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

C,USTE3,RS AND Ni.EBUll,A,'. 295
sitns of otrder olr s8ymmetry; but when viewc.d with tile (oreat
-eflelctor,'it develops thele wolnderful structure of a pecrfect
spiral.
4:2:6. Noe)ulrt were formerly dividled into two classes,.' c.o babdc anlltl'i resolv.bletic, tlhe folrtmr term impllyingl that thle
sbody wavas shown by thle t tolescoe to colnssist of stars, atd the
latter implying that t.ie body is not composed of' stars, but of a
sluillnlg,e cloudly Mkilnd of lattc' diffulled t.flrou) llout the lmass.
Astronomers, at presenlt, includee all resolvable netlbult under
the chead of cwte.slts, aplrolulriating tie term nlcb-tl' excllusi vel)y
tio suell of these bodies a s ashav e ncvcer been resolved(. Th.ec
question whvlether this clistinction is not merely relative to t]he
)powe\ s of tlhe tolesco)pe, alld we\thcer, oni tlhe increase of tlleso
p1(ves, thlis class of b odies would not all l)e resolved into stars,
is not easily determined, since the same increase of telescopic
power whtich covcerts existing' nebulnh iJnto clusters, b)ritngs to
liglht a g'reater nulnl)er of those whliclt are, irresolvable.
1These remlote ol)jeets of tthe universe occasionally exhibit
trace-s of' thlat regard to leauty whicll eve rywhere, in tlhese
nether worlds, caracterizes tile \worksl of thle (Creator. Itl tlhe
C~lt'ss, a brilliant constellation of tlhe southtern helisplhere, )1br
example, is a cluster surrounldling thle star Ktpp< C(ritcis8, whlichl
cons;ists of about I -O star s froml the seventlt mttagnitttde dolwtward, eighlt of tle more conspicuous of whlichl are colored vw. thl
vlarious shades of red), green, andl blue, so as to give to ti e
whole the appearancel of a rich piece of jewvelry.
427. iNebu7 oust. stars arc such as exhibit a sharp and bril-.
lialnt star, surrounded b)y a disk or atmosphere of neb)ulous
matter. TI'.lese attiosp]lcres inll some cases, present a cirtcular,
in otlhers an oval figure; and in certain instances, tleC nebula
consists of a. long, narrow, spilndle-shal)ed raiy, tapcring taway
at both ends to points. An-n.ulnzar Ai:Wbu.ido (lillng-shapled) are
among tlle rarest objects in tihe heavens. Thlle Jtmost cospl1)ictous of this class is in the.conlstellation,lyra, betweenl tlhe starls:Beta atd (ammna, about 6~ S.:E. of Alphla:Lyrta. This remarktable object is believed to be in fatct a resolva)le netbula
or cluster, and yet the greatost powe'rs of the telescope hlitherto
applied hIave oly effected such chlatngest as aire regarded as