ME. Gr. G-OEE ON ELECTEOTOESION. 
539 
the ordinary longitudinal magnetism if the wire was at right angles to the terrestrial 
magnetic meridian. 
As the torsions in these experiments with an iron wire depended upon the influence 
of both coil and axial currents, it is evident that the magnitude of them was limited by 
the weakest ; and as the residual longitudinal magnetism was feeble and the axial 
current strong, the magnitudes of the torsions varied with the amount of that residual 
magnetism. Assuming that the magnitude of the first torsion was to some extent in 
each case a measure of the residuary magnetism, and no interfering circumstances had 
occurred, the magnetism left in the wire by the coil-current which produced a north 
pole below was to that left by the same strength of current after producing a south 
pole as 4‘0 to 6 - 5 ; and this agrees with the fact that terrestrial magnetic influence 
weakens the magnetism of a vertical soft-iron wire, the north pole of which is below. 
Further investigation might perhaps disclose the exact conditions under which differ- 
ence of magnitude of the torsions constitutes a true measure of residual magnetism. 
Similar series of experiments were made with a steel wire 2 - 6 m. long and 2T6 mm. 
diameter ; the following are the results : — 
A. After making a north 'pole below. — Eighteen currents were passed : — 1. 1 6-0 ; 
2. | 5*25; 3. | 4/0; 4. f m+ 3*75; 5. | rm 3 - 0; 6. f 2 - 4; 7. | 2’0; 8. | ^h-2'0; 
9. | -hk 1-75 ; 10. | ^ 1*75 ; 11. | 1*5 ; 12. f **+ 1-5 ; 13. $ -nk 1*6 ; 14. f an- 1 ; 5 ; 
15. | 1*2 ; 16. f 1*33 ; 17. | 1*33 ; 18. f 1*0. No reversion of the direction 
of torsion or of magnetic polarity took place, and the deflections produced both by the 
upward and downward currents diminished throughout. The non-reversal of polarity, 
and the slowness of decrease of magnetism, compared with that which occurred in iron, 
were probably due to the greater coercive power of steel. 
B. After making a south pole below. — Sixteen currents were transmitted : — 1. 1 m+ 5’5 ; 
2. | +^6-0; 3. | 5-25; 4. f -mk 4-25 ; 5. | m 4-0 ; 6. J«k 4*0; 7. J an- 3-75 ; 
8. f 4^3-8; 9. |^3-75; 10. |-hk 3-5; 11. | an- 3-6; 12. f 4^3-4; 13. | aw- 3*5 ; 
14. | 4^3-4; 15. | an- 3-5; 16. f 4^ 3-4. 
On comparing the results of “ A ” and “ B,” we find that (as in iron) the magnetism 
was much more weakened when the north pole was below than when the south pole 
was beneath ; this result was of course due to the influence of terrestrial magnetism. 
With a south pole below, both with iron and steel, the polarity was diminished, but 
more so with steel than with iron. 
17. Effect of direction of axial currents upon the residuary longitudinal magnetism 
of iron and steel. 
I also examined the effect of a succession of axial currents, all in one direction, using 
the same battery-arrangement. 
A. In a soft-iron wire T75 mm. diameter. — 1. With a south pole below previously 
produced by the coil-current, six axial currents in succession were passed down it. 
The first produced a movement of 4-75 mm. to the left hand, the second 1-25 mm., and 
4 c 2 
