MAGNETISATION OF IRON AND OTHER MAGNETIC METALS. 
225 
§ 6. In the first instance, however, a Lowinoor bobbin of the dimensions shown in 
fig. 1, which had been used in the earlier observations, was tested in the Edinburgh 
magnet without being turned down. The following are the particulars of this experi¬ 
ment and the results :— 
Diameter of central neck, 9’23 mm. Length of neck, 3’5 mm. 
Diameter to middle of inner induction coil, 9’48 mm. 
Diameter to middle of outer induction coil, 10‘99 mm. 
Inner induction coil, a single layer of twelve turns of silk-covered wire, 0’25 mm. in 
diameter over the silk. 
Outer induction coil, a single layer of seven turns of the same wire. 
Table III.—Lowmoor Wrought Iron. 
Current in field 
Outside field. 
S — outside field 
magnets, ampferes. 
47r 
outside field 
15-0 
15,990 
36,460 
1630 
2-28 
18-5 
18,410- 
36,970 
1480 
2-01 
28-5 
18,380 
37,320 
1510 
2-04 
330 
18,570 
37,610 
1520 
2-03 
38-5 
18,900 
37,990 
1520 
2-01 
A Swedish iron sample of the same shape gave an induction of 37,G20 in a field of 
about the same force, with a current of 38 amperes in the field magnet coils. 
§ 7. To push the induction in the Lowmoor sample to a still higher value, the neck 
of the bobbin was turned down to a diameter of 3'97 mm., the slope of tlie conical 
ends being approximately maintained. The inner coil was re-wound with a mean 
diameter of 4’22 mm., and the outer coil with a mean diameter of 5'7 mm. The 
following are the results for a magnetising current of about 38 amperes, the mean of 
several measurements being taken ;— 
Outside field. 
^8, 
33 — outside field 
33 
47r 
outside field 
25,620 
4.3,500 
1430 
1-7 
§ 8. A final effort to raise the induction was then made by again turning down the 
neck of the sample to the size shown in fig. 3. The diameter of the neck was reduced 
to 2'6G mm., but its length was not reduced in the same proportion; to leave room 
for a sufficiently long induction coil, a little of the metal of the cones close to the necJr 
was cleared away in the manner shown by the sketch. The section of the neck was 
now less than y^oo that of the pole-pieces. The bobbin was annealed after being 
MDCCCLXXXIX.-A. 2 G 
