238 TELEGRAPHY ACROSS SPACE. 



telegraphs in the signal boxes of the railways in South London were 

 temporarily put out of order and rendered inoperative, while the 

 currents flowing in the earth were perceived in the telegraph instru- 

 ments so far northward as Leicester and so far south as in Paris. If 

 this could occur as a mere accident, it is obvious that, with properly 

 thought out arrangements, signals could easily be sent from one part 

 of the globe to another by conduction through earth or water. 



Most striking of all the cases of distance signaling by conductive 

 methods is that presented by the transmission of signals over nearly 3 

 miles, which was carried out in 1894 by Dr. W. Eathenau, Mr. E. 

 Rathenau, and Professor Rubens. They selected as a suitable place for 

 operations the open water of the Wannsee, which opens into the Havel, 

 near Potsdam. Here at the south end, near the Friedrich-Wilhelins- 

 briicke, they immersed two metal electrodes, each having about 15 

 square meters of surface, at the two ends of a base line about 550 feet 

 long. With 75 accumulators and a rotating interrupter, giving about 

 150 currents per second, and a Morse key they injected signals into 

 the base line. At a distance of 4£ kilometers, or nearly 3 miles 

 across the water, near the shore at Neu Cladow, they set up the 

 secondary base line, having electrodes of about 4 square meters each. 

 These were hung in the water from two boats between which the 

 connecting line, about 330 feet long, was stretched. In this line was 

 inserted a telephone receiver of usual pattern. The current used was 

 about 3 amperes, and there was not the slightest difficulty in hearing 

 the dot-and-dash messages. Several situations for the receiving base 

 line were tried ; it appeared that the interposition of a large sand bank 

 between the two stations made very little difference. 



II. — INDUCTION METHODS. 



Induction methods are of two varieties. An electric charge upon a 

 conductor may induce another electric charge at a distance by influence, 

 or electrostatic induction. An electric current in a wire, during such 

 time as it is increasing or diminishing, may induce another electric 

 current in another wire in its neighborhood by electro- magnetic 

 induction. 



So far as I am aware, the only case in which electrostatic induction 

 has been used in electric signaling is that of telegraphing (or telephoning) 

 to trains in motion, as suggested about thirteen years ago by Mr. 

 Wiley Smith, of Kansas City. If a wire suspended over a train is 

 electrified, either positively or negatively, charges are induced upon 

 the metallic roofs of the cars, and if these are suitably connected to 

 instruments on board the train, signals may be exchanged between 

 train and wire without any metallic connection between the two. This 

 suggestion was further developed about the year 1886 by Mr. Phelps 

 and by Messrs. Gilliland and Edison. Descriptions of their methods 

 will be found in the American electrical journals of that date. The 



