1897.] on Signalling through Space without Wires. 469 



neighbourhood is tben fouud in a state of stress forming what is 

 called a magnetic field. 



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

 surge to and fro with rhythmic regularity, exciting electric icaves 

 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 regularity — but with very diiferent frequencies — and 

 originate electromagnetic 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 housetops, 80 feet away. Ordinary tele- 

 graph circuits were found in 1885 to produce disturbances 2000 feet 

 away. Distinct speech by telephone was carried on through one 

 quarter of a mile, a distance that was increased to 1 j mile at a later 

 date. Careful experiments were made in 1886 and 1887 to prove 

 that those ejects 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 utilising parallel wires 

 on each side of the channel and transmitting signals across this 

 space by these electromacjnetic waves. 



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



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

 undulations per second in the primary wire. 



(h) An ordinary battery of about 100 Leclanche cells, of the 

 so-called dry and portable form. 



(c) A Morse telegraph key. 



(d) A telephone to act as receiver. 



(e) A switch to start and stop the rheotome. 



Good signals depend more on the rapid rise and fall of the 

 primary current than on the amount of energy thrown into vibration. 

 Leclanche cells give as good signals at 3*3 miles distant as 2 J H.P. 

 transformed into alternating currents by an alternator, owing to the 

 smooth sinusoidal curves of the latter. 260 vibrations per second 

 give a pleasant note to the ear, easily read when broken up by the 

 key into dots and dashes. 



In my electromagnetic system two parallel circuits are estab- 

 lished, one on each side of a channel or bank of a river, each circuit 

 becoming successively the primary and secondary ot an induction 

 system, according to the direction in which the signals are being 



Vol. XV. (No. 91.) 2 i 



