300 
MR. J. LARMOR OX A DYXAMICAL THEORY, Ac. 
H' — 3H/(/i + 2) and uniform magnetization T = (^ — l)H747r inside the iron, 
whether the law of induction is linear or not. Thus for this case of a sphere the 
mechanical loices exeited on the iron involve no distribution of forcive throug’hout its 
volume, but simply an outward normal traction of intensity {(p,^ — 1) sin- ^ ^ -f i] 
H -/Stt over its surface; that being so, the stresses agree with Kiechhoff’s values, 
and the elastic strain produced in the sphere is given by his formulfe,'"' the result of 
course involving only very slight deformation. In fact, taking the axis of ai along 
the direction of I', it is clear that an elastic displacement (?/, v, iv) of the tvpe 
u ax -\-hx (^y -f-s;') -f- ex, v = iv = a h x (^- + ex satisfies the conditions 
of the problem for the case of a sphere, the constants being determined by satisfying 
the equations of internal equilibrium and adjusting the surface tractions. In addition 
to this mechanical deformation there will be the intrinsic deformation above deter¬ 
mined (§ 83) arising from the molecular changes produced by the magnetic polarization. 
Precisely similar formulae express the mechanical stress in a .sphere of solid dielec¬ 
tric matter situated in a uniform electric field. 
I desire to express, as in previous Memoirs, my obligation tg the friendly criticism 
of Piofessoi G. F. FitzGerald, which has enabled me to remove obscurities and in 
various places to make my meaning clearer. 
* Kirchhoff, “Gesamm. AblianclL, 
§ 168 . 
Xaclitrag,” p. 
124; cf. also Love, Treatise on Elasticity,” I., 
