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POPULAR SCIENCE MONTHLY. 



the second terminal of which is connected to the earth. The secondary 

 circuit of this last oscillation transformer is cut in the middle and is 

 connected to the terminals of a small condenser. The outer terminals 

 of this secondary circuit are connected to the metallic filings tube or 

 other sensitive receiver and to a small condenser in parallel with it (see 

 Fig. 23). The terminals of the condenser which is inserted in the mid- 



H 



I -OPPtt— I 



B 



R 



Fig. 23. Marconi Tkansmittee and Receiver. I, induction coil ; A, aerial ; E, earth 

 plate ; HH, choking coils ; S, spark gap ; J, transmitting jigger ; K, receiving jigger ; R, relay 

 C, condenser; F, filings tube; B, battery. Many practical details are omitted. 



die of the secondary circuit of the oscillation transformer are connected 

 through two small inductance coils with a relay and a single cell. 

 This relay in turn actuates a Morse printer by means of a local bat- 

 tery. The two circuits of the oscillation transformer are tuned or 

 syntonized to one another, and also to the similar circuit of the trans- 

 mitting arrangement. When this is the case, the transmitter affects 

 the coresonant receiving arrangement, but will not affect any other 

 similar arrangement, unless it is within a certain minimum range of 

 distance. Owing to the inductance of the oscillation transformer 

 forming part of the receiving arrangements, the receiving circuit is, as 

 before stated, very stiff or irresponsive; the sensitive tube is therefore 

 not acted upon in virtue merely of the impact of the single wave against 

 the aerial, but it needs repeated or accumulated effects of a great many 

 waves, coming in proper time, to break down the coherer and cause the 

 recording mechanism to act. An inspection of the diagram will show 

 that as soon as the secondary electromotive force in the small oscillation 

 transformer or jigger of the receiving instrument is of sufficient ampli- 

 tude to break down the resistance of the coherer, the local cell in circuit 

 with the relay can send a current through it and cause the relay to act 

 and in turn make the associated telegraphic instrument record or sound. 

 Mr. Marconi described in the above-mentioned paper some other ar- 

 rangements for achieving the same result, but those mentioned all de- 

 pend for their operation upon the construction of a receiving circuit on 

 which the time-period of electrical oscillations is identical with that of 

 a transmitting arrangement. By this means he showed experiments 

 during the reading of his paper, illustrating the fact that two pairs of 

 transmitting and receiving arrangements could be so syntonized that 



