,illu/ration3 ,fig4 #a4 ,! ,con/ellation ( ,orion 7,hubble74 ,photograph$ ) a small cam]a l5s ( #a in* ap]ture & #e in*es focal l5g?4 ,! ?ree bright />s 9 ! c5tre ( ! picture =m ! belt ( ,orion4 ,j bel[1 9 ! sword h&le1 is an irregul> :ite pat* ab\t "o-eigh? ( an in* 9 diamet]4 ,?is is a small-scale image ( ! great nebula 9 ,orion1 %[n on a l>g] scale 9 ,fig4 #b4 ,,! ,,new ,,heav5s ,,by ,,george ,,ell]y ,,hale ,,director ,,( ,,! ,,m\nt ,,wilson ,,obs]vatory ,,( ,,! ,,c>negie ,,in/itution ,,( ,,wa%+ton ,,) ,,num]\s ,,illu/rations ,,new ,,york ,,*>les ,,scribn]',s ,,sons #aibb ,,to ,,my ,,wife ,,preface ,f\rte5 ye>s ago1 9 a book entitl$ ,! ,/udy ( ,/ell> ,evolution 7,univ]sity ( ,*icago ,press1 #aijh71 ,i attempt$ to give 9 unte*nical language an acc\nt ( "s mod]n me?ods ( a/rophysical rese>*4 ,?is book is n[ out ( pr9t1 & ! rapid progress ( sci5ce has left x completely out ( date4 ,z ,i h f\nd no opportunity to prep>e a new edition1 or to write ano!r book ( simil> purpose1 ,i h adopt$ ! simpl] exp$i5t ( contribut+ occasional articles on rec5t developm5ts to ,scribn]'s ,magaz9e1 ?ree ( :i* are includ$ 9 ! pres5t volume4 ,i am *iefly indebt$1 = ! illu/rations1 to ! ,m\nt ,wilson ,obs]vatory & ! pres5t & =m] memb]s ( its /aff ^: names appe> 9 ! captions4 ,special ?anks are due to ,mr4 ,f]d9& ,ell]man1 :o made all ( ! photographs ( ! obs]vatory build+s & in/rum5ts1 & prep>$ all mat]ial = reproduction4 ,! cut ( ! orig9al ,cav5di% app>atus is copi$ f ! ,philosophical ,transactions = #agih ) ! k9d p]mission ( ! ,royal ,society1 & ,i am also indebt$ to ! ,royal ,society & to ,pr(essor ,f[l] & ,fa!r ,cortie = ! privilege ( reproduc+ f ! ,proce$+s two illu/rations ( _! spectroscopic results4 ,g4 ,e4 ,h4 ,janu>y1 #aibb4 ,,cont5ts ,,*apt] ,i4 ,,! ,,new ,,heav5s ,,ii4 ,,giant ,,/>s ,,iii4 ,,cosmic ,,crucibles ,,illu/rations ,,fig4 #a4 ,! ,con/ellation ( ,orion 7,hubble7 #b4 ,! ,great ,nebula 9 ,orion 7,pease7 #c4 ,model by ,ell]man ( summit ( ,m\nt ,wilson1 %[+ ! obs]vatory build+s among ! trees & bu%es #d4 ,! #ajj-;in* ,hook] telescope #e4 ,erect+ ! pol> axis ( ! #ajj-;in* telescope #f4 ,l[e/ section ( tube ( #ajj-;in* telescope1 ready to leave ,pasad5a = ,m\nt ,wilson #g4 ,section ( a /eel gird] = dome cov]+ ! #ajj-;in* telescope1 on its way up ,m\nt ,wilson #h4 ,erect+ ! /eel build+ & revolv+ dome t cov] ! ,hook] telescope #i4 ,build+ & revolv+ dome1 #ajj feet 9 diamet]1 cov]+ ! #ajj-;in* ,hook] telescope #aj4 ,"o-hundr$-in* mirror1 j silv]$1 ris+ out ( ! silv]+-room 9 pi] be=e atta*m5t to l[] end ( telescope tube4 7,se5 above7 #aa4 ,! driv+-clock & worm-ge> t cause ! #ajj-;in* ,hook] telescope to foll[ ! />s #ab4 ,l>ge irregul> nebula & /> clu/] 9 ,sagitt>ius 7,duncan7 #ac4 ,fa9t spiral nebula 9 ! con/ellation ( ! ,hunt+ ,dogs 7,pease7 #ad4 ,spiral nebula 9 ,&rom$a1 se5 edge on 7,rit*ey7 #ae4 ,photograph ( ! moon made on ,septemb] #ae1 #aiai1 ) ! #ajj-;in* ,hook] telescope 7,pease7 #af4 ,photograph ( ! moon made on ,septemb] #ae1 #aiai1 ) ! #ajj-;in* ,hook] telescope 7,pease7 #ag4 ,hubble's ,v>iable ,nebula4 ,"o ( ! few nebul kn[n to v>y 9 brightness & =m #ah4 ,r+ ,nebula 9 ,lyra1 photograph$ ) ! #fj-;in* 7,rit*ey7 & #ajj-;in* 7,duncan7 telescopes #ai4 ,gase\s prom95ce at ! sun's limb1 #adj1jjj miles high 7,ell]man7 #bj4 ,! sun1 #hfe1jjj miles 9 diamet]1 f a direct photograph %[+ _m sun-spots 7,:itney7 #ba4 ,great sun-spot gr\p1 ,augu/ #h1 #aiag 7,:itney7 #bb4 ,photograph ( ! hydrog5 atmosph]e ( ! sun 7,ell]man7 #bc4 ,diagram %[+ outl9e ( ! #ajj-;in* ,hook] telescope1 & pa? ( ! two p5cils ( light f a /> :5 "u obs]vation ) ! #bj-;foot ,mi*elson int]f]omet] #bd4 ,tw5ty-foot ,mi*elson int]f]omet] = measur+ /> diamet]s1 atta*$ to upp] end ( ! skeleton tube ( ! #ajj-;in* ,hook] telescope #be4 ,! giant ,betelgeuse 7)9 ! circle71 famili> z ! conspicu\s r$ /> 9 ! "r %\ld] ( ,orion 7,hubble7 #bf4 ,arcturus 7)9 ! :ite circle71 kn[n to ! ,arabs z ! ,lance ,be>]1 & to ! ,*9ese z ! ,great ,horn or ! ,palace ( ! ,emp]ors 7,hubble7 #bg4 ,! giant /> ,ant>es 7)9 ! :ite circle71 notable = its r$ color 9 ! con/ellation ,scorpio1 & nam$ by ! ,greeks ,a ,rival ( ,m>s 7,hubble7 #bh4 ,diamet]s ( ! ,sun1 ,arcturus1 ,betelgeuse1 & ,ant>es comp>$ ) ! orbit ( ,m>s #bi4 ,aldeb>an1 ! lead] 7( ! ,pleiades71 0 also kn[n to ! ,arabs z ,! ,eye ( ! ,bull1 ,! ,he>t ( ! ,bull1 & ,! ,great ,camel 7,hubble7 #cj4 ,sol> prom95ces1 photograph$ ) ! spectroheliograph )\t an eclipse 7,ell]man7 #ca4 ,! #aej-;foot t[] telescope ( ! ,m\nt ,wilson ,obs]vatory #cb4 ,pasad5a ,laboratory ( ! ,m\nt ,wilson ,obs]vatory #cc4 ,sun-spot vortex 9 ! upp] hydrog5 atmosph]e 7,b5i(f7 #cd4 ,splitt+ ( spectrum l9es by a magnetic field 7,bacock7 #ce4 ,electric furnace 9 ! ,pasad5a ,laboratory ( ! ,m\nt ,wilson ,obs]vatory #cf4 ,titanium oxide 9 r$ />s #cg4 ,titanium oxide 9 sun-spots #ch4 ,! ,cav5di% exp]im5t #ci4 ,! ,trifid ,nebula 9 ,sagitt>ius 7,rit*ey7 #dj4 ,spiral nebula 9 ,ursa ,major 7,rit*ey7 #da4 ,m\nt ,san ,antonio z se5 f ,m\nt ,wilson ,,*apt] ,i ,,! ,,new ,,heav5s ,g out "u ! op5 sky1 on a cle> & moon-less night1 & try to c\nt ! />s4 ,if y\r /ation lies well beyond ! gl>e ( cities1 :i* is (t5 /rong en\gh to conceal all b ! bright] objects1 y w f9d ! task a difficult "o4 ,rang+ ?r\gh ! six magnitudes ( ! ,greek a/ronom]s1 f ! brilliant ,sirius to ! fa9te/ p]ceptible po9ts ( light1 ! />s are scatt]$ 9 great pr(usion ov] ! cele/ial vault4 ,_! numb] seems limitless1 yet actual c\nt w %[ t ! eye has be5 deceiv$4 ,9 a survey ( ! entire heav5s1 f pole to pole1 x w\ld n be possible to detect m ?an f six to sev5 ?\s& />s ) ! nak$ eye4 ,f a s+le viewpo9t1 ev5 ) ! ke5e/ vision1 only two or ?ree ?\s& c be se54 ,s _m ( ^! are at ! limit ( visibility t ,ptolemy's ,almage/1 a catalogue ( all ! />s ^: places 7 measur$ ) ! simple in/rum5ts ( ! ,greek a/ronom]s1 conta9s only #a1jbb />s4 ,back ( ,ptolemy1 ?r\gh ! speculations ( ! ,greek philosoph]s1 ! my/]ies ( ! ,egyptian sun-god1 & ! obs]vations ( ! anci5t ,*aldeans1 ! ri* & v>i$ traditions ( a/ronomy /ret* f> away into a %ad[y pa/4 ,all peoples1 9 ! fir/ /irr+s ( _! intellectual y\?1 drawn by ! nightly spl5dor ( ! skies & ! ceaseless motions ( ! planets1 h set up "s sy/em ( ! heav5s1 9 :i* ! s5se ( wond] & ! desire = k 7 no less conc]n$ ?an ! practical necessities ( life4 ,! measurem5t ( "t & ! ne$s ( navigation h always /imulat$ a/ronomical rese>*1 b ! intellectual dem& has be5 ke5 f ! fir/4 ,hipp>*us & ! ,greek a/ronom]s ( ! ,alex&rian s*ool1 %ak+ (f ! vag>ies ( magic & div9ation1 plac$ a/ronomy on a sci5tific basis1 ?\gh ! reaction ( ! ,middle ,ages caus$ ev5 su* a great a/ronom] z ,ty*o ,brahe himself to rev]t = a "t to ! practice ( a/rology4 ,,e>ly ,,in/rum5ts ,! transp>5t sky ( ,egypt1 r>ely obscur$ by cl\ds1 greatly favor$ ,ptolemy's obs]vations4 ,"h 0 prep>$ 8 great /> catalogue1 bas$ ^u ! e>li] obs]vations ( ,hipp>*us1 & de/9$ to rema9 alone 9 its field = m ?an twelve c5turies1 until ,ulugh ,bey1 ,pr9ce ( ,sam>c&1 repeat$ ! "w ( 8 ,greek pr$ecessor4 ,?r\gh\t ?is p]iod ! />s 7 look$ ^u ma9ly z po9ts ( ref]5ce = ! obs]vation ( planet>y motions1 & ! in/rum5ts ( obs]vation und]w5t little *ange4 ,! a/rolabe1 :i* consi/s ( a circle divid$ into degrees1 ) a rotat+ diametral arm = sight+ purposes1 embodies _! ess5tial pr9ciple4 ,9 its simple =m1 ! a/rolabe 0 susp5d$ 9 a v]tical plane1 & ! />s 7 obs]v$ by br++ ! sights on ! movable diamet] to be> ^u !m4 ,_! altitude 0 !n read (f on ! circle4 ,ultimately1 ! circle ( ! a/rolabe1 m\nt$ ) "o ( its diamet]s p>allel to ! e>?'s axis1 became ! armill>y sph]e1 ! precursor ( our mod]n equatorial telescope4 ,great /one quadrants fix$ 9 ! m]idian 7 also employ$ f v e>ly times4 ,out ( su* furni%+s1 little modifi$ by ! lapse ( c5turies1 0 provid$ ! elaborate in/rum5tal equipm5t ( ,uranib\rg1 ! great obs]vatory built by ,ty*o ,brahe on ! ,dani% isl& ( ,hu5 9 #aegf4 ,9 ?is ,city ( ! ,heav5s1 /ill dep5d5t solely ^u ! unaid$ eye z a collector ( />light1 ,ty*o made ^? invaluable obs]vations t enabl$ ,kepl] to d$uce ! true laws ( planet>y motion4 ,b aft] all ^! c5turies ! sid]eal _w embrac$ no objects1 b>r+ an occasional comet or tempor>y />1 t lay beyond ! vision ( ! e>lie/ a/ronom]s4 ,! conceptions ( ! /ell> univ]se1 except ^? t ignor$ ! solid gr\nd ( obs]vation1 7 limit$ by ! small ap]ture ( ! human eye4 ,b ! dawn ( ano!r age 0 at h&4 ,illu/ration3 ,fig4 #b4 ,! ,great ,nebula 9 ,orion 7,pease74 ,photograph$ ) ! #ajj-;in* telescope4 ,?is %ort-exposure photograph %[s only ! bright c5tral "p ( ! nebula4 ,a long] exposure reveals a va/ outly+ region4 ,! dom9ance ( ! sun z ! c5tral body ( ! sol> sy/em1 recogniz$ by ,ari/>*us ( ,samos ne>ly ?ree c5turies be=e ! ,*ri/ian era1 b subsequ5tly d5i$ "u ! au?ority ( ,ptolemy & ! tea*+s ( ! ,*ur*1 0 reaffirm$ by ! ,poli% monk ,cop]nicus 9 #aedc4 ,kepl]'s laws ( ! motions ( ! planets1 %[+ !m to revolve 9 ellipses in/ead ( circles1 remov$ ! la/ defect ( ! ,cop]nican sy/em1 & left no room = its rejection4 ,b bo? ! _w & ! ,*ur* clung to tradition1 & "s visible demon/ration 0 urg5tly ne$$4 ,?is 0 suppli$ by ,galileo ?r\gh 8 inv5tion ( ! telescope4 ,illu/ration3 ,fig4 #c4 ,model by ,ell]man ( summit ( ,m\nt ,wilson1 %[+ ! obs]vatory build+s among ! trees & bu%es4 ,! #fj-;foot t[] on ! extreme left1 :i* is at ! edge ( a precipit\s caon #a1ejj feet deep1 is ! v]tical telescope ( ! ,smi?sonian ,a/rophysical ,obs]vatory4 ,above x are ! ,mona/]y & o!r build+s us$ z qu>t]s by ! a/ronom]s ( ! ,m\nt ,wilson ,obs]vatory :ile at "w on ! m\nta94 7,! (fices1 comput+-rooms1 laboratories1 & %ops are 9 ,pasad5a47 ,foll[+ ! ridge1 we come successively to ! dome ( ! #aj-;in* photographic telescope1 ! p[]-h\se1 laboratory1 ,sn[ horizontal telescope1 #fj-;foot-t[] telescope1 & #aej-;foot-t[] telescope1 ^! la/ ?ree us$ = ! /udy ( ! sun4 ,! dome ( ! #fj-;in* reflect+ telescope is j bel[ ! #aej-;foot t[]1 :ile t ( ! #ajj-;in* telescope is f>!r to ! "r4 ,! altitude ( ,m\nt ,wilson is ab\t #e1ijj feet4 ,! cry/all9e l5s ( ! human eye1 limit$ by ! iris to a maximum op5+ ab\t "o-qu>t] ( an in* 9 diamet]1 0 ! only collector ( />light available to ! ,greek & ,arabian a/ronom]s4 ,galileo's telescope1 :i* 9 #afaj sudd5ly pu%$ out ! b\nd>ies ( ! kn[n /ell> univ]se & br\ght _m ?\s&s ( />s into range1 _h a l5s ab\t #b-a_/d in*es 9 diamet]4 ,! area ( ?is l5s1 proportional to ! squ>e ( its diamet]1 0 ab\t eighty-"o times t ( ! pupil ( ! eye4 ,?is great increase 9 ! am\nt ( light collect$ %\ld br+ to view />s d[n to magnitude #aj4e1 ( :i* ne>ly half a million are kn[n to exi/4 ,x is n too mu* to say t ,galileo's telescope revolutioniz$ human ?