Designed by Sir Oliver Lodge.
Dating to the early years of last century.

5 1/2” (14 cms) bulb.

Total weight  205 Grams  (7 oz.).

One electrode is a large aluminum spiral, connected to one side of the bulb, while the other is a small metal (Iron?) rod  in the distal part of the narrow stem, in the axis of the thin internal copper shielding protecting the surrounding glass (see x-ray picture).

Such tubes usually contain air at a very low pressure, and the rectification process is due to the important size asymmetry of the electrodes, with the current flowing much more easily in one direction than in the opposite one.

Note the looped platinum wire external connections of the electrodes, as usually found in very early x-ray tubes. Later makes of this rectifier are equipped with dome-shaped brass terminals.

The round mark on the glass bulb reads “Sir O.LODGE *Patent*240”.