The times., 1901-05-05
TELLING TIME BY STARS
Important Work Of Modern Astr0-
nomical 0bservat0ries.
Delicate Instruments Used by Har-
ward University0How the obser-
yations Are Nade-Naster Clocks
Regulate Distant Instruments.


Regulate Distant Instruments.
! CAMBRIDGE, Mass. May 4.-The de-
termination of the real and exact time
is one of the most important functions OF
an astronomical observatory. 1t IS the
! foundation on which all time is based; on
which the navigation Of the seas depends,
and every owner of a good watch Is IN
debted to astronomers for it's accuracy
/ secured by regulating it to star time.
In former days each observatory supplied
standard time to the country Immediately
surrounding it. The Allegheny Observa-
tory, for instance standardized Pitts
burg. Allegheny City and all Western
Pennsylvania.
In eastern Massachusetts the Harvard
Observatory had an important time plant,
owning it's own wires. which fairly criss
crossed Boston and its suburbs. But the
increased use of high potential currents
for electric lighting and street railway
purposes increased the liability of crossed
currents and resultant fires so that a
few years ago the corporation voted it
expedent to abandon outside>service, es-
pecialy in view of the fact that the Naval
Observatory at Washington had begun
! furnishing time free to all-comers, so that
the telegraph companies were able to dis
tribute it generally throughout the coun-
try.
In spite of this change however each
observatory still finds it necessary to de-
termine its own time. Far advanced as is
the skill of the clockmakers who work
| for scientists, they cannot compete in ac-
/ curacy with time star" Carefully
| as Washington may handle it's work, the
| sky may be overcast there while clear
elsewhere, so that greater accuracy would
/ be attained if several observatories in diff
ferent parts of the country were to coop
crate in determining the standard time to
be used by all.
All astronomical and many tro-physi-
cal observations and calculations are
! based on time, and the absolutely real
| time, distributed by electricity, controls
the greater part of the purely mechanical
! work of observing. This electrical dis
! tribution has been carried further per-
| haps by the staff of the Harvard Observ-
/ atory than elsewhere: not only in the
plant on the highest land in Cambridge
/ but at the branch station at the foot of
/ El Misti in the mountains of Arequipa
! Peru. and the temporary station at Man
! deville on the Blue Mountains of Jamaica,
! British " est Indies.
| The determination of the time at the
| Harvard Observatory, which is typical of
! the work at the others. is with the S-inch
! visual meridian circle. a telescope on
mighty masonry piers that swings ever in
the meridian of Cambridge. but which can
! swing so rs to follow that meridian from
/ one horizon to the other. The middle YER
! tical thread of spider web in it's field fol-
| lows the meridian as the operator moves
| the telescope, and when a star crosses
/ that vertical thread he knows that it
| crosses the meridlan.
This is the fundamental method Of time
| telling by the stars. The celestial heaV-
! ems the migbtiest and yet the most
| minutely accurate clock that exists
! given star crosses the meridian at just
| such an interval and nothing short of a
| catastrophe involving the probable de-
| struction of the. earth, can change that
! interval. The interval is not, however.
| the same as one-1revOlutiOn of the earth
on its axis-or "a d10urs-as one would nat
| urally think, but lis q sidereal day or q
| hours 56 minutes, and 4Q9 seconds, 366 of
these days equaling,, approXinately, a
| crepancy being that as the earth re-
| wolves on its axis it is also travelling
round the sun, 50 that it's position toward
the fixed stars changes aatriHe each day,
given star coming into view q trifie soon
er than II would If the earth were not
travelling on its orbit. but only revolving
on its axis.
While for ordinary purposes a single
vertical thread in the meridian circle
would suffice, it is not accurate enough
for science and so seven vertical cross
hairs are set on each side OF the one
which represents the meridian, the mean
or average time of a star crossing them
| being taken as its time of crossing the
meridian. reducing the possible error to
a very small amount. It Is here that cleo
tricity in its close partnership with time
/ in astronomical work makes its first APP
pearance i'll the Harvard Observatory.
BY the side of the observer using the
meridian circle is an ordinary telegraph /
key.
at. 11I,
cross hair the observer touches the key,
which is connected with a chronograph
or time register. This is an instrument
with a cylinder which revolVeS once every
minute and carries a sheet of paper on
which a fountain pen rests making, nor
mally, parallel straight SpiraIS around the
paper, for as the cylinder turns 1t auto
maticaHy moves TO a barely percepttble
degree toward one end. When the key at
the meridian circle is pressed, an electri-
cal connection is broken which operates a
miniature magnet, thus moving the pen,
which is drawn aside for an instant.
If the touch on a key is momentary, the
pen moves aside and then right back
leaving an inverted N-Shaped mark If
the key should be held down, the top of
the inverted V would be hattened. the
length Of the fiatness measuring the time
the key was held down. Meanwhile, the
standard clock also has been sending in
it's record to the cifronOgraph, operating
the pen. AS the clocks pendulum swings
back and forth. ii makes and breaks cir
cult which causes the pen to move back
and forth so that an Inverted represent
ing the pendulum beat appears at regu-
lar intervals. When star crosses a
thread at the same time as beat the
marks coincide. but where one is just |
before or just after the other the top of
the Y is lattcned.
The vertical threads i'm the field of the
telescope are so fine that a magnifying |
eye-piecc is used, in which only a few
threads at time are seen BY placing !
the threads at different intervals, a GER
tain prescribed irregularity results in the |
marks on the chronOgraph sheet, so that |
when the record is read ii becomes easy |
to determine which is the V made by the !
observer and which by the pendulum. At /
night the cross hairs are illuminated by a /
little lamp at the side. and shine golden /
against the deep blue of the sky and the !
silver dots of the stars.
Take the time star is one of the |
most delicate Of observations. the iI1Stru-
ment must be adjusted TO catch the star |
al the very point where it crosses the /
meridian. Certain stars. the positions OF /
which have been definitely determined, are |
used as clock stars, all observations
being reduced 10 the standard rate of /
stars In the celestial equator. The rea- |
son for this is that while every star takes |
the same tme-a sderedl day-to make its |
apparent passage around the earth-each |
travels at a. different rate, the Pole Star,
for instance. following a circle hardly
noticeable. so that les movement Is hard
to detect with the naked eye. a star fur
ther toward the celestial equator is on
a larger circle, and some on the equator (
on q vet larger or great circles seeming
to travel past the vertical threads at eX-
press speed. 1t is TO secure standard rec
ords that observations OF the clock stars
are all subsequently calculated on the
common equatorial basis. The work in
VOlVed in this seemingly simple obserVa-
ton gives an outsider an idea what mod
ern astronomy calls for in the observers