Fkbru.\by 1, 1900.] 



KNOWLEDGE. 



27 



from the souive, so that very little of the energy of 

 the source would reach this point, by far the larger 

 proportion being returned *o the soui'ce. 



We see. then, that the two conditions to be fulfilled 

 are diametrically opposed to each other, and it becomes 

 a matter for experimental investigation to determine 

 wh.at kind of wave lengths arc mo.st advantageous for 

 telegraph work under varying conditions as to distance 

 and other circumst^inces. 



The preceding brief outline of the principles under- 

 Iviug the Hertz wave method of wireless tclegraphv, 

 will enable the reader to follow the descriptions of ex- 

 periment^al work and practical details with greater 

 facility, and, I trust, also with greater interest, by 

 reason of his having obtained a general view of the 

 fascinating country through which I am to have the 

 privilege of acting as his guide. 



Before proceeding to this exploration, however, I will 

 ask him to linger with me for a moment to take a 

 passing glance at two other methods, which ai'o as yet 

 in the infantile stage, but one or both of- which may not 

 impossiblv in time outgrow their elder brother. 



These are, the system of conduction through the sea 

 or moist earth, and the system of electromagnetic in- 

 duction. 



In the earliest attempts at electric telegraphy, a 

 complete metallic circuit was employed, requiring a pair 

 of wires to connect any two stations. 



In the year 1838, Steinheil tried unsuccessfully to 

 utilise the two lines of rails of a railway in place of 

 overhead telegraph wires, but, as lias so often happened, 

 his investigations into the cause of his failure led him 

 to a most important discovery. 



He found the reason to be '^hat the earth was so good 

 a conductor, that the electric current from the 

 transmitting station, instead of flowing along one of 

 the rails to the distant station and returning by the 

 other, as he had anticipated, simply flowed across to 

 the other rail through the earth on which they rested, 

 and this at once suggested to him that it should only 

 be necessary to have one wire between the two stations, 

 provided this wire was earth-connected at each 

 station, and this he found to be the case. 



He also suggested that, the earth being so good a 

 conductor, it might be possible to do away with con- 

 necting wires altigether, but I am not aware of his 

 having devised any means by which this could be 

 done. 



Four years later the American, Professor Morse, who 

 took so large a share in the development of electric 

 telegraphy, succeeded in transmitting messages across 

 a canal, 80 feet in width, and afterwards across the 

 Susquehanna River, a distance of nearly a mile, by the 



^ 



\ . 



o 



-^^:^ 



Fig. 1. — Morse's method of transmitting messages across the 

 Susquehanna Eiver. 



method shown in Fig. 1, where B is a battery, N N a 

 pair of needle instrumeuts for transmitting and receiv- 



ing signals, and P Q R S ai'o metallic plates immersed 

 being connected with insulated wire. 



He obtained very good results when the distances 

 from P to Q and R to S were three times as great as 

 those from P to R and from Q to S. 



In this connection I cannot refrain from pausing for 

 a moment to refer to J. B. Lindsay, of Dundee, a Scotch 

 schoolmaster of the very slenderest means, who made 

 several importan'^ electrical discoveries, though unfortu- 

 nately very little w.is hoard of them except by his im- 

 mediate neighbours, until they were unearthed some 

 few years ago, when they were only of historical 

 interest. He carried out a long series of experiments 

 similar to those of Morse, quite independently but a 

 year later. 



After this, the subject appears to have excited very 

 little attention, until in the year 1880, Professor John 

 Trowbridge, of Harvard College, discovered that all the 

 neighbouring telephone circuits were affected by the 

 time signals sent from Harvai-d to Boston, some four 

 miles away. He investigated the cause of these dis- 

 turbances, and found that they were not due to in- 

 duction, but to earth currents produced by leakage from 

 the clock circuit. 



Trowbridge saw at once that this might be utilised 

 for the purpose of sending telegraphic messages without 

 connecting wires, and he proposed attempting to tele- 

 graph across the Atlantic by sending alternating 

 currents from a large dynar.io through an insulated 

 cable extending from Nova Scotia to Florida and 

 earthed at each end, and placing another long wire with 

 a telephone in its circuit down the coast of France. 



He proposed signalling to ships at sea by means of 

 similar means, and also by means of magnetic induction 

 between coils carrying interrupted currents and using 

 a telephone as detector, but he found that it would be 

 necessary to employ either coils, far too large for use 

 on board ship, or extremely heavy currents. 



During the following year Graham Bell, the inventor 

 of the telephone, began some interesting experiments 

 of which I will only describe one, which he carried out 

 on the Potomac River. 



A battery and an interrupter were placed in a boat 

 and connected by a wire about 100 feet long, one end 

 of which was soldered to a metallic plate immersed in 

 the water near the bow, while the other end was at- 

 tached to a similar plate, which was buoyed by a float 

 and allowed to trail astern. Bell himself was in another 

 boat similarly equipped, except that the battery and 

 interruptor wero replaced by a telephone, and he found 

 that he could clearly distinguish the signals at a dis- 

 tance of a mile and a quarter from the first boat. He 

 strongly urged that a similar method should be cm- 

 ployed for communicating between steamships, the 

 steamer's electric lighting dynamo being used to replace 

 the battery. 



In 1882, Mr. A/. H. Preece, now Sir William Preece, 

 began to turn his attention to the subject with a view 

 to effecting communication with lighthouses and light- 

 ships, where continual interruptions occur owing to the 

 cables being broken or damaged by the heavy seas. 



One of his earlier experiments was to establish a 

 telegraphic circuit between Southampton and Newport 

 in the Isle of Wight. 



As shown in Fig. 2, one wire was carried from 

 Portsmouth through Southampton to Hurst Castle, the 

 two ends being connected to large metallic plates im- 

 mersed in the sea at Southsea Pier and Hurst Castle 

 respectively. Another overhead wire was carried from 



