132 ANNUAL OF SCIENTIFIC DISCOVERY. 



ON THE PHYSICAL LINES OF MAGNETIC FORCE. 



THE following is an abstract of a lecture recently delivered before 

 the Royal Institution, England, by Prof. Faraday, " on the physical 

 lines of Magnetic Force." A magnet presents- a system of forces 

 perfect in itself, and able, therefore, to exist by its own mutual rela- 

 tions. It has the dual and antithetic character belonging to both 

 static and dynamic electricity ; and this is made manifest by what are 

 called its polarities - - i. <?., by the opposite powers of like kind found 

 at and towards its extremities. These powers are found to be abso- 

 lutely equal to each other ; one cannot be changed in any degree as 

 to amount without an equal change of the other ; and this is true 

 when the opposite polarities of a magnet are not related to each other, 

 but to the polarities of other magnets. The polarities, or the north- 

 ness and southness of a magnet, are not only related to each other, 

 through or within the magnet itself, but they are also related exter- ' 

 nally to opposite polarities, (in the manner of static electric induction,) 

 or they cannot exist ; and this external relation involves and necessi- 

 tates an exactly equal amount of ihe new opposite polarities to which 

 those of the magnet are related. So that if the force of a magnet a 

 is related to that of another magnet &, it cannot act on a third magnet 



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c, without being taken off from ft, to an amount proportional to its 

 action on c. The lines of magnetic force are shown by the moving 

 wire to exist both within and outside of the magnet ; also, they are 

 shown to be closed curves passing in one part of their course through 

 the magnet ; and the amount of those within the magnet, at its equa- 

 tor, is exactly equal in force to the amount in any section, including 

 the whole of those on the outside. The lines of force outside a mag- 

 net, can be affected in their direction by the use of various media 

 placed in their course. A magnet can in no way be procured, having 

 only one magnetism, or even the smallest excess of northness or south- 

 ness one over the other. When the polarities of a magnet are not 

 related externally to the forces of other magnets, then they are related 

 to each other ; i. e., the northness or southness of an isolated magnet 

 are externally dependant on and sustained by each other. Now all 

 these facts, and many more, point to the existence of physical lines of 

 force external to the magnets as well as within. They exist in 

 curved, as well as in straight lines ; for if we conceive of an isolated 

 straight bar magnet, or more especially of a round disc of steel mag- 

 netized regularly, so that its magnetic axis shall be in one diameter, 

 it is evident that the polarities must be related to each other exter- 

 nally, by curved lines of force ; for no straight line can at the same 

 time touch two points having northness and southness. Curved lines 

 of force can, as I think, only consist with physical lines offeree. The 

 phenomena exhibited by the moving wire confirm the same conclu- 

 sion. As the wire moves across the lines of force, a current of elec- 

 tricity passes or tends to pass through it, there being no such current 

 before the wire is moved. The wire when quiescent has no such 

 current, and when it moves, it need not pass into places where the 



