120 Mr. L. Schwendler on the General Theory 



The first of these, we find, is that the invention was in ad- 

 vance of the requirements of the age. Telegraph-lines had 

 already been constructed which were quite capable of carrying 

 the given traffic and even more. Further, any increase in traffic 

 could be easily met by an increase in the number of wires on the 

 existing telegraph-posts, instead of by resorting to a system which 

 had a complex appearance, and after all might not answer. 



However, although the above considerations explain the course 

 of events in certain limited instances, and up to a certain time, 

 they do nothing towards justifying the costly expedients that 

 have been generally adopted until recently in preference to in- 

 troducing duplex telegraphy — for instance, the reconstruction 

 and multiplying of long overland lines, and especially the laying 

 of a second submarine cable when the traffic became too great 

 for one. 



It is true that the successful application of any duplex me- 

 thod requires lines of a more constant electrical condition, re- 

 ceiving-instruments of a larger range*, and telegraph-operators 

 of a somewhat better professional education ; but surely these 

 three conditions have not all at once become fulfilled (since 1872), 

 so as. to make duplex telegraphy possible only just now? No; 

 the causes which have delayed its introduction so long have 

 been of a much less technical and more irrational nature. 



The mere fact of the duplex methods appearing complex pre- 

 vented telegraph-administrations from thinking seriously of in- 

 troducing them. The ingenious methods were never tried with 

 that zeal and perseverance which is necessary to carry a new 

 invention successfully through. They were indiscriminately 

 rejected after a few trials made without method or considera- 

 tion j and the real conditions of success or failure were never 

 examined or pointed out. Thus naturally a prejudice was 

 created against duplex telegraphy, and it was fostered by a 

 host of school literature up to the latest time, as pointed out 

 before. Further, not a single physicist or electrician investi- 

 gated the question with a view to ascertaining what quanti- 

 tative effect the variable condition of lines has on duplex work- 

 ing as compared with single working. 



If such an investigation had been made, it would have been 

 found that the technical obstructions in the way were by no 

 means so formidable as had been represented, and that the 



* By the " range " of a telegraph-instrument I understand the ratio of 

 the largest to the smallest force by which the instrument in question can 

 be worked without requiring afresh mechanical adjustment. For instance, 

 Siemens's beautiful relays can be easily adjusted to a range of 20 ; i. e. 

 they can be made to work with one cell through an external resistance 

 equal to their own resistance, and with ten cells through no external resist- 

 ance, without giving the tongue a fresh adjustment. 



