HIGH ffMQUKNVY and man POTENTIAL OURRKNTS. 309

thickness of oil all round. Where the oil is not specially needed,the space is tilled with pieces of wood, and for this purposeprincipally the wooden box is surrounding the whole is used.

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

In connection with the coil I use either the ordinary form ofdischarger or a modified form. In the former I have introducedtwo changes which secure some advantages, and which are ob-vious. If they are mentioned, it is only in the hope that someexperimenter may find them of use.

One of the changes is that the adjustable knobs A and b (Fig.133), of the discharger are held in jaws of brass, ,j j, by springpressure, this allowing of turning them successively into different

Fig. 133 .

positions, and so doing away with the tedious process of frequentpolishing up.

The other change consists in the employment of a strong elec-tromagnet x s, which is placed with its axis at right angles tothe line joining the knobs A and b, and produces a strong mag-netic field between them. The pole pieces of the magnet aremovable and properly formed so as to protrude between the brassknobs, in order to make the field as intense as possible ; but toprevent the discharge from jumping to the magnet the polepieces are protected by a layer of mica, m m, of sufficient thick-ness ; <?! and s 2 .v 2 are screws for fastening the wires. On each

side one of the screws is for large and the other for small wires,i. t. are screws for fixing in position the rods r r, which supportthe knobs.