Electrical MeterAfter electrical power began being delivered to homes and businesses, the electric industry needed a way to properly measure the amount of electricity that was being used. Tesla once again stepped up and created an Electrical Meter, which is composed of two carbon filaments inside of a glass vacuum tube. As an electric current passes from one filament to the other, tiny pieces of carbon also jump from one filament to the other. By measuring the resistance of each filament before and after, the amount of electricity used can be derived.
Image courtesy of Tesla Universe