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XVI. On Electrotorsion. By George Gore, F.B.S. 
Received November 26, 1873, — Head January 8, 1874*. 
Wiedemann has experimentally examinedf the influence of magnetism upon the mecha- 
nical torsion of iron wire, and has shown that an iron wire hung in the centre of a 
helix and twisted is more or less untwisted when a current traverses the helix. But 
as the torsion in his experiments was produced by the combined influence of a voltaic 
current and previous mechanical twist, and is quite a distinct phenomenon from that 
produced by the combined influence of electric currents only, which forms the subject 
of this communication, and as no one appears to have discovered the particular class 
of phenomena which are treated of in this investigation, I take an opportunity of 
making known my experiments and the new facts I have found. 
[Since the publication of the abstract of this paper in the ‘ Proceedings of the Royal 
Society,’ vol. xxii. p. 57, January 8, 1874, Professor Wiedemann (to whom I had sent 
a copy of that abstract) has kindly written to me as follows : — “ You have found inde- 
pendently some results which I had already published in the year 1862 in Poggen- 
dorff’s ‘ Annalen,’ vol. cxvii. p. 208. A short abstract of these experiments is also 
given in my ‘ Treatise on Galvanism, &c.’ (1st edition, vol. ii. p. 445 ; 2nd edition, vol. ii. 
p. 565), where you will find my complete theory of the relations between magnetism 
and torsion.”] 
1. Apparatus employed. 
I took a voltaic helix, 2*45 metres long and 1*5 centimetre internal diameter, of insu- 
lated copper wire 1*8 mm. thick, coiled as a double conductor and in two layers. To 
form a tube upon which to coil the wire, two half-round strips of wood, with a semi- 
circular groove in each, were glued together, and the superfluous glue removed from 
the interior whilst still warm by means of a rope soaked in hot water. A brass tube 
may be used instead of the wooden one, as it does not prevent the torsions. The helix 
was fixed in an upright pillar of wood (Plate XLII. fig. 1), and a string 24 metres long, 
supporting a leaden bullet, was attached to a pin near the top of the coil to enable the 
apparatus to be placed vertical. 
A straight rod of soft iron, 2*6 metres long and 11 mm. diameter, was entirely 
enclosed, except its ends, within the helix, and securely suspended by a brass clamp. 
* The passages enclosed in square brackets were added in July 1874. 
t Wiedemann’s ‘Die Lehre von Galvanismus und Elektromagnetismus,’ vol. ii. p. 559 ; Pogg. Ann. vol. ciii. 
p. 571, May 1856, and vol. cvi. p. 161, 1859 ; Annales de Chimie, vol. liii. 1858, p. 379, and vol. lvi. p. 373, 
1859. 
4 B 
MDCCCLXXIV. 
