Contact Theory

A theory devised to explain electrification, the charging of bodies by friction, or rubbing, and the production of current by the voltaic battery. It holds that two bodies, by mere contact become oppositely electrified. If such contact is increased in extent by rubbing together, the intensity of their electrification is increased. This electrification is accounted for by the assumption of different kinetic energy, or energy of molecular motion, possessed by the two bodies; there being a loss and gain of energy, on the two sides respectively, the opposite electrifications are the result. Then when separated, the two bodies come apart oppositely electrified.

The above accounts for the frictional production of electricity. In the voltaic battery, a separation of the atoms of hydrogen and oxygen, and their consolidation into molecules occurs, and to such separation and the opposite electrification of the electrodes by the oxygen and hydrogen, the current is attributed, because the hydrogen goes to one electrode, and the oxygen to the other, each giving up or sharing its own charge with the electrodes to which it goes. If zinc is touched to copper, the zinc is positively and the copper negatively electrified. In the separation of hydrogen and oxygen, the hydrogen is positively and the oxygen negatively electrified. In the battery, the current is due to the higher contact difference of oxygen and hydrogen compared to that between zinc and copper. It will be seen that the two contact actions in a battery work against each other, and that the current is due to a differential contact action. The zinc in a battery is electrified negatively because the negative electrification of the oxygen is greater in amount than its own positive electrification due to contact with the copper.