,transcrib]'s ,notes3 ,und]scores 80 be=e & aft] a ^w or phrase indicate italics 9 ! orig9al text4 ,equal signs 80 be=e & aft] a ^w or phrase indicate bold 9 ! orig9al text4 ,small capitals h be5 conv]t$ to ,,solid capitals4 ,illu/rations & footnotes h be5 mov$ s !y d n break up p>agraphs4 ,deprecat$ spell+s h be5 pres]v$4 ,typographical & punctuation errors h be5 sil5tly correct$4 ,,! ,,univ]se ,,ar\nd ,,u ,cambridge ,univ]sity ,press ,fett] ,lane1 ,london ,bombay1 ,calcutta1 ,madras ,toronto ,macmillan ,tokyo ,m>uz5 ,company1 ,ltd ,copyright$ 9 ! ,unit$ ,/ates ( ,am]ica by ! ,macmillan ,company ,all rights res]v$ ,illu/ration3 ,l[ell ,obs]vatory ,! ,discov]y ( ,pluto ,! two photographs 7 tak5 at ! ,l[ell ,obs]vatory on ! nights ( ,m>* #b & #e1 #aicj4 ,! object indicat$ by arr[s 0 se5 to h mov$ consid]ably 9 ! int]val1 & ?is prov$ t x 0 ( planet>y "*4 ,! bright object 9 ! bottom left-h& corn] is ! /> ,gem9orum 7see p4 #bfj74 ,,! ,,univ]se ,,ar\nd ,,u ,by ,,sir ,,james ,,jeans ,m4,a41 ,d4,sc41 ,sc4,d4 ,,ll4,d41 ,f4,r4,s4 ,illu/ration ,,cambridge ,,at ,,! ,,univ]sity ,,press #aicj ,fir/ ,edition1 ,septemb] #aibi ,repr9t$ ,novemb] #aibi 0 ,janu>y #aicj ,second ,edition1 ,octob] #aicj ,,pr9t$ ,,9 ,,great ,,brita9 ,,preface ,! pres5t book conta9s a brief acc\nt1 writt5 9 simple language1 ( ! me?ods & results ( mod]n a/ronomical rese>*1 bo? obs]vational & !oretical4 ,special att5tion has be5 giv5 to problems ( cosmogony & evolution1 & to ! g5]al /ructure ( ! univ]se4 ,my ideal1 p]haps nev] :olly atta9able1 has be5 t ( mak+ ! entire book intelligible to read]s ) no special sci5tific k4 ,p>ts ( ! book cov] ! same gr\nd z v>i\s lectures ,i h rec5tly deliv]$ to ,univ]sity & o!r audi5ces1 includ+ a c\rse ( wireless talks ,i gave la/ autumn4 ,x has be5 f\nd necess>y to re-write ^! almo/ 9 _! entirety1 s t v few s5t5ces rema9 9 _! orig9al =m1 b ^? :o h ask$ me to publi% my lectures & wireless talks w f9d ! sub/ance ( !m 9 ! pres5t book4 ,j4 ,h4 ,,jeans ,,dork+ #a ,may #aibi ,,preface ,,to ,,second ,,edition ,9 prep>+ a second edition1 ,i h tak5 advantage ( a great numb] ( sugge/ions made by correspond5ts & review]s1 to :om ,i (f] my s9c]e/ ?anks4 ,i h also ins]t$ discussions ( ! new planet ,pluto1 ! rotation ( ! galaxy1 ! app>5t expansion ( ! univ]se1 & o!r subjects :i* h become important s9ce ! fir/ edition 0 publi%$1 & 9 g5]al h tri$ to br+ ! book up to date4 ,j4 ,h4 ,,jeans ,,dork+ #b ,augu/ #aicj ,,cont5ts ,,page ,introduction--,! ,/udy ( ,a/ronomy #a ,*apt] ,i ,explor+ ! ,sky #af ,,ii ,explor+ ! ,atom #ib ,,iii ,explor+ 9 ,"t #aej ,,iv ,c>v+ out ! ,univ]se #aid ,v ,/>s #bec ,,vi ,beg9n+s & ,end+s #cbe ,index #cee ,,plates ,! ,discov]y ( ,pluto ,,frontispiece ,,plate ,,fac+ ,,page ,i ,! ,milky ,way 9 ! neighb\rhood ( ! ,s\!rn ,cross #bc ,,ii ,planet>y ,nebulae3 #a4 ,n4,g4,c4 #bjbb #b4 ,n4,g4,c4 #fgbj 7,! ,r+ ,nebula7 #c4 ,n4,g4,c4 #aeja #d4 ,n4,g4,c4 #gffb #bh ,,iii ,! ,nebula 9 ,cygnus #bi ,,iv ,! ,great ,nebula ,m #ca 9 ,&rom$a #cj ,v ,! ,nebula ,n4,g4,c4 #hia 9 ,&rom$a se5 edge-on #ca ,,vi ,! 8,horse's ,head0 9 ! ,great ,nebula 9 ,orion #cg ,,vii ,! ,trifid ,nebula ,m #bj 9 ,sagitt>ius #dd ,,viii ,/ell> ,spectra #ea ,,ix ,! ,globul> ,clu/] ,m #ac 9 ,h]cules #fc ,x ,! ,region ( ,ophiu*i #fe ,,xi ,magnification ( "p ( ! out] regions ( ! ,great ,nebula ,m #ca 9 ,&rom$a #gj ,,xii ,magnification ( ! c5tral region ( ! ,great ,nebula ,m #ca 9 ,&rom$a #ga ,,xiii ,! tracks ( - & -p>ticles #aac ,,xiv ,collisions ( -p>ticles ) ,atoms #aag ,,xv ,! ,nebula ,n4,g4,c4 #deid 9 ,virgo ,! ,nebula ,n4,g4,c4 #gbag #bjd ,,xvi ,a sequ5ce ( ,nebul> ,configurations3 #a4 ,n4,g4,c4 #ccgi #b4 ,n4,g4,c4 #dfba #c4 ,n4,g4,c4 #caae #d4 ,n4,g4,c4 #deid 9 ,virgo #e4 ,n4,g4,c4 #defe 9 ,b]5ice's hair #bjg ,,xvii ,! 8,:irlpool0 ,nebula ,m #ea 9 ,canes ,v5atici #baj ,,xviii ,! ,nebula ,m #ha 9 ,ursa ,major #baa ,,xix ,! ,nebula ,m #aja 9 ,ursa ,major #bab ,,xx ,! ,nebula ,m #cc 9 ,triangulum #bac ,,xxi ,! ,less] & ,great] ,magellanic ,cl\ds #bad ,,xxii ,two ,nebulae 7,n4,g4,c4 #dcie1 #ddja7 sugge/ive ( ,tidal ,action #bcf ,,xxiii ,! tw9 ,nebulae ,n4,g4,c4 #defg-h ,! ,nebula ,n4,g4,c4 #gdgi #bcg ,,xxiv ,saturn & its ,sy/em ( ,r+s #bej ,,introduction ,! ,/udy ( ,a/ronomy ,on ! ev5+ ( ,janu>y #g1 #afaj1 a fateful day = ! human race1 ,galileo ,galilei1 ,pr(essor ( ,ma!matics 9 ! ,univ]sity ( ,padua1 sat 9 front ( a telescope he _h made ) 8 own h&s4 ,m ?an ?ree c5turies previ\sly1 ,rog] ,bacon1 ! inv5tor ( spectacles1 _h expla9$ h[ a telescope c\ld be con/ruct$ s z 8to make ! />s appe> z ne> z we please40 ,he _h %ewn h[ a l5s c\ld be s %ap$ t x w\ld collect all ! rays ( light fall+ on x f a di/ant object1 b5d !m until !y met 9 a focus & !n pass !m on ?r\gh ! pupil ( ! eye on to ! ret9a4 ,su* an in/rum5t w\ld increase ! p[] ( ! human eye1 j z an e> trumpet increases ! p[] ( ! human e> by collect+ all ! waves ( s\nd :i* fall on a l>ge ap]ture1 b5d+ !m1 & pass+ !m ?r\gh ! orifice ( ! e> on to ! e> drum4 ,yet x 0 n until #afjh t ! fir/ telescope _h be5 con/ruct$ by ,lipp]%ey1 a ,flemi% spectacle-mak]4 ,on he>+ ( ?is in/rum5t1 ,galileo _h set to "w to discov] ! pr9ciples ( its con/ruction & _h soon made himself a telescope f> bett] ?an ! orig9al4 ,8 in/rum5t _h creat$ no small s5sation 9 ,italy4 ,su* extraord9>y /ories _h be5 told ( its p[]s t he _h be5 comm&$ to take x to ,v5ice & exhibit x to ! ,doge & ,s5ate4 ,! citiz5s ( ,v5ice _h !n se5 ! mo/ ag$ ( _! ,s5ators climb+ ! highe/ bell-t[]s to spy ?r\gh ! telescope at %ips :i* 7 too f> out at sea to be se5 at all )\t its help4 ,! telescope admitt$ ab\t a hundr$ times z mu* light z ! unaid$ human eye1 &1 accord+ to ,galileo1 x %ew$ an object at fifty miles z cle>ly z if x 7 only five miles away4 ,p]haps x ne$ h>dly be said t ?is is q insignificant 9 comp>ison ) ! p[] ( mod]n in/rum5ts4 ,! telescope ( #ajj-;in* ap]ture at ,m\nt ,wilson1 ,cali=nia1 ! l>ge/ at pres5t 9 exi/5ce1 admits #bejj times z mu* light z ,galileo's t9y in/rum5t1 & s #bej1jjj times z mu* light z ! unaid$ eye4 ,x is hop$ t a #bjj-;in* telescope w %ortly be built 9 ,cali=nia2 ?is w admit f\r times z mu* light z ! #ajj-;in* in/rum5t1 or ab\t a million times z mu* light z ! unaid$ eye4 ,! absorb+ int]e/ ( 8 new in/rum5t _h almo/ driv5 f ,galileo's m9d a problem to :i* he _h at "o "t giv5 mu* ?\ght4 ,ov] two ?\s& ye>s previ\sly1 ,py?agoras & ,philolaus _h taught t ! e>? is n fix$ 9 space b rotates on its axis e tw5ty-f\r h\rs1 ?us caus+ ! alt]nation ( day & night4 ,ari/>*us ( ,samos1 p]haps ! greate/ ( all ! ,greek ma!maticians1 _h fur!r ma9ta9$ t ! e>? n only turn$ on its axis1 b also describ$ a ye>ly j\rney r\nd ! sun1 ?is be+ ! cause ( ! cycle ( ! seasons4 ,!n ^! doctr9es _h fall5 into disfav\r4 ,ari/otle _h pron\nc$ aga9/ !m1 ass]t+ t ! e>? =m$ a fix$ c5tre to ! univ]se4 ,lat] ,ptolemy _h expla9$ ! tracks ( ! planets across ! sky 9 t]ms ( a complicat$ sy/em ( cycles & epicycles2 ! planets mov$ 9 circul> pa?s ar\nd mov+ po9ts1 :i* !mselves mov$ 9 circles ar\nd an immoveable e>?4 ,! ,*ur* _h giv5 its sanction & active support to ^! doctr9es4 ,inde$1 x is difficult to see :at else x c\ld h done1 = x seem$ almo/ impi\s to suppose t ! great drama ( man's fall & r$emption1 9 :i* ! ,son ( ,god _h ,himself tak5 "p1 c\ld h be5 enact$ on any less] /age ?an ! v c5tre ( ! ,univ]se4 ,yet1 ev5 9 ! ,*ur*1 ! doctr9e _h n ga9$ univ]sal acceptance4 ,oresme1 ,bi%op ( ,lisieux1 & ,c>d9al ,ni*olas ( ,cusa1 _h bo? decl>$ aga9/ x1 ! latt] writ+ 9 #addj3 ,i h long consid]$ t ?is e>? is n fix$1 b moves z d ! o!r />s4 ,to my m9d ! e>? turns ^u its axis once e day & night4 ,at a lat] date ^? :o held ^! views incurr$ ! active ho/ility ( ! ,*ur*1 & 9 #afjj ,giordano ,bruno 0 burn$ at ! /ake4 ,he _h writt53 ,x has seem$ to me unwor?y ( ! div9e goodness & p[] to create a f9ite _w1 :5 able to produce beside x ano!r & o!rs inf9ite2 s t ,i h decl>$ t !re are endless p>ticul> worlds simil> to ?is ( ! e>?2 ) ,py?agoras ,i reg>d x z a />1 & simil> to x are ! moon1 ! planets & o!r />s1 :i* are inf9ite 9 numb]1 & all ^! bodies are worlds4 ,! mo/ weighty attack on or?odox doctr9e _h1 h[ev]1 be5 deliv]$ nei!r by !ologians nor philosoph]s1 b by ! ,poli% a/ronom]1 ,nicolaus ,cop]nicus 7#adgc-aedc74 ,9 8 great "w ,de revolutionibus orbium coele/ium ,cop]nicus _h %ewn t ,ptolemy's elaborate /ructure ( cycles & epicycles 0 unnecess>y1 because ! tracks ( ! planets across ! sky c\ld be expla9$ q simply by suppos+ t ! e>? & ! planets all mov$ r\nd a fix$ c5tral sun4 ,! sixty-six ye>s :i* _h elaps$ s9ce ?is book 0 publi%$ _h se5 ^! !ories hotly debat$1 b !y 7 /ill nei!r prov$ nor disprov$4 ,galileo _h already f\nd t 8 new telescope provid$ a means ( te/+ a/ronomical !ories4 ,z soon z he _h turn$ x on to ! ,milky ,way1 a :ole cr[d ( leg5ds & fables z to its nature & /ructure _h vani%$ into ?9 air2 x prov$ to be no?+ m ?an a sw>m ( fa9t />s scatt]$ l gold5 du/ on ! black backgr\nd ( ! sky4 ,ano!r glance ?r\gh ! telescope _h disclos$ ! true nature ( ! moon4 ,x _h on x m\nta9s :i* ca/ %ad[s1 & s prov$1 z ,giordano ,bruno _h ma9ta9$1 to be a _w l our own4 ,:at if ! telescope %\ld n[ 9 "s way prove able to decide betwe5 ! or?odox doctr9e t ! e>? =m$ ! hub ( ! univ]se1 & ! new doctr9e t ! e>? 