both the parts are connected in series, this gives a ratio of conversion of about 1:2.7, and with the primaries in multiple, 1:5.4; but in operating with very rapidly alternating currents this ratio does not convey even an approximate idea of the ratio of the E.M.Fs. in the primary and secondary circuits.  The coil is held 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 knobs as soon as it is formed, and the fundamental discharges occur in quicker succession.