SECT, xxxii.] ACTION OF ELECTKIC CURRENTS. 363 



communication is made between the positive and negative 

 conductors. 



M. Ampere has established a theory of electro-magnetism 

 suggested by the analogy between electro-dynamic cylinders 

 and magnets, founded upon the reciprocal attraction of elec- 

 tric currents, to which all the phenomena of magnetism and 

 electro-magnetism maybe reduced, by assuming that the mag- 

 netic properties which bodies possess derive these properties 

 from currents of electricity circulating about every part in 

 one uniform direction. Although every particle of a magnet 

 possesses like properties with the whole, yet the general 

 effect is the same as if the magnetic properties were confined 

 to the surface. Consequently the internal electro-currents 

 must compensate one another, and therefore the magnetism 

 of a body is supposed to arise from a superficial current of 

 electricity constantly circulating in a direction perpendicular 

 to the axis of the magnet ; so that the reciprocal action of 

 magnets, and all the phenomena of electro-magnetism, are 

 reduced to the action and reaction of superficial currents of 

 electricity acting at right angles to their direction. Notwith- 

 standing the experiments made by M. Ampere to elucidate 

 the subject, there is still an uncertainty in the theory of the 

 induction of magnetism by an electric current in a body near 

 it. It does not appear whether electric currents which did 

 not previously exist are actually produced by induction, or if 

 its effect be only to give one uniform direction to the infinite 

 number of electric currents previously existing in the particles 

 of the body, and thus rendering them capable of exhibiting 

 magnetic phenomena, in the same manner as polarization 

 reduces those undulations of light to one plane which had 

 previously been performed in every plane. Possibly both 

 may be combined in producing the effect ; for the action of 

 an electric current may not only give a common direction to 

 those already existing, but may also increase their intensity. 

 However that may be, by assuming that the attraction and 

 repulsion of the elementary portions of electric currents vary 



