Metallic contact is not necessary for the production of Voltaic electricity, which is entirely due to chemical action. The intensity of the Voltaic electricity is in proportion to the intensity of the affinities concerned in its production, and the quantity produced is in proportion to the quantity of matter which has been chemically active during its evolution. Dr. Faraday considers this definite production to be one of the strongest proofs that electricity is of chemical origin. Galvanic or Voltaic electricity is manifested by two continuous forces or currents passing in opposite directions through the circuit: the zinc is the positive end or pole of the battery, and the copper the negative. Voltaic electricity is distinguished by two marked characters. Its intensity increases with the number of plates, its quantity with the extent of their surfaces. The most intense concentration of force is displayed by a numerous series of large plates: light and heat are copiously evolved, and chemical decomposition is accomplished with extraordinary energy; whereas the electricity from one pair of plates, whatever their size may be, is so feeble that it gives no sign either of attraction or repulsion. Common or static electricity is of greater intensity and has a greater power of overcoming resistance than Voltaic electricity, but it acts upon a smaller quantity of matter. However, by diminishing the size of the plates, and increasing their number, the intensity of a battery may be increased till it becomes equal to that of the electrical machine.