Liquid Dimmers (1915 - 1945)
Strand

Liquid Dimmer

Glazed earthenware jars, complete with fixed & moving lead cones.
(Made by a number of companies, not just Strand)

Also known as salt water dimmers and electrolytic dimmers.
Liquid dimmers can be used on DC or AC supplies.
The power supply is connected to two contacts in each dimmer. There's a fixed connection at the bottom the the dimmer jar, and a moving contact connected (via an insulator) to a steel wire which is moved by the control system (via pulleys). The distance between the contacts affects the voltage passed to the load (lantern). When the contacts are closest together (touching), maximum voltage is passed. As the contacts are moved apart, the amount of resistance increases, as more and more salt water is between them. At the lowest dimmer output, the water is taking on the energy of almost all of the voltage, and can even start to boil. The water must be topped up regularly.
The concentration of electrolytes in the water can be changed to enable the dimmer to be used on a range of diffferent loads. The salts are provided by washing soda crystals.

The last electrolytic dimmers were replaced in London in 1959.