56 POPULAR SCIENCE MONTHLY. 



brush being formed at the terminal. In making this adjustment of 

 inductance, we are tuning, as it is called, the Ley den jar discharge cir- 

 cuit to the resonating bobbin. A very small variation of the inductance 

 of the jar circuit causes the vacuum tube to change in luminosity. If, 

 however, the natural time periods of these bobbins do not lie very far 

 apart, then a faint luminosity will make its appearance in both the 

 vacuum tubes. Supposing therefore that we connect to the oscillating 

 circuit of the jar a number of bobbins having different time-periods of 

 oscillation, like organ-pipes, and supply them all with one common 

 alternating electromotive force. Those bobbins whose natural time- 

 period is very different to that of the oscillating circuit or impressed 

 electromotive force will not respond, but those bobbins of which the 

 natural time-period lies near to, even if not quite exactly the same as, 

 that of the impressed electromotive force will give evidence of being 

 set in oscillation. A very violent electromotive force will cause them 

 all to respond to some slight extent, no matter whether the period of 

 that impulse is tuned to their common period precisely or not. 



At this point questions arise of great practical importance. A 

 matter which has been in dispute in connection with practical Hertzian 

 wave telegraphy is how far this electrical tuning is a sufficient solution 

 of the practical problem of isolation. It is not denied that experiments 

 such as those made with Seibt's apparatus can be shown on a small 

 scale; and, on a still larger scale, Mr. Marconi gave to the author in 

 September, 1900, a demonstration in practical telegraphic work of 

 sending two independent Hertzian wave messages and receiving 

 them on two independent receivers attached to the same aerial. 



Since that date much experience has been gained and large power 

 stations erected, and a statement has been frequently made that syntony 

 is no protection against interference when one of the stations is sending 

 out very powerful waves. The contention has been raised that large 

 power stations producing electric waves will therefore play havoc with 

 Hertzian wave telegraphy on a smaller scale, such as the ship to shore 

 and intermarine communication. Under these circumstances, it ap- 

 peared to the author important to subject the matter to a special test, 

 and Mr. Marconi therefore offered to give a demonstration, with this 

 object, in support of the opinion that he has expressed positively that 

 waves from his power stations do not interfere with the working of 

 his ship installations. This matter is vital to the whole question of 

 practical Hertzian wave telegraphy, for the ship to shore communica- 

 tion is of stupendous importance ; and if Mr. Marconi had done nothing 

 else except render this possible and effective, he would have earned, as 

 he has done, the gratitude of humanity for all time. Accordingly, the 

 author embraced the opportunity of making some careful tests to settle 

 the question, whether the powerful waves sent out from a station such 

 as Poldhu did or did not affect the exchange of messages between ship 



