They've been a mainstay of Sci-Fi props for years but you'll be hard pressed to find someone on the street that can tell you what they actually do. They're Mercury Arc Rectifiers and our friends at Oobject have collected nine of the best.

If you're looking for more accouterments for your evil laboratory, might I suggest these Frankestein's Lab Items, this homage to the light bulb, or therse crazy Tesla Coils?

A three phase, six anode mercury arc rectifier, formerly used at a 600V DC traction substation of the Athens-Piraeus railway

Household Mercury Arc Rectifier

Mercury rectifier on display in Beromunster, Switzerland

Mercury Vapour Arc Rectifier from University of Aberdeen Collection

Rectifier at the Cengelhan Koc Museum in Turkey

Rectifier from Type 80 Early Warning Radar System

The two mercury arc rectifiers at Kempton Steam Museum, London

Twin Mercury Arc Rectifiers from the Doncaster Odeon movie theatre

Working Mercury Arc Rectifier