MR. &. GORE OjN t ELECTKOTORSION. 
54: 
this great difference was no doubt due to the much greater degree of retentive power 
which iron possesses for longitudinal than for tangential magnetism. 
The magnitude of the torsion produced by a given current depends not only upon the 
kind of current which immediately precedes it, but also upon the description of current 
which precedes that one. An axial current in a given direction succeeding a coil one 
nearly always produced a greater torsion if the coil one was preceded by an axial one in 
the opposite direction than if it followed one in the same direction. A similar but 
less general result occurs with coil-currents succeeding axial ones. A series of coil- 
currents producing north poles below, which gave an average deflection of T50 mm, 
when preceded by upward axial currents following coil ones of similar direction, yielded 
an average torsion of 3'25 mm. when the axial currents followed coil ones of opposite 
direction (see Section 30, page 549). 
Alternate coil and axial currents therefore produced the largest torsions when both 
kinds of currents were alternately reversed in direction. The torsions in general 
produced by alternate currents appear to be due, not only to the energy of the acting 
current, but also to the liberated potential energy of the residual magnetism left by 
previous currents. 
21. Apparently exceptional cases of torsion. 
On examining the notes of the experiments of the instances of apparently abnormal 
direction of torsion mentioned in Section 20, it was found that in each of the whole 
twelve instances detorsion and not opposite torsion alone occurred — as if the current in 
each case simply liberated the particles of the iron from their state of permanent twist, 
and allowed the pointer to return to zero. It is singular that the passage of an axial 
current after a coil one producing a south pole below enables a subsequent coil-current 
of similar direction thus to undo the effect of a former one, whilst no corresponding 
phenomenon occurs with an axial current following a coil one which produces a north 
pole (see Section 20). 
22. Effect of mechanical pull. 
When making the four series of experiments described in Section 20, I made four 
precisely similar series whilst a weight of 5| kilogrammes was suspended from the end 
of the wire. In the 1st Series. With coil-currents producing north poles below, alter- 
nated with downward axial ones, the torsions produced by coil-currents averaged T mm. 
less, and those yielded by axial ones T48 mm. greater magnitude than without the 
weight. In the 2nd Series. With upward axial currents, those yielded by coil-currents 
averaged T5 mm. more and those by axial ones *84 mm. less than without the weight. 
In the 3rd Series. With coil-currents producing south poles below, alternated with down- 
ward axial ones, the coil-current torsions averaged *03 mm. more and the axial-current 
ones 1*53 mm. more than without the weight. In the 4 th Series. With upward axial 
currents, the coil-current torsions averaged *46 mm. more and the' axial-current ones 
T2 mm. more than without the weight. No instance of reversal of direction of torsion, 
