28 
PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
Preserving the same current in the helix, and reversing the polarity of the magnet, 
the deflection was that shown in fig. 13. 
Preserving the magnet poles as in the last experiment, and reversing the current in 
the helix, the deflection was that shown in fig. 14. 
Fig. 13. Fig. 14. 
In these cases, the bar, in its final position of equilibrium, enclosed an angle of 
about 40 degrees with the axial line. 
Normal Diamagnetic Bar . — The above experiments exhibit to us the deportment 
of the normal paramagnetic body under a great variety of conditions, and our next 
step is to compare with it the deportment of the normal diamagnetic body under 
the same circumstances. 
For the sake of increasing the force, the helix was removed from its lateral position 
and placed between the two poles, as in fig. 6, p. 25. The normal diamagnetic bar 
was suspended within the helix and submitted to the self-same mode of examination 
as that applied in the case of the paramagnetic body. 
The polarity first excited was that shown in fig. 9, Plate I., and the position of rest, 
when the magnet alone acted, was at right angles to the line joining the poles ; on 
sending a current through the helix in the direction of the arrow, the deflection was 
towards the dotted line. 
Preserving the magnetic polarity as in the last experiment, the direction of the 
current through the helix was reversed, and the deflection was that shown in fig. 10. 
Reversing the polarity of the magnet, and sending the current through the helix 
in the direction of the last experiment, the deflection was that shown in fig. 11. 
Preserving the last magnetic poles, and sending the current through the helix in 
the opposite direction, the deflection was that shown in fig. 12. 
In the following four experiments the helix was excited first. 
Operated upon by the helix alone, the suspended bar set its length parallel to the 
convolutions, and perpendicular to the axis of the coil : the direction of the current 
was first that shown in fig. 13 : when the magnet was excited, the bar was deflected 
towards the dotted position. 
Interrupting both currents, and reversing the current in the helix ; when the mag- 
net was excited, as in the last experiment, the deflection was that shown in fig. 14. 
