450 
DR. J. HOPKINSON ON MAGNETIC AND OTHER PHYSICAL 
The area of section of the ring is 1’65 sq. cm. The area of the middle line of the 
secondary coil is estimated to be 2’32 sq. cms. 
The secondary coil had 56, the primary 98, convolutions. 
The resistance of the secondary and leads was 0'81 at 12° C. 
The ring was at once raised to a temperature at which it ceased to be magnetic ; 
with a magnetising force of 32’0, the total induction was observed to be 80‘8, giving 
the value of the permeability 1’12. 
The insulation resistance between the primary and the secondary was observed to 
be 12,000 ohms. 
The ring was now allowed to cool very slowly; at resistance of 3’00, corresponding 
to a temperature of 723° C., the ring was non-magnetic ; at 2‘99, corresponding to 
720° C., it w'as distinctly magnetic. 
The following five series of observations were made at descending temperatures, the 
means of two observations being in each case given ; the sample was demagnetised by 
reversals after each experiment :— 
Tables 9-13. 
Table 9, Curve XV. 
Table to, 
Curve XVI. 
Table 11, 
Curve XVII. 
Table 12, 
Curve XVIII. 
Table 13, 
Curve XIX. 
Resistance 
at I 
beginning of > 2'99 
2-71 
2-31 
1-80 
0-812 
experiment J 
Temperature 5 
at beginning 1 q 
of experi- f 
ment J 
630 
° C. 
500 
° C. 
333 
° C. 
12 " 
C. 
Resistance 
at 1 
end of ex- > 2'95 
2-75 
2-245 
1-80 
0-812 
periment 
Temperatui 
at end 
of l708°C. 
645 
° 0 . 
478 
° c. 
333 
° G. 
12° C. 
experiment J 
Magnetising 
force. 
Induction 
per sq. cm. 
Magnet¬ 
ising 
force. 
Induction 
per 
sq. cm. 
Magnet¬ 
ising 
force. 
Induction 
per 
sq. cm. 
Magnet¬ 
ising 
force. 
Induction 
per 
sq. cm. 
Magnet¬ 
ising 
force. 
induction 
per 
sq. cm. 
0-075 
607 
0-075 
140 
0-075 
77 
0-075 
73 
0-075 
19 
0-15 
1214 
0-15 
295 
0-15 
161 
0-15 
125 
0-15 
48 
0-3 
2031 
0-3 
1,098 
0-30 
396 
0-30 
293 
0-3^ 
119 
0-6 
2698 
0-6 
4,175 
0-60 
1,847 
0-6 
813 
0-6 
312 
1-2 
3181 
1-2 
6,163 
1-2 
5,217 
1-2 
4,552 
0-9 
884 
2-2 
3607 
21 
8,122 
2-1 
7,642 
2-1 
7,840 
1-7 
5,087 
7-6 
4118 
7-5 
10,900 
7-7 
11,586 
7-4 
12,232 
3-3 
9,535 
36-9 
4800 
.38-0 
12,074 
40-4 
14,816 
42-6 
15,180 
6-1 
12,387 
10-7 
13,991 
45-0 
16,313 
