Also known as "salt-water dimmer" or colloquially in the UK as a "piss-pot" dimmer, for obvious reasons that require no further detail in this forum. An archaic type of resistance dimmer that used a vessel of electrically conductive liquid (salt-water or copper-sulfate solution) and two long copper electrodes. Using ropes and pulleys, when the electrodes were completely out of the solution, the light would be off. The deeper the electrodes were lowered, the brighter the light. Obviously, inherently unsafe, as well as maintenance-intensive, as the solution would need to be replenished as it boiled off and evaporated; as well as the electrodes which corroded as they were eaten away. UK-based Lighting Designer Richard Pilbrow purports to have used this type of dimmer on a show as late as 1957. (Let There Be Light. Robert Bell. Entertainment Technology Press, 2004. p. 7.) Always homemade, as I have never found a mention of these being commercially manufactured by Century, Kliegl, Major, or in the UK, Strand Electric. See also http://www.compulite.com/stagelight/html/history-5/salt-dimmers.html and http://cuetocue.backstagejobs.com/?p=198 .