The Indianapolis times. [volume] (Indianapolis [Ind.]) 1922-1965, 1932-11-01
SCIENCE
BY DAVID DIETz.

When q Scientist Speaks of
a Vacuum, He Means a
Partial Vacuum; There Is
No Absolute Vacuum.
IDR. WILLIS R. WHITNEY, re-
~ search director Of the General
Electric Co, once gave an address
under some such title as The Vac
uum-There's Something in IT,
Arecent proof Of that contention
was given in another address by DR.
A. w. Hull, assistant director of the.
G. E. laboratories, who spoke on
New Vacuum Valves and Their Ap--
plications."
There's something in the vacuum.
to begin with, because no vacuum
ever attains the ideal of the diction-
airy definition, "a space entirely de-
void Of matter" -~-
A cubic inch of air has been esti-
mated to contain 800 million times
billion molecules. It would be
quite trick to get rid of them all.
When the scientist speaks about
vacuum, he really means a partial
vacuum, for he is interested and
concerned with the residue of gases
left in the vacuum tube.
The behavior of the tube is due
in large part to that residue.
The vacuum of 1880 used by Hit
tori, who made the forerunner of
the radio vacuum tube, and Crookes.
who made the forerunner of the x
ray tube, was equal to about one
thousandth of the atmospheric pres
sure. ss>
This meant that in the vacuum
of Hittorf and Crookes, there were
only 100000 billion molecules to the
Icubic inch.
DUT the vacuum of 1890 was use ,
- full. In fact, it still is useful.
In ordinary air, an electric current
requires a pressure of 10000 volts
TO jump a distance of third of an
inch.
But in low vacuum-the euuiva-
lent of the 1880 standard-the same
result can be obtained with a pres
sure of 300 volts.
AT this pressure the electrons-it
will be remembered that an electric
current is stream of electrons in
motion-have long, free paths. COL
lding with the atoms and molecules
OF the air remaining in the tube.
they cause them to become electri-
fed or ironized. -"
The result is faint glow in the
tube known as the glow-discharpe
But this glow discharge is an cleo
trio bridge along which current
can flow. IS
discharge" tubes have manyf
uses today. The rectifying tubes
which change alternating current to
direct current are of this sort. Thew
also are used as sources of illumiao
nation.
The neon tube, used in advertising
signs and in television devices, is a
gloW-discharge tube, the mixture of
residual gases of the ordinary tube
being replaced with a slight amount I
of neon gases.
by 19O0, the vacuum was reduced
to millionth of an atmosphere,
This sounds like considerable per-
1ormance, until it is remembered,
That there remained about 300 BILE
hon molecules to the cubic inch.
But molecules are exceedingly.
small and electrons are yet smaller
AS DR.. Hull points out, electrons,
passing through such a vacuum ONLY
occasionally bump into an atom or
molecule.
THhe vacuum of 1900 made posi-
Il bic the radio vacuum tube Of
De Forest. 1t also made possible"
the photo-electric cell. ~.
In other words, the vacuum of
1900 made possible the radio and
television.
Within recent years engineers have
felt the need Of still better vacuunns
than those of 1900. Modern ampu-.-
flying tubes, the so-called screen
grid tubes, may be "cascaded" to
give any desired amount of amplifi-
cation.
AS DR.. Hull says, "the sky is the
limit" But there is a practical
limit.
I'VE soon begin to hear the tube
itself" hes avs. "a steady hiss, of
no particular frequency, is what it
sounds like in a telephone receiver
These tube noises" as they are
called, are due to the fact that the
residual gases in the tube are cleo
trif1ed by the passage Of the cleo
irons.
They set up extraneous currents
which are not wanted, but which
make themselves noticeable with
sufficient amplifications as the hiss
ing noises referred to.
BY improving the vacuum In the
tube, the General Electric scientists.
have made one tube which they call
the PILL.
Its noise level Is one-tenth that of
the best simplifying tube previously
made. Consequently it will amplifv
ten times more than any tube now !.
| in existence. -
mo one knows what will be done
with this addition to the tube fans
ily," DR. Hull says. THE possibility
OF simplifying and observing things
ten times smaller than before sug-s
gests new discoveries, perhaps in the
field OF physiology, by measuring
heart-beats, nerve impulses, and the
like"