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 liis observations with that theory sufficiently proves that 

 they were made with great accuracy. 



11. 



Since 1831 Mr. Fai'aday 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 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, abun- 

 dantly disengaged on the surface of the zinc, does not contribute any- 

 thing to this effect. On taking a plate of amalgamated zinc, instead of 

 common zinc, or some amalgam of zinc, tliere 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 diflPerent 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 tiie 

 chemical action, to decompose bodies, is incontestably proved by the 

 numerous and ingenious experiments of Mr. Faraday. It will not be 

 long l)efore 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 

 • ffects are much more decided. Moreover a voltaic pair of plates of 



2 n2 