0 only "o ( a numb] ( bodies1 all circl+ r\nd ! sun l mo?s r\nd a c&le-flame8 ,& n[ ,galileo cat*es ,jupit] 9 ! field ( 8 telescope & sees f\r small bodies circl+ ar\nd ! great mass ( ! planet--l mo?s r\nd a c&le-flame4 ,:at he sees is an exact replica ( ! sol> sy/em z imag9$ by ,cop]nicus1 & x provides direct visual pro( t su* sy/ems are at lea/ n ali5 to ! ar*itectural plan ( ! univ]se4 ,on ,janu>y #cj? he writes to ,belis>io ,v9ta t ^! small bodies move r\nd ! f> great] mass ( ,jupit] 8j z ,v5us & ,m]cury1 & p]haps ! o!r planets1 move r\nd ! sun40 ,any l+]+ d\bts t ,galileo may h felt z to ! significance ( 8 discov]y are remov$ n9e mon?s lat] :5 he obs]ves ! phases ( ,v5us4 ,v5us might h be5 self-lum9\s1 9 :i* case %e w\ld always appe> z a full circle ( light4 ,if %e 7 n self-lum9\s b mov$ 9 a ,ptolemaic epicycle1 !n1 z ,ptolemy _h himself po9t$ out1 %e c\ld nev] %ew m ?an half h] surface illum9at$4 ,on ! o!r h&1 ! ,cop]nican view ( ! sol> sy/em requir$ t bo? ,v5us & ,m]cury %\ld exhibit 8phases0 l ^? ( ! moon1 _! %9+ surfaces rang+ 9 appe>ance f cresc5t-%ape ?r\gh half moon to full moon1 & !n back ?r\gh half moon to cresc5t-%ape4 ,t su* phases 7 n %ewn by ,v5us _h inde$ be5 urg$ z an objection to ! ,cop]nican !ory4 ,galileo's telescope n[ %ews t1 z ,cop]nicus _h =etold1 ,v5us passes ?r\gh ! full cycle ( phases1 s t1 9 ,galileo's own words1 we 8are n[ suppli$ ) a det]m9ation mo/ conclusive1 & appeal+ to ! evid5ce ( our s5ses1 ( two v important problems1 :i* up to ?is day h be5 discuss$ by ! greate/ intellects ) diff]5t conclusions4 ,"o is t ! planets are n self-lum9\s4 ,! o!r is t we are absolutely compell$ to say t ,v5us1 & ,m]cury also1 revolve ar\nd ! sun1 z d also all ! re/ ( ! planets1 a tru? believ$ inde$ by ! ,py?agorean s*ool1 by ,cop]nicus1 & by ,kepl]1 b nev] prov$ by ! evid5ce ( our s5ses1 z is n[ prov$ 9 ! case ( ,v5us & ,m]cury40 ,^! discov]ies ( ,galileo made x cle> t ,ari/otle1 ,ptolemy & ! majority ( ^? :o _h ?\ght ab\t ^! ?+s 9 ! la/ #bjjj ye>s _h be5 utt]ly & hopelessly wrong4 ,9 e/imat+ 8 position 9 ! univ]se1 man _h up to n[ be5 guid$ ma9ly by 8 own desires1 & 8 self-e/eem2 long f$ on b\ndless hopes1 he _h spurn$ ! simpl] f>e (f]$ by pati5t sci5tific ?\ght4 ,inexorable facts n[ de?ron$ him f 8 self-arrogat$ /ation at ! c5tre ( ! univ]se2 h5ce=? he mu/ reconcile himself to ! humble position ( ! inhabitant ( a speck ( du/1 & adju/ 8 views on ! mean+ ( human life accord+ly4 ,! adju/m5t 0 n made at once4 ,human vanity1 re9=c$ by ! au?ority ( ! ,*ur*1 contriv$ to make a r\gh road = ^? :o d>$ draw att5tion to ! e>?'s insignificant position 9 ! univ]se4 ,galileo 0 =c$ to abjure 8 beliefs4 ,well on into ! eighte5? c5tury ! anci5t ,univ]sity ( ,p>is taught t ! motion ( ! e>? r\nd ! sun 0 a conv5i5t b false hypo!sis1 :ile ! new] ,am]ican ,univ]sities ( ,h>v>d & ,yale taught ! ,ptolemaic & ,cop]nican sy/ems ( a/ronomy side by side z ?\gh !y 7 equally t5able4 ,yet m5 c\ld n keep _! heads buri$ 9 ! s& = ev]1 & :5 at la/ its full implications 7 accept$1 ! revolution ( ?\ght initiat$ by ,galileo's obs]vations ( ,janu>y #g1 #afaj1 prov$ to be ! mo/ cata/rophic 9 ! hi/ory ( ! race4 ,! cataclysm 0 n conf9$ to ! realms ( ab/ract ?\ght2 h5ce=? human exi/5ce itself 0 to appe> 9 a new light1 & human aims & aspirations w\ld be judg$ f a diff]5t /&po9t4 ,?is (t-told /ory has be5 told once aga91 9 ! hope t x may s]ve to expla9 "s ( ! int]e/ tak5 9 a/ronomy to-day4 ,! m mundane sci5ces prove _! wor? by add+ to ! am5ities & pleasures ( life1 or by alleviat+ pa9 or di/ress1 b x may well be ask$ :at rew>d a/ronomy has to (f]4 ,:y does ! a/ronom] devote ardu\s nights1 & /ill m ardu\s days1 to /udy+ ! /ructure1 motions & *anges ( bodies s remote t !y c h no conceivable influ5ce on human life8 ,9 "p at lea/ ! answ] w\ld seem to be t _m h begun to suspect t ! a/ronomy ( to-day1 l t ( ,galileo1 may h some?+ to say on ! en?rall+ "q ( ! relation ( human life to ! univ]se 9 :i* x is plac$1 & on ! beg9n+s1 mean+ & de/9y ( ! human race4 ,b$e records h[1 "s twelve c5turies ago1 human life 0 comp>$ 9 poetic simile to ! flight ( a bird ?r\gh a w>m hall 9 :i* m5 sit fea/+1 :ile ! w9t] /orms rage )\t4 ,! bird is safe f ! tempe/ = a brief mom5t1 b imm$iately passes f w9t] to w9t] aga94 ,s man's life appe>s = a little :ile1 b ( :at is to foll[1 or ( :at w5t be=e1 we "k no?+4 ,if1 !re=e1 a new doctr9e tells u some?+ c]ta91 x seems to des]ve to be foll[$4 ,^! words1 orig9ally spok5 9 advocacy ( ! ,*ri/ian religion1 describe :at is p]haps ! ma9 int]e/ ( a/ronomy to-day4 ,man only kn[+ ,life's little lant]n betwe5 d>k & d>k wi%es to probe fur!r into ! pa/ & future ?an 8 brief span ( life p]mits4 ,he wi%es to see ! univ]se z x exi/$ be=e man 01 z x w be aft] ! la/ man has pass$ aga9 into ! d>kness f :i* he came4 ,! wi% does n orig9ate solely 9 m]e intellectual curiosity1 9 ! desire to see ov] ! next range ( m\nta9s1 ! desire to atta9 a summit comm&+ a wide view1 ev5 if x be only ( a promis$ l& :i* he may nev] hope himself to ent]2 x has deep] roots & a m p]sonal int]e/4 ,be=e he c und]/& himself1 man mu/ fir/ und]/& ! univ]se f :i* all 8 s5se p]ceptions are drawn4 ,he wi%es to explore ! univ]se1 bo? 9 space & "t1 because he himself =ms "p ( x1 & x =ms "p ( him4 ,we may well admit t sci5ce _c at pres5t hope to say any?+ f9al on ! que/ions ( human exi/5ce & human de/9y1 b ?is is no ju/ification = n becom+ acqua9t$ ) ! be/ t x has to (f]4 ,x is r>e inde$ = sci5ce to give a f9al 8,yes0 or 8,no0 answ] to any "q prop\nd$ to h]4 ,:5 we are able to put a "q 9 su* a def9ite =m t ei!r ( ^! answ]s c\ld be giv5 9 reply1 we are g5]ally already 9 a position to supply ! answ] ourselves4 ,sci5ce advances r by provid+ a succession ( approximations to ! tru?1 ea* m accurate ?an ! la/1 b ea* capable ( endless degrees ( high] accuracy4 ,to ! "q1 8:]e does man /& 9 ! univ]se80 ! fir/ attempt at an answ]1 at any rate 9 rec5t times1 0 provid$ by ! a/ronomy ( ,ptolemy3 8at ! c5tre40 ,galileo's telescope provid$ ! next1 & incomp>ably bett]1 approximation3 8man's home 9 space is only "o ( a numb] ( small bodies revolv+ r\nd a huge c5tral sun40 ,n9ete5?-c5tury a/ronomy swung ! p5dulum /ill fur!r 9 ! same direction1 say+3 8!re are millions ( />s 9 ! sky1 ea* simil> to our sun1 ea* d\btless surr\nd$1 l our sun1 by a family ( planets on :i* life may be kept 9 be+ by ! light & heat receiv$ f its sun40 ,tw5tie?-c5tury a/ronomy sugge/s1 z we %all see1 t ! n9ete5? c5tury _h swung ! p5dulum too f>2 life n[ seems to be m ( a r>ity ?an our fa!rs ?\ght1 or w\ld h ?\ght if !y _h giv5 free play to _! intellects4 ,we are sett+ out to expla9 ! approximation to ! tru? provid$ by tw5tie?-c5tury a/ronomy4 ,no d\bt x is n ! f9al tru?1 b x is a /ep on t[>ds x1 & unless we are greatly 9 error x is v mu* ne>] to ! tru? ?an 0 ! tea*+ ( n9ete5?-c5tury a/ronomy4 ,x claims to be ne>] ! tru?1 n because ! tw5tie?-c5tury a/ronom] claims to be bett] at guess+ ?an 8 pr$ecessors ( ! n9ete5?-c5tury1 b because he has incomp>ably m facts at 8 disposal4 ,guess+ has gone out ( fa%ion 9 sci5ce2 x 0 at be/ a poor sub/itute = k1 & mod]n sci5ce1 es*ew+ guess+ sev]ely1 conf9es itself1 except on v r>e occasions1 to asc]ta9$ facts & ! inf]5ces :i*1 s f> z c be se51 foll[ unequivocally f !m4 ,x w\ld ( c\rse be futile to pret5d t ! :ole int]e/ ( a/ronomy c5tres r\nd ! que/ions j m5tion$4 ,a/ronomy (f]s at lea/ ?ree o!r gr\ps ( int]e/ :i* may be describ$ z utilit>ian1 sci5tific & ae/hetic4 ,at fir/ a/ronomy1 l o!r sci5ces1 0 /udi$ = ma9ly utilit>ian reasons4 ,x provid$ measures ( "t1 & enabl$ mank9d to keep a tally on ! flight ( ! seasons2 x taught him to f9d 8 way across ! trackless des]t1 & lat]1 across ! trackless ocean4 ,9 ! guise ( a/rology1 x held out hopes ( tell+ him 8 future4 ,!re 0 no?+ intr9sically absurd 9 ?is1 = ev5 to-day ! a/ronom] is l>gely occupi$ ) =etell+ ! future movem5ts ( ! heav5ly bodies1 al?\gh n ( human affairs--a consid]able "p ( ! pres5t book w consi/ ( an attempt to =etell ! future1 & pr$ict ! f9al end1 ( ! mat]ial univ]se4 ,:]e ! a/rolog]s w5t wrong 0 9 suppos+ t t]re/rial empires1 k+s & individuals =m$ su* important items 9 ! s*eme ( ! univ]se t ! motions ( ! heav5ly bodies c\ld be intimately b\nd up ) _! fates4 ,z soon z man began to realise1 ev5 fa9tly1 8 own insignificance 9 ! univ]se1 a/rology di$ a natural & inevitable dea?4 ,! utilit>ian aspect ( a/ronomy has by n[ %runk to v mode/ proportions4 ,! national obs]vatories /ill broadca/ ! "t ( day1 & help to guide %ips across ! ocean1 b ! c5tre ( a/ronomical int]e/ has %ift$ s completely t ! remote/ ( nebulae ar\se incomp>ably m en?usiasm ?an 8clock-/>s10 & ! av]age a/ronom] totally neglects our ne>e/ neighb\rs 9 space1 ! planets1 = />s s di/ant t _! light takes hundr$s1 ?\s&s1 or ev5 millions1 ( ye>s to rea* u4 ,rec5tly1 a/ronomy has acquir$ a new sci5tific int]e/ ?r\gh e/abli%+ its position z an integral "p ( ! g5]al body ( sci5ce4 ,! v>i\s sci5ces c no long] be treat$ z di/9ct2 sci5tific discov]y advances along a cont9u\s front :i* ext5ds unbrok5 f electrons ( a fraction ( a million? ( a million? ( an in* 9 diamet]1 to nebulae ^: diamet]s are measur$ 9 hundr$s ( ?