1874.] Mr. G. Gore on Electrotorsion. 57 



IV. "On Electrotorsion/' By GEORGE GORE, F.R.S. Received 



November 26, 1873. 



(Abstract.) 



This communication contains an account of a new phenomenon (of rods 

 and wires of iron becoming twisted while under the influence of elec- 

 tric currents), and a full description of the conditions under which it 

 occurs, the necessary apparatus, and the methods of using it. 



The phenomenon of torsion thus produced is not a microscopic one, 

 but may be made to exceed in some cases a twist of a quarter of a circle, 

 the end of a suitable index moving through a space of 80 centimetres 

 (=31 inches). It is always attended by emission of sound. 



The torsions are produced by the combined influence of helical and 

 axial electric currents, one current passing through a long copper- wire 

 coil surrounding the bar or wire, and the other, in an axial direction, 

 through the iron itself. The cause of them is the combined influence of 

 magnetism in the ordinary longitudinal direction induced in the bar by 

 the coil-current, and transverse magnetism induced in it by the axial 

 one. 



The torsions are remarkably symmetrical, and are as definitely related 

 in direction to electric currents as magnetism itself. The chief law of 

 them is A. current flowing from a north to a south pole produces left- 

 handed torsion, and a reverse one right-handed torsion (i. e. in the direction 

 of an ordinary screw). Although each current alone will produce its own 

 magnetic effect, sound, and internal molecular movement, neither alone 

 will twist the bar, unless the bar has been previously magnetized by the 

 other. Successive coil-currents alone in opposite directions will not 

 produce torsion, neither will successive and opposite axial ones. 



The torsions are influenced by previous mechanical twist in the iron, 

 by mechanical tension, and by terrestrial magnetic induction. The di- 

 rection of them depends both upon that of the axial and of the coil-currents, 

 but appears to be determined most by the former. A few cases occur in 

 which the currents, instead of developing torsion, produce detorsion ; but 

 only two instances, out of many hundreds, have been met with in which 

 torsion was produced in a direction opposite to that required by the law. 



Single torsions vary in magnitude from 0*5 millim. to nearly 30 millims. 

 of movement of the end of an index 47 centimetres long ; the smaller 

 ones occur when the two currents are transmitted alternately, and the 

 large ones when they are passed simultaneously ; the former generally 

 leave the bar in a twisted state, the latter do not. Those produced by 

 axial currents succeeding coil ones are nearly always much larger than 

 those yielded by coil-currents succeeding axial ones, because the residual 

 magnetism left by the coil-current is the strongest. The order of suc- 

 cession of the currents affects the torsions in all cases, altering their 

 magnitudes, and in some few instances even their directions. In steel 



