SIGNALING THROUGH SPACE WITHOUT WIRES. 



251 



In the first case the charges can be made to rise and fall, and to 

 surge to and fro with rhythmic regularity, exciting electric waves along 

 each line of electric force at very high frequencies, and in the second 

 case the currents can rise or alternate in direction with the same regu- 

 larity, but with very different frequencies, and originate electromag- 

 netic waves whose wave fronts are propagated in the same direction. 



The first is the method of Hertz, which has recently been turned to 

 practical account by Mr, Marconi, and the second is the method which 

 I have been applying, and which, for historical reasons, I will describe 

 to you first. 



In 1884 messages sent through insulated wires buried in iron pipes 

 in the streets of London were read upon telephone circuits erected on 

 poles above the house tops, 80 feet away. Ordinary telegraph circuits 

 were found in 1885 to produce disturbances 2,000 feet away. Distinct 

 speech by telephone was carried on through one-quarter of a mile, a 



CURRENT BREAKER 



UNE. 



Fig. 1. — Diagram of connections of Mr. Preece'a system. 



distance that was increased to 1£ miles at a later date. Careful experi- 

 ments were made in 1880 and 1887 to prove that these effects were due 

 to pure electromagnetic waves, and were entirely free from any- earth- 

 conduction. In 1892 distinct messages were sent across a portion of 

 the Bristol Channel, between Penarth and Flat Holm, a distance of 3.3 

 miles. 



Early in 1895 the cable between Oban and the Isle of Mull broke 

 down, and as no ship was available for repairing and restoring com- 

 munication, communication was established by utilizing parallel wires 

 on each side of the channel and transmitting signals across the space 

 by these electromagnetic waves. 



The apparatus (fig. 1) connected to each wire consists of — 

 (a) A rheotome or make and break wheel, causing about 260 undula- 

 tions per second in the primary wire. 



