Vol. 7, 1921 
PHYSICS: MILLIKAN AND BARBER 
15 
4. To remove surface films by heat and to determine the effect of such 
films both upon the critical potential (2) and upon the amount of re- 
emission (3). 
200 3OO 
Grid Voltage 
FIG. 3 
400 
500 
5. To determine the effect of temperature alone upon the critical po- 
tential and the amount of re-emission after the surface had been well 
cleaned by the method of (4). 
The apparatus designed in the endeavor to realize these aims and with 
which the following results have been obtained is shown, reduced to one- 
fourth natural size, in figure 1. 
350 
300 
250 
150 
50 
-50 
280 
\ 
Plata Vltava 
=■ 300. 
Preasuro » 6 x lO^on.-v;. 
PI lament Currant = 14 a-nparea 
k 
III- 
i 
3 
11 ii 
296 304 
Grid Voltage 
FIG. 4 
312 
320 
The thermionic emittor consists of a central platinum cylinder 3 mm. 
in diameter, coated with the oxides of barium and calcium, and heated 
indirectly by a central tungsten wire (No. 22) from which it is separated 
