t34 Thoughti en Magnetijk. 



A bar of iron not previoufly magnetic does not acquire this dlfpofitlon in the flighteft 

 degree while lying in a horizontal or nearly a horizontal difpofition, but if one end of it 

 be raifed It immediately acquires it in feme degree, as appears by approaching a magnetic 

 needle to either end, becaiife in that direction it is then expofed to the aftivity of the polac 

 ends of the great general magnet. 



But if a bar of iron be heated, though only at one end, and while hot fet in a vertical 

 or neatly a vertical pofition, it will acquire the magnetic power much more readily. 



So alfo if one end of a bar of iron not magnetic be ftruck againft the ground it will 

 become in feme degree magnetic, the lower end becoming a north pole, &c. and if after- 

 wards the other end be ftruck in the fame manner the poles will be reverfed. 



Hence it is evident that any motion communicated to the integrant particles of iron 

 placed in a proper fituation helps them to aflume the magnetic difpofition already im- 

 prefled upon them by the great general magnet. 



If the oppoCte poles of two magnets of equal power be approached to each other the 

 power of both is increafed ; and if one of them be more powerful than the other it will 

 increafe tiie magnetic difpofition, and confequently the power of the weaker. 



Soft iron, as its parts are moft eafily moved, receives the magnetic difpofition mofl eafily, 

 hard iron or tempered fteel more difficultly, and cnft iron, as being both hard and abound- 

 ing in the heterogeneous particles, moft difBcultly and imperfeftly. 



Whatever way iron is applied to a magnet the magnetic power is diffufed in the direc- 

 tion df its length. Hence it fliould feem that when a bar of iron is laid on a magnet the 

 contiguous ends of the iron become poles of the fame name with thofe of the magnet to 

 which they are contiguous, and hence may be derived the power of armed magnets ^ for the 

 furfaccs of the armour immediately beneath thofe of the magnet imprefs a dire£tion oppofite 

 to their own on thofe of the magnet, and confequently reftify fuch furfaces of the magnet 

 as may have been inaccurately direfted, and thus ftrengthen it. 



To communicate the magnetic power to iron by friction againft a magnet, it is neceflary 

 that its pole fliould Aide along the magnet feveral times in the fame direflion, for if the 

 directions be alternately oppofed the powers received will fucceflively deftroy each other. 



A fynonimous pole is formed at the end at which the fridion begins, to that of the 

 magnet applied, and an oppofite at that at which it terminates. 



Appropriation to Iron. 

 It has of old been obferved that the magnetic phaenomena were peculiar to iron, and 

 the reafons why they are fo have been already aflTigned, but of late fome femi-metals have 

 been obferved to partake of thefe properties, as Nickel, Kobalt and Manganefe ; this has 

 been thought to arife from a mixture of ferruginous particles from which they can be 

 fcarcely freed, and with refpeft to Manganefe, and in many cafes of the others alfo, this 

 feems to hold true ; but with refpeft to Nickel, and in fome inftances of the others alfo, 

 the magnetic properties they difcover feem to mc to proceed from their great attradlion to 



iron, 



