Theory and practice of the electric telegraph; a manual for operators and students (1875)
Churchill, Charles Henry, d. 1904. [from old catalog] · Oberlin, Ohio, Sherman & bros. · leaf 58
sound produced. 3. Can permanent magnets he made hy the current? If there is any hardness about the iron from hammering, fil-ing etc., a residual magnetism is developed. And if a steelbar be introduced into the helix, a permanent magnet results. 4. What if the bar is bent or too large for the… … the center. Turn the system overwithout separating and operate^ as before. Open the circuit be-fore removing the steel. 7. Power of the Electro-magnet.—1. What apparatus exhibits the power of the electro-magnet? A thick ring of soft iron is cut into semi* circular halves and a small helix is made…
Telegraph
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