Cathode Fall in Helium and Argon 



19 



smaller than with the fresh filhng. The comparison of the mobili- 

 ties in the two cases shows that the mobility has been increased to 

 a remarkable degree by allowing the gas to stand in the apparatus. 

 To make certain that this increase in mobility was not accidental 

 the system was thoroughly evacuated, washed out with fresh argon 



Table V 



Aluminium Wire Cathode 



Diam., 3.2 mm. ; exposed length, 3.2 cm. ; Argon, pressure = .75 mm. 



Dist. 



/i =.938X10-3 

 Amp. 



/i =1.25 Xio' 

 Amp. 



/i=i. 56X10- 

 Amp. 



ir) 



Cm. 



Obs. 



Calc. 



Obs. 



Calc. 



Obs. 



Calc. 



22. . 

 24. . 

 27. . 

 32. . 

 34- • 

 35-- 

 355- 

 36.. 

 365. 



U... 



Ui.. 



224.2 

 235.2 

 248.3 

 264.0 

 268.0 



269.7 

 270.7 



198. 1 

 224.3 



235-1 

 248.2 

 263.9 

 268.0 



270.2 

 270.7 



264.5 

 278.5 

 292.0 

 309.0 

 313.4 



231.3 

 262.8 

 275.6 

 290.4 

 309.2 

 313.2 



314-8 



314.8 



292.5 

 308.0 

 327.4 

 345-5 

 349.0 

 350.5 



257.7 

 293-2 

 307-9 

 325-1 

 345-5 

 349-6 

 350.5 



8.92X103 

 6.69 Xio' 



7.72 Xio' 

 5.79X103 



7.12 Xio3 

 5.34X103 



Average 

 5.94X103 



from the bulb to remove, as far as possible, the impurities from 

 the apparatus, and refilled with fresh argon at the same pressure — 

 .75 mm. A set of readings were taken immediately and are given 

 in Table V, with a graphical representation in Fig. 8. The curves 

 show nearly the same form as the curves of Fig. 6. The mobili- 

 ties show a reasonable agreement with the mobilities found in 

 Table III. 



The gas was then allowed to stand for several days and another 

 series of readings were taken. These gave values of U practically 

 identical with those found in Table IV, showing that the mobility 

 increases if the gas is allowed to stand in the apparatus. If this 

 increase were caused by impurities, as is believed, the impurities 

 must originate in the apparatus and be relatively minute in volume, 



