i877-] 
Recent Advances in Telegraphy. 
367 
Following Stark and Bosscha, other electricians in Europe 
during the following year invented methods for effecting the 
same purpose — notably Drs. Werner Siemens, Kramer, and 
Bernstein, of Berlin. All these early methods agree in 
principle, although they differ in detail. The problem of 
double transmission implies the use of two keys or sending 
instruments at one end of the line, and of two or more 
receiving instruments at the other. The use of two keys 
simultaneously involves four combinations of their action, 
namely 
1. When No. 1 is closed and No. 2 is open. 
2. When No. 2 is closed and No. 1 is open, 
3. When both are closed. 
4. When both are open. 
These four conditions of the key should give rise to four 
distinct electrical conditions of the line, which are capable 
of being interpreted by the receiving relays. In the method 
of Bosscha, Kramer, and others, these electrical conditions 
were, for— 
1. A positive current of strength 1 sent. 
2. A negative current of strength 1 sent. 
3. A positive or negative current of strength 2 sent. 
4. No current sent. 
They were interpreted at the receiving end of the line by 
one polarised and two neutral relays. In the method of 
Stark, Siemens, and others, the eleCtrical conditions were— 
1. A positive current of strength 1 sent. 
2. A positive current of strength 2 sent. 
3. A positive current of strength 3 sent. 
4. No current sent. 
These were interpreted at the receiving end of the line by 
three neutral or unpolarised relays of different degrees of 
sensitiveness. 
The defects of these early systems lay in part with the 
keys and in part with the receiving relays. When the keys 
were being worked there were momentary interruptions of 
the line-circuit in changing from one contaCt to another. It 
was found to be a difficult matter to keep the three relays 
at their proper degree of sensitiveness in Stark’s system. 
In Bosscha’s system the sudden reversal of magnetic po- 
larity in the neutral relay, caused by the reversal of currents, 
had the effeCt of breaking up the signals of the neutral 
relay. These difficulties, however, might all have been 
overcome had it not been for the additional disturbances or 
kicks ” due to the static induction of the line. These 
