Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity . only intervene, a considerable additional weightwill be supported. 301. Electro-Magnet, with Three Poles. —This instrument, represented in Fig. 129, consists Fio-. 129. ^^ ^^ i^o^ ^^^j wound with ^j3 insulated wire, which iscarried in one directionaround half the length ofthe rod, and then turns andis wound in the other di-rection. The eftect of thisarrangement is, that, whenconnection is made with thebattery by means of thescrew-cups on the stand, th
Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity . only intervene, a considerable additional weightwill be supported. 301. Electro-Magnet, with Three Poles. —This instrument, represented in Fig. 129, consists Fio-. 129. ^^ ^^ i^o^ ^^^j wound with ^j3 insulated wire, which iscarried in one directionaround half the length ofthe rod, and then turns andis wound in the other di-rection. The eftect of thisarrangement is, that, whenconnection is made with thebattery by means of thescrew-cups on the stand, the two extremities of thebar become similar poles, while the middle acquiresa polarity opposite to that of the ends. The middle,as well as the ends, will sustain a considerable weightof iron. By reversing the direction of the current,all the poles are reversed. The arrangement of thepoles may be shown by passing a magnetic needlealong the bar. 302. Communication of Magnetism to Steel bythe Electro-Magnet. — The great power possessedby the elerjtro-magnet renders it peculiarly fitted forinducing magnetism in steel hence it is very con*. STEEL MAGNETS CHARGED 189 venient for charging permanent magnets. A shortsteel bar, if applied like an armature to the polesof an electro-magnet of the U form, will becomestrongly magnetic, the end which was in contactwith the north pole acquiring south polarity. Alonger bar may be charged, by employing the sameprocess that has been described in 251, for touchingby steel magnets. 303. Bars of the U form are most readily mag-netized by drawing them from the bend to theextremities across the poles of the U-electro-magnet,in such a way that both halves of the bar may passat the same time over the poles to which they areapplied. This should be repeated several times,recollecting always to draw the bar in the samedirection. Then, if it has a considerable thickness,turn it in the hand, and repeat the process with itsopposite surface, keeping each ha
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectmagnetism, bookyear18
