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

tlte mloon's motion will 1)egin to be retarded, and tIlus ler
ricanl motions will oscillate forevcr about a mean value.
244. T.lic lunar' inlqualities \whichl have been considered
are suchl only as affect the 00oon's longitude; but t~he sutn's
disturbiwng force also caluses inequalities in thle rmoon's latittude
anld,para dll(-t.''Tlhose of latitude alone, reqluire no less tlan
twelve equations. Since the moon revolves in anl orlbit inCliied- to the ccli)tic, it is easy) to sec thlat the oblique action
of tile sun must admit; of a resolution into two forces, onle of
which beillg )elrpenldiculair to the mooeno's orbit, must cffect
changes in llher latitude. Silnce, also, several of the inequalities
alradly noticed, involve chalgres in thle lengthl of thle radius
vectorl it is obviovus that the moonh's parallax mulllt 1)e subject
to corresponding perturbations.
EC] PSES.
245. An eclie 0 of hew mon, happens when thlle moon in its
revolution about the clarth, fallts into thle artlh's shadow. An
eclipse qf the sumn, tapp)Cens when tile moon, comint between
the earth and te sun), covers citlelr a part or the wh]ole of the
solar disk. An eclipse of the sutl canll occur only at the time
of conjunlctioQn, or nC\vew moon1; and an colipse of tlhe moon only
at the tinme of opposition, or fuill 3moo1n. WeVcre thle mnoo0n's
orbit in the same plane with thlat of thte eartll, or did it coil-.
cid(e with thlle ecliptic, then an eclipse of the suni would take
place at every conjunction, and anl eclipse of the nioon at every
oppositionl; for as the sunil and earthl botlh lie in the eclliptic,
tlte shaldow of the cartht must also extend inll the same l)lale,
beilng, of course, always directly ol)posite to the sun tl; and sine,
as w\c slall soonT se, lthe length of thlis stadow is mulcl greater
than tie (tistance of the moon fiom tlc cartlh, the m0nooll, if it
revolved in thme plane of the celiptic, must pass throulghl tillh