This air compressor was installed in the Bunker Hill Mine power house in 1899. It was used to compress air for the mine to operate rock drills, small hoists, ore scrappers and some small air-powered locomotives. For the technically minded: It produced 1200 cubic feet of air per minute at 150 pounds per square inch. The entire machine weighed 73.5 tons with the huge flywheel accounting for 21 tons of the total weight. Originally powered by steam.