590 
Proceedings of Royal Society of Edinburgh. [sess. 
Table III. — Longitudinal and Circular Magnetizations in the 
Nickel Tube in various fields. 
Longitudinal. 
Circular. 
H. 
I. 
R/I. 
H'. 
I'. 
R'/r. 
246 
448 
*421 
14-5 
172 
•712 
196 
441 
•412 
12-5 
148 
•710 
146 
429 
•437 
io-i 
110 
•677 
99 
389 
•474 
8*44 
76 
•615 
69 
352 
•495 
6*78 
36-3 
*444 
49 
309 
•528 
5-13 
157 
•151 
29-5 
235 
•591 
4-33 
11-9 
•09 
19-5 
168 
•601 
3-44 
9-2 
•044 
9-9 
50 
•419 
2-64 
6-6 
•021 
1-75 
4-2 
•039 
As we should expect, the circular magnetization in a given field 
is greater than the longitudinal magnetization in the same field, 
simply because the demagnetizing factor is greater in the latter 
case. 
(4.) Comparison of the Joule and Wiedemann Effects. 
Let us consider the elongations X, g, v of Table I. as elongations 
in a strained elastic solid ; and let P, Q, E he the principal 
stresses corresponding to X, g, v. Then P is of the form MS + NX, 
where S ( = A + g + v) is the cubical dilatation ; and the correspond- 
ing expressions for Q and K are obtained by cyclical permutation 
of X, g, v. Expressed in terms of Young’s Modulus E and the 
rigidity n , the stresses become 
/E - 2 n \ 
P = -g 8 + 2X J, Q = etc., R •■= etc. 
Now assuming that the direction of the principal elongation X in 
the wall of the nickel tube is determined by the direction of the 
resultant magnetizing force, we see at once that a twist must 
accompany the combined action of longitudinal and circular magnetic 
fields. Let the corresponding principal stress P make angle 0 with 
