ON PHYSICAL LINES OF FOECE. 461 



placed in the field will be urged towards places of stronger magnetic intensity 

 with a force depending partly on its own capacity for magnetic induction, and 

 partly on the rate at which the square of the intensity increases. 



If the body be placed in a fluid medium, then the medium, as well as the 

 body, will be urged towards places of greater intensity, so that its hydrostatic 

 pressure will be increased in that direction. The resultant effect on a body 

 placed in the medium will be the difference of the actions on the body and 

 on the portion of the medium which it displaces, so that the body will tend 

 to or from places of greatest magnetic intensity, according as it has a greater 

 or less capacity for magnetic induction than the surrounding medium. 



In fig. 4 the lines of force are represented as converging and becoming 

 more powerful towards the right, so that the magnetic tension at B is stronger 

 than at A, and the body AB will be urged to the right. If the capacity for 

 magnetic induction is greater hi the body than in the surrounding medium, it 

 will move to the right, but if less it will move to the left. 



Fig. 4. Fig. 5. 



We may suppose in this case that the lines of force are converging to a 

 magnetic pole, either north or south, on the right hand. 



In fig. 5 the lines of force are represented as vertical, and becoming more 

 numerous towards the right. It may be shewn that if the force increases 

 towards the right, the lines of force will be curved towards the right. The 

 effect of the magnetic tensions will then be to draw any body towards the right 

 with a force depending on the excess of its inductive capacity over that of the 

 surrounding medium. 



"We may suppose that in this figure the lines of force are those surrounding 

 an electric current perpendicular to the plane of the paper and on the right 

 hand of the figure. 



These two illustrations will shew the mechanical effect on a paramagnetic 

 or diamagnetic body placed in a field of varying magnetic force, whether the 

 increase of force takes place along the lines or transverse to them. The form 



