n. An apparatus used in connection with many electrical instruments for reversing the currents from the battery without changing the arrangement of the conductors from the poles: as, Bertin's commutator.n. A contrivance for varying the strength of an electric current by bringing either a portion or the whole of the voltaic cells in a battery into the circuit.n. In electricity, that part of a continuous-current dynamo-electric machine which, by revolving in contact with the brushes, turns or directs the electrical actions in the armature coils of the machine so as to make the current and the voltage in the external circuit continuous.n. In photography, a device for automatically effecting the exposure of a number of photographic plates at various predetermined instants during a total eclipse of the sun.