MAGNETIC STRESS AND MAGNETIC DEFORMATION IN NICKEL. 
197 
to cause much difference in the curves. At the highest fields used the contractions 
were, however, rather greater with the greater tension. 
At low and moderate field-strengths the contraction is less, but at strong fields 
greater, than the value obtained by IVI.r. Nagaoka for an ellipsoid of nickel.* 
Water was kept flowing through the coil for a considerable time before readings 
were taken, and all temperature changes took place so slowly that their effects were 
easily distinguishable from the magnetic effect. 
All the readings were repeated several times, and the points representing the 
results always lay very near the curve (fig. 3). 
Final Fesults. 
On the right-hand side of the equation (3) the third term is much greater than the 
other two. Hence it was not necessary to know E and 0 with very great accuracy. 
The value of Young’s Modulus for a 98’1 per cent, nickel wire has recently been 
given by MeyerI as 21'3 X 10^^ C.G.S. This value of E was used, and the rigidity 
was measured by observing the torsional oscillations of the wire, to which a cylindrical 
vibrator was attached. This gave n = 7’75 X 10^'^ approximately. Hence 6 = 1*5. 
The greatest numerical value of ^ H (8I/8P) obtained was about 8'2 X 10“^, while 
the sfreatest value of the first two terms in (3), representing the elongation due to 
Maxwell’s stresses, was but 0'29 X 10“^ 
Tables I and H contain the values of H, I, the change SI of magnetisation caused 
by increasing the tension by 8P per unit area of section, the values of Sl/l calculated 
from equation (3), and the observed total contraction — a. 
Table I. 
Load = 2'4 kilogs. SP X section of wire = 2 kilogs. Temperature = 6° C. 
H. 
I. 
M. 
- . 106 
z 
calculated. 
a. 106 
observed. 
D . 10-6. 
7-49 
12-36 
36-3 
64-3 
85-5 
107-5 
159-0 
212-0 
31-0 
105 
270 
332 
365 
389 
428 
452 
- 1-6 
- 6-4 
- 17-0 
- 15-3 
- 13-4 
- 13-0 
- 9-7 
- 5-0 
- 0-063 
- 0-412 
- 3-23 
- 5-15 
- 6-00 
- 7-.30 
- 8-07 
- 5-45 
- 0-1 
- 0-3 
- 5-2 
- 11-35 
- 15-05 
- 18-35 
- 23-6 
- 27-4 
- -037 
+ T1 
- 1-97 
- 6-2 
- 9-05 
- 11-05 
- 15-53 
- 21-95 
0-92 
121-5 
5316 
12,140 
17,750 
22,890 
33,550 
41,730 
* ‘ Wied. Ann.,’ vol. 53, p. 487, 1894. 
f ‘ Wied. Ann.,’ vol. 59, p. 668, 1896. 
