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

198 I'1 K PL AN WVs.
plhere, wvIicllh occasionally render its dark body visible; atnd,
as the belts are found to traverse the disk il lines uniformtly
parallel to Jupiter's cquator:, t.hey ar e inferred to be conneltcfd
with the rotation of the planet up)on its axis, the great lrapidlity
of which -would naturally produce peculiarities in its:atmnosp)hIC'ic phelnomena.l
331 T1 he S~Satelites of Jupiter may b)e secn with a telescope
of -very mloderate pow eOrs. Evenlt a cot0lmmon spy-glass -will
enable us to discern them. t Indeed, beingi narly equal il l)brilliallcy to the smallest' stars visible to the nlhaked eye, a slight
increase of optical power brings them into view;t and somll ftw
persons, endowed withll xtraordinary pow\rs of vision, lhave
supl))osed that tlhey saw one of these little bodies withlout thec
aid of instl ruments; but on applying the telescope it lhas bclee
found that tlhree of the satellites lave approacl' llC so near together- as to app:ear like one.' n111 t]he largest telescopes, thley
severally appear as bright:as Sirius does to thle naked cce.'With such an instri enllt, the view of Jupiter Witlh his moonls
and belts is trul' a mragnificent, spectacle --— a world w withlin itself. As the orbits of the satellites (lo not deviate fiar friol the
plane of the ecliptic, and'but little froml tlhe equator of;the
planelt (whlich nearly coincides with the cclil)tic), they are
usuallyl seon almnost in a straight line extending across thle contral: part of the disk. (See -1Frontispiece.)
33o2. Jupiter's satellites are distingulished from one another
by tlle denolllilationlls of jrst, seco dl, th/irld, and fotrh, according to their relative distances firoml the primary, the first being
that whicll is nearest to him.t Th'llcir apparent motion is oscillatory, like thlat of a penhdulum, going alternately from their
greatest elonlgation oil oXne side to their greatest elongation on
the otlher, sometimes in a straight line, and sometinmes in an
elliptical curve, according to the different points of view in
0 Inlinl. Rev.. Mr. Sto-dalrd, a grfaduate of Yale College, missionary to the
Nestotianst, has repeatedly seen one of these.bodies with the nakedt eve, froml
Mount Suir, tneat Oroomiatl. 5Mr, Sto)dard is kitown\ to the author as an excellent observer, t antl his tes timonly oni this point maly be futlly relied oln.
-- Mythological namlines wNere longt sinco proposed for the satellites of Jupiter,
viz., to, Europa, Ganuymede, Calisto; biut the mode of designating them by nuimbers generally prevails.