MAGNETISM 



equal forces and their resultant bv NE, ES, and NS respectively 



NS.. m 



Then the intensity at E = 





ml 



ml 



NE3 ~^2 + W 



mi 



, 



~ * 



To a similar approximation as before the intensity at E is 



ml 

 ? 



or half that at D. 



It may easily be shown that if the force were inversely as the 

 pth power of the distance the intensity at D would be p times 

 that at E. 



Deflection method of verification. Thi> result may he 

 verified by the method of deflection. 



A small needle ?/,?, Fig. 163, is suspended so that it lies in the 







.v I 



i 

 i 

 i 

 i 



i 



i 



FIG. 163. 



magnetic meridian. A magnet NS is then brought up, say, to the 

 west of it in the line through its centre perpendicular to the 

 meridian. The magnet is said to be in the u end-on position." 

 Considering the horizontal action on the pole n of the needle, if its 

 strength is /x it will be acted on bv a force ull in the meridian. 

 where H is the horizontal intensity of the earth's action ; it will be 



acted on by a force // -- at right angles to the meridian, and t he- 



needle will set with its axis in the line of the resultant of these 

 two, since there are equal and opposite forces on the other pole, 8. 

 From the parallelogram of forces on the right hand of Fig. 

 it will be seen that if 9 be the angle of deflection, 





