46 Communicated Magnelifm. [Book t* 



iron ought to remain fbme time in contact with the 

 magnet. 



There are feveral curious phenomena which attend 

 .communicated magnetifm. The nature of the mag- 

 netifm communicated will frequently depend upon the 

 length of the iron bar which is brought into contact with 

 the magnet. If, for inftance, the north pole of a mag- 

 net is applied to the extremity of a long bar of iron, 

 that extremity will of courfe acquire a contrary virtue, 

 and become a fouth pole j at a part of the bar, hew- 

 ever, not very difcant, there will be found a new north 

 pole ; at fome diftance again a fouth pole 3 and fo al- 

 ternately, till the power is totally loft j the number of 

 thefe fuccefiive poles depending on the ftrength of the 

 magnetifm, and the length of the bar. If, however, 

 the bar is of a moderate length, there will be only two 

 regular ; poles * 



The polarity of .a bar of iron may be altered by 

 gradually moving the pole of a magnet along its fur- 

 face. Thus, if the north pole of a magnet is ap- 

 plied to that extremity of a magnetic bar of iron 

 which is the fouth pole, and moved gradually along, 

 the other (that is that which was the north) pole 

 of the bar will in that cafe be converted into a fouth 

 polef. ; 



If a piece of wire which has been rendered mag- 

 netic is twifted, its virtue will be ftrangely interrupted 

 and confufed. In fome parts it will attr.ict, in others 

 it will repel ; and even in fome places one fide of the 

 wire appears to be attracted, and on the other fide re- 

 pelled, by the fame pole of a loadftone J. This and 

 other phenomena icem to indicate, that much of the 



* Cav. pint i. c. 7. f Ib. 



J Rees's Cyclop, art. Magnet \ and Adams on Mag. 399. 



magnetic 



