﻿G L. Schwendler — On the general Tlieory of Duplex Telegraphy. [No. 1, 



Great lionour must therefore be given to Mr. Stearns who brought up 

 the subject again so prominently, and who by his zeal succeeded in introdu- 

 cing it on a large scale, and so elevated the ingenious methods from the ques- 

 tionable position of " interesting scientific experiments." 



I think far less of his idea of introducing condensers or Ruhmkorff's coils 

 to balance the charge and discharge of lines, than of his having taken the 

 neglected child up again, against the prejudice of his own profession, and 

 shown that it could have a healthy existence even in the backwoods of 

 America. I trust that these remarks will not be considered irrelevant in the 

 present investigation, since they tend to shew how real progress in one of 

 the youngest branches of applied science may be retarded for a considerable 

 period by nothing but prejudice of the profession themselves, for whom pro- 

 gress should be the first essential ; and administrations will see how much 

 the advance of Telegraphy will always depend on their recognizing and 

 encouraging by experiment inventions that are theoretically sound and tend 

 in the right direction. 



General Consideeations. 



Before entering on the solution of the problem for any particular 

 duplex method, it will be advisable once for all to state definitely the nature 

 of the general question before us. This will not only save time, but the 

 subsequent special solutions can then also be made under a general guide, 

 and thus being well linked together, the whole investigation will become 

 far more lucid and concise than it otherwise would be. 



While in ordinary (single) Telegraphy the signals are always produced 

 in the same way, i. e., by the signalling current arriving through the line 

 from the distant station, the signals in Duplex Telegraphy may be produced 

 in either of two ways, essentially different from each other. Namely, if the 

 times of sending from the two stations fall together, i. e., no current, or 

 double current, or any difference of currents, is in the line, the signals, so 

 long as this state of the line exists, are produced wholly or partly by the 

 battery of the receiving station. Signals produced in this way we shall 

 call " duplex signals," and these signals alone indicate the essential 

 difference between duplex and ordinary Telegraphy. 



If, however, the moments of sending from the two stations do not fall 

 together, the signals are then produced as in ordinary telegraphy, and may 

 be appropriately designated " single signals." 



It will be " clear then that when the two stations are at work at the 

 same time " duplex signals" and "single signals" must necessarily follow 

 each other in accidental succession. Nay, one and the same signal 

 produced in either station may be partly a " duplex" and partly a " single" 

 signal. 



