The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1875-03-22
OUR ASTRONOMERS IN CHINA.


THE SUCCESS ACHIEVED AT PEKN PORTRAYED
By PROFESSOR J. C. WATSON.
SHANGHAI, Jan. 13, 1875.
NY DEAR PRoFEssoR-I received your letter OF
the 22d October the night before We left Pekin
and send you this by the first mail which leaves
aimee our arrival here In Shanghai. l have writ
ten to-day TO Admiral Davis, stating fully our OPP
eratons since l last wrote him, and stating also
what had done in relation TO the return OF the
party and instruments 10 the United states. l
viii therefore advise you more fully in regard to
our observations. For the determination OF our
latitude We have about lao pairs observed and for
Dur longitude we nave iorty-iour OCCUPATIONS,
many OF them observed by three observers. and
We have in all cases complete time determinations
on the same evening. We have. think,
nearly, II not more than LOCO transits OF
stars for time and position OF instru-
ments. We have almost daily determinations
of the position OF the Photographic telescope. We
have numerous measures OF distance between
Dlatehoider and objective; photographs OF re-
versed lines OF platehoder, &c. We have also
made an accurate geodetic connection betV cen
Dur station and the French and Russian. We
have also the magnetic and other observations
provided for. l can think OF nothing which was
10 be done or ought to have been done which has
not been well done.
In regard 10 occultations computed all those
In the lists or OCCUPATIONS whose limits included
our latitude In the case OF the transit observa-
tions have not been aple TO make the reductions
for two reasons. First, the amount OF material
accumulated; second. the peculiarly OF the H.
strumcnt, which requires much more than ordi-
nary labor of reduction l have made prellmi-
nary reduction OF the observations 50 as to
keep the run OF the clocks and chronometers, and
TO know the errors oil the instrument; but
have been obliged TO defer the complete reduction
Of all the observations until my return TO the
United states. as | participated personally IN
nearly all the observations mace ana know ali
about them can give them thorough treatment,
and upon my return In Sep ember October mex.
1 viii complete the reductions and put all IN CON-
pete form for publication, winch will, trust, be
In good season.
THE DIFFICULTIES BEGUN.
In regard 70 the peculiarIties OF our transit In
strument ought 10 write you now. Upon re-
ducing my first observations | found great dis
crepancies in the value OF the colmation
found from reversal upon different stars, and
was Immediately convinced that the prism must
be loose IN Its cell. Professor Young suggested
also that there might be some 1exure OF the axis.
In order to test the instruments l measured the
coldmation carefully and repeatedly and also the
inequality OF the pivots. Then / reversed the
SO as to avoid the effect OF all
muth errors. and found that what I
suspected did actually exist. But since the error
OF the prism might act In two ways-viz., floose
in It's cell would simply change the position Of its
face so as to introduce an error, precisely the
same as that OF an inequality or the pivos. CORE
spending in amount; or If held tighter at one
corner, 1t would By its weight change the place OF
It's face in different positions OF the instrument,
introducing term depending upon the square OF
the cosne OF the zenith distance. reversed also
upon stars at different zenith distances The form
OF the bar which carries the counterposes Is such
that It's rightly is variable, and this will intro
duce, for the effect OF the 1exure OF the axis In
addition 70 the term depending on the coslne Of
the zenith distance-one depending on the square
OF this cosne. The amount OF the error first found
show ed that the prism must be loose, and accord
lngly we took 1t out, and found the transporta
ton had loosened the screws 1 therefore tight.
sLed the screws, and, upon repeating the
observations upon stars N the manner described.
the error was found 20 be reduced ABOUT one hail.
To test the iexure OF the axis we arranged the
striding spirit level so as to measure It quite APP
proximately, and 1t was found to be OF a magni.
Eude quite in accordance with the indications OF
she observations.
COMPLICATION OF INSTRUMENTAL ERRORS
Further observations by reversal upon stars at
various attitudes, colImation and level being &C.
cnrately measured directly, showed me that the
terms depending upon tie square OF the cosine
OF the zenith distances, due 70 the 1exure OF the
prism Ia its cell and the want CT rigidity In the
arm which carried the counterpolses, is by far the
most considerable term. and In order TO provide
well for the determination Of this term have
measured the coilimation carefully each night and
reversed the instrument upon stars OF various atl
tudes The means are thus provided In
me nnal discussion OF the observations
10 eliminate the enect Of all errors
peculiar 10 the instrument. These errors
viii explain TO you why decided to observe
more transiu OF stars than would otherwise have
seon necessary. need only add here that upon
sHSIeng ~ sssssshaas aus - those errors TIE