WIRELESS TELEGRAPHY 



electric waves. This little instrument is a glass tube less 

 than two inches long and of less diameter than the or- 

 dinary lead-pencil, having two silver plugs sealed into 

 it, each plug with a platinum wire extending from the 

 end of the tube. The silver plugs fit tightly into the 

 tube, completely filling it except for a little space be- 

 tween their ends in the middle of the tube, this space 

 being about one millimeter in length. The little cham- 

 ber so formed is filled about half full of nickel and silver 

 filings. The air in this space is exhausted and the tube 

 permanently sealed. 



Under ordinary circumstances the grains of the nickel 

 and silver powder in the little chamber between the ends 

 of the plugs lie about "higgledy-piggledy," just as any 

 ordinary filings would do under similar circumstances. 

 But when the electric waves fall upon them they are 

 polarized and assume definite positions, in much the 

 same manner as do iron filings on a piece of paper when 

 a magnet is passed beneath the sheet. Once the filings 

 in Marconi's coherer have been so arranged by the ac- 

 tion of the electric waves they tend to remain so, and 

 would thus furnish no further means of detecting suc- 

 ceeding waves unless they are disarranged in some 

 manner; but if the tube is tapped, the grains fall into 

 their original position of disarrangement, instantly 

 "lining up" as soon as the waves again fall upon them. 



For practical application in wireless telegraphy a 

 mechanical device is used which, by a series of extremely 

 rapid and gentle tappings, oscillates the little tube in a 

 manner barely perceptible to ordinary sight. This 

 oscillating tube is connected with a Morse printer, and 



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