…
174
8.
ELECTRÏCITY THROUGH GASES
_
At the higher pressures,
the cathode dark space is narrower and
the striations in the positive column, if present, are closer together.
As the pressure is reduced, the cathode dark space, or, as it
sometimes called, the Crookes’ dark space,
becomes longer
the striations are farthe‘r apart.
Experience will soon allow one
to estimate the pressure
in a tube from these phenomena. As a
rough indication, the cathode dark space
will be about 1 centimeter long when the pressure
is 0.08 millimeters.
At a given
pressure,
the distance from the cathode to the positive column has
-
an approximately xed value, whereas the positive column lls the
.
remainder of the tube, regardless of its length. In the neon advertising Signs, where the pressure
is several millimeters, it is the
positive column Which is seen. If, at a given pressure,
the anode
is moved toward the cathode, the positive column is reduced in
length, but little change occurs in the phenomena near the cathode.
When the anode is moved still closer to the cathode, into the
tive glow, changes in length occur and the discharge ceases just
as
the anode passes
into the cathode dark space.
With two
cathodes and two anodes, in connected, parallel tubes With one
pair of electrodes far apart and the other one separated by a dis—
tance less than the length of the cathode dark space,
the discharge
prefers the
“
alternate
"’
longer path. It is obvious, therefore,
that the region near the cathode is of great importance in the mam—
tènance of the discharge.
The potential which exists across a discharge tube is largely
_
determined by the pressure ”of the gas.
Consider 3. tube in series
'.
with a protective" resistance and a d.c. source of
Ifthe
e.m.f. of the source is increased, the current through the tube Wlll
ï
larger current causes a larger ir
1nthe
’
resistance and in»the internal resistance of thebattery
*
YeΑÉÉ—jthe;p0tential difference between the electrodes
‘
?ppfôäi1àt‘elÿ the same as before (a few hundred
@neof
characteristics of a glow discharge is thatalarge
the Cath0de
This 1s“shown
:"»LÎÏÏ. l
mg‘11‘68f14553ndîagain points to the importance of.the phenomena
be
the1rareas
174
8.
ELECTRÏCITY THROUGH GASES
_
At the higher pressures,
the cathode dark space is narrower and
the striations in the positive column, if present, are closer together.
As the pressure is reduced, the cathode dark space, or, as it
sometimes called, the Crookes’ dark space,
becomes longer
the striations are farthe‘r apart.
Experience will soon allow one
to estimate the pressure
in a tube from these phenomena. As a
rough indication, the cathode dark space
will be about 1 centimeter long when the pressure
is 0.08 millimeters.
At a given
pressure,
the distance from the cathode to the positive column has
-
an approximately xed value, whereas the positive column lls the
.
remainder of the tube, regardless of its length. In the neon advertising Signs, where the pressure
is several millimeters, it is the
positive column Which is seen. If, at a given pressure,
the anode
is moved toward the cathode, the positive column is reduced in
length, but little change occurs in the phenomena near the cathode.
When the anode is moved still closer to the cathode, into the
tive glow, changes in length occur and the discharge ceases just
as
the anode passes
into the cathode dark space.
With two
cathodes and two anodes, in connected, parallel tubes With one
pair of electrodes far apart and the other one separated by a dis—
tance less than the length of the cathode dark space,
the discharge
prefers the
“
alternate
"’
longer path. It is obvious, therefore,
that the region near the cathode is of great importance in the mam—
tènance of the discharge.
The potential which exists across a discharge tube is largely
_
determined by the pressure ”of the gas.
Consider 3. tube in series
'.
with a protective" resistance and a d.c. source of
Ifthe
e.m.f. of the source is increased, the current through the tube Wlll
ï
larger current causes a larger ir
1nthe
’
resistance and in»the internal resistance of thebattery
*
YeΑÉÉ—jthe;p0tential difference between the electrodes
‘
?ppfôäi1àt‘elÿ the same as before (a few hundred
@neof
characteristics of a glow discharge is thatalarge
the Cath0de
This 1s“shown
:"»LÎÏÏ. l
mg‘11‘68f14553ndîagain points to the importance of.the phenomena
be
the1rareas