DOVE ON THE ELECTHICITY OF INDUCTION. 145 



of wire. Hence it is explained why nickel in the form of a 

 solid rod, magnetized by the discharge of a Leyden jar, has 

 a more powerful inducing action than iron. It has the same 

 action as a bundle of wire in a badly conducting case : iron acts 

 as a bundle of wire in a case composed of a good conductor. 



y. The current induced by an unenclosed bundle of wire attains 

 sooner its maximum intensity than that induced by a solid 

 iron rod, or by a bundle of wire contained in an entire case, 

 when the quantity of electricity set in motion by both is the 

 same ; for, with two currents which compensate each other in 

 the galvanometer, the needle assumes an oscillatory motion, first 

 moving in the direction of the current from the bundle of wire, 

 then in favour of that induced by the solid iron. For the 

 same reason, equilibrium having been established in the galva- 

 nometer, the former cuiTent is more powerful than the latter in 

 its physiological action, in the property which it possesses of 

 magnetizing steel, and in the production of more vivid sparks. 



h. Cast iron exerts a more energetic physiological action than 

 could have been anticipated from its action on the galvanometer. 

 It is therefore more allied in its inducing action to an insulated 

 bundle of wire than to malleable iron. 



i. All kinds of iron produce more powerful induction-currents 

 on repeated electro-magnetizing, when they are magnetized alter- 

 nately in opposite directions, than when this is always effected 

 in the same direction. They all retain a poi'tion of the mag- 

 netism excited in them, and therefore undergo a more powerful 

 magnetic change when alternately magnetized in opposite direc- 

 tions, than when the same dii-ection is always preserved. 



6. S>ome remarks relating to the theory of Ampere. 



57. Starting from the axiom, that electric currents flowing 

 in the same direction attract each other, whilst they repel each 

 other when flowing in opposite directions. Ampere has shown 

 that every magnetic action can be traced to the action of closed 

 electrical currents. Ampere has gone a step further, and has 

 proclaimed the identity of electro-magnetic and magnetic phaeno- 

 mena, and assumed, consequently, that an electric current cir- 

 culates round every molecule of iron, which currents are in vari- 

 able directions in unmagnetic iron, and assume a parallel di- 

 rection under the influence of a magnet or of an electrical cur- 



VOI.. v. 1>AUT XVII. L, 



