202 SCIENCE-GOS SIP. 
the spark at break is elongated and the time of 
break lengthened. 
Figure 8 shows a more recent modification 
due to Dr. Max Levy. The connections are 
the same as above, but both contacts are movable. 
TSS 
Ls 
FiG.9. WeEHNELT’s ELECTROLYT:C INTERRUPTOR. 
As will be seen from the figure, the solid contact 
takes the form of a number of triangular strips of 
metal fixed on the edge of a disc, which rotates about 
a vertical axis. The liquid contact consists of a jet of 
. mercury forced by means of a self-contained pump 
through a horizontal nozzle and playing upon the 
metal strips. These latter are all in contact with one 
terminal of the break, and the mercury with the 
other. It will easily be seen that when 
the disc carrying the strips is rotated 
by means of the attached motor, con- 
tact will be made when any one strip 
latter is not running, there is no danger of the main 
current short-circuiting direct through the primary coil. 
Undoubtedly an achievement was made this year 
in the introduction, by Dr. Wehnelt, of the second 
kind of break—the electrolytic form, which is shown 
in fig. 9. Attention has already been called, in May 
last, to this break, in the Physics column of SCIENCE 
Gossip. It is constructed somewhat like an ordinary 
electrolytic cell, having two electrodes placed in 
dilute sulphuric acid in a suitable vessel. The 
cathode consists of a sheet of lead about 
17x12 cms., the anode taking the form of a 
platinum point, arranged horizontally opposite 
the cathode, and at a mean distance of about 3°5 cms. 
from it. The sulphuric acid is made up of one part 
of strong acid by volume to about seven parts of water. 
The anode can be moved nearer to or farther from the 
cathode, so as to adapt the working of the break to 
varying conditions, and to give different results upon 
the coil as required. In so adjusting the platinum 
wire it is moved in and out of an ebonite sheath. 
Originally it was sealed into a glass tube: It was, 
however, found that the latter was apt to break, owing 
probably to the great heat and to the expansion at the 
discharge point ; for when the instrument is working, 
the liquid round the anode is vaporised and the point 
becomes red hot. In fact, there isa kind of spheroidal 
condition kept up, and it is here that by far the greater 
part of the resistance of the break occurs. 
The theory of the action of this instrument is still 
under discussion, for although it is termed an electro- 
lytic break, it is by no means certain that electrolysis 
does take place. In fact, a recent communication to 
“‘Wiedemann’s Annalen” by H. T. Simon, points 
to the action being entirely attributable to heat; and 
that it may be explained at least parrly by Joule’s law 
of the heating effects of an electric current. More 
will be said later upon the manipulation of Wehnelt’s 
comes into the line of play of the 
mercury jet and will be broken as 
soon as it passes. The number of 
nterruptions may not only be varied 
by the speed of the motor, but also 
by altering the number of strips fixed 
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on the discs, these being easily screwed 
on and off. The relative times of 
make and break may also be varied 
by raising or lowering the jet of mercury, thus in- 
creasing or decreasing the duration of contact. For it 
will be seen that if the jet is raised, a greater surface 
of the strips comes into its path, thus giving a 
relatively less time for non-contact. All these 
adjustments are very useful, since different conditions 
are required to be fulfilled for photographic work, to 
those for fluorescent screen work. Another advan- 
tage this break possesses is due to the fact that the 
pump, producing the mercury jet, ceases acting 
immediately the motor stops. | When, therefore, the 
Fic. ro. SET or 8 Gane CELLs. 
form, when we consider different 
sources of current. 
Since this break was first brought 
out there have appeared modifica- 
tions of it by E. W. Caldwell, A. 
A. C. Swinton, and others. In 
Swinton’s form, the platinunranode 
is replaced by a second lead sheet, 
smaller than the cathode, and 
separated from it by being placed 
vertically ina large thick test tube. 
Fic. 10a. Zinc 
or GROVE CELL. 
