EXTENSION OF THE TELEPHONE SYSTEM TO SHIPS 153 



four channel telephone or telegraph operation and for the control and 

 monitoring of all channels. In the operation of the system one 

 operator, located at this switchboard, has complete control of the 

 entire transmitting plant. The operating board was especially built 



Fig. 6 



for the experiments, and altho not the final form contains features 

 which are of interest in that they illustrate well the technique in- 

 volved in combined wire and radio operation. 



The four vertical rows of jacks correspond to the four two-way 

 radio channels. At the top of each row will be seen the dials for 

 controlling amplification. On the apron are telegraph keys, telephone 

 keys, and operating cords. The cord circuits, by being plugged into 

 the jacks, interconnect any one of the New York toll circuits with 



