Evening star. [volume] (Washington, D.C.) 1854-1972, 1881-07-02
How the Work is Done 1t the Oh.
servatOfy-Definin Its Position

AstrOnOmiCally.
The unexpected coming OF the comet has de-
Veloped an unusual interest In astronomy. In
Old times these visitors were regarded as dread.
iul emens OF evil, but now methodical science
| lnspects them as coldly as physician would
vestgate some new found species of animal
lie. The present comet instead OF frightening
people, has only excited their curiosity. Every
one wants to see 1t, and to learn all The facts
| about It, He grumbles IL careful and delib rate
scientists are unwilling TO answer his questions
at once. This curiosity has attracted an unu-
during the past week.
observations are taken OF the comet as they
are taken OF any other heavenly BODY. though
lnefe ID an exciting interest In the work which
relieves 1t OF any sense OF dru1gery. An as.
| tTonomer
ON THE LOOKOUT FOR COMETS
uses g nerally small giaSS,-0ne that he can
handle easily and which has broad field. Toe
comet, having been discovered, the first point
to be determined is its position.-its right as
censon and declination corresponding 70 the
longitude and latitude, OF point On the face OF
the GLOBE. When this has been determined,
and three observations taken at eq1i distant
tlmes,-about week apat,-the astronomer,
Dy series OF computations, is enabled to de-
termine very accurately the elements OF the
oro1t, from which 1t is an easy matter for
The earth and rapidity OF motion OF the com ,J.
Perhaps he may be enabled to make preiic
ION as TO when Ii will return. Tle53 o033rvA
ions are taken on
TIE TRANSIT CIRCLE"
large glass, which is mounted, exactly on a
line with the meridian. This glass Is located
in little wing at the west Side Of the Ooserv-
atory. There is an opening through the roof
and In the north and south sides Uf the SO Iare
structure, looking as though some one mad C IL
slice from the middle OF It. The glass inside
- mounted, as accurately as science C Al mount
1t. SO that az 1t is revolved from north to south,
ii never sWerves hairs breadth to wards the
east or west. star seen through 1t, Is s1p-
supposed to be exactly over the meridian line.
by this glass the right ascension and declina-
non OF star, planet or comet, Is ascertained.
mate position in the heAvens Is known.
AID that can be determined with the
naked eye, before 1t reaches the meridian,
the glass Is set SO as to cover IL when
large wheels which reyolve with the glass
dnese wheels ere scaled and graduated 50
finely that microscopes have to be used TO READ
The measurements. Presenting that thu In
strument has been set right, the observer,
when he expects the star or comet peers
through the glass. The field OF the glass is
groups OF two, three and five. There are also
Two fine nair lines from right to left.
THs OBSERVER
has In his hand Geographic key. which con-
uects with an electric chronograph. When the
comet enters the field of the glass; as 1t Gro sses
each line, the observer taps the key. The two
horizontal hair lines are Adjustable By means
OF little screw In the eye piece OF the i1stru.
ment, and the observer so adjusts them, that
tie center or the nucleus is exactly between
tbe lines The comet Is not greatly magni-
fed in the glass; but Is very clearly de
liIe extending back from the head to a
point where the tail seems to split. When the
comet has passed over the meridian at its lower
elimination. which 1t does nov a little after II
o'clock at night. the Observers work really
commences. He has to note the time on
THE CLOCK.
This is no ordinary clock. but one set In
vault, where 1t is free from all disturbing nflu-
ences OF varying temperature, with nothing
but its face showing. It keeps sidereal time
The hour aud minute taken from the clock, aud
The records made by the chronograph give
down to the tenth part Of a second the time
tral hne on the field OF the glass representing
The meridian. The time OF the PASSAGE is easily
convertible to right ascension, or, in other
ude OF town can be calculated by noWing
lis time. The register or scale on the wheel Oh
II north OF the glass, considered together with
a little register connected with the screw regu-
a1Dg the horizontal lines on the field of the
glass; Indicates
THE ZENITH DISTANCE
CT the body observed, which Is readily convert.
| able into decl1nation or siJereal latitude. The
chronograph should be described here, in order
TO give correct Idea Of the accuracy with
hch the time can be determined. Ii consist q
OF a revolving cyliuder. covered with sheet I
paper, so placed that an iron from an electric
apparatus makes marks at regular Intervals
the interval Is exactly a secohd. The aoping
OF the key held by the observer makes An extra
mark, and any school boy wouli SOFA Learn to
tell. by means Of these marks the ex act tim of
fach tap When the astronomer has oot.lned
tie right ascension and declinat1on in til 10 m
Ler described, be really has just commences
MS WORK. he has before him the tedious task OF
CORRECTING ERRORS.
| 1t is always presumed that there are errors.
II ade by the clock and by the instrument or
lass. Though the most delicate appliances or
cience are used In mounting AMI a1jl:tny
these meridian glasses, 1t IS found that they
are so seldom accurate that astronomers
always take it for granted that there are some
errors In figures first obtained. A deviation of
hundredth part OF hairs breadth could
hardly DE detected on the earth, but where the
line OF vision extends millions Of miles into
space. 1t Is apt to seriously affect nice calcula-
ilons. SO the astronomer begins series of
intricate experiments and calculations TO Dr.
| rect the errors Of the clock and OF the instru.
| ment. The instrument Is tested with due
level Underneath set upon pillar which Is
quit upon the ground and is Independent of
The Observatory building. Is q pool or trough
| OF mercury. The observer. in order to satisfy
himself That the instrument when placed per-
pendicularly points directly to the zenith, must
from the mercury. So sensitive Is the mercury
to all disturbances that If wagon Is passing
near the building the surface IS so disturbed
mat no reflection can be seen at all when Look.
Ing through the glass; The observer, having
corrected the errors by long and tedious com
putatiOns, finally obtains q correct statement
OF the position OF the Comet. After taxing
three such observations, a week or more apart
he Is ready to compute the elements OF ths
comets or bit.
AN ASTRONOMERS LIFE.
ut is popular idea, said Mr.. Wlnlock, the
astronomer who explained the method OF TAX
ng observations to STAR reporter, "that an
astronomers life is a poetical one-.hat all he
has TO do Is to COntemplaIe-gaze through a
glass and think. Th6re Is considerable drudy-
cry and sameneSs about observing"
Can the computations so far made about the
comet be corTect?"
These computations are hasty. The figures
announce were based upon observations taken
very nearly together and at irregular times
nat Is what makes such a variation In the
statements OF astronomers In different parts OF
hec0untry. Nothing sure can be known until
Time has Deen allowed for careful observing"
In addition to the observations taken on the
transit" glass by which the mathematic al
,roportions OF the comet are ascertaiued some
vely interesting experiments With the spectre.
scope are In progress.
A LUCKY PARsON,-The Rev, Or. N W
lsnklDg, pastor OF the Rutgers Presbytarian
church, New York City, has recently arrived in
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