64 



POPULAR SCIENCE MONTHLY 



bell or sounder when the electric wire excites the iron filings. In 

 Fig. 2 this receiving apparatus is shown diagrammatically. B is the 

 battery which sends a current throus'h the sounder M and the 



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coherer IST when the magnetic whirls coming from the sending wire 

 W embrace the receiving wire W. 



The term wireless telegraphy is a misnomer, for without wires 

 the method would not be possible. The phenomenon is merely 

 an enlargement of one that we are fully conscious of in the case 

 of telegraph and telephone circuits, which is termed electro-mag- 

 netic induction. Whenever an electric current suddenly flows or 

 suddenly ceases to flow along a wire, electrical currents are caused 

 by induction in neighboring wires. The receiver employed by Mar- 

 coni is a delicate spark caused by this induction, which forms a 

 bridge so that an electric current from the relay battery can pass 

 and influence magnetic instruments. 



Many investigators had succeeded before Marconi in sending 

 telegraphic messages several miles through the air or ether be- 

 tween two points not directly connected by wires. Marconi has 

 extended the distance by employing a much higlier electro-motive 

 force at the sending station and using the feeble inductive effect 

 at a distance to set in action a local batterv. 



