ON THE MEASUREMENT OF MAGNETIC HYSTERESIS. 
(53 
occasions with different specimens and with various keys. We now give the results 
in the following table, where the third and fourth columns give respectively the 
value of W found by the ballistic galvanometer and the value of U found by the 
dynamometer; in the last column the section of the specimen is given. The 
numbers in this column, such as (3), refer to the first column. 
No. 
Date. 
Ho. 
Bo- 
AT) Chokiiui Coil used. 
1 
7 Nov., 1895 
7304 
16460 
7-98 
10340 
Iron wire, -0201 sq. centim. Ordinary key, 
§28. 
2 
9 Nov., 1895 
7409 
17780 
8-34 
10170 
Iron wire (1). Ordinary key. 
3 
11 Dec., 1895 
11500 
11620 
10-48 
8050 
Ring formed of iron wire, total section -8527 
sq. centim. Ordinary key. 
4 
16 Dec., 1895 
6850 
6710 
7-65 
5790 
Ring (3). Key of § 29. 
5 
16 Dec., 1895 
11570 
12480 
9-74 
14370 
Iron wire, -00697 sq. centim. Key of § 29. 
6 
24 Mar., 1896 
6160 
6288 
7-10 
7500 
Ring of iron wire, - 7611 sq. centim. Key of § 30. 
Choking Coil used. 
i 
25 Mar., 1896 
3470 
3616 
4-87 
5480 
Ring (6). Key of § 30. 
8 
25 Mar., 1896 
1013 
1013 
3-00 
2460 
Ring (6). Key of § 30. 
9 
27 July, 1897 
2827 
2946 
3-40 
6050 
Core of iron rings, 3-622 sq. centims. ; thick¬ 
ness of each ring, - 207 centim. ; radii, 3-83, 
6 - 02 centims Ordinary key. 
10 
12 July, 1898 
5260 
5408 
4-97 
8200 
Iron wire, -00708 sq. centim. Ordinary key. 
11 
14 July, 1898 
11905 
11960 
9-78 
13600 
Iron wire (10). Ordinary key. 
12 
19 July, 1898 
241-6 
330 
7 - 46 
950 
Six steel wires; total area, -02472 sq. centim. 
Ordinary key. 
13 
16 Aug., 1898 
1720 
1780 
8-09 
1980 
Mild steel rod, -0938 sq. centim. Key of § 30. 
14 
17 Aug., 1898 
633 
726 
8-09 
1200 
Steel rod (13) under torsion. Key of § 30. 
15 
7 Aug., 1900 
74250 
75200 
35-71 
16460 
Ten pianoforte steel wires; total cross-section, 
-0255 sq. centim. Key of § 30. 
16 
8 Aug., 1900 
16440 
17480 
35-71 
15550 
Ten soft iron wires, hardened by stretching ; 
total cross-section, -0412 sq. centim. Key 
of § 30. 
17 
16 Aug., 1900 
7098 
7400 
(") 
7275 
{>>) 
10-65 
9570 
Iron wires (16). Key of § 32. («) Before, 
(//) after observations for B—H curve. Com¬ 
pare § 46. 
$ 40. It will be seen that there is very fair agreement between the values found for 
W and U, except in the cases of (1) and (2), when there was no choking coil in the 
circuit, and only an ordinary mercury key was used. Except in (12) and (14) the 
agreement is perhaps as close as could be expected, when we consider how much the 
behaviour of iron, specially under small magnetic forces, depends upon its previous 
history. In making a cyclic B—H curve, if we change H from Hq to H^, and find 
that B changes from Bg to B^, then Bj^ is the value assumed by B after has acted 
for a finite time—about one-quarter of the period of vibration of the galvanometer 
needle. But in the dynamometer method H does not halt for any appreciable time 
at any intermediate value as it changes from Hq to — Hq, and thus the value of B 
