The second column of the preceding table, which contains the perimeter of the plates, represents at the same time the forces according to the law of M. dal Negro. That distinguished experimentalist did not make these experiments to verify the theory of M. Ohm; but the beautiful agreement of his observations with that theory sufficiently proves that they were made with great accuracy.
11.
Since 1831 Mr. Faraday has published from time to time experiments made with a view to investigate the nature of electricity and of its various effects. These experiments, both from their extent, the certainty and ingenious sagacity which they manifest, and the abundant results to which they have led, deserve to be ranked with the most eminent labours which have ever been made in physics. By a happy chance, which I cannot over-appreciate, these labours coincide with the efforts which I have made to render available the mechanical action of magnetism.
In observing a voltaic pair of plates of copper, silver or platina, and of common zinc plunged into acidulated water, we notice a great development of hydrogen gas. If the circuit be not closed this gas will be developed only on the surface of the zinc; but if the circuit be completed, there will be also a development of gas on the surface of the copper, or in general on the negative plate. This last quantity of gas is incomparably less than the first, and yet it is from this alone that the magnetic power of the connecting wire proceeds. The gas, abundantly disengaged on the surface of the zinc, does not contribute anything to this effect. On taking a plate of amalgamated zinc, instead of common zinc, or some amalgam of zinc, there will be no development of gas except when the circuit is closed; in breaking it this development ceases, the zinc in this combination not being attacked by the acid, or not being able of itself to decompose the water. It is not easy to explain this extraordinary fact. In such a pair of plates all the hydrogen gas, or its equivalent of zinc, serves to produce an electric current, whose magnetic force, calorifying power, and chemical action, are in a direct ratio to the quantity of disengaged gas or of oxidized zinc; and these different effects may equally serve to measure the quantity of electricity passing through the connecting wire, or even through the apparatus. The definite action of electricity, with regard to the chemical action, to decompose bodies, is incontestably proved by the numerous and ingenious experiments of Mr. Faraday. It will not be long before he will prove the law with regard to other effects; but the conviction of genius gives the right to anticipate experiment, and to announce great laws.
Amalgamated zinc is much more positive than common zinc, and its effects are much more decided. Moreover a voltaic pair of plates of
