PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
27 
helix were now interrupted, and the polarity of the magnet was reversed. On send- 
ing a current through the helix in the direction of the arrow, the deflection of the bar 
was from the position of the defined line to that of the dotted one, fig. 9. 
Fig. 9. Fig. 10. 
Interrupting the current through the helix, and permitting the bar to come to rest 
under the influence of the magnet alone, a current was sent through the helix in a di- 
rection opposed to its former one : the deflection produced was that shown in fig. 10. 
The position of equilibrium finally assumed by the bar depends, of course, upon 
the ratio of the forces acting upon it ; in these experiments, the bar, in its final posi- 
tion, enclosed an angle of about 50 degrees with the axial line. 
A series of experiments were next made, in which the bar was first acted on by 
the current passing through the helix, the magnet being brought to bear upon it 
afterwards. On the passage of the current through the helix, in the direction 
shown in fig. 11, the bar set its length parallel to the axis of the latter. On exciting 
the magnet so that its polarity was that indicated by the letters N and S in the 
figure, the deflection was towards the dotted position. 
Fig. 11. 
^ Fig. 12. 
Interrupting the current through both magnet and helix, and reversing the current 
through the latter, the bar came to rest, as before, parallel to the axis : on exciting 
the magnet, as in the last case, the deflection was that shown in fig. 12. 
