556 
ME. G-. GOEE ON ELECTEOTOESION. 
39. Torsions produced by the temporary action of one current during the continuance 
of another. 
Iron is extremely susceptible of being affected by an electric current, and consequently 
every different way of applying the two currents produces a difference of effect upon it. 
With the present method the current which is applied first, whether axial or coil, pro- 
duces little or no torsion according to the residuary magnetic state of the wire ; whereas 
the second one produces a very large, torsion, nearly or quite as great as would have 
occurred if the two currents commenced together. And, generally, if one of the two 
currents is stopped after the other, the discontinuance of the first, whether coil or axial, 
is attended by a much greater degree of detorsion than that of the second. The effects 
were modified if a weight was suspended from the wire. 
Some experiments were also made of commencing one current (A) soon after the 
other one (B), and continuing A a short time after B had ceased. Six Grove’s cells 
arranged as three were used for one circuit, and six similar ones for the other ; and 
the iron wire employed was T75 mm. diameter. Every possible combination and order 
of succession (eight in number) of the two currents was tried. In each case the first 
current produced at its commencement only a small movement, varying from 0 to 
5*5 mm., and the second a very large one, varying from 20 to 27*25 mm. The current 
which was first stopped, whether coil or axial, produced a detorsional movement, varying 
in magnitude from 15 to 19-5 mm. ; and on stopping the other current a further 
detorsion took place, varying in range from 3-5 to 6-25 mm.; the needle then settled 
either at zero or very near it. According to these results, and allowing a greater value 
to the degrees most distant from zero, more than three fourths of the torsion ceased 
when one only of the currents was stopped; probably this was partly a result of 
momentum of the recoil. The magnitudes of the torsions produced by the axial cur- 
rents in these experiments varied from 25 to 27 min., and averaged 25*5 mm. ; and of 
those yielded by the coil-currents ranged from 20 to 27*25 mm., and averaged 23*44 
mm., indicating a stronger preparatory condition produced by the coil-current and an 
excess of that current influence. 
In two experiments of these eight, the large torsion was in an opposite direction to 
that required by the law (see Section 6). In one of them a coil-current producing a 
south pole below was established during the continuance of a downw ard axial current, 
Avhich had been preceded by a coil one yielding a north pole below in an immediately 
previous experiment ; in the other a coil one producing a north pole below was com- 
menced during the flow of a downward axial one, which had followed a coil-current 
producing a south pole below in the previous experiment. 
These exceptions were not instances of detorsion, but actual reversals ; they were 
found to depend upon the residual coil-influences mentioned, and upon the successive 
commencement of the two acting currents, because they did not occur if the residual 
state was prevented (by terminating the two currents of the immediately preceding 
