Early 1900's cast iron rheostat box from the Wm. H. Swanson Film Motion Pictures For Sale

Early motion picture companies and travelling exhibitors built heavy electrical resistance boxes, known as rheostats, to control the direct current electricity supplied in theatres and town halls. These devices were manufactured by specialized electrical workshops in major American cities during the early days of silent cinema around the turn of the twentieth century. They were housed in robust cast iron cases to withstand the intense heat generated by stepping down high voltage municipal circuits for the carbon arc lamps used in film projectors.

Projectionists and travelling showmen used these rheostats inside projection booths to safely regulate the power flowing into their magic lanterns and early movie machines. Operators adjusted the internal resistance coils using external controls to maintain a steady, bright white light on the screen while preventing the fragile carbon rods from burning out too quickly. As alternating current became standard and projector lamps were redesigned with built-in electronic rectifiers, these heavy manual cast iron rheostats became obsolete and were discarded.