On the Electron Atmosphere {?) of Metals. 457 



from Ce to Ta, all these rare earths must contain the same 

 number of nuclear electrons. 



Should the a-particle be composed of 4 (H + ) + 2 electrons, 

 then the number of nuclear electrons should be for U 142, 

 that of the positive units 238, and, 380 particles occupying 

 about 2*7 x 10" 35 c.cm.*, the positive unit must be of equal 

 size, if not identical with the electron (0*5 x 10~ 37 ), but in a 

 different state. 



L. Note on the Electron Atmosphere (?) of Metals. 

 By Carl P. Engltjnd f . 



IN an article published last year % Professor P. W. Wood 

 has advanced a theory of an electron atmosphere to 

 account for some results which he obtained. Some experi- 

 ments performed by me, at Professor Millikan's suggestion, 

 in the Ryerson Laboratory in the University of Chicago, in 

 the spring of 1911, on sparking potentials at small distances, 

 gave results which appear irreconcilable with such a theory 

 and it is perhaps worth while to mention them here. 



A spark-gap was mounted on an interferometer ; one of 

 the electrodes was carefully insulated with ebonite, and both 

 electrodes were provided with mirrors so as to form a double- 

 fringe system. This eliminated the possibility of a defor- 

 mation in the supports which might render the sparking 

 distance between the electrodes at the instant of discharge 

 something less than the distance read upon the double inter- 

 ferometer system. The insulated electrode was connected 

 to a Wilson electroscope, the capacity of the electroscope 

 and electrode being only a few centimetres, and the other 

 electrode was connected to one terminal of a storage-battery 

 giving up to 500 volts. The other battery terminal and 

 electroscope-case were of course earthed (see figure for the 

 connexions). By this means the quantity of electricity dis- 

 charged during a spark was reduced to the smallest possible 

 amount and a minimum corrosion o£ the electrodes was 

 obtained. 



Measurements of the sparking potentials between silver, 

 nickel, and soft steel electrodes, one plane and the other 

 having a radius of 1 cm., from one half to four sodium wa re- 

 lengths apart, gave substantial verification of Hobbs's§ earlier 



* Rutherford, 'Eadioactive Substances,' 1913, p. 621. 

 f Communicated by Prof. R. A. Millikan. 

 t R. W. Wood, Phil. Mag. [6] xxiv. p. 316 (191:?). 

 § Hobbs, Phil. Mag-. [6] ix. p. 617 (1905). 



