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208 AMATEUR TALKING PICTURES
The equipment is simple, and owes its success primarily to the principle mentioned above. In all previous systems, so far as the writer is aware, synchronism between disc and projector is obtained in a continuous manner. That is to say, the turntable revolves continuously, and is either mechanically or electrically coupled to the projector, which also turns continuously and in direct ratio to the speed of the turntable.
In the new system the turntable revolves continuously but, the projector is intermittent only. As the turntable revolves it actuates electrical contacts which send impulses to the projector via suitable leads. Thus in the case of projecting four pictures per second, four electrical impulses are given from the turntable per second, which are impressed upon the electrical mechanism of the projector. At each impulse the mechanism of the projector drags down the film one picture length.
The experimental model tested by the writer is shown in Fig. 90, where at A we see an ordinary portable gramophone. Attached to the baseboard is a special type arm which lifts out of position for the placement of a record, and is held pressed tightly to the face of the record by suitable springs. The fixing of this arm to any gramophone takes only a few minutes with a screw-driver.
At B is the projector. The arm contains the contactmaking mechanism which is fed through wires running between the arm, projector, and mains plug which can either be plugged direct into the supply or alternatively be worked through the medium of storage batteries. This incidentally is another interesting feature of the system, namely that it can be employed in localities where electric fight is not yet available.
The actual principle of working of the projector is unique. No claws of any description are employed, and the intermittent movement takes place by means of a large sprocket wheel which engages three or four perforations of the film. We are at the present moment speaking of 16 mm. film, although, of course, the equipment can be made in 9 mm. without difficulty.
Reverting to the projector mechanism we find that the