4$ How Iron may acquire Magnetic Power. [Book I. 



expofure to the atmofphere ; it has been faid, there- 

 fore, that bars of foft iron, which have remained for a 

 long time in a magnetic direction, have acquired as 

 ftrong a power as good natural magnets *. 



A bar of iron made red hot, and left to cool, or 

 quenched in water in the pofition of the dipping nee- 

 dle, acquires a degree of magnetifm proportional to 

 its nature, and the circumftanccs of its cooling f. 



3dly. Magnetifm may be imparted to a bar of 

 iron, by placing it firm in thj direction of the dipping 

 needle, and rubbing it hard one way wi:h a polifhed 

 Heel inftrument J. 



4thly. Any violent percuffion will impart polarity, 

 and the other magnetic virtues, to a bar of iron in a 

 vertical pofition. A few ftrokes of a hammer will 

 produce this effect ; and by hitting firft one end of the 

 bar, and then the other, the poles may be charged. 

 If a long piece of wire is twifted feveral times b,.ck- 

 wards and forwards, and then broken off at the twifted 

 part, the broken end will be magnetic . 



5thly. Even hard iron tools, when heated by any 

 briflc action, as hammering, filing, &c. acquire an 

 impermanent magnetilrn, and, while warm, attract 

 thin filings, or fmall portions of iron |i. This fact, 

 I am inclined to fufpect, muft depend in a great mea- 

 fure on the unequal texture of thole tools : if we 

 fuppofe them to be compofed of hard and foft par- 

 ticles, the latter will eafily acquire an impermanent 

 magnetifm. 



6thly. Apparently all the three laft- mentioned 

 effects depend upon precifely the fame caufe j and, 

 perhaps, we may add to thefe, the magnetifm which 



^ Cav. f Adam?, and Cav. J Nichclfon's Phil. 292. 

 Adams on Mag. 444.. - || Rc-s's Cyclop, art. 



