TELEGRAPHY ACROSS SPACE. 237 



With this arrangement signals were passed in dot and dash which 

 could be read on the Morse system with ease, but telephonic speech 

 was not feasible. After many other experiments to be mentioned under 

 the next heading, Mr. Preece established communication, in the winter 

 of 1893-94, across the Kilbrannen Sound between the Isle of Arran and 

 Kin tyre, a distance of over 4 miles. He also maintained telephonic 

 speech across Loch Ness, a distance of 1J miles. 



In the experiments from Arran to Kintyre, parallel wires about 3 

 miles long were used as base lines along the coast, while in some of 

 the experiments two other base lines were used, being insulated wires 

 laid along each coast at a height about 500 feet above the sea level. 

 A detailed account of these experiments will be found in the report of 

 the British Association for 1894, and is also given in The Electrician, 

 Vol. XXXIII, August 17, 1891. 



A year earlier Mr. Preece had made some striking experiments in the 

 Bristol Channel between Lavernock Point on the South Wales coast 

 and the islands of the Flat Holm and the Steep Holm, the distances of 

 which are respectively 3.1 and 5.35 miles. His base line on the shore 

 at Lavernock Point was a pair of copper wires, weighing 400 pounds 

 per mile, suspended on poles for a length of 1,267 yards, their circuit 

 being completed through earth. An alternating current was sent into 

 this base line by an alternator worked by a 2-horse power steam engine, 

 the voltage being 150 volts, the frequency 192 periods per second, and 

 the current (maximum) 15 amperes. These alternations were broken 

 up into dots and dashes by use of a Morse key. The signals were read 

 on a pair of receiving telephones inserted in the distant base line, 

 which, in each case, ran across the island and dipped into the sea. 

 The length of these is not stated. Mr. Preece received messages easily 

 over the 3 miles separating the mainland from the Flat Holm, but with 

 Steep Holm 5. 35 miles away, though the signals were feebly perceptible, 

 telegraphic conversation was impracticable, as the sound could not be 

 differentiated into dots and dashes. Mr. Preece came to the conclusion 

 that with two base lines, each 10 miles long, he could with ease signal 

 across a distance of 10 miles. 



Professor Trowbridge, of Harvard, has also investigated the possibility 

 of transmitting signals through the earth by conduction, using a rapidly 

 interrupted primary current and a telephonic receiving apparatus. 



Many experiments have been made under accidental circumstances, 

 all tending to prove the possibility of this mode of transmitting signals 

 through the earth itself. The instruments in Greenwich Observatory 

 are affected by the stray currents that escape into the earth from the 

 badly insulated return circuit of the City and South London Electric 

 Railway, 4J miles away. Another example is afforded by an accident 

 which occurred some ten years since at the Ferranti electric lighting 

 station at Deptford, when one night one of the dynamos by some 

 derangement became connected to earth. The whole of the railway 



