Edison electrolyte meter, c 1881.
© Science Museum / Science & Society Picture Library
This early electricity meter was designed by Thomas Alva Edison (1847-1931) to use electrolysis to measure the consumption of electricity. When electricity pased through the copper sulphate solution (in the jars) the current would cause the copper on one plate to disolve and be deposited on the other plate. Therefore, the difference in weight of the copper plates was proportional to the amount of electricity used. The lamp and resistance wire at the bottom of the meter prevented the solutions from freezing in winter.