Chap. 6.] I&^ulfion of Magnets. 39 



the impure part will rather obftruct the action of the 

 other *. 



' The power of magnets is not at all times equally 

 active j they will at one time attract at a much greater 

 diftance than at others. To what this variation is 

 owing, is impofiibie to decide, while we remain fo per- 

 fectly ignorant as we are of the caufes of all the mag- 

 netic phenomena : probably it may depend upon the 

 temperature of the ftone, as the magnetic power is 

 always diminished by heat. 



There is in magnets a natural power of repulfion, 

 as well as of attraction. Two magnetic bars, for in- 

 ftance, will attract each other if the two extremities 

 or poles, which correfpond in each, are brought 

 within the fphere of attraction ; but if the extremities 

 which do not correfpond are brought into contact, 

 they will be mutually repelled f. This circumftance 

 will be better underftood when the polarity of the 

 magnet has been properly explained. The power of 

 repulfion is fuppofed by fome experlmentalifts to be 

 weaker than that of attraction. 



II. The fecond dlftinguifhing property of the mag- 

 net, is what is termed its polarity. In plain t terms, 

 if a magnet is placed in fuch a fituation that it. fhall 

 have liberty to affume that direction which is moft na- 

 tural to it j for inftance, if it is made to float on water 

 upon a piece of wood or cork, if fufpended by a (len- 

 der firing, or fupported by a pivot, as is the needle 

 in the common mariner's compafs, it will difpofe itfelf 

 longitudinally nearly in the plane of the meridian, that 

 is, one extremity towards the noith pole of the earth, 

 and the other towards the fouth. The two extremi- 

 ties which correfpond to the poles of the earth arc 



* Cav. on Mag. p. 37. f Adams on Mag. p. 389. 



D 4 called 



