HEINRICH HERTZ 361 



and with smaller self-inductions in the discharge circuit. 

 The fact that oscillations actually occur in such circumstances 

 was proved by Hertz satisfactorily in experimenting with 

 electric discharges, and this was the beginning of the series of 

 investigations, which led to complete success within two 

 years. 



In order to prove the presence of the invisible waves, and 

 indeed the actual existence of rapid oscillations in conductors 

 excited by spark discharge, Hertz made use of resonance. 

 This is the phenomenon of sympathetic oscillation, which 

 was quite rightly recognised by Galileo in connection with 

 sound waves, and it only takes place when the resonator is 

 tuned exactly to an equal period of oscillation. In the case 

 of electrical resonance, the two conductors which have been 

 tuned to equal electrical period of oscillation are suitably 

 placed alongside one another. If one of them, the 'oscil- 

 lator' or 'transmitter,' is then caused to oscillate by a spark 

 discharge, sparks are seen on the other, the 'resonator,' as a 

 sign that it also is oscillating in sympathy, and the presence 

 of an oscillation is thus proved. The fact that the propaga- 

 tion from oscillator to resonator takes place by means of 

 waves cannot be proved in this way; the phenomenon thus 

 observed can indeed be quite simply regarded as a process of 

 mutual induction, the oscillator being called the primary 

 conductor, and the resonator the secondary conductor. 



In order to prove the existence of waves, the two conduc- 

 tors must be sufficiently far apart, which gives rise to the 

 difficulty that the effect falls off rapidly as the distance in- 

 creases. Hence Hertz first attempted to conduct the oscil- 

 lations along wires. Since in the case of this kind of conduc- 

 tion the velocity of propagation is that of light, as had been 

 shown by Gauss and Weber upon the introduction of the 

 electric telegraph, waves should be demonstrable in the 

 wires of the same length as are required by Maxwell's theory 

 to exist in the free state around the oscillator. This proof 



