364 H, A. Rowland—Diamagnetic Constants of 
The first case to consider is that of a mass of crystal in a 
uniform magnetic field. The magnetic forces which enter the 
equation are those due to the magnetic action of the body as 
well as to the field in which the body is placed. In the case 
of very weak magnetic or diamagnetic bodies the forces are 
almost entirely those of the field alone. Hence in the case 
under consideration we may put Y=0 and Z=0. 
ence 
E=— 3 If X"((k,— k,) a + k,) dady dz, 
and if v is the volume of the body 
E=—3X*((k—-4,) a’ +h,)v 
As this expression is the same at all points of the field there 
is no force acting to translate the body from one part of the 
field to another. The moment of the force tending to inerease 
¢, where gy = cos “a, is 
get Sk bY 
= ion” (4,—k,) sin p cos p 
By observing the moment of the force which acts on 8 
crystal placed in a uniform magnetic field we can thus find the 
value of k,—k, or the difference of the magnetic constant along 
the axis and at right angles to it. The differences of the con- 
stants can also be found in the case of crystals with three axes 
by a similar process, ; 
_ The next case which I shall consider is that of a bar hanging 
in a magnetic field. Let the field be symmetrical around an 
horizontal axis, and also with reference to a plane perpendicular 
to that axis at the center. If the bar is very long with refer- 
ence to its section and a plane can be passed through it and 
the axis we must have Z=0, and the equation becomes 
E=—3 Uf \(X'+Y)k,+ (Xa+Ya')' (k,—h,)} dedy de 
Let the axis of X coincide with the long axis of the bar, as this 
x=— i a a ee 
also let the section of the bar be 
8 a= dy dz ‘oh 
and let the axis of the bar pass through the origin from whic2 
We have developed the potential in terms of spherical har- ag 
e can then wri 
VSA,Q,r+ A,,Q,,r° + Ay Que’ + ete. 
