SECT. XXXIV. MAGNETIC AND ELECTRIC INDUCTION. 341 



the coercive force in iron, and its energy in steel, with regard to 

 the paramagnetic force, is perfectly analogous to the facility of 

 transmission afforded to electricity by non- electrics, and the 

 resistance it experiences in electrics. At every step the analogy 

 between electricity and magnetism becomes more striking. The 

 agency of attraction and repulsion is common to both ; the posi- 

 tive and negative electricities are similar to the northern and 

 southern polarities, and are governed by the same laws namely, 

 that between like powers there is repulsion, and between unlike 

 powers there is attraction. Each of these four forces is capable 

 of acting most energetically when alone ; but as the electric 

 equilibrium is restored by the union of the two electric states, 

 and magnetic neutrality by the combination of the two polarities, 

 they respectively neutralise each other when joined. All these 

 forces vary inversely as the square of the distance, and conse- 

 quently come under the same mechanical laws. 



A like analogy extends to magnetic and electric induction. 

 Iron and steel are in a state of equilibrium when neutral ; but 

 this equilibrium is immediately disturbed on the approach of the 

 pole of a magnet, which by induction transfers one kind of 

 polarity to one end of an iron or steel bar, and the opposite kind 

 to the other effects exactly similar to electrical induction. 

 There is even a correspondence between the fracture of a magnet 

 and that of an electric conductor ; for if an oblong conductor be 

 electrified by induction, its two extremities will have opposite 

 electricities ; and if in that state it be divided across the middle, 

 the two portions, when removed to a distance from one another, 

 will each retain the electricity that has been induced upon it. 

 The analogy, however, does not extend to transference. A body 

 may transfer a redundant quantity of positive electricity to 

 another, or deprive another of its electricity the one gaining at 

 the expense of the other ; but a body cannot possess only one 

 kind of polarity. With that exception, there is such perfect cor- 

 respondence between the theories of magnetic attractions and 

 repulsions, and electric forces in conducting bodies, that they not 

 only are the same in principle, but are determined by the same 

 formulas. Experiment concurs with theory in proving the 

 identity of these two influences. Hence, if the electrical pheno- 

 mena be due to a modification of the ethereal medium, the mag- 

 netic phenomena must be owing to an analogous cause. 



Curved lines of magnetic force issue from every point of the 



