The Kelvin water dropper making sparks out of running water is so out of this world. How did this project evolve? Even with today's knowledge it wouldn't even come to mind to make something like that!
In 1859 Kelvin was studying atmospheric electricity, and he wanted to monitor how the atmospheric potential gradient varies over time. He invented a water-dropper equaliser, a simple and robust device that was capable of making continuous recordings of the potential gradient. 1 In 1867 he realised that two droppers could be arranged in a reciprocal way to produce an interesting water-dropper generator. 2