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Show I jS J With po1nts direc1ed to the polar fl:ars In one long ·line extend the temper' d bars ; 1'95 were fo powerful that one af them weighing three pounds averdupois would lift another of the fame weight. Philof. Tranf. After this Dr. Knight made very fuccefsful eKperiments on this fubjetl:, which, jtough he kept his method fecrct, feems to have excited others to turn their attention ~ m:.1gnetifm. At this time the Rev. Mr. Michell invented an equally efficacious and more expeditious way of making flrong artificial magnets, which he publifbed in the end of the year 17 so, in which he explained his method of what he called " the double touch ," and which, fincc Dr. Knight's method has been known., appears .to be femewhat different f10m it. This method of renderrng bars of hardened fl:eel magnetical.confilts in holding verti-... cally two or more magnetic bars nearly parallel to each other with their oppoGte poles ,-ny near each other, (but neverthelefs feparated to a fman difta11ce,) thefe are to be flided over a line of bars laid horizontally a few times backward and for ward. See Michell on Magnetifm., alfo a detailed account in Chambers's Dictionary. What Mr. Michell propofed by this method was to include a very fma11 portion {)f the horizontal bars, intemled to be made magnetical, between the joint forces of two or more bars already magnetical, and by !liding them from end to end every part of the line of bars became fu cce!Iively included, and thus bars poffeffed of a very fmall degree of magnetifm to begin wit~ would in a few times !lirung backwards and forwards make the other ones muc!Nnore ma_gneti ~al than themfdves, which a-re then to be takeu up and uled to touch the fOJ'mer, wJ1ich are in fucceffion tci be laid down horizontally in a line. There is fiill a great field remains for future difcoveries in magnetifm both in refpcB: ·to experiment ..and theory; the latter confilts of vague .conjectures the more probable of w hich are perhaps thofe of Epinus, as they affimilate it to electricity. ()ne conjectur_e I thall add, viz. that .the ,polarity of magnetifm may be owing to the -earth's rotatory-motion. If heat, electl'icity, and magnetifm are fuppofed to be fl uids of .different gravities, heat bei ng the heaviefl: of them~ electricity the next heavy, and mag ·netifm the lightefl:, it is evident that by the quick revolution of the earth the heat will be_ accumulated moH orer thc .line, electricity next beneath this, and that the magnetifm wil l be detruded to the poles and ax.is of the earth, like the atmofpheres of commou air and of inflammable: gas, as explained in the note on Ca-nto I. I. 123. Electri~ity and heat wi'll both of them difplace magnetifm, and this !hews that they may gravitate on each other; and hence when too great a quantity of the eletl:ric fluid becomes accum ul..tcd at th.e poles by defcending fnows, or other unknown caufes, it may have~ tendency to rife towards the tropics by its centrifugal force, and produce the northern lights. .Sec additional notes, No. I. I 79. 1 'Then thrice and thrice with fteady eye he guides,. And -o'.er the adhefive train the magnet :Oides ; 'The .obedient Steel with living inftinB: moves, And veers for ever to the pole it loves.. 2 oo ,, Hail, adamantine STEEL r Inagnetic Lord·! King of the prow, the plowfhare, and the fword! True to the pole, by thee the pilot guides His fteady- helm amid the ftruggling tides, B:raves with broad fail the immeafurable fea, 205 Cleaves. the dark air, and afks no ftar but Thee.- By thee the plowfhare rends the matted plain, Inhumes in level rows the living grain ; Intrufive forefts quit the cultured ground, And Ceres laughs with golden fillets crown' d.- 2 I o 0' er refl:lefs, realms when [cowling- Difcord flings Her fnakes, and loud the din of battle ririgs ; Expiring Strength, and vanqui.lh' d Courage feel. Thy arm :refifilefs, adamantf.n e sT EEL '• |
