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.]

The other form of discharger used in these and similar experiments is
indicated in Figs. 6 and 7. It consists of a number of brass pieces cc
(Fig. 6), each of which comprises a spherical middle portion m with an
extension e below--which is merely used to fasten the piece in a lathe
when polishing up the discharging surface--and a column above, which
consists of a knurled flange f surmounted by a threaded stem l
carrying a nut n, by means of which a wire is fastened to the column.
The flange f conveniently serves for holding the brass piece when
fastening the wire, and also for turning it in any position when it
becomes necessary to present a fresh discharging surface. Two stout
strips of hard rubber RR, with planed grooves gg (Fig. 7) to fit the
middle portion of the pieces cc, serve to clamp the latter and hold
them firmly in position by means of two bolts CC (of which only one is
shown) passing through the ends of the strips.

[Illustration: FIG. 7.--DISCHARGER WITH MULTIPLE GAPS.]

In the use of this kind of discharger I have found three principal
advantages over the ordinary form. First, the dielectric strength of a
given total width of air space is greater when a great many small air
gaps are used instead of one, which permits of working with a smaller
length of air gap, and that means smaller loss and less deterioration
of the metal; secondly by reason of splitting the arc up into smaller