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112 pulled apart against this attractive force, and energy is therefore required to produce this motion. It is this energy which, by the action of the machine, is converted into the potential energy represented by the electric field surrounding the two electrodes. To increase the charge it is customary to connect the electrodes with the knobs of two Ley den jars, since by the use of a condenser the quantity of electricity, which can be accumulated with a given difference of potential, is greatly augmented. That energy is used in producing electrification is distinctly felt when working the machine by hand. The machine gets charged after a few turns of the handle, and the operator feels that, as the charging progresses, it gets harder to turn the handle. In large machines the manual work becomes so heavy that it is convenient to use an electric motor for working the machine.