Thoughts on Magntlifm. Igj 



VII. 



Thoughts on Magntlifm, by Richard Kirwait, Efq; L L.D. F. R. S. and M.R.LA. 



{Concluded from page g^.) 



xF the fouth pole of a magnet be charged with filings of iron, and then approached to 

 a bar of iron Handing erefl, pan of the filings will drop off, becaufe the poles of the 

 . fame name, by exciting a contrary arrangement, weaken each other ; but if the filings were 

 fufpended from the north pole of the magnet it would take up ftill more of the filings, as 

 the oppofite poles ftrengthen each other, the uppermoft pole of the iron in this cafe 

 becoming magnetic by pofition. 



If the fyno>iimous poles of two magnets of unequal powers be approached to each other, 

 if the powers be very unequal the flronger immediately deftroys the weaker, and inducing 

 a contrary difpofition attrads inftead of repelling it; if the powers be lefs unequal it re- 

 quires a longer time ; fo alfo if one hefifter than the other. Even if their powers be equal, 

 yet after fome time the fofter will yield to the harder. If both be equally hard they only 

 ■weaken each other. 



If a magnet be cut in two, in a direftion parallel to the axis, the parts before conjoined 

 'will now repel each other, becaufe they ftill retain two fynonimous poles. 



But if the magnet be cut in two in a diredion perpendicular to the axis, the two ends 

 before conjoined will now attraft each other. 



If a magnetic wire be twifted, its powers are fo difordered that one fide of the wire, in 

 fome places of it, will be attrafted and the other fide repelled by the fame pole of the 

 magnet. 



The power of the mngntts {cateris parti.) is in proportion to their furfaces or as the 

 fquares of their diameters.— See Hutton's Magnetifm, p. 72. 



Communication. 



When iron is applied to or brought within the fphere of aftivity of a particular magjiet, 

 it acquires the arrangement requifite to form the heteronymous pole, and thus becomes 

 itfelf in fo.Tie degree magnetic in its whole length, if this length be not totally difpropor- 

 tioned to the power of the particular magnet. 



Hence the other end of fuch bar of iron acquires the the arrangement of the oppofite 

 pole, according to the laws of cryftalization already laid down. 



Iron becomes magnetic either by eonta£l or proximity to a magnet,, or by pofition, or 

 by internal commotion. 



If a bar of iron be placed in a vertical pofition its infenfible fibrillas' gi'adually acquire 

 the magnetic arrangement, fo that after fome years it becomes a complete magnet, its 

 htvejl part becoming a north pole, that is, pointing when free to the north, and the upper 

 3 fouth polc^ In the S. hemifphere the under end becomes a fouth pole.. 



A hat 



