MR. G-. GORE ON ELECTROTORSION. 
535 
jected to mechanical torsion, or does not twist it at all if it is free from such previous 
strain (see p. 533), it leaves a residuary condition in the iron which renders the bar 
capable of being afterwards freely twisted in opposite directions by opposite electric 
currents passed axially through it ; and the opposite magnetic polarities conferred by 
opposite directions of the coil-current enable an electric current passed axially in one 
direction through the bar to produce opposite directions of torsion. It follows from 
this that the direction of longitudinal magnetic polarity can be ascertained by means of 
the direction of electrotorsion. 
As in each of these experiments with an axial current in the iron itself the first 
movement of torsion in either direction was a large one, and the needle only slightly 
returned towards zero on the cessation of the current, the temporary action of an axial 
current succeeding a coil one leaves an iron bar in a twisted state, and the direction of 
the twist is opposite with opposite directions of the axial current. The results also 
show that when torsions are produced by this method, detorsion is prevented by some 
coercive or retaining influence within the bar itself, and thus potential mechanical 
power becomes stored up in the iron. 
11. Magnitudes of torsions produced by axial currents . 
The actual magnitudes of the torsions produced by this method were small, and varied 
with the length and thickness of the iron, its degree of magnetic polarity, and the 
strength of the battery. With iron wires 2*6 m. long, and from T75 to 2T7 mm. thick, 
possessing weak south poles at their lower ends, alternately reversed axial currents from 
12 cells arranged as 3 produced 3 to 4 mm. of movement of the end of the pointer, the 
pointer being 47 centims. long from its point of suspension to its extremity. With a wire 
3 mm. thick, and a weak south pole below, sustained by terrestrial magnetic influence 
only, alternately reversed axial currents produced from T5 to 3‘5 mm. of movement; but 
when these currents succeeded coil ones, the movements varied from 2-25 to 5-5 mm. : 
and with one 3*77 mm. thick, supporting 5|- kilogrammes, and having a weak south 
pole below sustained by terrestrial influence only, alternately opposite axial currents 
from the aforesaid battery produced T75 to T83 mm. of movement; but when those 
currents succeeded coil ones, the movements varied from *75 to 2’75 mm. The magni- 
tudes of the torsions diminished with increase of thickness of the iron. 
12. Are the torsions related to electromagnetic sounds \ 
Numerous axial currents in various series were transmitted through a wire 2T7 mm. 
diameter (up currents, down ones, and alternate up and down ones), and the sounds 
observed with the aid of a stethoscope, the circuit in each instance being completed 
by the mutual contact of wires, not by mercury, because of the interference of the 
snapping sound at the surface of that metal. 
In every case a more or less distinct sound occurred at the commencement of each 
current, and little or none at its cessation. Those emitted by currents which succeeded 
