The Wireless Telegraph 



ual bar and obstacle, under the influence of 

 electric waves from afar it changes instantly to a 

 coherent metallic link which at once completes 

 the circuit and delivers the message. 



An electric impulse, almost too attenuated for 

 computation, is here able to effect such a change 

 in a pinch of dust that it becomes a free avenue 

 instead of a barricade. Through that avenue a 

 powerful blow from a local store of energy makes 

 itself heard and felt. No device of the trigger 

 class is comparable with this in delicacy. An 

 instant after a signal has taken its way through 

 the coherer a small hammer strikes the tiny tube, 

 jarring its particles asunder, so that they resume 

 their normal state of high resistance. We may 

 well be astonished at the sensitiveness of the 

 metallic filings to an electric wave originating 

 many miles away, but let us remember how 

 clearly the eye can see a bright lamp at the same 

 distance as it sheds a sister beam. Thus far no 

 substance has been discovered with a mechanical 

 responsiveness to so feeble a ray of light; in the 

 world of nature and art the coherer stands alone. 

 The electric waves employed by Marconi are 

 about four feet long, or have a frequency of about 

 250,000,000 per second. Such undulations pass 

 readily through brick or stone walls, through 

 common roofs and floors indeed, through all 

 substances which are non-conductive to electric 

 \Vaves of ordinary length. Were the energy of a 

 Marconi sending-instrument applied to an arc- 

 lamp, it would generate a beam of a thousand 

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