RECENT ADVANCES IN WIRELESS TELEGRAPHY. 135 



An aiTangement consisting of a circuit containing a condenser and 

 a spark gap, fig. 8, constitutes a very persistent oscillator. Sir Oliver 

 Lodge has shown that by placing it near to another similar circuit 

 it is possible to demonstrate effects of tuning. The experiment is 

 usually referred to as *"• Lodge's sjaitonic jars," and is extremely 

 interesting, but, as Lodge himself points out in his book, the Work 

 of Hertz, a closed circuit such as this is '' a feeble radiator and a 

 feeble absorber, so that it is not adapted for action at a distance." 



If, however, such an oscillating circuit is inductively associated 

 with one of the author's elevated radiators, it is possible to cause 

 the energy contained in the closed circuit to radiate to great dis- 

 tances, the essential condition being that the natural })eriod of elec- 

 trical oscillation of the radiator should be equal 

 to that of the nearly closed circuit. 



All the latest syntonic transmitting arrange 

 ments are based on modifications of this combina 

 tion. 



The general arrangement is indicated in fig. 7 



The arrangement for sjaitonizing or tuning the 

 receivino- stations are shown in fia". 5. Here 



to WWc 



shown the usual vertical conductor connected to dOOOOOO C 



earth through the jorimary of a transformer, the 



secondar}' circuit of which contains a condenser. 



which is connected across the coherer or detector. 



In this case, also, it is necessary that the period 



of electrical oscillations of the vertical wire, which 



includes the primary of the transformer and earth 



connection, should be equal to that of, or in tune with, the secondary 



circuit of the said transformer, which circuit includes a condenser. 



Therefore, in order that a transmitter (fig. 7) should be in tune with 



the receiver (fig. 5), it is necessary that the periods of oscillation of 



the several oscillating circuits at both stations should be equal, or very 



approximately so. 



It is easy to understand that if we have several stations, each tuned 

 to a different period of electrical oscillation, the jjeriods of resonance 

 of which are known, it will not be difficult to transmit messages to 

 any one of them without the signals being picked up by the other 

 stations for which they are not intended. It is obvious that the 

 greater the difference in periods of the oscillation or tune between 

 two stations, the smaller will be the possibility of tapping and mutual 

 interference. 



It is also possible to connect to one sending wire, through the con- 

 nections of different inductances, several differently tuned trans- 

 mitters, and to a receiving wire a number of corresponding receivers, 

 as is shown in figs. 9 and 10. 



