Oti the Magnetic Polarity in Metallic Bodies. 325 



on its etlo-e on tlie stage, so that both poles were presented to 

 the same side of the disc. 



Without the magnet, 120 vibrations. 

 With the magnet, 90 vibrations. 



Two bar-magnets were next employed, the disc first vi- 

 brating between their north poles, and afterwards between a 

 north and a south pole. 



Experiment 14. — Between two north poles, 112 vibrations. 

 Between a north and a south pole, 80 vi- 

 brations. 

 The bar-magnets were next placed with both north poles 

 on one side of the disc, and afterwards with both south poles 

 on one side of it. 



Experiment 15.— With north poles, 109 vibrations. 

 With south poles, 102 vibrations. 

 I need not here remark that no other experiments in this 

 interesting inquiry have presented such an extraordinary dis- 

 crepancy of result's as those 1 have just described. They prove 

 in the most decisive manner that the energies of the magnet 

 become curiously modified by every change of its position, with 

 reference to the vibrating plate on which they are exercised ; 

 notwithstanding which, there does not appear to be any po- 

 sition in which it can be placed (provided it be sufficiently 

 powerful) that would entirely neutralize its influence on the 

 metal. 



The most favourable position in which the magnet can be 

 placed for displaying its influence, appears to be that in which 

 its north and south poles are presented to opposite sides of the 

 disc ; and the position of the poles, which appears to be the least 

 favourable for such a display, is when the poles that are pre- 

 sented to the opposite sides of it are of the same nature. This 

 curious circumstance is very different from anything which 1 

 had observed in my experiments on discs of iron; for with 

 that metal it had always appeared that when poles of the same 

 name were presented to any point in the edge of the disc, the 

 one above and the other below, the dipping-needle invariably 

 indicated the greatest polarity in the iron ; and least of all when 

 the edge of the disc was placed between the poles of a horse- 

 shoe magnet. Besides, the iron exhibits vigorous polarity 

 whilst at rest; but not a trace of polar action could be detected 

 in copper or zinc, unless those metals were in motion. The 

 only opportunity then of discovering the distribution of po- 

 larity in them, was whilst they were in that condition, either 

 vibrating or revolving on an axis. 



I began this tedious inquiry by suspending a magnetic needle 

 near to a vibrating disc of co[)per, sometimes when the magnet 



