of Magnetic Polarity in Metallic Bodies. 273 



of an exciting pole to collect and condense it, is found scat- 

 tered promiscuously in the area of the plate. 



This being understood, it is plain that the parts over which 

 the exciting pole last passes, will exhibit a series of polar points 

 more powerful than any other which it had previously aban- 

 doned ; and those near to a on the last excited limb, a more 

 powerful series than any other. The series of polar energy 

 will, therefore, be subordinate from some point near «, towards 

 h or d, according to the direction in which the revolving pole 

 proceeds round the disc. The needle will, therefore, not be 

 under the immediate influence of any individual point in the 

 iron, but will be operated on by the conjoint forces of the vi- 

 cinal poles, the aggregate of which is in the limb last excited ; 

 and the pole of the needle being of an opposite character, will 

 be attracted towards this aggregate pole. 



Experiment 4. — Let the south pole of the magnet be now 

 carried round the plate, from a to a, in the same manner as 

 the north pole was employed in Experiments 2 and 3, and in 

 the direction of the arrows in fig. 4. The needle will be 

 much agitated, but will eventually repose with its north pole 

 deflected towards the east of the magnetic meridian. 



In this case the aggregate pole of the last excited limb bda, 

 being of the same character as the vicinal pole of the needle, 

 the deflection is produced by repulsion. The needle is there- 

 fore driven from the last excited limb b of the plate, instead 

 of being attracted by it, as in the former cases when the de- 

 flections were produced by repulsion. 



Five separate revolutions of the south pole in the dii'ection 

 of the arrows in fig. 4. gave the following results : — 

 Degrees. 

 1st round 35"^ 



f"f '■''""^ t! I Deflection of the north pole, 



3rd round 33 ^ . r ' 



4th round 50 | 



5th round 40j 



Mean ... 40 

 When the revolutions of the magnet were performed in the 

 contrary direction, the results were as below : — 

 Degrees. 

 1st round 40"^ 



^^"«""'i f? I Deflection of the north pole, 



3rd round 45 > 



4th round 48 | ^^ 



5tli round G5j 



Mean ... 496 

 N. S. Vol. 1 1. No. 64. April 1832. 2 N The 



