[A] Philosophical Transactions, 1801, p. 247.

77.  Marianini has discovered and described a peculiar affection of the surfaces of metallic discs, when, being in contact with humid conductors, a current of electricity is passed through them; they are then capable of producing a reverse current of electricity, and Marianini has well applied the effect in explanation of the phenomena of Ritter’s piles[A].  M.A. de la Rive has described a peculiar property acquired by metallic conductors, when being immersed in a liquid as poles, they have completed, for some time, the voltaic circuit, in consequence of which, when separated from the battery and plunged into the same fluid, they by themselves produce an electric current[B].  M.A.  Van Beek has detailed cases in which the electrical relation of one metal in contact with another has been preserved after separation, and accompanied by its corresponding chemical effects[C].  These states and results appear to differ from the electro-tonic state and its phenomena; but the true relation of the former to the latter can only be decided when our knowledge of all these phenomena has been enlarged.

  [A] Annales de Chimie, xxxviii. 5.

  [B] Ibid. xxviii. 190.

  [C] Ibid. xxxviii. 49.

78.  I had occasion in the commencement of this paper (2.) to refer to an experiment by Ampere, as one of those dependent upon the electrical induction of currents made prior to the present investigation, and have arrived at conclusions which seem to imply doubts of the accuracy of the experiment (62. &c.); it is therefore due to M. Ampere that I should attend to it more distinctly.  When a disc of copper (says M. Ampere) was suspended by a silk thread and surrounded by a helix or spiral, and when the charge of a powerful voltaic battery was sent through the spiral, a strong magnet at the same time being presented to the copper disc, the latter turned at the moment to take a position of equilibrium, exactly as the spiral itself would have turned had it been free to move.  I have not been able to obtain this effect, nor indeed any motion; but the cause of my failure in the latter point may be due to the momentary existence of the current not allowing time for the inertia of the plate to be overcome (11. 12.).  M. Ampere has perhaps succeeded in obtaining motion from the superior delicacy and power of his electro-magnetical apparatus, or he may have obtained only the motion due to cessation of action.  But all my results tend to invert the sense of the proposition stated by M. Ampere, “that a current of electricity tends to put the electricity of conductors near which it passes in motion in the same direction,” for they indicate an opposite direction for the produced current (26. 53.); and they show that the effect is momentary, and that it is also produced by magnetic induction, and that certain other extraordinary effects follow thereupon.

79.  The momentary existence of the phenomena of induction now described is sufficient to furnish abundant reasons for the uncertainty or failure of the experiments, hitherto made to obtain electricity from magnets, or to effect chemical decomposition or arrangement by their means[A].