290 SIGNALLING THROUGH SPACE 



ducting a current be regarded, the lines circle round and round 

 the wire. Whereas Marconi had devoted his attention to radia- 

 tions of the former kind, he himself had confined his attention to 

 the study of the latter. * 



" Some few years ago the authorities of the Post Office had been 

 puzzled to account for the fact that messages to the north of Eng- 

 land were being deciphered at an office in Gray's Inn Road not in 

 any way connected with the system, and finally it was found that 

 the messages sent by wires underground were communicated by 

 induction to wires eighty feet above the ground. Through this 

 circumstance the matter had been taken up experimentally by Mr. 

 Preece, and it was found that the influence of a current was per- 

 ceptible not only at eighty, but at a distance of two thousand feet. 

 The. experiment of sending a message across Loch Ness, a distance 

 of over a mile, was afterwards successfully carried out, and on the 

 Bristol Channel, in signalling from Lavernock Point, near Penarth, 

 to islands off the coast, still greater success was met. By using a 

 mile and a quarter of wire at Lavernock Point, and about six 

 hundred yards of wire on the island of Flatholm, messages were 

 communicated over a distance of three miles. Later, with the use 

 of the same apparatus, signals were sent as far as Steepholm, an 

 island five and a quarter miles distant. An alternating current, 

 making about 250 alternations p'er second, was used as the source 

 of energy. 



" To illustrate the principle, a coil consisting of several large 

 loops was connected with a telephone, and held opposite a similar 

 one attached to a battery. When a current was caused to pass in 

 the latter, connection being made and broken by a Morse key, a 

 sound was emitted by the telephone due to the induced current, 

 If one coil was held in a plane perpendicular to that of the other 

 the sound ceased ; it also diminished when one coil was made to 

 recede from the other. Another model more nearly illustrated the 

 apparatus actually employed. It consisted of a pair of rectangular 

 wood frames facing each other from opposite sides of the theatre 

 on which the wires were coiled. The induction from one to the 

 other of these frames could not, however, be demonstrated to the 

 whole audience, the sounds produced not being so loud as those 



