192 
DR. E. TAYLOR JONES ON THE RELATION BETWEEN 
Professor J. J. Thomson has shown that the strains due to the dependence of 
magnetisation upon strain are given by the equations 
0L/3e = 0, 0L/^ = 0, SL/0^ = 0. 
'i.e., 
IH 
06 
m (e +/+ g) - -f- g) = 0, 
^ - m (e +/+ ff) -n(f-g-e) = 0, 
- m (e +/+ g) -n{g - e -/) = 0. 
3/ 
S' 
*> -LJ- 
- og 
In the case of a long cylindrical wire with axis along ox, we have g = f, and 
01/0^ = dljdf, hence solving for e 
ne 
— 1 
■m 
„ 01 ^ m — V ^01 J tn „ / 01 m — n 01 
Zm — n de ^ 3 m —n df ~ '3 m ~ n \ 0e 
m oj 
• (4). 
Now if a tension SP per unit area be applied to the wire and produce an increase 
SI in the magnetisation and strains Se, Sy’ = S^, then 
SI = |be + 2|8y; 
But if the elastic properties of the material are not altered by magnetisation, 
therefore 
Hence (4) becomes 
therefore 
S/= 
ra 
, oe rn oj j 
lie 
_ 1 
3 m — a 8e 
e = — H S' = J-H S' 
2E Se ^ SP 
This strain will be the same at all points of the wire, which is supposed uniformly 
magnetised, and will therefore be that part of a which is due to these stresses. 
