CONNECTION OF ELECTEICITY AND MAGNETISM. 247 



scieuce, and to consider the attributes of these forces enumerated 

 above as the general and necessary attributes of all ultimate forces of 

 nature. 



In order to distinguish the forces of this description by a short name, 

 I may be allowed to call them forces of the first class. Forces the 

 intensity of which depends either on time or on velocity may be dis- 

 posed of in a second class. 



Are there really alternate and elementary forces, which are to be 

 reckoned into this second class, which cannot be reduced into an aggre- 

 gate of forces of the first class, and do not bend under that great gen- 

 eralization, like the majority of other physical and chemical forces? 

 This is, evidently, a question of the highest theoretical interest, and 

 the problem of electro-dynamics turns out so important, because the 

 so-called electro-dynamic forces, acting between two electric currents, or 

 between one such current and a magnet, seemed really to aJ^brd an 

 example of the second class. 



First among them we have the discovery by Oersted of the forces 

 mov-ing ponderable matter, [pondero-motor forces, according to Prof. C. 

 Neumann's nomenclature,) and the laws of their action were brought 

 into a relatively simple, accurate, and comprehensive formula by 

 Ampere. These forces are comi)letely latent as long as electricity is in 

 a state of rest; they become active when electricity begins to flow 

 tbrough conducting bodies. This appears as a first fundamental differ- 

 ence between electro-dynamic forces and those of the first class, a gen- 

 eral characteristic of which is, that their action is not at all altered 

 by any motion of the points between which they act. Secondly, the 

 electro-magnetic force of a galvanic wire carries the pole of a magnet 

 round the wire without end and without ever leading it to a pla(% of 

 equilibrium and rest. All the forces of the first class, on the contrary, 

 tend to carry the bodies which they move to a certain final resting- 

 l^lace. This relation, moreover, is reciprocal; for just as a magnetic 

 pole is carried around an electric current, a galvanic wire can be carried 

 around a magnet or around a coil of wire, through which an electric cur- 

 rent passes. 



A second class of electro-dynamic phenomena are the induced currents 

 discovered by Faraday in 1831. In these cases, the electro-dynamic forces 

 do not act on ponderable matter, but they act as electro-motor forces on 

 electricity itself. They drive the opposite electric fluids of a wire into 

 opposite directions, either when another wire carrying an electric cur- 

 rent is in motion relatively to the first wire, or when the intensity of the 

 current in the second wire is altered. Instead of the second wire, a 

 magnet may be substituted. It produces an induced electro-motoric 

 force either when it is moved or when the intensity of its magnetism is 

 altered. For all these electro-dynamic actions, a magnet may be con- 

 sidered always as a system of electric currents, flowing circularly around 

 the magnetic axis of every magnetized particle. 



