Evening star., 1932-02-07

With the chronograph Mr. Loomis
has compared the accuracy Of his three
pendulum-regulated Short clocks with
the crystal oscillatorS of the Bell Tele-
phone Laboratories, and has actually
been able to demonstrate the error IN
the pendulum clocks caused by the
gravitational pull of the moon. The
periodic gain and loss in time caused
by the moon was found to cause a va
Ration in indicated time of about two
milhonthS of a second per lunar day.
which is about two weeks.
The extreme accuracy with which
such apparatus can measure variations
of gravitational attraction has already
enabled observers to chart and measure
areas of the earth where graVitational
attraction varies from other parts.
These measurements are expected to
yield many valuable secrets about the
interior of the earth and the move
ments Of its crust, perhaps even 10
make possible the prediction of earth
quakes.
The international scientific expedi-
ton which sailed last week for an ex-
tenSlVe investigation of gravitatiOnal
phenomena in the Caribbean area will
make use of pendulum apparatus op-
Grating on this principle and will take
measurements from the interior of a
submarine submerged to depth which
will insure relatively quiet water. The
time OF the pendulumS will have to be
compared with that of accurate master
clocks on land which are regularly cor
rected by star observations.
In this work the Navy is cooperating.
and the time corrections will be fur
nlShed by the clocks of the United
States Naval Observatory These are
OF the pendulum type, but they are
corrected at frequent intervals by OBJ
Servations of the fixed stars. Such
observations, in fact, give the time
standard of the world.
Navy Time.
For more than 100 years the NAVY
has discharged the important duty of
keeping the Nations time accurate.
The service, originated principally for
mariners, has been increased and ex-
panded to take in homes, Offices, rail-
way stations and scientific expeditions.
Time, accurate to a hundredth of a
second, is now regularly computed and
broadcast by the Naval Observatory,
and at present the observatory is plan
ming more efficient apparatus for the
retranSmiSsiOn of time signals bv Way
OF san Francisco which may be the
first step in the installation of a serv-
ice that can be heard around the world
The time service of the Naval OBJ
SerVatory was described before the
American Institute of Electrical Engi-
neers by Capt. Frederick HeIlwig. super
ntendent of the observatory. He told
OF the new vault built at the observa-
tory at Arlington, Va, which will house
seven clocks especially designed for ac-
curacy. These clocks will be main
tamed in the vault under constant
temperature. and air pressure in order
10 minimize the effect of changes in
the weather.
Coupled with these far-reaching i'm
proyementS in methods of measuring
time has come a recent improvement
In tlmekeeping apparatus available to
home owners. Before 1916 no such
thing as SynchronouS clock was
known, and even if one had been in
vented the irregularity of alternating
current generators then in use would
have made the use of such clocks i'm
practicable in the home.
Since that time, however, number
OF inexpensive synchronous clocks, reg
ulated directly by the pulses of the
alternating current which operates
them, have been devised. How this
development has come about was de-
scribed In the time symposium by H. E.
Warren, one of the pioneers in this
held. Mr.. Warren stated that more
than 100000 synchronous clocks were
sold in 1880, and even more last year.
whereas 10 years ago these timekeep-
ers were almost unknown.
The secret of the accuracy of alter
nating-current house clocks lies in the
master clock at the power house. Until
these master clocks had been devised
the variation in alternating current
cycles was so great that keeping time
by them would have been out of the
question. Now, in most systems, the
cycles are so closely regulated that
synchronous clocks are often better
timekeepers than the best spring.
driven clocks