From the Journal of the Society.]
BY PROFESSOR SILVANUS P. THOMPSON, D. SC., B.A., M.I.E.E.
III.
RESEARCHES OF PROFESSOR HUGHES.
[Illustration: FIG. 51.--HUGHES' ELECTROMAGNET.]
His object was to find out the best form of electromagnet, the best
distance between the poles, and the best form of armature for the
rapid work required in Hughes' printing telegraphs. One word about
Hughes' magnets. This diagram (Fig. 51) shows the form of the well
known Hughes' electromagnet. I feel almost ashamed to say those words
"well known," because on the Continent everybody knows what you mean
by a Hughes' electromagnet. In England scarcely anyone knows what you
mean. Englishmen do not even know that Professor Hughes has invented a
special form of electromagnet. Hughes' special form is this: A
permanent steel magnet, generally a compound one, having soft iron
pole pieces, and a couple of coils on the pole pieces only. As I have
to speak of Hughes' special contrivance among the mechanisms that will
occupy our attention later on, I only now refer to this magnet in one
particular. If you wish a magnet to work rapidly, you will secure the
most rapid action, not when the coils are distributed all along, but
when they are heaped up near, not necessarily entirely on, the poles.
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