CHAPTER 8
THE PASSAGE OF ELECTRICITY THROUGH GASES
8—1.
Introduction.—When electricity passes through a
many new phenomena are observed which do not exist for metallic Î
conduction.
The particles of the gas are in rapid motion, some.
.
are charged while others are neutral.
Both positive and
charges are free to move, whereas in a metal the free electrons
alone serve to carry the current.
Some of the charged particles
in the gas drift slowly under the applied potential, others rapidly.
‘
New charges are created at various points along the gaseous path
‘
whilebthers recombine with charges of opposite sign and are lost‘
as electrical carriers, whereas in a metal there are no
“
sources
”
or
“
sinks,” the current is the same from point to point. The
emission of light from a wire occurs only when the current is com—
paratively large, whereas it is a familiar phenomenon in gas
duction. It is as though the slender wires were greatly enlarged
and illuminated so that the details can be studied not only along“
the length of the pathbut at the various parts of a given crosssection.
As a result of the multiplicity of phenomena which occur
at the same time in gas conduction, the known laws are largely
_
empirical and approximate. Ohm’s law is valid in only a
limited cases.
amount of electricity which passes, and henœ
_
_
the conductivity, changes markedly with the pressure
of the
«
_
In this chapter,the passage of electricity through gases at
atmospheric pressure will be considered rst.
will befol—
“_ —
,
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