PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 3 APRIL 15. 191 7 Number 4 
A RE-DETERMINATION OF THE VALUE OF THE ELECTRON 
AND OF RELATED CONSTANTS 
By R. A. Millikan 
RYERSON PHYSICAL LABORATORY, UNIVERSITY OF CHICAGO 
Communicated, February 5, 1917 
This re-determination of the most fundamental of physical constants 
was entered upon three years ago for three reasons. 
First, in 1913 results began to be published from Vienna/ which though 
obtained by a modification of my method,^ were wholly irreconcilable 
with those which I had found; and I accordingly wished to see whether 
I could find conditions under which the method failed. 
Second, there developed a tendency,, especially among British physi- 
cists, to adopt a value of e about 2% lower than that which I had ob- 
tained, and as this difference was much greater than the necessary error 
in my method I was anxious to see, by entirely new work, whether a 
numerical error could have crept into the former determination. 
Third, the electron has recently taken on added importance because 
it has been found to carry with it not merely all molecular and atomic 
magnitudes, as heretofore, but also all of the most significant of the 
radiation constants, such as Planck's the Stefan-Boltzmann constant 
(7, the Wien constant C2, all X-ray constants, i.e., the wave lengths of 
characteristic X-rays, etc.^ It seemed worth while therefore to drive 
my method, which is certainly exceedingly exact if its validity is granted, 
to the utmost limit of its possible precision. 
The method is the same as that used in the preceding determination,^ 
but the apparatus is new throughout and every constant entering into 
the value of e has been redetermined with increased care and precision. 
The condenser plates MN (fig. 1) consist of two optically flat brass 
surfaces 22 cm. in diameter, held apart by three small pieces of echelon 
plates about 1 cm. square and 14.9174 mm. thick placed at points 60° 
231 
