A power in nature, a manifestation of energy,
   exhibiting itself when in disturbed equilibrium or in activity by a
   circuit movement, the fact of direction in which involves polarity, or
   opposition of properties in opposite directions; also, by attraction
   for many substances, by a law involving attraction between surfaces of
   unlike polarity, and repulsion between those of like; by exhibiting
   accumulated polar tension when the circuit is broken; and by producing
   heat, light, concussion, and often chemical changes when the circuit
   passes between the poles or through any imperfectly conducting
   substance or space. It is generally brought into action by any
   disturbance of molecular equilibrium, whether from a chemical,
   physical, or mechanical, cause.