26 
PROF. 0. W. RICHARDSON ON THE EMISSION OF ELECTRONS 
Apart from the hump near — 2 volts, the characteristic in fig. 12 is not very different 
from that in fig. 4. The horizontal stretch from the 50 per cent, point to the 1 per cent, 
point is for fig. 12, x , 1 -40 volts, as compared with the value 1 -20 volts of the stretch 
from the 50 per cent, to the 1 per cent, point for the curve in fig. 4. On the other hand, 
the stretch from the 90 per cent, to the 50 per cent, point in fig. 12 is only 0 -46 volt, 
whereas it is 0 -65 volt in fig. 4. The total stretch from the 90 per cent, to the 1 per cent, 
point is practically the same in both cases, the difference between the two curves being 
that fig. 12 is relatively steeper near the top. The data in fig. 12 are only relied on to 
give the shape of the characteristic. It is not supposed that the relative currents and 
voltages had these values when the photo-electric data were being determined. The 
instantaneous values of the relative chemical currents were determined at the same 
time as the photo-electric data. 
In taking the data in fig. 12 the pressure in each series was less than 0-001 mm. at 
the beginning and equal to 0 -004 mm. at the end. 
The determination of the threshold frequency v 0 was carried out immediately after 
the series x of fig. 12 was completed, the pressure in the apparatus being 0 -0045 mm. 
The measurements are shown in the following table, — 3 being used for the saturation 
voltage :— 
Table V. 
Nature of light 
used. 
Electrometer de¬ 
flection in scale 
divisions per minute. 
Additional capacity 
microfarads. 
Deflection due to 
light. 
Deflection per unit 
light energy. 
No light. 
47 
0-01 
A 4055 
162 
0-01 
116 
14-15 
No light. 
45 
0-01 
A 4355 
160 
0-01 
117-5 
8-00 
No light. 
40 
0-01 
A 4916 
39 
0-01 
0-5 
0-5 
No light. 
37 
0-01 
A 5460 
35 
0-01 
-0-5 
- 0-027 
No light. 
34 
0-01 
The deflections in the second column when no light was used are due to the chemical 
effect which was falling slowly and steadily during these experiments. The values in 
the fourth column are got by subtracting the instantaneous chemical effect (got by taking 
the means of the preceding and following measurements) from the combined effect due 
to light and chemical action when the light is on the drop. The values in the last column 
are got by dividing those in the fourth column by the relevant energy data given in 
Table IV. 
The deflections per unit-light energy are plotted against the frequency of the exciting 
