MR. G. GORE ON ELECTROTORSION. 
541 
a large torsional movement, the index returning a small distance on stopping the 
current ; and each subsequent contact produced in the same direction the small move- 
ment only : the large deflections, therefore, could not be produced in the same direction 
a second time without intervening reversal. I have not examined whether the small 
detorsions which occur on the cessation of each single coil-current succeeding an axial 
one are due to the ordinary elasticity of the metal. The directions of the large and 
small movements are shown by figures 1, 2, 3, 4, Class B, Plate XLII.* 
These results confirm the view that to produce torsion freely requires the two currents 
(see Section 10, p. 535), and that although each current alone will produce its own 
magnetic effect, neither alone will twist the bar if the iron is free from mechanical strain. 
They also show that, although a coil-current alone produces no torsion in an annealed 
iron bar (see p. 533), the previous passage of a current axially through the bar puts the 
iron into such a magnetic state that it becomes capable of being afterwards freely 
twisted in opposite directions by opposite coil-currents, and that opposite axial currents 
cause the iron to assume two opposite directions of such state, because they enable one 
direction of coil-current to produce opposite directions of torsion. The results further 
show that the two ends of an iron rod, wire, or tube, through which an electric current 
has been axially passed, possess opposite properties. 
It appears also that each of the opposite longitudinal magnetic states produced by 
the two directions of coil-current is different from each of the conditions produced by 
opposite axial currents, because previous magnetization of an iron bar by a coil-current 
in either direction did not enable the subsequent magnetization of that bar by an oppo- 
site coil-current to produce twist, whereas the previous passage, in either direction, of 
an axial current through it did enable such subsequent treatment of it to produce 
torsion ; and, further, because an axial current does not lengthen an iron bar (see p. 530), 
but a coil-current does ; the acoustic effects of the two directions of current are also 
different (compare Sections 12 & 23). [All these conclusions agree with the view that 
the axial current imparts poleless magnetism tangentially to the outer layer of molecules 
of the iron, and that each of the four different directions of current imparts to the free 
end of the iron a different property.] 
As in each of these experiments with a coil-current the first movement of torsion 
was a large one, and the index returned only a small distance back on cessation of the 
current, the temporary action of a coil-current succeeding an axial one (like that of an 
axial current succeeding a coil one, see Section 10) leaves an iron bar in a twisted state; 
and the direction of that twist is opposite with opposite directions of the coil-current. 
By this method, therefore, as well as by the previous one (see Section 10), detorsion is 
prevented by some influence within the bar, and mechanical power becomes stored up. 
The results of these experiments, and of those previously described (see Section 10), 
show that the direction of torsion in all of them depends upon that of each of the two 
currents, and that it was reversed by reversing either the axial or coil-current, but not 
* Some cases, apparently, of torsion in reverse directions to those of figs. 1 and 4 are described on p. 552. 
