534 
ME. G. GOEE ON ELEOTEOTOESION. 
battery arranged as above. By passing the current down the wire a small movement 
of the index, equal to 1 mm., to the left hand occurred ; and by passing it up an equal 
amount of movement to the right hand took place. I also repeated the experiment 
with a copper wire 2-75 mm. diameter; the movements produced by each first current 
agreed in direction with those stated above, but by each subsequent current in the 
same direction opposite torsions of small extent occurred. The transmission of these 
currents diminished the residuary magnetism of the tube if the lower end was a north 
pole. These results show that an axial electric current in a separate conductor inside 
the iron acts inductively, and produces a small amount of torsion. 
9. Production of torsion by axial currents. 
To determine if an axial current in the bar or wire itself would produce torsion, I 
excluded the helix from the circuit, and passed the current from 12 cells in one 
direction, first up the bar (of 11 mm. diameter), making several successive contacts, and 
then down it several times. In each case a decided torsion took place on the first 
contact, and the index returned a small portion of the distance on stopping the current ; 
and feeble torsions occurred in the same direction by each after-contact, the pointer 
returning a similar small distance on disconnecting. 
10. Will a previous coil-current enable an axial one to produce torsion' 1 . 
The above-mentioned torsions produced by an axial current alone were, to a certain 
extent, dependent upon the iron being previously magnetic. To ascertain this I con- 
verted the lower end of the bar, first into a south pole by momentary application of the 
coil-current and then passed the axial current downwards several times, then converted 
it into a north pole and again passed the axial current downwards several times. I 
then applied the coil-current to form a south pole, and passed the axial current upwards 
repeatedly ; and then to form a north pole, and again passed the axial current upwards. 
In each case the first application of the axial current produced a comparatively large 
torsion, the pointer returning a small distance on stopping the current, and each sub- 
sequent contact produced in the same direction the smaller movements already 
mentioned; the large deflections, therefore, could not be produced in the same 
direction without intervening reversal. The directions of movement were such that an 
axial current proceeding from a south to a north pole imparted a left-handed twist to 
the iron, and one in the opposite direction produced a right-handed torsion, as shown 
in figs. 1, 2, 3, 4, Class A, Plate XLII. 
With the thin iron tube of 10 mm. diameter, using 12 Geove’s cells arranged as 6, 
I obtained much larger movements than with the bar. Both with the bar and tube 
the magnitudes of the torsions in opposite directions were generally alike. 
It appears from these results that to produce electrotorsion freely requires the appli- 
cation of a coil-current and of an axial one in the iron itself, and that although the 
former alone only slightly twists a bar or tube of iron which has been previously sub- 
