Gaslight

Gaslights were a form of lighting that were first used in London around 1840. They encouraged the city's thriving night life.

Blackthorne Gasworks provided the gas for many of these lights and Morjanus chose it as the location for her proto-morphic lifeform. After three years, the lifeform was fully integrated into the gas system. It caused the lights to shatter and Pyrodines to be released from them. (DWM: The Curious Tale of Spring-Heeled Jack)

The Gelth, being gaseous lifeforms, could survive in the gaslights. When they came to Earth in 1869, they gravitated to the gaslights, returning to them when they could no longer control human corpses. (DW: The Unquiet Dead)