of MM. P. Curie and C. Cheneveau. 359 



Suppose first that the body is paramagnetic. 



When the magnet is situated so that the body coincides 



centre G, the force will again be zero, as -j^f- is 

 je centre (position II, fig. 2). 



with the 

 zero at t\\Q 



Fig-. 2. 





TIT 



V 



s >n 





Hence the force / is zero when x = ~jo and x = and it 

 passes through a maximum in the interval, which occurs at 

 a certain point 0' where the product of the field H y by its 



gradient - y is a maximum. 



If the magnet is continually turned in the same sense of 

 rotation, so that its centre G passes through the point and 

 arrives at G' (position III, fig. 2), we observe that the force, 

 which was nil at 0, reaches a minimum or negative maximum 

 at a point 0" symmetrical with O f , relatively to 0, and 

 becomes zero again after the magnet is withdrawn far from 

 the body. 



Hence the curve in fig. 3 shows the variation of the force 

 / with the displacement x. The body is first displaced in 

 the direction of the arrow marked 1 from to 0', where it 

 stops and moves back with the magnet along the arrow 



