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POPULAR SCIENCE MONTHLY 



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. Kemoving 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 under- 

 neath 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 : 



LINE 



Fig. 26. 



