MIRACLES OF SCIENCE 



strated. The methods involved as outlined by Pro- 

 fessor J. A. Fleming, included electrical conduction 

 through soil or sea; magnetic induction through 

 space; a combination of these methods, and electro- 

 static induction. But after Hertz made his famous 

 demonstration with electric waves, it became appar- 

 ent that this form of radiation offered possibilities 

 surpassing all others. 



Two great difficulties confronted the experiment- 

 ers: the production of electric waves of great power, 

 and the detection of the waves at a distance. The 

 first important clue to a practical method of detect- 

 ing the waves was given by the Frenchman Branly, 

 who showed in 1890 that a loose metallic powder is 

 changed from a poor to a good conductor by the in- 

 fluence of the Hertzian waves. Sir Oliver Lodge ex- 

 tended the experiments along this line and in 1894 ex- 

 hibited a little apparatus which he called a coherer, 

 which consisted essentially of metallic filings in 

 a tube connected with an electric circuit. These fil- 

 ings, loosely arranged, resist the passage of eletric- 

 ity; but when influenced by Hertzian waves, sent 

 through the air from a distance, the filings "cohere" 

 and readily permit the passage of the electric cur- 

 rent. A tap on the tube restores the filings to their 

 original condition of non-conductivity. 



Sir William Crookes, as early as 1892, suggested 

 that Branly's discovery regarding the metal filings 

 might be utilized in the sending of wireless tele- 

 graphic messages. But no one showed practically 

 how this might be effected until Signer Marconi 

 began his investigations. In 1896 Marconi had per- 



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