Relation of Electrode Fall to Contact Potential Series. 387 
[Nore (June 12th).—In a letter to ‘Nature’ of June 9th 
Prof. Nagaoka states that his system is not electrically 
neutral, but that the central charge is very large compared 
to the total charge of the ring; the remaining negative 
electrons necessary to make the whole system neutral are 
left out of account. This no doubt renders part of my 
criticism inapplicable, because by sufficiently increasing the 
central charge the ring can certainly be made stable ; but 1s 
this allowable ? 
It is not clear that the negative electrons outside the ring 
can be left out of account in discussing the ring, for their 
charge is comparable in amount with the central charge ; 
let us however assume, with Prof. Nagaoka, that they can. 
The equation of steady motion, (11) p. 450, gives w*=S, for 
K is small because the negative electrons of the ring are few. 
2 : 2 
With S= “. we get wa? = ~~; wais the velocity of the ring: 
ma” ma 
this must be less than the velocity of light, else the problem 
is fundamentally altered ; with the usual values of a, = and e, 
this gives v< 50,000. Next, the equation (12) p. 450 gives 
for the imaginary frequency —n’?=6yuJ, whence 
@ V 
for a ring of 10 electrons J=34, and with v=50,000 we get 
in other words, the disturbance would increase 2°7 fold in 
about 3 revolutions. The system is again far too unstable. | 
Yours faithfully, 
G. A. ScHort. 
XXXVIII. The Relation of Electrode Fall in Gases to the 
Contact Potential Series. By CLARENCE A. SKINNER, 
Ph.D., Assistant Professor of Physics in the University of 
Nebraska, Lincoln*. 
a a former paper { the writer suggested that the series of 
metals, obtained when these were arranged according 
to the magnitude of the fall of potential at the electrodes when 
the glow-discharge passes through a rarefied gas, is closely 
related to the contact-potential series. 
* Communicated by the Author. 
f* Phil. Mag. [6] 11. p. 637 (1901) 
