in Magnetism and Electricity. 97 



dually became red-hot, while the thicker wire at N, though 

 hotter than could be endured by the finger, was not made 

 visibly red during the maintenance of the battery-contact. 



161. On reversing the battery-connexions, by joining the end 

 A to the platinum and the end B to the zinc by means of the 

 thicker wire at N, this wire immediately became bright red-hot, 

 while the thinner wire at C D remained cold ; but on continu- 

 ing the battery-contact for about a minute, the thicker wire at 

 N gradually became less bright, until it finally ceased to be 

 visibly red, when the thin wire at C D again became red-hot ; 

 and as often as the battery-connexions were reversed, so often 

 did the wires at the battery and distant ends of the coils become 

 alternately, but never simultaneously red-hot. 



162. Another phenomenon attending the alternate heating of 

 the iron wires was the liberation' of hydrogen from the double 

 coil only during such time as the thin wire at C D was main- 

 tained at a red heat, but never while the thicker wire at N was 

 heated ; for as often as the battery-connexions were reversed, 

 the liberation of hydrogen from the coil immediately ceased, and 

 did not reappear until the thin wire at C D was reheated. 



163. Moreover, on making and breaking contact between the 

 ends A, B of the double coil after they had been maintained in 

 connexion with the Grove's cell for a short time with the ends 

 C, D disconnected, sparks could be obtained from the coil for 

 more than five minutes after all connexion with the electromotor 

 had been broken ; the galvanometer, as might have been expected, 

 always indicated a strong secondary current from the coils, in 

 the reverse direction to that transmitted by the electromotor. 



164. From a consideration of the foregoing experiment, made 

 with the view of explaining the absence of any appearance of 

 electrolyzation of the water in the tub by the alternating currents 

 from the electromagnetic machines, it will be evident, from the 

 heating of the thin wire at CD when contact was first made 

 between the battery and the double coil, that the hydrogen 

 evolved by the electrolyzation of the water formed an insulating 

 envelope surrounding one of the conductors, which thereby 

 enabled a considerable portion of the current from the electro- 

 motor to traverse the conductors instead of being transmitted 

 through the water. But when the battery-contacts were re- 

 versed, the cessation of the stream of hydrogen from the coil, 

 and the non-heating of the thin wire at C D, indicated the re- 

 union of the hydrogen envelope with the liquid in contact with 

 the conductor ; while the hydrogen evolved by the new current 

 on the other conductor did not become visible until its affinity 

 for the oxide produced by the previous current had been satis- 

 fied. But by continuing the battery-contact, a new hydrogen 



Phil. Mag. S. 4. Vol. 36. No. 241. Aug. 1868. H 



