An effect produced upon the plates of a voltaic
   battery, or the electrodes in an electrolytic cell, by the deposition
   upon them of the gases liberated by the action of the current. It is
   chiefly due to the hydrogen, and results in an increase of the
   resistance, and the setting up of an opposing electro-motive force,
   both of which tend materially to weaken the current of the battery, or
   that passing through the cell.