A supplement to Ures Dictionary of Arts, Manufactures, and Mines, : containing a clear exposition of their principles and practice. . ovementor signal is produced by the joint action of attraction and repulsion, and the return to itsnormal state by the same joint action. Each pole of Henleys electro-magnet has a doubleinstead of the single termination, that we have been considering in all preceding cases. Apiece of soft iron, like a crescent, is screwed upon eacii of the poles; the horns or cuspsof the respective crescents are facing and near to each other ; and a magnetized steel needleis l)a
A supplement to Ures Dictionary of Arts, Manufactures, and Mines, : containing a clear exposition of their principles and practice. . ovementor signal is produced by the joint action of attraction and repulsion, and the return to itsnormal state by the same joint action. Each pole of Henleys electro-magnet has a doubleinstead of the single termination, that we have been considering in all preceding cases. Apiece of soft iron, like a crescent, is screwed upon eacii of the poles; the horns or cuspsof the respective crescents are facing and near to each other ; and a magnetized steel needleis l)alanced between thein. This arrangement is scunewhat like the following ( | ). Solong as no current is circulating in the coils of the electro-magnet, the cn-scents are impas-sive soft iron, and no one point of either of them has more tendency than any other pointto attract either end of the magnetized needle that is between them. But while a currentis circulating, one of the crescents is endowed with north magnetic polarity, which is espe-cially developed at its horns, and the other with south polarity. Suppose the horns of the. L 50G ELECTRO-TELEGEAPHY. right-hand crescent are north poles, those of the left south poles, and the top end of theneedle is north. Four forces will conspire to move the needle to the left. Its top will beattracted by the left-hand crescent and repelled by the right; its bottom will be repelled bvthe left, and attracted by the right. When this current ceases to circulate, the simpleattraction between the magnetized needle and the soft iron of the crescent tends to retainit in a deflected position. This tendency is increased by a little residual magnetism, that isapt to remain in the best iron, notwithstanding every care in its preparation. In order,therefore, to restore the needle to its normal position, a short quick current in the reversedirection is given. These instruments are single or double. Only one kind of deflectionof the needle is available
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Keywords: ., bookcentury1800, bookdecade1860, bookpublishernewyo, bookyear1864
