CHAPTER XXI. 



WIRELESS TELEGRAPHY. 



Broadly speaking, " Wireless Telegraphy " 

 is any method of transmitting intelligible sig- 

 nals to a distance without wires; and this in- 

 cludes the old Semaphore systems of visual 

 signals, such as flags and long arms of 

 wood by day, and lights by night; also the 

 Heliograph (an apparatus for flashing sun- 

 light), and Sound Signals, made either through 

 the air or water. Electrical conduction, either 

 through rarefied air or the earth, also comes 

 under this heading. 



The name " Wireless Telegraphy," however, 

 is specifically applied to a system of signaling 

 by means of ether-waves induced by electrical 

 discharges of very high voltage. Ether-waves 

 of a greater or less degree are always set up 

 whenever there are sudden electrical disturb- 

 ances, however slight. Ether-waves, electric- 

 ally induced, are probably as old as the uni- 

 verse. When " there were thunders and 

 lightnings" from the cloud that hovered over 

 Mount Sinai in the time of Moses, ether-waves 

 of great power were sent out through the camp 

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