\s&s ( millions ( millions ( miles4 ,a ga9 ( a/ronomical k may add to our k ( physics & *emi/ry1 & vice v]sa4 ,! />s h long ago ceas$ to be treat$ z m]e po9ts ( light4 ,ea* is n[ reg>d$ z an exp]im5t on a h]oic scale1 a high temp]ature crucible 9 :i* nature h]self op]ates ) ranges ( temp]ature & pressure f> beyond ^? available 9 our laboratories1 & p]mits u to wat* ! results4 ,9 s do+1 we may happ5 ^u prop]ties ( matt] :i* h elud$ ! t]re/rial physici/1 ow+ to ! small range ( physical conditions at 8 comm&4 ,= in/ance matt] exi/s 9 nebulae ) a d5sity at lea/ a million times l[] ?an any?+ we c approa* on e>?1 & 9 c]ta9 />s at a d5sity ne>ly a million times great]4 ,h[ c we expect to und]/& ! :ole nature ( matt] f laboratory exp]im5ts 9 :i* we c comm& only "o "p 9 a million million ( ! :ole range ( d5sity kn[n to nature8 ,yet = ea* "o :o feels ! purely sci5tific appeal ( a/ronomy1 !re are probably a doz5 :o are attract$ by its ae/hetic appeal4 ,_m ev5 ( ^? :o seek aft] k = its own sake1 driv5 by t intellectual curiosity :i* provides ! fundam5tal di/9ction betwe5 !mselves & ! bea/s1 f9d _! ma9 int]e/ 9 a/ronomy1 z ! mo/ poetical & ! mo/ ae/hetically gratify+ ( ! sci5ces4 ,!y want to ex]cise _! faculties & imag9ations on some?+ remote f ev]yday trivialities1 to f9d an occasional respite f 8! long littl5ess ( life10 & !y satisfy _! desires 9 contemplat+ ! s]5e imm5sities ( ! out] univ]se4 ,to _m1 a/ronomy provides some?+ ( ! vision )\t :i* ! p p]i%4 ,be=e proce$+ to describe ! results ( ! mod]n a/ronom]'s survey ( ! sky1 let u try to envisage 9 its prop] p]spective ! plat=m f :i* 8 obs]vations are made4 ,lat] on1 we %all see h[ ! e>? 0 born out ( ! sun1 some?+ l two ?\s& millions ( ye>s ago4 ,x 0 born 9 a =m 9 :i* we %\ld f9d x h>d to recognise ! solid e>? ( to-day ) its seas & riv]s1 its ri* vegetation & ov]fl[+ life4 ,our home 9 space came into be+ z a globe ( int5sely hot gas on :i* no life ( any k9d c\ld ei!r ga9 or reta9 a foo?old4 ,gradually ?is globe ( gas cools d[n1 becom+ fir/ liquid1 !n pla/ic4 ,f9ally its out] cru/ solidifies1 rocks & m\nta9s =m+ a p]man5t record ( ! irregul>ities ( its e>li] pla/ic =m4 ,vap\rs cond5se into liquids1 & riv]s & oceans come into be+1 :ile ! 8p]man5t0 gases =m an atmosph]e4 ,gradually ! e>? assumes a condition suit$ to ! adv5t ( life1 :i* f9ally appe>s1 we "k n h[1 :5ce or :y4 ,x is n easy to e/imate ! "t s9ce life fir/ appe>$ on e>?1 b x c h>dly h be5 m ?an a small fraction ( ! :ole #bjjj million ye>s ( ! e>?'s exi/5ce4 ,/ill1 !re 0 probably life on e>? at lea/ #cjj million ye>s ago4 ,! fir/ life appe>s to h be5 :olly aquatic1 b gradually fi%es *ang$ into reptiles1 reptiles into mammals1 & f9ally man em]g$ f mammals4 ,! evid5ce fav\rs a p]iod ( ab\t #cjj1jjj ye>s ago = ?is la/ ev5t4 ,?us life has inhabit$ ! e>? = only a fraction ( its exi/5ce1 & man = only a t9y fraction ( ?is fraction4 ,to put x 9 ano!r way1 ! a/ronomical "t-scale is incomp>ably long] ?an ! human "t-scale--! g5]ations ( man1 & ev5 ! :ole ( human exi/5ce1 are only ticks ( ! a/ronom]'s clock4 ,mo/ ( ! #aj1jjj or s ( g5]ations ( m5 :o connect u up ) our ape-l ance/ry mu/ h liv$ lives :i* did n diff] greatly f ^? ( _! animal pr$ecessors4 ,hunt+1 fi%+ & w>f>e fill$ _! lives1 leav+ b little "t or opportunity = intellectual contemplation4 ,!n1 at la/1 man began to awake f 8 long intellectual slumb]1 &1 z civilisation sl[ly dawn$1 to feel ! ne$ = occupations o!r ?an ! m]e fe$+ & clo?+ ( 8 body4 ,he began to discov] revelations ( inf9ite beauty 9 ! grace ( ! human =m or ! play ( light on ! myriad-smil+ sea1 :i* he tri$ to p]petuate 9 c>efully *isell$ m>ble or exquisitely *os5 words4 ,he began to exp]im5t ) metals & h]bs1 & ) ! effects ( fire & wat]4 ,he began to notice1 & try to und]/&1 ! motions ( ! heav5ly bodies1 = to ^? :o c\ld read ! writ+ 9 ! sky1 ! nightly ris+ & sett+ ( ! />s & planets provid$ evid5ce t beyond ! conf9es ( ! e>? lay an unkn[n univ]se built on a f> gr&] scale4 ,9 ?is way ! arts & sci5ces came to e>?1 br++ a/ronomy ) !m4 ,we _c q say :51 b comp>$ ev5 ) ! age ( ! human race1 !y came b ye/]day1 :ile 9 comp>ison ) ! :ole age ( ! e>?1 _! age is b a tw9kl+ ( ! eye4 ,sci5tific a/ronomy1 z di/+ui%$ f m]e />-gaz+1 c h>dly claim an age ( m ?an #cjjj ye>s4 ,x is less ?an ?is s9ce ,py?agoras1 ,ari/>*us & o!rs expla9$ t ! e>? mov$ ar\nd a fix$ sun4 ,yet ! really significant figure = our pres5t purpose is n s mu* ! "t s9ce m5 began to make conjectures ab\t ! /ructure ( ! univ]se1 z ! "t s9ce !y began to unravel its true /ructure by ! help ( asc]ta9$ fact4 ,! important l5g? ( "t is t :i* has elaps$ s9ce t ev5+ 9 #afaj :5 ,galileo fir/ turn$ 8 telescope on to ,jupit]--a m]e ?ree c5turies or s4 ,we beg9 to grasp ! true significance ( ^! r\nd-numb] e/imates :5 we re-write !m 9 tabul> =m4 ,we h3 ,age ( e>? ab\t #b1jjj1jjj1jjj ye>s ,age ( life on e>? 0 #cjj1jjj1jjj 0 ,age ( man on e>? 0 #cjj1jjj 0 ,age ( a/ronomical sci5ce 0 #c1jjj 0 ,age ( telescopic a/ronomy 0 #cjj 0 ,:5 ! v>i\s figures are display$ 9 ?is =m we see :at a v rec5t ph5om5on a/ronomy is4 ,its total age is only a hundr$? "p ( ! age ( man1 only a hundr$-?\s&? "p ( ! "t t life has inhabit$ ! e>?4 ,dur+ #ii1iii p>ts out ( ! #ajj1jjj ( its exi/5ce1 life on e>? 0 h>dly conc]n$ ab\t any?+ beyond ! e>?4 ,b :]eas ! pa/ ( a/ronomy is to be measur$ on ! human "t-scale1 a hundr$ g5]ations or s ( m51 !re is e reason to expect t its future w be measur$ on ! a/ronomical "t-scale4 ,we %all discuss ! probable future /ret*+ be=e ! human race 9 a lat] *apt]4 ,= ! mom5t x is n unreasonable to suppose t ?is future w probably be t]m9at$ by a/ronomical causes1 s t its l5g? is to be measur$ on ! a/ronomical "t-scale4 ,z ! e>? has already exi/$ = #bjjj million ye>s1 x is priori reasonable to suppose t x w exi/ = at lea/ some?+ ( ! ord] ( #bjjj million ye>s yet to come1 & humanity & a/ronomy ) x4 ,actually we %all f9d reasons = expect+ x to la/ f> long] ?an ?is4 ,b if once x is conc$$ t its future life is to be e/imat$ on ! a/ronomical "t-scale1 no matt] 9 :at exact way1 we see t a/ronomy is /ill at ! v op5+ ( its exi/5ce4 ,?is is :y its message c claim no f9ality--we are n describ+ ! mature convictions ( a man1 s mu* z ! fir/ impressions ( a new-born babe :i* is j op5+ its eyes4 ,ev5 s !y are bett] ?an ! idle introspective dream+s 9 :i* x indulg$ be=e x _h le>n$ to look ar\nd itself & away f itself4 ,& s we set out to le>n :at a/ronomy has to tell u ab\t ! univ]se 9 :i* we live our lives4 ,our inquiry w n be entirely limit$ to ?is "o sci5ce4 ,we %all call ^u o!r sci5ces1 physics1 *emi/ry & geology1 z well z ! m closely alli$ sci5ces ( a/rophysics & cosmogony1 to give help1 :5 !y c1 9 int]pret+ ! message ( obs]vational a/ronomy4 ,! in=mation we %all obta9 w be fragm5t>y4 ,if x mu/ be comp>$ to any?+1 let x be to ! pieces ( a jig-saw puzzle4 ,c\ld we get hold ( all ! pieces1 !y w\ld1 we are confid5t1 =m a s+le complete consi/5t picture1 b _m ( !m are /ill miss+4 ,x is too mu* to hope t ! incomplete s]ies ( pieces we h already f\nd w disclose ! :ole picture1 b we may at lea/ collect !m toge!r1 arrange !m 9 "s sort ( me?odical ord]1 fit toge!r pieces :i* are obvi\sly contigu\s1 & p]haps haz>d a guess z to :at ! f9i%$ picture w prove to be :5 all its pieces h be5 f\nd & f9ally fitt$ toge!r4 ,,*apt] ,i ,explor+ ! ,sky ,we h se5 h[ man1 aft] inhabit+ ! e>? = #cjj1jjj ye>s1 has )9 ! la/ #cjj ye>s--! la/ "o-?\s&? "p ( 8 life on e>?--become possess$ ( an optical means ( /udy+ ! out] univ]se4 ,9 ! pres5t *apt] we %all try to describe ! impressions he has =m$ ) 8 newly-awak5$ eyes4 ,! description w be arrang$ 9 a v r\gh *ronological ord]4 ,?is is also an ord] ( increas+ telescopic p[]1 or aga9 ( see+ fur!r & fur!r into space1 s t our ord] ( arrangem5t might equally be describ$ z "o ( increas+ di/ance f ! sun4 ,we %all n attempt any sort ( cont9u\s record1 b %all m]ely m5tion a few l&m>ks s z to %ew 9 broad outl9e ! ord] 9 :i* t]ritory 0 won & consolidat$ 9 man's survey ( ! univ]se4 ,,! ,,sol> ,,sy/em ,we may conv5i5tly />t ) ! sol> sy/em1 ! /ructure ( :i* 0 unravell$ by ,galileo & 8 successors4 ,! sun's family ( planets falls naturally into di/9ct gr\ps4 ,ne> to ! sun are ! f\r small planets1 ,m]cury1 ,v5us1 ! ,e>? & ,m>s4 ,at mu* great] di/ances are ! f\r great planets1 ,jupit]1 ,saturn1 ,uranus & ,neptune4 ,beyond all ^! is ! newly discov]$ planet ,pluto1 ! out]mo/ memb] ( our sy/em s f> kn[n4 ,m]cury is ne>e/ ( all to ! sun2 next comes ,v5us4 ,! orbits ( ^! two planets lie betwe5 ! e>?'s orbit & ! sun4 ,z se5 f ! e>?1 ^! planets appe> to describe relatively small circles r\nd ! sun1 & s mu/ necess>ily appe> ne> to ! sun 9 ! sky4 ,z a consequ5ce1 !y c only be se5 ei!r 9 ! e>ly morn+1 if !y happ5 to rise j be=e ! sun1 or 9 ! ev5+ if !y set aft] ! sun4 ,! anci5ts n altoge!r recognis+ t ! same planets c\ld appe> bo? z morn+ & ev5+ />s1 gave !m diff]5t names accord+ z !y figur$ z ! "o or ! o!r4 ,z a morn+ /> ,v5us 0 call$ ,phosphoros by ! ,greeks & ,lucif] by ! ,romans2 z an ev5+ /> x 0 call$ ,hesp]us by bo?4 ,next beyond ! e>?1 proce$+ outw>d f ! sun into space1 comes ,m>s1 complet+ ! gr\p ( small planets4 ,m>s1 ,v5us & ,m]cury are all small] ?an ! e>? 