X-ray Electrons. 1117 



Innes in 1907, and it appeared from their results that the 

 speed lay between 6 and 8 x 10 9 cm./sec. and was inde- 

 pendent of the intensity of the X-rays. 



In 1912 the writer attacked the problem from a different 

 angle by interpreting the absorption experiments of Beatty* 

 in the light of the fourth-power law of velocity diminution 

 previously established j\ 



Beatty having measured the range in air of X-ray 

 electrons, it was possible to translate the range into terms 

 of initial speed, and it was shown that this ejection speed 

 was nearly equal to 10 8 x A, where A is the atomic weight 

 of the element supplying the X-rays f. 



It was pointed out recently that this result — frankly 

 approximate in view of the nature of the experiments — was 

 expressible in terms of atomic number, and that for these 

 fastest X-ray electrons a formula similar to that of Moseley 

 for X-rays was approximately true %. 



It is to be noted, however, thai the method just mentioned 

 is only capable of determining, approximately, the speed of 

 the fastest electrons, and is incapable of proving with cer- 

 tainty the existence of independent groups of smaller speed — 

 unless, of course, such groups are very widely separated §. 



The present work was undertaken with the object of 

 extending these results, and during its progress de Broglie || 

 has published most important results bearing on the same 

 problem. His results, w T hich will be referred to in more 

 detail later, are confirmed in the main by my own ob- 

 servations. 



The Apparatus. 



The apparatus used to determine the speed of the X-ray 

 electrons is indicated in fig. 1 ^[. 



A quartz bulb B is fitted with cathode and rhodium- 

 faced target T, water-cooled through the tubes D 1? D 2 . 



The cathode also was air-cooled by the copper radiator 

 fins R. 



Just under T and about a centimetre above it is mounted 

 the aluminium slit chamber J (shown enlarged to the right), 



* Beatty, Proc. Roy. Soc. (1910). 



t Whiddington, Proc. Roy. Soc. (1912). 



f Whiddington, Phil. Mag. vol. xxxix. p. 694 (1920). 



§ Simons, Phil. Mag. (1921), has repeated Beatty's experiments very 

 carefully, and has shown the existence of such groups. 



|| de Broglie, Comptes Rendvs (1921). 



51 A preliminary account was given in Proc. Camb. Phil Soc 

 (1921). 



