266 Prof. Tyndall on tlie Nature of t/ie Force by which 



cular to its lenjrtli : the mode of experiment was the same as 

 that applied in the other cases. 



Acted upon by the magnet alone, the bar set its length from 

 pole to pole : the magnetic excitation being that denoted by 

 fig. 39, a c\u-rent was sent through the helix in the direction of 

 the arrow ; the bar was deflected to the dotted position. 



Keversing 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 cm-rent through the helix, the deflection was 

 that sho^vn 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 con- 

 volutions, and parallel to the axis of the helix ; when the mag- 

 netism was excited as in fig. 25, the deflection was to the dotted 

 position. 



When the cun-ent was sent through the helix in an opposite 

 du'ection, the deflection was that shown in fig. 26. 



Interrupting both cm-rents, 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 nor- 

 mal paramagnetic bar with that of the normal diamagnetic one, 

 that the position of equilibrium taken up by the latter, when 

 opei'ated 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 equa- 

 torial, the contrast or coincidence, as the case may be, of the de- 

 flections from this common position by the second force will 

 be more strikingly evident. 



To eff'ect the comparison in the manner here indicated, the 

 figures have been collected together and arranged upon Plate III. 

 The first column repi'esents the deportment of the normal para- 

 magnetic bar under all the conditions described; the second 



