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

,tLUNAR Ili l:GULAEAlifT I1S. 1'29
the secondt constitutes a disturbing force; to which lt e l ay
add anotllctre, nltamelly, tthat arising fi'om thle obliq.ue a ct'ionL of'
the solar orlce, Since this actioin is not directed in parallel
l itcs, but ill lies tflhat meett ill thte centtel of thle stll; and oHeO
parte of this oblique action is tnm2 thlte orbit of tile moonl, beilg'
nIow cast of thie earth, atind tlien west of it; and the otlher part
is fr'.wn tle orbit towtard thle platle of the ecliptic.
226. T'o s3ee the ctflects of this process, lot Ius suppose tlhat
the projectile motions of tlie earth atil moon were destroyed,
1alnd that they lwere allowed to fall freely towsvard the sun. If
the 10l1oo \\fwas ill coljluncltion -with the sun, or in tlhat.part of
hle orbit w\ichl is niearest to him, the mioon would ble moro
attracted than the earth, antd tall wit.h greater velocity toward
ttie suin; so t}lat tfhe distance of the moon fiomin the earth Nould
be incrctieased inl the ftidl. If thle mloon \twas ill oppositionl, or ill
the part of her orlbit whicht is fir1tlhest; from the slun site would
be3 less, attracted than tle ear'th by the sunt, and would faill
witt a less velocitt toward t:e Slll, and would J)e left behindll;o tlat the distance of tle moon from the earthl would be incrteltsed in this case a1so. If the mttoolt was ill oie, of tlie qutarters, thlen the earth and moon l being bothl attracted towtard thle
teiter of tlle sun, thltcy ould both tdesctenl directly toward
that centert, and by apptl>i' ltihing it, thtey \voulld necessar ily', at;
the same time, al)proach eachl other, tand ill this case thleit
dlisttulce fr'ont eacl other wO oul d bt e dimiiiished. IN'ow whtelnever tite action of telle suitl would increase teir distanclle, if
tlthey were 1a.llowed to fill toward the sun, then thre suil's ac'tion,
iby endeavoring to sepa'ate t.hem, dimitnisltes thlit grlavity, to
eacht othter; wthenever tllhe st-un's actilon wouldtt limliiish the
distance, t[ien it; increases thleir mutual gravitatiolln. tlcc,
in t[lie conj untction and o)lposition, t[hat is, in l s'/t //es,
their gravity toward ea:cht other is dimiiltshetd by thle action of
tlte stuni, while in thle quadrlatulres it is increased.,lut it must
l:e relnen}ll.erled t}tltt it is not tile total actiolt of tleO sun ll On
ttchi that disturbs [their motiotns, but only that pi1art ot it
}vticlt tends at onie time to separate teimni, and at anotheltr time
to thirlng thellcl tearer trogethler. lThe otlher and fitr greater p)art,
}Its nto other efft'ect than to rltain ttli ill theil' annual course
ttr-outtl0 d t[ie suit.
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