1909] 



on Modern Submarine Telegraphy. 



533 



In the mechanical iUustration I have therefore indicated the 

 weights B and W as squares having this proportion, to give a visual 

 indication of what this means in the balance. 



The proportion I have given is only the relation of tlie sending 

 voltage to that received. 



If the balance were out to this proportion, the sending voltage 

 would affect the receiver with disturbances equal in size to those due 

 to the receiving voltage: the duplex would then be very badly indeed 

 out of balance. 



To receive properly, the sending voltage must produce no move- 

 ment of the receiver whatever ; that is to say, that any disturbance 



w 



S AL 



Fig. 6. 



Fig. 7. 



RR are the two resistances or the arms of the balance. 

 S is the receiver or indicator, which shows a differ- 

 ence of voltage or weight. 

 B is the battery voltage or weights in the pan. 

 C and AL are cable and artificial line respectively, 

 or the two pans of the balance. 



due to this cause must certainly be under j-V ^^ that due to the arrival 

 current. 



Taking the figures I have given, we see that the balance must be 

 obtained and maintained so that applying -lO volts to the cable and 

 artificial line, the two currents dividing must not vary more than 

 what will produce ^^^ volt ; that is, must be balanced to an accuracy 

 of 8000 to 1. 



If, after the duplex has been established, the artificial line varies in 

 its electrical properties as much as « oVo of its value, the balance would 

 require adjustment so as to keep it useful for receiving. The sensi- 

 tiveness under these conditions may be considered as equivalent to the 



