the water, noted.  Without moving the plates, the acid between the copper and zinc was agitated by the introduction of a feather.  The bubbles were immediately evolved more rapidly, above twice the number being produced in the same portion of time as before.  In this instance it is very evident that agitation by a feather must have been a very imperfect mode of restoring the acid in the cells against the plates towards its first equal condition; and yet imperfect as the means were, they more than doubled the power of the battery.  The first effect of a battery which is known to be so superior to the degree of action which the battery can sustain, is almost entirely due to the favourable condition of the acid in contact with the plates.

1040.  A second cause of diminution in the force of the voltaic battery, consequent upon its own action, is that extraordinary state of the surfaces of the metals (969.) which was first described, I believe, by Ritter[A], to which he refers the powers of his secondary piles, and which has been so well experimented upon by Marianini, and also by A. De la Rive.  If the apparatus, fig. 103. (1096.), be left in action for an hour or two, with the wire 3 in contact with the plate p, so as to allow a free passage for the current, then, though the contact be broken for ten or twelve minutes, still, upon its renewal, only a feeble current will pass, not at all equal in force to what might be expected.  Further, if P^{1} and P^{2} be connected by a metal wire, a powerful momentary current will pass from P^{2} to P^{1} through the acid, and therefore in the reverse direction to that produced by the action of the zinc in the arrangement; and after this has happened, the general current can pass through the whole of the system as at first, but by its passage again restores the plates P^{2} and P^{1} into the former opposing condition.  This, generally, is the fact described by Ritter, Marianini, and De la Rive.  It has great opposing influence on the action of a pile, especially if the latter consist of but a small number of alternations, and has to pass its current through many interpositions.  It varies with the solution in which the interposed plates are immersed, with the intensity of the current, the strength of the pile, the time of action, and especially with accidental discharges of the plates by inadvertent contacts or reversions of the plates during experiments, and must be carefully watched in every endeavour to trace the source, strength, and variations of the voltaic current.  Its effect was avoided in the experiments already described (1036. &c.), by making contact between the plates P^{1} and P^{2} before the effect dependent upon the state of the solution in contact with the zinc plate was observed, and by other precautions.

  [A] Journal de Physique, lvii. p. 349.

1041.  When an apparatus like fig. 98. (1017.) with several platina plates was used, being connected with a battery able to force a current through them, the power which they acquired, of producing a reversed current, was very considerable.