IDUrelese 



producing and detecting ether-waves, and he 

 did a great deal to awaken an interest in the 

 subject, so that others began investigations 

 that have led to its present use as a means of 

 u Wraphing to a distance of many miles. 



In 1891 Professor Branly of Paris invented 

 the coherer. In 1894 it was improved by 

 Lodge and by him used as a detector of ether- 

 waves. In 1896, ten years after Dolbear had 

 used it with the kite at the transmitting-end 

 and telephone at the receiving-end, Marconi, 

 an Italian, substituted the coherer of Branly 

 for the telephone of Dolbear. This coherer is 

 constructed and operated as follows: 



It consists of a glass tube, of comparatively 

 small diameter, loosely filled with metal filings 

 of a certain grade. This body of metal-dust is 

 made a part of a local battery circuit in which 

 i< placed an ordinary electric bell or tele- 

 graphic sounder. The resistance of this body 

 cif tilings is so great that current enough will 

 not pass through it to ring the bell or actuate 

 the sounder until an ether-wave strikes it and 

 tin- wire attached to it, when the metal par- 

 ticles are made to cohere to such an extent that 

 the conduct ivity of the mass is greatly in- 

 -d; so that a current of sufficient volume 

 will now pass through the hdl-ma^net to ring 

 it. Before the next signal mines the filings 

 must be made to dc-colii-iv : aixl to accomplish 

 this a little " tapper," that works automat i<-all\ 



