28 



KNOWLEDGE. 



[February 1, 1900. 



Ryde through Newport to Sconce Point, and the ends 

 connected as before to metallic jjlatcs immersed in the 

 sea. 



tsmout/i 



Fio. 2.— Preece's mpthod of transmission between Soutliamptou 

 and Newport. 



With 30 Leclanche cells and a buzzer and Morse key 

 at Southampton, ■l^he signals were found to be perfectly 

 audible at Newport in a telephone on the circuit. 



Three years later Mr. Preece arranged some interest- 

 ing experiments on wireless telegraphy by electromag- 

 netic induction in the neighbourhood of Newcastle, 

 which were carried out by Mr. A. W. Heaviside. Two 

 squares of wire, each side a quarter of a mile in length, 

 were placed a*^ dis*ances a quarter of a mile to 1,000 

 yards apart. In the former case the signals could be 

 easily read by a telephone in the receiving circuit, and 

 audible sounds were produced even at the greater dis- 

 tance. 



Further experiments were made with parallel lines 

 of telegraph, ten and a quar'^er miles apart, between 

 Durham and Darlington, and it was found that the 

 ordinary working currents in one line produced dis- 

 tinctly audible sounds in a telephone in the other. 

 Equally successful experiments were made between 

 parallel lines Jt telcgrapii on the East and Weso Coasts 

 about forty miles apart, but in these experiments there 

 aiose the question whether the effects might not be due 

 in part to leakage from the network of telegraph wires 

 covering the intervening country. 



The fii-st practical application of the results of these 

 experiments was to establish communication between 

 Lavernock Point near Cardiff and two islands, Flat 

 Holm at a distance of about tliree and a third miles, and 

 >Steep Holm at a distance of rather more than five and 

 a third miles. (See Fig. 3.) 



Fio. 3. — Preece's method of transmission between Lavernock 

 Point and the Islands Steep Holme and Fhit Holme. 



On the shore a copjier wire 1,267 yards in length was 

 suspended on poles and earthed at each end. In this 

 circuit was an alternating dynamo capable of giving a 

 current up to 15 amperes, and a Morse key for breaking 

 up the alternations into signals. At a distance of 600 

 yards from this circuit, on the sand at low water mark, 

 a secondary circuit, composed of two gutta percha 

 covered and one bare copper wires, were laid down and 

 their ends buried in the ground. On the two islands, 



gutta percha covered wires, each 600 yards long, and 

 parallel to those on shore, were laid down. Jhe signals 

 in the telephone on Steep Holm were audible, but not 

 sufficiently distinct to be read, but messages were easily 

 read off in the telephone on Flat Holm. 



I will conclude this article by a brief reference 

 to a method devised and patented by Mr. Willoughby 

 Smith, and a modification patented by him in eon- 

 junction with Mr. W. P. Granville. 



Fio. 4. — Willoughby Smith's method of communication 

 between a lighthouse and the shore. 



In Fig. 4 a lighthouse is shown at A, and insulated 

 wires lead from the terminals of a telephone in the 

 lighthouse to metallic plates, M N, submerged on oppo- 

 site) sides of the rock. Two other plates, P and Q, submer- 

 ged to a sufficient depth to be unaffected by waves, are 

 connected by an insulated cable, having in circuit with 

 it a battery, B, and an interruptor, C. The course of the 

 current is shown by the arrows. The modification of 

 Mr. Willoughby Smith's method is shown in Fig. 5, 

 which illustrates its application to communication be- 

 tween the Fastnet Rock, off the S.W. coast of Ireland, 



Fsstnef Rocti 



Fig. 5. — Method of Willoughby Smith and Granville employed in 

 communicating between Crookhaven and the Fastnet Eock. 



and the town of Crookhaven, eight miles away. An 

 insulated cable from the shore is earthed at the shore 

 end, and also by means of a heavy copper anchor, C, 



