AUTOMATIC AND MULTIPLEX TELEGRAPHY. 11 



The advantage of such arrangement in rapid signalling is that the line is connected 

 to earth through a path of no appreciable resistance between each signal, the cessation of 

 the signal and the grounding being simultaneous ; thus the largest portion of static 

 induction escapes at the transmitting end, leaving the minor portion to be contended 

 with at the other terminus. 



After passing through the recorder the current reaches the condenser and thence to 

 earth, controlled in the usual manner by resistance coils. 



The electric signal, after leaving its record upon the chemically prepared paper, 

 enters and charges the condenser to a degree more or less approaching its own potential. 

 When the signal impulse begins to weaken, the static charge near the receiving end tends 

 to follow and prolong the record, but is met by the coiinter charge of the condenser, and 

 is thus neutralized, the resistance in the condenser shunt being from four to six times 

 greater than that of the line. 



Herein is shown the further advantage of the perfect grounding of the line at the 

 sending end by the more complete discharge of the condenser between each signal ; for if 

 the usual arrangement of transmission by direct open and close contact of line and bat- 

 tery be substituted, the condenser becomes so completely charged after two or three sig- 

 .nals that no further record can be obtained unless the resistance in the shunt is so far 

 reduced as to impair its clearness. 



Hitherto automatic systems have worked best in wet weather, owing to the lessened 

 static induction from leakage ; but the new system works equally well in all weathers. 

 It is also free from the necessity of continuous readjustments. 



The record obtained is also remarkably well defined even at the reported speed of 

 3,000 words per minute over a copper wire of two ohms per mile resistance and 351 

 miles in length, experimentally utilized, between New York and Washington cities. 



Again repeated work at 600 words per minute has been produced over a copper-wired 

 line between New York and Chicago, 1,02*7 miles in length, as clearly as it would have 

 been by direct transmission. {Vide Plate No. 1.) 



The possibility of obtaining a multiplicity of signalling circuits in a given line wire 

 by methods other than those comprised in quadruplex telegraphy is presented in the 

 systems that have been devised to transfer the line wire from one set of instruments to 

 another similar set successively at both ends of the circuit, and thus afford to each cor- 

 responding apparatus an intermittent connection so rapidly recurring as to be practically 

 continuous. This is the principle of the established Delany system, whereby six circuits 

 can be obtained on a single line wire. 



It has, however, been found in practice that such number of circuits are limited to 

 100 mile distances, or four over 200 miles. Again the receiving apparatus is actuated by 

 currents emanating from the transmitting end only, and thus rendering the system inap- 

 plicable for intermediate stations. Thirty-four current impulses per second = three 

 impulses per dot signal, are also necessary for operating it at the ordinary maximum rate 

 of transmission. 



By the Keeley system signals are manifested by pulsations emanating from both ter- 

 minal stations concurrently, such currents being of alternative polarity, occurring twenty- 

 four times in a second, the position of each key in the circuit determining the polarity of 

 the current passing through it. 



