The times. [volume] (Washington [D.C.]) 1897-1901, 1901-05-05
TELLING fIMB BY STARS
Important Work Of Modern Astr0-
nOmical 0bservat0ries.
Deiicnte Instruments Used by Har-
ward University1How the Obser-
yations Are Made-Master Clocks
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 n 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 its own wires. which fairly crisis
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 1t
expedient to abandon outside Service. es-
pecially 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
| IL
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 a time star" Carefully
as Washington may handle its 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 astro-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
FL 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
y
! 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 as to follow that meridian from
one horizon to thB other. The middle YER
| teal thread of spiderJ web in its 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 meridian
This is the fundamental method Of time
| telling by the stars. The celestial heav-
ems are the migbtiest and yet the most
infinitely accurate clock that exists. a
given star crosses the meridian at just
such an interval and nothing short of
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 ihnurs-as one would nat
uraily think, but lis q sidereal day or q
hours S. minutes, and 90 seconds, 366 of
these days edualing, rpXirnately,
crepancy being that as the earth
wolves on its axis it is also travelling
round the sun, that its position toward
the fixed stars changes astriHe each day,
given star coming into view a trifie soon
err than II would If the earth were not
travelling on its orbit. but only revolving
on its axis. fa
While for ordinary purposes single
vertical thread in the meridian circle
would suffice, 1t 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 its time OF crossing the
meridian, reducing the possible error to
a very small amount 1t Is here that cleo
tricty in its close partnership with time
in astronomical work makes its first ap-
pearance in the Harvard Observatory.
BY the side of the observer using the
meridian circle is an ordinary telegraph
key.
As a given clock star" passes each
cross hair the observer touches the key,
which is connected with a chronograph
or time register. This is an instrument
with cylinder which revolves once every
minute and carries a sheet of paper on
which fountain pen rests. making, nor
mally, parallel straight spirals around the
paper, for as the cylinder turns 1t auto
matically moves to a barely perceptible
degree toward one end. When the key at
the meridian circle is pressed. an electro
cal connection is broken which operates a
miniature magnet, thus moving the pen,
which is drawn aside for an instant.
If the touch on key is momentary, the
pen moves aside and then right back,
leaving an inverted V-shaped mark. If
the key should be held down. the top of
the inverted V would be fattened, the
length of the fairness measuring the time
the key was held down. Meanwhile. the
standard clock also has been sending in
its record to the ehronograph, operating
the pen. AS the clocks pendulum swings
back and forth. 1t makes and breaks a 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 tie same time as a beat the
marks coincide, but where one is just
before or just after the other the top of
the is fattened.
The vertical threads in the field of the
telescope are so fine that magnifying
eye-piece is used, in which only few
threads at time are seen. By placing
the threads at different intervals GER
tain prescribed irregularity results in the
marks on the chronograph sheet, so that
when the record is read it becomes easy
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 instru-
ment must be adjusted to catch the star
at 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 20 the standard rate of
stars in the celestial equator. The rea-
for this is that while every star takes
the same time-a sidereal day-to make its
apparent passage around the earth-each
travels at q, different rate, the Pole Star.
for instance, following a circle hardly
noticeable, 50 that les movement is hard
to detect with the naked eye. a star fur
Their toward the celestial equator Is on
a larger circle and hone on the equator
on a 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 bnss. The work in
VolVed in this seemingly simple observa-
ton gives an outsider an idea what mod |