( «54 ) 



/ llie patli-leiiglli, and n a coiistaut, wliicli accoixling to Drudk 



. , 2 

 amounts to ' \, according to Lokknt/^) (o 



djr 



So we get : 



2R m 2R nl 



?•" Ne^ r' Ou 



At 7':= 300 we may put z^ = 1,75.10'. Moreover we liave 

 (j =: 6,J4.10— * tor silvei', and we shall assume /= 10— ^. This yields: 



R 



L — - . 5. 10 y. 



This is. about 7,^ of the value found foi- bismuth, and not less 

 than Viuoo' ^^^ we expected. The error caused by neglecting Z' amounts 

 therefore for a circle of sihei' wire of /i? = "25 cm. and /' = 0,05 cm. 

 to ± 0,00017„. 



It seems to me as yet impossible to compute for L' a value which 

 may be trusted to be accurate. Yet 1 think that the above calcula- 

 tions make it probable that for coils which are wound in such a 

 manner that they have a large self-induction, the value of L' may 

 be neglected compared with Jj ; but that on the other hand iJ may 

 not always be neglected if the coil is wound in such a way that L 

 is as small as possible. In the latter case it might perhaps be possible 

 to determine L' experimentally, at least if L can then be culculated 

 with a sufticient degree of accuracy. And if it should prove to be 

 possible to determine the different values of // for different metals, 

 this would be a valuable datum for the extension of our knowledge 

 of the^ motion of the electrons in metals. 



Finally it may be remarked that we shall also find a considerable 

 value for L' for a current which does not pass a metallic wire, but 

 for instance a Röntgen-iube. The high value of the velocity of the 

 electrons in this case, gives rise to a high amount of kinetic energy, 

 and this "energy of the kathode-rays" will no doubt reveal itself as 

 an increase of the self-induction of the circuit in which the tube has 

 been inserted. 



■^) H. A. LoRENTz. These ProceeLJings VII, p. 418. 1904 



