3265. ... I have elsewhere called the electric current, or the line of electro-dynamic force, "an axis of power having contrary forces exactly equal in amount in contrary directions" (517.). The line of magnetic force may be described in *precisely the same terms*; and these two axes of power, considered as right lines, are perpendicular to each other; and this additional condition, which determines their mutual direction, that they are separated by a right line perpendicular to both.
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Published before 1923