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

PRIMARY AN)) SECOND)ARY PLANrESC. 175
that time till 8415, Ilnone lere added; but since 1845, scarce fa
year lhas 1)assed ill which one or mort have not been discoverled(; al(1 soetclimes ive i1o six have cieen found ill a singltc
year. Ti'lotugh naellcs have generally b)een givell then, telly
(lare mtoirle co0mll101l1y dlesignlated by' a iib',, il the order of
tlheii (liscovery, thle tllnlt)er being inclosed inl a circle, whicl
is intendedl to represenit the tlanetary dlisk.'lle fore')inl,,p' are called wunar?/ i' lanlts. SCveral of thellse
have one oi mor3 attendants, 1or satellites, whlichl revolve iround.thitem as thlcy revolve around tlhe sun. l'|le ClEartlt las one satcllite, namely, tle lmoonl; JTipiter llas fotbur; Siaturln, eightl;
U'iranus, six;:' andI Nep)tuie, one.'I'lcse b)odics, also, are
ptalnets, but in distinction from the others, thley are called
sec(ioldatr planets. (lroupl)ilng thIe lplanetoidds; togetlher, and
g<i-ving tlhem the ralnk of one plrilary lanlet (thlourgl all unlited
wrould maltoe bilt a small one), there are Di'ne primaries and
atwenty secondaries.
29)7. 11The primary plalnets all (with the excepltion of tleo
asteroitds) have tleif' orbits nearly ill tlhe siname pl)ltac, atlrd are
never seel f1ar friolnl tile ecliptic. Melrcury, whose otrbit. is most
inclined of all, never leparts furthler front the celiptic tlar.
about; 7, while mtost of the otlher pIlants pursue very n]early
the satC p)atll with t lic eartlh, ill their annual revolutiotl
around t(he sun. Tlei asteroids(, howevler, make wider excunrsionlS fi'o)l tllc ptlane of tIle ccliptic, amounltinlg, in the catse of
P]allas, to 3-t —
298. IAlrcurt y and Velnus are (called i/r'or p)lanets, becaus-e tleir orbits' are iearer to the sni than thluat of tile cartlh;
while all til others bcing, more (distant from tIt slunl ttanl tile
earlth, are called s1Tp'iOP planets.'Theli pilanets presenati great
diversi tics alllnon) tlhecscelves iil respect, to distance ftrom tile
sun1, nlagnitude, tinme of revolution, antd desit,y. T y dife'
also ill'regard to satellites, of whlich, as we hIave seCe, tlle
Earth and N c3pt unIe have chact olc, J upiter has four, Saturn
eighllt, and Urlanus six; hrllib Ale\rcury, Vels, aii(l Malas, hlave
x Tl.'srctigt the imnbIcr of Fsattellit.es leltngjiltr to tU'Iltus, tll le is some doubt,
which will.be consideted ldulllt theu history of thalt phtlct.