538 
ME. G. GOEE ON ELECTEOTOESION. 
16. Axial currents a test of residuary longitudinal magnetism in iron and steel. 
As the electromagnetic torsions constituted a new means by which residuary longi- 
tudinal magnetism might be detected, I endeavoured to ascertain more exactly and 
completely the effect of repeated axial currents upon that condition. I suspended in 
the helix a soft-iron wire 2*6 metres long and 2 - 22 mm. diameter, and measured the 
various torsions produced by a current from 12 cells arranged as 3. 
A. After making a north 'pole below by means of the battery. — The current was 
passed 14 times through the wire, alternately in opposite directions, commencing with 
an upward one. The following are the magnitudes of the several torsions, expressed 
in millimetres of movement of the end of the pointer (the vertical arrows indicate the 
directions of the axial currents, and the horizontal ones those of the movements) : — 
1. 1 +**4-0; 2. | ^-f2 - 0; 3. | ssh-TO; 4. f +^2*75; 5. | ^+2‘5; 6. f -h^3'75; 7. | *h- 3‘75; 
8. f^4-33; 9. |^4-25; 10. f -hk 4-75; 11.J*m-4-25; 12.J-hk 4*75; 13. | an- 4-0; 
14. | 4 - 9. On applying a compass-needle, the lower end of the wire was found 
magnetically neutral at the 3rd contact, and a feeble south-pole at the 10th. On 
examining the directions of the torsions, it will be observed that a change took 
place between the 2nd and 3rd currents, the directions of those previous to that change 
agreeing with the existence of a north pole below, and of those after it with a south 
one ; and on comparing the magnitudes of the movements, we find that previous to 
that change of polarity they diminished, and after it those of the torsions produced by 
the upward currents increased to the 10th contact only, whilst those of the downward 
ones increased throughout. 
B. After making a south pole below. — Ten alternately reverse currents were trans- 
mitted, commencing with an upward one ; and the following are the results : — 1. | m+6-5; 
2. | -h^ 8’0; 3. | m+6‘75; 4. | i-m 5’33; 5. | 5*25; 6. f -hs 5‘5; 7. | 5‘0; 8. | -t-^6‘0; 
9. |^+5'25; 10. |+^5’5. 
The results set down under “ A ” show that the north polarity was first diminished 
and reversed, and then the south polarity increased until a downward current produced 
& movement of 4’9 to the left (and was still increasing) ; and those under “ B ” show 
that the south polarity decreased until a downward current produced a movement of 
5 - 5 to the left — as if in each case the iron was gradually approaching a normal mag- 
netic state by the influence of a disturbing cause and terrestrial magnetism. These 
results support the hypothesis that the axial current loosens the molecules of the iron, 
and enables terrestrial magnetic influence to reduce the iron to its normal degree of 
magnetism with south polarity downwards. But assuming such explanation to be true, 
it is not complete, because axial currents of opposite direction leave the iron in oppo- 
site states (see p. 535). The result's generally also indicate that a magnetized soft-iron 
bar may be rendered normally magnetic by placing it vertical, and passing alternately 
reversed electric currents axially through it until it ceases to show a changing degree 
of torsion. I have not examined whether axial-electric currents would entirely remove 
