Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity . he whole mag-netism disappears, and the magnet, if of good iron,will not even be able to lift an ounce. The purestiron retains, for a time, a certain amount of mag-netic power, after being strongly magnetized, evenwhen an armature is not applied. This amountincreases with the size of the bar. 297. The poles of the magnet are, of course,reversed by changing the direction of the the change is made rapidly, while the arma-ture is applied, it
Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity . he whole mag-netism disappears, and the magnet, if of good iron,will not even be able to lift an ounce. The purestiron retains, for a time, a certain amount of mag-netic power, after being strongly magnetized, evenwhen an armature is not applied. This amountincreases with the size of the bar. 297. The poles of the magnet are, of course,reversed by changing the direction of the the change is made rapidly, while the arma-ture is applied, it does not fall off. If a considerableweight is suspended from it, it may fall a very slightdistance, and be attracted again. The time requiredto destroy the previously existing polarity, and torenew it in the opposite direction, is exceedinglyshort. 298. Electro-Magnet, in Case. — An electro-magnet of considerable power is represented in , fixed horizont \lly in a case. The poles project POWER OF ELECTRO —MAGNETS. 187 from one end, and a semicircular armature may beapplied to them, as in the cut. At the other end of Fig. 128. .. the case are seen two screw-cups, for making con-nection with the battery. There are two strongrings, one attached to the bend of the magnet, andthe other to the armature. The magnet, with itscase, may be suspended by the former ring andweights hung from the latter. 299. Yery large electro-magnets have been madeto lift 3000 lbs. The proportion of the power to theweight of the bar increases as their size is diminished,up to a certain limit; and a small electro-magnetmay be made to sustain 400 or 500 times its ownweight, excluding that of the coil. Increasing thebattery current does not increase the magnetism in-definitely. Small bars acquire their full power, oibecome saturated with magnetism, with a moderatebattery. A current from the thermo-electric battery(Fig. 41), when transmitted through the wires ofan electro-magnet, induces a considera
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectmagnetism, bookyear18
