328 On tJie Magnetic Polarity in Metallic Bodies. 



It would, however, be no great stretch of the imagination to 

 suppose a disturbance oFtbe electric fluid by magnetic action, 

 as it would be only a kind of re-action to that which takes place 

 in electro-magnetism. If this be really the case, (although I do 

 not at present assert that it is so,) the electric force would 

 rush from the magnetic poles in the direction of the small 

 arrows in fig. 11, when the plate rotates in the direction in- 

 dicated by the large exterior arrow. This force is the most 

 energetic, or intense, on that side which is nearest the poles ; 

 it becomes diffused in the other parts of the disc, especially if 

 it be large, and attenuated so as to have scarcely any action 

 on the needle on the extreme parts opposite to the magnet. 

 It returns to the magnet again by various windings, and be- 

 comes more compact in proportion to its approach. 



This is what the needle indicates to be taking place in the 

 general surface of the disc ; so that the deflections near to the 

 left edge are different to those which are observed nearer to 

 the centre on that side of the magnet. The force, therefore, 

 appears as if it were first projected, or driven /iofu the mag- 

 netic poles in an opposite direction to that in which the plate 

 revolves, but soon divides itself into two distinct tides, which 

 sweep the area of the plate, recurving to the poles again in 

 opposite directions, as indicated by the two systems of arrows 

 in fig. 11. 



The line of greatest energy is the resultant of the two systems 

 of forces emanating from the left side of the magnetic pole ; 

 and is a curve determined amongst the feathers of the ascend- 

 ing arrows. It branches off with the aggregate of each of the 

 two recurving systems of force, returning near to the edge on 

 the left hand, but more in the area of the plate on the right 

 hand, side of the magnet. 



There are also neutral lines, or lines in which the needle 

 would constantly be arranged by the operation of these forces, 

 if unsolicited by any other. These lines are determined at 

 right angles to the resultant of the curve forces, indicated by 

 the arrows over which the needle is placed ; their positions 

 will consequently appear to vary with almost every variation 

 in the length of the needle employed. 



This curious distribution of magnetic polarity, or whatever 

 force it may be that actuates the needle, by the present ar- 

 rangement, is decidedly peculiar to the direction of motion 

 indicated by the exterior arrow, fig. 11 ; there being no simi- 

 lar distribution, as in fig. 12, by simply I'eversing the direction 

 of revolution. If, however, the magnetic poles and the direc- 

 tion of motion be both reversed at the same time, then there 

 is, on the upper surface, a distribution of force in every respect 



similar 



