,,extra-,,galactic ,,nebulae#a ,by ,,edw9 ,,hubble ,transcrib]'s ,note3 ,?is etext 0 produc$ f3 ,! ,a/rophysical ,j\rnal1 ,vol4 ,,lxiv1 pp4 #cba-cfi1 #aibf4 ,! pla9 text v]sion ( ?is ebook includes ma!matical =mulae 9 ,te,x notation4 ,^! =mulae are enclos$ betwe5 doll> signs4 ,! ,,html v]sion includes ! same =mulae r5d]$ 9 _! orig9al =m4 ,,ab/ract ,?is contribution gives ! results ( a /ati/ical inve/igation ( #djj extra-galactic nebulae = :i* ,holets*ek has det]m9$ total visual magnitudes4 ,! li/ is complete = ! bright] nebulae 9 ! nor!rn sky & is repres5tative to #ab4e mag4 or fa9t]4 ,! classification employ$ is bas$ on ! =ms ( ! photographic images4 ,ab\t #c p] c5t are irregul>1 b ! rema9+ nebulae fall into a sequ5ce ( type =ms *>act]iz$ by rotational symmetry ab\t dom9at+ nuclei4 ,! sequ5ce is compos$ ( two sections1 ! elliptical nebulae & ! spirals1 :i* m]ge into ea* o!r4 ,lum9osity relations4--,! di/ribution ( magnitudes appe>s to be uni=m ?r\gh\t ! sequ5ce4 ,= ea* type or /age 9 ! sequ5ce1 ! total magnitudes are relat$ to ! log>i?ms ( ! maximum diamet]s by ! =mula1 m,t ,c - #e log d1 :]e ,c v>ies progressively f type to type1 indicat+ a v>iation 9 diamet] = a giv5 magnitude or vice v]sa4 ,by apply+ corrections to ,c1 ! nebulae c be r$uc$ to a /&>d type & !n a s+le =mula expresses ! relation = all nebulae f ! ,magellanic ,cl\ds to ! fa9te/ t c be classifi$4 ,:5 ! m9or diamet] is us$1 ! value ( ,c is approximately con/ant ?r\gh\t ! entire sequ5ce4 ,! coeffici5t ( log d corresponds ) ! inv]se-squ>e law1 :i* sugge/s t ! nebulae are all ( ! same ord] ( absolute lum9osity & t app>5t magnitudes are measures ( di/ance4 ,?is hypo!sis is support$ by simil> results = ! nucle> magnitudes & ! magnitudes ( ! brighte/ />s involv$1 & by ! small range 9 lum9osities among nebulae ^: di/ances are already kn[n4 ,di/ances & absolute dim5sions4--,! mean absolute visual magnitude1 z d]iv$ f ! nebulae ^: di/ances are kn[n1 is -#ae4b4 ,! /ati/ical expression = ! di/ance 9 p>secs is !n log ,d #d4jd #j4b m,t1 :]e m,t is ! total app>5t magnitude4 ,?is leads to mean values = absolute dim5sions at v>i\s /ages 9 ! sequ5ce ( types4 ,masses appe> to be ( ! ord] ( #b4fajh 4 ,di/ribution & d5sity ( space4--,to app>5t magnitude ab\t #af4g1 correspond+ to an exposure ( "o h\r on fa/ plates ) ! #fj-;in* reflector1 ! numb]s ( nebulae to v>i\s limits ( total magnitude v>y directly ) ! volumes ( space repres5t$ by ! limits4 ,?is indicates an approximately uni=m d5sity ( space1 ( ! ord] ( "o nebula p] #ajag cubic p>secs or #a4eaj-ca 9 ,c4,g4,s4 units4 ,! correspond+ radius ( curvature ( ! f9ite univ]se ( g5]al relativity is ( ! ord] ( #b4gajaj p>secs1 or ab\t #fjj times ! di/ance at :i* normal nebulae c be detect$ ) ! #ajj-;in* reflector4 ,rec5t /udies h emphasiz$ ! fundam5tal nature ( ! division betwe5 galactic & extra-galactic nebulae4 ,! relation%ip is n g5]ic2 x is r t ( ! "p to ! :ole4 ,galactic nebulae are cl\ds ( du/ & gas m+l$ ) ! />s ( a p>ticul> /ell> sy/em2 extra-galactic nebulae1 at lea/ ! mo/ conspicu\s ( !m1 are n[ recogniz$ z sy/ems complete 9 !mselves1 & (t5 incorporate cl\ds ( galactic nebulosity z compon5t p>ts ( _! organization4 ,def9ite evid5ce z to di/ances & dim5sions is re/rict$ to six sy/ems1 includ+ ! ,magellanic ,cl\ds4 ,! simil> nature ( ! c\ntless fa9t] nebulae has be5 inf]r$ f ! g5]al pr9ciple ( ! uni=mity ( nature4 ,! extra-galactic nebulae =m a homog5e\s gr\p 9 :i* numb]s increase rapidly ) dim9i%+ app>5t size & lum9osity4 ,f\r are visible to ! nak$ eye2#b #da are f\nd on ! ,h>v>d 8,sky ,map02#c #gjj are on ! ,frankl9-,adams plates2#d #cjj1jjj are e/imat$ to be )9 ! limits ( an h\r's exposure ) ! #fj-;in* reflector4#e ,^! data indicate a wide range 9 di/ance or 9 absolute dim5sions4 ,! pres5t pap]1 to :i* is prefac$ a g5]al classification ( nebulae1 discusses su* obs]vational mat]ial z we n[ possess 9 an attempt to det]m9e ! relative importance ( ^! two factors1 di/ance & absolute dim5sions1 9 _! be>+ on ! appe>ance ( extra-galactic nebulae4 ,! classification ( ^! nebulae is bas$ on /ructure1 ! individual memb]s ( a class diff]+ only 9 app>5t size & lum9osity4 ,x is f\nd t = ! nebulae 9 ea* class ^! *>act]i/ics are relat$ 9 a mann] :i* closely approximates ! op]ation ( ! inv]se-squ>e law on comp>able objects4 ,! presumption is t disp]sion 9 absolute dim5sions is relatively unimportant1 & h5ce t 9 a /ati/ical s5se ! app>5t dim5sions repres5t relative di/ances4 ,! relative di/ances c be r$uc$ to absolute values ) ! aid ( ! nebulae ^: di/ances are already kn[n4 ,,"p ,i4 ,,classification ,,( ,,nebulae ,,g5]al ,,classification ,! classification us$ 9 ! pres5t inve/igation is ess5tially ! detail$ =mulation ( a prelim9>y classification publi%$ 9 a previ\s pap]4#f ,x 0 develop$ 9 #aibc1 f a /udy ( photographs ( sev]al ?\s& nebulae1 includ+ practically all ! bright] objects & a ?or\ghly repres5tative collection ( ! fa9t] ones4#g ,x is bas$ prim>ily on ! /ructural =ms ( photographic images1 al?\gh ! =ms divide !mselves naturally into two gr\ps3 ^? f\nd 9 or ne> ! ,milky ,way & ^? 9 mod]ate or high galactic latitudes4 ,9 s f> z possible1 ! sy/em is indep5d5t ( ! ori5tation ( ! objects 9 space4 ,) m9or *anges 9 ! orig9al notation1 ! complete classification is z foll[s1 al?\gh only ! extra-galactic division is "h discuss$ 9 detail3 ,,classification ,,( ,,nebulae ,i4 ,galactic nebulae3 ,symbol ,example ,a4 ,planet>ies ,p ,n4,g4,c4 #gffb ,b4 ,diffuse ,d #a4 ,pr$om9antly lum9\s ,,dl ,n4,g4,c4 #ffah #b4 ,pr$om9antly obscure ,,d ,b>n>d #ib #c4 ,conspicu\sly mix$ ,,dlo ,n4,g4,c4 #gjbc ,,ii4 ,extra-galactic nebulae3 ,a4 ,regul>3 _/ ,n4,g4,c4 #ccgi ,e#j #a4 ,elliptical ,en _/ #bba ,e#b 7n #a1 #b1 4441 #g indicates ! #dfba ,e#e ellipticity ( ! image #baag ,e#g )\t ! decimal po9t7 #b4 ,spirals3 a7 ,normal spirals ,s 7#a7 ,e>ly ,sa ,n4,g4,c4 #deid 7#b7 ,int]m$iate ,sb #bhda 7#c7 ,late ,sc #edeg b7 ,b>r$ spirals ,,sb 7#a7 ,e>ly ,s,ba ,n4,g4,c4 #bhei 7#b7 ,int]m$iate ,s,bb #ccea 7#c7 ,late ,s,bc #gdgi ,b4 ,irregul> ,irr ,n4,g4,c4 #dddi ,extra-galactic nebulae too fa9t to be classifi$ are designat$ by ! symbol 8,q40 ,,regul> ,,nebulae ,! *>act]i/ic feature ( extra-galactic nebulae is rotational symmetry ab\t dom9at+ non-/ell> nuclei4 ,ab\t #ig p] c5t ( ^! nebulae are regul> 9 ! s5se t !y %[ ?is feature conspicu\sly4 ,! regul> nebulae fall into a progressive sequ5ce rang+ f globul> masses ( unresolv$ nebulosity to widely op5 spirals ^: arms are sw>m+ ) />s4 ,! sequ5ce comprises two sections1 elliptical nebulae & spirals1 :i* m]ge into ea* o!r4 ,al?\gh delib]ate ef=t 0 made to f9d a descriptive classification :i* %\ld be entirely indep5d5t ( !oretical consid]ations1 ! results are almo/ id5tical ) ! pa? ( developm5t d]iv$ by ,jeans#h f purely !oretical inve/igations4 ,! agreem5t is v sugge/ive 9 view ( ! wide field cov]$ by ! data1 & ,jeans's !ory might h be5 us$ bo? to int]pret ! obs]vations & to guide rese>*4 ,x %\ld be borne 9 m9d1 h[ev]1 t ! basis ( ! classification is descriptive & entirely indep5d5t ( any !ory4 ,elliptical nebulae4--,^! give images rang+ f circul> ?r\gh flatt5+ ellipses to a limit+ l5ticul> figure 9 :i* ! ratio ( ! axes is ab\t #a to #c or #d4 ,!y %[ no evid5ce ( resolution1#i & ! only claim to /ructure is t ! lum9osity fades smoo?ly f bright nuclei to indef9ite edges4 ,diamet]s are functions ( ! nucle> brightness & ! exposure times4 ,illu/ration3 ,,plate ,,xii ,elliptical & ,irregul> ,nebulae ,e#j ,,ngc #ccgi1 ,e#b ,,ngc #bba 7,m #cb71 ,e#e ,,ngc #dfba 7,m #ei71 ,e#g ,,ngc #caae1 ,,ngc #cjcd 7,m #hb71 ,,ngc #dddi ,! only crit]ion available = fur!r classification appe>s to be ! degree ( elongation4 ,elliptical nebulae h accord+ly be5 designat$ by ! symbol 8,e10 foll[$ by a s+le figure1 num]ically equal to ! ellipticity 7a - b7_/a ) ! decimal po9t omitt$4 ,! complete s]ies is ,e#j1 ,e#a1 4441 ,e#g1 ! la/ repres5t+ a def9ite limit+ figure :i* m>ks ! junction ) ! spirals4 ,! frequ5cy di/ribution ( ellipticities %[s m r\nd or ne>ly r\nd images ?an c be acc\nt$ = by ! r&om ori5tation ( disk-%ap$ objects alone4 ,x is presum$1 !re=e1 t ! images repres5t nebulae rang+ f globul> to l5ticul>1 ori5t$ at r&om4 ,no simple me?od has yet be5 e/abli%$ = diff]5tiat+ ! actual f ! project$ figure ( an individual object1 al?\gh ref9$ inve/igation furni%es a crit]ion 9 ! relation betwe5 nucle> brightness & maximum diamet]s4 ,= ! pres5t1 h[ev]1 x mu/ be realiz$ t any li/ ( nebulae hav+ a giv5 app>5t ellipticity w include a numb] ( tilt$ objects hav+ great] actual ellipticities4 ,! /ati/ical av]age w be too l[1 except = ,e#g1 & ! error w increase ) decreas+ ellipticity4 ,normal spirals4--,all regul> nebulae ) ellipticities great] ?an ab\t ,e#g are spirals1 & no spirals are kn[n ) ellipticities less ?an ?is limit4 ,at ?is po9t 9 ! sequ5ce1 h[ev]1 ellipticity becomes ins5sitive z a crit]ion & is replac$ by conspicu\s /ructural features :i* n[ become available = classification4 ,( ^!1 practically speak+1 !re are ?ree :i* fix ! position ( an object 9 ! sequ5ce ( =ms3 7#a7 relative size ( ! unresolv$ nucle> region2 7#b7 ext5t to :i* ! arms are unw\nd2 7#c7 degree ( resolution 9 ! arms4 ,! =m mo/ ne>ly relat$ to ! elliptical nebulae has a l>ge nucle> region simil> to ,e#g1 ar\nd :i* are closely coil$ arms ( unresolv$ nebulosity4 ,!n foll[ objects 9 :i* ! arms appe> to build up at ! exp5se ( ! nucle> regions & unw9d z !y gr[2 9 ! end1 ! arms are wide op5 & ! nuclei inconspicu\s4 ,e>ly 9 ! s]ies ! arms beg9 to break up into cond5sations1 ! resolution comm5c+ 9 ! out] regions & work+ inw>d until 9 ! f9al /ages x rea*es ! nucleus itself4 ,9 ! l>g] spirals :]e critical obs]vations are possible1 ^! cond5sations are f\nd to be actual />s & gr\ps ( />s4 ,! /ructural transition is s smoo? & cont9u\s t ! selection ( division po9ts = fur!r classification is r arbitr>y4 ,! ends ( ! s]ies are unmi/akable1 h[ev]1 &1 9 a g5]al way1 x is possible to diff]5tiate a middle gr\p4 ,^! ?ree gr\ps are designat$ by ! non-committal lett]s 8a10 8b10 & 8c0 atta*$ to ! spiral symbols 8,s10 &1 ) ref]5ce to _! position 9 ! sequ5ce1 are call$ 8e>ly10 8int]m$iate10 & 8late0 types4#aj ,a m precise subdivision1 on a decimal scale = example1 is n ju/ifi$ 9 ! pres5t /ate ( our k4 ,9 ! e>ly types1 ! gr\p ,sa1 mo/ ( ! nebulosity is 9 ! nucle> region & ! arms are closely coil$ & unresolv$4 ,n4,g4,c4 #ccfh & #dbgd are among ! late/ ( ?is gr\p4 ,! int]m$iate gr\p1 ,sb1 includes objects hav+ relatively l>ge nucle> regions & ?9 r op5 arms1 z 9 ,m #ha1 or a small] nucle> region ) closely coil$ arms1 z 9 ,m #id4 ,^! two nebulae repres5t ! lat]al ext5sion ( ! sequ5ce 9 ! int]m$iate section4 ,! ext5sion along ! sequ5ce is approximately repres5t$ by ,n4,g4,c4 #dhbf1 among ! e>lie/ ( ! ,sb1 & ,n4,g4,c4 #ceef & #gcca1 :i* are among ! late/4 ,! resolution 9 ! arms is seldom conspicu\s1 al?