A method for suppressing sparking in working electro-magnets
intermittently. The magnet core is wound with a number (from four to
twenty) of separate layers of fine wire. A separate wire is taken for
each layer and all are wound in the same direction, from one end to the
other of the space or bobbin without returning. The ends are then joined
so as to bring all the wires in parallel. The effect of this is that as
the coils vary in diameter the time constants of each is different from
that of the others, the coefficient of self-induction being less, and
the resistance being greater for the coils farthest from the central
axis. Thus the extra currents run differently in the different coils,
and only a comparatively small spark can be produced owing to the
division of forces thus brought about.