the Absurdity of Diamagnetic Polarity. 255 



tism, which asserts that whatever changes take place in the 

 magnetization of a system, the quantity of magnetism remains 

 constant. 



In the ordinary text-books, the fundamental definitions &c. 

 are given in a manner which we cannot accept. Thus, let 

 A, B be two long magnets which may be supposed to possess 

 the magnetic properties only in their ends, and let them be so 

 placed that we need only consider the positive pole of each, 

 viz., P on A and Q on B. Then, if these poles are equal, and 

 if, when they are placed " in air " at a distance of one centi- 

 metre, a force of one dyne is required to overcome the force 

 which tends to separate them, the strength of each pole is 

 defined to be unity, and it is asserted that at a distance of r 

 centimetres u in air,'"' the force which tends to separate them 



is — dynes. In our method of treating the subject, we should 



say that the force which tends to separate the two poles is 

 partly due to the magnetisms of the poles themselves, partly 

 to the magnetization of the air in which the two magnets are 

 placed, and partly to the inequalities in the pressure of the 

 air. In some experiments, the pressure of the air is the most 

 important factor. The so-called definitions of the text-books 

 are therefore not definitions at all, but propositions in the 

 Kinetic Theory of Gases, and are possibly incorrect. 



Having now explained the fundamental principles of the 

 subject, we must consider how magnetism is distributed in 

 bodies. In the first place, it is evident that a finite quantity 

 of magnetism cannot be concentrated into a point — that is 

 into an indefinitely small sphere ; for any two parts of the 

 sphere would exert very great forces on each other, and the 

 sphere would fly to pieces. 



A finite quantity of magnetism can be distributed on a finite 

 area. For if a be the quantity of magnetism per unit area, 

 or the surface density, on an infinite plate, this plate will 

 exert a magnetic force 2iram on a body P with a quantity of 

 magnetism m. If P be a second plate on which the surface- 

 density is cr', the force exerted by the infinite plate on each 

 unit of area of P will always have the finite value 27r<7</. 



If we break a magnet into any number of pieces, each 

 piece is found to be a complete magnet. From this it is in- 

 ferred that each atom or molecule is a complete magnet with 

 equal quantities of positive and negative magnetism at its 

 ends. The total quantity of magnetism on each atom or 

 molecule is therefore zero, and the distribution on it may 

 be supposed to be a surface distribution. To prevent any 

 difficulty being felt with respect to surface distributions of 



