DOVE ON THE ELECTRICITY OF INDUCTION. 149 



action of a solid electro-magnet into that of a bundle of wires, 

 the latter must be surrounded by a conducting case. A solid 

 electro-magnet would then be iron, in which, besides the elec- 

 tric currents running parallel to each other round the individual 

 particles, the whole is moreover surrounded by peripherical cur- 

 rents. The electro-magnetization of iron would then be an ar- 

 rangement of already existing electric currents; and besides 

 this, a production of new currents, and moreover of a different 

 kind, as the action of the latter interferes with that of the for- 

 mer. If however we are forced to distinguish the electric cur- 

 I'ents M^hich can be shown in iron from those which are hypo- 

 thetical, it would appear to be simpler to go a step further and 

 proclaim electricity and magnetism to be two distinct forces of 

 nature. The question now arises, what phaenomena of induc- 

 tion are presented by a bar of iron in which magnetism is eva- 

 nescent, without the simultaneous excitation of electric currents 

 in the iron ; and what phcenomena are presented by non-mag- 

 netic metals in which the peripherical electric currents are de- 

 stroyed by breaking them up into wires ? The answer to these 

 questions is the subject of the two following sections. 



V. Currents induced by the approach of solid iron and bundles 

 of iron wire to a steel magnet. 



60. If, in the apparatus described at § 40, and constructed 

 upon the principle of Saxton's machine, the compensator having 



the position , an equilibrium of current has been established, 



with empty spirals, for physical, chemical and physiological 

 tests, then a disturbance of this equilibrium of current by the in- 

 sertion of different substances into the cylinders, will show that 

 the inserted substances have a different action ; and from the di- 

 rection of the resulting current, it can be ascertained which is 

 the most powerful. For this purpose solid iron cylinders and 

 bundles of wires were employed. '1 he solid iron cylinders 

 had a diameter of 13"'-6, and a height of 22"'-5. The bundles of 

 w ires were of the same dimensions, except as regards length : 

 the brass plate at the end of the surrounding case must be de- 

 ducted, and from the diameter the thickness of the surrounding 

 case of paper, wood or brass. As the separation of the sliding 

 spring must always be effected in the same manner in relation 



