MAGNETISATION OF IRON AND OTHER MAC^NETJC METALS. 223 
necks 6'5 mm. in diameter and 5 mm. long. The magnetic force was measured in an 
annular space between the inner and outer induction coils, about 1 ’3 mm. wide and 
closely contiguous to the iron neck : for brevity we shall call the magnetic force thus 
measured in the surrounding air space the “ outside field.” Tables I. and II. below, 
which are copied for convenience of reference from our earlier paper, give observed 
values of the induction 33, and of the outside 6eld for various strengths of current in 
the coils of the field magnets. They also give values of the quantity (33 — outside 
field)/47r, which would be a measure of the intensity of magnetisation ^ if the outside 
field were fairly representative of the mean magnetic force within the metal of the 
neck itself (since 33 = + >§) 5 and also of the quantity 33/outside field, which on 
the same proviso would measure the permeability p,. The residual induction S,. was 
510 in the Lowmoor and 500 in the Swedish sample. The magnetic quantities are 
stated in c.g.s. units. 
Table I.—Lowmoor Wrouglit Iron. 
Current in field 
magnets, ampferes. 
Outside field. 
4^. 
'4? — outside field ^ 
Ttt 
outside field 
1-98 
3,630 
24,700 
1680 
6-80 
4-04 
6,680 
27,610 
1670 
4-13 
5-81 
7,800 
28,870 
1680 
3-70 
7-60 
8,810 
29,350 
1630 
3-33 
11-0 
9,500 
30,200 
1650 
3-18 
1.3-5 
9,780 
30,680 
1660 
314 
16-2 
10,360 
30,830 
1630 
2-98 
21-0 
10,840 
31,370 
1630 
2-89 
26-8 
11,180 
31,560 
1620 
2-82 
Table II. — Swedish Wrought Iron. 
Current in field 
Outside field. 
— outside field 
magnets, ampferes. 
47r 
outside field 
4-08 
6,690 
27,960 
1700 
. ■ 
4-18 
7-77 
8,900 
29,730 
1660 
3-34 
10-9 
9,510 
30,820 
1700 
3-24 
14-2 
10,000 
31,210 
1690 
3-12 
16-5 
10,360 
31,630 
1700 
3-05 
18-9 
10,810 
31,720 
1670 
2-94 
22-9 
10,880 
32,060 
1690 
2-95 
26-5 
11,200 
32,360 
1690 
2-90 
Results closely accordant with these were also obtained with samples of the form 
shown in fig. 2; and, as bobbins with flat ends were most convenient, especially in very 
strong fields, the subsequent experiments were all made with the flat-ended type. 
