Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity . rotation is not reversed bychanging the direction of the current, as it is when asteel magnet is used, since the poles of both electro-magnets are reversed at the same time, and theirrelative polarity remains the same. 340. Revolving Bell Engine. — This instru-ment, represented in Fig. 147, is similar in principle Fig. 147. to the one last figured, theU-magnet, however, being in-verted, so that the revolvingelectro-magnet is near thebaseboard ; the po
Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity . rotation is not reversed bychanging the direction of the current, as it is when asteel magnet is used, since the poles of both electro-magnets are reversed at the same time, and theirrelative polarity remains the same. 340. Revolving Bell Engine. — This instru-ment, represented in Fig. 147, is similar in principle Fig. 147. to the one last figured, theU-magnet, however, being in-verted, so that the revolvingelectro-magnet is near thebaseboard ; the pole-changeris on the axis below it. Thereis, in addition, an arrangementfor striking a bell, which isfixed above the magnet. Tothe axis of the revolving baris attached an endless screw ;this screw acts on a toothedwheel, which is provided witha pin projecting laterally, forthe purpose of moving thehammer. As the wheel turns,the pin presses upon the han-dle of the hammer, raising itfrom the bell until it is released by the pin at acertain point of the revolution; when a spiral spring,fixed to the handle, impels the hammer against ROTATION BY EARThs ACTION. 215 341. If the wheel has 100 teeth, as in the cut,the electro-magnet must revolve 100 thnes in orderto produce one revolution of the wheel, and con-sequently one stroke upon the bell. The velocityof the rotating bar is measured by counting thenumber of strokes in a given time ; it may make 100or more revolutions in a second. In order that themotion of the wheel may raise the hammer, it isnecessary to transmit the battery current so that thebar shall rotate in the proper directi n. 342. Registering Revolving Magnet. — Fig. Fig. 148. 148 represents an instrument inwhich the number of revolutionsof the electro-magnet in a giventime is registered by means ofclock-work connected with theshaft. On the dial-plate are threepointers, which mark the revo-lutions up to 1000. The timeoccupied by any known numberof revolution
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectmagnetism, bookyear18
