English: One of the first mercury arc rectifier bulbs, invented by Peter Cooper Hewitt in 1902. It consists of a partially evacuated glass bulb with a cathodeelectrode at the bottom consisting of a pool of the liquid metal mercury, and two graphite anode electrodes at top. The mercury arc rectifier was used into the 1970s to provide high power DC current to power industrial motors, electric locomotives, streetcars, and battery chargers.
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