rd 
.the time of obfer 
of ea 
DECLINATION. 
index error being thus found, may be teats to 
any i or planet that has keen obfe med th e pofi- 
tion of the inflrument, We jn cir a Ae wo feet 
diameter will, in the hands of a careful ieee always m 
give camara true to 2” ; 
nith diftances being brought up to the beginning 
of the an fhould be eel inatable. The polar dif- 
tance is obtained by applying the co.-lat. of the place of 
obfervation ; but this fhould be confidered as an equation 
known at fir only as an cd sive vos to the trut ae an 
months fore an obfer o is anxious to 
attain eee on, will be fatisfied-with ihe wae of this 
effential element in his calculations. In ufing large inftru- 
ments on ftone piers, which cannot be sen eg without great 
is preferable oe 
obferver muft bea as fcrupulous in his attentiomto afcertain 
‘this point accurately, as to find the latitude in the ufual 
-method. 
-Obfervations of circum-polar ftars are in each 
cafe to be {elected for the purpofe. 
Of the Corredtions to be applied to the Obfervations. 
Thefe are of two kinds, one depending on the mechanical 
eee €tion of the infroments, the other entirely aftrono 
mica], and intended to reduce the apparent altitude-as feen 
at the place of the ay pa to that which d have been 
obferved from fome other fituation, as the centre of the 
= or even at fome other period, as the beginning of the 
“The corretions arifing from the conftrudtion of aftrono- 
mical circles are very few, as thefe inftruments have the 
means of avoiding moft of the — that Valarie 
are fubjedt to. e index error, as above defcribed, is the 
principal correétien in page haa oe and ha if the 
thicknefs of the wire of the ometer fhould be taken 
into the calculation, where one of i its edges has béen made 
a tangent to the upper or lower limb of the fun, moon, or 
web, this a need not be a 
i Spade > reducing the apparent zen. difte a 
the centre 
from refraction, Alia aberration, nutation, preceffio OD, 
and femi-annual folar-equation. For an explanation of 
thefe agra ‘a the refpedtive articles ABERRATION, 
NUTATION, 
Among the rs “fubjoined will -be found thofe of the 
ev. oll which are much the convenient 
ef any that have yet been publifhed for reducing obferva- 
tions of this kind. By means of thefe tables the obferver will 
be enabled, with the greateft eafe, to regifter is obferva 
tions, with their leche « corrections, in one column, 
e e 
her correction is required t than. for 
the change of altitude in the flar, for the given interval, 
which will be found in the tables for the -ufe of the French 
repeating circle. 
a may be when the ftar has-confidere 
ab] eng a ape of the field, in this cafe a doubl 
correction plied. to reduce the ob- . 
The 
ferved altitude, € that which sould have been given by 
But when the aes el is formed by fine cob- © 
the inftrument, if the ftar had been obferved on the veitie 
cal wire; the fecond is the fame as above mentioned, namely, 
to allow for the change of altitude in the flar fine ™mo- 
ent of its tranfit over the meridian. The rre 
tion is given in e argument on the left: hand 
column is = altitude, and on the top the dift. from the 
vertical w 
Ts obferve the Declination of the Sun. 
. This obfervation oe the following corre€tions: error 
of collimation, refra » parallax, femidiameter of the fun, 
and for half the thicknefs of the mmicranactes wire, when it !s 
efe quantities are 
s the uppe 
If the circle is of {mall pe 
ions, a turns TT In azimuth, two or more obfervations 
sath be obtained in ay, an allowance being made for 
he fun’s ete in ae hoabiae to fuc 
be given wken we come to more particularly of the 
French repeating circle. To “obfer ving the fun, the inftru 
ment wee = carefully protected from its rays till the moa- 
ment of obfervation 
Example ra an weicatn of the Sun, made at Weftbury in So+ 
Fi ilies ith a circular Inftrument conftruGed by Mr. 
Tre 
vSor. 21 June. 
© U.L. - - 62° 30’ 30%5 
Error of coll, -. - 0 0 34.5 
62 29 56 
3 aol Zen. a “ 27 32 4 
Retr: = Oo oO 29 
27 30 33 
Parallax = 8 ) a 8 
27 39 29 
Semidiameter © = « Oo 15 47 
i 27 46 16 
Lat. of the place of obfervation 51 14 47 
Declination of the © - 23 «28 a 
; Lactaremeeiereanetnineares. ag 
1801. 22 June. 
Zen. dit. © LL. - 28 2 7.5 
° O 345 
Error of Coll, =e - 28 ££ 33 
Refration - - - Q@ O 30.1 
28 2 38 
Parallax - . oo 4 
28 1 59 
Semidiameter © - - 0 If 47 
‘ 27 46 12 
Latitude . - Si 14 17 
; : 23 28 5 
The mean of thefe two obfervations wil will give the declina- 
tion of the © at the intermediate midnight very accurately 
= 2 9° 
. The 
