FIRST RESEARCHES IN PHYSICS 51 



oscillation was next lucidly imaged by Kelvin, as the swing 

 of ' the electric pendulum/ But is the energy of these 

 electric oscillations simply dissipated through resistance, 

 and into heat, as in the incandescent particles of the spark 

 we see ? Maxwell had predicted that there must also be 

 some such radiation for electric waves ; so here arises an 

 experimental test between his theory and preceding ones, 

 by which no such phenomenon had been imagined, or is 

 even possible. 



Here then is where at length Hertz came in, soon 

 with decisive experiments. First he had to devise a fresh 

 apparatus for exciting the oscillating discharges more 

 steadily and more rapidly (a shortened electric pendulum, 

 as it were), and with the discharges more fully under 

 observation and control. In this he succeeded, but not 

 without great difficulties, traced especially to the uncertain 

 and irregular behaviour of the brass balls between which 

 the oscillating discharge took place. But next, how was he 

 to know whether the electric waves, which Maxwell had 

 foreseen, and which he was seeking for, were really being 

 projected into space from his radiator's oscillating dis- 

 charge, or no ? Here, obviously, he needed some kind of 

 receiver for the anticipated rays ; and to contrive it was 

 a new and perplexing experimental problem. His method 

 was to place in the path of the expected rays an exploring 

 apparatus a pair of closely approximated metallic rods, 

 in which the rays should induce an electric tension ; which 

 should then, when strong enough, give minute sparks 

 between its adjacent poles. Alas ! no spark could be 

 observed ; yet Hertz was not discouraged. Realising that 

 such induced currents must needs be extremely small, he 

 had recourse to the microscope. The poles could thus be 

 brought to within a minute distance ; and then he had the 

 joy of success, for a minute but unmistakable spark now 

 appeared with every impulse from the exciting apparatus 

 at some distance off. Here, then, in this tiny spark was at 

 once the success of the primary experiment so long needed 