9 size1 al?\gh ,v5us is only slightly s4 ,!re is a wide gap betwe5 ! orbit ( ,m>s1 ! la/ ( ! small planets1 & t ( ,jupit]1 ! fir/ ( ! great planets4 ,?is is n empty2 x is occupi$ by ! orbits ( ?\s&s ( t9y planets kn[n z a/]oids4 ,none ( ^! approa*es ! e>? 9 size2 ,c]es1 ! l>ge/1 is only #dhj miles 9 diamet]1 & only f\r are kn[n ) diamet]s ( m ?an #ajj miles4 ,! planets ,m]cury1 ,v5us & ,m>s h all be5 kn[n f remote antiquity1 b ! a/]oids only ent]$ a/ronomy ) ! n9ete5?-c5tury1 ,c]es1 ! fir/ & l>ge/1 hav+ be5 discov]$ by ,piazzi on ,janu>y #a1 #ahja4 ,beyond ! a/]oids come ! f\r great planets ,jupit]1 ,saturn1 ,uranus & ,neptune1 all ( :i* are f> l>g] ?an ! e>?4 ,jupit]1 ! l>ge/1 has1 accord+ to ,sampson1 a diamet] ( #hh1fdj miles1 or m ?an elev5 times ! diamet] ( ! e>?2 f\rte5 hundr$ bodies ( ! size ( ! e>? c\ld be pack$ inside ,jupit]1 & leave room to sp>e4 ,saturn1 :i* comes next 9 ord]1 is second only to ,jupit] 9 size1 hav+ a diamet] ( ab\t #gj1jjj miles4 ,^! two are by f> ! l>ge/ ( ! planets4 ,uranus & ,neptune h ea* ab\t f\r times ! diamet]1 & s ab\t sixty-f\r times ! volume1 ( ! e>?4 ,! size ( ,pluto is n yet kn[n ) accuracy1 b x c h>dly be l>g] ?an ! e>? & is probably consid]ably small]4 ,jupit] & ,saturn =m su* conspicu\s objects 9 ! sky t !y h necess>ily be5 kn[n f ! e>lie/ times1 b ,uranus & ,neptune are comp>atively rec5t discov]ies4 ,sir ,william ,h]s*el discov]$ ,uranus q accid5tally 9 #agha1 :ile look+ ?r\gh 8 telescope ) no motive o!r ?an ! hope ( f9d+ some?+ int]e/+ 9 ! sky4 ,by contra/1 ,neptune 0 discov]$ 9 #ahdf z ! result ( intricate ma!matical calculations1 :i* _m at ! "t reg>d$ z ! greate/ triumph ( ! human m9d1 at any rate s9ce ! "t ( ,newton4 ,x 0 a triumph ( y\?4 ,! hon\r mu/ be apportion$ 9 approximately equal %>es betwe5 an ,engli%man1 ,john ,c\* ,adams1 !n only #bg ye>s old1 :o 0 aft]w>ds ,pr(essor ( ,a/ronomy at ,cambridge1 & a "y ,fr5* a/ronom]1 ,urba9 ,j4 ,j4 ,lev]ri]1 :o 0 only eight ye>s 8 s5ior4 ,bo? attribut$ c]ta9 vag>ies 9 ! obs]v$ motion ( ,uranus to ! gravitational pull ( an ext]ior planet1 & bo? set to "w to calculate ! orbit 9 :i* ?is suppos$ out] planet mu/ move to expla9 ^! vag>ies4 ,adams f9i%$ 8 calculations fir/1 & in=m$ obs]v]s at ,cambridge z to ! "p ( ! sky 9 :i* ! new planet ought to lie4 ,z a result1 ,neptune 0 obs]v$ twice1 al?\gh )\t be+ imm$iately id5tifi$ z ! want$ planet4 ,be=e ?is id5tification _h be5 e/abli%$ at ,cambridge1 ,lev]ri] _h f9i%$ 8 computations & communicat$ 8 results to ,galle1 an assi/ant at ,b]l91 :o 0 able to id5tify ! planet at once1 ,b]l9 possess+ bett] />-*>ts ( ! region ( ! sky 9 "q ?an 7 accessible at ,cambridge4 ,gradually x em]g$ t ! gravitational pull ( ,neptune 0 inadequate to acc\nt = all ! vag>ies 9 ! motions ( ,uranus1 :ile simil> vag>ies began to appe> 9 ,neptune's own motion4 ,?is po9t$ to ! exi/5ce ( yet ano!r planet1 fur!r out ev5 ?an ,neptune4 ,j z ,adams & ,lev]ri] _h done on ! =m] occasion1 s ,dr ,p]cival ,l[ell1 ( ,flag/aff ,obs]vatory1 ,arizona1 comput$ ! orbit 9 :i* ! conjectur$ new planet1 8,planet ,x10 ought to move1 b x 0 only rec5tly 7,m>* #aicj71 aft] _m ye>s ( c>eful se>*1 t ! ,flag/aff obs]v]s discov]$ ! planet ,pluto1 mov+ 9 almo/ precisely ! orbit :i* ,l[ell _h pr$ict$ fifte5 ye>s previ\sly4 ,z f> back z #aggb1 ,bode _h po9t$ out a simple num]ical relation connect+ ! di/ances ( ! v>i\s planets f ! sun4 ,?is is obta9$ z foll[s3 ,write fir/ ! s]ies ( numb]s #j #a #b #d #h #af #cb #fd #abh #bef 9 :i* ea* numb] aft] ! fir/ two is d\ble ! prec$+4 ,multiply ea* by ?ree1 ?us obta9+ #j #c #f #ab #bd #dh #if #aib #chd #gfh & add f\r to ea*1 giv+ #d #g #aj #af #bh #eb #ajj #aif #chh #ggb ,^! numb]s are v approximately proportional to ! actual di/ances ( ! planets f ! sun1 :i* are 7tak+ ! e>?'s di/ance to be #aj73 ,m]cury #ci ,v5us #gb ,e>? #ajj ,m>s #aeb ,a/]oids #bfe ,jupit] #ebj ,saturn #ied ,uranus #aiai ,neptune #cjjg ,pluto #djj ,! law 0 enunciat$ be=e ,uranus & ! a/]oids _h be5 discov]$1 s t x is some:at rem>kable t ^! fit s well into _! pr$ict$ places4 ,on ! o!r h&1 ! law fails completely = ,neptune & ! newly discov]$ ,pluto1 s t x seems m ?an likely t x is a m]e co9cid5ce ) no und]ly+ rational explanation4 ,! out]mo/ planets are at enorm\s di/ances f ! sun4 ,an inhabitant ( ,pluto1 if su* exi/$1 w\ld receive only a sixte5-hundr$? "p z mu* light & heat f ! sun z an inhabitant ( ! e>? receives4 ,x c be calculat$ t if ,pluto's surface 7 w>m$ only by ! heat ( ! sun1 x w\ld be at a v l[ temp]ature inde$1 some:]e 9 ! neighb\rhood ( -#bcj ,c5tigrade1 or m ?an #djj degrees ( fro/ on ! ,fahr5heit scale4 ,a telescope collects heat z well z light4 ,n only is ! heat-ga!r+ p[] ( a l>ge telescope trem5d\s1 b extremely s5sitive in/rum5ts h be5 design$ to measure ?is heat4 ,! #ajj-;in* telescope at ,m\nt ,wilson is said to be capable ( detect+ ! heat receiv$ f a s+le c&le on ! banks ( ! ,mississippi1 #bjjj miles away4 ,?is great s5sitiv5ess has made x possible to measure ! inf9itesimal am\nts ( heat receiv$ f s+le />s & planets1 & s to e/imate ! temp]atures ( _! surfaces4 ,rec5t measurem5ts indicate t ! surface ( ,jupit] is at a temp]ature ( ab\t -#aej ,c5tigrade1 :i* is j ab\t t at :i* x w\ld be ma9ta9$ by ! sun's heat alone4 ,on ! o!r h& simil> measurem5ts assign temp]atures ( -#aej & -#agj respectively to ,saturn & ,uranus1 bo? ( :i* are r high] ?an w\ld be expect$ if ^! planets _h no s\rce ( heat beyond ! sun's radiation4 ,b x seems cle> t any s\rces ( int]nal heat mu/ be q small1 & t all ! major planets are v cold inde$4 ,!re c be nei!r seas nor riv]s on _! surfaces1 s9ce all wat] mu/ be froz5 into ice1 nei!r c !re be ra9 or wat]-vap\r 9 _! atmosph]es4 ,x has be5 sugge/$ t ! cl\ds :i* obscure our view ( ,jupit]'s surface may be cond5s$ p>ticles ( c>bon-dioxide1 or "s o!r gas :i* boils at temp]atures f> bel[ ! freez+ po9t ( wat]4 ,! physical conditions ( ! small] planets are mu* m l ^? ) :i* we are famili> on e>?4 ,ow+ to its great] di/ance f ! sun1 ,m>s is some:at1 b n enorm\sly1 cold] ?an ! e>?4 ,its day ( #bd h\rs #cg m9utes is only slightly long] ?an our own1 s t its surface mu/ exp]i5ce alt]nations ( w>m? by day & cold by night simil> to ^? we f9d on e>?4 ,9 ! equatorial regions ! temp]ature rises well above ! freez+ po9t at noon1 occasionally rea*+ #ej ,fahr5heit or ev5 m4 ,b ev5 "h x falls bel[ freez+ "s "t be=e sunset1 & f !n until well on 9 ! next day1 ! climate mu/ be v cold4 ,! pol> regions are ( c\rse cold] /ill1 ! temp]ature ( ! sn[cap :i* cov]s ! poles be+ some:]e ab\t -#gj ,c5tigrade or -#id ,fahr5heit--#abf degrees ( fro/6 ,v5us1 be+ ne>] ! sun1 mu/ h a high] av]age temp]ature ?an ! e>?4 ,b z ea* ( its days & nights is sev]al days ( our t]re/rial "t1 ! diff]5ce betwe5 ! temp]atures ( day & night mu/ be f> great] ?an ) u1 s t its surface mu/ exp]i5ce great extremes ( heat by day & ( cold by night4 ,! night temp]ature appe>s to be fairly uni=mly equal to ab\t -#be ,c5tigrade or -#ac ,fahr5heit4 ,at any po9t on ! planet's surface weeks ( ?is bitt]ly cold night temp]ature mu/ alt]nate ) weeks ( a roa/+ day temp]ature4 ,m]cury is s ne> ! sun t its av]age temp]ature is necess>ily f> high] ?an t ( ! e>?4 ,x reflects only a t9y fraction--ab\t a f\rte5?--( ! light & heat x receives f ! sun4 ,all ! re/ goes to heat+ up its surface4 ,a numb] ( consid]ations make x likely t ! planet always turns ! same face to ! sun1 j z ! moon always turns ! same face to ! e>?4 ,if s ! unw>m$ half ( its surface mu/ be int5sely cold1 & ! w>m$ half int5sely hot4 ,x c be calculat$ t 9 ?is case ! w>m$ hemisph]e ought to h a temp]ature ( ab\t #ceg ,c5tigrade2 if h[ev] ! planet 0 9 fairly rapid rotation1 its :ole surface w\ld h a temp]ature ( only ab\t #agj ,c5tigrade4 ,q rec5tly ,pettit & ,ni*olson h measur$ ! am\nt ( heat receiv$ on e>? f ! w>m$ hemisph]e1 & f9d t its temp]ature mu/ be ab\t #cej ,c5tigrade or #ffb ,fahr5heit1 ?us confirm+ t ! planet always turns ! same face to ! sun4 ,its w>m hemisph]e is at a temp]ature :i* melts lead2 ! o!r hemisph]e1 et]nally d>k & unw>m$1 is probably cold] ?an any?+ we c imag9e4 ,illu/ration3 ,,plate ,i ,frankl9-,adams ,*>t ,! ,milky ,way 9 ! neighb\rhood ( ! ,s\!rn ,cross ,galileo's discov]y ( ! f\r satellites ( ,jupit] 0 foll[$ 9 "t by ! discov]y t e planet 0 att5d$ by satellites1 except ! two ^: orbits lay inside ! e>?'s4 ,9 #afee ,huygh5s discov]$ ,titan1 ! l>ge/ ( ,saturn's satellites1 & by #afhd ,cass9i _h discov]$ f\r m4 ,!n1 aft] ! lapse ( a full c5tury1 ,sir ,william ,h]s*el discov]$ two satellites ( ,uranus 9 #aghg & two m satellites ( ,saturn 9 #aghi4 ,we %all discuss ! full sy/em ( planet>y satellites & also ! small] bodies ( ! sol> sy/em--comets1 meteors & %oot+-/>s--9 a lat] *apt]1 :5 we come to deal ) ! way !y came into be+4 ,,! ,,galactic ,,sy/em ,our next l&m>k is ! survey ( ! />s by ! two ,h]s*els1 ,sir ,william ,h]s*el1 ! fa!r 7#agch-ahbb7 & ,sir ,john ,h]s*el1 ! son 7#agib-ahga74 ,:at ,galileo _h done = ! sol> sy/em1 ! two ,h]s*els set out to d = ! huge family ( />s--! 