'"'0 AET. 7. — K. IIOXDA AXI) T. TEKADA. 



effect accompanying magnetfzation. This explanation agrees well 

 with the facts brought out bv tlie present experiment. 



§ 4. RECIPROCAL RELATIONS. 



Among several important reciprocal relations obtained l)y 

 J.J. Thomson, the two relations, which have the connection with 

 the present experiment, are referred to below. 



Let a cylindrical bar of soft iron, whose axis coincides with 

 the axis of x, be magnetized along its axis. Let e, f, g, be the 

 dilatations of the bar parallel to the axes of x, y, z respectively ; 

 J.J. Thomson obtained the relation 



"9/2-4 KtilJefJ hm-n xI\deJjT.f,g 



_^n-^i{^\ \ ^1) 



Am— n. xl \ (If / }r,e.o) 



where /, H, /. have the usual meanings, n represents the coefficient 

 of rigidity, and m is connected with the modulus of compiession 

 k by the relation h = m — r//3. In his original work, the factor 

 k is dropped in the right hand member of the above equation ; 

 the error is to be traced back to his equation (41). 



Since dI=xdH+Hdx, we have the relation, supposing the 

 strain to be kept constant. 



'i)I ).j,, I 0/ 



Hence equation (I) may be written 



''*'' ( "^^ \ - JH. ( J^L}\ - ^ "'~'^ ( ^^ \ ■ (2) 



Again if T is the tension per unit oF area, we have 



