PARAMAGNETIC AND VIAMAGNETIO FORCES 341 



ffjid are suspended from the point a, so that both magnets 

 Bwing in the same horizontal plane. It is so arranged 

 that the poles n' s' are opposite to the central or neutral 

 point of the helix, so that when a current is sent through 

 the latter, the magnets, as before explained, are unaffected. 

 Here then we have an excited helix which itself has no 

 action upon the magnets, and we are thus enabled to ex- 

 amine the action of a body placed within the helix and 

 excited by it, undisturbed by the influence of the latter. 

 The helix being 12 inches high, a cylinder of soft iron 

 6 inches long, suspended from a string and passing over a 

 pulley, can be raised or lowered within the helix. When 

 it is so far sunk that its lower end rests upon the table, 



^ 



NC 



1^ 



3S' 



nu 



Fio. 10. 



the upper end finds itself between the poles n' s' of the 

 astatic system. The iron cylinder is thus converted into a 

 strong magnet, attracting one of the poles, and repelling 

 the other, and consequently deflecting the entire astatic 

 system. When the cylinder is raised so that the upper 

 end is at the level of the top of the helix, its lower end 

 comes between the poles n' s'; and a deflection opposed in 

 direction to the former one is the immediate consequence. 

 To render these deflections more easily visible, a mirror 

 m is attached to the system of magnets; a beam of light 

 thrown upon the mirror being reflected and projected as a 

 bright disk against the wall. The distance of this image 

 from the mirror being considerable, and its angular mo- 