\ght4 ,turn$ to ! moon1 x reveal$ m\nta9s1 pla9s1 & valleys1 :ile ! sun1 previ\sly suppos$ immaculate 9 its p]fection1 0 se5 to be blemi%$ ) d>k spots *ang+ f day to day4 ,jupit]1 %[n to be accompani$ by f\r encircl+ satellites1 af=d$ a picture 9 m9iature ( ! sol> sy/em1 & /rongly support$ ! ,cop]nican view ( its organization1 :i* 0 conclusively demon/rat$ by ,galileo's discov]y ( ! *ang+ phases ( ,v5us & ! v>iation ( its app>5t diamet] dur+ its revolution ab\t ! sun4 ,galileo's pro( ( ! ,cop]nican !ory m>k$ ! d[nfall ( m$ivalism & e/abli%$ a/ronomy on a firm f\ndation4 ,b :ile 8 telescope multipli$ a hundr$fold ! numb] ( visible />s1 m ?an a c5tury elaps$ be=e ! true possibilities ( sid]eal a/ronomy 7 p]ceiv$4 ,illu/ration3 ,fig4 #d4 ,! #ajj-;in* ,hook] telescope4 ,,/ructure ,,( ,,! ,,univ]se ,sir ,william ,h]s*el 0 ! fir/ a/ronom] to make a s]i\s attack ^u ! problem ( ! /ructure ( ! /ell> univ]se4 ,9 8 fir/ memoir on ! ,con/ruction ( ! ,heav5s1 read be=e ! ,royal ,society 9 #aghd1 he wrote z foll[s3 ,hi!rto ! sid]eal heav5s h1 n inadequately = ! purpose design$1 be5 repres5t$ by ! concave surface ( a sph]e 9 ! c5tre ( :i* ! eye ( an obs]v] might be suppos$ to be plac$4444 ,9 future we %all look ^u ^? regions into :i* we may n[ p5etrate by means ( su* l>ge telescopes1 z a naturali/ reg>ds a ri* ext5t ( gr\nd or *a9 ( m\nta9s conta9+ /rata v>i\sly incl9$ & direct$ z well z consi/+ ( v diff]5t mat]ials4 ,on turn+ 8 #ah-;in* reflect+ telescope to a "p ( ! ,milky ,way 9 ,orion1 he f\nd its :iti% appe>ance to be completely resolv$ into small />s1 n sep>ately se5 ) 8 =m] telescopes4 ,! glori\s multitude ( />s ( all possible sizes t pres5t$ !mselves "h to my view are truly a/oni%+2 b z ! dazzl+ brightness ( glitt]+ />s may easily mislead u s f> z to e/imate _! numb] great] ?an x really is1 ,i endeavor$ to asc]ta9 ?is po9t by c\nt+ _m fields1 & comput+ f a mean ( !m1 :at a c]ta9 giv5 portion ( ! ,milky ,way might conta94 ,by ?is means1 appli$ n only to ! ,milky ,way b to all p>ts ( ! heav5s1 ,h]s*el det]m9$ ! approximate numb] & di/ribution ( all ! />s )9 rea* ( 8 in/rum5t4 ,by comp>+ _m hundr$ gauges or c\nts ( />s visible 9 a field ( ab\t "o-qu>t] ( ! area ( ! moon1 ,h]s*el f\nd t ! av]age numb] ( />s increas$ t[>d ! great circle :i* mo/ ne>ly con=ms ) ! c\rse ( ! ,milky ,way4 ,n9ety degrees f ?is plane1 at ! pole ( ! ,milky ,way1 only f\r />s1 on ! av]age1 7 se5 9 ! field ( ! telescope4 ,9 approa*+ ! ,milky ,way ?is numb] increas$ sl[ly at fir/1 & !n m & m rapidly1 until x rose to an av]age ( #abb />s p] field4 ,illu/ration3 ,fig4 #e4 ,erect+ ! pol> axis ( ! #ajj-;in* telescope4 ,^! obs]vations 7 made 9 ! nor!rn hemisph]e1 & subsequ5tly ,sir ,john ,h]s*el1 us+ 8 fa!r's telescope at ! ,cape ( ,good ,hope1 f\nd an almo/ exactly simil> increase ( app>5t /> d5sity = ! s\!rn hemisph]e4 ,accord+ to 8 e/imates1 ! total numb] ( />s 9 bo? hemisph]es t c\ld be se5 di/9ctly en\gh to be c\nt$ 9 ?is telescope w\ld probably be ab\t five & "o-half millions4 ,! ,h]s*els conclud$ t ! />s ( our firmam5t1 in/ead ( be+ scatt]$ 9 all directions indiff]5tly ?r\gh space1 =m a /ratum ( :i* ! ?ickness is small1 9 comp>ison ) its l5g? & bread?2 & 9 :i* ! e>? occupies a place some:]e ab\t ! middle ( its ?ickness1 betwe5 ! po9t :]e x subdivides into two pr9cipal lam9 incl9$ at a small angle to ea* o!r4 ,?is view does n diff] ess5tially f our mod]n conception ( ! =m ( ! ,galaxy2 b z ! ,h]s*els 7 unable to see />s fa9t] ?an ! fifte5? magnitude1 x is evid5t t _! conclusions apply only to a re/rict$ region surr\nd+ ! sol> sy/em1 9 ! mid/ ( ! enorm\sly ext5d$ sid]eal univ]se :i* mod]n in/rum5ts h br\ght )9 our range4 ,,mod]n ,,me?ods ,! rem>kable progress ( mod]n a/ronomy is ma9ly due to two great in/rum5tal advances3 ! rise & developm5t ( ! photographic telescope1 & ! application ( ! spectroscope to ! /udy ( cele/ial objects4 ,^! new & p[]ful in/rum5ts1 supplem5t$ by _m accessories :i* h completely revolutioniz$ obs]vatory equipm5t1 h n only reveal$ a va/ly great] numb] ( />s & nebul3 !y h also r5d]$ feasible obs]vations ( a type =m]ly reg>d$ z impossible4 ,! *emical analysis ( a fa9t /> is n[ s easy t x c be accompli%$ 9 a v %ort "t--z quickly1 9 fact1 z an equally complex sub/ance c be analyz$ 9 ! laboratory4 ,! spectroscope also measures a />'s velocity1 ! pressure at diff]5t levels 9 its atmosph]e1 its approximate temp]ature1 & n[1 by a new & +5i\s me?od1 its di/ance f ! e>?4 ,x det]m9es ! velocity ( rotation ( ! sun & ( nebul1 ! exi/5ce & p]iods ( orbital revolution ( b9>y />s too close to be sep>at$ by any telescope1 ! pres5ce ( magnetic fields 9 sunspots1 & ! fact t ! entire sun1 l ! e>?1 is a magnet4 ,illu/ration3 ,fig4 #f4 ,l[e/ section ( tube ( #ajj-;in* telescope1 ready to leave ,pasad5a = ,m\nt ,wilson4 ,su* new possibilities1 ) _m o!rs result+ f ! application ( physical me?ods ( ! mo/ div]se "*1 h greatly enl>g$ ! a/ronom]'s outlook4 ,he may n[ attack two great problems3 7#a7 ,! /ructure ( ! univ]se & ! motions ( its con/itu5t bodies1 & 7#b7 ! evolution ( ! />s3 _! nature1 orig91 gr[?1 & decl9e4 ,^! two problems are intimately relat$ & mu/ be /udi$ z "o499 ,footnote 993 ,a ?ird great problem op5 to ! a/ronom]1 ! /udy ( ! con/itution ( matt]1 is describ$ 9 ,*apt] ,,iii4 ,if space p]mitt$1 x w\ld be int]e/+ to survey ! progress already accompli%$ by mod]n me?ods ( a/ronomical rese>*4 ,hundr$s ( millions ( />s h be5 photograph$1 & ! b\nd>ies ( ! /ell> univ]se h be5 pu%$ f> into space1 b h n be5 atta9$4 ,globul> /> clu/]s1 conta9+ t5s ( ?\s&s ( />s1 are on s great a scale 7accord+ to ,%apley7 t light1 travell+ at ! rate ( #ahf1jjj miles p] second1 may take #ejj ye>s to cross "o ( !m1 :ile ! mo/ di/ant ( ^! objects may be m ?an #bjj1jjj light-ye>s f ! e>?4 ,! spiral nebul1 m ?an a million 9 numb]1 are va/ :irl+ masses 9 process ( developm5t1 b we are n yet c]ta9 :e!r !y %\ld be reg>d$ z isl& univ]ses or z subord9ate to ! /ell> sy/em :i* includes our m9ute gr\p ( sun & planets1 ! great /> cl\ds ( ! ,milky ,way1 & ! di/ant globul> /> clu/]s4 ,illu/ration3 ,fig4 #g4 ,section ( a /eel gird] = dome cov]+ ! #ajj-;in* telescope1 on its way up ,m\nt ,wilson4 ,^! few p>ticul>s may give a slight conception ( ! scale ( ! kn[n univ]se1 b a ^w mu/ be add$ reg>d+ "s ( its mo/ /rik+ ph5om5a4 ,! great majority ( ! />s ^: motions h be5 det]m9$ belong to "o or ! o!r ( two great /> /reams1 b ! "p play$ by ^! /reams 9 ! sid]eal sy/em z a :ole is /ill obscure4 ,! />s h be5 gr\p$ 9 classes1 presumably 9 ! ord] ( _! evolutional developm5t1 z !y pass f ! e>ly /ate ( gase\s masses1 ( l[ d5sity1 ?r\gh ! successive /ages result+ f loss ( heat by radiation & increas$ d5sity due to %r9kage4 ,/rangely en\gh1 _! velocities 9 space %[ a correspond+ *ange1 increas+ z !y gr[ old] or p]haps dep5d+ ^u _! mass4 ,x is impossible )9 ^! limits to d m ?an to give "s indication ( ! scope ( ! new a/ronomy4 ,en\gh has be5 said1 h[ev]1 to assi/ 9 appreciat+ ! increas$ opportunity = inve/igation1 & ! nature ( ! heavy dem&s made ^u ! mod]n obs]vatory4 ,b be=e pass+ on to describe "o ( ! late/ additions to ! a/ronom]'s in/rum5tal equipm5t1 a ^w %\ld be add$ reg>d+ ! *ief classes ( telescopes4 ,,refractors ,,& ,,reflectors ,a/ronomical telescopes are ( two types3 refractors & reflectors4 ,a refract+ telescope consi/s ( an object-glass compos$ ( two or m l5ses1 m\nt$ at ! upp] end ( a tube1 :i* is po9t$ at ! cele/ial object4 ,! light1 aft] pass+ ?r\gh ! l5ses1 is br\ght to a focus at ! l[] end ( ! tube1 :]e ! image is exam9$ visually ) an eyepiece1 or photograph$ ^u a s5sitive plate4 ,! l>ge/ in/rum5ts ( ?is type are ! #cf-;in* ,lick telescope & ! #dj-;in* refractor ( ! ,y]kes ,obs]vatory4 ,illu/ration3 ,fig4 #h4 ,erect+ ! /eel build+ & revolv+ dome t cov] ! ,hook] telescope4 ,reflect+ telescopes1 :i* are p>ticul>ly adapt$ = photographic "w1 ?\gh also excell5t = visual obs]vations1 are v diff]5tly con/ruct$4 ,no l5s is us$4 ,! telescope tube is usually built 9 skeleton =m1 op5 at its upp] end1 & ) a l>ge concave mirror support$ at its base4 ,?is mirror s]ves 9 place ( a l5s4 ,its upp] surface is p>aboloidal 9 %ape1 z a sph]ical surface w n unite 9 a %>p focus ! rays com+ f a di/ant object4 ,! light passes ?r\gh no glass--a great advantage1 especially = photography1 z ! absorption 9 l5ses cuts out mu* ( ! blue & violet light1 to :i* photographic plates are mo/ s5sitive4 ,! reflection occurs on ! upp] surface ( ! mirror1 :i* is cov]$ ) a coat ( pure silv]1 r5ew$ sev]al times a ye> & always kept highly burni%$4 ,silv]$ glass is bett] ?an metals or o!r sub/ances = telescope mirrors1 *iefly because ( ! p]fection ) :i* glass c be gr\nd & poli%$1 & ! ease ( r5ew+ its silv]$ surface :5 t>ni%$4 ,! great reflectors ( ,h]s*el & ,"l ,rosse1 :i* 7 provid$ ) mirrors ( speculum metal1 7 f> inf]ior to mu* small] telescopes ( ! pres5t day4 ,) ^! in/rum5ts ! /> images 7 wat*$ z !y 7 c>ri$ ?r\gh ! field ( view by ! e>?'s rotation1 or kept r\ghly 9 place by mov+ ! telescope ) ropes or *a9s4 ,photographic plates1 :i* reveal invisible />s & nebul :5 expos$ = h\rs 9 mod]n in/rum5ts1 7 n !n available4 ,9 any case !y c\ld n h be5 us$1 9 ! abs5ce ( ! p]fect me*anism requir$ to keep ! /> images accurately fix$ 9 place ^u ! s5sitive film4 ,illu/ration3 ,fig4 #i4 ,build+ & revolv+ dome1 #ajj feet 9 diamet]1 cov]+ ! #ajj-;in* ,hook] telescope4 ,photograph$ f ! summit ( ! #aej-;foot-t[] telescope4 ,x w\ld be int]e/+ to trace ! long conte/ = supremacy betwe5 refract+ & reflect+ telescopes1 ea* ( :i*1 at c]ta9 /ages 9 its developm5t1 appe>$ to be unrivall$4 ,9 mod]n obs]vatories bo? types are us$1 ea* = ! purpose = :i* x is be/ adapt$4 ,= ! photography ( nebul & ! /udy ( ! fa9t] />s1 ! reflector has special advantages1 illu/rat$ by ! "w ( su* in/rum5ts z ! ,crossley & ,mills reflectors ( ! ,lick ,obs]vatory2 ! great #gb-;in* reflector1 rec5tly br\ght into effective s]vice at ! ,dom9ion ,obs]vatory 9 ,canada2 & ! #fj-;in* & #ajj-;in* reflectors ( ! ,m\nt ,wilson ,obs]vatory4 ,! unaid$ eye1 ) an available area ( "o-tw5tie? ( a squ>e in*1 p]mits u to see />s ( ! six? magnitude4 ,h]s*el's #ah-;in* reflector1 ) an area #e1jjj times z great1 r5d]$ visible />s ( ! fifte5? magnitude4 ,! #fj-;in* reflector1 ) an area #eg1fjj times t ( ! eye1 reveals />s ( ! eighte5? magnitude1 :ile to rea* />s ( ab\t ! tw5tie? magnitude1 photographic exposures ( f\r or five h\rs suffice ) ?is in/rum5t4 ,e ga9 ( a magnitude means a great ga9 9 ! numb] ( />s r5d]$ visible4 ,/>s ( ! second magnitude are #c4d times z num]\s z ^? ( ! fir/1 ^? ( ! eigh? magnitude are ?ree times z num]\s z ^? ( ! sev5?1 :ile ! sixte5? magnitude />s are only #a4g z num]\s z ^? ( ! fifte5? magnitude4 ,?is /eadily decreas+ ratio is probably due to an actual ?9n+ out ( ! />s t[>d ! b\nd>ies ( ! /ell> univ]se1 z ! mo/ exhau/ive te/s h fail$ to give any evid5ce ( absorption ( light 9 its passage ?r\gh space4 ,b 9 spite ( ?is decrease1 ! ga9 ( a s+le additional magnitude may mean ! addition ( _m millions ( />s to ! total ( ^? already %[n by ! #fj-;in* reflector4 ,"h is "o ( ! *ief s\rces ( int]e/ 9 ! possibilities ( a #ajj-;in* reflect+ telescope4 #ajj-;,,in* ,,telescope ,illu/ration3 ,fig4 #aj4 ,"o-hundr$-in* mirror1 j silv]$1 ris+ out ( ! silv]+-room 9 pi] be=e atta*m5t to l[] end ( telescope tube4 7,se5 above47 ,9 #aijf ! late ,john ,d4 ,hook]1 ( ,los ,angeles1 gave ! ,c>negie ,in/itution ( ,wa%+ton a sum suffici5t to con/ruct a telescope mirror #ajj in*es 9 diamet]1 & ?us l>ge en\gh to collect #afj1jjj times ! light receiv$ by ! eye4 7,fig4 #aj47 ,! ca/+ & anneal+ ( a suitable glass disk1 #aja in*es 9 diamet] & #ac in*es ?ick1 weigh+ f\r & "o-half tons1 0 a mo/ difficult op]ation1 f9ally accompli%$ by a great ,fr5* glass company at _! factory 9 ! ,=e/ ( ,/4 ,goba94 ,a special optical laboratory 0 erect$ at ! ,pasad5a headqu>t]s ( ! ,m\nt ,wilson ,obs]vatory1 & "h ! long task ( gr9d+1 figur+1 & te/+ ! mirror 0 successfully c>ri$ out by ! obs]vatory opticians4 ,?is op]ation1 :i* is "o ( great delicacy1 requir$ ye>s = its completion4 ,mean:ile ! build+1 dome1 & m\nt+ = ! telescope 7 design$ by memb]s ( ! obs]vatory /aff1 & ! work+ draw+s 7 prep>$4 ,an opportune addition by ,mr4 ,c>negie to ! end[m5t ( ! ,c>negie ,in/itution ( ,wa%+ton1 ( :i* ! obs]vatory is a bran*1 p]mitt$ ! necess>y appropriations to be made = ! completion & erection ( ! telescope4 ,?