218 
MR. A. Ll. hughes ON THE 
With a small accelerating potential there was a decided leak with X 2967, hut not 
with X 3126. 
From these three experiments with different surfaces of cadmium distilled in vacuo, 
it appears conclusive that the results satisfy tlie energy law accurately, and that 
LADENBUKcfs law is incorrect. This conclusion is based on the results for X 2537, 
X 2257, and X 1849. Additional support is derived from the fact that the photo-electric 
effect sets in at the wave-length predicted by the theory. 
Zinc .—Experiments similar to those on cadmium were carried out with surfaces of 
distilled zinc. The energy law was found to be obeyed as accurately as in the case 
of cadmium. As the experimental results for zinc (and for all the metals subsequently 
mentioned) are very similar to those for cadmium, it is unnecessary to reproduce them 
here. The velocities in any experiment can be calculated from the values of h and Vy 
which follow. (Each pair of values for k and represents a separate distillation and 
a table similar to Tables IL, Til,, and IV.) 
h Vo 
370x 10-1' 372 volts. 
3-82 ► 379 
3-83 3-83 
379 373 
Mean . . . 379 377 
Magnesium .—Rather more difficulty was experienced in working with magnesium 
than with zinc or cadmium. Except in., the experiment where V^ = 2‘91 volts, the 
effect for X 1849 was rather smaller than in the other experiments, and it was therefore 
more difficult to determine the corresponding maximum velocity. The results of the 
experiments are :— 
k. 
Vo. 
3-45 X 10-1' 
2’91 volts. 
3-33 
3-25 
Mean . 
• 
. 3-39 
3-08 
Bismuth .—The results for bismuth are summarised by the following values for k 
and Vq :— 
7". Vo. 
3'60xl0-i' 3-49 volts. 
3-65 
3-48 
3-63 
3-14 
Mean . . . 3'63 
3-37 
