PARAMAGNETIC AND DIAMAGNETIC FORCES. 325 



manifest that if a second helix be placed between the 

 poles s N with a cylinder within it, the action upon the 

 astatic magnet may be exalted. This was the arrange- 

 ment made use of in the actual enquiry. Thus to 

 intensify the feeble action, which it is here our object 

 to seek, we have in the first place neutralized the action 

 of the earth upon the magnets, by placing them astatic- 

 ally. Secondly, by making use of two cylinders, and 

 permitting them to act simultaneously on the four 

 poles of the magnets, we have rendered the deflecting 

 force four times what it would be, if only a single pole 

 were used. Finally, the whole apparatus was enclosed 

 in a suitable case which protected the magnets from 

 air-currents, and the deflections were read off through 

 a glass plate in the case, by means of a telescope and 

 scale placed at a considerable distance from the in- 

 strument. 



A pair of bismuth cylinders was first examined. 

 Sending a current through the helices, and observing 

 that the magnets swung perfectly free, it was first ar- 

 ranged that the bismuth cylinders within the helices 

 had their central or neutral points opposite to the poles 

 of the magnets. All being at rest the number on the 

 scale marked by the cross wire of the telescope was 

 572. The cylinders were then moved, one up the other 

 down, so that two of their ends were brought to bear 

 simultaneously upon the magnetic poles: the magnet 

 moved promptly, and after some oscillations * came to 

 rest at the number 612; thus moving from a smaller to 

 a larger number. The other two ends of the bars were 

 next brought to bear upon the magnet: a prompt de- 

 flection was the consequence, and the final position of 

 equilibrium was 526: the movement being from a 

 larger to a smaller number. We thus observe a mani- 

 * To lessen these a copper damper was made use of. 



