Photo-emission of electrons from an electrode into a solution has seemed to be well described by the quantum mechanical theory of Brodsky and Gurevich 1 and recently Rotenberg et al. 2 have shown that if more fully developed forms of the theory 3'4 are used, and allowance is made for effects connected with (a) the finite thickness of the discrete part of the double layer and (b) the slight dependence of the average distance for hydrated electron deposition on potential, the variation of threshold potential with quantum energy deduced from experimental data using the B G theory is in harmony with expectations and earlier s discrepancies can be understood. Pleskov and co-workers conclude that, since the quantum efficiency shows no marked dependence on wavelength, the attenuation of the light within the mercury phase must be extremely rapid. Thus it would seem that one of the postulates of the original form of the B-G theory, namely that emission results from interaction between electrons at the interface and the component of the electric vector normal to the interface, may be almost realised in practice. This postulate leads to a dependence of emission on the square of the cosine of the angle between the plane of incidence and the plane of polarisation (the direction of the electric vector) when linearly polarized light is employed. The work of De Levie 5 and of Korshunov and co-workers 6 suggests that such a dependence does occur. On the other hand in view of (a) the expected appreciable penetration of the electrode by light and (b) the fact that photo-emission into vacuo is known 7 to involve the formation of "hot" electrons by homogeneous absorption of light in the metallic phase, it would seem that electron emission from mercury into solution could take place by the evaporation from the mercury surface of energetic electrons formed, on the average, at a distance from the interface large compared with the thickness of the discrete part of the double layer. Such "hot" electrons are likely before evaporation to be scattered** by the ions and electrons of the mercury phase and hence the dependence of emission on the direction of the electric vector could * Attached from Istituto Chimico "G. Ciamician" e Centro di Studio di Elettrochimica Teorica e Preparativa dell'Universitfi, Laboratorio di Fotochimica e