\gh delay$ by ! w>1 dur+ :i* ! me*anical & optical facilities ( ! obs]vatory %ops 7 utiliz$ = milit>y & naval purposes1 ! telescope is n[ 9 regul> use on ,m\nt ,wilson4 ,! in/rum5t is m\nt$ on a massive pi] ( re9=c$ concrete1 #cc feet high & #eb feet 9 diamet] at ! top4 ,a solid wall ext5ds s\? f ?is pi] a di/ance ( #ej feet1 on ! we/ side ( :i* a v p[]ful spectrograph1 = photograph+ ! spectra ( ! brighte/ />s1 w be m\nt$4 ,)9 ! pi] are a photographic d>k room1 a room = silv]+ ! l>ge mirror 7:i* c be l[]$ into ! pi]71 & ! clock-room1 :]e /&s ! p[]ful driv+-clock1 ) :i* ! telescope is caus$ to foll[ ! app>5t motion ( ! />s4 7,fig4 #aa47 ,illu/ration3 ,fig4 #aa4 ,! driv+-clock & worm-ge> t cause ! #ajj-;in* ,hook] telescope to foll[ ! />s4 ,! telescope m\nt+ is ( ! ,engli% type1 9 :i* ! telescope tube is support$ by ! decl9ation trunnions betwe5 ! arms ( ! pol> axis1 built 9 ! =m ( a rectangul> yoke c>ri$ by be>+s on massive p$e/als to ! nor? & s\?4 ,^! be>+s mu/ be align$ exactly p>allel to ! axis ( ! e>?1 & mu/ support ! pol> axis s freely t x c be rotat$ ) p]fect precision by ! driv+-clock1 :i* turns a worm-:eel #ag feet 9 diamet]1 clamp$ to ! l[] end ( ! axis4 ,z ?is motion mu/ be suffici5tly uni=m to c\nt]act exactly ! rotation ( ! e>? on its axis1 & ?us to ma9ta9 ! /> images accurately 9 position 9 ! field ( view1 ! greate/ c>e _h to be tak5 9 ! con/ruction ( ! driv+-clock & 9 ! spac+ & cutt+ ( ! tee? 9 ! l>ge worm-:eel4 ,"h1 z 9 ! case ( all ( ! m ref9$ p>ts ( ! in/rum5t1 ! "w 0 done by skill$ ma*9i/s 9 ! obs]vatory %ops 9 ,pasad5a or on ,m\nt ,wilson aft] ! assembl+ ( ! telescope4 ,! massive sections ( ! in/rum5t1 "s ( :i* weigh z mu* z t5 tons ea*1 7 con/ruct$ at ,qu9cy1 ,mass41 :]e ma*9]y suffici5tly l>ge to build battle%ips 0 available4 ,!y 7 !n %ipp$ to ,cali=nia1 & transport$ to ! summit ( ,m\nt ,wilson ov] a road built = ?is purpose by ! con/ruction division ( ! obs]vatory1 :i* also built ! pi] on :i* ! telescope /&s1 & erect$ ! /eel build+ & dome t cov] x4 ,illu/ration3 ,fig4 #ab4 ,l>ge irregul> nebula & /> clu/] 9 ,sagitt>ius 7,duncan74 ,photograph$ ) ! #fj-;in* telescope4 ,illu/ration3 ,fig4 #ac4 ,fa9t spiral nebula 9 ! con/ellation ( ! ,hunt+ ,dogs 7,pease74 ,photograph$ ) ! #fj-;in* telescope4 ,! p>ts ( ! telescope :i* are mov$ by ! driv+-clock weigh ab\t #ajj tons1 & x 0 necess>y to provide means ( r$uc+ ! great friction on ! be>+s ( ! pol> axis4 ,to accompli% ?is1 l>ge holl[ /eel cyl9d]s1 float+ 9 m]cury held 9 ca/-iron tanks1 7 provid$ at ! upp] & l[] ends ( ! pol> axis4 ,almo/ ! entire weight ( ! in/rum5t is ?us float$ 9 m]cury1 & 9 ?is way ! friction is s greatly r$uc$ t ! driv+-clock moves ! in/rum5t ) p]fect ease & smoo?ness4 ,! #ajj-;in* mirror re/s at ! bottom ( ! telescope tube on a special support sy/em1 s design$ z to prev5t any b5d+ ( ! glass "u its own weight4 ,electric motors1 =ty 9 numb]1 are provid$ to move ! telescope rapidly or sl[ly 9 "r asc5sion 7ea/ or we/7 & 9 decl9ation 7nor? or s\?71 = focuss+ ! mirrors1 & = _m o!r purposes4 ,!y are also us$ = rotat+ ! dome1 #ajj feet 9 diamet]1 "u :i* ! telescope is m\nt$1 & = op5+ ! %utt]1 #bj feet wide1 ?r\gh :i* ! obs]vations are made4 ,a telescope ( ?is k9d c be us$ 9 sev]al diff]5t ways4 ,! #ajj-;in* mirror has a focal l5g? ( ab\t #db feet1 & 9 "o ( ! arrangem5ts ( ! in/rum5t1 ! photographic plate is m\nt$ at ! c5tre ( ! telescope tube ne> its upp] end1 :]e x receives directly ! image =m$ by ! l>ge mirror4 ,9 ano!r arrangem5t1 a silv]$ glass mirror1 ) plane surface1 is support$ ne> ! upp] end ( ! tube at an angle ( #de1 s z to =m ! image at ! side ( ! tube1 :]e ! photographic plate c be plac$4 ,9 ?is case1 ! obs]v] /&s on a plat=m1 :i* is mov$ up & d[n by electric motors 9 front ( ! op5+ 9 ! dome ?r\gh :i* ! obs]vations are made4 ,illu/ration3 ,fig4 #ad4 ,spiral nebula 9 ,&rom$a1 se5 edge on 7,rit*ey74 ,photograph$ ) ! #fj-;in* telescope4 ,o!r arrangem5ts ( ! telescope1 = :i* auxili>y convex mirrors c>ri$ ne> ! upp] end ( ! tube are requir$1 p]mit ! image to be photograph$ at ! side ( ! tube ne> its l[] end1 ei!r ) or )\t a spectrograph2 or ) a v p[]ful spectrograph m\nt$ )9 a con/ant-temp]ature *amb] s\? ( ! telescope pi]4 ,9 ?is la/ case1 ! light ( a /> is s reflect$ by auxili>y mirrors t x passes d[n ?r\gh a hole 9 ! s\? end ( ! pol> axis & br+s ! /> to a focus on ! slit ( ! fix$ spectrograph4 ,,atmosph]ic ,,limitations ,! huge dim5sions ( su* a p[]ful eng9e ( rese>* z ! ,hook] telescope are n 9 !mselves a s\rce ( satisfaction to ! a/ronom]1 = !y involve a decid$ increase 9 ! labor ( obs]vation & entail v heavy exp5se1 ju/ifiable only 9 case important results1 beyond ! rea* ( o!r in/rum5ts1 c be secur$4 ,! con/ruction ( a telescope ( ^! dim5sions 0 necess>ily an exp]im5t1 = x 0 by no means c]ta91 aft] ! optical & me*anical difficulties _h be5 ov]come1 t ev5 ! favorable atmosph]e ( ,cali=nia w\ld be suffici5tly tranquil to p]mit %>ply def9$ cele/ial images to be obta9$ ) s l>ge an ap]ture4 ,x is !re=e important to le>n :at ! telescope w actually accompli% "u cu/om>y obs]v+ conditions4 ,=tunately we are able to measure ! p]=mance ( ! in/rum5t ) c]ta9ty4 ,close beside x on ,m\nt ,wilson /&s ! #fj-;in* reflector1 ( simil> type1 erect$ 9 #aijh4 ,! two telescopes c ?us be rigor\sly comp>$ "u id5tical atmosph]ic conditions4 ,! l>ge mirror ( ! #ajj-;in* telescope has an area ab\t #b4h times t ( ! #fj-;in*1 & !re=e receives ne>ly ?ree times z mu* light f a />4 ,"u atmosph]ic conditions p]fect en\gh to all[ all ( ?is light to be conc5trat$ 9 a po9t1 x %\ld be capable ( record+ on a photographic plate1 ) a giv5 exposure1 />s ab\t "o magnitude fa9t] ?an ! fa9te/ />s )9 rea* ( ! #fj-;in*4 ,! increas$ focal l5g?1 p]mitt+ su* objects z ! moon to be photograph$ on a l>g] scale1 %\ld also reveal small] details ( /ructure & r5d] possible high] accuracy ( measurem5t4 ,f9ally1 ! great] !oretical resolv+ p[] ( ! l>g] ap]ture1 provid+ x c be utiliz$1 %\ld p]mit ! sep>ation ( ! memb]s ( close d\ble />s beyond ! range ( ! small] in/rum5t4 ,,critical ,,te/s ,! _m te/s already made indicate t ! advantages expect$ ( ! new telescope w be realiz$ 9 practice4 ,! increas$ light-ga!r+ p[] w mean ! addition ( _m millions ( />s to ^? already kn[n4 ,spectroscopic obs]vations n[ 9 regul> progress h c>ri$ ! range ( ^! inve/igations f> beyond ! possibilities ( ! #fj-;in* telescope4 ,a great class ( r$ />s1 = example1 almo/ all ! memb]s ( :i* 7 inaccessible to ! #fj-;in*1 are n[ be+ made ! subject ( special /udy4 ,& 9 o!r fields ( rese>* equal advantages h be5 ga9$4 ,! increase 9 ! scale ( ! images ov] ^? giv5 by ! #fj-;in* telescope is illu/rat$ by two photographs ( ! ,r+ ,nebula 9 ,lyra1 reproduc$ 9 ,fig4 #ah4 ,! ,great ,nebula 9 ,orion1 photograph$ ) ! #ajj-;in* telescope ) a comp>atively %ort exposure1 suffici5t to br+ out ! bright] regions1 is reproduc$ 9 ,fig4 #b4 ,x is int]e/+ to comp>e ?is picture ) ! small-scale image ( ! same nebula %[n 9 ,fig4 #a4 ,illu/ration3 ,fig4 #ae4 ,photograph ( ! moon made on ,septemb] #ae1 #aiai1 ) ! #ajj-;in* ,hook] telescope 7,pease74 ,! r+-l =mations are ! s-call$ crat]s1 mo/ ( !m f> l>g] ?an any?+ simil> on ! e>?4 ,t 9 ! l[] left corn] ) an isolat$ m\nta9 9 ! c5tre is ,albategnius1 sixty-f\r miles 9 diamet]4 ,peaks 9 ! r+ rise to a height ( fifte5 ?\s& feet above ! c5tral pla94 ,note ! long sunset %ad[s ca/ by ! m\nta9s on ! left4 ,! level region bel[ on ! "r is an ext5sive pla91 ! ,m>e ,nubium4 ,illu/ration3 ,fig4 #af4 ,photograph ( ! moon made on ,septemb] #ae1 #aiai1 ) ! #ajj-;in* ,hook] telescope 7,pease74 ,! m\nta9s above & to ! left are ! lun> ,ap5n9es2 ^? on ! left j bel[ ! c5tre are ! ,alps4 ,bo? ranges include peaks f fifte5 ?\s& to tw5ty ?\s& feet 9 height4 ,9 ! upp] "r corn] is ,cop]nicus1 ab\t fifty miles 9 diamet]4 ,! l>ge/ ( ! conspicu\s gr\p ( ?ree j bel[ ! ,ap5n9es is ,ar*im$es & at ! l[] end ( ! ,alps is ,plato4 ,note ! long sunset %ad[s ca/ by ! isolat$ peaks on ! left4 ,! c5tral portion ( ! picture is a va/ pla91 ! ,m>e ,imbrium4 ,! %>pness ( ! images giv5 by ! new telescope may be illu/rat$ by "s rec5t photographs ( ! moon1 obta9$ ) an equival5t focal l5g? ( #acd feet4 ,9 ,fig4 #ae is %[n a rugg$ region ( ! moon1 conta9+ _m r+-l m\nta9s or crat]s4 ,fig4 #af %[s ! great arc ( ! lun> ,ap5n9es 7above7 & ! ,alps 7bel[71 to ! left ( ! broad pla9 ( ! ,m>e ,imbrium4 ,! />like po9ts along ! moon's t]m9ator1 :i* sep>ates ! d>k area f ! region ^u :i* ! sun 7on ! "r7 %9es1 are ! m\nta9 peaks1 ab\t to disappe> at sunset4 ,! long %ad[s ca/ by ! m\nta9s j )9 ! illum9at$ area are pla9ly se54 ,"s ( ! peaks ( ! lun> ,ap5n9es atta9 a height ( #bj1jjj feet4 ,9 less p[]ful telescopes ! />s at ! c5tre ( ! great globul> clu/]s are s closely cr[d$ toge!r t !y _c be /udi$ sep>ately ) ! spectrograph4 ,moreov]1 mo/ ( !m are mu* too fa9t = exam9ation ) ?is in/rum5t4 ,at ! #acd-;foot focus ! #ajj-;in* telescope gives a l>ge-scale image ( su* clu/]s1 & p]mits ! spectra ( />s z fa9t z ! fifte5? magnitude to be sep>ately photograph$4 ,illu/ration3 ,fig4 #ag4 ,hubble's ,v>iable ,nebula4 ,"o ( ! few nebul kn[n to v>y 9 brightness & =m4 ,photograph$ ) ! #ajj-;in* telescope 7,hubble74 ,,close ,,d\ble ,,/>s ,a rem>kable use ( ! #ajj-;in* telescope1 :i* p]mits its full !oretical resolv+ p[] to be n m]ely atta9$ b to be d\bl$1 has be5 made possible by ! fir/ application ( ,mi*elson's int]f]5ce me?od to ! measurem5t ( v close d\ble />s4 ,:5 employ+ ?is1 ! #ajj-;in* mirror is completely cov]$1 except = two slits4 ,beams ( light f a />1 ent]+ by ! slits1 unite at ! focus ( ! telescope1 :]e ! image is exam9$ by an eyepiece magnify+ ab\t five ?