560 Specific Ionization produced by Corpuscles of Radium. 



When the lower plate is charged positively pp will collect 

 positive ions from the gas, and the total current will be 



y 1 = — N e + ^ Q e f apd. 



When the field is reversed pp will collect negative ions from 

 the gas, and the current will be 



y 2 = — N^ — IStf'ctpd. 



It has been shown by many experimenters that e/m, the 

 ratio of the charge to the mass, is approximately the same for 

 cathode-rays, Becquerel rays, the ions producing the Zeeman 

 effect, and the ions given off by Zn under the action of ultra- 

 violet light, and 1000 times greater than that for the H ion 

 in electrolysis. It has also been shown by J. J. Thomson * 

 (by direct measurement of both) that the charge carried by 

 the ions given out by Zn is the same as the charge on the 

 ions produced in air by Rontgen rays. Townsend t has 

 proved, by direct comparison, that the charges on the ions 

 produced in air by Rontgen rays, Becquerel rays, and point 

 discharges, and on the ions given off by Zn are all equal to 

 the charge carried by the H ion in electrolysis. 



The same experimenter has shown (' Nature/ loc. cit.) that 

 the ions produced in air are identical as regards mass and 

 charge with the ions given off by Zn under the action of 

 ultra-violet light. 



From these facts Prof. Thomson has concluded that in all 

 these cases the charges carried by the negative ions are all 

 equal, and the mass of the carrier about 1000 times smaller 

 than the H atom. Hence in the equations 1 and 2 we may 

 put e = e' and we have 



yi=-N e «(l--<g>d) (1) 



7 S =-No*<l.+apd) (2) 



Prom which we obtain 



— N e=i(Yi+7 2 ) 

 and 1 /yo—yA 



~~ pd\y x + yJ' 



To find the average distance travelled by the corpuscles be- 

 tween PP and pp we know from Becquerel's experiments on 

 the velocity of the deflectable Becquerel rays, that the cor- 

 puscles are projected in all directions from the surface of the 

 radium, hence in these experiments d will lie between 13 '5 mm. 

 (the perpendicular distance between the plates) and 14*3 mm. 

 and cannot be far from 14 mm. 



* Phil. Mag. Dec. 1899. 

 t Phil. Trans. 1899, 1900. 



