DECEMBER 17, 1897. ] 
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 regularity—but with 
very different frequencies—and 
originate electro-magnetic waves 
whose wave fronts are propa- 
gated 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 telegraph circuits 
were found in 1885 to produce disturbances 
2,000 feet away. Distinct speech by tele- 
phone was carried on through one-quarter 
of a mile, a distance that was increased to 
14 miles at a later date. Careful experi- 
ments were made in 1886 and 1887 to 
prove that these effects were due to pure 
electro-magnetic waves, and were en- 
tirely 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 restor- 
ing communication, communication was es- 
tablished by utilizing parallel wires on each 
side of the Channel and transmitting signals 
across this space by these electro-magnetic 
waves. 
Soe 
SCIENCE. 
891 
CURRENT BREAKER 
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ADJUSTABLE 
RESISTANCE 
CRVING MOTOR 
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. Diagram of connections of Mr. Preece’s system. 
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. 
(b) An ordinary battery of about 100 
Leclanché 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 rheo- 
tome. 
Good signals depend more on the rapid 
rise and fall of the primary current than on 
the amount of energy thrown into vibration. 
Leclanché cells give as good signals at 3.3 
miles distant as 24 H.P. transformed into 
alternating currents by an alternator, ow- 
ing 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 electro-magnetic system two paral- 
lel circuits are established, one on each side 
of a channel or bank of a river,each circuit 
becoming successively the primary and sec- 
ondary of an induction system, according to 
the direction in which the signals are being 
sent. Strong alternating or vibrating cur- 
