DISCONTINUITY OF PUTENTIAL AT SURFACE OF GLOWING CARBON. 315 
Temperature Discontinuity 
absolute. of potential. 
Sodium .  490°-— 700° ... 2°46 volts. 
PRiatinum Soo etore: — love oa. 4:1 ae 
Carbon elo On iOn en Wal: 
These results which are not appreciably altered by 
recalculation with the new value of the ionic charge deter- 
mined by Professor Rutherford and Dr. Geiger,’ seem 
singularly high. If bR/e really represents the discontinuity 
of potential, the fact that the discontinuity varies some- 
what rapidly with temperature for higher values shows 
that b cannot be considered altogether constant. 
In a recent paper Professor Richardson and Mr. Brown? 
originate the theory of a method for finding the kinetic 
energy of the electrons projected from heated materials, 
and they have experimentally determined the component, 
perpendicular to the hot surface, of the velocity with which 
electrons are projected from glowing platinum, the result 
for a temperature of 1650° absolute being 1°5 x 10’ centi- 
metres per second. This velocity of projection, in the case 
of glowing carbon,- may, on certain assumptions, be esti- 
mated from the results already given in the present paper. 
As suggested by one of us’ a point of view is possible from 
which the work done ia connection with the passage of 
the electrons through the surface layer may be considered 
as represented by their translational energy when they 
emerge into the gas. In such a case the surface discon- 
tinuity of potential, V, may be expressed by the equation, 
|= = ier 
where m is the mass of the electron, e the ionic charge, 
and v the component, in the direction of the field, of the 
1 Proc. R.S., A. 81, p. 162, 1908. 
* Phil. Mag., 16, p. 353, Sept. 1908. 
3 Pollock, Proc. Elect. Assoc. N.S.W., 1908-9. 
