EAKTH'S ACTION ON A NEEDLE. 



39 



in determining the law of magnetic attraction and 

 repulsion. 



21. Investigation of the action of a magnet, whose 

 poles are very widely separated, upon a needle whose 

 center is in the line of these poles and whose axis is 

 inclined to that line. 



Fig. 16. 



In Figure 16, the repulsion of the magnetic red 

 mass S upon the red mass fiby at the point y of the 

 needle is 



#./% (c 2 + 2cy cos + y z ) "^; 



which being resolved into a part acting endways of the 

 needle and a part parallel to c gives for the latter part 



-m-l 



(c 2 + 



