On Electro-magnetic Induction. 425 



these bodies is moveable. They have studied the remarkable 

 effects which the magnet produces upon the voltaic arc, and 

 the sounds which it gives rise to in the conductors traversed 

 by discontinuous currents. But they appear not to have in- 

 vestigated the influence which might be exercised by the mag- 

 netic or diamagnetic state developed in various substances on 

 their conducting power. The following experiments are in- 

 tended to fill up this blank. 



217. An electro-magnet was set in action by a Grove's 

 battery of ten large pairs, and rendered capable of raising 

 several hundredweight. The conductors of the battery com- 

 municated with two little cups filled with mercury. The 

 wires of the electro-magnet terminated in two other similar 

 cups. In effecting the junctions by the aid of the commutator 

 already described (152.), the direction of the magnetization 

 was made to vary at will, and very rapidly. 



218. A zinc and copper pair, of small dimensions, was 

 plunged into distilled water. The current was conveyed by 

 long strips of thick copper, intended to comprise in their cir- 

 cuit the bodies to be magnetized, and an excellent Ruhm- 

 korfl's rheometer far enough off to experience no perturbation. 



219. The first conductor submitted to trial was the soft- 

 iron armature of the electro-magnet, isolated from the poles 

 by the interposition of a thin sheet of paper. Whatever were 

 the energy of the magnetism produced, and its direction rela- 

 tively to the direction of the current which traversed the ar- 

 mature, the index of the rheometer remained in one constant 

 position. 



220. Being desirous of giving greater certitude to this re- 

 sult, I employed a soft iron wire, perfectly annealed, and 

 twisted fifty-eight times upon itself. The whole length of this 

 wire was two metres, and the length of the convolutions equal 

 to the distance of the poles from the magnet. After isolating 

 all the folds with very dry paper, I substituted this wire, three 

 millimetres thick, for the armature of the previous experi- 

 ment. The multiplier was not affected by the production 

 of sixty contrary polarities conferred consecutively and at 

 equal intervals during the passage of the voltaic current. 



221. A solution of sulphate of protoxide of iron was dis- 

 posed axially on the poles. Its conductibility was not modi- 

 fied by the magnetization. b 



222. I then replaced the iron and its solution by diamag- 

 netic metals. Some bars of bismuth and others of antimony 

 were first tried in the axial position. They were then placed 

 equatorially, after covering them with a thin piece of paper to 

 isolate them from two soft-iron armatures, of the same length 



Pliil. Mag. S. 3. Vol. 36. No. 245. June 1 850. 2 F 



