MR. Gr. GORE ON ELECTROTORSION. 
533 
current flowing from a south to a north pole produces a left-handed torsion, and one 
from a north to a south pole produces a right-handed one*. B. With a coil-current. A 
coil-current with its south pole below, circulating round a vertical rod of iron through 
which an electric current proceeds upwards, produces left-handed torsion, and a reverse 
one produces right-handed torsion, in the sense already employed *. 
Each of these laws, but the latter one the most frequently, is affected in a very limited 
proportion of cases by the order of succession in which the currents are applied. 
7. Will a coil-current alone produce torsion \ 
I passed the current from 12 Grove’s cells through the coil surrounding the iron bar 
11 mm. thick (see page 529), in each direction. In each case a very small movement of 
the pointer to the left hand (= right-handed torsion*) occurred on connecting the 
battery, and to the right on disconnecting it. By including the index (but not the 
bar) in the circuit, continued vibration could be obtained by placing the contact-screw 
against the right-hand side of the pointer in such a position that the vertical movement 
alone did not break the contact, but not by placing it at the left-hand side. Similar 
but smaller movements in the same direction were obtained with a thinner rod, by 
passing the current either way. With a thin iron wire, strained by a weight, no torsions 
could be obtained by such means. By employing a thin tube of soft iron 10 mm. outer 
diameter, having the same weight of 5^ kilogrammes attached, much larger torsions 
occurred ; but each of the movements in this case was to the right on connecting the 
battery, and to the left on disconnecting, irrespective of the direction of the current. 
It is probable that the difference of direction of torsion in the bars and tube was due to 
difference of internal mechanical strain, because I have found that twisting a bar before 
passing the coil-current enables that bar to exhibit small torsions; Wiedemann also (see 
note, p. 529) had previously investigated that circumstance. Torsions produced by 
electric currents only are reversed by reversing either of the currents, but those pro- 
duced by the combined influence of a coil-current and previous mechanical twist were 
not. 
8. Will a parallel current produce torsion' 1 . 
I suspended an iron wire 1*7 mm. diameter, provided with the pointer, in the axis 
of a brass tube 2 - 6 metres long, the tube being in one case 1T7 mm. diameter, and 
in another case only 7 mm. diameter. The current from the 12 Grove’s cells, 
arranged as 3, was in each case passed up the tube, also down it ; but no perceptible 
torsion was manifested. 
I substituted for the brass tube a thin one of soft iron 10 mm. external diameter, 
and for the iron wire a cotton-covered copper one T7 mm. thick, with a lead weight 
suspended from it to keep it straight, the pointer being attached to the tube aild the 
* By “ right-handed ” torsion, in the foregoing sentences, I mean twist in the direction of the thread of an 
ordinary screw ; but a right-handed movement of the index (sometimes also called torsion) in all other parts of 
this paper means the reverse of this. 
