148 DOVE ON THE ELECTRICITY OF INDUCTION. 



current produced on the ceasing of the primary current, and 

 having the same direction with it, acts in a contrary direction 

 to that produced by the magnetism. If the magnetism has 

 had time to develope itself during the longer continuance of the 

 current, as is the case with galvanic magnetization, its action 

 overpowers the opposing action of the electric current pro- 

 duced on the cessation of the primary current. All means there- 

 fore that are used to hinder the formation of electric currents, 

 increase the action already exerted by the solid iron. If how- 

 ever the primary current is of an exceedingly transient nature, 

 as that caused by the discharge of an electric battery, and the 

 magnetism has consequently not time to develope itself com- 

 pletely, then the electric current produced on the cessation of 

 the primary current overpowers the action of the evanescent 

 magnetism*. The dissolution of these electrical currents by 

 breaking up the mass into wires, or the obstruction to their for- 

 mation by a badly conducting mass, as nickel, completely re- 

 verses this action, for the excess which before this separation 

 was in favour of the electric currents, is now brought in the 

 first instance in favour of the evanescent magnetism. But the 

 limit of equilibrium for both is not the same for the calorific, 

 the physiological and the magnetizing actions, because the de- 

 pendence of each of these upon the intensity of the evanescent 

 magnetism will be different from their respective change by the 

 opposing electric current ; for the magnetizing action, the 

 power of the evanescent magnetism will still remain predomi- 

 nant, when for the calorific effects the electric current is the 

 more powerful, and the physiological phsenomena fall on both 

 sides of this line. 



Ampere first considered a magnet as an iron rod which was 

 peripherically surrounded by electric currents. As, however, 

 according to Coulomb's view, we can only account for the distri- 

 bution of magnetism in an iron bar by supposing it made up of 

 linear magnetic elementary lamellae arranged side by side. Am- 

 pere substituted for his first assumption an electro-dynamic 

 solenoid, the most nearly approaching realization of which is an 

 electro-magnetized bundle of wires. But to resolve the inducing 



* At § 77 the same result is obtained by other means with magneto-electric 

 induction, namely, weakening the physiological action of a cunent by the in- 

 sertion of massive iron, and increasing the same by bundles of iron wire. 