8galactic0 sy/em1 b\nd$ by ! ,milky ,way--( :i* our sun is a memb]4 ,on a cle> moonless night ! ,milky ,way is se5 to /ret*1 l a great ar* ( fa9t light1 f horizon to horizon4 ,x is f\nd to be only "p ( a full circle ( light--! galactic circle--:i* /ret*es completely r\nd ! e>? & divides ! sky into two equal halves1 =m+ a sort ( cele/ial 8equator10 ) ref]5ce to :i* a/ronom]s are accu/om$ to measure latitude & longitude 9 ! sky4 ,galileo's telescope _h %ewn t x consi/s ( a cr[d ( fa9t />s1 ea* too dim to be se5 individually )\t telescopic aid 7see ,plate ,i74 ,&1 z might be expect$1 ! prop] int]pretation ( ?is great belt ( fa9t />s has prov$ to be fundam5tal 9 und]/&+ ! ar*itecture ( ! univ]se4 ,if />s 7 scatt]$ uni=mly ?r\gh inf9ite space1 we %\ld at la/ come to a /> 9 :atev] direction we look$1 s t ! sky w\ld appe> z a uni=m blaze ( intol]able light4 ,x is true t ?is w\ld n be ! case if light 7 dimm$ or blott$ out aft] travell+ a c]ta9 di/ance1 b ev5 !n1 ! sky w\ld appe> ! same 9 all directions1 = !re w\ld be no reason :y "o "p ( ! sky %\ld be m lavi%ly spangl$ ) />s ?an ano!r4 ,?us ! exi/5ce ( ! ,milky ,way %ews t ! sy/em ( ! />s does n ext5d uni=mly to inf9ity4 ,x mu/ h a def9ite /ructure1 & x 0 ! ar*itecture ( ?is t ,sir ,william ,h]s*el set himself to unravel4 ,! "w he did = ! nor!rn half ( ! sky 0 subsequ5tly ext5d$ to ! s\!rn hemisph]e by 8 son1 ,sir ,john ,h]s*el4 ,we %all be/ und]/& ! me?od employ$ by ! ,h]s*els if we fir/ imag9e all ! />s 9 ! sky to be intr9sically simil> objects4 ,ea* w\ld !n emit ! same am\nt ( light1 s t ! ne>] />s w\ld appe> bright1 & ! fur!r />s fa9t1 m]ely z an effect ( di/ance4 ,! way 9 :i* app>5t brightness decreases ) di/ance is ( c\rse well kn[n2 ! law is t ( ! 8inv]se squ>e ( ! di/ance10 :i* means t ! app>5t brightness decreases j z rapidly z ! squ>e ( its di/ance increases2 a /> :i* is twice z di/ant z a second simil> /> appe>s only a qu>t] z bright1 & s on4 ,?us if all />s emitt$ ! same am\nt ( light1 we c\ld e/imate ! relative di/ances ( any two />s 9 ! sky f _! relative brightnesses4 ,by cutt+ wires ( l5g?s proportional to ! di/ances ( v>i\s />s1 & po9t+ ^! 9 ! directions ( ! />s to :i* !y ref]r$1 we c\ld =m a model ( ! arrangem5t ( ! />s 9 ! sky4 ,we %\ld1 9 fact1 "k ! :ole /ructure ( ! sy/em ( />s except = its scale4 ,to repres5t ! fa9t />s ( ! ,milky ,way1 a great numb] ( v long wires w\ld be ne$$4 ,9 ! model ^! w\ld all po9t t[>ds diff]5t p>ts ( ! ,milky ,way1 =m+ a flat :eel-l /ructure4 ,! problem :i* confront$ ,sir ,william ,h]s*el 0 m intricate because he knew t ! />s 7 ( diff]5t intr9sic brightness z well z at diff]5t di/ances1 & bo? factors comb9$ to produce diff]5ces ( app>5t brightness4 ,"o ( ! ma9 difficulties ( a/ronomy1 bo? to ! ,h]s*els & to ! a/ronom] ( to-day1 is t ^! two factors h to be dis5tangl$ be=e any def9ite conclusions are rea*$4 ,h]s*el f\nd t ! numb] ( />s visible 9 8 telescope-field v>i$ enorm\sly ) diff]5t directions 9 space4 ,x 0 ( c\rse greate/ :5 ! telescope 0 po9t$ at ! ,milky ,way1 & fell (f1 /eadily & rapidly1 z ! telescope 0 mov$ away f ! ,milky ,way4 ,g5]ally speak+1 two telescope-fields :i* 7 at equal di/ances f ! ,milky ,way conta9$ ab\t ! same numb] ( />s4 ,9 ! te*nical language ( a/ronomy1 ! ri*ness ( ! />-field dep5d$ ma9ly on ! galactic latitude1 j z ! e>?'s climate dep5ds ma9ly on ! geographic latitude1 & n to any great ext5t on ! longitude4 ,fields at diff]5t di/ances f ! ,milky ,way 7 f\nd to diff] 9 quality z well z 9 numb] ( />s4 ,! brighte/ />s ( all occurr$ ab\t equally 9 all fields1 ! diff]5ce 9 ! fields result+ ma9ly f fa9t />s1 & p>ticul>ly ! fa9te/ />s ( all1 becom+ enorm\sly m abundant z ! ,milky ,way 0 approa*$4 ,sir ,william ,h]s*el rightly int]pret$ ?is z %ew+ t ! sy/em ( />s surr\nd+ ! sun began to ?9 out )9 di/ances rea*$ by 8 telescope1 & t !y began to ?9 out soone/ 9 directions fur!/ away f ! ,milky ,way4 ,he suppos$ ! g5]al %ape ( ! galactic sy/em ( />s to be t ( a bun or a biscuit or a wat*1 ! />s be+ mo/ ?ickly scatt]$ ne> ! c5tre1 & occurr+ m sp>sely 9 ! out] regions4 ,! plane ( ! ,milky ,way ( c\rse =m$ ! c5tral plane ( ! /ructure4 ,! fact t ! ,milky ,way divides ! sky into two almo/ exactly equal halves sugge/$ to him t ! sun mu/ be v ne>ly 9 ?is c5tral plane1 & ?is is confirm$ by ! rec5t v ref9$ inve/igations ( ,se>es & van ,rhijn1 & o!rs4 ,f ! fact t p>ts ( ! sky :i* 7 equidi/ant f ! ,milky ,way appe>$ ab\t equally bright1 ,h]s*el inf]r$ t ! sun n only lay 9 ! c5tral plane ( ! sy/em1 b 0 v ne> to its actual c5tre4 ,?is view has prevail$ until q rec5tly1 b ! rese>*es ( ,%apley & o!rs n[ %ew x to be unt5able 7see p4 #fe bel[74 ,fig4 #a %ews a cross-section ( ! g5]al k9d ( /ructure :i* ,sir ,william ,h]s*el assign$ to ! galactic sy/em1 al?\gh ! detail$ di/ribution ( />s %ewn 9 ! diagram is t giv5 at a mu* lat] date 7#aibb7 by ,kapteyn4 ,x is easy to see h[ a /ructure ( ?is type w\ld acc\nt = ! g5]al appe>ance ( ! sky4 ,^? />s :i* appe> brighte/ ( all are1 g5]ally speak+1 ! ne>e/2 !y are s ne> t no appreciable ?9n+ out ( />s occurs )9 ?is di/ance4 ,= ?is reason ! v bright />s occur 9 ab\t equal numb]s 9 all directions4 ,! />s :i* appe> v fa9t are mo/ly v di/ant1 s di/ant t ! great dep? ( ! sy/em 9 directions 9 or ne> to ! galactic plane is br\ght into play4 ,9 su* directions1 lay] aft] lay] ( />s1 rang$ almo/ endlessly "o beh9d ! o!r1 give rise to ! app>5t conc5tration ( fa9t />s :i* we call ! ,milky ,way4 ,illu/ration3 ,fig4 #a4 ,! ,/ructure ( ! ,galactic ,sy/em accord+ to ,h]s*el & ,kapteyn4 ,! f9al acceptance ( ! ,cop]nican view ( ! /ructure ( ! sol> sy/em 0 9 a l>ge measure due to ,galileo's discov]y ( ! simil> sy/em ( ,jupit]1 :i* 0 s situat$ 9 space t a t]re/rial obs]v] c\ld obta9 a bird's-eye view ( x z a :ole4 ,we c nev] obta9 a bird's-eye view ( ! sol> sy/em z a :ole because we c only see x f inside1 s t optical pro( t su* sy/ems c\ld exi/1 c\ld come only f ! discov]y ( o!r simil> sy/ems1 :i* we c\ld see f outside4 ,sir ,william ,h]s*el believ$ he _h confirm$ 8 own view ( ! /ructure ( ! galactic sy/em 9 ! same way1 by discov]+ simil> sy/ems1 ( :i* he c\ld obta9 a bird's-eye view because !y 7 entirely extrane\s to ! galaxy4 ,he spoke ( ^! objects z 8isl& univ]ses0 & believ$ !m to be cl\ds ( />s4 ,!y 7 ( hazy nebul> appe>ance1 & al?\gh x 0 impossible to di/+ui% ! sep>ate />s 9 !m1 he believ$ t suffici5t telescopic p[] w\ld make ?is possible1 j z x _h enabl$ ,galileo to see ! sep>ate />s 9 ! ,milky ,way4 ,^! objects1 :i* we %all describe almo/ imm$iately1 are g5]ally kn[n z 8extra-galactic nebulae8 f _! position1 al?\gh we %all frequ5tly f9d x conv5i5t to use ! brief] t]m 8great nebulae10 to :i* _! imm5se size fully entitles !m4 ,,nebulae ,a telescope exhibits a planet z a disc ( appreciable size1 & an eye-piece :i* magnifies #fj times w make ,jupit] look z l>ge z ! moon4 ,yet an eye-piece :i* magnifies #fj times1 or any great] numb] ( times1 c nev] make a /> look z l>ge z ! moon4 ,no magnification )9 our comm& causes any /> to appe> z any?+ o!r ?an a m]e po9t ( light4 ,! />s are ( c\rse enorm\sly l>g] ?an ,jupit]1 b !y are also enorm\sly m di/ant1 & x is ! di/ance t w9s4 ,illu/ration3 ,,plate ,,ii ,n4,g4,c4 #bjbb ,n4,g4,c4 #fgbj ,n4,g4,c4 #aeja ,n4,g4,c4 #gffb ,mt ,wilson ,obs]vatory ,planet>y ,nebulae ,illu/ration3 ,,plate ,,iii ,mt ,wilson ,obs]vatory ,! ,nebula 9 ,cygnus ,! telescope nev]!less %ews a numb] ( objects :i* appe> bigg] ?an m]e po9ts ( light4 ,!y are g5]ally ( a fa9t1 hazy appe>ance1 & s h receiv$ ! g5]al "n ( 8nebulae40 ,detail$ inve/igation has %ewn t ^! fall into ?ree di/9ct classes4 ,,planet>y ,,nebulae4 ,! fir/ class are g5]ally describ$ z 8,planet>y ,nebulae40 ,!re is no?+ ( a planet>y nature ab\t !m beyond ! fact t1 l ! planets1 !y %ew z f9ite discs 9 a telescope4 ,a few hundr$s only ( ^! objects are kn[n1 f\r typical examples be+ illu/rat$ 9 ,plate ,,ii4 ,!y all lie )9 ! galactic sy/em4 ,we %all discuss _! physical /ructure bel[ 7p4 #cba74 ,= ! mom5t1 x is en\gh to say t !y are probably ( ! nature ( />s :i* h 9 "s way become surr\nd$ by lum9\s atmosph]es ( enorm\s ext5t4 ,if s !y ( c\rse disprove our g5]al /atem5t t no /> ev] appe>s z any?+ b a po9t ( light 9 a telescope2 we mu/ make an exception 9 fav\r ( ! planet>y nebulae4 ,,galactic ,,nebulae4 ,! second class are g5]ally describ$ z 8,galactic ,nebulae10 examples be+ %ewn 9 ,plates ,,iii1 ,,vi 7p4 #cg7 & ,,vii 7p4 #dd74 ,^! are completely irregul> 9 %ape4 ,_! g5]al appe>ance is t ( huge gl[+ wisps ( gas /ret*+ f /> to />1 & 9 effect ?is is pretty mu* :at !y are4 ,l ! planet>y nebulae1 !y lie entirely )9 ! galactic sy/em4 ,ev5 a cursory glance %ews t ea* irregul> nebula conta9s sev]al />s enme%$ ) x2 m9ute telescopic exam9ation (t5 ext5ds ! dim5sions ( ! nebula almo/ indef9itely1 s t we may h almo/ ! :ole ( a con/ellation wrapp$ up 9 a s+le nebula4 ,!re is b little d\bt z to ! physical nature ( ^! nebulae4 ,! space betwe5 ! />s is n utt]ly void ( matt]1 b is occupi$ by a ?9 cl\d ( gas ( a t5uity :i* is g5]ally almo/ beyond description4 ,"h & !re ?is cl\d may be d5s] ?an usual2 "h & !re aga9 x may be light$ up & made to inc&esce by ! radiation ( ! />s )9 x4 ,9 o!r places x may be entirely opaque to light1 ly+ l a black curta9 across ! sky4 ,! v>iations ( d5sity1 opacity & lum9osity 9 comb9ation produce all ! fanta/ic %apes & v>i$ degrees ( light & %ade we see 9 ! galactic nebulae4 ,?is same opacity is responsible = ! d>k pat*es :i* occur 9 ! g5]al arrangem5t ( ! />s4 ,a conspicu\s example occurs 9 ! "p ( ! ,milky ,way %ewn 9 ,plate ,i 7p4 #bc74 ,! d>k pat*1 :i* looks at fir/ l a hole 9 ! sy/em ( />s1 is graphically describ$ z 8,! ,coal ,sack40 ,^! black pat*es 9 ! sky _c repres5t actual holes1 because x is inconceivable t !re %\ld be s _m empty tunnels ?r\gh ! />s all po9t+ exactly e>?w>d1 s t we are compell$ to int]pret !m z veils ( obscur+ matt] :i* dim or ext+ui% ! light ( ! />s beh9d !m4 ,,extra-,,galactic ,,nebulae4 ,! ?ird class ( nebula is ( an altoge!r diff]5t nature4 ,its memb]s are = ! mo/ "p ( def9ite & regul> %ape1 & %ew v>i\s o!r *>act]i/ics :i* make !m easy ( id5tification4 ,!y us$ to be call$ 8:ite nebulae0 f ! quality ( ! light !y emitt$4 ,lat] ,"l ,rosse's giant #f-;foot telescope reveal$ t _m ( !m _h a spiral /ructure2 ^! 