840 FRAGMENTS OF SCIENCE 



like that of magnetism would not be able to transact the 

 business of the universe. 



The object of this discourse is to inquire whether the 

 force of diamagnetism, which manifests itself as a repul- 

 sion of certain bodies by the poles of a magnet, is to be 

 ranged as a polar force, beside that of magnetism; or as 

 an unpolar force, beside that of gravitation. When a 

 cylinder of soft iron is placed within a wire helix, and 

 surrounded by an electric current, the antithesis of its 

 two ends, or, in other words, its polar excitation, is at 

 once manifested by its action upon a magnetic needle; 

 and it may be asked why a cylinder of bismuth may not 

 be substituted for the cylinder of iron, and its state simi- 

 larly examined. The reason is, that the excitement of the 

 bismuth is so feeble that it would be quite masked by 

 that of the helix in which it is enclosed; and the problem 

 that now meets us is, so to excite a diamagnetic body that 

 the pure action of the body upon a magnetic needle may 

 be observed, unmixed with the action of the body used 

 to excite' the diamagnetic. 



How this has been effected may be illustrated in the 

 following manner: When through an upright helix of 

 covered copper wire a voltaic current is sent, the top 

 of the helix attracts, while its bottom repels, the same 

 pole of a magnetic needle; its central point, on the con- 

 trary, is neutral, and exhibits neither attraction nor repul- 

 sion. Such a helix is caused to stand between the two 

 poles N' s' of an astatic system. ' The two magnets s N' 

 and s' N are united by a rigid cross piece at their centres, 



1 The reversal of the poles of the two magnets, which were of the same 

 strength, completely annulled the action of the earth as a magnet. 



