18 ON MAGNETISM. 



that the direction in which the red pole (for instance) 

 of the needle is drawn is everywhere determined by 

 the composition of two forces, namely, attraction to the 

 blue pole of the magnet and repulsion from the red 

 pole: the influence of the more distant pole (which- 

 ever it may be) diminishing very rapidly with the 

 increase of distance. Thus, in the neighbourhood of 

 each pole of the magnet, the attractive force on one 

 pole of the needle and repulsive force on the other 

 sensibly draw the needle into the same position as if 

 the distant pole of the magnet did not exist ; opposite 

 the middle of the magnet's length, the distances of the 

 needle from the two poles of the magnet are equal, 

 the attraction of the needle's red pole to the magnet's 

 blue pole and its repulsion from the red pole (and the 

 opposite for the needle's blue pole) are sensibly equal, 

 and the needle lies parallel to the magnet but in the 

 opposite direction. Thus it is seen that the action 

 of a pole of the magnet is not limited to the direction 

 longitudinal from the pole or even transversal from the 

 pole, but that it is equally distinct in a direction nearly 

 backwards from the pole. It is not so easy to judge of 

 the magnitude of the force which one pole exerts in 

 different directions, because it is soon complicated by 

 the effect of the other pole : but, on trying it at small 

 distances by the time of vibration of the needle, there 

 appears to be good reason for thinking that the force 

 when the needle's center is at a transversal separation 

 from the magnet's pole is exactly the same as the force 

 when the needle's center is at a longitudinal separation 



