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56 MOTION PICTURE PROJECTION
member 6a is provided at its inner end with a forward projecting stop 8a arranged to engage one edge of the opposite member 6. Each of the switch arms is provided with an operating handle 9, 9a, secured at or near the front end of the rotatably mounted holders 10, lOa, respectively.
The operation of the apparatus is as follows: When the switch arms 3, 3a, are in the position shown in Fig. 1, both are in the zero position in which no current is passing through either of the resistances. If it is desired to switch on the arc, connected with the contact studs 2, the switch arm 3 is rotated in an anti-clockwise direction, that is, into the position shown in full lines in Fig. 2 in which position the maximum amount of current is switched on in one circuit, while no current is passing in the other. If now it is desired to switch on the current in the circuit connected with the contact studs 2a, the switch arm 3a will have to be rotated in a clockwise direction as will be readily understood. The stops 8, 8a, on the inner ends of the members 6, 6a, are so arranged that the maximum movement of the switch arms is reached, when for instance, one arm is moved to the position in which the full current is allowed to pass and the opposite arm is in zero position. If the switch arm 3a is now rotated in a clockwise direction, the opposite arm 3 will be moved back towards its zero position, to a corresponding extent to which the switch arm 3a is advanced.
If it is desired to switch on full current in the circuit connected to the contact studs 2a, the switch arms will assume the position shown in dotted lines in Fig. 2, in which the switch arm 3 is returned to its zero position.