in Magnetism and Electricity. 99 



own law of definite electrolysis, when experimenting with a similar 

 pair of plates, had no real existence. Nevertheless, as exception 

 might probably be taken to the fact that the coil was made of an 

 oxidizable metal (though I have no doubt that a coil of platinum 

 wires would behave in precisely the same manner), and in order 

 that a question that has excited so much discussion amongst 

 physicists, and is still regarded by some as an undetermined 

 point in electrical science, might be definitely settled, I was in- 

 duced to repeat Faraday's experiment as nearly as possible in 

 the manner in which he himself conducted it*, but with certain 

 variations which suggested themselves to me while observing the 

 effects produced by the alternating current from the single 

 Grove's cell upon the double coil when immersed in the tub of 

 salt water. 



170. Two glass vessels, Q and R, fig. 15, were filled with the 

 same dilute sulphuric acid, spec. grav. 1*25. The vessel Q con- 

 tained a single pair of amalgamated zinc and platinum plates, which 

 were connected respectively, by means of thick copper wires, 

 with two platinum plates immersed in the vessel R. On introdu- 

 cing a very sensitive galvanometer, or a bit of bibulous paper 

 saturated with a solution of iodide of potassium, into the circuit 

 of one of the connecting wires, the deflection of the needle or the 

 evolution of iodine indicated the passage of an electric current 

 through the liquids in both vessels; but no matter for what 

 length of time connexion was maintained between the electro- 

 motor Q and the electrodes in R (by means of the thick wires), 

 no liberation of gas appeared on the platinum plates in either of 

 the vessels. Hence it was that Faraday inferred that a feeble 

 current might be transmitted from an electromotor without the 

 electrolyzation of the liquids in contact with the electrodes. So 

 convinced;, however, was I that the absence of any appearance of 

 electrolyzation in this case was due to the resistance and reac- 

 tions of the nascent gases enveloping the platinum plates in Q and 

 R, that it only appeared necessary for me to alternately invert 

 the direct current from the electromotor Q, before it arrived at 

 the electrodes in R, in order that the same recombination of gas 

 on the electrodes and increased discharge from the electromotor 

 might be brought about as when the alternating current from 

 the Grove's cell was transmitted through the coil immersed in 

 the tub of salt water. 



171. This alternation of the direction of the current was 

 effected by means of a commutator, S, fig. 15, placed between the 

 vessels Q and R. Care was taken that the alternating metals 

 of the commutator were separated from each other by a sufficient 

 thickness of insulating material to prevent the metals which re- 



* Philosophical Transactions, vol. exxiv. p. 448. 

 H 2 



