of Determining the Elementary Electrical Charge, 225 



§ 8. The Most Probable Value of the Elementary 

 Electrical Charge, 



There are four recent independent determinations of e in 

 addition to the above, the results of which seem to be 

 deserving in each case of much weight. They are : — 



1. Planck's value* 4*69 x 10 -10 based upon theoretical con- 

 siderations, and Kurlbaum^ experimental data. 



2. Rutherford and Geiger's value f, 4'65 x 10~ 10 , obtained 

 by counting the number of a. particles emitted by a known 

 quantity of radium and measuring the total electrical charge 

 carried by these particles. 



3. Regener's value $ } 4*79 x 10 ~ 10 , obtained by remarkablv 

 careful and consistent work in the counting of the number 

 of scintillations produced by the a particles emitted by a 

 known amount of polonium and measuring the total charge 

 carried by these same particles. (Regener estimates his 

 error at not more than 3 per cent.) 



4. Begeman's recent and as yet unpublished value of 

 4*67 x 10" 10 , obtained as a mean of a very large number of 

 consistent observations made in the Ryerson Laboratory by 

 Wilson's method. 



As already indicated the chief source of error in the pre- 

 ceding determination by Begeman and the author, using 

 Wilson's method, was the wrong assumption as to the 

 viscosity of the gas through which the cloud fell. In the 

 light of the results obtained above both as to this matter and 

 as to the rate of evaporation of multiply-charged drops, 

 Wilson's method, although still involving theoretically more 

 elements of uncertainty than the method herewith presented, 

 may yet be made, as liegeman's results demonstrate, a con- 

 sistent and apparently a reliable means of determining e, 

 particularly if the observations in the electrical field are 

 made upon multiply-charged layers. Begeman's observations 

 so made show a most satisfactory concordance. 



In addition to the rive independent determinations above 

 considered there are four other important and interesting 

 pieces of work by Ehrenhaft, Broglie, Perrin, and Moreau, 

 all of which lead to estimates as to the value of e. These 

 estimates have not been included in the final mean given 

 below for the reason that the methods employed by these 



* Planck, Warme Strahlung (Barth), p. 163 (1906). 



f Rutherford and Geiger, Proc. Rov. Soc. A, vol. lxxxi. pp. 141 & 161 

 (1908). 



X Regener, Sitz.-Ber. der K. Preuss. Acad, der Wiss. vol. xxxviii. 

 p. 948 (1909). 



Phil. Mag. S. 6. Vol. 19. No. 110. Feb. 1910. Q 



