MAGNETISM. 



<f polarity ; but more commonly any one of these causes in;; 

 the magnetic power. Professor Robinson found, that when a good 

 m.i^net \\as struck for three quarters of an hour, and allowed in the 

 menu time to ring, its efficacy was destroyed ; although the same 

 operation had little effect when I he ringing was impeded : so that 

 the continued exertion of the cohesive and repulsive powers appears 

 to favour the transmission of the magnetic as well as of the electric 

 fluid. The internal agitation, produced in bending a magnetic wire 

 round a cylinder, also destroys its |>olarity, and the operation of a 

 file has the same effect. Mr. Cavallo has found that brass becomes 

 in general much more capable of being attracted when it has been 

 hammered, even between two flints ; and that this property is again 

 diminished by fire: in this case it may be conjectured that hammer- 

 ing increases the conducting power of the iron contained in the 

 brass, and thus renders it more susceptible of magnetic action. 

 Mr. Cavallo also observed that a magnetic needle was more 

 powerfully attracted by iron filings during their solution in 

 acids, especially in the sulphuric acid, than either before or after 

 the operation : others have not always succeeded in the expert, 

 ment ; but there is nothing improbable in the circumstance, and 

 there may have been some actual difference in the results, de. 

 pendent on causes too minute for observation. In subjects so little 

 understood as the theory of magnetism, we are obliged to admit 

 some paradoxical propositions, which are only surprising on account 

 of the imperfect state of our knowledge. Yet, little as we can un- 

 derstand the intimate nature of magnetical actions, they exhibit to 

 us a number of extremely amusing, as well as interesting, pheno- 

 mena ; and the principles of crystallization, and even of vital growth 

 and reproduction, are no where so closely imitated, as in the 

 arrangement of the small particles of iron in the neighbourhood of 

 a magnet, and in the production of a multitude of complete magnets, 

 from the influence of a parent of the same kind. 



[Young's Natural Philosophy. 



