Each of the copper electrodes of the cell was coated chemically with a layer of cuprous oxide. The electrolyte used was a one percent solution of lead nitrate. With an amplifier and cathodehyphen;ray oscilloscope the open circuit e.m.f. of the cell was studied for sinusoidally varying illumination of one electrode. The frequency response, the spectral response, and the phase shift between e.m.f. and illumination were determined. A.c. bridge measurements showed that the capacitance of the cell was large and that the greater portion of it conforms to the relation for electrolytic capacitance,C=C0/ffrac12;. The capacitance increases with illumination. The results are interpreted in terms of an equivalent electrical network whose elements have values corresponding to those of the cell as measured with the bridge. The computed results for the network are in excellent agreement with the observed results for the cell throughout the whole frequency range (0 to 10,000) when it is assumed, (1) that the primary effect of illumination is to cause electrons to pass through the ``barrier layer'' from the oxide to the copper, and, (2) that the number of such electrons is linearly proportional to the intensity of the light. The results thus lead to the conclusion that the photoactivity of this cell is to be explained in the same manner as that of the dry cuprous oxide cell, except that the electrolyte takes the place of the front electrode in making contact with the oxide.
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