PROGRESS I\ WIRELESS TELEGRAPHY." 



r.y Willi \M Mavi:i:. Jr.'' 



Tlu' possibility of (('Icirraphini: \vi(li()ii( w ii-cs hy incniis of electric 

 Avavos in free space was deinoustrated when Dr. H. Hertz, in 1S8T 

 and 18SS, holdinij a so-c-alltM] "electric eye," consist in, i; of a rin<; of 

 copper wire ahont IC inches in diameter and broken at one point, 

 a few feet from tlio s|)ark ijap of an indnction coil, or oscillator, was 

 al)k> to detect minnto s})arks jninpinij: across the break in the copper 

 rino:. 



In ISSO Doctor Branly discovered that metal filini;s, which, when 

 made part of an electric circuit, liad normally a very high electi-ical 

 i-esistance, but became good conductors of electricity wdien electric 

 oscillations were set up in the circuit, and that they retained their 

 con<lucting qualities until shaken up. 



The ai't of wireless telegraphy took a long forward step when, in 

 1S94, Dr. (now- Sir") Oliver Lodge made his notable experiments 

 before the Royal Institution, in which he used, as a transmitter of 

 electric waves, the Hertz or Righi oscillator, and as a detector of those 

 waves, -the Rranly coherer, consisting of a tube filled with metal 

 filings in an electric circuit containing an electric bell. To insure 

 the filings resuming their state of nonconductivity upon the cessa- 

 tion of the electric oscillations. Doctor Lodge caused a " tappei-," 

 operated by clockwoi-k, to strike the tube continuously. A b(>ll or 

 relay in the cohei-er cii-cuit could thus be kc\){ in vibration during 

 the continuance of electric oscillations and woidd become passive 

 when the oscillations ceased, aiul in this way signals cotdd be trans- 

 mitted. Lodge believed that the limit of sensitiveness of this ap- 

 paratus would be half a mile, but even this distance woidd ha\'e ad- 

 vanced the signaling distance four-hundredfold beyond the j)oint at 

 which Doctor Hertz had left it. 



a Reprinted by permission, after revision by author, from Cassier's Magazine. 

 June. l!»o;{. In connection witli tills article it may be found interesting and 

 profitable to refer to his earlier one. " Wireless toietrrapby — its jiast and jtrosont 

 status and its iirospects," Cassier's Mafrazine. .I.iiui;iry. lUO'j. nnd (Jenci-:!! 

 Aiipendix to Sndtbsonian Report. 1002. pape 2''»1. 



''Author of "American telegraphy " and " Maver's wireless t(>le},'rapby." 



275 



