WIRELESS TELEGRAPHY. 65 



It is evident that wires are needed at the sending station from 

 every point of which magnetic and electric waves are sent out, and 

 wires at the receiving station which embrace, so to speak, these 

 waves in the manner shown bv our photographs. These waves 

 produce minute sparks in the receiving instrument, which act like 

 a suddenly drawn flood gate in allowing the current from a local 

 battery to flow through the circuit in which the spark occurs, and 

 thus produce a click on a telegraphic instrument. 



"We have said that messages had been sent by what is called 

 wireless telegraphy before Marconi made his experiments. These 

 messages had also been sent by induction, signals on one wire be- 

 ing received by a parallel and distant wire. To Marconi is due 

 the credit of greatly extending the method by using a vertical 

 wire. The method of using the coherer to detect electric pulses 

 is not due, however, to Marconi. It is usually attributed to Branly; 





Fi(i. 5. — Magnetic whirls about the receiving wire. 



it had been employed, however, by previous observers, among 

 whom is Hughes, the inventor of the microphone, an instrument 

 analogous in its action to that of the coherer. In the case of the 

 microphone, the waves from the human voice shake up the par- 

 ticles of carbon in the microphone transmitter, and thus cause an 

 electrical current to flow more easily through the minute contacts 

 of the carbon particles. 



