1909] on Modern Submarine Telegraphy. 539 



its local circuit precisely the same as the signals or combination 

 sent through the cable that work it and are at the same time causing 

 the variable zero. 



Current is therefore taken from tlie local circuit and passed 

 through an electrical retarding device, which is called the "local 

 correction circuit," consisting of a series of inductances and shunting 

 resistances. 



The local circuit is so adjusted in its value that the current at 

 the far end rises exactly as there is a drop in the received signalling 

 current through the series condenser. 



The correction current is passed through a separate winding on 

 the suspended coil of the relay, and produces an effect on the coil 

 exactly opposite to that produced on the main winding by the 

 variable zero itself, that is to say, two variable zeros of equal 

 strength but of opposite directions are superimposed on the suspended 

 coil, and thus neutralise one another. The variable zero of the signals 

 themselves is thus eliminated. 



Local correction is a very important part of the relay adjust- 

 ment, and cannot very well be dispensed with. 



During the last year the Eastern Telegraph Company have most 

 generously lent me their lines for a trial of my " high speed " 

 system of working. 



The cable over which the tests have taken place stretches from 

 Porthcurnow in Cornwall to Gibraltar, and is normally worked at 

 170 letters per minute, each way, with the siphon recorder as 

 receiver. 



With the new method, using a special relay (Fig. 9), traffic 

 has been carried continuously, duplex, at 230 letters per minute. 



On special trial runs, not carrying traffic, and not sending into 

 the cable at the receiving station, although on duplex conditions, 

 a speed of 280 letters per minute has been obtained. 



The principle of operation is as follows : When a submarine 

 cable is forced much beyond its normal speed of working the quick 

 changing signals, such as make up the letter c, are the first to fail, 

 or, in other words, do not arrive with sufficient strength to work the 

 receiver. 



It was found on trial that allowing more of the current from 

 the cable to flow through the receiver, say by increasing the size of 

 the receiving condenser, the first and last signal of a series of 

 reversals could be obtained with sufficient strength to efficiently 

 work the relay. 



The relay once started is arranged to bring in fresh energy from 

 its local battery, through a special retarding circuit, to add to the 

 strength of the quick-changing currents, on its own coil, and thus 

 the reversals are made strong enough to give a record, which without 

 this aid they would have been unable to do. 