\gh 9 ,m #ca1 a typical ,sb1 x is v pron\nc$ 9 ! out] portions4 ,illu/ration3 ,,plate ,,xiii ,normal & ,b>r$ ,spirals ,sa ,,ngc #deid1 ,s,ba ,,ngc #bhei1 ,sb ,,ngc #bhda1 ,s,bb ,,ngc #ehej1 ,sc ,,ngc #edeg 7,m #aja71 ,s,bc ,,ngc #gdgi ,! *>act]i/ics ( ! late types1 ! gr\p ,sc1 are m def9ite--an inconspicu\s nucleus & highly resolv$ arms4 ,individual />s _c be se5 9 ! small] nebulae ( ?is gr\p1 b knots are conspicu\s1 :i*1 9 l>g] objects1 are kn[n to be gr\ps & clu/]s ( />s4 ,! ext5t to :i* ! arms are op5$ v>ies f ,m #cc to ,m #aja1 bo? typical ,sc nebulae4 ,b>r$ spirals4--,9 ! normal spiral ! arms em]ge f two opposite po9ts on ! p]iph]y ( ! nucle> region4 ,!re is1 h[ev]1 a small] gr\p1 conta9+ ab\t #bj p] c5t ( all spirals1 9 :i* a b> ( nebulosity ext5ds diametrically across ! nucleus4 ,9 ^! spirals1 ! arms spr+ abruptly f ! ends ( ?is b>4 ,^! nebulae also =m a sequ5ce1 :i* p>allels t ( ! normal spirals1 ! arms app>5tly unw9d1 ! nuclei dw9dle1 ! cond5sations =m & "w inw>d4 ,h4 ,d4 ,curtis#aa fir/ call$ att5tion to ^! nebulae :5 he describ$ sev]al 9 ! int]m$iate /ages ( ! s]ies & call$ !m -type spirals4 ,! b>1 h[ev]1 nev] ext5ds beyond ! inn] spiral arms1 & ! /ructure1 especially 9 ! e>ly portion ( ! sequ5ce1 is m accurately repres5t$ by ! ,greek lett] 4 ,f a dynamical po9t ( view1 ! di/9ction has consid]able significance4 ,s9ce ,greek lett]s are inconv5i5t = catalogu+ purposes1 ! ,engli% t]m1 8b>r$ spiral10 is propos$1 :i* c be contract$ to ! symbol 8,,sb40 ,! ,,sb s]ies1 l t ( ! normal spirals1 is divid$ into ?ree r\ghly equal sections1 di/+ui%$ by ! app5d$ lett]s 8a10 8b10 & 8c40 ,! crit]ia on :i* ! division is bas$ are simil> 9 g5]al to ^? us$ 9 ! classification ( ! normal spirals4 ,9 ! e>lie/ =ms1 ,s,ba1 ! arms are n diff]5tiat$1 & ! patt]n is t ( a circle cross$ by a b>1 or1 z has be5 m5tion$1 t ( ! ,greek lett] 4 ,:5 ! b> is ori5t$ ne>ly 9 ! l9e ( sight1 x appe>s =e%ort5$ z a bright & def9ite m9or axis ( ! elongat$ nebul> image4 ,su* curi\s =ms z ! images ( ,n4,g4,c4 #ajbc & #cchd are expla9$ 9 ?is mann]4 ,! late/ gr\p1 ,s,bc1 is repres5t$ by ! ,s-%ap$ spirals su* z ,n4,g4,c4 #gdgi4 ,,irregul> ,,nebulae ,ab\t #c p] c5t ( ! extra-galactic nebulae lack bo? dom9at+ nuclei & rotational symmetry4 ,^! =m a di/9ct class :i* c be t]m$ 8irregul>40 ,! ,magellanic ,cl\ds are ! mo/ conspicu\s examples1 &1 inde$1 are ! ne>e/ ( all ! extra-galactic nebulae4 ,n4,g4,c4 #fhbb1 a curi\sly fai?ful m9iature ( ! ,cl\ds1 s]ves to bridge ! gap betwe5 !m & ! small] objects1 su* z ,n4,g4,c4 #dbad & #dddi4 ,9 ^! latt]1 a few individual />s em]ge f an unresolv$ backgr\nd1 & occasional isolat$ spots give ! emission spectrum *>act]i/ic ( diffuse nebulosity 9 ! galactic sy/em1 9 ! ,cl\ds1 & 9 ,n4,g4,c4 #fhbbab ,^! features are f\nd 9 o!r irregul> nebulae z well1 notably 9 ,n4,g4,c4 #aaef & #dfef1 & are j ^? to be expect$ 9 sy/ems simil> to ! ,cl\ds b situat$ at increas+ly great] di/ances4 ,! sy/em outl9$ above is prim>ily = ! =mal classification ( photographic images obta9$ ) l>ge reflectors & portrait l5ses4 ,= ea* in/rum5t1 h[ev]1 !re is a limit+ size & lum9osity bel[ :i* x is impossible to classify ) any confid5ce4 ,except 9 r>e in/ances1 ^! small nebulae are extra-galactic1 & _! numb]s1 brightness1 dim5sions1 & di/ribution are am5able to /ati/ical inve/igation4 ,= catalogu+ purposes1 !y require a designat+ symbol1 & ! lett] 8,q0 is sugge/$ z conv5i5t & n too widely us$ ) o!r significations4 ,illu/ration3 ,,plate ,,xiv ,irregul> ,nebula ,n4,g4,c4 #dbad ,direct photograph ) #ajj-;in* reflector ,m>* #ah1 #aibe4 ,scale #a mm #c4c ,slitless spectrogram at prim>y focus ( #ajj-;in* reflector1 ,m>* #ai1 #aibe ,,"p ,,ii4 ,,/ati/ical ,,/udy ,,( ,,extra-,,galactic ,,nebulae ,,! ,,data ,! mo/ homog5e\s li/ ( nebulae = /ati/ical /udy is t compil$ by ,h>dca/le#ac conta9+ all nebulae f\nd on ! ,frankl9-,adams *>ts4 ,^! are uni=m exposures ( two h\rs on fa/ plates made ) a ,cooke a/rographic l5s ( #aj-;in* ap]ture & #de-;in* focal l5g?4 ,! scale is #a mm #c4 ,! entire sky is cov]$1 b s9ce ! plates are c5t]$ ab\t #ae ap>t & ! def9ition decreases v appreciably ) di/ance f ! optical axis1 ! mat]ial is n /rictly homog5e\s4 ,moreov]1 ! publi%$ li/ suff]s f ! usual errors att5dant on r\t9e catalogu+2 = in/ance1 f\r conspicu\s ,messi] nebulae1 ,m #fj1 ,m #hg1 ,m #id1 & ,m #aja1 are miss+4 ,9 g5]al1 h[ev]1 ! li/ is ?or\ghly repres5tative d[n to ab\t ! ?irte5? photographic magnitude & v few conspicu\s objects are ov]look$4 ,x plays ! role ( a /&>d ) :i* o!r catalogues ( ! bright] nebulae may be comp>$ = complet5ess1 & numb]s 9 limit$ areas may be ext5d$ to ! entire sky4 ,:5 kn[n galactic nebulae1 clu/]s1 & ! objects 9 ! ,magellanic ,cl\ds are we$$ out1 ! rema9+ #gjj nebulae may be treat$ z extra-galactic4 ,v few c be classifi$ f ! ,frankl9-,adams plates2 = ?is purpose photographs on a mu* l>g] scale are requir$4 ,until fur!r data on ! individual objects are available1 ,h>dca/le's li/ c be us$ only = ! /udy ( di/ribution ov] ! sky4 ,?is %[s ! well-kn[n features--! great] d5sity 9 ! nor!rn galactic hemisph]e1 ! conc5tration 9 ,virgo1 & ! re/riction ( ! v l>ge nebulae to ! s\!rn galactic hemisph]e4 ,=tunately1 num]ical data d exi/ 9 ! =m ( total visual magnitudes = _m ( ! nebulae 9 ! nor!rn sky4 ,^! det]m9ations 7 made by ,holets*ek1#ad :o attempt$ to obs]ve all nebulae )9 rea* ( 8 #f-;in* refractor4 ,he lat] re/rict$ 8 program2 b ! f9al li/ is reasonably complete = ! m conspicu\s nebulae nor? ( decl9ation -#aj1 & is repres5tative d[n to visual magnitude ab\t #ab4e4 ,out ( #dag extra-galactic nebulae 9 ,holets*ek's li/1 #djh are nor? ( -#aj1 z comp>$ ) #djj 9 ,h>dca/le's4 ,! two li/s agree v well = ! bright] objects1 b div]ge m & m ) decreas+ lum9osity4 ,at ! twelf? magnitude ab\t half ( ,holets*ek's nebulae are includ$ by ,h>dca/le4 ,s9ce ! two li/s comp>e favorably 9 complet5ess ov] s l>ge a region ( ! sky1 ,holets*ek's may be *os5 z ! basis = a /ati/ical /udy & advantage tak5 ( ! valuable num]ical data on total lum9osities4 ,hopmann#ae has revis$ ! scale ( magnitudes by photometric measures ( ! comp>ison />s us$ by ,holets*ek4 ,new magnitudes 7 ?us obta9$ = #he individual nebulae & f ^! 7 d]iv$ mean correction tables applicable to ! entire li/4 ,! revis$ magnitudes are us$ ?r\gh\t ! foll[+ discussion4 ,hopmann's corrections ext5d to ab\t #ab4j mag41 & h be5 extrapolat$ on ! assumption t !y are con/ant = ! fa9t] magnitudes4 ,! errors involv$ are unimportant 9 view ( selective effects :i* mu/ be pres5t among ! obs]v$ objects ne> ! limit ( visibility4 ,! nebulae 7 classifi$ & _! diamet]s measur$ f photographs ( ab\t #cjj ( !m tak5 ) ! #fj-;in* & #ajj-;in* reflectors at ,m\nt ,wilson4 ,mo/ ( ! o!rs are includ$ 9 ! great collection ( nebul> photographs at ,m\nt ,hamilton1 :i* h be5 describ$ by ,curtis2#af &1 ?r\gh ! c\rtesy ( ! ,director ( ! ,lick ,obs]vatory1 x has be5 possible to confirm ! classification inf]r$ f ! publi%$ description by actual inspection ( ! orig9al negatives4 ,types1 diamet]s1 & total visual magnitudes are ?us available = "s #djj ( ! nebulae 9 ,holets*ek's li/4 ,! few unclassifi$ objects are all fa9t] ?an #ab4e mag4 ,! data are li/$ 9 ,tables ,i-,,iv1 9 :i* ! ,n4,g4,c4 numb]s1 ! total magnitudes1 & ! log>i?ms ( ! maximum diamet]s 9 m9utes ( arc are giv5 = ea* type sep>ately4 ,a summ>y is giv5 9 ,table ,v1 9 :i* ! relative frequ5cies & ! mean magnitudes ( ! v>i\s types w be f\nd4 ,,relative ,,lum9osities ,,( ,,! ,,v>i\s ,,types ,! frequ5cy di/ribution ( magnitudes = all types toge!r & = ! elliptical nebulae & ! spirals sep>ately is %[n 9 ,table ,,vi & ,figure #a4 ,) ! exception ( ! two out/&+ spirals1 ,m #ca & ,m #cc1 ! app>5t lum9osities are ab\t uni=mly di/ribut$ among ! diff]5t types4 ,! relative numb]s ( ! elliptical nebulae z comp>$ ) ! spirals decrease some:at ) decreas+ lum9osity1 b ?is is v probably an effect ( selection4 ,! elliptical nebulae are m compact ?an ! spirals & become m /ell> ) decreas+ lum9osity4 ,= ?is reason "s ( ! fa9t] nebulae are miss$ :5 small-scale in/rum5ts are us$1 al?\gh ! same lum9osity spread ov] a l>g] area w\ld /ill be easily detect$4 ,! effect is v pron\nc$ on photographic plates4 ,x acc\nts also = ! slightly bright] mean magnitude ( ! elliptical nebulae z comp>$ ) ! spirals 9 ,table ,v4 ,,table ,i ,elliptical ,nebulae ,n4,g4,c4 m,t log d ----------------------------- ,e#j 7#ag7 ----------------------------- #djd #aa4a #j4aa #dgd #ab4f - 4#dj #adjg #aj4i 4#ae #ccdh #aa4h - 4#ae #ccgi99 #i4d 4#cj #dbhc #ab4b - 4#eb #ddhf99 #i4g 4#cj #ddid99 #aj4a - 4#ae #deeb99 #i4i 4#bc #dehi #aa4d - 4#cj #dfdh #ab4c 4#eb #ejdd #aa4h 4#cj #ebaf #ac4c 4#gj #ebgc #ab4a 4#eb #eeeg #ab4c 4#dj #ehab #ab4j - 4#dj #ehdf #aj4i #j4j -------------------- ,mean #aa4dj -#j4bjd ------------------------------ ,e#a 7#ac7 ------------------------------ #dfg #ac4j -#j4gj #eif #aa4h 4#bb #adjj #aa4a 4#bb #bhhj #ab4j 4#eb #cbbf #ab4j 4#aj #cifb #aa4h - 4#cj #dbgh99 #aj4h 4#j #dcgd99 #i4i 4#jh #ddgb #h4h 4#cj #ddgh #aa4e - 4#aj #dfcf #aj4i 4#jh #ehac #ab4f - 4#cj #gfbf #ab4c -#j4cj ------------------------------ ,mean #aa4dc -#j4agg ------------------------------ ,e#b 7#ad7 ------------------------------ #bba99 #h4h #j4db #adec #aa4i - 4#aj #bfgb #ab4h - 4#dj #caic #ab4a #j4j #ceii #ab4j -#j4cj #cfjh #aa4f 4#bb #cfdj #aa4a - 4#je #dbfa #aa4a 4#bj #dbia #ab4c - 4#eb #dcgg #aa4i - 4#je #ddjf99 #aj4j 4#cj #ddgf #ab4h - 4#cj #dfdi99 #i4e 4#cj #eabg #ac4c -#j4eb ------------------------------ ,mean #aa4eb -#j4jhh ------------------------------ ,e#c 7#aj7 ------------------------------ #ajeb #aa4h -#j4ae #afjj #ab4g 4#ag #cbbb #ac4c - 4#ae #dcai #ab4h - 4#eb #dcfe #aa4d 4#jd #dchf #ab4c - 4#eb #ecbb99 #i4f 4#ae #eihb #aa4d 4#j #gefb #ab4h - 4#bb #gfai #aa4h - 4#ae ------------------------------ ,mean #aa4ii -#j4acc ------------------------------ ,e#d 7#ac7 ------------------------------ #ehd #aj4i #j4cj #agjj #ab4e - 4#aj #bigd #aa4h 4#ae #cfje #ab4e - 4#eb #cfaj #aa4h 4#ae #chid #ab4h - 4#je #dabe99 #aj4c 4#cj #dcgh #ab4a - 4#ae #dchb99 #aj4j 4#dh #deea #ab4h 4#jd #dgdb #ab4c 4#j #eegf #ab4c - 4#ae #gded #ac4c #j4j ------------------------------ ,mean #aa4ie -#j4jaa ------------------------------ ,e#e 7#f7 ------------------------------ #gbj #aj4i 4#aa #bfic #ab4c - 4#ae #ccgg #aj4i 4#ag #ddgc #aj4c 4#aa #dfba99 #aj4j 4#cj #dffj #aa4d #j4j ------------------------------ ,mean #aj4ig #j4jij ------------------------------ ,e#f 7#g7 ------------------------------ #hba #aa4h #j4j #bgfh #aj4g 4#ah #cfac #aa4h 4#be #dagi #aa4h 4#cd #ddce99 #aj4e 4#aa #dedf99 #aj4c 4#ah #dfig99 #i4f #j4dh ------------------------------ ,mean #aj4ic #j4bbj ------------------------------ ,e#g 7#e7 ------------------------------ #caae99 #i4e #j4fj #daaa #aj4a 4#ed #dbgj #ab4a 4#j #degj #aa4a 4#ch #ecjh #ab4c #j4bh ------------------------------ ,mean #aa4jb #j4cfj ------------------------------ ,peculi> 7#h7 ------------------------------ #ahe #ab4c #j4dh #bje99 #i4c 4#ij #ebd #aa4i 4#da #cfjg #i4i 4#aa #ciih #ab4a 4#bc #ddei #aa4c - 4#bb #edhe #ab4c 4#je #egci #ac4c -#j4dj ------------------------------ ,! v>i\s types are homog5e\sly di/ribut$ ov] ! sky1 _! spectra are simil>1 & ! radial velocities are ( ! same g5]al ord]4 ,^! facts1 toge!r ) ! equality ( ! mean magnitudes & ! uni=m frequ5cy di/ribution ( magnitudes1 are consi/5t ) ! hypo!sis t ! di/ances & absolute lum9osities z well are ( ! same ord] = ! diff]5t types4 ,?is is an assumption ( consid]able importance1 b un=tunately x _c yet be subject$ to positive & def9ite te/s4 ,none ( ! individual simil>ities necess>ily implies ! adopt$ int]pretation1 b ! totality ( !m1 toge!r ) ! intimate s]ies relations among ! types1 :i* w be discuss$ lat]1 sugge/s x z ! mo/ reasonable work+ hypo!sis1 at lea/ until inconsi/5cies %\ld appe>4 ,,table ,,ii ,b>r$ ,spirals ,n4,g4,c4 m,t log d ------------------------------ ,s,ba 7#bf7 ------------------------------ #icf #aa4a #j4dh #ajbc99 #aj4b 4#gh #bgcb #ab4c 4#aa #bgha #ab4c 4#aa #bghg #aa4d 4#cf #bhei #aa4a 4#bh #biej #aa4f 4#ae #cchd99 #aj4g 4#dh #cdab99 #aa4b 4#dj #cdah #ac4a 4#j #cdeh #ab4h - 4#bb #cide #aa4e 4#bj #djbf #aa4a 4#dh #dbjc #aa4a 4#cf #dcdf #ab4j 4#bj #dcga #ab4j 4#ah #ddba #ab4h 4#ag #dddb #aj4i 4#ej #ddgg #aj4i 4#dj #deif #ab4j 4#be #dfdc #aa4a 4#bf #dged #aj4i 4#dh #edgc #ab4j 4#jh #eegd #ac4j - 4#je #efhi #ab4j 4#cj #egja #ab4c #j4ag -------------------- ,mean #aa4ff #j4bfg ------------------------------ ,s,bb 7#af7 ------------------------------ #ajbb #aa4h #j4jd #bfej #ab4h 4#j #ccea99 #aa4d 4#dh #cdjj #ab4e - 4#aj #cdad #aa4e 4#bf #cejd #aa4d 4#cj #cgah #aa4h #j4dh #dajb #ab4j #j4cf #dbde #aa4a 4#ae #dcid #aa4e 4#fj #dedh #aa4a 4#fj #dfii99 #aj4j 4#eg #dgbe99 #i4b 4#gj #ebah #ab4h 4#be #eeff #aa4a 4#bj #ggbc #aa4h #j4ah -------------------- ,mean #aa4dh #j4cag ------------------------------ ,s,bc 7#ae7 ------------------------------ #fac #aj4f #j4fj #ggi #ab4a 4#dh #cbjf #ac4c 4#de #ccdd #aa4d 4#fj #ccdf #ab4c 4#dj #cfbe #ac4c 4#j #cfhf #ab4j 4#cj #cgfi #ab4h 4#dc #ciec #aa4a 4#gd #ciib #aa4e 4#he #dcjc99 #aj4f 4#gh #degi99 #i4g 4#de #echc #ab4f 4#dj #eiba #ab4h 4#gj #gdgi #ab4a #j4dh -------------------- ,mean #aa4hg #j4eji ------------------------------ ,peculi> 7#b7 ------------------------------ #bghb #ab4c #j4bf #dcad #aa4a #j4cd ------------------------------ ,,table ,,iii ,normal ,spirals ,n4,g4,c4 m,t log d ------------------------------ ,sa 7#di7 ------------------------------ #dhh #aa4h #j4dh #fgf #ac4c 4#cj #accb #aj4i 4#dc #bfee #aa4a 4#fj #bfha #aj4g 4#dh #bgge #aj4i 4#cb #bhaa #ab4c 4#bh #bhee #ab4h 4#aa #cafi #ab4c 4#fj #cbde #aa4h 4#cj #ccja #ab4d 4#ae #ccfh99 #aj4j 4#he #ceaf #ab4a 4#bj #cfai #ab4c 4#j #cfbf99 #aa4c 4#bh #cffe #ab4j 4#j #cfhb #ab4a 4#jh #chih #ab4j 4#dc #cida #aj4c 4#cj #djcf #aj4i 4#fj #dach #ab4a 4#bj #dadc #aa4c 4#aa #daej #ab4j 4#aa #dbea #aj4d 4#bf #dbfh #ab4h 4#j #dbgd #aa4a #j4ed #dbha #aa4e #j4ah #ddbi #aa4e 4#dh #ddeb #ab4f 4#ae #debf #aa4a 4#gj #deej #ab4a 4#dc #degj #aa4a 4#ch #deid #i4a 4#he #dffe #aa4h 4#jh #dfhd #ab4b - 4#bb #dfih #aa4i 4#dc #dgaj #aa4h 4#ed #dgfb #aa4e 4#eg #dhff #ab4j 4#ej #dieh #aa4d 4#fj #ecgg #aa4h 4#dh #echi #ab4e 4#be #edbb #ab4a 4#dj #efca #ab4j - 4#je #ehff99 #aa4g 4#dh #gjac #ab4h 4#jh #gdeg #ab4h 4#cj #ggbg #aa4c 4#dc #ghad99 #aa4d #j4dh -------------------- ,mean #aa4fi #j4ccc ------------------------------ ,sb 7#gj7 ------------------------------ #bbd #e4j #b4be #fgb #ab4h #j4ed #ggb #aa4a 4#gj #idi #ac4c 4#j #iee #ab4i 4#dj #ajfh #i4a 4#dj #acji #ab4j 4#ae #bfci #ab4b 4#j #bgae #ab4e 4#dj #bgdh #ab4j 4#cb #bhda99 #i4d 4#gh #bihe #aa4d #j4dh #cjca99 #h4c #a4bj #cahb #ab4i -#j4bb #caij #aa4i 4#dh #cbbg #ab4j 4#dh #cbgg #ab4f 4#j #ccaj #aj4d 4#ah #cchj #ab4a - 4#je #cdhi99 #aa4b #j4dj #ceef #aa4a #j4ij #ceic #aa4i 4#fj #cfbc99 #i4i 4#ij #cfbg99 #i4a #j4ij #cfbh #aa4d #a4jh #cfcb #ac4c -#j4aj #cfge #aa4d 4#dh #cfha #ac4j 4#j #cfhd #ac4j 4#jh #chie #ac4c - 4#je #cijj #ab4a 4#be #cich #ab4a 4#fe #djbj #ab4c 4#ag #djcj #aa4a 4#cj #djea99 #aa4i 4#fj #djhe #ab4e 4#cf #daea #ab4j 4#dj #daib #aj4i 4#ij #dbaf99 #aj4h #j4he #dbdd #ab4c #a4aa #dbeh99 #h4g #a4cj #dbgc #aa4h #j4bj #ddch99 #aj4c 4#ed #dddh #aa4h 4#dh #ddej #aj4f 4#eg #ddea #ab4h - 4#ae #dejj #ab4h #j4ag #defe99 #aa4j #a4ag #dgcf99 #h4d #j4gj #dgej #aa4h 4#bf #dhjj #aa4h 4#jd #dhad #ab4g 4#ef #dhbf #i4j 4#ij #ejee99 #i4f 4#ij #ecgf #ab4h 4#ag #ecgi #ab4i -#j4je #ecid #ac4c #j4ag #efcc #ac4j - 4#aj #egac #ab4c 4#cb #egdj #ab4c 4#dh #egdf #aj4d 4#hg #egej #ab4h 4#ae #eggb #ab4j 4#be #ehjf #ab4c 4#cj #eihe #ab4j 4#fj #fbjg #aa4h 4#cj #ffdc #aa4i 4#dh #gcca99 #aj4d 4#ie #geda #ab4g 4#da #gfjf #ab4j #j4gh -------------------- ,mean #aa4ee #j4dga ------------------------------ ,sc 7#aae7 ------------------------------ #aeg #aa4d #j4dj #bec #i4c #a4cd #bgh #ab4j #j4jh #dgj #ac4a #j4bj #eih #g4j #a4gh #fae #ab4c #j4dc #fbh99 #aj4f 4#ij #ijh #aa4i 4#fj #ajhd #aa4d 4#cd #ajhg #ab4a 4#cf #afcg #ab4f 4#dh #bcci #ac4a #j4bh #bdjc99 #h4g #a4bj #becb #ac4c #j4ag #bfhc #i4i #a4jj #bgab #ab4c #j4bj #bgdb #aa4h 4#dj #bggf #ab4c #j4cd #bijc99 #i4a #a4jd #bifd #aa4f 4#dj #bigf #ab4j 4#ej #cjjc #ac4c 4#gh #cjba #ab4c 4#aa #cjgi #ab4j 4#ij #cadg #aa4d 4#cj #caff #ab4j 4#j #cahd #ab4g 4#gh #caih #ac4j 4#ie #cbed #ab4h 4#fj #cbid #ab4j 4#dh #cchi #ac4a #j4cj #ccie #ab4f #j4aa #ccif #ac4c - 4#aj #cdcj #ab4f 4#di #cdcb #ab4j 4#gi #cdcg #ab4d 4#bh #cdde #ac4a 4#jh #cddh #ab4c 4#bf #cdhf #aa4h 4#eh #cdhh #ab4h 4#be #ceab #ab4c 4#j #ceba99 #aj4a 4#fe #cedi #ac4c 4#dc #ceif #ac4c 4#fj #cfca #aa4h 4#ff #cfdb #ab4j 4#gc #cfee #aa4i 4#jd #cfff #aa4h 4#ed #cfgb #ac4j 4#ed #cfhc #ab4j 4#ae #cghj #ac4j 4#dj #chaj #aa4c 4#fb #chac #ab4c 4#cb #chgg #aa4h 4#fd #chhg #ab4c 4#dj #chic #aa4h 4#fa #cidi #aa4h 4#cd #cihb #ab4a 4#cf #djac #ac4c 4#fj #djda #aa4d 4#cj #djfb #ab4f 4#dh #djhh #aa4e #j4gb #djif #ab4c #j4gh #dajj #ab4c 4#fj #dade #ab4c 4#gj #daeg #ab4c 4#gg #dbab #ab4c 4#cj #dbbj #ab4a #j4dj #dbcf #ab4h #a4jd #dbed #aj4d #j4fe #dcba99 #aj4e 4#gj #ddad #aj4a 4#dh #ddai #aa4h 4#cf #ddfj #ab4a 4#bj #ddij99 #aj4b 4#fj #deja99 #aj4e 4#gj #dejd #ab4a #j4dh #deag #ab4e #a4jj #decf #ab4c #j4he #deei #aj4g 4#ij #defi99 #aj4i 4#fe #dehj #ab4c 4#ae #dfje #i4i #j4dh #dfca99 #i4e #a4jh #dfcb #ac4a #j4ej #dfff #ab4j 4#fj #dgac #ab4c 4#ch #dgha #aa4h 4#dh #dgic #ab4d 4#bj #dhjh #ab4f #j4cd #diie #aa4h #j4cf #ejje99 #aa4a 4#gj #ejab #aa4i 4#dc #ejcc99 #aa4h #j4gh #eaid99 #g4d #a4jh #ebjd #ab4h #j4ei #ebcf #aj4d #a4jj #ebdg #ac4c #j4gj #ebdh #aa4e 4#ej #ebij #ab4e 4#dh #ebig #ab4f 4#fj #ecfd #ac4c 4#fj #ecie #ab4h #j4cj #edeg #i4i #a4cd #edgd #ab4j #j4fj #eehe #ab4c 4#fj #efgf #aa4h 4#dh #efgh #aa4h 4#da #ehcb #ac4a #j4ef #eijg #aa4i #a4jd #faha #ab4e #j4cj #fbag #ab4a 4#be #fejc #i4i 4#gj #gddh #aa4h 4#cj #gfga #ac4c - 4#ae -------------------- ,mean #aa4ge #j4ecg ------------------------------ ,peculi> ,spirals 7,unclassifi$7 ------------------------------ #igb #ac4c #j4ag #becg #ac4c 4#j #dijj #aa4h #j4bc ------------------------------ ,,relation ,,betwe5 ,,lum9osities ,,& ,,diamet]s ,among ! nebulae ( ea* sep>ate type are f\nd l9e> correlations betwe5 total magnitudes & log>i?ms ( diamet]s4 ,^! are %[n 9 ,figures #b-e = ! beg9n+1 middle1 & end ( ! sequ5ce ( types & also = ! irregul> nebulae4 ,9 ,figures #b & #c adjac5t types h be5 gr\p$ 9 ord] to increase ! mat]ial1 & 9 ,figure #e ! ,magellanic ,cl\ds h be5 add$ to increase ! range4 ,! correlations c be express$ 9 ! =m m,t ,c - ,k log d1 7#a7 :]e ,k is con/ant f type to type1 b ,c v>ies progressively ?r\gh\t ! sequ5ce4 ,! value ( ,k _c be accurately det]m9$ f ! scatt]$ data = any p>ticul> type1 b1 )9 ! limits ( unc]ta9ty1 x approximates ! r\nd numb] #e4j1 ! value :i* is repres5t$ by ! l9es 9 ,figures #b-e4 ,:5 ,k is kn[n1 ! value ( ,c c be comput$ f ! mean magnitude & ! log>i?m ( ! diamet] = ea* type4 ,?is am\nts to read+ f ! curves ! magnitudes correspond+ to a diamet] ( "o m9ute ( arc1 b avoids ! unc]ta9ty ( e/abli%+ ! curves :]e ! data are limit$4 ,,table ,,iv ,irregul> ,nebulae ,n4,g4,c4 m,t log d ------------------------------ #bifh #ab4f #j4jh #cjcd99 #i4j 4#he #cjgg #aa4d 4#dh #cgbi #aa4h 4#ag #dbad99 #aa4c 4#ij #dddi99 #i4e 4#fe #dfah #ab4c #j4dj #dfef #aa4e #a4cj #dgec #aa4d #j4dc #eadd #ab4h - 4#cj #ecfc #aa4a #j4bj ------------------------------ ,mean #aa4cd #j4dfi ------------------------------ ,,notes ,,to ,,tables ,i-,,iv 99 ,magnitude f ,hopmann4 ,n4,g4,c4 #ebd & #ciih are late elliptical nebulae 9 :i* ! equatorial planes are p]p5dicul> to ! l9e ( sight4 ,!y might be includ$ ) ! ,e#f or ,e#g nebulae4 ,absorption v conspicu\s4 ,n4,g4,c4 #cfjg1 #ddei1 & #edhe appe> to be elliptical nebulae ) n>r[ b&s ( absorption betwe5 ! nuclei & ! p]iph]ies4 ,! progressive *ange 9 ! value ( ,c ?r\gh\t ! sequ5ce may be express$ z a v>iation ei!r 9 ! magnitude = a giv5 diamet] or 9 ! diamet] = a giv5 magnitude4 ,bo? effects are li/$ 9 ,table ,,vii & are illu/rat$ 9 ,figure #f1 9 :i* magnitudes & diamet]s ?us f\nd are plott$ aga9/ types4 ,) ! exception ( ! lat] elliptical nebulae1 = :i* ! data are :olly inadequate = reliable det]m9ations1 ! po9ts fall on smoo? curves4 ,9 ! region ( ! e>li] elliptical nebulae1 ! curves %\ld be some:at /eep] 9 ord] to all[ = objects ( great] ellipticities :i* are probably includ$4 ,,r$uction ,,( ,,nebulae ,,to ,a ,,/&>d ,,type ,! slope1 ,k1 9 ! =mula relat+ magnitudes ) diamet]s1 appe>s to be closely simil> = ! v>i\s types1 b accurate det]m9ations are re/rict$ by ! limit$ & scatt]$ nature ( ! data = ea* type sep>ately4 ,) a k ( ! p>amet] ,c1 h[ev]1 x is possible to r$uce all ! mat]ial to a /&>d type & h5ce to det]m9e ! value ( ,k f ! totality ( ! data4 ,! mean ( ,e#g1 ,s,ba1 & ,sa 0 *os5 = ! purpose1 z repres5t+ a hypo!tical transition-po9t betwe5 ! elliptical nebulae & ! spirals1 & 0 designat$ by ! symbol 8,s#j40 ,! correspond+ value ( ,c1 9 r\nd numb]s1 is #ac4j4 ,corrections 7 appli$ to ! log>i?ms ( ! diamet]s ( ! nebulae ( ea* obs]v$ class1 am\nt+ to ,delta log d #j4b 7#ac4j - ,c7 :]e ,c is ! obs]v$ value = a p>ticul> class4#ag ,:5 ! values ( ,c are read f ! smoo? curve 9 ,figure #f1 ^! corrections are z %[n 9 ,table ,,viii4 ,,table ,v ,frequ5cy ,di/ribution ( ,types ,type ,numb] ,p]c5tage ,mean ,mag4 ---------------------------------------- ---- ,elliptical ,nebulae ---------------------------------------- ---- ,e#j #ag #ah #aa4dj #a #ac #ad #aa4dc #b #ad #ae #aa4eb #c #aj #aa #aa4ii #d #ac #ad #aa4ie #e #f #f #aj4ig #f #g #h #aj4ic #g #e #e #aa4jb ,pec #h #i #aa4ee ----------------------------------- ,total #ic #bc99 #aa4ec ---------------------------------------- ---- ,normal ,spirals ---------------------------------------- ---- ,sa #di #ba #aa4fi b #gj #bi #aa4ee c #aae #di #aa4ge ,pec #c #a #ab4hj ----------------------------------- ,total #bcg #ei99 #aa4fh ---------------------------------------- ---- ,b>r$ ,spirals ---------------------------------------- ---- ,s,ba #bf #dd #aa4ff b #af #bg #aa4dh c #ae #bf #aa4hg ,pec4 #b #c #aa4gj ----------------------------------- ,total #ei #ae99 #aa4ff ---------------------------------------- ---- ,irregul> ,nebulae ---------------------------------------- ---- #aa #c99 #aa4cd ---------------------------------------- ---- ,totals ---------------------------------------- ---- ,all types #djj #ajj #aa4fc ---------------------------------------- ---- 99 ,p]c5tages ( #djj1 ! total numb] ( nebulae inve/igat$4 ,! p]c5tages ( ! subtypes ref] to ! numb] ( nebulae 9 ! p>ticul> type4 ,,table ,,vi ,frequ5cy ,di/ribution ( ,magnitudes ,numb]s ( ,nebulae ,magnitude ,int]val ------------------------ ,e ,s ,all ---------------------------------------- ---- #h4a- #h4e #j #b #b #h4f- #i4j #b #d #g #i4a- #i4e #d #f #aa #i4f-aj4j #g #g #ai #aj4a-aj4e #g #ac #bj #aj4f-aa4j #h #ad #cb #aa4a-aa4e #i #bd #di #aa4f-ab4j #ba #eg #hh #ab4a-ab4e #bj #eb #hf #ab4f-ac4j #aj #cc #ea ---------------------------------------- ---- ,! correct$ values ( log d 7 !n plott$ aga9/ ! obs]v$ magnitudes4 ,?is am\nts to %ift+ ! approximately p>allel correlation curves = ! sep>ate types along ! axis ( log d until !y co9cide4 ,s9ce ! mean magnitudes ( ! v>i\s types are ne>ly con/ant1 ! relative %ifts w v ne>ly equal ! diff]5ces 9 ! mean obs]v$ log d1 & h5ce ! effect ( errors 9 ! fir/ approximation to ! values ( ,k w be negligible4 ,illu/ration3 ,fig4 #a4--;,frequ5cy di/ribution ( app>5t magnitudes among nebulae 9 ,holets*ek's li/4 ,illu/ration3,fig4 #b4--,relation betwe5 lum9osity & diamet] among nebulae at ! beg9n+ ( ! sequ5ce ( types--,e#j & ,e#a nebulae4 ,! plot is %[n 9 ,figure #g1 9 :i* ! two ,magellanic ,cl\ds h be5 includ$ 9 ord] to /r5g!n ! bright end ( ! curve :i* w\ld o!rwise be unduly influ5c$ by ! s+le object1 ,m #ca4 ,! magnitudes #j4e & #a4e1 :i* 7 assign$ to ! ,cl\ds1 are e/imates bas$ ^u publi%$ descriptions4 ,illu/ration3 ,fig4 #c4--,relation betwe5 lum9osity & diamet] among nebulae at ! middle ( ! sequ5ce ( types--,e#g1 ,sa1 & ,s,ba nebulae4 ,illu/ration3 ,fig4 #d4--,relation betwe5 lum9osity & diamet] among nebulae at ! end ( ! sequ5ce ( types--,sc & ,s,bc nebulae4 ,! correlation ( ! data is v closely repres5t$ by ! =mula m,t #ac4j - #e log d4 7#b7 ,?is falls betwe5 ! two regression curves d]iv$ f lea/-squ>e solutions & c\ld be obta9$ exactly by assign+ appropriate weights to ! two me?ods ( gr\p+4 ,! nature ( ! data is su* t a clos] agreem5t c sc>cely be expect$4 ,no correction to ! assum$ value ( ! slope appe>s to be requir$4 ,! mat]ial ext5ds ov] a range ( #ab mag41 & ! few cases :i* h be5 inve/igat$ indicate t ! correlation c be ext5d$ ano!r #c mag41 to ! limit at :i* nebulae c be classifi$ ) c]ta9ty on photographs made ) ! #ajj-;in* reflector4 ,! relation may !re=e be consid]$ to hold ?r\gh\t ! entire range ( obs]vations4 ,illu/ration3,fig4 #e4--,relation betwe5 lum9osity & diamet] among ! irregul> nebulae4 ,! ,magellanic ,cl\ds are includ$4 ,n4,g4,c4 #dfef is an exceptional case 9 t x %[s a n>r[1 greatly elongat$ image 9 :i* absorption effects are v conspicu\s2 h5ce ! maximum diamet] is exceptionally l>ge = its app>5t lum9osity4 ,! residuals )\t reg>d to sign av]age #j4hg mag41 & !re appe>s to be no sy/ematic effect due ei!r to type or lum9osity4 ,! scatt]1 h[ev]1 is mu* great] = ! spirals1 especially 9 ! lat] types1 ?an = ! elliptical nebulae4 ,! limit+ cases are expla9$ by peculi> /ructural features4 ,! nebulae :i* fall well above ! l9e usually h bright /ell> nuclei1 & ^? :i* fall l[e/ are spirals se5 edge-on 9 :i* belts ( absorption are conspicu\s4 ,,table ,,vii ,type m,t log d ,c99 d ---------------------------------------- --- ,e#j #aa4dj -#j4bjd #aj4ch #a4b #a #aa4dc 4#agg #aj4ed #a4c #b #aa4eb 4#jhh #aa4jh #a4f #c #aa4ii 4#acc #aa4cc #a4h #d #aa4ie - 4#jaa #aa4ij #b4d #e #aj4ig 4#jij #aa4db #a4i #f #aj4ic 4#bbj #ab4jc #b4e #g #aa4jb 4#cfj #ab4hb #c4g ,sa #aa4fi 4#ccc #ac4ce #d4g b #aa4ee 4#dga #ac4ij #f4j c #aa4gd 4#edj #ad4dd #g4g ,s,ba #aa4ff 4#bfg #ac4jj #d4j b #aa4dh 4#cag #ac4af #d4c c #aa4hg 4#eji #ad4da #g4f ,irr #aa4cd #j4dfi #ac4fh #e4d ------- --------------------------------- 99 ,c ov]l9em,t #e ov]l9elog d4 log d #j4b 7,c -- m,t72 m,t #aj4j4 ,,effects ,,( ,,ori5tation ,! effect ( ! ori5tation is appreciable among ! spirals 9 g5]al4 ,9 ord] to illu/rate ?is feature1 !y h be5 divid$ into ?ree gr\ps consi/+ ( ^? ^: images are r\nd or ne>ly r\nd1 elliptical1 & edge-on1 or ne>ly s4 ,! mean values ( m,t #e log d 7 !n comput$ & comp>$ ) ! !oretical value1 #ac4j4 ,! residuals are negative :5 ! nebulae are too bright = _! diamet]s & positive :5 !y are too fa9t4 ,! results are giv5 9 ,table ,,ix1 :]e mean residuals are foll[$ by ! numb]s ( nebulae1 9 p>5!ses1 :i* are repres5t$ by ! means4 ,! numb]s ( ! b>r$ spirals are too limit$ to inspire confid5ce 9 ! results1 b among ! normal spirals !re is conclusive evid5ce t ! highly tilt$ & edge-on nebulae are fa9t] = a giv5 diamet] ?an ^? se5 9 ! r\nd4 ,a /udy ( ! individual images indicates t ! effect is due v l>gely to d>k absorption cl\ds1 :i* become m conspicu\s :5 ! nebulae are highly tilt$4 ,^! cl\ds are g5]ally1 b n univ]sally1 p]iph]al features4 ,an ext5sive inve/igation w be necess>y be=e any residual effect due to absorption by lum9\s nebulosity c be e/abli%$ ) c]ta9ty4 ,ev5 %\ld su* exi/1 x cle>ly _c be excessive4 ,illu/ration3 ,fig4 #f4--,progressive *>act]i/ics 9 ! sequ5ce ( types4 ,! upp] curve repres5ts ! progression 9 total magnitude ) type = nebulae hav+ maximum diamet]s ( "o m9ute ( arc4 ,! elliptical nebulae & ! normal spirals are includ$ z repres5t+ ! normal sequ5ce1 b ! b>r$ spirals & ! irregul> nebulae are omitt$4 ,! figures give ! numb] ( objects obs]v$ 9 ea* type4 ,among ! lat] elliptical nebulae ! numb]s are s small t means ( adjac5t types h be5 plott$4 ,! l[] curve repres5ts ! progression 9 diamet] along ! normal sequ5ce = nebulae ( ! t5? magnitude4 ,,table ,,viii ,type ,c log d -------------------------- ,e#j #aj4cj #j4ed #a #aj4fe 4#dg #b #aa4jj 4#dj #c #aa4ce 4#cc #d #aa4gj 4#bf #e #ab4je 4#ai #f #ab4dj 4#ab #g #ab4ge #j4je ,sa #ac4ca -#j4jf ,sb #ac4ij 4#ah ,sc #ad4de 4#bi ,s,ba #ac4jj 4#jj ,s,bb #ac4af 4#jc ,s,bc #ad4da 4#bh ,irr #ac4fh -#j4ad ------------------------- ,illu/ration3 ,fig4 #g4--,relation betwe5 lum9osity & diamet] among extra-galactic nebulae4 ,! nebulae h be5 r$uc$ to a /&>d type1 ,s#j1 :i*1 be+ ! mean ( ,e#g1 ,sa1 & ,s,ba1 repres5ts a hypo!tical transition po9t betwe5 elliptical nebulae & spirals4 ,! ,magellanic ,cl\ds h be5 includ$ 9 ord] to /r5g!n ! bright] end ( ! plot4 ,,significance ,,( ,,! ,,lum9osity ,,relation ,! correlations ?us f> d]iv$ are betwe5 total lum9osities & maximum diamet]s4 ,9 ! mo/ g5]al s5se1 !re=e1 !y express laws ( mean surface brightness4 ,! value1 ,k #e4j1 9 =mula 7#a7 indicates t ! surface brightness is con/ant = ea* sep>ate type4 ,! v>iations 9 ,c indicate a progressive dim9ution 9 ! surface brightness f class to class ?r\gh\t ! entire sequ5ce4 ,! consi/5cy ( ! results amply ju/ifies ! sequ5ce z a basis ( classification1 s9ce a progression 9 physical dim5sions is indicat$1 :i* accompanies ! progression 9 /ructural =m4 ,al?\gh ! correlations d n necess>ily e/abli% any g5]ic relation among ! obs]v$ classes1 !y support 9 a v evid5t mann] ! hypo!sis t ! v>i\s /ages 9 ! sequ5ce repres5t diff]5t phases ( a s+le fundam5tal type ( a/ronomical body4 ,moreov]1 ! quantitative v>iation 9 ,c is consi/5t ) ?is int]pretation1 z is app>5t f ! foll[+ consid]ations4 ,,table ,,ix ,residuals 9 m,t #e log d z a ,function ( ,ori5tation ,type ,r\nd ,elliptical ,edge-,on ---------------------------------------- --------------- ,sa -#j4jb 7#ac7 -#j4bg 7#ac7 #j4eg 7#bc7 ,sb 4#gg 7#bd7 4#j 7#ce7 #a4ga 7#aa7 ,sc -#j4jh 7#ce7 -#j4ac 7#eg7 #j4ff 7#bb7 ,all ,s -#j4bf 7#gb7 -#j4aa 7#aje7 #j4hc 7#ef7 ,s,ba #j4j 7#aj7 -#j4cj 7#g7 #j4ca 7#h7 ,s,bb - 4#af 7#aj7 4#jg 7#f7 ,s,bc #j4ai 7#i7 -#j4ej 7#d7 #j4cb 7#b7 ,all ,,sb #j4ja 7#bi7 -#j4ba 7#ag7 #j4ca 7#aj7 ,all spirals -#j4bb 7#aja7 -#j4ac 7#abb7 #j4gc 7#ff7 ---------------------------------------- --------------- ,among ! elliptical nebulae x is obs]v$ t ! nuclei are %>p & di/9ct & t ! color di/ribution is uni=m ov] ! images4 ,?is indicates t !re is no appreciable absorption1 ei!r g5]al or selective1 & h5ce t ! lum9osity ( ! project$ image repres5ts ! total lum9osity ( ! nebula1 reg>dless ( ! ori5tation4 ,if ! obs]v$ classes 7 pure1 t is1 if ! app>5t ellipticities 7 ! actual ellipticities1 =mula 7#a7 c\ld be writt5 ,ce m,t #e log b - #e log 7#a - e71 7#c7 :]e b is ! m9or diamet] 9 m9utes ( arc & e is ! ellipticity4 ,! t]m m,t #e log b is obs]v$ to be con/ant = a giv5 type4 ,if x 7 con/ant = all elliptical nebulae1 !n ! t]m ,ce #e log 7#a - e7 w\ld be con/ant also4 ,on ?is assumption1 ,ce #e log 7#a - e7 ,c#j1 :]e ,c#j is ! value ( ,c = ! pure class ,e#j4 ,h5ce ,ce - ,c#j -#e log 7#a - e71 7#d7 a relation :i* c be te/$ by ! obs]vations4 ,an analysis ( ! mat]ial indicates t ?is is actually ! case1 & h5ce t among ! elliptical nebulae 9 g5]al1 ! m9or diamet] det]m9es ! total lum9osity1 at lea/ to a fir/ approximation4#ah ,! obs]v$ values ( ,c v>y ) ! class1 z is se5 9 ,table ,,vii & ,figure #f1 b1 except+ t = ,e#g1 !y are too l>ge because ( ! mixture ( lat] types ( nebulae among ^? ( a giv5 obs]v$ class4 ,x is possible1 h[ev]1 to calculate ! values ( ,ce - ,c#j = ! pure classes & !n to make approximate corrections = ! obs]v$ mixtures on ! assumption t ! nebulae ( any giv5 actual ellipticity are ori5t$ at r&om4 ,9 ?is mann]1 mean !oretical values c be comp>$ ) ! obs]v$ values4 ,! comp>isons are %[n 9 ,table ,,xii 9 ! =m ,c#g - ,ce1 because ,e#g is ! only obs]v$ class t c be consid]$ z pure4 ,! significance ( ! table w be discuss$ lat]4 ,! foll[+ me?od has be5 us$ to det]m9e ! relative frequ5cies ) :i* nebulae ( a giv5 actual ellipticity1 ori5t$ at r&om1 w be obs]v$ z hav+ v>i\s app>5t ellipticities4 ,9 ,figure #h1 let ! co-ord9ate axes ,,ox & ,,oy co9cide ) ! major & m9or axes1 a & b1 ( a m]idian section ( an ellipsoid ( revolution4 ,let ,,oo be ! l9e ( sight to ! obs]v]1 mak+ an angle i ) ,,ox1 & let ,,or be p]p5dicul> to ,,oo4 ,let ,,pp be a tang5t to ! ellipse1 p>allel to & at a di/ance f ,,oo4 ,let x#j & y#j be ! int]cepts ( ! tang5t on ! ,x- & ,y-axis1 respectively4 ,! app>5t ellipticity is det]m9$ by bx1 :i*1 = v>i\s values ( ! angle i1 ranges f b to a4 ,! problem is to det]m9e ! relative areas on ! surface ( a sph]e ^: c5t] is ,o1 )9 :i* ! radius ,,oy mu/ pass 9 ord] t ! values ( b#a1 & h5ce ( ! app>5t