On June 11, 1889, the G.M. Davis Regulator Company of Chicago, Illinois patented the Victor No. 2, an automatic air vent for steam radiators. It worked by the expansion of a composition element. It would be years before the industry produced a truly reliable air vent that didn't squirt water all over the curtains but this was a nice start. Nowadays, we take air vents for granted but they did not arrive easily.