275. The instantaneous charge of a Leyden battery by the poles of a voltaic apparatus is another proof of the tension, and also the quantity, of electricity evolved by the latter. Sir H. Davy says[A], "When the two conductors from the ends of the combination were connected with a Leyden battery, one with the internal, the other with the external coating, the battery instantly became charged; and on removing the wires and making the proper connexions, either a shock or a _spark_ could be perceived: and the least possible time of contact was sufficient to renew the charge to its full intensity." [A] Elements of Chemical Philosophy, p. 154. 276. _In motion:_ i. _Evolution of Heat._--The evolution of heat in wires and fluids by the voltaic current is matter of general notoriety. 277. ii. _Magnetism._--No fact is better known to philosophers than the power of the voltaic current to deflect the magnetic needle, and to make magnets according to _certain laws_; and no effect can be more distinctive of an electrical current. 278. iii. _Chemical decomposition._--The chemical powers of the voltaic current, and their subjection to _certain laws_, are also perfectly well known. 279. iv. _Physiological effects._--The power of the voltaic current, when strong, to shock and convulse the whole animal system, and when weak to affect the tongue and the eyes, is very characteristic. 280. v. _Spark_.--The brilliant star of light produced by the discharge of a voltaic battery is known to all as the most beautiful light that man can produce by art. * * * * * 281. That these effects may be almost infinitely varied, some being exalted whilst others are diminished, is universally acknowledged; and yet without any doubt of the identity of character of the voltaic currents thus made to differ in their effect. The beautiful explication of these variations afforded by Cavendish's theory of quantity and intensity requires no support at present, as it is not supposed to be doubted.