714 



TELEGRAPHY, WIRELESS. 



Telegraphy by Earth or Water Conduction. 



The earliest experimenters on telegraphy without 

 connecting wires endeavored to utilize the conduc- 

 tivity of water or earth. As earlv as 1842 experi- 

 ments along this line, due to S. F. B. Morse, were 

 carried out by Gale on the Susquehanna river. 



In 1854 James Bowman Lindsay, a teacher of 

 Dundee, Scotland, patented a device for establish- 

 ing electrical communication through water with- 

 out connecting wires (see Fig. 1), and in the same 



FIG. 1. 



year he thus telegraphed across a body of water 

 500 yards wide, at Portsmouth, England. In 1859 

 he telegraphed across the Tay at Glencarse, where 

 it is half a mile wide. Since Lindsay's time similar 

 results have been obtained elsewhere, and numerous 

 patents have been taken out in various countries. 

 In England the Solent was traversed by messages 

 in 1882, and in 1896 the English postal telegraph 

 communicated with Fastnet light by a conduction 

 method due to Willoughby Smith. In India prac- 

 tical communication has been kept up across rivers 

 by a system devised by Melhuish. In France some 

 experiments by Abbe Michel have successfully 

 utilized the conductivity of moist earth, using tele- 

 phones as receivers and transmitters. These 

 methods, however, do not promise success at con- 

 siderable distances, and are much interfered with 

 in cities by leakage currents, and by short circuiting 

 due to pipes arid rails. An application of this 

 method to signaling between ships seems to offer a 

 chance of success. In the patent granted in Ger- 

 many to Somzee in 1888, " each ship carries a pair 

 of plates submerged in the water, one at the bow, 

 the other at the stern, the plates being connected by 

 wires which include a signal-receiving instrument, 

 such as a telephone or a galvanometer. Shoals 

 may be indicated by suitable stationary plates, the 

 current from which is diverted into the receiving 

 circuit on the ship whenever the vessel approaches 

 shallow water." Similar methods have been pat- 

 ented in Great Britain by Stevenson in 1892, and in 

 the United States by Blake in 1894. In a report to 

 the General Electric Society, Rathenau (" Elektro- 

 technische Zeitschrift." Nov 8, 1894) suggested that 

 a telephone receiver be used to receive the signals. 

 " The metallic diaphragm of the telephone would 

 be replaced by a light tongue, which should be 

 tuned to respond to the predetermined rate of vi- 

 bration of the transmitting circuit. This rate 

 would be imposed upon the circuit by a suitable 

 tuning fork operating a circuit breaker." The in- 

 vestigator stated that communication had been 

 effected over a distance of 3 miles. (See also " Uses 

 and Limitations," at the end of this article.) That 

 wireless telegraphy by conduction through earth 

 may have possibilities before it is shown by an ac- 

 cident that occurred in the Ferranti electric-light- 



ing station at Deptford, London, about 1888. One 

 of the dynamos became connected to earth at night, 

 with the result that every telegraph in South Lon- 

 don became unworkable, and the effect on electrical 

 apparatus was detected in the central counties of 

 England, and even as far away as Paris. Prof. 

 Thompson, discussing this accident, concludes that 

 " it is obvious that by proper forethought and due 

 expenditure of money on the requisite machinery a 

 telegraph without wires might be established be- 

 tween London and Paris, or for that matter between 

 any two places. It is believed by Nikola Tesla that 

 by properly disturbing the earth's electric charge, 

 signals can be transmitted to any point on the 

 earth's surface, and he claims to have obtained ex- 

 perimental evidence of this ; but other electricians 

 believe this result to be beyond the power of any 

 apparatus yet invented, and explain his experi- 

 ments differently. 



The same electrician has patented a method of 

 transmitting electric energy by conduction through 

 the upper air, which becomes a conductor when 

 sufficiently rarified, and for oscillatory currents of 

 very high frequency. He believes that great 

 quantities of energy can thus be transmitted, and 

 proposes to operate automobile torpedoes without 

 connecting wires ; but it does not appear that his 

 inventions have reached the practical stage. The 

 experiments of Prof. John Trowbridge, of Harvard, 

 support his theory of the conductivity of the upper 

 air; but Prof. Trowbridge believed that it would be 

 impossible to avoid vertical leakage to the earth. 



But the greatest success in long-distance electric 

 telegraphy without direct wires has been obtained 

 not by conduction but by induction. The earliest 

 form of wireless induction telegraphy was probably 

 that employed in signaling to a moving train. The 

 first patent to describe such a method was issued to 

 Smith (No. 247,127, Sept. 13, 1881), and numerous 

 others followed, including one to Edison (486,634, 

 Nov. 22, 1892). In Smith's method (see an article 

 by William Bissing, " Electrical World," Jan. 21, 

 1899) " the metallic roof of the car, which should be 

 insulated, is connected to a wire which leads to one 

 terminal of a telephone receiver, the other terminal 

 of the receiver being grounded through the wheels 

 and rails. A telegraph line is strung along the 

 track in closer proximity to the car than is custom- 

 ary for Morse signaling. On telephoning over the 

 line from a station on the road the car roof is af- 

 fected inductively, and a current is produced in the 

 receiver on the car, the line and the roof forming 

 the two plates of a condenser. An advantage of 

 this method of transmitting signals is that the line 

 wire along the track may be used for telegraphing 

 according to the ordinary Morse system, without 

 disturbing the telephonic 'signals. The current in- 

 duced in the car circuit in this patent is probably 

 due to both electro-magnetic and electrostatic induc- 

 tion." 



Successive improvements have been made in these 

 methods, which are mentioned here only on account 

 of their historical interest in connection with wire- 

 less telegraphy. Of experiments in space tele- 

 graphy proper, the earliest methods have used dy- 

 namic and the latest static electricity. 



Telegraphy by Dynamic Induction. The fact 

 that an electric current passing through a wire cre- 

 ates a magnetic field around it has been known 

 since the time of Ampere, and the fact that an 

 electric current is set up in a second neighboring 

 wire by any variation in the field, due to motion of 

 either wire or to variation of the current, has been 

 known since Faraday's researches in 1831. It was 

 scarcely realized to what a distance such a magnetic 

 field might extend until the invention of the tele- 

 phone gave a means of detecting very slight varia- 