7 call$ 8spiral nebulae40 ,! mo/ conspicu\s ( all ! spiral nebulae is ! ,great ,nebula ,m #ca 9 ,&rom$a1 %ewn 9 ,plate ,,iv1 :i* is j1 & only j1 visible to ! nak$ eye4 ,m>ius1 obs]v+ x telescopically 9 #afab1 describ$ x z look+ 8l a c&le-light se5 ?r\gh horn40 ,plate ,v %ews a second example1 probably ( v simil> /ructure1 :i* is view$ f ano!r angle1 s z to appe> almo/ exactly edge-on4 ,illu/ration3 ,,plate ,,iv ,y]kes ,obs]vatory ,! ,great ,nebula ,m #ca 9 ,&rom$a ,illu/ration3 ,,plate ,v ,mt ,wilson ,obs]vatory ,! ,nebula ,n4,g4,c4 #hia 9 ,&rom$a se5 edge-on ,x is n[ abundantly prov$ t nebulae ( ?is type all lie outside ! galactic sy/em1 s t ! t]m 8extra-galactic nebulae0 adequately describes !m4 ,_! size is colossal4 ,ei!r ( ! photographs %ewn 9 ,plates ,,iv & ,v w\ld h to be enl>g$ to ! size ( ! :ole ( ,europe be=e a body ( ! size ( ! e>? became visible 9 x1 ev5 "u a p[]ful microscope4 ,_! g5]al %ape is simil> to t :i* ,sir ,william ,h]s*el assign$ to ! galactic sy/em1 & x 0 ?is t orig9ally l$ him to reg>d !m z 8isl& univ]ses0 simil> to ! galactic sy/em4 ,we %all see lat] h[ f> 8 conjecture has be5 confirm$ by rec5t rese>*4 ,,! ,,di/ances ,,( ,,! ,,/>s ,! ye> #ahch provides our next l&m>k2 x is ! ye> 9 :i* ! di/ance ( a /> 0 fir/ measur$4 ,9 ! second c5tury aft] ,*ri/1 ,ptolemy _h argu$ t if ! e>? mov$ 9 space1 its position relative to ! surr\nd+ />s mu/ cont9ually *ange4 ,z ! e>? swung r\nd ! sun1 its inhabitants w\ld be 9 ! position ( a *ild 9 a sw+4 ,&1 j z ! sw++ *ild sees ! ne>] trees1 p]sons & h\ses oscillat+ rhy?mically aga9/ a remote backgr\nd ( di/ant hills & cl\ds1 s ! inhabitants ( ! e>? ought to see ! ne>] />s cont9ually *ang+ _! position aga9/ _! backgr\nd ( m di/ant />s4 ,yet night aft] night ! con/ellations rema9$ ! same1 or s ,ptolemy argu$2 ! same />s circl$ et]nally 9 ! same relative positions ar\nd ! pole1 & conspicu\s gr\ps ( />s su* z ! sev5 />s ( ! ,great ,be>1 ! ,pleiades or ! con/ellation ( ,orion %ew$ no signs ( *ange4 ,= aught ! unaid$ human eye c\ld tell1 ! />s might be spots ( lum9\s pa9t on a canvas backgr\nd1 ) ! e>? z ! unmov+ pivot ar\nd :i* ! :ole /ructure swung4 ,9 opposition to ?is1 ! ,cop]nican !ory ( c\rse requir$ t ! ne>] />s %\ld be se5 to move aga9/ ! backgr\nd ( ! m di/ant />s1 z ! e>? p]=m$ its ye>ly j\rney r\nd ! sun4 ,yet ye> aft] ye>1 & ev5 c5tury aft] c5tury1 pass$ )\t any su* motion be+ detect$4 ,! old ,ptolemaic cont5tion t ! e>? =m$ ! fix$ c5tre ( ! univ]se might almo/ h rega9$ its =m] position1 _h x n be5 t v>i\s l9es ( evid5ce _h begun to %ew t ev5 ! ne>e/ />s 7 necess>ily v di/ant1 s di/ant1 inde$1 t _! app>5t want ( motion ne$ cause no surprise4 ,! *ild 9 a sw+ _c expect to h optical evid5ce ( its motion if ! ne>e/ object x c see is tw5ty miles away4 ,v few />s appe> bright] ?an ,saturn at its brighte/2 x looks ab\t z bright z ,altair1 ! elev5? brighte/ /> 9 ! sky4 ,yet ,saturn %9es only by ! light x reflects f ! sun1 & its di/ance f ! sun is su* t x receives only ab\t "o "p 9 #bejj million ( ! total light emitt$ by ! sun4 ,&1 z ! surface ( ,saturn only reflects back ab\t two-fif?s ( ! light x receives1 x foll[s t ,saturn %9es ) only a #fjjj million? "p ( ! light ( ! sun4 ,if1 z ,kepl] & o!rs _h ma9ta9$1 ,altair 0 ess5tially simil> to ! sun1 x w\ld probably be ( ab\t ! same c&le-p[] z ! sun1 & s w\ld give out ab\t #fjjj million times z mu* light z ,saturn4 ,! fact t ,altair & ,saturn appe> ab\t equally bright 9 ! sky c only mean t ,altair is #hj1jjj times z di/ant z ,saturn#a4 ,?is argum5t is ess5tially id5tical ) "o :i* ,newton gave 9 8 ,sy/em ( ! ,_w to %ew t ev5 ! brighte/ />s1 su* z ,altair1 mu/ be v di/ant inde$4 #a ,= ! app>5t brightness ( an object falls (f z ! inv]se squ>e ( its di/ance1 & ! squ>e ( #hj1jjj is approximately equal to #fjjj million4 ,& su* has prov$ to be ! case4 ,all ef=ts to discov] ! app>5t sw++ motion ( ! />s--8p>allactic motion10 z x is te*nically call$--:i* results f ! e>?'s orbital motion fail$ until #ahch1 :5 ?ree a/ronom]s1 ,bessel1 ,h5d]son1 & ,/ruve1 almo/ simultane\sly detect$ ! p>allactic motions ( ! ?ree />s1 #fa ,cygni1 ,c5tauri & ,lyrae respectively4 ,! am\nt ( _! p>allactic motion made x possible to calculate ! di/ances ( ! />s1 s t ! inhabitants ( ! e>? 7 n only plac$ 9 possession ( def9ite ocul> pro( t !y 7 sw++ r\nd ! sun1 b f ! visible effects ( ?is sw+ !y 7 able to compute ! di/ances ( ! ne>] />s4 ,! calculat$ values 7 n accurate :5 judg$ by mod]n /&>ds1 b !y provid$ ! fir/ def9ite e/imates ( ! scale on :i* ! univ]se is built4 ,let u pause = a m9ute to consid] h[ ?is scale is built up4 ,! fir/ /ep is to select a conv5i5t base-l9e a few miles 9 l5g? on ! surface ( ! e>?1 & to measure ?is 9 t]ms ( /&>d y>ds or metres4 ,/>t+ out f ?is base-l9e1 a geodetic survey maps out a long n>r[ /rip ( ! e>?'s surface1 pref]ably runn+ due nor? & s\?4 ,! diff]5ce ( latitude at ! two ends is !n measur$ by a/ronomical me?ods1 z = in/ance by notic+ ! diff]5ce 9 ! altitude ( ! pole-/> at ! two places4 ,z ! l5g? ( ! /rip is already kn[n 9 miles1 ?is imm$iately gives ! dim5sions ( ! e>?4 ,accord+ to ,hay=d 7#aiji71 ! e>?'s equatorial radius is #fcghchh kilometres1 or #cifccd miles1 its pol> radius be+ #fcefiji kilometres or #cidiii miles4 ,! next /ep is to det]m9e ! size ( ! sol> sy/em 9 t]ms ( t ( ! e>?4 ,:5 ! sun is eclips$ by ! moon1 ! "t at :i* ! moon fir/ beg9s to cov] ! sun's disc is diff]5t = diff]5t /ations on ! e>?'s surface1 & ! obs]v$ diff]5ces ( "t enable u to measure ! moon's di/ance 9 t]ms ( kn[n di/ances on ! surface ( ! e>?4 ,9 ?is way ! mean di/ance ( ! moon is f\nd to be #chd1djc kilometres or #bch1heg miles4 ,9 ! same way ! transit ( ! planet ,v5us across ! disc ( ! sun provides an opportunity = det]m9+ ! scale ( ! sol> sy/em 9 t]ms ( ! dim5sions ( ! e>?4 ,! a/]oid ,eros provides /ill bett] opportunities4 ,! ,p>is ,conf]5ce 7#aiaa7 adopt$ #adi1dej1jjj kilometres1 or #ib1hgj1jjj miles1 z ! mo/ likely value = ! mean di/ance ( ! e>? f ! sun4 ,! next & f9al /ep1 :i* ! ye> #ahch saw accompli%$1 is t ( us+ ! diamet] ( ! e>?'s orbit z base-l9e1 & det]m9+ ! di/ances ( ! />s4 ,! fir/ /ep1 f ! /&>d y>d or metre to ! measur$ base-l9e on ! e>?'s surface1 involves an increase ( sev]al ?\s&-fold 9 l5g?4 ,! increase involv$ 9 ! next /ep1 f ! base-l9e to ! e>?'s diamet]1 is aga9 "o ( ?\s&s4 ,& aga9 ! next /ep1 f ! diamet] ( ! e>? to t ( ! e>?'s orbit1 involves an increase ( ?\s&s4 ,b ! la/ /ep ( all1 f ! e>?'s orbit to /ell> di/ances1 involves a million-fold increase4 ,rec5t measurem5ts %ew t ! ne>e/ />s are at almo/ exactly a million times ! di/ances ( ! ne>e/ planets4 ,at its ne>e/ approa* to ! e>?1 ,v5us is #bf million miles di/ant1 :ile ! ne>e/ />1 ,proxima ,c5tauri1 is #be1jjj1jjj million miles away2 ?is latt] /> is a fa9t companion ( ! well-kn[n bright /> ,c5tauri 9 ! s\!rn hemisph]e4 ,! di/ances ( ! planets :5 at _! ne>e/1 & ( ! ne>e/ />s1 are %ewn 9 ! foll[+ table3 ---------------------------------------- -------------------------- ,,planets ,,/>s ---------------------------------------- ----------------------- ,di/ance ,"n ,di/ance ,"n ,di/ance 7light- 7miles7 7miles7 ye>s7 ---------------------------------------- ----------------------- ,v5us #bf1jjj1jjj ,proxima ,c5tauri #be1jjj1jjj million #dbg ,c5tauri #dca ,m>s #ce1jjj1jjj ,muni* #aejdj #cf1jjj1jjj 0 #fjf ,wolf #cei #dg1jjj1jjj 0 #hjg ,m]cury#dg1jjj1jjj ,lal&e #baahe #di1jjj1jjj 0 #hcc ,sirius #ea1jjj1jjj 0 #hfe ---------------------------------------- ----------------------- ,z x is almo/ impossible to visualise a million1 ! m]e /atem5t t ! />s are a million times z remote z ! planets gives only a feeble indication ( ! imm5sity ( ! gap t divides ! sol> sy/em f its ne>e/ neighb\rs 9 space4 ,p]haps ! app>5t fixity ( ! />s gives a m vivid impression4 ,! e>? p]=ms its ye>ly j\rney r\nd ! sun at a spe$ ( ab\t #ah miles a second1 :i* is ab\t #abjj times ! spe$ ( an express tra94 ,! sun moves ?r\gh ! />s at ne>ly ! same rate--to be precise1 at ab\t #hjj times ! spe$ ( an express tra94 ,&1 broadly speak+1 ! ne>] planets & ! majority ( ! />s move ) simil> spe$s4 ,we %all n obta9 a bad approximation to ! tru? if we imag9e t all a/ronomical bodies move ) exactly equal spe$s1 let u say1 to fix our ?