Evening star., 1932-02-07
EARTH IS MOST PERFECT
TINIEkEEPER, SANANTS SAY
Vibrations of Crystals and Momentum of
Heavy Machinery Cut Errors to
Surprising Degree.

locked in absolute synchronism with
the higher, is one of 1000 cycles. Each
pole of the synchronous motor driven
by this current. therefore, corresponds
to one thousandth of second of time.
Consequently, any variation in the
operation of the motor can amount at
the most to small fraction Of a thou
Sandth of second.
When the simplicity of this device is
compared with the complicated electri-
cal and mechanical mechanism neces-
sary to increase the accuracy of pen
dulum clock the advantages of the crys-
tal-regulated timekeeper are easy to see.
Crystals have been operated continually
able variation in the number Of vibra-
tions per second. and without wearing
out, heating up or losing accuracy in
any way Practically the only large
difficulty which may cause irregularity
in such clocks is the ageing of the
vacuum tubes. which must be used in
the circuit, and it is expected that this
trouble can be reduced considerably. E.
In order to increase the accuracy and
to adjust the system for minute varia-
tions brought about by any Of hundreds
of small factors. the Bell Telephone
Laboratories use three such crystal
oScillators instead of one. The result is
a timekeeper of such extreme accuracy
that special instruments have had to
be devised to detect variations.
The most accurate Of these instru-
ments is the Loomis chronograph, in
vented by Mr.. Loomis and used in his
laboratory at Asbury Park Also in his
laboratory are three Shortt pendulum
regulated clocks of the most accurate
design. on which experiments and re-
finements are being made. eliminating
as far as possible the variational factors
which contribute to the inaccuracy of
such clocks.
Factors That Influence Clocks.
Some idea of the smallness of the
forces involved and the tremendous
complexity which greater and greater
accuracy introduces into the problem
OF such pendulum clocks may be gained
by a consideration of some OF these
error producing factors
These include changes of the center
of gravity of the pendulum due to vary
Ing buoyancy in air of the two or more
materials of which it is made; change
of motion due to the amount of air
carried along with the stroke; the fric-
tional effect of the air; minute wear
ing at the knife-edge which supports
the pendulum-or if 1t is spring sus-
pended changes in the elasticity of
the spring; change of movement caused
by the effects of temperature, by the
inaccuracies of the apparatus which
transmits power to the pendulum, by
the friction of the various parts, by
the gravitational effect of the earth,
and the varying gravitational effect of
the moon and other heavenly bodies.
Coupled with these troubles are
vibrations of the earth caused by earth
quakes, traffic, or other unpredictable
movements, the sympathetic action of
one pendulum on another, even when
operating in vacuum, and changes
in the pull of the earth's gravity when
the clock is slightly raised or lowered.
This last is very serious effect, and
is sometimes uncomfortable. If pen
dulum clock be raised l foot, its rate
will be changed by one part in twenty
million, and its accumulated loss as a
timekeeper will be one and one-half
seconds in a year, due to the change
in the force of gravity as the distance
CONTINUED % Fourth Pazt.I