AN ISLAND ELECTRIFIED.

Tuapeka Times, Volume III, Issue 137, 22 September 1870, Page 3

AN ISLAND ELECTRIFIED.

A curious discovery has been made by Mr Gott, the Superintendent of the French Company's telegraph station at the little island of St. Pierre Miquelon. There are two telegraph stations on the island. One, worked in connection with the Anglo-American Company's lines by an American company, receives messages from Newfoundland, and sends them on to Sydney, using for the latter purpose a powerful battery and the ordinary Morse signals. The second station is worked by the French Transatlantic Company, and is furnished with exceedingly delicate receiving instruments, the invention of Sir Willaim Thomson, and used to receive messages from Brest and Duxbury. These very sensitive instruments were found to be seriously affected by earth currents, that is currents depending upon some rapid changes in the electrical condition' of the island ; these numerous changes caused currents to flow in and out of the French company's cables, intei-fering very much with the current indicating true signals. This phenomenon is not an uncommon one, and the inconvenience was removed by laying an insulated wire about three miles long back from the station to the sea, in which a large metal plate is immersed. The plate is used in practice as the earth of the St. Pierre station, the changes in the electrical condition or potential of the sea being small and low in comparison with the dry rocky soil of St. Pierre. After this had been done, it was found that part of the so-called earth currents had been due to the signals sent by the American company into their own lines, for, when the delicate recieving instrument was placed between the earth at the station and the earth at sea, so as to be in circuit with the three miles of insulated wire, the messages sent by the rival company were clearly indicated, so clearly, indeed, that they have been automatically recorded by the Sir William Thomson siphon rocorder. It must be clearly undcrsood that the American line came nowhere into contact with, or even into the neighbourhood of the French line. The two stations are several hundred yards apart, and yet messages set at one station are distinctly read at the other station ; the only connection between the two being through the earth ; and it is quite clear that they would be so received and read at fifty stations in the neighbourhood all at once. The explanation is obvious enough ; the potential of the ground in the neighbourhood of the station is alternately raised and lowered by the powerful battery used to send the American signals. The potential of the sea at the other end of the short insulated line remains almost if not wholly un iflected by these, and thus the island acts like a sort of great Leyden jar, continually charged by the American battery, and discharged in part through the short insulated French line. Each time the ihnerican operator depresses his sending key, he not only sends a current through his liucs, but electrifies the whole island, and this electrification is detected and recorded by the rival company's instruments. No similar experiment could be made in the neighbourhood of a station from which many simultaneous signals were being sent ; but it is perfectly clear that, unless special precautions are taken at isolated stations, an inquisitive neighbour owning a short insulated wire might steal all messages without any connection between his instrument and the cable and land line. Stealing messages by attaching an instrument to the line was a familiar incident in the American war ; but now messages may be stolen with perfect secrecy by persons who nowhere come within a quarter of a mile of the line.