14 
PHYSICS: MILLIKAN AND BARBER Proc. N. A. S- 
the gaseous form. A considerable group of investigations has accordingly 
been begun in the Ryerson Laboratory for the purpose of determining, 
in the best vacua obtainable with modern means, the effect of surface con- 
ditions upon the emission of electrons from solids and liquids. Pre- 
liminary results from one of these investigations are reported herewith. 
The aims sought were : 
1. To differentiate between the primary electrons which are reflected 
from a copper surface, and those which are emitted by such a surface 
because of the bombardment of the primaries. 
400 
350 
X 
300 
a 2 5o 
a 
s -' 200 
150 
50 
1 
\ 
X 
Plate Voltage = 100. 
Treasure = 1.2 x lO-^ci.H? 
?ll»rent Current = 14 ampe 
1 i 
40 
80 120 
Grid Voltage 
FIG. 2 
160 
2. To determine the exact potential at which the surface begins to re- 
emit under such bombardment. This will be called the ionizing potential 
of the surface. 
3. To determine the number of electrons re-emitted per impinging 
electron as a function of the energy of impact. 
