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

miglht apprelctnd tlt at: Ibl slccessive, apl))'oaclles to each ot]tter
thle equltor 5and ecliptic would fintally, coincide; inbut astrono-.
tlers have atscerttined by, anl investigatiml, founded on tlhe
p)riniplel s of universal "gravitationl thlat this variation is confined withinl certain narr 1 ow limit's, and thatt the obl)iqnity,
after dilminishing for some10 tlonstands of years, will thelCt ilcrease for a similar plelriod(, andv will thus vibrate forever about
a meanll valle.
with its own?aqnit.tde atre imme se.
Since the distance of the earth from thie sunr is 95,000,000):iles, land the length of the entire orbit nearly 600000,000()
mles, it will btle fotud, ot calculation, that the etrth noves
I,06t:0,00(0 miles per day, 68,000 miles per hour, 11.t 00 miles he)r
milte, and nearly 19 mniles every second, ( a velocity nearly
fifty tillmes as gre-at as tle maximunl ve(locity of aI eantnon-h)all.
A. place onl the earth's equalitor ttllris, in tihe diurnal revolut.iOl,
at; tlle r1ate of abolut 1,000 miles -llan hour, and f of a. mile p)er
second. The lmotioln around tile sun, t1hereftore is nearly i70
times as swift as thle fg)reatest motioion around the axis.
TUEt}S SEvA.SONYS.t 59.. /Iet citangze qi seasos' (hye(tfs o01 two causes, (1) 1ew
obl't/i!t y/ )qf ttI ecl/ili;c, and (2) t/ie ear/lt',/ aet-is alwhaysf rema.'tnitin(p7lalf'!/t to'it sefY. I'tad thte tearth's axis >been perpendicular
to the planell of its orblit, the equator wouild have coincidled
wvith the. ecliptic, anld tle sun wAiould have conlstantly aplm)eared
ill the equator. T'1'o the inhablitants of thle equatorial regions,
th}e sutn w\ould alwayss }hlave aplpeared to move in thle princ
vertical; and to the inhallbitants of eitlher pole, tie would avlways
have been in the Ihorizonl. lit thle axis being tlurnedfl out of a.
perplendicular direction 283 28', thle equator is turned the salnot
distance out of the ecliptic; and( since thlte equator and eeliptic(
are two great circles whXich< cut each ot.etr in two opposite
pIoints, thoe sunl, whlfile perfotrming his circuit in the ecliptic,
mulst, evidently, )be once a year inl each of those points, andl
Imust d(ellart fromt the equator of the heavens to a d(istane onl
eithter side equal to the inclination of the two circles thatt is,
2'238'. (Art. 22.)