ld in position in the oil on wooden supports, there being about 5
centimetres thickness of oil all round. Where the oil is not specially
needed, the space is filled with pieces of wood, and for this purpose
principally the wooden box B surrounding the whole is used.

The construction here shown is, of course, not the best on general
principles, but I believe it is a good and convenient one for the
production of effects in which an excessive potential and a very small
current are needed.

In connection with the coil I use either the ordinary form of
discharger or a modified form. In the former I have introduced two
changes which secure some advantages, and which are obvious. If they
are mentioned, it is only in the hope that some experimenter may find
them of use.

[Illustration: FIG. 4.--ARRANGEMENT OF IMPROVED DISCHARGER AND
MAGNET.]

One of the changes is that the adjustable knobs A and B (Fig. 4),
of the discharger are held in jaws of brass, JJ, by spring pressure,
this allowing of turning them successively into different positions,
and so doing away with the tedious process of frequent polishing up.

The other change consists in the employment of a strong electromagnet
NS, which is placed with its axis at right angles to the line joining
the knobs A and B, and produces a strong magnetic field between them.
The pole pieces of the magnet are movable and properly formed so as to
protrude between the brass knobs, in order to make the field as
intense as possible; but to prevent the discharge from jumping to the
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 knob