\s& diamet]s4 ,across ! enl>g$ /> image a s]ies ( f9e1 %>p fr+es is se51 ev5 :5 ! atmosph]ic conditions are poor4 ,if ! /> is s+le ! fr+es rema9 visible1 :atev] ! di/ance betwe5 ! slits4 ,b 9 ! case ( a /> l ,capella1 previ\sly inf]r$ to be d\ble f ! p]iodic displacem5t ( ! l9es 9 its spectrum1 b ) compon5ts too close toge!r to be di/+ui%$ sep>ately1 ! fr+es behave diff]5tly4 ,z ! slits are mov$ ap>t a po9t is rea*$ :]e ! fr+es completely disappe>1 only to reappe> z ! sep>ation is cont9u$4 ,?is effect is obta9$ :5 ! slits are at "r angles to ! l9e jo9+ ! two />s ( ! pair1 f\nd by ?is me?od to be #j4jdah ( a second ( arc ap>t 7on ,decemb] #cj1 #aiai74 ,subsequ5t measures1 ( f> great] precision ?an ^? obta9able by o!r me?ods 9 ! case ( easily sep>at$ d\ble />s1 %[ ! rapid orbital motion ( ! compon5ts ( ! sy/em4 ,?is device w be appli$ to o!r close b9>ies1 hi!rto beyond ! rea* ( measurem5t4 ,illu/ration3 ,fig4 #ah4 ,r+ ,nebula 9 ,lyra1 photograph$ ) ! #fj-;in* 7,rit*ey7 & #ajj-;in* 7,duncan7 telescopes4 ,%[+ ! increas$ scale ( ! images giv5 by ! l>g] in/rum5t4 ,)\t ent]+ into fur!r details ( ! te/s1 x is evid5t t ! new telescope w af=d b\ndless possibilities = ! /udy ( ! /ell> univ]se499 ,! /ructure & ext5t ( ! galactic sy/em1 & ! motions ( ! />s compris+ x2 ! di/ribution1 di/ances1 & dim5sions ( ! spiral nebul1 _! motions1 rotation1 & mode ( developm5t2 ! orig9 ( ! />s & ! successive /ages 9 _! life hi/ory3 ^! are "s ( ! great que/ions :i* ! new telescope mu/ help to answ]4 ,9 su* an emb>rassm5t ( ri*es ! *ief difficulty is to )/& ! temptation t[>d scatt]+ ( ef=t1 & to =m an obs]v+ programme direct$ t[>d ! solution ( crucial problems r ?an ! accumulation ( va/ /ores ( miscellane\s data4 ,?is programme w be supplem5t$ by an ext5sive /udy ( ! sun1 ! only /> ne> en\gh ! e>? to be exam9$ 9 detail1 & by a s]ies ( laboratory inve/igations involv+ ! exp]im5tal imitation ( sol> & /ell> conditions1 ?us aid+ 9 ! int]pretation ( cele/ial ph5om5a4 ,footnote 993 ,x is n adapt$ = "w on ! sun1 z ! mirrors w\ld be di/ort$ by its heat4 ,?ree o!r telescopes1 especially design$ = sol> obs]vations1 are 9 use on ,m\nt ,wilson4 ,,*apt] ,,ii ,,giant ,,/>s ,our ance/ral sun1 z pictur$ by ,laplace1 orig9ally ext5d$ 9 a /ate ( lum9\s vapor beyond ! b\nd>ies ( ! sol> sy/em4 ,rotat+ ^u its axis1 x sl[ly contract$ ?r\gh loss ( heat by radiation1 leav+ beh9d x portions ( its mass1 :i* cond5s$ to =m ! planets4 ,/ill gase\s1 ?\gh n[ d5s] ?an wat]1 x cont9ues to p\r out ! heat on :i* our exi/5ce dep5ds1 z x %r9ks imp]ceptibly t[>d its ultimate condition ( a cold & d>k5$ globe4 ,laplace's hypo!sis has be5 subject$ 9 rec5t ye>s to mu* criticism1 & !re is good reason to d\bt :e!r 8 description ( ! mode ( evolution ( our sol> sy/em is correct 9 e p>ticul>4 ,all critics agree1 h[ev]1 t ! sun 0 once enorm\sly l>g] ?an x n[ is1 & t ! planets orig9ally =m$ "p ( its di/5d$ mass4 ,ev5 9 its pres5t dim9i%$ /ate1 ! sun is huge beyond easy conception4 ,our own e>?1 ?\gh s m9ute a fragm5t ( ! primeval sun1 is nev]!less s l>ge t "s p>ts ( its surface h n yet be5 explor$4 ,se5 beside ! sun1 by an obs]v] on "o ( ! planets1 ! e>? w\ld appe> z an insignificant speck1 :i* c\ld be swall[$ ) ease by ! :irl+ vortex ( a sun-spot4 ,if ! sun 7 holl[1 ) ! e>? at its c5tre1 ! moon1 ?\gh #bdj1jjj miles f u1 w\ld h room & to sp>e 9 :i* to describe its orbit1 = ! sun is #hfe1jjj miles 9 diamet]1 s t its volume is m ?an a million times t ( ! e>?4 ,illu/ration3 ,fig4 #ai4 ,gase\s prom95ce at ! sun's limb1 #adj1jjj miles high 7,ell]man74 ,photograph$ ) ! spectroheliograph1 us+ ! light emitt$ by gl[+ calcium vapor4 ,! comp>ative size ( ! e>? is indicat$ by ! :ite circle4 ,b :at ( ! />s1 prov$ by ! spectroscope to be self-lum9\s1 int5sely hot1 & =m$ ( ! same *emical elem5ts t con/itute ! sun & ! e>?8 ,are !y comp>able 9 size ) ! sun8 ,d !y occur 9 all /ages ( developm5t1 f infancy to old age8 ,& if su* /ages c be detect$1 d !y af=d indications ( ! gradual dim9ution 9 volume :i* ,laplace imag9$ ! sun to exp]i5ce8 ,illu/ration3 ,fig4 #bj4 ,! sun1 #hfe1jjj miles 9 diamet]1 f a direct photograph %[+ _m sun-spots 7,:itney7 ,! small black disk 9 ! c5tre repres5ts ! comp>ative size ( ! e>?1 :ile ! circle surr\nd+ x corresponds 9 diamet] to ! orbit ( ! moon4 ,,/> ,,images ,prior to ! application ( ! p[]ful new eng9e ( rese>* describ$ 9 ?is article we h _h no means ( measur+ ! diamet]s ( ! />s4 ,we h measur$ _! di/ances & _! motions1 det]m9$ _! *emical composition1 & obta9$ und5iable evid5ce ( progressive developm5t1 b ev5 9 ! mo/ p[]ful telescopes _! images are s m9ute t !y appe> z po9ts r ?an z disks4 ,9 fact1 ! l>g] ! telescope & ! m p]fect ! atmosph]ic conditions at ! obs]v]'s comm&1 ! small] d ^! images appe>4 ,on ! photographic plate1 x is true1 ! />s are record$ z measurable disks1 b ^! are due to ! spread+ ( ! light f _! bright po9t-l images1 & _! diamet]s increase z ! exposure "t is prolong$4 ,f ! images ( ! bright] />s rays ( light project 9 /raight l9es1 b ^! also are in/rum5tal ph5om5a1 due to diffraction ( light by ! /eel b>s t support ! small mirror 9 ! tube ( reflect+ telescopes4 ,9 a ^w1 ! />s are s remote t ! l>ge/ & mo/ p]fect telescopes %[ !m only z extremely m9ute ne$le-po9ts ( light1 )\t any trace ( _! true disks4 ,illu/ration3 ,fig4 #ba4 ,great sun-spot gr\p1 ,augu/ #h1 #aiag 7,:itney74 ,! disk 9 ! corn] repres5ts ! comp>ative size ( ! e>?4 ,h[1 !n1 may we hope to measure _! diamet]s8 ,by us+1 z ! man ( sci5ce mu/ s (t5 d1 indirect means :5 ! direct attack fails4 ,mo/ ( ! rem>kable progress ( a/ronomy dur+ ! la/ qu>t]-c5tury has result$ f ! application ( new & +5i\s devices borr[$ f ! physici/4 ,^! h multipli$ to su* a degree t "s ( our obs]vatories are lit]ally physical laboratories1 9 :i* ! sun & />s are exam9$ by p[]ful spectroscopes & o!r optical in/rum5ts t h rec5tly advanc$ our k ( physics by leaps & b\nds4 ,9 ! pres5t case we are indebt$ = our />-measur+ device to ! di/+ui%$ physici/ ,pr(essor ,alb]t ,a4 ,mi*elson1 :o has contribut$ a long array ( novel app>atus & me?ods to physics & a/ronomy4 ,,! ,,int]f]omet] ,! in/rum5t 9 "q1 kn[n z ! int]f]omet]1 _h previ\sly yield$ a rem>kable s]ies ( results :5 appli$ 9 its v>i\s =ms to ! solution ( fundam5tal problems4 ,to m5tion only a few ( ^? t h help$ to e/abli% ,mi*elson's fame1 we may recall t our exact k ( ! l5g? ( ! int]national metre at ,sevres1 ! _w's /&>d ( measurem5t1 0 obta9$ by him ) an int]f]omet] 9 t]ms ( ! inv>iable l5g? ( light-waves4 ,a diff]5t =m ( int]f]omet] has m rec5tly enabl$ him to measure ! m9ute tides )9 ! solid body ( ! e>?--n ! great tides ( ! ocean1 b ! slight de=mations ( ! e>?'s body1 :i* is z rigid z /eel1 t are caus$ by ! v>y+ attractions ( ! sun & moon4 ,f9ally1 to m5tion only "o m case1 x 0 ! ,mi*elson-,morley exp]im5t1 made ye>s ago ) /ill ano!r =m ( int]f]omet]1 t yield$ ! basic idea f :i* ! !ory ( relativity 0 develop$ by ,lor5tz & ,e9/e94 ,illu/ration3 ,fig4 #bb4 ,photograph ( ! hydrog5 atmosph]e ( ! sun 7,ell]man74 ,made ) ! spectroheliograph1 %[+ ! imm5se vortices1 or :irl+ /orms l tornadoes1 t c5tre 9 sun-spots4 ,! comp>ative size ( ! e>? is %[n by ! :ite circle trac$ on ! l>ge/ sun-spot4 ,! hi/ory ( ! me?od ( measur+ /> diamet]s is a v curi\s "o1 %[+ h[ ! mo/ promis+ opportunities = sci5tific progress may lie unus$ = decades4 ,! fundam5tal pr9ciple ( ! device 0 fir/ sugge/$ by ! great ,fr5* physici/ ,fizeau 9 #ahfh4 ,9 #ahgd ! !ory 0 develop$ by ! ,fr5* a/ronom] ,/phan1 :o obs]v$ int]f]5ce fr+es giv5 by a l>ge numb] ( />s1 & rightly conclud$ t _! angul> diamet]s mu/ be mu* small] ?an #j4aeh ( a second ( arc1 ! smalle/ measurable ) 8 in/rum5t4 ,9 #ahij ,mi*elson1 unaw>e ( ! e>li] "w1 publi%$ 9 ! ,philosophical ,magaz9e a complete description ( an int]f]omet] capable ( det]m9+ ) surpris+ accuracy ! di/ance betwe5 ! compon5ts ( d\ble />s s close toge!r t no telescope c sep>ate !m4 ,he also %[$ h[ ! same pr9ciple c\ld be appli$ to ! measurem5t ( /> diamet]s if a suffici5tly l>ge int]f]omet] c\ld be built = ?is purpose1 & develop$ ! !ory mu* m completely ?an ,/phan _h done4 ,a ye> lat] he measur$ ! diamet]s ( ,jupit]'s satellites by ?is means at ! ,lick ,obs]vatory4 ,b ne>ly ?irty ye>s elaps$ be=e ! next /ep 0 tak54 ,two causes h d\btless contribut$ to ?is delay4 ,bo? !ory & exp]im5t h demon/rat$ ! extreme s5sitiv5ess ( ! int]f]5ce fr+es1 on ! obs]vation ( :i* ! me?od dep5ds1 & x 0 g5]ally suppos$ by a/ronom]s t di/urbances 9 ! e>?'s atmosph]e w\ld prev5t !m f be+ cle>ly se5 ) l>ge telescopes4 ,fur!rmore1 a v l>ge int]f]omet]1 too l>ge to be c>ri$ by any exi/+ telescope1 0 requir$ = ! />-diamet] "w1 ?\gh close d\ble />s c\ld h be5 easily /udi$ by ?is device ) sev]al ( ! l>ge telescopes ( ! e>ly n9eties4 ,b :atev] ! reasons1 a p[]ful me?od ( rese>* lay unus$4 ,! approa*+ completion ( ! #ajj-;in* telescope ( ! ,m\nt ,wilson ,obs]vatory l$ me to sugge/ to ,pr(essor ,mi*elson1 be=e ! ,unit$ ,/ates ent]$ ! w>1 t ! me?od be ?or\ghly te/$ "u ! favorable atmosph]ic conditions ( ,s\!rn ,cali=nia4 ,he 0 at t "t at "w on a special =m ( int]f]omet]1 design$ to det]m9e :e!r atmosph]ic di/urbances c\ld be disreg>d$ 9 plann+ l>ge-scale exp]im5ts4 ,b ! w> int]v5$1 & all ( our ef=ts 7 conc5trat$ = two ye>s on ! solution ( w> problems499 ,9 #aiai1 z soon z ! #ajj-;in* telescope _h be5 complet$ & te/$1 ! "w 0 resum$ on ,m\nt ,wilson4 ,footnote 993 ,pr(essor ,mi*elson's mo/ important contribution dur+ ! w> p]iod 0 a new & v effici5t =m ( range-f9d]1 adopt$ = use by ! ,u4 ,s4 ,navy4 ,a ,,laboratory ,,exp]im5t ,! pr9ciple ( ! me?od c be mo/ readily se5 by ! aid ( an exp]im5t :i* any "o c easily p]=m = himself ) simple app>atus4 ,make a n>r[ slit1 a few ?