ellipticity1 e#a may fall )9 c]ta9 designat$ limits4 ,?is requires t ! angle i be express$ 9 t]ms ( b#a4 ,illu/ration3 ,fig4 #h ,f ! equation ( ! tang5t1 ,,pp1 y -x tani sqrta#b tan#b;i b#b y#j sqrta#b tan#b;i b#b ,s9ce b#a y#j cos7i7 b#ab a#b s9#b;i b#b cos#b;i4 ,let a #a1 !n cos#b;i frac#a - b#aba - b#b1 :]e b#a #a - e#a12;b i - e4 ,f ^! equations1 ! values ( i c be det]m9$ = all possible values ( e#a4 ,! limits = ! obs]v$ classes ,e#j to ,e#g 7 *os5 midway betwe5 ! consecutive t5?s1 ,e#j rang+ f e #j to e #j4je2 ,e#a1 f e #j4je to e #j4ae2 ,e#g1 f e #j4fe to e #j4ge4 ,! relative frequ5cies ( ! v>i\s obs]v$ classes are !n proportional to ! diff]5ces 9 s9 i correspond+ to ! two limit+ values ( e#a4 ,^! frequ5cies mu/ be calculat$ sep>ately = nebulae ( diff]5t actual ellipticities4 ,! results are giv5 9 ,table ,x1 :]e ! actual ellipticities1 li/$ 9 ! fir/ column1 are foll[$ across ! table by ! p]c5tages :i*1 on ! assumption ( r&om ori5tation1 w be obs]v$ z hav+ ! v>i\s app>5t ellipticities4 ,! bottom r[ w be se5 to %[ ! p]c5tages ( app>5t ellipticities obs]v$ 9 an assembly ( nebulae 9 :i* ! numb]s = ea* actual ellipticity are equal & all are ori5t$ at r&om4 ,,table ,x ,actual ,app>5t --------------------------------------- ,e#j ,e#a ,e#b ,e#c ,e#d ---------------------------------------- ------- ,e#g #j4jee #j4aaa #j4aad #j4aaf #j4aba ,e#f 4#jei 4#abc 4#abf 4#acc 4#adh ,e#e 4#jfg 4#adj 4#adh 4#aff 4#baf ,e#d 4#jgi 4#afi 4#aij 4#bej #j4cab ,e#c 4#ajj 4#bbe 4#bii #j4cgf ,e#b 4#ade 4#cgh #j4dgg ,e#a #j4cjj #j4gjj ,e#j #a4jjj --------------------------------------- ,total #a4hje #a4hdf #a4ced #a4jda #j4gig #j4bbf #j4bca #j4afi #j4acj #j4ajj ---------------------------------------- ------- ,actual ,app>5t ---------------------------------------- -- ,e#e ,e#f ,e#g ,total ---------------------------------------- -- ,e#g #j4acb #j4afd #j4ahg #a4jjj ,e#f 4#ahg #j4bbd ,e#e #j4bfc ---------------------------------- ,total #j4ehb #j4chh #j4ahg #h4jjj #j4jgc #j4jdi #j4jbc #a4jjj ---------------------------------------- -- ,f ?is table & ! actual numb]s 9 ! obs]v$ classes z read f a smoo!d curve1 ! numb]s ( ea* actual ellipticity m+l$ 9 ! obs]v$ classes c be det]m9$4 ,= in/ance1 ! f\r nebulae obs]v$ z ,e#g repres5t #j4ahg ( ! total numb] ( actual ,e#g4 ,! o!rs are di/ribut$ among ! obs]v$ classes ,e#j to ,e#f accord+ to ! p]c5tages li/$ 9 ,table ,x4 ,six nebulae are obs]v$ z ,e#f1 b #c4f ( ^! are actually ,e#g4 ,! rema9+ #b4d actual ,e#f nebulae repres5t #j4bbd ( ! total numb] ( t actual ellipticity1 ! o!rs1 z be=e1 be+ scatt]$ among ! obs]v$ classes ,e#j to ,e#e4 ,table ,,xi gives ! complete analysis & is simil> to ,table ,x except t ! p]c5tages 9 ! latt] are replac$ by ! actual numb]s indicat$ by ! obs]vations4 ,f9ally1 ! mean values ( ,c#g - ,ce are calculat$ f ! numb]s ( nebulae 9 ! v>i\s columns ( ,table ,,xi toge!r ) ! values ( ,c#g - ,ce = ! pure classes z d]iv$ f =mula 7#d74 ,! results are li/$ 9 ! f\r? column ( ,table ,,xii foll[+ ^? = ! pure & ! obs]v$ classes4 ,9 det]m9+ ! obs]v$ values1 ,n4,g4,c4 #ebd & #ciih are includ$ z ,e#j & ,e#a1 al?\gh 9 ,table ,i !y are li/$ z peculi>1 because !y are obvi\sly mu* flatt5$ nebulae ^: m9or axes are close to ! l9e ( sight4 ,,table ,,xi ,app>5t ,actual ------------------------------------- ,e#j ,e#a ,e#b ,e#c ,e#d ---------------------------------------- --------- ,e#g #a4b #b4d #b4e #b4e #b4f ,e#f 4#f #a4c #a4d #a4e #a4f ,e#e 4#h #a4g #a4h #b4j #b4g ,e#d 4#h #a4g #a4i #b4e #c4a ,e#c #j4i #b4a #b4h #c4e ,e#b #a4a #b4i #c4f ,e#a #a4g #c4i ,e#j #i4i ---------------------------------------- --------- ,total99 #ag4j #af4j #ad4j #ab4j #aj4j ---------------------------------------- --------- ,app>5t ,actual ------------------------------- ,e#e ,e#f ,e#g ,total ---------------------------------------- ,e#g #b4i #c4f #d4j #ba4g ,e#f #b4j #b4d #aj4h ,e#e #c4a #ab4a ,e#d #aj4j ,e#c #i4c ,e#b #g4f ,e#a #e4f ,e#j #i4i ---------------------------------------- ,total99 #h4j #f4j #d4j #hg4j ---------------------------------------- 99 ,! totals repres5t ! numb]s 9 ! obs]v$ classes z read f a smoo? curve4 ,! obs]v$ values 9 g5]al fall betwe5 ^? = ! pure classes & ^? correspond+ to r&om ori5tation4 ,!y are ( ! same ord] z ! latt]1 & ! discrepancies are p]haps n unacc\ntably l>ge 9 view ( ! nature & ! limit$ ext5t ( ! mat]ial4 ,!re is a sy/ematic diff]5ce1 h[ev]1 av]ag+ ab\t #j4b mag41 9 ! s5se t ! obs]v$ values are too l>ge1 & increas+ ) decreas+ ellipticity4 ,"o explanation is t ! obs]v$ classes are pur] ?an is expect$ on ! assumption ( r&om ori5tation4 ,?is view is support$ by ! relatively small disp]sion 9 ,c1 z may be se5 9 ,table ,i & ,figure #b1 among ! nebulae ( a giv5 class1 b x is difficult to acc\nt = any su* selective effect 9 ! obs]vations4 ,! discrepancies may be l>gely elim9at$ by an arbitr>y adju/m5t ( ! numb]s ( nebulae ) v>i\s degrees ( actual ellipticity2 = in/ance1 ! values 9 ! la/ column ( ,table ,,xii1 calculat$ on ! assumption ( equal numb]s1 agree v well ) ! obs]v$ values1 al?\gh ! result+ numb]s hav+ ! v>i\s app>5t ellipticities diff] slightly f ^? obs]v$4 ,! obs]v$ values1 h[ev]1 c aga9 be acc\nt$ = by ! inclusion ( "s flatt] nebulae among ! classes ,e#f & ,e#g4 ,v e>ly ,sa or ,s,ba nebulae might easily be mi/ak5 = ,e nebulae :5 ori5t$ edge-on1 al?\gh !y w\ld be readily recogniz$ :5 ev5 slightly tilt$4 ,if ! num]ical results fully repres5t$ actual /ati/ical laws1 ! explanation w\ld be s\ght 9 ! physical nature ( ! nebulae4 ,! *ange f ellipsoidal to l5ticul> figures1 noticeable 9 ! lat]-type nebulae1 w\ld affect ! results 9 ! prop] direction1 z w\ld also a progressive %ort5+ ( ! pol> axis4 ,! discrepancies1 h[ev]1 are second-ord] effects1 & s9ce !y may be due to accid5tal v>iations f r&om ori5tation1 a fur!r discussion mu/ await ! accumulation ( m data4 ,,table ,,xii ,diff]5tial ,values ( ,c ,r&om ,ori5tation --------------------- ,class ,pure ,classes ,obs]v$ ,no4 z ,obs]v$ ,equal ,no4 ---------------------------------------- -------------------- ,c#g-;,c#g #j4jj #j4jj #j4jj #j4jj ,c#f #j4fc #j4ce99 #j4be #j4ce ,c#e #a4aj #j4gj99 #j4eh #j4gj ,c#d #a4ea #j4he #a4aa #a4ja ,c#c #a4hd #a4db #j4hg #a4bh ,c#b #b4ac #a4fg #a4cc #a4ee ,c#a #b4ci #b4ja #a4ed #a4hc ,c#j #b4fb #b4ag #b4ae #b4be ---------------------------------------- -------------------- 99 ,read f smoo? curve 9 ,fig4 #f4 ,! small numb]s ( obs]v$ ,e#e & ,e#f nebulae ju/ify ?is proc$ure4 ,! o!r values are ! means actually obs]v$4 ,n4,g4,c4 #ebd & #ciih are includ$ z ,e#j & ,e#a1 respectively4 ,mean:ile1 x is evid5t t1 to a fir/ approximation at lea/1 ! pol> diamet]s alone det]m9e ! total lum9osities ( all elliptical nebulae1 & ! entire s]ies c be repres5t$ by ! v>i\s configurations ( an orig9ally globul> mass exp&+ equatorially4 ,a s+le =mula repres5ts ! relation1 9 :i* ! value ( ,c is t correspond+ to ! pure type ,e#j4 ,f ,table ,,xii1 ?is is f\nd to be #b4fb mag4 less ?an ! value ( ,c#g ,! latt] is obs]v$ to be #ab4ge1 h5ce m,t #e log b #aj4ac4 7#e7 ,if ?is relation held = ! spirals z well1 ! pol> diamet]s c\ld be calculat$ f ! measur$ magnitudes4 ,un=tunately1 x has n be5 possible to measure accurately ! pol> diamet]s directly1 & h5ce to te/ ! "q1 b !y h be5 comput$ = ! mean magnitudes ( ! ,sa1 ,sb1 & ,sc nebulae z giv5 9 ,table ,,iii1 & ! ratios ( ! axes h be5 d]iv$ by a comp>ison ( ^! hypo!tical values ) ! means ( ! measur$ maximum diamet]s4 ,! results1 #a to #d4d1 #a to #e4g1 & #a to #g4c1 respectively1 al?\gh ( ! "r ord]1 appe> to be some:at too high4 ,an exam9ation ( ! photographs indicates values ( ! ord] ( #a to #e4e1 #a to #h1 & #a to #aj1 b ! mat]ial is meag] & may n be repres5tative4 ,! comp>ison emphasizes1 h[ev]1 ! homog5eity & ! progressive nature ( ! entire sequ5ce ( nebulae & l5ds "s additional color to ! assumption t x repres5ts v>i\s aspects ( ! same fundam5tal type ( sy/em4 ,f ! dynamical po9t ( view1 ! empirical results are consi/5t ) ! g5]al ord] ( ev5ts 9 ,jeans's !ory4 ,?us int]pret$1 ! s]ies is "o ( expansion1 & ! scale ( types becomes ! "t scale 9 ! evolution>y hi/ory ( nebulae4 ,9 two respects ?is scale is n entirely arbitr>y4 ,among ! elliptical nebulae ! successive types diff] by equal increm5ts 9 ! ellipticity or ! degree ( flatt5+1 & among ! spirals ! int]m$iate /age is midway betwe5 ! two end-/ages 9 ! /ructural features z well z 9 ! lum9osity relations4 ,"o o!r feature ( ! curves may be discuss$ f ! po9t ( view ( ,jeans's !ory be=e return+ to ! /rictly empirical attitude4 ,! close agreem5t ( ! diamet]s = ! /ages ,e#g & ,sa sugge/s t ! transition f ! l5ticul> nebula to ! normal spiral =m is n cataclysmic4 ,if ! transition 7 gradual1 h[ev]1 we %\ld expect to obs]ve occasional objects 9 ! v process1 b among ! ?\s& or s nebulae ^: images h be5 inspect$1 n "o cle> case ( a transition =m has be5 detect$4 ,! obs]vations jump sudd5ly f l5ticul> nebulae ) no trace ( /ructure to spirals 9 :i* ! arms are fully develop$4 ,if ! num]ical data c\ld be fully tru/$1 ! ,s,ba =ms w\ld fill ! gap4 ,among ^! nebulae1 ! transition f ! l5ticul> to ! spiral ) arms is gradual & complete4 ,x is tempt+ to suppose t ! b>r$ spirals d n =m an indep5d5t s]ies p>allel ) t ( ! normal spirals1 b t all or mo/ spirals beg9 life ) ! b>1 al?