326 



Professor Oliver Lodge 



[Juno I, 



Fig. 6. 



swings, Fig. 1. Hence it follows that it has a wide range of excita- 

 tion ; i. e. it can excite sparks in conductors barely at all in tune 

 with it. 



The two conditions, conspicuous energy of radiation and persis- 

 tent vibration electrically produced, are at present incompatible. 

 Whenever these two conditions coexist, con- 

 siderable power or activity will, of course, be 

 necessary in the source of energy. At present 

 they only coexist in the sun and other stars, in 

 the electric arc and in furnaces. 



The receiver Hertz used was chiefly a circular 

 resonator, Fig. 6, not a good absorber but a per- 

 sistent vibrator, well adapted for picking up 

 disturbances of precise and measurable wave- 

 length. Its mode of vibration when excited by 

 an emitter in tune with it is depicted in Fig. 2. 

 I find that the circular resonators can act as 

 senders too ; here is one (Fig. 6a) exciting quite 

 long sparks in a second one. 

 Electric Syntony : — that was his discovery, but he did not stop 

 there. He at once proceeded to apply his discovery to the verification 

 of what had already been predicted about the waves, and by labori- 

 ous and difficult interference experiments he ascertained that the 



Circular Resonator. 

 (The knobs ought 

 to nearly touch 

 each other.) 



Fig. 6a. 



Any circular resonator can be used as a sender by bringing its knobs 

 near the sparking knobs of a coil ; but a simple arrangement is to 

 take two semicircles, as in above figure, and make them the coil 

 terminals. The capacity of the cut ends can be varied, and the period 

 thereby lengthened, by expanding them into plates. 



previously calculated length of the waves was thoroughly borne out by 

 fact. These interference experiments in free space are his greatest 

 achievement. 



He worked out every detail of the theory splendidly, separately 

 analysing the electric and the magnetic oscillation, using language 



