An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

MOTIONS OF TIEli FIXEID) lTARS. 299
Tlh1eo a.9irt0rent change of place in thle stars arbisilsn from tilo
precession of the equinloxecs tle nutation of the earth's axis, tile
diminution of,tlle obliquity of thle ecliptic, and tlhe aberration
of litlt,. lhave b)een already mentioned; )but after all these correcctions are made, changes of llace still occur, whlich cannot
result fi'rom any changes in the earth), lut must arise fi'omtl
lanles inl the stars tihemslves. Such motions are calledl tlhe.pirtfer motirns of the stars. Ncarly 2000 years ago, Ililpparl
clttus anld Ptolemy made tile most accourate (1 determinttions in
their powertl of tile relative situationls of tihe starMs, and their observations have bccn transmittedl to us illn ltolemy's Almageost;
froml w\ich it ap)pears that the stars retain at least very lear(ly
thell same places now as thely did at that period. Still, tlle
morle accurate metlhods of modern astronomers, lave biro(iught
to lightt millite cllaingcs ill thle places of certain stars wAlich
force upon tus tlhe conclusion, eith/cr that oare solar systerm catuses
fRt c(lt//iPrCt yiaioslacemelt qi eerafaia. sits'ys, a ftloion of its
ofwn w l.)p(ace), or /thgl tiey have tfiemselves a prq)er' oi0t0on.
Possibly, indeccd, Ioth these causes may operate.
432'.'f the stu, and of course the eartlh which accompanies
h]ilm is actially ill motion the fact may become manifiest firom
tlthe apparent?approach of the star's in thle recgiolln which ll e is
leaving, andi tle recession of those which lie in tlle )part of the
hIeavents toward which hle is traveling. Were twro groves of
trees situated o0l a plain at somei distance apart, and we should
go ftiom on to the on ter, the t t, t rees betore us would gradually
appear further and further asunder, while those we left bellind
would ap)earl to laplproah each other. Some years since, Sir
William I1c8rsehcl supposed he had detected changues, of this
idud alnong two sets of stars in op)ositC points of the heavels,
and announced that the solar system was ill motion toward a,
loint ill the constellation Iecrc-tlces.' As, for many years after
this alnnouncc ment, other astronomers failed to filld evidence
of suchl a motion of tie solar system, the doctrine was., genterally
liscredited, until, within'a few years, new\ and very refined
rasearches have Ibeen instituted b)y several of tile imost eminent
isti'oilonoers, whicht have filly confirmed the observations oi
* Phil. T'ras., 17'83, 1805, and 1800.