Wheeling Sunday register. [volume] (Wheeling, W. Va.) 1882-1934, 1901-09-29
RECKONING LONGITUDE
BY STARS AND CLOCKS.

Mr.. Edwin Smith, of the United States
Coast and Geodetic Survey In the OBJ
seryatory In Cambridge was the sarae
as that set up by his fellow Observer
Mr.. w. B. Fairfield. in the temporsr~
observatory at Provincetown. the oniy
difference being in the movement OF
the two chronometers. which are in
evitably subject 10 slight inaeeu acies
when compared with the movements
Of the time stars chosen for observa-
ton. To correct these inaccuracies-
which might have been quite disre-
garded in anything less delicate than
astronomical observation was. in
short, the important purpose OF the
work undertaken; not only to correct
both clocks but TO compare the cor
rected time at the same instant with
out allowing either timepieee 10 be-
come once more infnitesimally mac
ccurate. To accomplish the two OBJ
servers. two similar sets Of delicate in
struments, direct telegrapaic communi-
cation. and careful altered konings 20
eliminate even the time taken mp by
the transmission Of telegrapliic mes
sage. were all required.
The apparatus consisted OF a transit
for observing the stars. a chronometer
for keeping the local time OF the OBJ
servaticns, chronograph for record
ing the exact instant when each star
crossed the meridian. and n tele-
graphic switchboard by means of
which the Cambridge and Province
town observatories were kept in direct
communication and the observations
at each recorded on both chrome
graphs. OF these Instruments the
transit may be roughly described as a
telescope so mounted that II sweeps a
great half circle Of the heavens. keep
ing always in the plane Of the meri
dian, to which it offers n field crossed
BY II hair lines over which the tran
sit of a star may be exactly noted.
The chronograph is revolving roller
on which a fountain pen, operated by
electrical connection with the observa-
tory chronometer, draws q straight
line marked into seconds. as. second
hY second. A1e chronometer makes and
breaks the circuit The Pen is con-
troled also by a Telegram ic key. a
touch on which records or the chron-
agraph the exact moment when the
star crosses each line into which the
field is divided
Twenty stars, the usual number.
were chosen for observation, in sets OF
10 each OF these stars 1G-that Is to
say, four in each group Of five-were
time stars chosen because it was
already known from the publications
OF the Naval Observatory at Washing
ton and from Greenwich. at what mo-
ment each would culmlnate,-or cross
a given meridian, this elimination
marking the correct siderial time by
which even the most perfectly con-
structed chronometers must be regu-
lated AS each Of these stars, one
after the other crossed the fine lines
of the telescope field. first at enc sta
ton, then at the other. the observer
recorded it on his chroncgraph. AS
each set of stars was noted, signals
were exchanged between the two sta
tons and the data thus supplied for a
comparison of the two chronometers.
If man and instrument had been abso-
utely accurate p single star would
have been sufficient TO establish the
required longitude. for by means of the
telegraph each observer would have
had at once a record of the elimination
of time star as seen from both sta
tons. and therefore a means of COM
paring the sderial times at either
point The difference in siderial time
would be the difference substracted