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

JLUNARl I1I001eO ULARITI lES. 1411
has a greater effect in pr'oportion as the sunll is neare1r,l' consequently all thle inequalities depending onl this influence must
varyf at dlifferent seasons of thle year. J-lence, the amount of
this effct; due to any particular tinle of the ]year is called the
Annual iquation.
242. I'The foregoing E athe tlargest of the inequalities of the
o1100eon's motions, anld may serve ats specirns of thie corrections
that are to 1e appllied to the Imean place of tle moon in order
to find her true place. lThese were first discovered by actual
observationl; but a far greater numbelr, though most of thelm
are exceedingly minute, have bccn tmade known by tlhe ilnvestigatiolns of P].hysical Astronomy, in followinm g out all the consequences of universal gravitation. In the best tables, albout
30 equations are applied to the mean motions of the moon.
Tlhlat is, we first compute the place of thie moon on the supposition thlat she moves uniformly il a circle,. Thlis givets us her
1meanr placce. We tllen proceed, by thle aid of thle Iunar'lables, to apply the different corrections, such Cas tihe equation of
the center, cvcetion, variation, the annual equation, and so o1n,
to tile number of 28. ]Numcrous, as these corrections ap)petar,
yet L,a Place inflrms us, tthat the whole number bclongilng to
the moon's longitude is no less than 60; and that to give t}he
tables all the requisite decree of precis.ion, additiontal investigations will be necessary, as extensive at least as those already
madei.t' Thle best tables illn use in the time of Tyhelo:Brahle,
gave the moon'Q s place olly by a distant approximation. The
tables iln use in tlhe time of Neowton (IValloy's tables), apl)proximated within'7 minutes. Tlables at preItsent in uIse give the
lool0's p)lace to 5 seconds. These additional dcgrees of accuracy have been attained only by immellilnse labor, and b1y the
llited offorts of Pfhysical Astronomy an1d the most refincd obsiervatiOls.
243. The inequalities of the moon's motions are divided
into periodical Siand secular..P:eriodiealC inequalities are tlhose
whicht are completd i n comparatively short p1eriod(s, like cvceo Varyin reciprocally as the cube of tihe sull's distance from the earth.
Syst. tdu Monde., 1, iv., c. 5.