174 WEBER ON THE CONNEXION OF DIAMAGNETISM 



and the strengthened diaraagnetism of the bismuth particle 



From this it follows, that while to impart by a given mag- 

 netizing force the strongest magnetism to a given mass of iron, 

 we must convert it into the form of a long thin bar, and set its 

 length parallel to the direction of magnetization ; in order to 

 impart the maximum diamagnetism to a given mass of bismuth, 

 we convert it into the thinnest plate possible, and set its thick- 

 ness parallel to the direction of the magnetizing force. The 

 further development of these laws of the reciprocal action of 

 diamagnetic molecules, compared with that of magnetic mole- 

 cules, leads finally to a simple distinction of magnetic and dia- 

 magnetic substances, which is worthy of more particular exa- 

 mination. 



Distinction between Magnetic and Diamagnetic Bodies, through 

 the Positive and Negative Values of a Constant. 



For the sake of unity, let us limit ourselves to the considera- 

 tion of an ellipsoid of revolution of iron or of bismuth, the prin- 

 cipal axis of which is parallel to the magnetizing force X ; for 

 the case of iron, Neumann has proved that the magnetic moment 

 of the ellipsoid is 



«t;X 



l-h47r/cS' 

 where v denotes the volume and S a quantity derived from the 

 ratio of the axes of the ellipsoid, namely, 



s=.(..-i){iiog^;_i} 



=\/(-fx)' 



r and -/(rr— XX) the axes of the ellipsoid, k is supposed here 

 to possess a constant value for iron, and to it Neumann has 

 given the name of the magnetic constant of iron ; this constant 

 quantity in the case of iron, as of all other magnetic bodies, is 

 necessarily positive. 



The quantity k serves, therefore, by the different positive 

 values which it assumes, as a mark of distinction of the various 



