ON PARAMAGNETIC AND DIAMAGNETIC FORCES. 377 



by which the investigation was conducted. It is mani- 

 fest 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 asta- 

 tically. 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 en- 

 closed 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 tele- 

 scope and scale placed at a considerable distance from 

 the instrument. 



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 simul- 

 taneously upon the magnetic poles : the magnet moved 

 promptly, and after some oscillations 1 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 deflec- 

 tion was the consequence, and the final position of 

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



