomplished directly on the projector, or by a separate rewinding machine which is generally driven by a motor. In many states a rewinding machine is necessary because of the laws that prohibit rewinding in the operating booth. When the film is to be rewound on the projector, the operating crank is arranged so that the speed of rewind is much greater than the ordinary projecting speed. This makes it possible to rewind a film in two minutes that took twenty to project. The rewind speed may be obtained either by shifting a lever on the machine, or by transferring the crank to an independent rewind shaft. MOTOR DRIVE FOR PROJECTORS. Motor driven projectors have many advantages but are prohibited in practically all of the larger cities as the use of the motor makes it possible for the operator to leave the machine when in operation. If the motor should stop, or the film break during his absence the chances for a disastrous fire would be greatly increased over the ordinary method of operation. Practically the only remedy for this condition would be a spring controlled switch that would cut out the light as soon as the operator removed his hand from the machine, making it impossible for him to leave the booth with the machine running. As it is difficult to construct a switch so that it cannot be tied or braced in the running position by the operator, the use of the motor has so far been condemned. Some progress in designing automatic stops for motor driven projectors has been made, however. THE SCREEN. The screen acts simply as a reflector, the function of which is to reflect every image thrown on it by the projector back into the eyes of the audience. With a screen having a high reflecting value, it is possible to secure bright pictures with a small amount of current in the lamp, which naturally gives a low operating cost. In the attempt to cut down the current consumption of the lamp, and to increase the brilliancy of the screen image, many manufacturers have conducted experiments with different materials such as aluminum, aluminum bronze, and mirrors with ground surfaces for use in building screens. The aluminum has been used both in the metallic form, and in the form of bronze paint which has been applied either on the plaster of the wall or on muslin screens. The mirror screens, while having a high first cost, have proved very efficient. The selection of a proper screen material is of great importance to the theater owner, both in regard to operating economy, and to the attractiveness of the show. With the usual rates for illuminating current, a mirror screen or aluminum screen will soon pay the difference in first cost over the common muslin or plaster surface. The relative values of the different surfaces are given in the