THEORY OF GALVANISM. 133 



strument may |3e rendered either positive or nega- 

 tive, by connecting it with the conductor or rubber 

 of the electrical machine; and yet its operation is 

 riot in any degree affected. He also contrived an 

 apparatus, in which there were three wires placed 

 between the extremities of the pile, two of them 

 connected with the ends of the pile, and the third 

 in the centre ; the wires having water interposed 

 between them, and electrometers so situated, as to 

 ascertain the electric condition of the w^ires. In 

 the ordinary state of the apparatus, the terminal 

 ing. wires were one positive and the other negative, 

 corresponding to the ends of the pile to which they 

 were attached, while the central wire was neutral ; 

 yet the ends of this neutral wire produced opposite 

 electrical effects, one separating oxygen, and the 

 other hydrogen. By altering the apparatus, the 

 electrical state of the wires was altered ; the cen- 

 tral wire was rendered at one time positive, and 

 afterwards negative, and the state of the termin- r&s?i*iD 

 ating wires was reversed; yet no change took 

 place in the chemical action of the wires, each of 

 them continuing to evolve oxygen and hydrogen 

 as at first, and the two ends of the central wire 

 separating oxygen and hydrogen respectively at 

 its extremities, in the same manner whether the 

 Avire itself was positive, negative, or neutral.* 



Mr. Singer has proposed an objection to Sir H. singer's <rt>, 

 Davy's hypothesis, very similar to this of De Luc. jet 



* Nicholson's Journal, xxvi. 124-, et alibi. 



