1909] on Modern Suhnarine Telegrapliy. 535 



The automatic transmitter is a motor-driven instrument, adapted 

 to feed the perforated ribbon over the ends of a pair of blunt needles. 

 These needles are kept perpetually moving up against and away from 

 the moving ribbon, but if there is a hole in the paper, that particular 

 needle over which it is fed will find it, and the needle will move a 

 little way through the hole. Attached to the two needles are con- 

 tact levers which connect the cable with one or the other pole of the 

 sending battery. 



When there are no holes in the paper ribbon, the needles move 

 up against the paper, and the further movement is arrested, and the 

 contact with the battery is not closed, but the battery circuit is closed 

 when there is a hole in the paper, because there is nothing now to 

 block the needle, and the further movement through the hole enables 

 the contact lever to close the battery circuit and thus send the signal. 



The sending levers do one or other of two things : they join the 

 cable to earth (in other words, they short-circuit the cable end), or 

 they disconnect the cable from earth and connect it to the battery, 

 so that the battery may send a signal. 



At the end of each signal the cable is automatically put to 

 " earth." 



Every signalling impulse due to each hole in the paper is, there- 

 fore, divided into two parts, the battery or signalling and the earth- 

 ing portion. These two portions are adjustable relatively to one 

 another ; when the best relationship has been found, it is maintained 

 at that adjustment. 



The object of earthing the cable after the battery contact is to 

 allow the cable to discharge itself, and thus clear itself for the next 

 signal. 



Automatic transmitters constructed on this principle are called 

 " plain " automatics, and are in universal use. 



The " curb " was a device applied to an automatic transmitter to 

 sharpen the signalling impulse, and thus gain greater definition and 

 increased speed by reversing the battery at the termination of every 

 battery period. The reverse battery voltage helped to neutralise the 

 charge already in the cable, and thus discharge the cable in quicker 

 time than by simply earthing the cable as in the " plain " automatic. 



Unfortunately, the use of the " curb " results in a greater voltage 

 stress on the sending end of the cable, for the reason that the reverse 

 voltage of the " curb " is added to the voltage already in the cable 

 ready to discharge, and the rapid reversal of current resulting upon 

 the application of the " curb " is liable to cause " jar " disturbances 

 on the duplex balance. For these reasons " curb " automatics are 

 not now employed. 



Instruments adapted to receive messages at the end of long 

 submarine cables must of necessity work at the highest possible speed 

 that the cable will allow, and are of extreme sensitiveness, and as a 

 consequence are of great delicacy. 



YoL. ZIX. (No. 103) 2 N 



