WEBER'S HYPOTHESIS ON MAGNETISM AND DIAMAGNETISM. 543 



which was originally zero, the strength is given by equation (64). 

 If 6 is the angle which the magnetising force X makes with the 

 perpendicular to the plane of the circuit, we have 



Q = XAcos(9. 



The magnetic moment of the current is I A, and its projection 

 in the direction of the magnetising force is 



V A2 



IAcos0=- -cos 2 <9. 

 L 



Suppose that there are n molecules in unit volume, and that 

 the axes of the circuits are distributed indifferently in all directions. 

 The zone corresponding to the angle dQ about the direction of the 

 magnetising force is 27rsin#</0, so that the mean value of cos 2 is 



n A 2 

 The magnetic moment is therefore --- X ; the magnetisation 



3 L 



is directly opposed to the magnetising force, which is in conformity 

 with the phenomena of diamagnetism, and the value of the coefficient 

 of magnetisation is 



If the distribution of the axes of the molecular channels is 



A 2 



not uniform, the sum V cos 2 # extended to the whole of the 

 * L 



molecules will have different values according to the direction of 

 the magnetising force, and we thus come upon the known properties 

 of anisotropic diamagnetic substances. 



562. Suppose that each molecule is a perfect conductor, or 

 (what amounts to the same thing) that it is surrounded by a layer, 

 the conductivity of which is perfect. 



The total flow of magnetic induction LI + Q which traverses any 

 circuit traced on the surface is constant. 



It follows that the perpendicular component of the force at each 

 point of the surface is constant. If the flow of induction which 

 proceeds from the molecule is originally null, any external magnetic 

 system will produce induced currents, such that the resultant 



