WIRELESS TELEGRAPHY 



in Paris which was extremely sensitive to these Hert- 

 zian waves and by means of which the presence of such 

 waves might be detected. Doctor Branly, therefore, 

 is usually credited with having developed the little 

 instrument that made possible the modern wireless 

 telegraph. But it seems that as early as 1880 the dis- 

 covery of such a coherer had been made by Prof. D. E. 

 Hughes, although this discovery had attracted com- 

 paratively little attention. When the discovery of 

 Doctor Branly's became known, Sir William Crookes 

 at once recalled that he had seen a somewhat similar 

 device made ten years before by Professor Hughes. 

 Investigation of this showed that Professor Hughes had 

 anticipated Doctor Branly's discovery by several years, 

 although Dr. Branly's coherer, rather than that of 

 Professor Hughes', must be credited with playing the 

 important'part in the development of wireless telegraphy. 

 The principle of this coherer depended upon the 

 action of brass filings confined within a vacuum tube, 

 these filings being so sensitive to the Hertzian waves 

 that the latter may be detected at great distances. Ma- 

 king practical application of this discovery, Sir Oliver 

 Lodge, in 1893, experimented with a pair of knobs, each 

 connected with a Leyden jar placed in the same circuit, 

 and a battery and a bell. By this instrument, strokes 

 of the bell could be produced by "syntonic" response 

 of the electric vibration created by a signal jar some 

 distance away. In order to produce this effect the jars 

 and their circuit had to be accurately "tuned" that is, 

 have a corresponding number of electric vibrations per 

 second. 



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