DECLINATION. 
motion in = whole folar fy = directed to a particular-point 
in the i € proper motion of each far in declina- 
mparing (ae refent piace a that de- 
feveral nes fince : if its change in declination is 
ip equal a fe which fhould take place from the ca pei 
— aera we prefume the ftar to have no proper 
; but if any difference fhould be found between its pan 
eile and aki declination, and particularly if exceed 
the probable errors of obfervation, then we radaae that dif- 
ference to arife from the proper motion of ‘the flar. 
have annexed Dr. Bradley’s catalogue of fais obferved 
about the year 1756, as they se the molt exact term of 
i eta for modern obfervation 
e moft ancient method of serquaie the declination 
of che fun or moon, -was by means.of a gnomon or fhadow 5 
and till algae were applied to aftronomical iftruments, 
a more exaét method could not eafily have been devifed 
Triangular or  parallaGtic rules were ufed by Ptolemy, 
and = A\rabian attronomers. 
ral quadrants have been employed in the moft cele- 
brated obfervatories of Europe for this purpofe, till the late 
t n of aftronomical circles 
uad- 
a) 
thing h ch relate ice of fin the 
le of celeftial bodies, is intended only | 
nomical circles e ris réferred to the article 
pone for {uch sorfeOiaus as-are peculiar.to that .inftru- 
men 
Avmillary fpheres-were ufed by the ancients, and equa- 
torial i ae which bear fome refemblance to them, 
by the moderns, to obferve the declinations of heavenly 
bodies, peer the - meridian ; ch obfervations are only 
fuited to wend mal cafes, faeh as ie comets or planets when 
they cannot be feen oh the meridian. All obfervations in- 
tended to ferve as a foundation for aftronomy fhould be 
made when the objeét is on the meridian. 
Method of obferving Declinations with the aftronomical Circle. 
Tf she inftrument is conftru@ed with an azimuth circle, this 
d in-a horizontal pofition ; this verifica- 
next t m 
and if the level hes changed its pofition, half the deviation is 
to be corrected ‘by: 1 ither of the feet {crews that are parallel 
to it, and oe other half by any fcrew that moft conveniently 
acts on the level. The level muft next be brought perpen- 
dicular to its ied pofition, and the whole of its deviation cor- 
rected by the other foot-ferew. 
The axis of the circle fhould next be made horizontal. 
This is known to be accomplifhed, when the hanging level 
remains fationary during a whole revolution of the circle 
round its horizontal axis. Sometimes the level is not fixed 
to the axis, but only intended to be oceafionally applied to 
the pivots ; in this cafe it muft be reverfed end for end, and 
if the bulb of the level refts at the fame point in each pofition, 
the axis is horizontal. 
The pofition of the micrometer wire fhould now be ex- 
amined, a diftin€& obje& fhould be eae ag the whole 
tangent-ferew 
rometer ™m in 
‘flrument, that it js not much to 
in azimuth, - this \ slagen may be per Feed by the ver- 
tical wire, taking for g¢ = that the horizontal wire is at 
fa ge to it, or ios e examined, by .obferving if .a 
he equator rae bifected curing its paflage 
through the field of the telefcope 
The line of collimation fhould next be ah to defcribe a 
great circle of the fphere. This is done when the inftru- 
ment admits of it by reverfing the circle ie Y’s, and.ob- 
ferving if the fame objeé is bifected in each pofition when 
this cannot be done, the inflrument mu ned half 
round in azimuth 5 by this means the line of ioilaston is 
rendered Se eeiate to horizontal axis. 
e will now fuppofe that the mechanical adjuftments 
have been accurately aes od, and the inftrument placed in 
the apes and. that the objet of the obferver is to under- 
take a eerie aa the purpofe of. determining 
the declinations of the fi syand other celeftial objeéts. 
So é G&ed on the meridian, 
t minutes. 
curately bif 
from the fun, and from eee currents of air. Solar ob- 
fervations dhould always be omitted, where they do not form 
an effential part of the obje& of invettigation, as they have a 
great. tendency” i derange fome of the nicer adjuflments of 
thefe inftrumen 
As foon as ve ftar appears in the telefcope, it fhould be 
brou ht to the.middle wire b e micrometer {crew, 
eh it is effential: to accomplifh the bifection near 
middle wire. The obfervation fhould be immediately 
read off at each microfcope, and the fame precaution fhould 
be obferved in the.management of their fcrews, as was recom- 
mended above in the ufe of the micrometer-{crew. 
With tranfit circles, not fixed on.fone-piers but on frame 
work, fuch as defcribed-by Mr. Wollafton, vide Circe, and 
Ph. Tranf.; this method of bifeGting the plumb-line point, 
and the ftar, at the fame inftant, cannot be adopted ; and fo 
ak mutt depend on the ftability - every part of the. in- 
vie at Aes thefe 
inftruments have not been very facet 
e ftate of t arometer an mometer (the lat- 
ic the tube of the tele{cope,if Fpoflible fhould be noted 
Te is eafy to fee that by this obfervation alone, the ob- 
erver can derive no infor 
t rovide 
known near enoues for the pie a calculating pe pid 
ODS. 
