PKOGRESS IN AYIRELESS TELEGRAPHY." 



By Wir.LTAM AIavi.ii, Jr.'' 



The possibility of telograpliinij \vitlu)iit wires by means of electric 

 waves in free space was demonstrated wlien Dr. H. ITertz, in 18S7 

 and 1888, holdinij; a so-called " electric eye," consisting of a ring of 

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

 a few feet from the sparlv gap of an induction coil, or oscillator, was 

 able to detect minute sparks jumjiing across the l)reak in the cop])er 

 ring. 



In 1880 Doctor Branly discovered that metal filings, which, when 

 made ]:)art of an electi'ic circuit, had normally a very high electrical 

 resistance, but became good condnctoi-s of electricity when electric 

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

 conducting qualities until shaken up. 



The art of wireless telegraj)hy took a long forward step when, in 

 1894, Dr. (now Sir) Oliver Lodge made his notable experiments 

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

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

 waves, the ]')raidy coherer, consisting of a tube filled wnth 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 clockwork, to strike the tube continuously. A bell or 

 relay in the coherer circuit could thus be kept in vibration during 

 the continuance of electric oscillations and would become ])assive 

 Avhen the oscillations ceased, and in this way signals could be trans- 

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

 paratus would be half a mile, l)ut even this distance w^ould have ad- 

 vanced the signaling distance four-hundredfold bevond the jXHut at 

 which Doctor Hertz had left it. 



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

 June, 190.3. In connection with tills iirticlc it may lu' found intcrcstini,' and 

 profitalde to refer to his earlier one, " Wireless (eh'.m-.npliy — its i):ist and pi-esent 

 status and its prospects," Cassier's Magazine. Jainiary, 1!»U'_'. and (Jenei'al 

 Appendix to Sndthsonian Report. 1!)02, page 2' 11. 



^Author of "American telegraphy " and " IMavor's wireless telegraphy." 



275 



