PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
31 
Reversing the current through the helix, the deflection was that shown in fig. 30. 
Interrupting both currents and reversing the magnetic poles ; on sending a current 
through the helix as in the last experiment, the deflection was that shown in fig. 31. 
Reversing the current through the helix, the deflection was that shown in fig. 32. 
In the subsequent four experiments the helix was excited first. 
Sending a current through the helix in the direction denoted by the arrow, the 
bar set its length at right angles to the convolutions, and parallel to the axis of the 
helix ; when the magnetism was excited as in fig. 25, the deflection was to the dotted 
position. 
When the current was sent through the helix in an opposite direction, the deflec- 
tion was that shown in fig. 26. 
Interrupting both currents, and reversing the poles of the magnet ; on sending a 
current through the helix as in the last experiment, the deflection was that shown in 
fig. 27. 
Reversing the current in the helix, the deflection was that shown in fig. 28. 
In all these cases the position of equilibrium due to the first force was attained, 
before the second force was permitted to act. 
It will be observed, on comparing the deportment of the normal paramagnetic 
bar with that of the normal diamagnetic one, that the position of equilibrium taken 
up by the latter, when operated on by the helix alone, is the same as that taken up by 
the former when acted on by the magnet alone : in both cases the position is from 
pole to pole of the magnet. A similar remark applies to the abnormal para- and 
diamagnetic bars. It will render the distinction between the deportment of both 
classes of bodies more evident, if the position of the two bars, before the application 
of the second force, be one and the same. When both the bars, acted on by one of 
the forces, are axial, or both equatorial, the contrast or coincidence, as the case may 
be, of the deflections from this common position by the second force will be more 
strikingly evident. 
To eflfect the comparison in the manner here indicated, the figures have been col- 
lected together and arranged upon Plate I. The first column represents the deport- 
ment of the normal paramagnetic bar under all the conditions described ; the second 
column, that of the normal diamagnetic bar; the third shows the deportment of the 
abnormal paramagnetic bar, and the fourth that of the abnormal diamagnetic bar. 
A comparison of the first two columns shows us that the deportment of the normal 
magnetic bar is perfectly antithetical to that of the normal diamagnetic one. When, 
on the application of the second force, an end of the former is deflected to the right, 
the same end of the latter is deflected to the left. When the position of equilibrium 
of the magnetic bar, under the joint action of the two forces, is from N.E. to S.W., 
then the position of equilibrium for the diamagnetic bar is invariably from N.W. to 
S.E. There is no exception to this antithesis, and I have been thus careful to vary 
the conditions of experiment in all possible ways, on account of the divergent results 
