EXPERIMENTAL RESEARCHES ON DRAWN STEEL. 
17 
Table VI — Effects of Heating and Cooling on Kesidual Magnetism with Demagne¬ 
tisation between each Step. Relation of Intensity to Temperature Coefficient, 
Annealed Iron Wire. 
Residual intensity. 
Magnetising 
force, 
H. 
Induced 
intensity, 
I. 
Initially, 
before heating 
and cooling. 
If* 
Finally, 
after heating 
and cooling, 
\f- 
Temperature 
coefficient, 
a. 
Permanent 
change, 
/?. 
Susceptibility, 
K = I/H. 
3-03 
115 
78 
75 
X lO-i 
-2-14 
X 10-2 
- 3-67 
37-9 
4-93 
346 
279 
275 
-1-49 
- 1-57 
70-2 
6-01 
616 
527 
518 
-1-24 
- 1-71 
102-5 
8-53 
824 
704 
690 
- 1-45 
- 2-02 
96-6 
14'13 
1027 
855 
837 
-1-45 
- 2 • 1 -4 
72-6 
40-70 
1248 
952 
931 
-1-40 
- 2-14 
30-6 
87-50 
1346 
962 
941 
-1-45 
- 2-19 
15-4 
- 2-69 
733 
750 
752 
- 1-44 
+ 0-35 
- 3-14 
677 
699 
702 
- 1-28 
+ 0-38 
- 3-81 
218 
271 
276 
- 1-68 
+ 1-70 
— 
39 
100 
104 
-1-68 
+ 4-62 
- 4-26 
- 92 
- 24 
- 16 
+ 1-63 
-35-00 
— 
Here the temperature coefficient is negative throughout for rising forces; as the 
intensity progresses it diminishes to a minimum value when I is about 518 and then, 
increasing again, becomes nearly constant. For reversed forces the coefficient 
diminishes to another low value at about 700 units (a higher intensity than before), 
and then again increases, but if the reversed force is just sufficient to leave a 
small inverse magnetisation, the coefficient changes sign and becomes 'positive. It 
appears then that in iron similar features present themselves in the relation of a 
to I as in drawn steel, but in iron the coefficient is in general negative, and in drawn 
steel positive, and in each the sign of the coefficient can be reversed when a small 
inverse magnetisation succeeds a strong direct magnetisation. 
The permanent change, is larger for low intensities than for high ones, and 
fluctuates in sympathy witii a; for reversed forces it changes sign, that is to say, 
there is a gain of magnetism due to cyclic temperature changes as there was with 
diawn sheet. Throughout it will be noticed that in soft iron /3, as well as a, is much 
smaller than in drawn steel. The table shows that a very long soft iron wire may 
have a temperature coefficient of less than —0'00015 per degree centigrade ; also, 
that if a small reversed force be applied after magnetisation to saturation, no loss of 
residual magnetism takes place due to heating and cooling, but the intensity tends 
to increase. 
15. The experiments which have been narrated, show that the sign and the 
VOL. COT.—A. D 
