Page:Popular Science Monthly Volume 70.djvu/324

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pany found it advisable to sanction the addition of a secrecy-switch to the magneto bells supplied by the different manufacturers. One form of this lock-out switch is shown on the front of the magneto box in Fig. 25. Removing the receiver or hand telephone from the box caused the latter to fly up, just as the hook on the side of the modern telephone does. If the subscriber desired to converse with some one on the line to the right of his telephone, he would turn the switch to the right, thus shutting out all subscribers to the left, but still leaving it possible for eavesdroppers on the right to listen in. If the switch was turned to the left, the subscribers to the right were cut out. To operate the bell it was only necessary to turn the crank at a moderate speed and at the same time to press the button underneath the box the number of times that corresponded with the number of rings required to call the given station.

The next change came in the adoption of the first of the vertical boxes as a transmitter in connection with the magneto-call bell, and the use of the hand telephone as a receiver. In method of operation both instruments were identical, either could be used as transmitter or receiver, and both were fastened to the wall side by side (Fig. 26). The approved method of calling then in vogue is also shown (Fig. 27). The circular of instructions sent out with this early wall set read:

PSM V70 D324 Wall mounted transmitter and receiver units.png

Fig. 26.