\s&?s ( an in* 9 wid?1 9 a %eet ( black pap]1 & support x v]tically be=e a brilliant s\rce ( light4 ,obs]ve ?is f a di/ance ( #dj or #ej feet ) a small telescope magnify+ ab\t #cj diamet]s4 ,! object-glass ( ! telescope %\ld be cov]$ ) an opaque cap1 pi]c$ by two circul> holes ab\t "o-eigh? ( an in* 9 diamet] & half an in* ap>t4 ,! holes %\ld be on opposite sides ( ! c5tre ( ! object-glass & equidi/ant f x1 & ! l9e jo9+ ! holes %\ld be horizontal4 ,:5 ?is cap is remov$ ! slit appe>s z a n>r[ v]tical b& ) mu* fa9t] b&s on bo? sides ( x4 ,) ! cap 9 place1 ! c5tral bright b& appe>s to be rul$ ) n>r[ v]tical l9es or fr+es produc$ by ! int]f]5ce99 ( ! two p5cils ( light com+ ?r\gh diff]5t p>ts ( ! object-glass f ! di/ant slit4 ,cov] "o ( ! holes1 & ! fr+es in/antly disappe>4 ,_! production requires ! jo9t effect ( ! two light-p5cils4 ,footnote 993 ,= an explanation ( ! ph5om5a ( int]f]5ce1 see any encyclopedia or book on physics4 ,n[ suppose ! two holes ov] ! object-glass to be 9 movable plates1 s t _! di/ance ap>t c be v>i$4 ,z !y are gradually sep>at$ ! n>r[ v]tical fr+es become less & less di/9ct1 & f9ally vani% completely4 ,measure ! di/ance betwe5 ! holes & divide ?is by ! wavel5g? ( light1 :i* we may call #a_/ejjjj ( an in*4 ,! result is ! angul> wid? ( ! di/ant slit4 ,kn[+ ! di/ance ( ! slit1 we c at once calculate its l9e> wid?4 ,if = ! slit we sub/itute a m9ute circul> hole1 ! me?od ( measurem5t rema9s ! same1 b ! angul> diamet] z calculat$ above mu/ be multipli$ by #a4bb499 ,footnote 993 ,m complete details may be f\nd 9 ,mi*elson's ,l[ell ,lectures on ,light-,waves & ,_! ,uses1 ,univ]sity ( ,*icago ,press1 #aijg4 ,to measure ! diamet] ( a /> we proce$ 9 a simil> way1 b1 z ! angle x subt5ds is s small1 we mu/ use a v l>ge telescope1 = ! small] ! angle ! f>!r ap>t mu/ be ! two holes ov] ! object-glass 7or ! mirror1 9 case a reflect+ telescope is employ$74 ,9 fact1 :5 ! holes are mov$ ap>t to ! full ap]ture ( ! #ajj-;in* ,hook] telescope1 ! int]f]5ce fr+es are /ill visible ev5 ) ! /> ,betelgeuse1 ?\gh its angul> diamet] is p]haps z great z t ( any o!r />4 ,?us1 we mu/ build an atta*m5t = ! telescope1 s arrang$ z to p]mit u to move ! op5+s /ill f>!r ap>t4 ,illu/ration3 ,fig4 #bc4 ,diagram %[+ outl9e ( ! #ajj-;in* ,hook] telescope1 & pa? ( ! two p5cils ( light f a /> :5 "u obs]vation ) ! #bj-;foot ,mi*elson int]f]omet]4 ,a photograph ( ! int]f]omet] is %[n 9 ,fig4 #bd4 ,,! #bj-;,,foot ,,in/rum5t ,! #bj-;foot int]f]omet] design$ by ,messrs4 ,mi*elson & ,pease1 & con/ruct$ 9 ! ,m\nt ,wilson ,obs]vatory in/rum5t-%op1 is %[n 9 ! diagram 7,fig4 #bc7 & 9 a photograph ( ! upp] end ( ! skeleton tube ( ! telescope 7,fig4 #bd74 ,! light f ! /> is receiv$ by two flat mirrors 7,ml1 ,m#d7 :i* project beyond ! tube & c be mov$ ap>t along ! support+ arm4 ,^! take ! place ( ! two holes ov] ! object-glass 9 our exp]im5t4 ,f ^! mirrors ! light is reflect$ to a second pair ( flat mirrors 7,m#b1 ,m#c71 :i* s5d x t[>d ! #ajj-;in* concave mirror 7,m#e7 at ! bottom ( ! telescope tube4 ,aft] ?is ! c\rse ( ! light is exactly z x w\ld be if ! mirrors ,m#b1 ,m#c 7 replac$ by two holes ov] ! #ajj-;in* mirror4 ,x is reflect$ to ! convex mirror 7,m#f71 !n back 9 a less rapidly conv]g5t beam t[>d ! l>ge mirror4 ,be=e rea*+ x ! light is caught by ! plane mirror 7,m#g7 & reflect$ ?r\gh an op5+ at ! side ( ! telescope tube to ! eye-piece ,e4 ,"h ! fr+es are obs]v$ ) a magnification rang+ f #a1ejj to #c1jjj diamet]s4 ,illu/ration3 ,fig4 #bd4 ,tw5ty-foot ,mi*elson int]f]omet] = measur+ /> diamet]s1 atta*$ to upp] end ( ! skeleton tube ( ! #ajj-;in* ,hook] telescope4 ,! pa? ( ! two p5cils ( light f ! /> is %[n 9 ,fig4 #bc4 ,= a photograph ( ! entire telescope1 see ,fig4 #d4 ,9 ! practical application ( ?is me?od to ! measurem5t ( /> diamet]s1 ! *ief problem 0 :e!r ! atmosph]e w\ld be quiet en\gh to p]mit %>p int]f]5ce fr+es to be produc$ ) light-p5cils m ?an #ajj in*es ap>t4 ,aft] successful prelim9>y te/s ) ! #dj-;in* refract+ telescope ( ! ,y]kes ,obs]vatory1 ,pr(essor ,mi*elson made ! fir/ attempt to see ! fr+es ) ! #fj-;in* & #ajj-;in* reflectors on ,m\nt ,wilson 9 ,septemb]1 #aiai4 ,he 0 surpris$ & delight$ to f9d t ! fr+es 7 p]fectly %>p & di/9ct ) ! full ap]ture ( bo? ^! in/rum5ts4 ,doctor ,&]son1 ( ! obs]vatory /aff1 !n devis$ a special =m ( int]f]omet] = ! measurem5t ( close d\ble />s1 & appli$ x ) ! #ajj-;in* telescope to ! measurem5t ( ! orbital motion ( ! close compon5ts ( ,capella1 ) results ( extraord9>y accuracy1 f> beyond any?+ atta9able by previ\s me?ods4 ,! success ( ?is "w /rongly enc\rag$ ! m ambiti\s project ( measur+ ! diamet] ( a />1 & ! #bj-;foot int]f]omet] 0 built = ?is purpose4 ,! difficult & delicate problem ( adju/+ ! mirrors ( ?is in/rum5t ) ! necess>y extreme accuracy 0 solv$ by ,pr(essor ,mi*elson dur+ 8 visit to ,m\nt ,wilson 9 ! summ] ( #aibj1 & ) ! assi/ance ( ,mr4 ,pease1 ( ! obs]vatory /aff1 int]f]5ce fr+es 7 obs]v$ 9 ! case ( c]ta9 />s :5 ! mirrors 7 z mu* z #ah feet ap>t4 ,all 0 ?us 9 read9ess = a decisive te/ z soon z a suitable /> pres5t$ itself4 ,,! ,,giant ,,betelgeuse ,russell1 ,%apley1 & ,edd+ton _h po9t$ out ,betelgeuse 7,arabic = ! giant's %\ld]71 ! bright r$ /> 9 ! con/ellation ( ,orion 7,fig4 #be71 z ! mo/ favorable ( all />s = measurem5t1 & ! la/-nam$ _h giv5 its angul> diamet] z #j4jea ( a second ( arc4 ,?is d$uction f !ory appe>$ 9 8 rec5t presid5tial address be=e ! ,briti% ,association = ! ,advancem5t ( ,sci5ce1 9 :i* ,pr(essor ,edd+ton rem>k$3 ,probably ! greate/ ne$ ( /ell> a/ronomy at ! pres5t day1 9 ord] to make sure t our !oretical d$uctions are />t+ on ! "r l9es1 is "s means ( measur+ ! app>5t angul> diamet] ( />s4 ,he !n ref]r$ to ! "w already 9 progress on ,m\nt ,wilson1 b anticipat$ t atmosph]ic di/urbance w ultimately set ! limit to :at c be accompli%$4 ,illu/ration3 ,fig4 #be4 ,! giant ,betelgeuse 7)9 ! circle71 famili> z ! conspicu\s r$ /> 9 ! "r %\ld] ( ,orion 7,hubble74 ,measures ) ! int]f]omet] %[ its angul> diamet] to be #j4jdg ( a second ( arc1 correspond+ to a l9e> diamet] ( #bae1jjj1jjj miles1 if ! be/ available det]m9ation ( its di/ance c be reli$ ^u4 ,?is det]m9ation %[s ,betelgeuse to be #afj light-ye>s f ! e>?4 ,light travels at ! rate ( #ahf1jjj miles p] second1 & yet sp5ds #afj ye>s on its j\rney to u f ?is />4 ,on ,decemb] #ac1 #aibj1 ,mr4 ,pease successfully measur$ ! diamet] ( ,betelgeuse ) ! #bj-;foot int]f]omet]4 ,z ! out] mirrors 7 sep>at$ ! int]f]5ce fr+es gradually became less di/9ct1 z !ory requires1 & z ,doctor ,m]rill _h previ\sly se5 :5 obs]v+ ,betelgeuse ) ! int]f]omet] us$ = ,capella4 ,at a sep>ation ( #aj feet ! fr+es disappe>$ completely1 giv+ ! data requir$ = calculat+ ! diamet] ( ! />4 ,to te/ ! p]fection ( ! adju/m5t1 ! telescope 0 turn$ to o!r />s1 ( small] angul> diamet]1 :i* %[$ ! fr+es ) p]fect cle>ness4 ,turn+ back to ,betelgeuse1 !y 7 se5 beyond d\bt to be abs5t4 ,assum+ ! mean wave-l5g? ( ! light ( ?is /> to be #egej_/ajjjjjjj ( a millimetre1 its angul> diamet] comes out #j4jdg ( a second ( arc1 ?us fall+ betwe5 ! values--#j4jea & #j4jca ( a second--pr$ict$ by ,edd+ton & ,russell f slightly diff]5t assumptions4 ,subsequ5t corrections & repeat$ measurem5t w *ange ,mr4 ,pease's result some:at1 b x is almo/ c]ta9ly )9 #aj or #ae p] c5t ( ! tru?4 ,we may !re=e conclude t ! angul> diamet] ( ,betelgeuse is v ne>ly ! same z t ( a ball "o in* 9 diamet]1 se5 at a di/ance ( sev5ty miles4 ,illu/ration3 ,fig4 #bf4 ,arcturus 7)9 ! :ite circle71 kn[n to ! ,arabs z ! ,lance ,be>]1 & to ! ,*9ese z ! ,great ,horn or ! ,palace ( ! ,emp]ors 7,hubble74 ,its angul> diamet]1 measur$ at ,m\nt ,wilson by ,pease ) ! #bj-;foot ,mi*elson int]f]omet] on ,april #ae1 #aiba1 is #j4jbb ( a second1 9 close agreem5t ) ,russell's pr$ict$ value ( #j4jai ( a second4 ,! mean p>allax ( ,arcturus1 bas$ ^u sev]al det]m9ations1 is #j4jie ( a second1 correspond+ to a di/ance ( #cd light-ye>s4 ,! l9e> diamet]1 comput$ f ,pease's measure & ?is value ( ! di/ance is ab\t #ba million miles4 ,b ?is repres5ts only ! angle subt5d$ by ! />'s disk4 ,to le>n its l9e> diamet]1 we mu/ "k its di/ance4 ,f\r det]m9ations ( ! p>allax1 :i* det]m9es ! di/ance1 h be5 made4 ,elk91 ) ! ,yale heliomet]1 obta9$ #j4jcb ( a second ( arc4 ,s*les+]1 f photographs tak5 ) ! #cj-;in* ,allegh5y refractor1 d]iv$ #j4jaf4 ,adams1 by 8 spectroscopic me?od appli$ ) ! #fj-;in* ,m\nt ,wilson reflector1 obta9$ #j4jab4 ,lee's rec5t value1 secur$ photographically ) ! #dj-;in* ,y]kes refractor1 is #j4jbb4 ,! heliomet] p>allax is d\btless less reliable ?an ! photographic ones1 & ,doctor ,adams /ates t ! spectral type & lum9osity ( ,betelgeuse make 8 value less c]ta9 ?an 9 ! case ( mo/ o!r />s4 ,if we take a 7weight$7 mean value ( #j4jbj ( a second1 we %all probably n be f> f ! tru?4 ,?is p>allax repres5ts ! angle subt5d$ by ! radius ( ! e>?'s orbit 7#ic1jjj1jjj miles7 at ! di/ance ( ,betelgeuse4 ,by comp>+ x ) #j4jdg1 ! angul> diamet] ( ! />1 we see t ! l9e> diamet] is ab\t two & "o-?ird times z great z ! di/ance f ! e>? to ! sun1 or approximately #bae1jjj1jjj miles4 ,?us1 if ?is measure ( its di/ance is n consid]ably 9 error1 ,betelgeuse w\ld ne>ly fill ! orbit ( ,m>s4 ,all me?ods ( det]m9+ ! di/ances ( ! />s are subject to unc]ta9ty1 h[ev]1 & subsequ5t measures may r$uce ?is figure v appreciably4 ,b !re c be no d\bt t ! diamet] ( ,betelgeuse exce$s #ajj1jjj1jjj miles1 & x is probably mu* great]4 ,! extremely small angle subt5d$ by ?is enorm\s disk is expla9$ by ! great di/ance ( ! />1 :i* is ab\t #afj light-ye>s4 ,t is to say1 light travell+ at ! rate ( #ahf1jjj miles p] second sp5ds #afj ye>s 9 cross+ ! space t lies betwe5 u & ,betelgeuse1 ^: trem5d\s proportions !re=e seem s m9ute ev5 9 ! mo/ p[]ful telescopes4 ,,/ell> ,,evolution ,?is actual measure ( ! diamet] ( ,betelgeuse supplies a new & /rik+ te/ ( ,russell's & ,h]tzsprung's !ory ( dw>f & giant />s4 ,j be=e ! w> ,russell %[$ t our old me?ods ( classify+ ! />s accord+ to _! spectra mu/ be radically *ang$4 ,/>s 9 an e>ly /age ( _! life hi/ory may be reg>d$ z diffuse gase\s masses1 enorm\sly l>g] ?an our sun1 & at a mu* l[] temp]ature4 ,_! d5sity mu/ be v l[1 & _! /ate t ( a p]fect gas4 ,^! are ! giants4 ,9 ! sl[ process ( "t !y contract ?r\gh con/ant loss ( heat by radiation4 ,b1 despite ?is loss1 ! heat produc$ by contraction & f o!r s\rces 7see p4 #hb7 causes _! temp]ature to rise1 :ile _! color *anges f r$ to blui% :ite4 ,! process ( %r9kage & rise ( temp]ature goes on s long z !y rema9 9 ! /ate ( a p]fect gas4 ,b z soon z contraction has increas$ ! d5sity ( ! gas beyond a c]ta9 po9t ! cycle rev]ses & ! temp]ature beg9s to fall4 ,! blui%-:ite light ( ! /> turns yell[i%1 & we ent] ! dw>f /age1 ( :i* our own sun is a repres5tative4 ,! d5sity increases1 surpass+ t ( wat] 9 ! case ( ! sun1 & go+ f> beyond ?is po9t 9 lat] /ages4 ,9 ! lapse ( millions ( ye>s a r$di% hue appe>s1 f9ally turn+ to deep r$4 ,! fall+ temp]ature p]mits ! *emical elem5ts1 exi/+ 9 a gase\s /ate 9 ! out] atmosph]e ( ! />1 to unite into comp\nds1 :i* are r5d]$ conspicu\s by _! *>act]i/ic b&s 9 ! spectrum4 ,f9ally comes ext9ction ( light1 z ! /> approa*es its ultimate /ate ( a cold & solid globe4 ,illu/ration3 ,fig4 #bg4 ,! giant /> ,ant>es 7)9 ! :ite circle71 notable = its r$ color 9 ! con/ellation ,scorpio1 & nam$ by ! ,greeks ,a ,rival ( ,m>s 7,hubble74 ,! di/ance ( ,ant>es1 ?