WITH MAGNETISM AND ELECTRICITY. 17^ 



magnetic substances ; but the use of the quantity ic as a means 

 of distinction may be rendered more general by applying it to 

 all bodies, and permitting it to assume negative values, the phy- 

 sical explanation being attached, that a body which gives a nega- 

 tive value for k is a diamagnetic body. [The name anti-magnetic 

 or negative-magnetic would, therefore, be more suitable to these 

 bodies.] The negative value of k found for a diamagnetic body 

 may be called the magnetic constant of the diamagnetic body, or 

 we may call the positive value obtained by changing the sign, 

 the diamagnetic constant of the body. Denoting this alivays- 

 positive diamagnetic constant by h, to distinguish it from the 

 likewise always-positive magnetic constant /c, we obtain, in the 

 same manner as Neumann has determined the magnetic moment 

 of a magnetic ellipsoid, the diamagnetic moment of a diamag- 

 netic ellipsoid, 



_ hvX 



~ 1— 47r/^S" 



Now for an infinitely elongated ellipsoid, for a sphere, and for 

 an infinitely flattened ellipsoid, we obtain successively 



S = 0, S=l, S = l; 



hence the corresponding magnetic moments are, successively, 



the corresponding diamagnetic moments, on the contrary, are 



hvX hvX 



—hvX, 



l-|7rA' l-47rA' 



The most lengthened form corresponds, therefore, to the weakest, 

 the most flattened form to the strongest diamagnetism ; exactly 

 the reverse of what is true for magnetism, as above proved. As, 

 however, the diamagnetic constant h possesses in all known 

 diamagnetic bodies a value which almost vanishes in comparison 

 with the unit, the diamagnetic moment of all these bodies may, 

 without sensible error, be regarded as independent of their form ; 

 it may be set 



= — /ivX; 



and this expression may be compared with that already obtained 



