Samuel Gardiner's lamp-hour meter (1872) Up
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This was one of the earliest meters and the first known model to be patented. It was used with the earliest DC arc-lamp systems and only measured the time energy was supplied to the load as all the lamps connected to this meter were controlled by one switch. The internal workings were nothing more than a clock that was started and stopped by a electromagnet that was connected in series with the load. With the introduction of Edison's light bulb, subdividing lighting circuits became practical and this meter became obsolete, replaced by meters such as Edison's chemical meter and the Thomson Recording Wattmeter. Gardiner meter
Westinghouse Handbook of Watthour Meters