El Paso herald. (El Paso, Tex.) 1901-1931, 1910-06-13
The Naval Observatory
FOR KEEPING AMERICAS TIME

| SONIGHT one of the four moons of
| \ Jupiter viii be in, transit across
| the face of that big planet and
| another Will pass behind it in eclipse.
1t was through observations of the
| movements of the moons of Jupiter that
| the theory of the velocity of light was
/ eVolYed-a discovery of prime import
! ance in astronomy. Observations of
their movements were being made in
order TO assist seamen to reckon their
| positions, and it was found that the
eclipses occurred % minutes earlier when
| the earth was nearest to Jupiter than
when it was at its most distant point
1t was concluded that it required p
/ minutes for light to cross the orbit of
, the earth. 1t was later found that the
motion of the earth and other things
| had TO be taken into the reckoning, and
| then the actual velocity of light was
! determined
Delicate Instruments Used.
! After the solution was worked out
! Indirectly it was concluded that it must
| be worked out directly, and many in
geniOus machines were brought out to
| do So Perhaps the most accurate and
conclusive tests of light velocity ever
| made were those of the late Simon
Newcomb and A. A. MichallsOn, acting
| on behalf of the Naval Observatory at
Washington. To measure the velocity
! of something which flies so fast that
| ii will race around the earth seven and
| half times in a single second might
seem an impossible task; but these two
representatives of the Naval Observa-
torW set themselves resOlutely to it.
Az the base of the Washington monu-
| mnet they set up big mirror. In the
grounds at Fort Myer, two and a
quarter miles distant across the Poto-
mac river in Virginia, they stationed
| mir wifi of
revolutions to the second.
BY revolving this mirror with great
rapidity they were able to note how far
it would turn in the time required for
a ray of light to flash across the inter
veping space between Fort Myer and
the Washington monument and back
| again. They found it would cover the
distance in the 40-thOusandth part of
second, and thus they were able to
settle positively the question of the
velocity of light Their instruments
were so delicately adjusted that they
would measure the millionth part of a
second as easilyaas a carpenter meas
ureS a board
Naval Observatory Supplies Time.
The Naval Observatory is one of the
sights of Washington that the tourist
seldom sees. and. in fact, its work is of
FNsuch character that TO make show
place of it would interfere with its
usefulness. 1t is here that America gets
its time.
The day was when sun time was ac-
curate enough for any man, but with
the advent of the railroad and the teIe-
graph, standard time became a neces-
sity, and the complex conditions OF
modern civilization requires time &C
curacy near TO the absolute as may
be. In the single matter of navigation,
an error in time might lead the COM
mander of a fleet to miScalculate his
position, and a war might be decided
through the disadvantage Of fleet
which did not have the correct time.
Clock in Vault.
If there is a necessity for corr ect
time the Naval Observatory l., the re-
suit of that necessity. It's great master
clock, kept iB an isolated vault, in a
sealed case, the temper& tura of which
is not allowed to vary more than the
hundredth part of a degree, is one of
the wonders of the world of delicate
scientific instruments. 1t is so accur-
ate that ii never varies more than
three-tenths of one second, and at times
has run for weeks without getting out
of the way more than the hundredth
part of a second. In the sealed case
in which it is kept there is little Their
moStat and an electric light. a change
Of the hundredth part of a degree of
temperature viii affect that delicate
thermOStat as much as change of 10
degrees will affect a human being
When ii gets the twO-hundredth part of
a degree colder than normal the Their
mOStat ShiverS and turns on the little
light, which serves it as an automatic
stove. When ii gets the two-hundredth
part of a degree hotter than normal the
thermOstat begins TO mop its brow and
turns off its electric stove. Not only
must the temperature. but also the
barometric pressure, be kept constant
Careful Watch Maintained.
Yet with all the wonderful accuracy
of this clock a careful check must be
kept upon its performance, in the do
ing of which one finds a precision al
most startling in its care In little
square house on the Naval Observatory
grounds there is an instrument which
YerifieS the time two or three times a
week, and is, after ALL the source of
the nations time. 1t is mounted on
two great pillars of granite, and looks |
like a cross between a cannon and
telescope. 1t is on the exact meridian /
of Washington, and can be pointed only !
north and south.
To make its readings worth while 1t !
must be adjusted with a delicauy al !
most unbelievable 1t cannot rest with |,
but a small percentage Of its weight on |
its pivots. The entire weight, except |
for a few pounds, is supported by a /
sling arrangement. only enough of the |
weight being allowed on the real bear |
ings to give it steadineSS and to pre- !
vent wear. At its side there are two