TO THE MOVEMENT OF MACHINES. 517 
The second column of the preceding table, which contains the perime- 
ter 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. 
Lite 
Since 1831 Mr. Faraday has published from time to time experi- 
ments made with a view to investigate the nature of electricity and of 
its various effects. These experiments, both from their extent, the cer- 
tainty and ingenious sagacity which they manifest, and the abundant 
results to which they have led, deserve to be ranked with the most emi- 
nent 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 zine 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, abun- 
dantly disengaged on the surface of the zinc, does not contribute any- 
thing to this effect. On taking a plate of amalgamated zine, instead of 
common zine, or some amalgam of zinc, there will be no develop- 
ment of gas except when the circuit is closed ; in breaking it this de- 
velopment 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 quan- 
tity 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 zine is much more positive than common zine, and its 
effects are much more decided. Moreover a voltaic pair of plates of 
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