A rectifier changes AC (alternating current) electricity to DC (Direct Current). Modern rectifiers use silicon diodes, but this vintage glass version has six electrodes (for rectifying three phase current). Current applied to the electrode at the base both heats the mercury to make an electrically-conductive vapour, then forms an arc in the mercury vapour to each electrode in turn. This example was used in the Istanbul Kadiköy-Moda tramway power supply.
Y: 63 cm G: 55 cm