Practical electricity .. with questions and answers (1911)
Cleveland armature works, [from old catalog] comp, Lincoln, John C. [from old catalog] · [Cleveland, Ohio, Cleveland armature works] · leaf 56
Figure 18 Floating helix and electromagnet. 45 If now a piece of soft iron be placed in the helix allthe above actions become much stronger, but this is theonly difference. A piece of hard steel may be made into apermanent magnet by being inserted into a helix carryingcurrent. A helix with a large… … Figure 19 .Magnetic spectrum of a helix; compare with spectrumof bar magnet.
Electricity
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