HERTZIAN WAVE WIRELESS TELEGRAPHY. 



6i 



each receiver responded only to its particular transmitter and not to the 

 other. 



With arrangements of substantially the same nature, he made ex- 

 periments in the autumn of 1900 between Niton, in the Isle of Wight, 

 near Bournemouth, a distance of about thirty miles, in which inde- 

 pendent messages were sent and received on the same aerial. 



Dr. Slaby and Count von Arco, working in Germany, have followed 

 very much on the same lines as Mr. Marconi, though with appliances 

 of a somewhat different nature. As constructed by the General Elec- 

 tric Company, of Berlin, the Slaby- Arco syntonic system of Hertzian 

 telegraphy is arranged in one form as follows: The transmitter con- 

 sists of a vertical rod like a lightning conductor, say 100 or 150 feet in 

 height. At a point six or nine feet above the ground, a connection is 



a. 



tf 



)0 



s 



B, R 



M 



-/2j?jZJ^-i^nzn)L 



m 



Fig. 24. Slaby-Arco Syntonic Transmitter and Reckivkr. J, induction coil ; M, multi- 

 plier ; B, battery ; A, aerial ; F, filings tube ; R, relay ; E, earthplate ; C, condenser. 



made to a spark ball (see Fig. 24), and the corresponding ball is con- 

 nected through a variable inductance with one terminal of a condenser, 

 the other terminal of which is connected to the earth. The two spark 

 balls are connected to an induction coil, or alternating current trans- 

 former, and by variation of the inductance and capacity the frequency 

 is so arranged that the wave-length corresponding to it is equal to four 

 times the length of that portion of the aerial which is above the spark 

 ball connection. The method by which this tuning is achieved is to 

 insert in the portion of the aerial below the spark balls, between it and 

 the earth, a hot wire ammeter of some form. It has already been 

 shown that in the case of such an earthed aerial, when electrical oscil- 

 lations are set up in it, there is a potential node at the earth and a po- 

 tential antinode or loop at the summit, if it is vibrating in its funda- 

 mental manner; also, there is a node of current at the summit of the 

 aerial and an antinode at the base. This amounts to saying that the 

 amplitude of the potential vibrations is greatest at the top end of the 

 aerial, and the amplitude of the current vibrations is greatest at the 

 bottom or earthed end. Accordingly, the inductance and capacity of 

 the lateral branch of the transmitter is altered until the hot wire am- 

 meter in the base of the aerial shows the largest possible current. 



The corresponding receiver is constructed in a very similar manner. 



