HERTZIAN WAVE WIRELESS TELEGRAPHY. 



63 



messages at the same time on the same aerial. Subsequently to the date 

 of the above-mentioned demonstration of multiplex wireless telegraphy 

 by Mr. Marconi, an exhibition of a similar nature was given by Pro- 

 fessor Slaby in a lecture given in Berlin on December 22, 1900.* 



Both the above described syntonic systems of Mr. Marconi and Dr. 

 Slaby are 'earthed' systems, but arrangements for syntonic telegraphy 

 have been devised by Sir Oliver Lodge and Professor Braun, which are 

 'non-earthed.' 



Sir Oliver Lodge and Dr. Muirhead have devised also syntonic sys- 

 tems. According to their last methods, the syntonic transmitting and 

 receiving arrangements are as shown in Fig. 25. f On examining the 



Tz=r 





C 



L. 



C 



B- 



c 



I ouoas.(iV(i 



R 



-q: 



3E 



m 



Fig. 25. LoDGE-MuiRHEAD Syntonic Receiver. I, induction coil; S, spark gap; A, 

 aerial; C, C , condensers ; JS, eartli plate; iJ, relay; i, variable inductance; i^, filings tube; 

 B, battery. 



diagrams, it will be seen that the secondary terminals of the induction 

 coil are, as usual, connected to a pair of spark balls, and that these 

 spark balls are connected by a condenser and by a variable inductance. 

 One terminal of the condenser is earthed through another condenser 

 of large capacity, and the remaining terminal of the first condenser is 

 connected to an aerial. It should therefore be borne in mind in deal- 

 ing with electrical oscillations that a condenser of sufficient capacity 

 is practically a conductor, and an inductance coil of sufficient induct- 

 ance is practically a non-conductor. Hence the insertion of a large 

 capacity in the path of the aerial wire is no advantage whatever and 

 makes no essential difference in the arrangement. In order to obtain 

 any powerful radiation, the length of the aerial or sky wire, as they 

 call it, must be so adjusted that its length is one quarter the wave 

 length corresponding to the oscillation circuit, consisting of the con- 

 denser and variable inductance. 



The receiving arrangement consists of a similar sky wire or aerial 

 earthed through a condenser of large capacity and having in the portion 

 above this last condenser another condenser of similar capacity. At 

 the earthed side of this last condenser a connection is made to a reso- 

 nant circuit, consisting of a variable inductance, and another con- 



* See Electrician, January 18, 1900, Vol. XL VI., p. 475. Also reprint of 

 a paper of Professor A. Slaby, * Abgestimmte und mehrfache Funkentelegraphie.' 

 t See British Specification, No. 11,348 of 1901. 