\gh only a few ma9ta9 x conspicu\sly ?r\gh\t _! hi/ory4 ,?is w\ld also acc\nt = ! fact t ! relative numb]s ( ! ,s,ba nebulae are int]m$iate to ^? ( ! l5ticul> & ( ! ,sa4 ,! normal spirals become m num]\s z ! sequ5ce progresses1 :ile ! numb]s ( b>r$ spirals1 on ! contr>y1 actually decrease ) advanc+ type4 ,,relation ,,betwe5 ,,nucle> ,,lum9osities ,,& ,,diamet]s ,visual magnitudes h be5 det]m9$ by ,hopmann = ! nuclei ( #cg ( ! nebulae includ$ 9 ! pres5t discussion4 ,^! data1 toge!r ) types & diamet]s ( ! nebulae1 are li/$ 9 ,table ,,xiii4 ,:5 ! magnitudes are plott$ directly aga9/ ! log>i?ms ( ! diamet]s1 !y %[ little or no correlation4 ,:51 h[ev]1 ! nebulae are r$uc$ to ! /&>d type 7by apply+ corrections = diff]5ces 9 diamet] along ! sequ5ce71 a decid$ correlation is f\nd ^: coeffici5t is #j4gf4 ,?is is %[n 9 ,figure #i4 ,! simple mean ( ! two regression curves is mn #ad4de - #d4id log d1 7#f7 :]e ! slope diff]s by ab\t #a p] c5t f t 9 =mula 7#b74 ,! li/ conta9s #af elliptical nebulae1 #ae normal1 & #f b>r$ spirals4 ,! nebulae are fairly repres5tative1 except t few late-type spirals are includ$4 ,?is is an effect ( selection due to ! fact t nuclei become less & less conspicu\s z ! sequ5ce progresses4 ,! same result c be d]iv$ f a /udy ( ! diff]5ces1 mn - m,t1 = ! individual nebulae4 ,! mean value is #a4ee #j4jh1 & ! av]age residual is #j4fj mag4 ,means = ! sep>ate types are to be f\nd 9 ,table ,,xiv4 ,,table ,,xiii ,diamet]s & ,nucle> ,magnitudes ,n4,g4,c4 ,type log d mn ,hopmann mn ,r$uc$ ---------------------------------------- ------------------- #bba ,e#b #j4db #i4hd #aa4he #ajbc ,s,ba 4#gh #aa4hf #aa4hf #bhda ,sb #j4gh #ab4jh #aa4ai #cjca ,sb #a4bj #aj4id #aj4je #caae ,e#g #j4fj #aj4hc #aa4ji #ccea ,s,bb 4#dh #ab4ca #ab4ae #ccfh ,sa 4#he #aa4fh #aa4dc #ccgi ,e#j 4#cj #aa4ee #ad4bg #cdab ,s,ba 4#dj #aa4ei #aa4ei #cdhi ,sb 4#dj #aa4ed #aj4fe #cfbf ,sa 4#bh #ab4cg #ab4ab #cfbg ,sb 4#ij #ab4jc #aa4ad #dabe ,e#d 4#cj #aa4gd #ac4jd #dbaf ,sb 4#he #aa4fe #aj4gf #dbgh ,e#a 4#j #ab4jb #ad4ch #dcgd ,e#a 4#jh #aa4dc #ac4gi #dchb ,e#d 4#dh #aa4gg #ac4jg #ddce ,e#f 4#aa #aa4fe #ab4bf #ddch ,sb 4#ed #aa4hc #aj4id #ddhf ,e#j 4#cj #aa4bc #ac4ie #dedf ,e#f 4#ah #aa4ge #ab4cf #deeb ,e#j 4#bc #aa4ei #ad4ca #defi ,sc 4#fe #ab4je #aj4eg #degi ,s,bc 4#de #aa4dh #aj4jg #dfba ,e#e 4#cj #aa4fj #ab4ef #dfcf ,e#a 4#jh #aa4ig #ad4cc #dfdi ,e#b 4#cj #aa4eg #ac4eh #dfig ,e#f 4#dh #aj4ij #aa4ea #dfii ,s,bb 4#eg #aj4gb #aj4ef #dgbe ,s,bb 4#gj #aa4ig #aa4ha #dgcf ,sb 4#gj #aj4cf #i4dg #ejje ,sc 4#gj #ab4jd #aj4ef #ejcc ,sc #j4gh #ab4ch #aj4ij #eaid ,sc #a4jh #aa4ch #i4ij #ecbb ,e#c #j4ae #ab4aj #ac4gf #ehff ,sa 4#dh #aa4gf #aa4ea #gcca ,sb #j4ie #aa4hb #aj4ic ,means #j4eji #aa4fj #aa4ij ---------------------------------------- ------------------- ,! l[ value = ,sa-,s,ba is due to ,n4,g4,c4 #ehff1 = :i* ! magnitude diff]5ce ( #j4jf is c]ta9ly 9 error1 & ! high value = ,sc & ,s,bc1 to ,m #ea1 = :i* ! diff]5ce ( #c4ih mag4 is n repres5tative4 ,! latt] is acc\nt$ = 9 "p by ! fact t ! m,t ref]s to ! comb9$ magnitude ( ! ma9 spiral & ! outly+ mass1 ,n4,g4,c4 #eaie4 ,:5 ^! two cases are disc>d$1 ! f9al mean becomes #a4eb #j4je1 & ! av]age residual1 #j4eb mag41 is consi/5t ) ! probable errors ( ! magnitude det]m9ations4 ,! small numb]s ( objects )9 ea* class are insuffici5t = reliable conclusions conc]n+ slight v>iations along ! sequ5ce4 ,f ! con/ancy ( mn - m,t1 ! relation express$ by =mula 7#f7 necess>ily foll[s1 ! small diff]5ce 9 ! con/ant be+ acc\nt$ = by ! diff]5t me?ods ( h&l+ ! data4 ,illu/ration3 ,fig4 #i4--,relation betwe5 nucle> magnitudes & diamet]s4 ,! nebulae h be5 r$uc$ to ! /&>d type by apply+ corrections to ! magnitudes4 ,! p>allelism ( ! two curves repres5t+ =mulae 7#b7 & 7#f7 indicates t ! regul> extra-galactic nebulae1 :5 r$uc$ to ! /&>d type1 are simil> objects4 ,! mean surface brightness is con/ant1 & ! lum9osity ( ! nucleus1 z measur$ by ,hopmann1 is a con/ant fraction1 ab\t "o-f\r?1 ( ! total lum9osity ( ! nebulae4 ,if !re is a consid]able range 9 absolute magnitude & h5ce 9 actual dim5sions1 ! small] nebulae mu/ be fai?ful m9iatures ( ! l>g] ones4 ,,absolute ,,magnitudes ,,( ,,extra-,,galactic ,,nebulae ,reliable values ( di/ances1 & h5ce ( absolute magnitudes1 are re/rict$ to a v few ( ! brighte/ nebulae4 ,^! are d]iv$ f a /udy ( individual />s involv$ 9 ! nebulae1 among :i* c]ta9 types h be5 id5tifi$ ^: absolute magnitudes 9 ! galactic sy/em are well kn[n4 ,! me?od assumes t ! />s involv$ 9 ! nebulae are directly comp>able ) ! />s 9 our own sy/em1 & ?is is support$ by ! consi/5cy ( ! results d]iv$ f ! sev]al diff]5t types :i* h be5 id5tifi$4 ,,table ,,xiv ,type mn - m,t ,numb] ---------------------------------------- ---------------------------- ,e#j-;,e#c #a4fd 7#i7 ,e#d-;,e#g #a4dc 7#g7 ,sa-,s,ba #j4ig 7#e7 #a4bg :5 ,n4,g4,c4 #ehff is omitt$ ,sb-,s,bb #a4gj 7#aa7 ,sc-,s,bc #a4gf 7#e7 #a4ai :5 ,n4,g4,c4 #eaid is omitt$ ---------------------------------------- ------------- ,unweight$ mean #a4ej 7#cg7 #a4de 7#ce7 ,weight$ mean #a4ee 7#cg7 #a4eb 7#ce7 ---------------------------------------- ---------------------------- ,,table ,,xv ,absolute ,magnitudes ( ,nebulae ,sy/em ,m,t ,m,s ---------------------------------------- ------ ,galaxy -#e4e ,m #ca -#ag4a #f4e ,,lmc #ag4j #h4j ,,smc #af4j #e4e ,m #cc #ae4a #f4e ,n4,g4,c4 #fhbb #ac4g #e4h ,m #aja #ac4e -#f4c ,m #cb -#ac4c --------------------------------- -#f4c -#i4j ,m,s - ,m,t --------------------------------- ,means -#ae4a -#ae4c ,adopt$ -#ae4b ---------------------------------------- ------ ,9 ,table ,,xv are li/$ absolute magnitudes ( ! entire sy/em & ( ! brighte/ />s involv$1 = ! galaxy & ! sev5 nebulae ^: di/ances are kn[n4 ,! data = ! ,magellanic ,cl\ds are tak5 f ,%apley's inve/igations4 ,! absolute magnitudes ( ! rema9+ nebulae 7 d]iv$ f ,holets*ek's app>5t magnitudes & ! di/ances z det]m9$ at ,m\nt ,wilson1 :]e ! /ell> magnitudes 7 also det]m9$4 ,m #cb is g5]ally assum$ to be associat$ ) ! great spiral ,m #ca1 because ! radial velocities are ne>ly equal & are unique 9 t !y are ! only l>ge negative velocities t h be5 f\nd among ! extra-galactic nebulae4 ,m #aja has be5 add$ to ! li/ on r weak evid5ce4 ,! brighte/ />s involv$ are slightly bright] ?an app>5t magnitude #ag4j1 & sev]al v>iables h be5 f\nd ) magnitudes at maxima fa9t] ?an #ai4j4 ,suffici5t obs]vations h n yet be5 accumulat$ to det]m9e ! light-curves ( ! v>iables1 b f analogy ) ! o!r nebulae !y are presum$ to be ,cepheids4 ,on ?is assumption1 bo? ! /> c\nts & ! v>iables lead to a di/ance ( ! ord] ( #a4g times ! di/ance ( ,m #cc4 ,! inclusion ( ,m #aja does n *ange ! mean magnitude ( ! brighte/ />s involv$1 b r$uces ! mean magnitude ( ! nebulae by #j4b4 ,! range 9 ! />s involv$ is ab\t #b4e mag41 & 9 ! total lum9osities ( ! nebulae1 ab\t #c4h mag4 ,?is latt] is consi/5t ) ! scatt] 9 ! diagram exhibit+ ! relation betwe5 total lum9osities & diamet]s4 ,! associat$ objects1 ,m #ca & #cb1 repres5t ! extreme limits among ! kn[n sy/ems1 & ! mean ( ^! two is v close to ! mean ( !m all4 ,,lum9osity ,,( ,,/>s ,,involv$ ,,9 ,,nebulae ,! numb] ( nebulae ( kn[n di/ance is too small to s]ve z a basis = e/imates ( ! range 9 absolute magnitude among nebulae 9 g5]al4 ,fur!r in=mation1 h[ev]1 c be d]iv$ f a comp>ison ( total app>5t magnitudes ) app>5t magnitudes ( ! brighte/ />s involv$1 on ! reasonable assumption1 support$ by su* evid5ce z is available1 t ! brighte/ />s 9 isolat$ sy/ems are ( ab\t ! same intr9sic lum9osity4 ,! mo/ conv5i5t proc$ure is to te/ ! con/ancy ( ! diff]5ces 9 app>5t magnitude betwe5 ! brighte/ />s involv$ & ! nebulae !mselves1 ov] z wide a range z possible 9 ! latt] quantities4 ,an exam9ation ( ! photographs 9 ! ,m\nt ,wilson collection has reveal$ no />s 9 ! v fa9t objects or 9 ! bright elliptical nebulae & e>ly-type spirals4 ,?is 0 to be expect$ f ! conclusions previ\sly d]iv$4 ,obs]vations 7 !re=e conf9$ to int]m$iate- & late-type spirals & ! irregul> nebulae to ! limit+ visual magnitude #aj4e4 ,! ,magellanic ,cl\ds & ,n4,g4,c4 #fhbb 7 add$ to ! nebulae 9 ,holets*ek's li/4 ,altoge!r1 data 7 available = #cb objects1 or ab\t #fj p] c5t ( ! total numb] 9 ! sky to ! adopt$ limit4 ,= ?is reason x is believ$ t ! results are ?or\ghly repres5tative4 ,,table ,,xvi ,diff]5ce 9 ,magnitude betwe5 ,nebulae & ,_! ,brighte/ ,/>s ,n4,g4,c4 ms m,t ms - m,t ---------------------------------------- ---------- ,sb ---------------------------------------- ---------- #bbd #ae4e #e4j #aj4e #ajfh #ag4e #i4a #h4d #bhda #ai4e #i4d #aj4a #cjca #ah4e #h4c #aj4b #ccaj #ai4j #aj4d #h4f #cfbc #bj4j #i4i #aj4a #cfbg #ah4e #i4a #i4d #ddch #ai4j #aj4c #h4g #ddej #ai4e #aj4j #i4e #dgcf #ag4c #h4d #h4i #dhbf #ai4e #i4b #aj4c #ejee #ai4j #i4f #i4d #egdf #ai4e #aj4d #i4a #gcca #ai4j #aj4d #h4f ---------------------------------------- ---------- ,s,bb ---------------------------------------- ---------- #dfii #ai4e #aj4j #i4e ---------------------------------------- ---------- ,sc ---------------------------------------- ---------- #bec #ah4c #i4c #i4j #eih #ae4f #g4j #h4f #bdjc #ag4c #h4g #h4f #bfhc #bj4j #i4i #aj4a #bijc #ai4j #i4a #i4i #dbed #ah4e #aj4d #h4a #dcba #ah4h #aj4e #h4c #ddad #ai4e #aj4a #i4d #ddij #ah4h #aj4b #h4f #eaid #ag4c #g4d #i4i #ebcf #ah4f #aj4d #h4b #edeg #ag4j #i4i #g4a ---------------------------------------- ---------- ,irr4 ---------------------------------------- ---------- ,,lmc #i4e #j4e #i4j ,,smc #ab4j #a4e #aj4e #cjcd #ai4e #i4j #aj4e #dddi #ag4h #i4e #h4c #fhbb #ae4h #h4e #g4c ---------------------------------------- ---------- ,! data are li/$ 9 ,table ,,xvi & are %[n graphically 9 ,figure #aj4 ,! lum9osities ( ! brighte/ />s are giv5 9 photographic magnitudes4 ,= ! ,magellanic ,cl\ds1 ,m #cc1 & ,n4,g4,c4 #fhbb1 ^! 7 obta9$ f publi%$ /> c\nts4 ,= ,m #ca1 #ea1 #fc1 #ha1 #id1 & ,n4,g4,c4 #bdjc1 !y dep5d ^u unpubli%$ c\nts1 = :i* ! magnitudes 7 det]m9$ by comp>isons ) ,select$ ,areas4 ,= ! rema9+ nebulae1 ! magnitudes ( />s 7 e/imat$ ) v>y+ degrees ( precision1 b are probably less ?an #j4e mag4 9 error4 ,illu/ration3 ,fig4 #aj4--,relation betwe5 total magnitudes ( extra-galactic nebulae & magnitudes ( ! brighte/ />s involv$4 ,diff]5ces betwe5 total visual magnitudes ( nebulae & ! photographic magnitudes ( ! brighte/ />s are plott$ aga9/ ! total magnitudes4 ,! dots repres5t cases 9 :i* ! />s c\ld actually be detect$2 ! incomplete crosses repres5t cases 9 :i* />s c\ld n be detect$1 & h5ce give l[] limits = ! magnitude diff]5ces4 ,! diagonal l9e indicates ! approximate limits ( obs]vation1 fix$ by ! circum/ance t1 9 g5]al1 />s fa9t] ?an #ai4e probably w\ld n be detect$ on ! nebul\s backgr\nd4 ,! slop+ l9e to ! "r 9 ,figure #aj repres5ts ! limits ( ! obs]vations1 =1 f a /udy ( ! plates !mselves1 x appe>$ improbable t />s fa9t] ?an ab\t #ai4e c\ld be detect$ ) c]ta9ty on a nebul\s backgr\nd4 ,po9ts repres5t+ nebulae 9 :i* individual />s c\ld n be f\nd %\ld lie 9 ?is exclud$ region above ! l9e1 & _! scatt] is presumably comp>able ) t ( ! po9ts actually det]m9$ bel[ ! l9e4 ,:5 all[ance is made = ?is inaccessible region1 ! data c be int]pret$ z %[+ a mod]ate disp]sion ar\nd ! mean ord9ate ms - m,t #i4j4 7#g7 ,! range 9 total magnitudes is suffici5tly l>ge 9 comp>ison ) ! disp]sion to l5d consid]able confid5ce to ! conclusion4 ,! total range ( f\r1 & ! av]age disp]sion ( less ?an #a mag41 are comp>able ) ^? 