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. 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 encountered great difficulties in working with an exhausted tube. [Illustration: FIG. 5.--ARRANGEMENT WITH LOW-FREQUENCY ALTERNATOR AND IMPROVED DISCHARGER.] [Illustration: FIG. 6.--DISCHARGER WITH MULTIPLE GAPS.]