ME. A. Ll. HUC4HES ON THE 
It would follow from this, that only those electrons which do not undergo any 
scattering (or, more accurately, which do not suffer any reduction in velocity through 
scattering) can emerge. It is proposed to investigate this important point in. further 
experiments. 
(iv.) The values of k and (Table V.) for the elements investigated in this 
research change in the same direction, though the changes in Vy are considerably 
greater than those in L The variations in k are a little larger than the possible 
errors of experiment. 
The photo-electric effect was one of the first phenomena to be interpreted on the 
quantum theory of radiation. If the energy of the photo-electron is equal to that in 
the quantum, Jm, where h is Planck’s constant, then we should have 
Ve = h7i. 
This gives a definite value for our k. The value of hje is numerically equal to 
4T9 X The experimental values of k, which vary from 3’17 x to 3'79 x 10“^*, 
suggest, on this view, that only a fraction of the energy of the quantum is ti’ansferred 
to the electron. Had the experimental values for k been grouped about the theoretical 
value hje, one would almost be compelled to conclude that k was a constant for all 
metals and equal to the quotient of these two universal constants. However, as the 
experimental values are well outside the theoretical value, there is no reason on the 
quantum theory why they should be the same lor all elements, as the sharing of 
the energy between the electron and the parent molecule may depend on the nature 
of the element. 
The view that the quantum is a localised vehicle for radiant energy of dimensions 
comparable with those of a molecule is not now accepted. The earlier view led to a 
very simple explanation of photo-electricity. Nevertheless, some new way of 
considering the phenomena in terms of the quantum theory may explain many of the 
results. A molecule may have to be in a condition to accumulate energy to the 
amount hn before it can emit an electron carrying away a definite and, for any one 
substance, a constant fraction of the energy away with it. In some way such as this 
the energy law coidd be accounted for. 
(v.) Sir J. J. Thomson'^ has given a theory of the photo-electric effect, based on 
resonance, which leads to the law verified in these experiments, that the energy of 
the photo-electron is proportional to the frequency of the light. It was shown that 
if an electron rotates on a certain cone at whose apex there is an electrical doublet, 
its energy of motion is proportional to the frequency. If light of the same period 
passes over the system, resonance takes place, and the electron is expelled with about 
the same energy as it had in its orbit. 
(vi.) The experimental relation V = hi — suggests that the electron starts initially 
* Sir J. J. Thomson, ‘Phil. Mag.,’ XX., p. 238, 1910. 