\gh n v accurately kn[n1 is probably n f> f #cej light-ye>s4 ,its angul> diamet] ( #j4jdj ( a second w\ld ?us correspond to a l9e> diamet] ( ab\t #djj million miles4 ,we may ?us =m a new picture ( ! two bran*es ( ! temp]ature curve1 long s9ce sugge/$ by ,locky]1 on v diff]5t gr\nds1 z ! outl9e ( /ell> life4 ,on ! asc5d+ side are ! giants1 ( va/ dim5sions & m diffuse ?an ! air we brea!4 ,!re are good reasons = believ+ t ! mass ( ,betelgeuse _c be m ?an t5 times t ( ! sun1 :ile its volume is at lea/ a million times z great & may exce$ eight million times ! sun's volume4 ,!re=e1 its av]age d5sity mu/ be l t ( an att5uat$ gas 9 an electric vacuum tube4 ,?ree-qu>t]s ( ! nak$-eye />s are 9 ! giant /age1 :i* comprises su* famili> objects z ,betelgeuse1 ,ant>es1 & ,aldeb>an1 b mo/ ( !m are mu* d5s] ?an ^! greatly inflat$ bodies4 ,! p9nacle is rea*$ 9 ! int5sely hot :ite />s ( ! helium class1 9 ^: spectra ! l9es ( ?is gas are v conspicu\s4 ,! d5sity ( ^! />s is p]haps "o-t5? t ( ! sun4 ,sirius1 also v hot1 is ne>ly twice z d5se4 ,!n comes ! cool+ /age1 *>act]iz$1 z already rem>k$1 by increas+ d5sity1 & also by increas+ *emical complexity result+ f fall+ temp]ature4 ,?is life cycle is probably n foll[$ by all />s1 b x may hold true = millions ( !m4 ,! exi/5ce ( giant & dw>f />s has be5 fully prov$ by ! rem>kable "w ( ,adams & 8 associates on ,m\nt ,wilson1 :]e 8 me?od ( det]m9+ a />'s di/ance & intr9sic lum9osity by spectroscopic obs]vations has already be5 appli$ to #b1jjj />s4 ,discussion ( ! results leads at once to ! recognition ( ! two great classes ( giants & dw>fs4 ,n[ comes ! "w ( ,mi*elson & ,pease to cap ! climax1 giv+ u ! actual diamet] ( a typical giant />1 9 close agreem5t ) pr$ictions bas$ ^u !ory4 ,f ?is diamet] we may conclude t ! d5sity ( ,betelgeuse is extremely l[1 9 h>mony ) ,russell's !ory1 :i* is fur!r support$ by spectroscopic analysis ( ! />'s light1 reveal+ evid5ce ( ! comp>atively l[ temp]ature call$ = by ! !ory at ?is e>ly /age ( /ell> exi/5ce4 ,,two ,,o!r ,,giants ,! diamet] ( ,arcturus 0 successfully measur$ by ,mr4 ,pease at ,m\nt ,wilson on ,april #ae4 ,z ! mirrors ( ! int]f]omet] 7 mov$ ap>t1 ! fr+es gradually decreas$ 9 visibility until !y f9ally disappe>$ at a mirror sep>ation ( #ai4f feet4 ,adopt+ a mean wave-l5g? ( #efjj_/ajjjjjjj ( a millimetre = ! light ( ,arcturus1 ?is gives a value ( #j4jbb ( a second ( arc = ! angul> diamet] ( ! />4 ,if we use a mean value ( #j4jie ( a second = ! p>allax1 ! correspond+ l9e> diamet] comes out #ba1jjj1jjj miles4 ,! angul> diamet]1 z 9 ! case ( ,betelgeuse1 is 9 rem>kably close agreem5t ) ! diamet] pr$ict$ f !ory4 ,ant>es1 ! ?ird /> measur$ by ,mr4 ,pease1 is ! l>ge/ ( all4 ,if x is actually a memb] ( ! ,scorpius-,c5taurus gr\p1 z we h /rong reason to believe1 x is fully #cej light-ye>s f ! e>?1 & its diamet] is ab\t #djj1jjj1jjj miles4 ,illu/ration3 ,fig4 #bh4 ,diamet]s ( ! ,sun1 ,arcturus1 ,betelgeuse1 & ,ant>es comp>$ ) ! orbit ( ,m>s4 ,sun1 diamet]1 #hfe1jjj miles4 ,arcturus1 diamet]1 #ba1jjj1jjj miles4 ,betelgeuse1 diamet]1 #bae1jjj1jjj miles4 ,ant>es1 diamet]1 #djj1jjj1jjj miles4 ,x n[ rema9s to make fur!r measures ( ,betelgeuse1 especially because its m>k$ *anges 9 brightness sugge/ possible v>iations 9 diamet]4 ,we mu/ also apply ! int]f]omet] me?od to />s ( ! v>i\s spectral types1 9 ord] to af=d a sure basis = future /udies ( /ell> evolution4 ,un=tunately1 only a few giant />s are c]ta9 to fall )9 ! range ( our pres5t in/rum5t4 ,an int]f]omet] ( #gj-;feet ap]ture w\ld be ne$$ to measure ,sirius accurately1 & "o ( twice ?is size to deal ) less brilliant :ite />s4 ,a #ajj-;foot in/rum5t1 if feasible to build1 w\ld p]mit objects repres5t+ mo/ ( ! *ief /ages ( /ell> developm5t to be measur$1 ?us contribut+ 9 ! highe/ degree to ! progress ( our k ( ! life hi/ory ( ! />s4 ,=tunately1 ?\gh ! me*anical difficulties are great1 ! optical problem is insignificant1 & ! co/ ( ! entire app>atus1 ?\gh necess>ily high1 w\ld be only a small fraction ( t ( a telescope ( correspond+ ap]ture1 if su* c\ld be built4 ,a #ajj-;foot int]f]omet] might be design$ 9 _m diff]5t =ms1 & "o ( ^! may ultimately be f\nd to be )9 ! range ( possibility4 ,mean:ile ! #bj-;foot int]f]omet] has be5 improv$ s mat]ially t x n[ promises to yield approximate measures ( />s at fir/ suppos$ to be beyond its capacity4 ,illu/ration3 ,fig4 #bi4 ,aldeb>an1 ! lead] 7( ! ,pleiades71 0 also kn[n to ! ,arabs z ,! ,eye ( ! ,bull1 ,! ,he>t ( ! ,bull1 & ,! ,great ,camel 7,hubble74 ,l ,betelgeuse & ,ant>es1 x is notable = its r$ color1 :i* acc\nts = ! fact t its image on ?is photograph is h>dly m conspicu\s ?an ! images ( />s :i* are actually mu* fa9t] b conta9 a l>g] proportion ( blue light1 to :i* ! photographic plates "h employ$ are m s5sitive ?an to r$ or yell[4 ,aldeb>an is ab\t #ej light-ye>s f ! e>?4 ,int]f]omet] measures1 n[ 9 progress on ,m\nt ,wilson1 indicate t its angul> diamet] is ab\t #j4jbj ( a second4 ,:ile ! !ory ( dw>f & giant />s & ! measurem5ts j describ$ af=d no direct evid5ce be>+ on ,laplace's explanation ( ! =mation ( planets1 !y %[ t />s exi/ :i* are comp>able 9 diamet] ) our sol> sy/em1 & sugge/ t ! sun mu/ h %runk f va/ dim5sions4 ,! mode ( =mation ( sy/ems l our own1 & ( o!r sy/ems num]\sly illu/rat$ 9 ! heav5s1 is "o ( ! mo/ fasc9at+ problems ( a/ronomy4 ,mu* light has be5 ?r[n on x by rec5t inve/igations1 r5d]$ possible by ! developm5t ( new & p[]ful in/rum5ts & by advances 9 physics ( ! mo/ fundam5tal "*4 ,all ! evid5ce confirms ! exi/5ce ( dw>f & giant />s1 b mu* "w mu/ be done be=e ! entire c\rse ( /ell> evolution c be expla9$4 ,,*apt] ,,iii ,,cosmic ,,crucibles ,%elt] dur+ ,raids1 m>k+ ! entrance to und]gr\nd passages1 0 a sign ( common occurr5ce & s9i/] sugge/ion ?r\gh\t ,london dur+ ! w>4 ,) *>act]i/ic +5uity & craft9ess1 o/5sibly = purposes ( peace b ) bomb-c>ry+ capacity z a prime specification1 ! ,zeppel9 _h be5 develop$ by ! ,g]mans to a po9t :]e x s]i\sly ?reat5$ bo? ,london & ,p>is4 ,se>*lights1 range-f9d]s1 & anti-aircraft guns1 surpass$ by ! d>+ v5tures ( ,briti% & ,fr5* airm51 w\ld h s]v$ b little aga9/ ! night invad] except = its "o fatal defect--! inflammable nature ( ! hydrog5 gas t kept x al(t4 ,a s+le explosive bullet s]v$ to trans=m a ,zeppel9 into a heap ( scor*$ & twi/$ metal4 ,?is *>act]i/ic ( hydrog5 caus$ ! failure ( ! ,zeppel9 raids4 ,_h ! w> la/$ a few mon?s long]1 h[ev]1 ! "w ( ,am]ican sci5ti/s w\ld h made our c\nt]-attack 9 ! air a =midable "o4 ,at ! sign+ ( ! armi/ice hundr$s ( cyl9d]s ( compress$ helium lay at ! docks ready = %ipm5t abroad4 ,extract$ f ! natural gas ( ,texas wells by new & +5i\s processes1 ?is sub/itute = hydrog51 almo/ z light & absolutely un9flammable1 produc$ 9 quantities ( millions ( cubic feet1 w\ld h made ! dirigibles ( ! ,allies ma/]s ( ! air4 ,! special prop]ties ( ?is rem>kable gas1 previ\sly obta9able only 9 m9ute quantities1 w\ld h suffic$ to rev]se ! situation4 ,,sol> ,,helium ,helium1 z its "n implies1 is ( sol> orig94 ,9 #ahfh1 :5 ,locky] fir/ direct$ 8 spectroscope to ! great flames or prom95ces t rise ?\s&s ( miles1 sometimes hundr$s ( ?\s&s1 above ! surface ( ! sun1 he in/antly id5tifi$ ! *>act]i/ic r$ & blue radiations ( hydrog54 ,9 ! yell[1 close to ! position ( ! well-kn[n d\ble l9e ( sodium1 b n q co9cid5t ) x1 he detect$ a new l9e1 ( great brilliancy1 ext5d+ to ! highe/ levels4 ,its simil>ity 9 ?is respect ) ! l9es ( hydrog5 l$ him to recognize ! exi/5ce ( a new & v light gas1 unkn[n to t]re/rial *emi/ry4 ,_m ye>s pass$ be=e any *emical laboratory on e>? 0 able to mat* ?is product ( ! great laboratory ( ! sun4 ,9 #ahif ,ramsay at la/ succe$$ 9 sep>at+ helium1 recogniz$ by ! same yell[ l9e 9 its spectrum1 9 m9ute quantities f ! m9]al uran9ite4 ,once available = /udy "u electrical excitation 9 vacuum tubes1 helium 0 f\nd to h _m o!r l9es 9 its spectrum1 :i* h be5 id5tifi$ 9 ! spectra ( sol> prom95ces1 gase\s nebul1 & hot />s4 ,inde$1 !re is a /ell> class kn[n z helium />s1 because ( ! dom9ance ( ?is gas 9 _! atmosph]es4 ,illu/ration3 ,fig4 #cj4 ,sol> prom95ces1 photograph$ ) ! spectroheliograph )\t an eclipse 7,ell]man74 ,9 ^! lum9\s gase\s cl\ds1 :i* sometimes rise to elevations exce$+ half ! sun's diamet]1 ! new gas helium 0 discov]$ by ,locky] 9 #ahfh4 ,helium 0 n f\nd on ! e>? until #ahif4 ,s9ce !n x has be5 %[n to be a prom95t con/itu5t ( nebul & hot />s4 ,! *ief importance ( helium lies 9 ! clue x has af=d$ to ! con/itution ( matt] & ! transmutation ( ! elem5ts4 ,radium & o!r radioactive sub/ances1 su* z uranium1 spontane\sly emit negatively *>g$ p>ticles ( extremely small mass 7electrons71 & also positively *>g$ p>ticles ( mu* great] mass1 kn[n z alpha p>ticles4 ,ru!r=d & ,geig] actually succe$$ 9 c\nt+ ! numb] ( alpha p>ticles emitt$ p] second by a kn[n mass ( radium1 & %[$ t ^! 7 *>g$ helium atoms4 ,to discuss m at l5g? ! extraord9>y *>act]i/ics ( helium1 :i* plays s l>ge a "p 9 cele/ial affairs1 w\ld take u too f> afield4 ,let u !re=e pass to ano!r case 9 :i* a fundam5tal discov]y1 ?is "t 9 physics1 0 fir/ =e%ad[$ by a/ronomical obs]vation4 ,,sun-,,spots ,,z ,,magnets ,no ar*ologi/1 :e!r ,"y or ,*ampollion deciph]+ ! ,rosetta ,/one1 or ,rawl9son copy+ ! cunei=m inscription on ! cliff ( ,behi/un1 0 ev] fac$ by a m fasc9at+ problem ?an t :i* confronts ! sol> physici/ engag$ 9 ! int]pretation ( ! hi]oglyphic l9es ( sun-spot spectra4 ,! colossal :irl+ /orms t con/itute sun-spots1 s va/ t ! e>? w\ld make b a mom5t's scant m\?ful = !m1 diff] mat]ially f ! g5]al light ( ! sun :5 exam9$ ) ! spectroscope4 ,obs]v+ !m visually _m ye>s ago1 ! late ,pr(essor ,"y1 ( ,pr9ceton1 f\nd among _! complex features a numb] ( d\ble l9es :i* he naturally attribut$1 9 h>mony ) ! physical k ( ! "t1 to ! effect ( rev]sal by sup]pos$ lay]s ( vapors ( diff]5t d5sity & temp]ature4 ,:at he actually saw1 h[ev]1 z 0 prov$ at ! ,m\nt ,wilson ,obs]vatory 9 #aijh1 0 ! effect ( a p[]ful magnetic field on radiation1 n[ kn[n z ! ,zeeman effect4 ,illu/ration3 ,fig4 #ca4 ,! #aej-;foot t[] telescope ( ! ,m\nt ,wilson ,obs]vatory4 ,an image ( ! sun ab\t #af in*es 9 diamet] is =m$ 9 ! laboratory at ! base ( ! t[]4 ,bel[ ?is1 9 a well ext5d+ #hj feet into ! e>?1 is ! p[]ful spectroscope ) :i* ! magnetic fields 9 sun-spots & ! g5]al magnetic field ( ! sun are /udi$4 ,f>aday 0 ! fir/ to detect ! influ5ce ( magnetism on light4 ,betwe5 ! poles ( a l>ge electromagnet1 p[]ful = ^? days 7#ahde71 he plac$ a block ( v d5se glass4 ,! plane ( pol>ization ( a beam ( light1 :i* pass$ unaffect$ ?r\gh ! glass be=e ! swit* 0 clos$1 0 se5 to rotate :5 ! magnetic field 0 produc$ by ! fl[ ( ! curr5t4 ,a simil> rotation is n[ famili> 9 ! well-kn[n te/s ( sug>s--lvulose & dextrose--:i* rotate plane-pol>iz$ light to left & "r1 respectively4 ,b 9 ?is fir/ discov]y ( a relation%ip betwe5 light & magnetism ,f>aday _h n tak5 ! m important /ep t he covet$--to det]m9e :e!r ! vibration p]iod ( a light-emitt+ p>ticle is subject to *ange 9 a magnetic field4 ,he attempt$ ?is 9 #ahfb--! la/ exp]im5t ( 8 life4 ,a sodium flame 0 plac$ betwe5 ! poles ( a magnet1 & ! yell[ l9es 7 wat*$ 9 a spectroscope :5 ! magnet 0 excit$4 ,no *ange c\ld be detect$1 & none 0 f\nd by subsequ5t inve/igators until ,zeeman1 ( ,leid51 ) m p[]ful in/rum5ts made 8 fam\s discov]y1 ! tw5ty-fif? anniv]s>y ( :i* has rec5tly