630 ELECTRICAL ENGINEERING 



of transmission of rapid electrical impulses for telegraphic pur- 

 poses seem to agree fairly well on one point at least; it is this: 

 The alternating current is the most suitable form of electrical trans- 

 mission for telegraphic purposes. The solution of the general tele- 

 graphic problem by means of automatic transmission, and by the 

 adoption of multiplex methods with all the possible refinements 

 of which these methods are capable, cannot be reached unless the 

 alternating-current method of transmission is adopted. But then 

 we should have in telegraphy the same practical difficulties which 

 telephone engineers met in the early days of telephony. These 

 difficulties are summed up by the telephone engineer and con- 

 densed into a single word, cross-talk. It means conveyance of 

 electric energy from one wire to another by electrostatic as well 

 as by electromagnetic induction. It is the more powerful the higher 

 the frequency of the alternating current employed in the trans- 

 mission. The telephone engineer overcame this difficulty gradu- 

 ally by giving up the employment of the earth as the common re- 

 turn conductor for all his transmission wires, and from that day 

 dates the symmetrical conducting loop of the metallic return cir- 

 cuit. Having adopted this expediency it was then a comparatively 

 easy matter to avoid cross-talk, due to induction, by a suitable 

 transposition of the neighboring circuits with respect to each other. 



The introduction of the alternating current into telegraphic 

 transmission would compel the telegraph engineer to resort to this 

 same expediency which was long ago adopted by the telephone 

 engineer, otherwise he would expose himself to the serious diffi- 

 culties arising from cross-signaling. 



Considering the fact that practically all telegraph lines in the 

 country employ the ground return, it is clear that the general in- 

 troduction of the alternating current into telegraph work would 

 involve practically a reconstruction of a large part of the vast 

 network of telegraph wires in the United States. I do not know 

 of a single telegraph engineer in this country who would have the 

 courage to assume the responsibility of advocating before his board 

 of directors a policy of this kind. And so, as far as this country at 

 least is concerned, the solution of the general telegraphic problem 

 seems to be a matter of the dim and distant future. 



