Masterpieces of Science 



Channel, and Flat Holme, an island three and a 

 third miles off. As the channel at this point is 

 a much-frequented route and anchor ground, 

 the cable was broken again and again. As a 

 substitute for it Mr. Preece, in 1898, strung wires 

 along the opposite shores, and found that an 

 electric pulse sent through one wire instantly 

 made itself heard in a telephone connected with 

 the other. It would seem that in this etheric 

 form of telegraphy the two opposite lines of 

 wire must be each as long as the distance which 

 separates them; therefore, to communicate across 

 the English Channel from Dover to Calais would 

 require a line along each coast at least twenty 

 miles in length. Where such lines exist for 

 ordinary telegraphy, they might easily lend them- 

 selves to the Preece system of signalling in case 

 a submarine cable were to part. 



Marconi, adopting electrostatic instead of 

 electromagnetic waves, has won striking results. 

 Let us note the chief of his forerunners, as they 

 prepared the way for him. In 1864 Maxwell 

 observed that electricity and light have the same 

 velocity, 186,400 miles a second, and he formu- 

 lated the theory that electricity propagates itself 

 in waves which differ from those of light only 

 in being longer. This was proved to be true by 

 Hertz, who in 1888 showed that where alternat- 

 ing currents of very high frequency were set up 

 in an open circuit, the energy might be conveyed 

 entirely away from the circuit into the surround- 

 ing space as electric waves. His detector was 

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