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POPULAR SCIENCE MONTHLY. 



ceiver is as follows: When the wave strikes the aerial it sets up in it 

 electrical oscillations with a potential antinode at the summit, and at 

 the same time a potential antinode is created at the outer end of the 

 spiral attached near the base of the aerial; this spiral being called by 

 Professor Slaby a multiplicator. As long as the coherer tube remains 

 non-conductive, the local cell can not send a current through the 

 relay, but, as soon as the resistance is broken down by the impact of a 

 wave, the local cell sends a current through the coherer tube which, 

 passing down to the earth through the base of the aerial and up through 

 the earth connection to the condenser, completes its circuit through the 

 relay. Many variations of this arrangement have been made by Slal^y 

 and Von Arco and by the Allgemeine Elektricitats Gesellschaft of Berlin. 

 In 1898, Mr. Marconi made a great advance in the construction 

 of his receiving apparatus by the insertion of his 'jigger' or oscilla- 

 tion transformer in the aerial receiving cir- 

 cuit.* In this arrangement, the primary 

 coil of an air core transformer wound in a 

 particular way is inserted between the re- 

 ceiving aerial and the earth, and the sec- 

 ondary circuit is cut in the middle and con- 

 nected to the two surfaces of a condenser, 

 these surfaces being also connected through 

 the circuit of an ordinary telegraphic relay 

 and a single cell (see Fig. 30). The ends 

 of the secondary circuit of this oscillation 

 transformer are also connected to the terminals of the coherer tube, 

 and these again are short-circuited by a small condenser. 



The operation of this receiver is as follows: The oscillations set up 

 in the aerial pass through the primary circuit of the jigger, and these 

 induce other oscillations in the secondary circuit : the electromotive 

 force or difference of potential between the primary terminals being 

 transformed up in any desired ratio. It is this exalted electromotive 

 force Avhich is made to act on the coherer tube, and, inasmuch as 

 the jigger operates in virtue of a current passing througli its 

 primary circuit and this current is at a maximum at the lower end of 

 the aerial, the arrangement is exceedingly effective, because it, so to 

 speak, converts current into voltage. At the lower end of the aerial, 

 although the amplitude of the potential oscillations is a minimum, the 

 amplitude of the current oscillations is a maximum, and the jigger 

 transforms these large current oscillations into large potential oscilla- 

 tions, provided it is constructed in the light manner. We can also 

 transform up or increase the amplitude of the small potential varia- 

 tions near the bottom of the aerial by employing the principle of 



Fig. 20. Marconi Receiver, 

 A, aerial; J, jigger; CO, con- 

 densers ; F, filings tube ; T, tap- 

 per ; R, relay ; B, battery ; M, 

 Morse printer. 



Seo (J. Maifoni, Biiti.sh Patent Specification, No. 12,32(), of June 1, 189S. 



