334 Mr. C. A. Chant on the Variation of 



curious results were recorded for which no explanations were 

 forthcoming "*. 



It may be worth while to recall how the wave-length of 

 Hertz's plate oscillator was determined. He obtained it with 

 the aid of his circular resonator, but, as has been already 

 remarked, the wave-length thus found is always eight times 

 the diameter of the resonator. If, then, we could know when 

 the resonator was exactly in unison with the oscillator, the 

 wave-length could be deduced with considerable accuracy. 

 But this is not at all possible ; the resonance is far from 

 being sharply defined. Indeed, Hertz says that the same 

 resonator, of diameter 70 cms., was in resonance with three 

 different oscillators. The first consisted of two spheres of 

 diameter 30 cms., connected by a wire 70 cms. long, with a 

 spark-gap in the middle ; the second, of two plates 40 cms. 

 square, joined by a wire 70 cms. long with a spark-gap as 

 before ; the third had plates of the same size, but the wire 

 was 60 cms. longf. 



Thus the wave-length emitted by each of these was taken 

 to be the same, namely, 560 cms. Now the period and wave- 

 length of the first oscillator have been found theoretically. 

 Hertz ± calculates the period to be 1*26 hundred-millionths 

 of a second, and the wave-length to be 4*6 m., while Drude § 

 makes the latter 4*8 m. Both values differ considerably from 

 that obtained by resonance. Again, the second and third 

 oscillators differ considerably in period, though that of the 

 second was found to be the same as that of the first (see 

 below). We must conclude that the wave-length 5' 6 m. is 

 not a very close approximation. 



In the experiments to be described presently it will be seen 

 that oscillators of the same type may differ decidedly in their 

 behaviour ; that some seem able to force their vibrations upon 

 a wire, while others cannot. The wave-length of an oscillator 

 the same as the third of the three just described was concluded 

 to be 5* 88 metres. 



II. Experimental Arrangement. 



While engaged during the session 1900-1, in the Jefferson 

 Physical Laboratory of Harvard University, on another 



* 'Nature,' vol. xliv. p. 454 (1891). 



f Hertz, < Electric Waves,' Art. V. pp. 81-2 ; Art. YI. pp. 96-7 ; 

 Art. VII. pp. 108 & 113. 



+ Hertz, ibid. pp. 51 & 270 (note 6). 



§ Drude, Physik des Aethers, p. 397. See also J. J. Thomson, ' Recent 

 Researches,' Arts. 289 & fol. 