\ghts1 a spe$ equal to #ajjj times ! spe$ ( an express tra94 ,! di/ances ( a/ronomical objects are n[ betray$ by ! spe$ ) :i* !y appe> to move across ! sky--! sl[] _! app>5t motion ! great] _! di/ances1 & vice v]sa4 ,n[ ! planets move across ! sky s rapidly t x is q easy to detect _! motion f night to night & ev5 f h\r to h\r2 ! />s move s sl[ly t1 except ) telescopic aid1 no motion c be detect$ f g5]ation to g5]ation1 or ev5 f age to age4 ,ev5 ! conspicu\s con/ellations 9 ! sky1 :i* on ! :ole are =m$ ( ! ne>] />s1 h reta9$ _! pres5t appe>ance ?r\gh\t ! :ole ( hi/oric times4 ,! contra/ betwe5 ! planets :i* *ange _! positions e h\r1 & ! />s :i* fail to %ew any appreciable *ange 9 a c5tury1 gives a vivid impression ( ! ext5t to :i* ! />s are m di/ant ?an ! planets4 ,x is f> m difficult to visualise ! actual di/ances ( ! />s4 ,! /atem5t t ev5 ! ne>e/ ( !m is #be1jjj1jjj million miles away h>dly conveys a def9ite picture to ! m9d1 b we may f>e bett] ) ! alt]native /atem5t t ! di/ance is #dbg light-ye>s--t is to say ! di/ance t light1 travell+ at #ahf1jjj miles a second1 takes 9 #dbg ye>s to trav]se4 ,illu/ration3 ,,plate ,,vi ,mt ,wilson ,obs]vatory ,! 8,horse's ,head0 9 ! ,great ,nebula 9 ,orion ,light travels ) ! same spe$ z wireless signals because bo? are waves ( electric di/urbance4 ,incid5tally ?is spe$ is j ab\t a million times t ( s\nd4 ,! enorm\s disp>ity 9 ! spe$s ( s\nd & ( electric waves is vividly br\ght out 9 ! ord9>y process ( broadca/+4 ,:5 a speak] broadca/s f ,london 8 voice takes long] to travel #c feet f 8 m\? to ! microphone z a s\nd wave1 ?an x does to travel a fur!r #efj miles to ,b]l9 or ,milan z an electric wave4 ,wireless li/5]s 9 ,au/ralia he> ! music ( a broadca/ conc]t soon] ?an an ord9>y li/5] at ! back ( ! conc]t hall :o relies on s\nd alone2 !y he> x a fifte5? ( a second aft] x is play$4 ,yet light1 or wireless waves travell+ ) ! same spe$ z light1 takes #dbg ye>s to rea* ! ne>e/ />1 s t ! inhabitants ( ,proxima ,c5tauri w\ld be ov] f\r & a qu>t] ye>s late 9 he>+ a t]re/rial conc]t4 ,& 9 "t we %all h to consid] o!r & ev5 m di/ant />s :i* t]re/rial music w\ld n yet h rea*$ _h x />t$ on its j\rney be=e ! ,norman ,conque/1 be=e ! ,pyramids 7 built1 ev5 be=e man appe>$ on e>?4 ,,! ,,photographic ,,epo* ,if we 7 only all[$ to select "o m l&m>k 9 ! progress ( a/ronomy1 we might well *oose ! application ( photography to a/ronomy 9 ! clos+ ye>s ( ! n9ete5?-c5tury2 ?is op5$ ! floodgates ( progress m ?or\ghly ?an any?+ else _h done s9ce ! inv5tion ( ! telescope4 ,hi!rto ! telescope1 aft] collect+ & b5d+ rays ( light f ! sky1 _h project$ ! conc5trat$ beam ( light ?r\gh ! pupil ( ! human eye on to ! ret9a2 9 future x 0 to project x on to ! incomp>ably m s5sitive photographic plate4 ,! eye c reta9 an impression only = a fraction ( a second2 ! photographic plate adds up all ! impressions x receives = h\rs or ev5 days1 & records !m practically = ev]4 ,! eye c only measure di/ances betwe5 a/ronomical objects by ! help ( an intricate ma*9]y ( cross-wires1 screws & v]ni]s2 ! photographic plate records di/ances automatically4 ,! eye1 betray$ by preconceiv$ ideas1 impati5ce or hope1 c & does make e conceivable type ( error2 ! cam]a _c lie4 ,& s x comes ab\t t if we try to pick out l&m>ks 9 tw5tie?-c5tury a/ronomy we f9d t1 9 a s5se1 x consi/s ( no?+ b l&m>ks2 ! sl[1 ardu\s me?ods ( conque/ ( ! n9ete5? c5tury h giv5 place to a sort ( gold-ru% 9 :i* claims are /ak$ out1 ! surface scrat*$1 ! m conspicu\s nuggets collect$1 & ! excavation ab&on$ = some?+ m promis+1 all ) su* rapidity t any attempt to describe ! position is out ( date almo/ be=e x c be pr9t$4 ,we c only attempt a g5]al impression ( ! new t]ritory1 & ) ?is w be inextricably mix$ a discussion ( old t]ritory se5 9 ! light ( new k4 ,,gr\ps ,,( ,,/>s ,,& ,,b9>y ,,sy/ems ,a glance at ! sky1 or1 bett]1 at a photograph ( a fragm5t ( ! sky1 sugge/s t1 9 ! ma91 ! />s are scatt]$ at r&om ov] ! sky1 except = ! conc5tration ( fa9t />s 9 & t[>ds ! ,milky ,way1 :i* we h already consid]$4 ,any small bit ( ! sky does n look v diff]5t f :at x w\ld if bright & fa9t />s _h be5 spr9kl$ haphaz>d out ( a cele/ial pepp]pot4 ,yet ?is is n q ! :ole /ory4 ,"h & !re gr\ps ( conspicu\s />s are to be se51 :i* c h>dly h come toge!r purely by accid5t4 ,orion's belt1 ! ,pleiades1 ,b]5ice's hair1 ev5 ! ,great ,be> itself1 d n look l accid5ts1 & 9 po9t ( fact are n4 ,x is ! exi/5ce ( ^! natural gr\ps ( />s t lies at ! root (1 & ju/ifies1 ! division ( ! />s into con/ellations4 ,we %all expla9 lat] h[ ! physical prop]ties ( ! />s are /udi$2 = ! pres5t x is en\gh to rem>k t physical /udy confirms ! suspicion t gr\ps su* z ^? j m5tion$ are1 g5]ally speak+1 true families1 & n m]e accid5tal conc\rses1 ( />s4 ,! />s ( any "o gr\p1 su* z ! ,pleiades1 n only %ew ! same physical prop]ties1 b also h id5tical motions ?r\gh space1 ?us j\rney+ p]petually ?r\gh ! sky 9 "o ano!r's society4 ,z su* a gr\p ( />s are bo? physically simil>1 & travel 9 company1 !y might appropriately be describ$ z a family ( />s4 ,! a/ronom]1 h[ev]1 pref]s to call !m a 8mov+ clu/]40 ,^! families are ( almo/ all sizes1 ! smalle/ & commone/ type consi/+ ( only two memb]s4 ,aft] ?is ! next commone/ type consi/s ( ?ree memb]s2 our ne>e/ ?ree neighb\rs 9 space1 ,proxima ,c5tauri & ! two />s ( ,c5tauri1 =m su* a triple sy/em4 ,!n come sy/ems ( f\r1 five & six memb]s1 & s on indef9itely4 ,let u fir/ turn our att5tion to families consi/+ ( only two memb]s--8b9>y sy/ems10 z !y are g5]ally call$4 ,ev5 if ! />s _h be5 spr9kl$ on to ! sky at r&om out ( a pepp]pot1 ! laws ( *ance w\ld require t 9 a c]ta9 numb] ( cases1 pairs ( />s %\ld appe> v close toge!r4 ,& a /udy ( a photograph ( any />-field %ews t a l>ge numb] ( su* close pairs actually exi/4 ,! numb] is1 h[ev]1 great] ?an c be expla9$ by ! laws ( *ance alone4 ,"s pairs ( />s may be close toge!r by accid5t1 b a physical cause is ne$$ to acc\nt = ! rema9d]4 ,we c unravel ! my/]y by photograph+ ! field at int]vals ( a few ye>s & comp>+ ! v>i\s results obta9$4 ,"s ( ! />s :i* orig9ally appe>$ z close pairs w be f\nd to move /eadily ap>t4 ,^! are ! pairs ( />s :i*1 al?\gh !y appe>$ close toge!r 9 ! sky1 7 n s 9 space2 "o /> m]ely happ5$ to be almo/ exactly 9 l9e ) ! o!r z se5 f ! e>?4 ,o!r pairs d n break up ) ! passage ( "t2 ! two compon5ts *ange _! relative positions b nev] become completely sep>at$4 ,9 ! simple/ case ( all "o /> may be f\nd to describe an approximately circul> orbit ab\t ! o!r1 j z ! e>? does r\nd ! sun1 & ! moon r\nd ! e>?1 & = precisely ! same reason3 gravitation keeps !m toge!r4 ,,! ,,law ,,( ,,gravitation4 ,drop a cricket ball f y\r h& & x falls to ! gr\nd4 ,we say t ! cause ( its fall is ! gravitational pull ( ! e>?4 ,9 ! same way1 a cricket ball ?r[n into ! air does n move on = ev] 9 ! direction 9 :i* x is ?r[n2 if x did x w\ld leave ! e>? = good1 & voyage (f into space4 ,x is sav$ f ?is fate by ! e>?'s gravitational pull :i* drags x gradually d[n1 s t x falls back to e>?4 ,! fa/] we ?r[ x1 ! fur!r x travels be=e ?is occurs2 a simil> ball project$ f a gun w\ld travel = _m miles be=e be+ pull$ back to e>?4 ,illu/ration3 ,fig4 #b4 ,! law gov]n+ all ^! ph5om5a is q simple4 ,x is t ! e>?'s gravitational pull causes all bodies to fall #af feet e>?w>d 9 a second4 ,?is is true ( all bodies :i* are free to fall1 no matt] h[ !y are mov+2 e body :i* is n 9 "s way held up aga9/ gravitation is #af feet l[] at ! end ( any second ?an x w\ld h be5 if gravitation _h n act$ ?r\gh t second4 ,to illu/rate :at ?is means1 let ! big circul> curve ,b,a,c 9 fig4 #b repres5t ! e>?'s surface1 & imag9e t a %ot is fir$ horizontally f ,a1 ! top ( an elevation ,,aa4 ,if ! %ot 7 n pull$ e>?w>ds by gravitation1 x w\ld travel indef9itely along ! l9e ,,ab out into space4 ,if ,,ab is ! di/ance x w\ld travel 9 a second "u ^! imag9>y conditions1 ! end ( a second's actual flight does n f9d x at ,b1 b at a po9t #af feet ne>] ! e>?1 gravitation hav+ pull$ x d[n ?is #af feet dur+ its flight4 ,= in/ance1 if ,,bb 9 fig4 #b %\ld happ5 to be #af feet1 ! %ot w\ld /rike ! e>? at ,b aft] a flight ( precisely "o second4 ,z ano!r example1 let u suppose t ! #af-;foot fall bel[ ,b does n drag ! %ot d[n to e>? b only to a po9t b1 :i* is at precisely ! same height above ! e>?'s surface z ! po9t ,a at :i* ! %ot />t$4 ,if gravitation 7 n act+1 s t ! %ot travell$ along ! l9e ,,ab1 its height above ! e>? w\ld cont9ually increase4 ,actually 9 ! case we are n[ consid]+1 gravitation pulls ! %ot d[n at j su* a rate z to neutralise ! increase ( height :i* w\ld o!rwise occur1 s t ! height ( ! %ot nei!r increases nor decreases2 x nei!r flies (f into space nor drops to e>?1 b cont9ues to describe circles r\nd ! e>? indef9itely4 ,a simple geometrical calculation %ews t = ! di/ance ,bb to be #af feet1 ! di/ance ,,ab travell$ 9 "o second mu/ be #be1hhj feet or #dij miles#b4 ,?us if we c\ld fire a %ot horizontally ) a spe$ ( #dij miles a second1 x w\ld describe endless circles r\nd ! e>?1 ! e>?'s gravitational pull exactly neutralis+ ! natural t5d5cy ( ! %ot to fly away along ! /raight l9e ,,ab4 #b ,let ,c be ! c5tre ( ! e>?1 & b,c,d ! diamet] ?r\gh