magnet the pole pieces are protected by a layer of mica, MM, of
sufficient thickness. s_1 s_1 and s_2 s_2 are screws for fastening the
wires. On each side one of the screws is for large and the other for
small wires. LL are screws for fixing in position the rods RR, which
support the knobs.

In another arrangement with the magnet I take the discharge between
the rounded pole pieces themselves, which in such case are insulated
and preferably provided with polished brass caps.

The employment of an intense magnetic field is of advantage
principally when the induction coil or transformer which charges the
condenser is operated by currents of very low frequency. In such a
case the number of the fundamental discharges between the knobs may be
so small as to render the currents produced in the secondary
unsuitable for many experiments. The intense magnetic field then
serves to blow out the arc between the knobs as soon as it is formed,
and the fundamental discharges occur in quicker succession.

Instead of the magnet, a draught or blast of air may be employed with
some advantage. In this case the arc is preferably established between
the knobs AB, in Fig. 2 (the knobs ab being generally joined, or
entirely done away with), as in this disposition the arc is long and
unsteady, and is easily affected by the draught.

When a magnet is employed to break the arc, it is better to choose
the connection indicated diagrammatically in Fig. 5, as in this case
the currents forming the arc are much more powerful, and the magnetic
field exercises a greater influence. The use of the magnet permits,
however, of the arc being replaced by a vacuum tube, but I have