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

2:40'T'1M PL,AN T,'.B,
hlave confirmed them, except in cases where the force was too
mlinute to be, reached by tlhe most refined obser-vation. Periodical p1erltlbations amiong the bodies of the solar system
may be compared to the regular flux and reflux of the tildes,
by whlichl the ocean daily oscillates about its rmeani level,
withlout anlly permanent change of level; Nwhile secular peirturbationls would resemble anly slow clhanges of level, whiicl, accuntmllalting from time to tiltm, imight filnally become obvious
to measures of the deptlhs of thlt oceant as recorded froml agem
to age. As ant example of the extreme minutenless of some of
these secular perturbati ons, we ma)y instlance the chlanges ill
the eccentrtlicity of the earth's orbit. The entiro eccentricity is
so Sllsall that the figure, wheln drawn onl )ape' iln just prop)ortions, can scarcely be distinguished from a circle, thle fiell of
the ellipse being distant from the center only about -o- part of
the semi-major a.xis. But the ci/agye of eccentricity ill a
certiury is only tile twenty-five tlollusa nd tll par11t of thle whNole,
or the fifteen hundred tlhousandth part of the semi-mllajor axis.
384. But, although the secular inequalities of the planetary
motionls are exceedingly slow, yet may thley not, in time, accumulate so as to derangel the whiole,system; and (ldo thet not,
at least, indicate that the system carties withlin it thle seeds of
its own dissolution? So far is this fiom beingl the caset ltat
the dltabiity (ft t/e s0ol/ar sylstcm is a tact establish(l onl the
most satisfactory evidence, and its (lemonstnration is among) tihe
finest triumphs of plhysical astlronomy. IEvct a sll)erlieial[
view of the system will convince us t.ltat care lhas been bestowed oin thlis point by seve'ral ol)bviols farrallllCments. Oe10
is, thlat the planlets have, severally, so sinall mnasses, colllarted
with the slun, as to intertore but little, at most, w\\ith tle
supremacy of hiis control over thle pllaicetaIry llmotionis. A inothler is, tlhat thle planets are placcdl at such glncat dlistances
firolm cach otheri. —a distance whlichl is grreater amnong tlehlargests b)odies, as Jupiter all Satumn, tltatll amlongt tle staller',
as tle 1arthl and -Venus; aii(l anlotler still, thlat tihe orbits are
less ccccntriAic whilc tile lmasses of tile bodies are gr'tertl' by
wh]iclh pro\vision they are always maintainedl at a renIote dlistance firom the sunii. Were tthe orbit of JuP)iter as ecent( ric as
that of A:tars, Ile would appiroach so near the eartll at lhis pcri