106 



METHODS OF COMMUNICATION FOR FOREST PROTECTION 



Equipment necessary: One 47-A repeating coil, two double-pole, double-throw, 

 baby knife-switches, one double-pole, single-throw, baby knife-switch, one extension 

 bell, and one telephone set. This circuit is arranged with one, telephone and signal 

 bell, so that a person at the station may talk on either line by using the same telephone. 

 The operation of the switches is as follows: Switch 1 closed down, switch 2 open, 

 switch 3 closed telephone on metallic line direct. Switch 3 open, switch 1 closed 

 down, switch 2 closed down telephone on grounded line direct. Switch 3 closed, 



Fig. 60 



Connecting grounded to metallic line by use of switches and one 

 telephone 



switch 1 closed up, switch 2 closed up grounded line cut on to metallic line through 

 repeating coil direct, instrument remaining across entire line. This circuit is so 

 arranged that the instrument may be left on the grounded line and the extension bell 

 will ring if a person at this station on metallic line is called. Switches 1 and 2 should 

 never be closed down at the same time without opening switch 3, as by so doing the' 

 metallic line would be made very noisy. 



6 SUPERIMPOSING TELEPHONE ON TELEGRAPH CIRCUIT 



It is readily possible to use a telegraph line either grounded or metallic for simul- 

 taneous telephone service without interference, providing automatic sending-instru- 

 ments are not being used on the telegraph circuit or on adjacent ones on the same 

 poles. At least two distinct methods of superimposing are employed, each of which 

 has several modifications affording a considerable number of different systems adapted 

 to various conditions. It will usually be found that the object sought is to employ 

 an existing telegraph line for forest protection telephone service, but since the exact 

 system that must be used will depend in each case on the arrangement and character- 

 istics of the telegraph circuit it will be necessary that each case be referred separately 

 to the district inspector for instructions. When reporting to the inspector state the 

 number of telegraph wires available, whether they are operated as grounded or metallic 



