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

,UNA: t IRtE:OULARIIES. 1 27
to oscillate on l her own patht as already sltown.'\hen thoe
Imoolt is ill conjuntctionl, the attraction of thle eartll dilintiishles
ils tcli(tIlcly to ttle situ, and tlh crefore its distanlce inlcreascs, till
it com-tes to the oppositionl; aildl whtilc thlls tceu)din.yg, b),eing
ill thle reart of thlse arth, it is accelerated bt y t1 anid l' ocs pa1st it
at t}he mnoment of opplositioit. lin3t now the attraection of thle
tartt (col.p>i'cs p \ith that of tile sint, s5o thltat the t.loo)t (c'.anl not
Jkeel) in a ciirc.ular orbit at lit tat distance., an(lld tletreftl're d/t.s>s'c'ends
again toward the conjunction. While descendin,, beini ) 1cw
firall towar t Qj llt e: lile ttsoCItltt: l lcr tioo
in advance of the earth, it is retarded by it, and loses' so imuchl)
of its velocity, that onl reatl'ing the Corljunctions, thle earth
p3asses it again cas before. Th ls tle moon, by thle earth's
inflluen(e, alcproa:chits th]e sun, alil t(len recedes fri'ml it, and
also tains velocity, atd ttlie loses it, istlclrinllg tlhesC ehalllle4S
as sligtlht disturbances ill its great annual revolution about tile
Still.
T.'lie eartht is also affected in preccisely te same malelr,
thlougrlt ill a far less dcg'rccS by tltC moonl; it is thle center of
gravit>y of thit two, whlichl deseribes the antlmal elliptietdl orbit.
223s*. If a chord be supposed drawn in the earttl's orbit
(I IFigt. It), hiteteein sulccessiv.e points of quadrature, it is tfoundl
tlhtat, tlis chotlrd, at its middlet poiiit, fatlls al)out 600,)0 niilc;
witltin tlhe orbit), while the nloon is only.) 238,00.0 milets withlin
it at tie ojtllunction. -lc'r pathl is, tlherefilore, so near thtat of
the cart tas to be always concave toward tle sulln.
I... v.. %<.+ tg~~.......... + 10 - ~:::. -
C I1A TI? I'T f: V [.
L'UNZAR itEOUL< itlltS.
224. CoNs'Im:mlo 0t1c thooon's motion simplly int its relationl
to the earthl, we hlave thltus fa-r spoken of its J)ath as an ellipse,
withl the earth1 ill oIne focus. Bult tcarlefl obscervationsls haxve
t)roved tlit this elliptical reNvolution is sulbject to nllmncrous
irrgularttities. T'lle law of utlivtrsal gravittion has been applied with wonderfiul success to tlheir investiga"titon, and its