122 Dr. E. Weintraub on the Are in 
discharge ends the alternating current assumes anew the 
direction CB, in which it can discharge itself through the 
tube, and the same process is repeated. The essential point 
of the arrangement is the existence of one common cathode 
to the alternating-current wave which has the proper direction 
and to the discharge of the reactance placed in shunt with AB 
and in series with CB. 
The currents in AB, CB, as well as in the main line, are 
pulsating, while in the reactance the current is unidirectional 
and diminishes to zero for only a very short interval of time. 
Plate VIII. is the most interesting in this connexion. It 
shows the currents through CB and AB in their proper 
relation to the time, and confirms completely the above given 
explanation for the action of the reactance. 
The use of direct current is done away with by this arrange- 
ment, but only one half-wave of the alternating current is 
utilized, and the resulting rectified current is far from being 
steady. In order to utilize both halves of the alternating 
wave two reactances must be used in a perfectly symmetrical 
manner. 
ixperiment 19.—The connexions, as shown in PI. IIL. 
fig. 13, require no explanation. One half of the alternating 
wave goes in the direction CBA, the other in the direction 
HEBD. The zero-point of the alternating current, as well as 
the period during which the value of the alternating current 
is small, is bridged over by the discharge of the reactances L 
and L, through those parts of the arc to which they are in 
shunt respectively. All four currents have the same common 
cathode K. Plate LX. shows that the current in the line N, 
where all the currents are superposed in the same direction, 
is adirect current nearly constant in its intensity. In the 
supply-line there flows, as is shown in Plate X. a regular 
alternating current. The unidirectional current in one of 
the reactances is shown by Plate XI. This arrangement 
represents, therefore, an almost ideal rectifier. The efficiency 
is, with 100 volts applied, counting in the losses in the are, 
as well as in the reactances (copper-loss, hysteresis, &c.), 
very high, and goes up as the voltage is increased. The 
power factor can, by proper adjustment of the reactances, be 
made very near to unity. 
The two electrodes C and E can be made of graphite, iron, 
or similar material, so as to avoid the superfluous mercury 
vapour which comes from the mercury anodes and disturbs 
the stability of the are (see § 3). A condensing-chamber 
must, of course, be provided in all of the tubes, in order to 
keep down the pressure of the mercury vapour. ‘The very 
