the Lines of Magnetic Force. 409 



each other through the magnet itself (an idea very difficult to con- 

 ceive after the experimental demonstration of the course of the 

 lines as closed curves (31 17.3230.)), still it would follow, that upon 

 the forces being determined externally, a change in the sum of 

 force both within and without the magnet should be caused. We 

 can now, however, take cognizance of both these portions of force ; 

 and it appears that, with a good magnet, whether alone or under 

 the influence of soft iron or other magnets of fourfold strength, 

 the sum of forces without (32.23.), and therefore also within 

 (3117. 3121.) the magnet, remains the same. 



3261. If the northness and southness be considered so far 

 independent of each other as to be compared to two fluids dif- 

 fused over the two ends of the magnet (like the two electricities 

 over a polarized conductor), then breaking the magnet in half 

 ought to leave the two parts, one absolutely or differentially north 

 in character, and the other south. Each should not be both 

 north and south in equality of proportion, considering only the 

 external force. But this never happens. If it be said that the 

 new fracture renders manifest, externally, two new poles, oppo- 

 site in kind but equal in force (which is the fact), because of the 

 necessity of the case, then the same necessity exists also for the 

 dependence and relation of the original poles of the original 

 magnet, no matter what or where the first source of the power 

 may be. But in that case the curved lines of force between the 

 poles of the original magnet follow as a consequence ; and the 

 curvature of these lines appears to me to indicate their physical 

 existence. 



3262. If the magnetic poles in a bar-magnet be supposed to 

 exert some kind of power internally, backward, as if they were 

 centres of force, both within and without the magnet, by which 

 they are able, upon the breaking of the magnet, to develope the 

 contrary poles and their force, then that power cannot be the 

 identical portion which is at the same time exerted externally; 

 and if not the same, then when the magnet is broken, the two 

 halves ought to have a degree of north or south charge. They 

 ought not to be determinate magnets having equipotcntial poles. 

 But they are so ; and we may break a hard magnet in half whilst 

 oppOBed to another powerful magnet which ought most to disturb 

 the forces, and yet the broken halves are perfect magnets, equi- 

 valent in their polarities, just as if, when they were made by 

 breaking, the dominant magnet was away. The power at the 

 old poles is neither increased nor diminished, but remains in 

 amount and in polar direction unchanged. 



3263. Falling back, therefore, upon the case of a hard, well- 

 made and well-charged straight bar-magnet, subject onlyto its own 

 powers, it appears to me that we must either deny the joint cxter- 



