This photocell looks to be a specialist component and the moulded screw top cap is typical of early 1930s practice. The anode encircles the envelope and has a rectangular window cut into it to allow light in. Running vertically down this window are three fine wires. The cold cathode is semi-circular. The separation of the electrode by placing the anode connection at the top cap could suggest a very high impedance device of operation at elevated Voltages.

The side window envelope is 40 mm in diameter and is 120 mm tall.

Reference: Observation.