be5 celebrat$4 ,illu/ration3 ,fig4 #cb4 ,pasad5a ,laboratory ( ! ,m\nt ,wilson ,obs]vatory4 ,%[+ ! l>ge magnet 7on ! left7 & ! spectroscopes us$ = ! /udy ( ! effect ( magnetism on radiation4 ,a s+le l9e 9 ! spectrum is split by ! magnetic field into f ?ree to tw5ty-"o compon5ts1 z illu/rat$ 9 ,fig4 #cd4 ,! correspond+ l9es 9 ! spectra ( sun-spots are split up 9 precisely ! same way1 ?us indicat+ ! pres5ce ( p[]ful magnetic fields 9 ! sun4 ,8 me?od ( proc$ure 0 simil> to ,f>aday's1 b 8 magnet & spectroscope 7 mu* m p[]ful1 & a !ory due to ,lor5tz1 pr$ict+ ! nature ( ! *ange to be expect$1 0 available z a *eck on 8 results4 ,:5 ! curr5t 0 appli$ ! l9es 7 se5 to wid54 ,9 a /ill m p[]ful magnetic field ea* ( !m split into two compon5ts 7:5 ! obs]vation 0 made along ! l9es ( =ce71 & ! light ( ! compon5ts ( ea* l9e 0 f\nd to be circul>ly pol>iz$ 9 opposite directions4 ,/rictly 9 h>mony ) ,lor5tz's !ory1 ?is splitt+ & pol>ization prov$ ! pres5ce 9 ! lum9\s vapor ( exactly su* negatively *>g$ electrons z _h be5 indicat$ !re previ\sly by v diff]5t exp]im5tal me?ods4 ,9 #aijh great cyclonic /orms1 or vortices1 7 discov]$ at ! ,m\nt ,wilson ,obs]vatory c5tr+ 9 sun-spots4 ,su* :irl+ masses ( hot vapors1 inf]r$ f ,sir ,joseph ,?omson's results to conta9 electrically *>g$ p>ticles1 %\ld give rise to a magnetic field4 ,?is hypo!sis at once sugge/$ t ! d\ble l9es obs]v$ by ,"y might really repres5t ! ,zeeman effect4 ,! te/ 0 made1 & all ! *>act]i/ic ph5om5a ( radiation 9 a magnetic field 7 f\nd4 ,?us a great physical exp]im5t is con/antly be+ p]=m$ = u 9 ! sun4 ,e l>ge sunspot conta9s a magnetic field cov]+ _m ?\s&s ( squ>e miles1 )9 :i* ! spectrum l9es ( iron1 manganese1 *romium1 titanium1 vanadium1 calcium1 & o!r metallic vapors are s p[]fully affect$ t _! wid5+ & splitt+ c be se5 ) telescopes & spectroscopes ( mod]ate size4 ,,! ,,t[] ,,telescope ,bo? ( ^! illu/rations %[ h[ ! physici/ & *emi/1 :5 adequately arm$ = a/ronomical attack1 c take advantage 9 _! /udies ( ! /up5d\s processes visible 9 cosmic crucibles1 heat$ to high temp]atures & influ5c$1 z 9 ! case ( sun-spots1 by int5se magnetic fields4 ,c]ta9 mod]n in/rum5ts1 l ! #fj-;foot & #aej-;foot t[] telescopes on ,m\nt ,wilson1 are especially design$ = obs]v+ ! c\rse ( ^! exp]im5ts4 ,! second ( ^! telescopes produces at a fix$ po9t 9 a laboratory an image ( ! sun ab\t #af in*es 9 diamet]1 ?us enl>g+ ! sun-spots to su* a scale t ! magnetic ph5om5a ( _! v>i\s p>ts c be sep>ately /udi$4 ,?is analysis is accompli%$ ) a spectroscope #hj feet 9 l5g?1 m\nt$ 9 a subt]ranean *amb] b5ea? ! t[]4 ,! v>i$ results ( su* inve/igations _c be describ$ "h4 ,only "o ( !m may be m5tion$--! discov]y t ! entire sun1 rotat+ on its axis1 is a great magnet4 ,h5ce we may reasonably inf] t e />1 & probably e planet1 is also a magnet1 z ! e>? has be5 kn[n to be s9ce ! days ( ,gilb]t's ,de ,magnete4 ,"h lies "o ( ! be/ clues = ! physici/ :o seeks ! cause ( magnetism1 & attempts to produce x1 z ,b>nett has rec5tly succe$$ 9 do+1 by rapidly :irl+ masses ( metal 9 ! laboratory4 ,illu/ration3 ,fig4 #cc4 ,sun-spot vortex 9 ! upp] hydrog5 atmosph]e4 7,b5i(f74 ,photograph$ ) ! spectroheliograph4 ,! electric vortex t causes ! magnetic field ( ! spot lies at a l[] level1 & is n %[n by su* photographs4 ,p]haps a ^w ( caution %\ld be int]polat$ at ?is po9t4 ,sol> magnetism 9 no wise acc\nts = ! sun's gravitational p[]4 ,inde$1 its attraction _c be felt by ! mo/ delicate in/rum5ts at ! di/ance ( ! e>?1 & w\ld /ill be unkn[n 7 x n = ! influ5ce ( magnetism on light4 ,auroras1 magnetic /orms1 & su* electric curr5ts z ^? t rec5tly d]ang$ sev]al ,atlantic cables are due1 n to ! magnetism ( ! sun or its spots1 b probably to /reams ( electrons1 %ot out f highly di/urb$ areas ( ! sol> surface surr\nd+ great sun-spots1 trav]s+ n9ety-?ree million miles ( ! e!r ( space1 & p5etrat+ deep into ! e>?'s atmosph]e4 ,^! /rik+ ph5om5a lead u into ano!r *apt] ( physics1 :i* limitations ( space =bid u to pursue4 ,,/ell> ,,*emi/ry ,let u turn aga9 to *emi/ry1 & see :]e exp]im5ts p]=m$ 9 cosmic laboratories c s]ve z a guide to ! inve/igator4 ,a sp9n+ sol> tornado1 incomp>ably great] 9 scale ?an ! deva/at+ :irlw9ds t s (t5 cut n>r[ pa?s ( de/ruction ?r\gh t[n & c\ntry 9 ! ,middle ,we/1 gradually gives rise to a sun-spot4 ,! expansion produc$ by ! c5trifugal =ce at ! c5tre ( ! /orm cools ! int5sely hot gases ( ! sol> atmosph]e to a po9t :]e *emical union c occur4 ,titanium & oxyg51 too hot to comb9e 9 mo/ regions ( ! sun1 jo9 to =m ! vapor ( titanium oxide1 *>act]iz$ 9 ! sunspot spectrum by flut$ b&s1 made up ( hundr$s ( regul>ly spac$ l9es4 ,simil>ly magnesium & hydrog5 comb9e z magnesium hydride & calcium & hydrog5 =m calcium hydride4 ,none ( ^! comp\nds1 /able at ! high temp]atures ( sun-spots1 has be5 mu* /udi$ 9 ! laboratory4 ,! regions 9 :i* !y exi/1 ?\gh cool] ?an ! g5]al atmosph]e ( ! sun1 are at temp]atures ( sev]al ?\s& degrees1 atta9$ 9 our laboratories only ) ! aid ( su* devices z p[]ful electric furnaces4 ,illu/ration3 ,fig4 #cd4 ,splitt+ ( spectrum l9es by a magnetic field 7,babcock74 ,! upp] & l[] /rips %[ l9es 9 ! spectrum ( *romium1 obs]v$ )\t a magnetic field4 ,:5 subject$ to ! influ5ce ( magnetism1 ^! s+le l9es are split into sev]al compon5ts4 ,?us ! fir/ l9e on ! "r is resolv$ by ! field into ?ree compon5ts1 "o ( :i* 7plane pol>iz$7 appe>s 9 ! second /rip1 :ile ! o!r two1 :i* are pol>iz$ 9 a plane at "r angles to t ( ! middle compon5t1 are %[n on ! ?ird /rip4 ,! next l9e is split by ! magnetic field into twelve compon5ts1 f\r ( :i* appe> 9 ! second /rip & eight 9 ! ?ird4 ,! magnetic fields 9 sun-spots affect ^! l9es 9 precisely ! same way4 ,x is int]e/+ to foll[ our l9e ( reason+ to ! />s1 :i* diff] widely 9 temp]ature at v>i\s /ages 9 _! life-cycle499 ,a sun-spot is a sol> tornado1 :]e9 ! int5sely hot sol> vapors are cool$ by expansion1 giv+ rise to ! comp\nds already nam$4 ,a r$ />1 9 ,russell's s*eme ( /ell> evolution1 is a cool] sun1 va/ 9 volume & f> m t5u\s ?an atmosph]ic air :5 9 ! initial p]iod ( ! giant /age1 b compress$ & d5s] ?an wat] 9 ! dw>f /age1 into :i* our sun has already ent]$ z x gradually approa*es ! la/ phases ( its exi/5ce4 ,!re=e we %\ld f9d1 ?r\gh\t ! entire atmosph]e ( su* />s1 "s ( ! same comp\nds t are produc$ )9 ! comp>atively small limits ( a sun-spot4 ,?is1 ( c\rse1 on ! correct assumption t sun & />s are made ( ! same sub/ances4 ,f[l] has already id5tifi$ ! b&s ( titanium oxide 9 su* r$ />s z ! giant ,betelgeuse1 & 9 o!rs ( its class4 ,x is safe to pr$ict t an int]e/+ *apt] 9 ! *emi/ry ( ! future w be bas$ ^u ! /udy ( su* comp\nds1 bo? 9 ! laboratory & "u ! progressive temp]ature conditions af=d$ by ! c\ntless /ell> giants & dw>fs t prec$e & foll[ ! sol> /ate4 ,footnote 993 ,see ,*apt] ,,ii4 ,illu/ration3 ,fig4 #ce4 ,electric furnace 9 ! ,pasad5a laboratory ( ! ,m\nt ,wilson ,obs]vatory4 ,) :i* ! *emical ph5om5a obs]v$ 9 sun-spots & r$ />s are exp]im5tally imitat$4 ,,a/rophysical ,,laboratories ,x is precisely 9 ?is long sequ5ce ( physical & *emical *anges t ! a/rophysici/ & ! a/ro*emi/ c f9d ! means ( pu%+ home _! attack4 ,x is true1 ( c\rse1 t ! laboratory inve/igator has a great advantage 9 8 ability to control 8 exp]im5ts1 & to v>y _! progress at w4 ,b by judici\s use ( ! transc5d5tal temp]atures1 f> out rang+ ^? ( 8 furnaces1 & extreme conditions1 :i* he c only p>tially imitate1 af=d$ by ! sun1 />s1 & nebul1 he may greatly wid5 ! range ( 8 inquiries4 ,! sequ5ce ( ph5om5a se5 dur+ ! gr[? ( a sun-spot1 or ! obs]vation ( spots ( diff]5t sizes1 & ! long s]ies ( successive /eps t m>k ! rise & decay ( /ell> life1 resemble ! *anges t ! exp]im5t] br+s ab\t z he increases & dim9i%es ! curr5t 9 ! coils ( 8 magnet or raises & l[]s ! temp]ature ( 8 electric furnace1 exam9+ f "t to "t ! spectrum ( ! gl[+ vapors1 & not+ ! *anges %[n by ! v>y+ appe>ance ( _! l9es4 ,illu/ration3 ,fig4 #cf4 ,titanium oxide 9 r$ />s4 ,! upp] spectrum is t ( titanium 9 ! flame ( ! electric arc1 :]e its comb9ation ) oxyg5 gives rise to ! b&s ( titanium oxide 7,f[l]74 ,! l[] /rip %[s ! spectrum ( ! r$ /> ,mira 7,omicron ,ceti71 z drawn by ,cortie at ,/onyhur/4 ,! b&s ( titanium oxide are cle>ly pres5t 9 ! />4 ,illu/ration3 ,fig4 #cg4 ,titanium oxide 9 sun-spots4 ,! upp] /rip %[s a portion ( ! spectrum ( a sun-spot 7,ell]man72 ! l[] "o ! correspond+ region ( ! spectrum ( titanium oxide 7,k+74 ,! flut$ b&s ( ! oxide spectrum are easily id5tifi$ 9 ! spot1 :]e !y indicate t titanium & oxyg51 too hot to comb9e 9 ! sol> atmosph]e1 unite 9 ! spot because ( ! cool+ produc$ by expansion 9 ! vortex4 ,a/ronomical obs]vations ( ?is "*1 x %\ld be not$1 are mo/ effective :5 con/antly te/$ & int]pret$ by laboratory exp]im5t4 ,inde$1 a mod]n a/rophysical obs]vatory %\ld be equipp$ l a great physical laboratory1 provid$ on ! "o h& ) telescopes & accessory app>atus ( ! greate/ atta9able p[]1 & on ! o!r ) e device kn[n to ! inve/igator ( radiation & ! relat$ physical & *emical ph5om5a4 ,its telescopes1 especially design$ ) ! aims ( ! physici/ & *emi/ 9 view1 br+ images ( sun1 />s1 nebul1 & o!r heav5ly bodies )9 ! rea* ( p[]ful spectroscopes1 s5sitive bolomet]s & !rmopiles1 & ! long array ( o!r appliances available = ! measurem5t & analysis ( radiation4 ,its electric furnaces1 arcs1 sp>ks1 & vacuum tubes1 its app>atus = increas+ & decreas+ pressure1 v>y+ *emical conditions1 & subject+ lum9\s gases & vapors to ! influ5ce ( electric & magnetic fields1 provide ! means ( imitat+ cele/ial ph5om5a1 & ( repeat+ & int]pret+ ! exp]im5ts obs]v$ at ! telescope4 ,& ! advantage ?us d]iv$1 z we h se51 is n conf9$ to ! a/ronom]1 :o has (t5 be5 able1 by mak+ fundam5tal physical & *emical discov]ies1 to repay 8 debt to ! physici/ & *emi/ = ! app>atus & me?ods :i* he owes to !m4 ,,newton ,,& ,,e9/e9 ,take1 = ano!r example1 ! greate/ law ( physics--,newton's law ( gravitation4 ,huge balls ( lead1 z us$ by ,cav5di%1 produce by _! gravitational effect a m9ute rotation ( a delicately susp5d$ b>1 c>ry+ small] balls at its extremities4 ,b no su* feeble means suffic$ = ,newton's purpose4 ,to prove ! law ( gravitation he _h rec\rse to ! trem5d\s pull on ! moon ( ! entire mass ( ! e>?1 & !n ext5d$ 8 rese>*es to ! mutual attractions ( all ! bodies ( ! sol> sy/em4 ,lat] ,h]s*el appli$ ?is law to ! suns :i* con/itute d\ble />s1 & to-day ,adams obs]ves f ,m\nt ,wilson />s fall+ ) great velocity t[>d ! c5tre ( ! galactic sy/em "u ! comb9$ pull ( ! millions ( objects t compose x4 ,?us full advantage has be5 tak5 ( ! possibility ( utiliz+ ! great masses ( ! heav5ly bodies = ! discov]y & application ( a law ( physics & its reciprocal use 9 expla9+ cele/ial motions4 ,illu/ration3 ,fig4 #ch4 ,! ,cav5di% exp]im5t4 ,two lead balls1 ea* two in*es 9 diamet]1 are atta*$ to ! ends ( a torsion rod six feet long1 :i* is susp5d$ by a f9e wire4 ,! exp]im5t consi/s 9 measur+ ! rotation ( ! susp5d$ sy/em1 caus$ by ! gravitational attraction ( two lead sph]es1 ea* twelve in*es 9 diamet]1 act+ on ! two small lead balls4 ,or consid] ! ,e9/e9 !ory ( relativity1 ! tru? or falsity ( :i* is no less fundam5tal to physics4 ,its inception sprang f ! ,mi*elson-,morley exp]im5t1 made 9 a laboratory 9 ,clevel&1 :i* %[$ t motion ( ! e>? ?r\gh ! e!r ( space c\ld n be detect$4 ,all ( ! ?ree *ief te/s ( ,e9/e9's g5]al !ory are a/ronomical--because ( ! great masses requir$ to produce ! m9ute effects pr$ict$3 ! motion ( ! p]ihelion ( ,m]cury1 ! deflection ( ! light ( a /> by ! attraction ( ! sun1 & ! %ift ( ! l9es ( ! sol> spectrum t[>d ! r$--que/ions n yet completely answ]$4 ,b x is 9 ! /udy ( ! con/itution ( matt] & ! evolution ( ! elem5ts1 ! deepe/ & mo/ critical problem ( physics & *emi/ry1 t ! extremes ( pressure & temp]ature 9 ! heav5ly bodies1 & ! preval5ce ( o!r physical conditions n yet successfully imitat$ on e>?1 promise ! greate/ progress4 ,x =tunately happ5s t a/rophysical rese>* is n[ at ! v apex ( its developm5t1 f\nd$ z x is ^u _m c5turies ( a/ronomical inve/igation1 rejuv5at$ by ! introduction into ! obs]vatory ( all ! mod]n devices ( ! physici/1 & /r5g!n$ ) in/rum5ts ( truly extraord9>y range & p[]4 ,^! in/rum5ts br+ )9 rea* exp]im5ts t are 9 progress on "s m9ute region ( ! sun's disk1 or 9 "s /> too di/ant ev5 to be glimps$ ) ord9>y telescopes4 ,inde$1 ! huge a/ronomical l5ses & mirrors n[ available s]ve = ^! remote light-s\rces exactly ! purpose ( ! l5s or mirror employ$ by ! physici/ to project ^u ! slit ( 8 spectroscope ! image ( a sp>k or arc or vacuum tube )9 :i* atoms & molecules are expos$ to ! influ5ce ( ! electric dis*>ge4 ,! physici/ has ! advantage ( complete control ov] ! exp]im5tal conditions1 :ile ! a/rophysici/ mu/ obs]ve & int]pret ! exp]im5ts p]=m$ = him 9 remote laboratories4 ,9 actual practice1 ! two classes ( "w mu/ be done 9 ! close/ conjunction1 if adequate utilization is to be made ( ei!r4 ,& ?is is only natural1 = ! tr5d ( rec5t rese>* has made cle> ! fact t "o ( ! ?ree greate/ problems ( mod]n a/ronomy & a/rophysics1 rank+ ) ! /ructure ( ! univ]se & ! evolution ( cele/ial bodies1 is ! con/itution ( matt]4 ,let u see :y ?is is s4 ,,transmutation ,,( ,,! ,,elem5ts ,! dream ( ! al*emi/ 0 to transmute "o elem5t into ano!r1 ) ! prime object ( produc+ gold4 ,su* transmutation has be5 actually accompli%$ )9 ! la/ few ye>s1 b ! process is inv>iably "o ( dis9tegration--! m complex elem5ts be+ brok5 up into simpl] con/itu5ts4 ,mu* rema9s to be done 9 ?is same direction2 & "h ! />s & nebul1 :i* %[ ! spectra ( ! elem5ts "u a great v>iety ( conditions1 %\ld help to po9t ! way4 ,! progressive *anges 9 spectra1 f ! exclusive indications ( ! simple elem5ts hydrog51 helium1 nitrog51 possibly c>bon1 & ! t]re/rially unkn[n gas nebulium 9 ! gase\s nebul1 to ! long li/ ( famili> sub/ances1 includ+ sev]al *emical comp\nds1 9 ! r$ />s1 may prove to be fundam5tally significant :5 adequately /udi$ f ! /&po9t ( ! inve/igator ( atomic /ructure4 ,! exi/+ evid5ce seems to favor ! view1 rec5tly express$ by ,saha1 t _m ( ^! diff]5ces are due to v>y+ degrees ( ionization1 ! out] electrons ( ! atoms be+ split (f by high temp]ature or electrical excitation4 ,x is ev5 possible t cosmic crucibles1 unrivall$ by t]re/rial ones1 may help mat]ially to reveal ! secret ( ! =mation ( complex elem5ts f simpl] ones4 ,physici/s n[ believe t all ( ! elem5ts are comp\nd$ ( hydrog5 atoms1 b\nd toge!r by negative electrons4 ,?us helium is made up ( f\r hydrog5 atoms1 yet ! atomic weight ( helium 7#d7 is less ?an f\r times t ( hydrog5 7#a4jjh74 ,! diff]5ce may repres5t ! mass ( ! electrical en]gy releas$ :5 ! transmutation occurr$4 ,illu/ration3 ,fig4 #ci4 ,! ,trifid ,nebula 9 ,sagitt>ius 7,rit*ey74 ,! gas nebulium1 n yet f\nd on ! e>?1 is ! mo/ *>act]i/ic con/itu5t ( irregul> nebul4 ,nebulium is recogniz$ by two gre5 l9es 9 its spectrum1 :i* cause ! gre5 color ( nebul ( ! gase\s type4 ,edd+ton has speculat$ 9 a mo/ int]e/+ way on ?is possible s\rce ( /ell> heat 9 8 rec5t presid5tial address be=e ! ,briti% ,association = ! ,advancem5t ( ,sci5ce 7see ,nature1 ,septemb] #b1 #aibj74 ,he po9ts out t ! old contraction hypo!sis1 accord+ to :i* ! s\rce ( sol> & /ell> heat 0 suppos$ to reside 9 ! sl[ cond5sation ( a radiat+ mass ( gas "u ! action ( gravity1 is :olly inadequate to expla9 ! obs]v$ ph5om5a4 ,if ! old view 7 correct1 ! e>li] hi/ory ( a />1 f ! giant /age ( a cool & diaphan\s gas to ! p]iod ( highe/ temp]ature1 w\ld be run ?r\gh )9 eighty ?\s& ye>s1 :]eas we h ! be/ ( evid5ce t _m ?\s&s ( c5turies w\ld n suffice4 ,"s o!r s\rce ( en]gy is imp]atively ne$$4 ,if #e p] c5t ( a />'s mass consi/s orig9ally ( hydrog5 atoms1 :i* gradually comb9e 9 ! sl[ process ( "t to =m m complex elem5ts1 ! total heat ?us lib]at$ w\ld m ?an suffice to acc\nt = all dem&s1 & x w\ld be unnecess>y to assume ! exi/5ce ( any o!r s\rce ( heat4 ,illu/ration3 ,fig4 #dj4 ,spiral nebula 9 ,ursa ,major 7,rit*ey74 ,lum9\s matt]1 9 e v>iety ( physical & *emical /ate1 is available = /udy 9 ! mo/ div]se cele/ial objects1 f ! spiral & irregul> nebul ?r\gh all ! types ( />s4 ,doctor van ,maan5's measures ( ! ,m\nt ,wilson photographs indicate outw>d motion along ! arms ( spiral nebul1 :ile ! spectroscope %[s !m to be :irl+ at enorm\s velocities4 ,,cosmic ,,pressures ,?is1 x may fairly be said1 is v speculative1 b ! fact rema9s t cele/ial bodies appe> to be ! only places 9 :i* ! complex elem5ts may be 9 actual process ( =mation f _! kn[n s\rce--hydrog54 ,at lea/ we may see :at a va/ v>iety ( physical conditions ^! cosmic crucibles af=d4 ,at "o end ( ! scale we h ! excessively t5u\s nebul1 ! lum9osity ( :i*1 my/]i\s 9 its orig91 resembles ! electric gl[ 9 our vacuum tubes4 ,"h we c detect only ! lighte/ & simple/ ( ! elem5ts4 ,9 ! giant />s1 also extremely t5u\s 7! d5sity ( ,betelgeuse c h>dly exce$ "o-?\s&? ( an atmosph]e7 we obs]ve ! spectra ( iron1 manganese1 titanium1 calcium1 *romium1 magnesium1 vanadium1 & sodium1 9 addition to titanium oxide4 ,! out] "p ( ^! bodies1 f :i* light rea*es u1 mu/ !re=e be at a temp]ature ( only a few ?\s& degrees1 b va/ly high] temp]atures mu/ prevail at _! c5tres4 ,9 pass+ up ! temp]ature curve m & m elem5ts appe>1 ! surface temp]ature rises1 & ! int]nal temp]ature may rea* millions ( degrees4 ,at ! same "t ! pressure )9 mu/ also rise1 rea*+ enorm\s figures 9 ! la/ /ages ( /ell> life4 ,cook has calculat$ t ! pressure at ! c5tre ( ! e>? is betwe5 #d1jjj & #aj1jjj tons p] squ>e in*1 & ?is mu/ be only a v small fraction ( t atta9$ )9 l>g] cele/ial bodies4 ,jeans has comput$ ! pressure at ! c5tre ( two collid+ />s z !y /rike & flatt51 & f9ds x may be ( ! ord] ( #a1jjj1jjj1jjj tons p] squ>e in*--suffici5t1 if _! diamet] be equal to t ( ! sun--to vaporize !m #ajj1jjj times ov]4 ,comp>e ^! pressures ) ! highe/ t c be produc$ on e>?4 ,if ! ,g]man gun t bomb>d$ ,p>is 7 load$ ) a solid /eel projectile ( suitable dim5sions1 a muzzle velocity ( #f1jjj feet p] second c\ld be rea*$4 ,suppose ?is to be fir$ into a tap]$ hole 9 a great block ( /eel4 ,! in/antane\s pressure1 accord+ to ,cook1 w\ld be ab\t #g1jjj tons p] squ>e in*1 only #a_/aejjjj ( t possible ?r\gh ! collision ( ! l>ge/ />s4 ,illu/ration3 ,fig4 #da4 ,m\nt ,san ,antonio z se5 f ,m\nt ,wilson4 ,mi*elson is measur+ ! velocity ( light betwe5 /ations on ,m\nt ,wilson & ,m\nt ,san ,antonio4 ,a/ronomical obs]vations af=d ! be/ means1 h[ev]1 ( detect+ any possible diff]5ce betwe5 ! velocities ( light ( diff]5t colors4 ,f /udies ( v>iable />s 9 ! clu/] ,messi] #e ,%apley concludes t if !re is any diff]5ce betwe5 ! velocities ( blue & yell[ light 9 free space x _c exce$ two in*es 9 "o second1 ! "t 9 :i* light travels #ahf1jjj miles4 ,f9ally1 we may comp>e ! effects ( light pressure on ! e>? & />s4 ,tw5ty ye>s ago ,ni*ols & ,hull succe$$1 ) ! aid ( ! mo/ s5sitive app>atus1 9 measur+ ! m9ute displacem5ts produc$ by ! pressure ( light4 ,! effect is s slight1 ev5 ) ! brighte/ light-s\rces available1 t great exp]im5tal skill is requir$ to measure x4 ,yet 9 ! case ( "s ( ! l>g] />s ,edd+ton calculates t "o-half ( _! mass is support$ by radiation pressure1 & ?is aga9/ _! enorm\s gravitational attraction4 ,9 fact1 if _! mass 7 z great z t5 times t ( ! sun1 ! radiation pressure w\ld s ne>ly ov]come ! pull ( gravitation t !y w\ld be likely to break up4 ,b en\gh has be5 said to illu/rate ! wide v>iety ( exp]im5tal devices t /& at our s]vice 9 ! laboratories ( ! heav5s4 ,"h ! physici/ & *emi/ ( ! future w m & m frequ5tly supplem5t _! t]re/rial app>atus1 & f9d new clues to ! complex problems :i* ! amaz+ progress ( rec5t ye>s has already done s mu* to solve4 ,,practical ,,value ,,( ,,rese>*es ,,on ,,! ,,con/itution ,,( ,,matt] ,! layman has no difficulty 9 recogniz+ ! practical value ( rese>*es direct$ t[>d ! improvem5t ( ! inc&esc5t lamp or ! increas$ effici5cy ( ! telephone4 ,he c see ! results 9 ! greatly decreas$ co/ ( electric illum9ation & ! rapid ext5sion ( ! range ( ! human voice4 ,b ! v m5 :o h made ^! advances1 ^? :o h succe$$ beyond all expectation 9 accompli%+ ! economic purposes 9 view1 are mo/ emphatic 9 _! insi/5ce ^u ! importance ( rese>* ( a m fundam5tal "*4 ,?us ,vice-,presid5t ,j4 ,j4 ,c>ty1 ( ! ,am]ican ,telephone & ,telegraph ,company1 :o directs its great ,dep>tm5t ( ,developm5t & ,rese>*1 & ,doctor ,w4 ,j4 ,:itney1 ,director ( ! ,rese>* ,laboratory ( ! ,g5]al ,electric ,company1 h repeat$ly express$ _! indebt$ness to ! inve/igations ( ! physici/1 made ) no ?\ght ( imm$iate practical return4 ,f>aday1 /udy+ ! laws ( electricity1 discov]$ ! pr9ciple :i* r5d]$ ! dynamo possible4 ,maxwell1 ,h5ry1 & ,h]tz1 equally unconc]n$ ) mat]ial advantage1 made wireless telegraphy practicable4 ,9 fact1 all truly great advances are ?us d]iv$ f fundam5tal sci5ce1 & ! future progress ( ! _w w be l>gely dep5d5t ^u ! provision made = sci5tific rese>*1 especially 9 ! fields ( physics & *emi/ry1 :i* und]lie all bran*es ( eng9e]+4 ,! con/itution ( matt]1 !re=e1 in/ead ( appeal+ z a subject to rese>* only to ! natural philosoph] or to ! g5]al /ud5t ( sci5ce1 is a "q ( ! greate/ practical conc]n4 ,already ! by-products ( inve/igations direct$ t[>d its elucidation h be5 num]\s & useful 9 ! highe/ degree4 ,helium has be5 already cit$2 ,x-rays h>dly require m5tion2 radium1 :i* has s mat]ially aid$ suff]]s f canc]1 is /ill bett] kn[n4 ,wireless telephony & transcont95tal telephony ) wires 7 bo? r5d]$ possible by /udies ( ! nature ( ! electric dis*>ge 9 vacuum tubes4 ,?us ! practical man1 ) 8 di/ru/ ( pure sci5ce1 ne$ n res5t inve/m5ts made = ! purpose ( advanc+ our k ( su* fundam5tal subjects z physics & *emi/ry4 ,on ! contr>y1 if true to 8 "n1 he %\ld help to multiply !m _m fold 9 ! int]e/ ( economic & comm]cial developm5t4