9 ,table ,,xv & 9 ,figure #g1 & agree ) ! =m] 9 indicat+ a con/ant ord] ( absolute magnitude4 ,! mean absolute magnitude ( ! brighte/ />s 9 ! nebulae li/$ 9 ,table ,,xv1 comb9$ ) ! mean diff]5ce betwe5 nebulae & _! brighte/ />s1 furni%es a mean absolute magnitude ( -#ae4c = ! nebulae li/$ 9 ,table ,,xvi4 ,?is diff]s by only #j4b mag4 f ! av]age ( ! nebulae 9 ,table ,,xv1 & ! mean ( ! two1 -#ae4b1 c be us$ z ! absolute magnitude ( int]m$iate- & late-type spirals & irregul> nebulae ^: app>5t magnitudes are bright] ?an #aj4e4 ,! disp]sion is small & c safely be neglect$ 9 /ati/ical inve/igations4 ,?is is z f> z ! positive evid5ce c be foll[$4 ,= reasons already giv51 h[ev]1 x is presum$ t ! e>li] nebulae1 ! elliptical & ! e>ly-type spirals1 are ( ! same ord] ( absolute magnitude z ! lat]4 ,! "o elliptical nebula ^: di/ance is kn[n1 ,m #cb1 is consi/5t ) ?is hypo!sis4 ,conclusions conc]n+ ! intr9sic lum9osities ( ! app>5tly fa9t] nebulae are 9 ! nature ( extrapolations ( ! results f\nd = ! bright] objects4 ,:5 ! nebulae are r$uc$ to a /&>d type1 !y are f\nd to be con/ruct$ on a s+le model1 ) ! total lum9osities v>y+ directly z ! squ>e ( ! diamet]s4 ,! mo/ g5]al int]pretation ( ?is relation is t ! mean surface brightness is con/ant1 b ! small range 9 absolute magnitudes among ! bright] nebulae indicates t1 among ^! objects at lea/1 ! relation m]ely expresses ! op]ation ( ! inv]se-squ>e law on comp>able objects di/ribut$ at diff]5t di/ances4 ,! actual obs]v$ range cov]$ by ?is re/rict$ int]pretation is f app>5t magnitude #j4e to #aj4e4 ,! homog5eity ( ! correlation diagrams & ! complete abs5ce ( evid5ce to ! contr>y ju/ify ! extrapolation ( ! re/rict$ int]pretation to cov] ! #b or #c mag4 beyond ! limits ( actual obs]vation4 ,^! consid]ations lead to ! hypo!sis t ! nebulae treat$ 9 ! pres5t discussion are all ( ! same ord] ( absolute magnitude2 9 fact1 !y l5d consid]able color to ! assumption t extra-galactic nebulae 9 g5]al are ( ! same ord] ( absolute magnitude &1 )9 ea* class1 ( ! same ord] ( actual dim5sions4 ,"s support to ?is assumption is f\nd 9 ! obs]v$ abs5ce ( individual />s 9 ! app>5tly fa9t] late-type nebulae4 ,if ! lum9osity ( ! brighte/ />s involv$ is indep5d5t ( ! total lum9osity ( a nebula1 z is c]ta9ly ! case among ! bright] objects1 !n1 :5 no />s bright] ?an #ai4e are f\nd1 ! nebulae mu/ 9 g5]al be bright] ?an absolute magnitude m,t - #be4h :]e m,t is ! total app>5t magnitude4 ,on ?is assumption1 ! fa9te/ ( ! ,holets*ek nebulae are bright] ?an -#ab4e & h5ce ( ! same g5]al ord] z ! bright] nebulae4 ,once ! assumption ( a uni=m ord] ( lum9osity is accept$ z a work+ hypo!sis1 ! app>5t magnitudes become1 = /ati/ical purposes1 a measure ( ! di/ances4 ,= a mean absolute magnitude ( -#ae4b1 ! di/ance 9 p>secs is log ,d #j4b m,t #d4jd4 7#h7 ,,dim5sions ,,( ,,extra-,,galactic ,,nebulae ,:5 ! di/ances are kn[n1 x is possible to d]ive actual dim5sions & h5ce to calibrate ! curve 9 ,figure #f1 :i* exhibits ! app>5t diamet]s z a function ( type1 or /age 9 ! nebul> sequ5ce1 = nebulae ( a giv5 app>5t magnitude4 ,! mean maximum diamet]s 9 p>secs correspond+ to ! diff]5t mean types are giv5 9 ,table ,,xvii4 ,= ! elliptical nebulae1 values are giv5 bo? = ! /ati/ical mean obs]v$ diamet]s & = ! diamet] z calculat$ = ! pure types4 ,spirals at ! la/ /age 9 ! obs]v$ sequ5ce h diamet]s ( ! ord] ( #cjjj p>secs4 ,assum+ #a3aj z ! ratio ( ! two axes1 ! correspond+ volume is ( ! ord] ( #a4daji cubic p>secs1 & ! mean lum9osity d5sity is ( ! ord] ( #g4g absolute magnitudes p] cubic p>sec z comp>$ ) #h4ae = ! galactic sy/em 9 ! vic9ity ( ! sun4 ,^! results agree ) ^? ( ,se>es :o1 f a /udy ( surface brightness1 conclud$ t ! galactic sy/em mu/ be plac$ at ! end (1 if n actually outside1 ! s]ies ( kn[n spirals :5 arrang$ accord+ to d5sity4#ai ,,table ,,xvii ,type ,diamet] 9 ,p>secs ,type ,diamet] 9 ,p>secs ---------------------- ,obs4 ,cal4 ---------------------------------------- ------------------ ,e#j #cfj #cdj ,sa #adej ,e#a #dcj #chj ,sb #aijj ,e#b #ejj #dcj ,sc #bejj ,e#c #eij #dij ,e#d #gjj #egj ,s,ba #abhj ,e#e #haj #fhj ,s,bb #acbj ,e#f #ifj #hej ,s,bc #bbej ,e#g #aacj #aacj ,irr #aejj ---------------------------------------- ------------------ ,,masses ,,( ,,extra-,,galactic ,,nebulae ,spectroscopic rotations are available = ! spirals ,m #cabj & ,n4,g4,c4 #deid1ba & f ^! x is possible to e/imate ! masses on ! assumption ( orbital rotation ar\nd ! nucleus4 ,! di/ances ( ! nebulae are involv$1 h[ev]1 & ?is is kn[n accurately only = ,m #ca2 = ,n4,g4,c4 #deid x mu/ be e/imat$ f ! app>5t lum9osity4 ,ano!r me?od ( e/imat+ masses is t us$ by pik#bb 9 d]iv+ 8 e/imate ( ! di/ance ( ,m #ca4 ,x is bas$ on ! assumption t lum9\s mat]ial 9 ! spirals has ab\t ! same coeffici5t ( emission z ! mat]ial 9 ! galactic sy/em4 pik comput$ ! ratio ( lum9osity to mass = our own sy/em 9 t]ms ( ! sun z unity1 us+ ,jeans's value#bc = ! relative proportion ( lum9\s to non-lum9\s mat]ial4 ,! relation is ,mass #b4f,l4 7#i7 ,! application ( ?is me?od ( det]m9+ ord]s ( masses seems to be ju/ifi$1 at lea/ 9 ! case ( ! lat]-type spirals & irregul> nebulae1 by ! _m analogies ) ! galactic sy/em itself4 ,moreov]1 :5 appli$ to ,m #ca1 :]e ! di/ance is fairly well kn[n1 x leads to a mass ( ! same ord] z t d]iv$ f ! spectrographic rotation3 ,,mass ,,( ,m #ca ,spectrographic rotation #c4eaji pik's me?od #a4faji ,! di/ance ( ,n4,g4,c4 #deid is unkn[n1 b ! assumption t x is a normal nebula ) an absolute magnitude ( -#ae4b places x at #gjj1jjj p>secs4 ,! ord]s ( ! mass by ! two me?ods are !n ,,mass ,,( ,n4,g4,c4 #deid ,spectrographic rotation #b4jaji pik's me?od #b4fajh ,"h aga9 ! result+ masses are ( ! same ord]4 ,!y c be made to agree z well z ^? = ,m #ca by ! n unreasonable assumption t ! absolute lum9osity ( ! nebula is #b mag4 or s bright] ?an normal4 pik's me?od leads to values t are reasonable & fairly consi/5t ) ^? obta9$ by ! indep5d5t spectrographic me?od4 ,!re=e1 9 ! abs5ce ( o!r res\rces1 its use = d]iv+ ! mass ( ! normal nebula appe>s to be p]missible4 ,! result1 #b4f #ajh 1 correspond+ to an absolute magnitude ( -#ae4b1 is probably ( ! "r ord]4 ,! two te/ cases sugge/ t ?is value may be slightly l[1 b ! data are n suffici5t to w>rant any empirical corrections4 ,,numb]s ,,( ,,nebulae ,,to ,,diff]5t ,,limit+ ,,magnitudes ,! numb]s ( nebulae to diff]5t limit+ magnitudes c be us$ to te/ ! con/ancy ( ! d5sity function1 or1 on ! hypo!sis ( uni=m lum9osities1 to det]m9e ! di/ribution 9 space4 ,! nebulae bright] ?an ab\t ! t5? magnitude are kn[n individually4 ,^? n includ$ 9 ,holets*ek's li/ are3 ! ,magellanic ,cl\ds1 ! two nebulae ,n4,g4,c4 #ee & #ajig1 betwe5 #i4j & #i4e mag41 & ! sev5 nebulae ,n4,g4,c4 #acd1 #bhi1 #acfe1 #aecc1 #aeei1 #agib1 & #cgbf1 all betwe5 #i4e & #aj4j mag4 ,a fair e/imate ( ! numb] betwe5 #aj4j & #aa4j mag4 c be d]iv$ f a comp>ison ( ,holets*ek's li/ ) t ( ,h>dca/le1 an inspection ( images on ! ,frankl9-,adams *>ts & o!r photographs1 & a correlation betwe5 kn[n total magnitudes & ! descriptions ( size & brightness 9 ,drey]'s catalogues4 ,x appe>s t v few ( ^! objects 7 miss$ by ,holets*ek 9 ! nor!rn sky--n m ?an six ( ,h>dca/le's nebulae4 ,= ! s\!rn sky1 beyond ! region obs]v$ by ,holets*ek1 ! results are v unc]ta91 b probable upp] & l[] limits 7 det]m9$ z #ej & #bj1 respectively4 ,! bright] nebulae are kn[n to be sc>ce 9 ^? regions4 ,a mean value ( #ce leads to a total #bie = ! entire sky1 & ?is is at lea/ ( ! prop] ord]4 ,! numb] ( nebulae betwe5 #aa4j & #ab4j mag4 c be e/imat$ on ! assumption t ! two li/s1 ,holets*ek's & ,h>dca/le's1 are ab\t equally complete )9 ?is range4 ,!y are kn[n to be comp>able = ! bright] nebulae1 &1 moreov]1 ! total numb]s includ$ 9 ! two li/s = ! same area ( ! sky1 t nor? ( decl9ation -#aj1 are v ne>ly equal--#djj z comp>$ ) #djh4 ,! p]c5tages ( ,holets*ek's nebulae includ$ by ,h>dca/le 7 fir/ det]m9$ z a function ( magnitude4 ,)9 ! half-magnitude int]val #aa4j to #aa4e1 = in/ance1 #fj p] c5t are 9 ,h>dca/le's li/4 ,if ! two li/s are equally complete &1 tak5 toge!r1 are exhau/ive1 ! total numb] 9 ! int]val w be #a4d times ! numb] ( ,holets*ek's nebulae4 ,! latt] is f\nd to be #ej f smoo!d frequ5cy curves ( ! magnitudes li/$ 9 ,tables ,i-,,iv4 ,! total numb] nor? ( -#aj is !re=e #gj4 ,?is c be correct$ to repres5t ! entire sky by apply+ ! factor #a4ge1 :i* is ! ratio ( ! total numb] ( ,h>dca/le's nebulae1 #gjj1 to ! numb] nor? ( -#aj1 #djj4 ,9 ?is mann] a reasonable e/imate ( #abc is obta9$ = ! numb] ( nebulae 9 ! entire sky betwe5 #aa4j & #aa4e mag4 ,simil>ly1 betwe5 #aa4e & #ab4j1 :]e #ej p] c5t ( ,holets*ek's nebulae are includ$ 9 ,h>dca/le's li/1 ! total numb] = ! entire sky is f\nd to be #bcf4 ,! greate/ unc]ta9ty 9 ^! figures arises f ! assumption t ! two li/s toge!r are complete to ! twelf? magnitude4 ,! figures are probably too small1 b no /&>ds are available by :i* !y c be correct$4 ,x is believ$1 h[ev]1 t ! errors are c]ta9ly less ?an #ej p] c5t & probably n m ?an #be p] c5t4 ,?is w n be excessive 9 view ( ! possible deviations f uni=m di/ribution :]e s limit$ a numb] ( objects is consid]$4 ,beyond #ab4j mag4 ! li/s quickly lose _! aspect ( complet5ess & _c be us$ = ! pres5t purpose4 ,!re are available1 h[ev]1 ! c\nts by ,fa?#bd ( nebulae f\nd on plates ( ,select$ ,areas made ) ! #fj-;in* reflector at ,m\nt ,wilson4 ,! exposures 7 uni=mly #fj m9utes on fa/ plates & cov] ! ,areas 9 ! nor!rn sky d[n to & includ+ ! -#ae zone4 ,! limit+ photographic magnitudes = />s av]age ab\t #ah4e4 ,! c\nts h be5 c>efully revis$ by ,se>es#be & are ! basis = 8 e/imate ( #cjj1jjj nebulae 9 ! entire sky d[n to ?is limit4 ,approximate limit+ total magnitudes = ! nebulae 9 two ( ! ri*e/ fields1 ,s4,a4 #ef & #hj1 h be5 det]m9$ f extra-focal exposures ) ! #ajj-;in* reflector4 ,! results are #ag4g 9 ea* case1 & ?is1 correct$ by ! normal color-index ( su* objects1 gives a limit+ visual magnitude ( ab\t #af4g1 :i* c be us$ = comp>ison ) ! c\nts ( ! bright] nebulae4 ,! v>i\s data are collect$ 9 ,table ,,xviii1 :]e ! obs]v$ numb]s ( extra-galactic nebulae to diff]5t limits ( visual magnitude are comp>$ ) ^? comput$ on ! assumption ( uni=m di/ribution ( objects hav+ a con/ant absolute lum9osity4 ,! =mula us$ = ! computation is log ,n #j4f m,t textrm,con/ant1 :]e ! con/ant is ! value ( log ,n = m,t #j4 ,! value --#d4de is f\nd to fit ! obs]vational data fairly well4 ,! agreem5t betwe5 ! obs]v$ & comput$ log ,n ov] a range ( m ?an #h mag4 is consi/5t ) ! d\ble assumption ( uni=m lum9osity & uni=m di/ribution or1 m g5]ally1 indicates t ! d5sity function is indep5d5t ( ! di/ance4 ,! sy/ematic decrease 9 ! residuals ,o - ,c ) decreas+ lum9osity is probably )9 ! obs]vational errors1 b x may also be expla9$ z due to a clu/]+ ( nebulae 9 ! vic9ity ( ! galactic sy/em4 ,! clu/] 9 ,virgo alone acc\nts = an appreciable "p4 ,?is is a second-ord] effect 9 ! di/ribution1 h[ev]1 & w be discuss$ at l5g? 9 a lat] pap]4 ,,table ,,xviii ,numb]s ( ,nebulae to ,v>i\s ,limits ,,log ,n99 m,t ------------------ ,o - ,c ,,log ,d ,o ,c ---------------------------------------- ----- #h4e #j4he #j4fe #j4bj #e4gd #i4j #a4jh #j4ie 4#ac #e4hd #i4e #a4de #a4be 4#bj #e4id #aj4j #a4gc #a4ee 4#ah #f4jd #aj4e #a4ie #a4he 4#aj #f4ad #aa4j #b4ag #b4ae 4#jb #f4bd #aa4e #b4dc #b4de - 4#jb #f4cd #ab4j #b4gj #b4ge 4#je #f4dd #af4g #e4dh #e4eg -#j4ji #g4ch 7#ah4j7 7#f4ce7 7#g4fd7 ---------------------------------------- ----- 99 ,log ,n #j4f m,t - #d4de4 ,log ,d #j4b m,t #d4jd4 ,di/ances correspond+ to ! diff]5t limit+ magnitudes1 z d]iv$ f =mula 7#h71 are giv5 9 ! la/ column ( ,table ,,xviii4 ,! #cjj1jjj nebulae e/imat$ to ! limits repres5t$ by an h\r's exposure on fa/ plates ) ! #fj-;in* reflector appe> to be ! inhabitants ( space out to a di/ance ( ! ord] ( #b4d #ajg p>secs4 ,! #ajj-;in* reflector1 ) long exposures "u good