Sangamo Electric Company Type F Wattmeter, circa 1909

In the late 1800s, companies that supplied electricity to consumers needed a way to measure how much customers used--and then charge them accordingly. Induction-type wattmeters proved reliable and would become the industry standard, but until 1910 Westinghouse held the patents. Sangamo Electric Company, which had not been granted a license from Westinghouse, produced this mercury-motor alternative.