212 On the Constitution of the Electric Fluid. 



charged torrents of electricity and gave sparks 22 inches long, 

 could only produce a deflection of 20° or 30°. 



In my experiments already described, a bit of copper wire 

 weighing yyVa^d of a grain, in connexion with a platinum wire, 

 by a momentary contact with nitric acid, caused the needle to 

 whirl round three times, that is, with an effect incomparably 

 greater than the maximum in the experiments of Colladon and 

 Faraday. An atom of gold-leaf weighing ^^dthof a grain caused 

 deflection to 180°. In neither case was perhaps the ten-thou- 

 sandth part of a grain of metal dissolved before deflection com- 

 menced. Is it possible that such a chemical action, which almost 

 exceeds comprehension for minuteness of effect and of duration, 

 should, in its results on the galvanometer, rival the enormous 

 pow ers of the plate machine and the hydro-electric machine, if 

 the agent in both cases had been the same? Some scientific 

 questions are best decided by common sense ; and if common 

 sense decides that a particle of copper scarcely visible dipped in 

 nitric acid for an instant, producing no obvious effect of electri- 

 city, does notwithstanding evolve more of that fluid than a 

 hydro-electric machine, which pours out an incessant stream of 

 long sparks, I must then admit that my arguments are worthless. 



But there is one experiment of Faraday which deserves parti- 

 cular notice. He found that, without any Leyden battery, he 

 could produce deflection merely by conducting electricity from 

 the prime conductor to one end of the galvanometer coil, while 

 the other end was in communication with a discharging train, 

 that is, a metallic connexion with the gas-pipes and water-pipes 

 in the street. Thus the electric fluid passed from the conductor 

 directly through the galvanometer, and hence to the common 

 reservoir. The principal feature in this experiment is, that no 

 negative conductor was employed, nor were means used for 

 bringing the negative state of electricity into operation ; the de- 

 flection was therefore obtained by a current of positive electricity 

 only. The condition for producing deflection by voltaic elec- 

 tricity, is invariably by means of two polar conductors, one of 

 which is said to carry positive electricity, the other negative, no 

 matter whether these be different states or different fluids ; both 

 of the poles must be in operation, and the moment either is 

 withdrawn, by interrupting the circuit, the power that causes 

 deflections, and all the other phenomena, ceases to act. But in 

 Professor Faraday's experiment this condition was not fulfilled. 

 There was no connexion of two polar conductors with the coil ; 

 positive and negative electricity were not in operation; there 

 was no circuit ; in fine, the circumstances were totally different 

 from those under which voltaic deflection is produced. In the 

 voltaic series, the negative wire is not passive, like the discharging 