conditions1 w probably rea* ! total visual magnitude #ah4j1 & ?is1 by a slight extrapolation1 is e/imat$ to repres5t a di/ance ( ! ord] ( #d4dajg p>secs or #a4dajh light-ye>s1 )9 :i* x is expect$ t ab\t two million nebulae %\ld be f\nd4 ,?is seems to repres5t ! pres5t b\nd>ies ( ! obs]vable region #c ( space4 ,,d5sity ,,( ,,space ,! data are n[ available = d]iv+ a value = ! ord] ( ! d5sity ( space4 ,?is is accompli%$ by means ( ! =mulae = ! numb]s ( nebulae to a giv5 limit+ magnitude & = ! di/ance 9 t]ms ( ! magnitude4 ,9 nebulae p] cubic p>sec1 ! d5sity is beg9align log rho log ,n - log ,v 7#j4f m,t - #d4de7 - logfrac #dc - #c7d4jd #j4b m,t7 -#ag4ai endalign 7#aa7 ,?is is a l[] limit1 = ! abs5ce ( nebulae 9 ! plane ( ! ,milky ,way has be5 ignor$4 ,! curr5t explanation ( ?is ph5om5on 9 t]ms ( obscuration by d>k cl\ds :i* encircle ! ,milky ,way is support$ by ! extra-galactic nature ( ! nebulae1 _! g5]al simil>ity to ! galactic sy/em1 & ! frequ5cy ) :i* p]iph]al belts ( obscur+ mat]ial are enc\nt]$ among ! spirals4 ,! kn[n cl\ds ( d>k nebulosity are int]ior features ( our sy/em1 & !y d n =m a cont9u\s belt4 ,9 ! regions :]e !y are lea/ conspicu\s1 h[ev]1 ! extra-galactic nebulae approa* ne>e/ to ! plane ( ! ,milky ,way1 _m be+ f\nd )9 #aj4 ,?is is consi/5t ) ! hypo!sis ( a p]iph]al belt ( absorption4 ,! only positive objection :i* has be5 urg$ to ?is explanation has be5 to ! effect t ! nebul> d5sity is a direct function ( galactic latitude4 ,accumulat+ evid5ce#bf has fail$ to confirm ?is view & indicates t x is l>gely due to ! influ5ce ( ! great clu/] 9 ,virgo1 "s #ae f ! nor? galactic pole4 ,!re is no correspond+ conc5tration 9 ! neighborhood ( ! s\? pole4 ,if an out] belt ( absorption is assum$1 :i*1 comb9$ ) ! kn[n inn] cl\ds1 obscures extra-galactic nebulae to a mean di/ance ( #ae f ! galactic plane1 ! value d]iv$ = ! d5sity ( space mu/ be increas$ by ne>ly #dj p] c5t4 ,?is w n *ange ! ord] ( ! value previ\sly det]m9$ & is )9 ! unc]ta9ty ( ! masses z d]iv$ by pik's me?od4 ,! new value is !n #iaj-ah nebulae p] cubic p>sec4 7#ab7 ,! correspond+ mean di/ance betwe5 nebulae is ( ! ord] ( #egj1jjj p>secs1 al?\gh 9 sev]al ( ! clu/]s ! di/ances betwe5 memb]s appe> to be a t5? ( ?is am\nt or less4 ,! d5sity c be r$uc$ to absolute units by sub/itut+ ! value = ! mean mass ( a nebula1 #b4fajh 4 ,!n1 s9ce ! mass ( ! sun 9 grams is #bajcc & #a p>sec is #c4aajah cm1 #a4eaj-ca grams p] cubic c5timet]4 7#ac7 ,?is mu/ be consid]$ z a l[] limit1 = loose mat]ial scatt]$ betwe5 ! sy/ems is entirely ignor$4 ,!re are no means ( e/imat+ ! ord] ( ! necess>y correction4 ,no positive evid5ce ( absorption by int]-nebul> mat]ial1 ei!r selective or g5]al1 has be5 f\nd1 nor %\ld we expect to f9d x unless ! am\nt ( ?is mat]ial is _m times t :i* is conc5trat$ 9 ! sy/ems4 ,,! ,,f9ite ,,univ]se ,,( ,,g5]al ,,relativity ,! mean d5sity ( space c be us$ to det]m9e ! dim5sions ( ! f9ite b b\ndless univ]se ( g5]al relativity4 ,de ,sitt]#bg made ! calculations "s ye>s ago1 b us$ values = ! d5sity1 #aj-bf & great]1 :i* are ( an entirely diff]5t ord] f t indicat$ by ! pres5t inve/igations4 ,z a consequ5ce1 ! v>i\s dim5sions1 bo? = sph]ical & = elliptical space1 7 small z comp>$ ) ! range ( exi/+ in/rum5ts4 ,= ! pres5t purpose1 ! simplifi$ equations :i* ,e9/e9 has d]iv$ = a sph]ically curv$ space c be us$4#bh ,:5 ,r1 ,v1 ,m1 & repres5t ! radius ( curvature1 volume1 mass1 & d5sity1 & k & c are ! gravitational con/ant & ! velocity ( light1 ,r fraccsqrt#dk cdot frac#asqrtrho1 7#ad7 ,v #bb,r#c1 7#ae7 ,m c#b_/bk ,r4 7#af7 ,sub/itut+ ! value f\nd = 1 #a4eaj-ca1 ! dim5sions become ,r #h4eajbh cm #b4gajaj p>secs1 7#ag7 ,v #a4aajhh cm #c4eajcb cubic p>secs1 7#ah7 ,m #a4hajeg grams #iajbb 4 7#ai7 ,! mass corresponds to #c4eajae normal nebulae4 ,! di/ance to :i* ! #ajj-;in* reflector %\ld detect ! normal nebula 0 f\nd to be ( ! ord] ( #d4dajge p>secs1 or ab\t #afjj ! radius ( curvature4 ,unusually bright nebulae1 su* z ,m #ca1 c\ld be photograph$ at sev]al times ?is di/ance1 & ) reasonable increases 9 ! spe$ ( plates & size ( telescopes x may become possible to obs]ve an appreciable fraction ( ! ,e9/e9 univ]se4 ,m\nt ,wilson ,obs]vatory ,septemb] #aibf #a ,contributions f ! ,m\nt ,wilson ,obs]vatory1 ,no4 #cbd4 #b ,^! are ! two ,magellanic ,cl\ds1 ,m #ca1 & ,m #cc4 #c ,bailey1 ,h>v>d ,annals1 #fj1 #aijh4 #d ,h>dca/le1 ,mon?ly ,notices1 #gd1 #fii1 #aiad4 #e ,?is e/imate by ,se>es is bas$ on a revision ( ,fa?'s c\nts ( nebulae 9 ,select$ ,areas 7,mt4 ,wilson ,contr41 ,no4 #big2 ,a/rophysical ,j\rnal1 #fb1 #afh1 #aibe74 #f 8,a ,g5]al ,/udy ( ,diffuse ,galactic ,nebulae10 ,mt4 ,wilson ,contr41 ,no4 #bda2 ,a/rophysical ,j\rnal1 #ef1 #afb1 #aibb4 #g ,! classification 0 pres5t$ 9 ! =m ( a memor&um to ! ,commission on ,nebulae ( ! ,int]national ,a/ronomical ,union 9 #aibc4 ,copies ( ! memor&um 7 di/ribut$ by ! *airman to all memb]s ( ! ,commission4 ,! classification 0 discuss$ at ! ,cambridge meet+ 9 #aibe1 & has be5 publi%$ 9 an acc\nt ( ! meet+ by ,mrs4 ,rob]ts 9 ,l',a/ronomie1 #dj1 #afi1 #aibf4 ,fur!r consid]ation ( ! matt] 0 left to a subcommittee1 ) a resolution t ! adopt$ sy/em %\ld be z purely descriptive z possible1 & free f any t]ms sugge/+ ord] ( physical developm5t 7,transactions ( ! ,i4,a4,u41 #b1 #aibe74 ,mrs4 ,rob]ts' report also indicates ! pref]5ce ( ! ,commission = ! t]m 8extra-galactic0 9 place ( ! orig9al1 & !n necess>ily non-committal1 8non-galactic40 ,mean:ile ,k4 ,lundm>k1 :o 0 pres5t at ! ,cambridge meet+ & has s9ce be5 appo9t$ a memb] ( ! ,commission1 has rec5tly publi%$ 7,arkiv fr ,matematik1 ,a/ronomi o* ,fysik1 ,b& #ai;,b1 ,no4 #h1 #aibf7 a classification1 :i*1 except = nom5clature1 is practically id5tical ) t submitt$ by me4 ,dr4 ,lundm>k makes no ackn[l$gm5ts or ref]5ces to ! discussions ( ! ,commission o!r ?an ^? = ! use ( ! t]m 8galactic40 #h ,problems ( ,cosmogony & ,/ell> ,dynamics1 #aiai4 #i ,n4,g4,c4 #ddhf 7,m #hg7 may be an exception4 ,on ! be/ photographs made ) ! #ajj-;in* reflector1 num]\s exce$+ly fa9t images1 app>5tly ( />s1 are f\nd ar\nd ! p]iph]y4 ,x 0 among ^! t ,belan[sky's nova ( #aiai appe>$4 ,! obs]vations are describ$ 9 ,publications ( ! ,a/ronomical ,society ( ! ,pacific1 #ce1 #bfa1 #aibc4 #aj 8,e>ly0 & 8late10 9 spite ( _! temporal connotations1 appe> to be ! mo/ conv5i5t adjectives available = describ+ relative positions 9 ! sequ5ce4 ,?is sequ5ce ( /ructural =ms is an obs]v$ ph5om5on4 ,z w be %[n lat] 9 ! discussion1 x exhibits a smoo? progression 9 nucle> lum9osity1 surface brightness1 degree ( flatt5+1 major diamet]s1 resolution1 & complexity4 ,an anti!tical pair ( adjectives d5ot+ relative positions 9 ! sequ5ce is desirable = _m reasons1 b none ( ! progressive *>act]i/ics are well adapt$ = ! purpose4 ,t]ms :i* apply to s]ies 9 g5]al are available1 h[ev]1 & ( ^! 8e>ly0 & 8late0 are ! mo/ suitable4 ,!y c be assum$ to express a progression f simple to complex =ms4 ,an accept$ prec$5t = ?is usage is f\nd 9 ! s]ies ( /ell> spectral types4 ,!re also ! progression is assum$ to be f ! simple to ! complex1 & 9 view ( ! great conv5i5ce ( ! t]ms 8e>ly0 & 8late10 ! temporal connotations1 aft] a full consid]ation ( _! possible consequ5ces1 h be5 delib]ately disreg>d$4 #aa ,publications ( ! ,lick ,obs]vatory1 #ac1 #ab1 #aiah4 #ab ,h is bright] ?an ,n#b4 ,pat*es ) simil> spectra are (t5 f\nd 9 ! arms ( late-type spirals--,n4,g4,c4 #bec1 ,m #cc1 ,m #aja4 ,! typical planet>y spectrum1 :]e ,h is fa9t] ?an ,n#b1 is f\nd 9 ! r>e cases ( app>5tly /ell> nuclei ( spirals2 = in/ance1 9 ,n4,g4,c4 #ajfh1 #djea1 & #daea4 ,"h also ! emission spectra are localiz$ & d n ext5d ov] ! nebulae4 #ac ,mon?ly ,notices4 #gd1 #fii1 #aiad4 #ad ,annal5 d] ,wi5] ,/]nw>te1 #bj1 #aijg4 #ae ,a/ronomis*e ,na*ri*t51 #bad1 #dbe1 #aiba4 #af ,publications ( ! ,lick ,obs]vatory1 #ac1 #aiah4 #ag ,s9ce ,c is con/ant = all nebulae 9 a giv5 class1 ! l9e> relation betwe5 log d & ,c = ! diff]5t classes is some?+ m ?an a m]e geometrical relation aris+ f ! obs]v$ equality ( ! mean m,t 9 ! v>i\s classes4 #ah ,?is is app>5t ev5 among ! obs]v$ classes4 ,ref]r+ to =mula 7#c71 m,t #e log b w be con/ant 9 s f> z ,ce #e log 7#a - e7 is con/ant4 ,! foll[+ table indicates t ! latt] t]m is approximately con/ant ?r\gh\t ! sequ5ce ( elliptical nebulae4 ,! values ( ,ce 7 read f ! smoo? curve 9 ,fig4 #f4 e ,ce #e log 7#a - e7 ,c#j ,res4 ---------------------------------------- ------------ #j #aj4cj #j4j #aj4cj -#j4ad #a #aj4fe - 4#bc #aj4db - 4#jb #b #aa4jj 4#dh #aj4eb 4#aj #c #aa4ce #j4gh #aj4eg 4#ac #d #aa4gj #a4aa #aj4ei 4#ae #e #ab4je #a4ej #aj4ee 4#aa #f #ab4dj #a4ii #aj4da - 4#jc #g #ab4ge -#b4fb #aj4ac -#j4ca ---------------------------------------- ------ ,mean #aj4dd #j4ab ---------------------------------------- ------------ #ai ,mt4 ,wilson ,contr41 ,no4 #aia2 ,a/rophysical ,j\rnal1 #eb1 #afb1 #aibj4 #bj ,pease1 ,mt4 ,wilson ,comm41 ,no4 #ea2 ,proce$+s ( ! ,national ,academy ( ,sci5ces1 #d1 #ba1 #aiah4 #ba ,pease1 ,mt4 ,wilson ,comm41 ,no4 #cb3 ibid41 #b1 #eag1 #aiaf4 #bb ,a/rophysical ,j\rnal1 #ee1 #djf1 #aibb4 #bc ,mon?ly ,notices1 #hb1 #acc1 #aibb4 #bd ,a/ronomical ,j\rnal1 #bh1 #ge1 #aiad4 #be ,mt4 ,wilson ,contr41 ,no4 #big2 ,a/rophysical ,j\rnal1 #fb1 #afh1 #aibe4 #bf ,! late/ & mo/ reliable results be>+ on ! di/ribution ( fa9t 7h5ce app>5tly di/ant7 nebulae are f\nd 9 ,se>es's revision & discussion ( ! c\nts made by ,fa? on plates ( ! ,select$ ,areas ) ! #fj-;in* reflector4 ,:5 ! influ5ce ( ! clu/] 9 ,virgo is elim9at$ ! d5sity appe>s to be r\ghly uni=m = all latitudes great] ?an ab\t #be4 #bg ,mon?ly ,notices1 #gh1 #c1 #aiag4 #bh ,haas1 ,introduction to ,!oretical ,physics1 #b1 #cgc1 #aibe4 ,transcrib]'s ,notes #a4 ,footnotes h be5 r5umb]$ & mov$ to ! end ( ! pap]4 #b4 ,tables h be5 mov$ to avoid splitt+ p>agraphs4 ,9 "s cases ! tables h be5 reconfigur$ or split 9 ord] to "w bett] ) e-read]s4 #c4 ,except z m5tion$ above e ef=t has be5 made to replicate ?is text z fai?fully z possible1 includ+ non-/&>d punctuation1 inconsi/5tly hyph5at$ words1 etc4 #d4 ,! orig9al pr9t$ text is available f ,hathi,trust at3 https3_/_/hdl4h&le4net_/#bjbg_/uc#a4;b#c hjefhj 7see pg #cec74 ,! outl9e 8,,classification ,,( ,,nebulae0 />t+ on page #c li/s ,n4,g4,c4 #baag z a type ,e#g nebula4 ,! v]sion ( ?is pap] pr9t$ 9 ,contributions f ! ,m\nt ,wilson ,obs]vatory ,no4 #cbd li/s ,n4,g4,c #caae4 ,o!rwise ! pap]s are ess5tially id5tical4 ,special notation = ! pla9 text v]sion3 #a4 ,text enclos$ by und]scores 80 is italicis$4 #b4 ,text enclos$ by macrons 80 has a l9e draw ov] x4 #c4 ,text enclos$ 9 braces foll[+ an und]score 8 0 is subscript4 #d4 ,text enclos$ 9 braces foll[+ a circumflex acc5t 8 0is sup]script4 ,if only a s+le "*1 ! braces may be omitt$4 #e4 ,text enclos$ 9 heavy angle brackets 8 0 is bold4 #f4 ,text enclos$ 9 doll> signs is 9 ,te,x notation4