Hydro-electric machine invented in 1840 by William George Armstrong, after an engine man tending a steam engine received an electric shock when he put one hand on the safety valve of his boiler while his other hand was exposed to a jet of steam.

This specimen, made by Watkins & Hill, is incomplete: the insulating glass legs and the chimney of the iron boiler are missing. The stop-cock at the top of the dome allows the steam to enter the brass box fitted with four nozzles. The box contained cold water so that the steam underwent partial condensation before escaping through the jets, for Michael Faraday had discovered that if the steam was perfectly dry (i.e., contained no water droplets in suspension), no electricity was produced. The electricity was collected by a separate insulated conductor. In the hydro-electric machine, water drops in the jets of steam became electrically charged because of friction with the wooden walls of the nozzles. This system was the largest source of high-voltage static electricity at that time. However, it caused a rapid increase in the humidity of the room where it operated, making electrostatic experiments difficult to perform. Provenance: Lorraine collections.