b4 ,!n ,,ba ,bb ,,bd1 :]e ,bb #af feet1 & ,,bd1 :i* is #af feet m ?an ! e>?'s diamet] #da1ijj1jjj feet4 ,f ?is we readily calculate t ,,ba #be1hhj feet4 ,?is calculation ( c\rse neglects ! height ( ! hill ,,aa by comp>ison ) ! e>?'s diamet]4 ,9 #affe ,newton began to suspect t ?is same gravitational pull might be ! cause ( ! moon describ+ a circul> orbit ar\nd ! e>? in/ead ( runn+ away at a tang5t into space4 ,! moon's di/ance f ! e>?'s c5tre is #bch1heg miles1 or #fjbg times ! radius ( ! e>?4 ,z ! moon describes a circle ( ?is size e mon? 7#bg days1 #d h\rs1 #dc m9utes1 #aae seconds71 we c calculate t its spe$ 9 its orbit is #bbhg miles an h\r4 ,aft] "o second x w h travell$ #ccej feet1 & if x kept to a /rictly rectil9e> c\rse ?is w\ld c>ry x #jjjdd feet fur!r away f ! e>?4 ,?us1 to keep 9 an exact circul> orbit ar\nd ! e>?1 x mu/ fall #jjjdd feet 9 a second4 ,?is is f> less ?an a body falls 9 a second at ! e>?'s surface1 b ,newton conjectur$ t ! =ce ( gravity mu/ weak5 z we rec$e f ! e>?'s surface4 ,actually a body at ! e>?'s surface falls #cfcb times z fa/ z ! moon's e>?w>d fall 9 its orbit4 ,n[ #cfcb is ! squ>e ( #fjbg 7or #cfcb #fjbg #fjbg71 :5ce ,newton saw t ! moon's fall w\ld be ( exactly ! "r am\nt if ! =ce ( gravity fell (f z ! inv]se squ>e ( ! di/ance--t is to say1 if x decreas$ j z rapidly z ! squ>e ( ! di/ance increas$4 ,z we %all see lat]1 a/ronomical obs]vation confirms ! tru? ( ?is law 9 innum]able ways4 ,?is l$ ,newton to put =w>d 8 fam\s law ( gravitation accord+ to :i* ! gravitational pull ( any body1 su* z ! e>?1 falls (f inv]sely z ! squ>e ( ! di/ance f ! body4 ,illu/ration3 ,fig4 #c4 ,pr(essor ,c4 ,v4 ,boys & o!rs h measur$ ! gravitational pull :i* a few tons ( lead ex]t 9 ! laboratory1 &1 ) ?is k1 x is easy to calculate h[ _m tons ! e>? mu/ conta9 s z to ex]t its obs]v$ gravitational pull on bodies outside x4 ,x is f\nd t ! e>?'s weight mu/ be j "u six ?\s& million million million tons#c1 or1 z we %all write x1 #f #aj tons#d4 #c ,"h1 z ?r\gh\t ! book1 we use ! ,fr5* or metric ton ( a million grammes or #bbjde lbs4 ,! ,engli% ton ( #bbdj lbs4 is equal to #ajafj ,fr5* tons4 #d ,! notation #f #aj /&s = ! numb] =m$ by a #f foll[$ by #ba z]os1 ?is %or?& notation be+ ess5tial1 9 ! int]e/s ( brevity1 9 discuss+ a/ronomical numb]s4 ,a million is #aj1 a million million is #aj & s on4 ,a simil> notation is ne$$ to express v small numb]s4 ,! expression #aj is writt5 = #a_/aj & s on4 ,?us #f #aj /&s = #f_/a1jjj1jjj or #jjjjjjf4 ,illu/ration3 ,,plate ,,vii ,mt ,wilson ,obs]vatory ,! ,trifid ,nebula ,m #bj 9 ,sagitt>ius ,j z ! e>?'s gravitational pull keeps ! moon p]petually describ+ circles ar\nd x1 s ! sun's gravitational pull keeps ! e>? & all ! o!r planets describ+ circles ar\nd ! sun4 ,kn[+ ! di/ance ( any planet f ! sun1 & also its spe$ 9 its orbit1 we c calculate ! di/ance ?is planet falls t[>ds ! sun 9 a second4 ,?is tells u ! am\nt ( ! sun's gravitational pull1 & f ?is we c calculate t ! sun's weight mu/ be ab\t #ccb1jjj times ! weight ( ! e>?1 or almo/ exactly #b #aj tons4 ,:i*ev] ( ! planets we use1 we obta9 exactly ! same weight = ! sun4 ,?is n only gives u confid5ce 9 our result1 b incid5tally x also provides /rik+ confirmation ( ! tru? ( ,newton's law ( gravitation1 = if ?is law 7 inexact or untrue1 ! diff]5t planets w\ld n all tell exactly ! same /ory z to ! sun's weight4 ,e9/e9 has rec5tly %ewn t ! law is n absolutely exact1 b ! am\nt ( inexactness is inappreciable except = ! ne>e/ planet1 ,m]cury1 & ev5 "h x is s exce$+ly small t we ne$ n tr\ble ab\t x = our pres5t purpose4 ,j z we c weigh ! sun & e>? by /udy+ ! motion ( a body gripp$ by _! gravitational pull--or 89 _! gravitational fields10 z ! ma!matician w\ld say--s we c weigh any o!r body :i* keeps a second small body mov+ r\nd x by its gravitational attraction4 ,! motions ( ,jupit]'s satellites make x possible to weigh ,jupit]2 its weight is f\nd to be ab\t #aib #aj tons1 :i* is #cag times t ( ! e>?1 al?\gh only _/ ( t ( ! sun4 ,simil>ly ! weight ( ,saturn is f\nd to be #ega #aj tons or ab\t #idi times t ( ! e>?4 ,,weigh+ ,,! ,,/>s4 ,& n[ we come to a /rik+ application ( ! pr9ciples j expla9$--:5 we obs]ve two />s 9 ! sky describ+ orbits ab\t "o ano!r1 we c weigh ! />s f a /udy ( _! orbits4 ,g5]ally ! problem is n q s simple z ^? we h j discuss$4 ,= its adequate treatm5t1 we mu/ once aga9 levy toll on ! ma!matical "w ( ,newton4 ,we h se5 t a projectile fir$ horizontally ) a spe$ ( #dij miles a second1 w\ld describe endless circles r\nd ! e>?4 ,:at w\ld happ5 if x 7 fir$ 9 "s o!r direction & ) "s o!r spe$8 ,! answ] 0 provid$ by ,newton4 ,he %ew$ t :5 a small body is all[$ to move freely "u ! gravitational pull ( a big body1 x w run away altoge!r if its spe$ exce$s a c]ta9 critical am\nt1 9 :i* case its orbit is ! curve call$ a hyp]bola4 ,b if its spe$ is less ?an ?is critical am\nt1 its orbit w always be an ellipse--a sort ( pull$ out circle or oval curve#e 7fig4 #d1 p4 #dg74 ,previ\s to ?is ,kepl] _h f\nd t ! actual pa?s ( ! planets r\nd ! sun 7 n exact circles b ellipses1 al?\gh = ! mo/ "p ellipses :i* did n diff] greatly f circles2 !y are :at ! ma!matician calls 8ellipses ( small ecc5tricity40 ,?is provides /ill fur!r confirmation ( ,newton's law ( gravitation1 = x c be prov$ t if ! =ce ( gravitation falls (f 9 any way o!r ?an accord+ to ,newton's law ( ! inv]se squ>e ( ! di/ance1 ! orbits ( ! planets w n be elliptical4 #e ,! simple/ def9ition ( an ellipse is t x is ! curve drawn by a mov+ po9t ,p :i* moves 9 su* a way t ! sum ( its di/ances ,,ps1 ,,pt f two fix$ po9ts ,s1 ,t rema9s always ! same4 ,9 practice we c mo/ easily draw an ellipse by slipp+ an endless /r+ ,,spts r\nd two draw+ p9s ,s1 ,t /uck into a draw+ bo>d4 ,/ret* ! /r+ tight ) a p5cil at ,p1 & on lett+ ! p5cil move r\nd1 keep+ ! /r+ always tight1 we %all draw an ellipse4 ,if ! p9s ,s1 ,t 9 ! draw+ bo>d are plac$ ne> to "o ano!r ! curve describ$ by ! p5cil ,p is ne>ly circul>4 ,! ratio ( ! di/ance ,,/ to ! l5g? ( ! rema9d] ( ! /r+ ,,sp ,,pt is call$ ! 8ecc5tricity0 ( ! ellipse2 x is necess>ily less ?an unity1 because two sides ( a triangle are toge!r great] ?an ! ?ird side4 ,9 ! limit+ case 9 :i* ! ecc5tricity is made z]o1 ! ellipse becomes a circle4 ,if ! ecc5tricity is ne>ly z l>ge z unity1 ! ellipse is v elongat$4 ,all ! diff]5t %apes ( ellipses are obta9$ by lett+ ! ecc5tricity *ange f #j to #a1 & ^! repres5t all ! diff]5t %apes ( orbit t a small body c describe ar\nd a heavy gravitat+ mass4 ,! po9ts ,s1 ,t are call$ ! foci ( ! ellipse1 & ! big attract+ body always occupies "o or o!r ( ! two foci ( ! ellipse4 ,illu/ration3 ,fig4 #d4 ,! oval curve is an ellipse2 ! po9ts ,s1 ,t are its 8foci40 ,:5 ! a/ronom] /udies ! motions ( a b9>y /> 9 ! sky1 he g5]ally f9ds t ! two compon5ts d n move 9 circles ab\t "o ano!r b 9 ellipses#f4 ,once aga91 ,newton's law is confirm$1 & we are entitl$ to assume t ! =ces :i* keep b9>y />s toge!r are ! same gravitational =ces z keep ! moon f runn+ away f ! e>?1 or ! planets f ! sun4 ,by a /udy ( ^! ellipses x becomes possible to weigh ! />s4 ,if "o ( ! compon5t masses 7 enorm\sly heavi] ?an ! o!r1 ! =m] w\ld /& /ill :ile ! light] compon5t describ$ an ellipse ar\nd x1 ! motion be+ ess5tially simil> to t ( a planet ar\nd ! sun4 ,su* cases are n obs]v$ 9 actual b9>y />s because ! two compon5ts are g5]ally comp>able 9 weight1 & ?is br+s new complications into ! "q4 ,!re is no ne$ to ent] into ma!matical details "h4 ,suffice x to say t nei!r /> /&s /ill2 ! two compon5ts describe ellipses ( diff]5t sizes1 & f a /udy ( ^! two ellipses ! weights ( bo? ! compon5ts c be det]m9$4 #f ,:at he actually obs]ves is ! 8projection0 ( ! orbit on ! sky1 b x is a well-kn[n !orem ( geometry t ! projection ( an ellipse is always an ellipse4 ,! foll[+ table %ews ! result ( weigh+ ! f\r b9>y sy/ems ne>e/ ! sun 9 ?is way1 ! sun's weight be+ tak5 z unity3 ,/ell> ,weights ,b9>y sy/ems ne> ! sun4 ---------------------------------------- ----------------------- ,di/ance 9 ,weights ( compon5ts ,/> light-ye>s 9 t]ms ( sun's ,lum9osity f ! sun weight 7see p4 #di7 ---------------------------------------- ----------------------- ,c5tauri ,a #dca #aad #aab 0 ,b #jig #jcb ---------------------------------------- ----------------------- ,sirius ,a #hfe #bde #bfc 0 ,b #jhe #jjjbf ---------------------------------------- ----------------------- ,procyon ,a #aje #abd #ee 0 ,b #jci #jjjjjc ---------------------------------------- ----------------------- ,krug] #fj ,a #abg #jbe #jjjbf 0 ,b #jbj #jjjjg ---------------------------------------- ----------------------- ,we see t ! weights ( ^! />s d n diff] greatly f t ( ! sun1 al?\gh naturally ! :ole ( space provides a great] range ?an ! f\r />s ( our table :i* happ5 to be ne> ! sun4 ,b ev5 9 ! :ole ( space1 no /> ^: weight is kn[n ) any accuracy has a weight less ?an ,krug] #fj ,b1 al?\gh at ! o!r end ( ! scale !re are _m />s ) f> great] weights ?an any 9 our table4 ,( />s ^: weights are kn[n ) fair accuracy1 ! /> ,h4,d4 #accg 7,pe>ce's />7 is ! weightie/1 its two compon5ts be+ respectively #cfc & #cch times z heavy z ! sun4 ,plaskett's /> ,b4,d4 #f #acji is c]ta9ly heavi] /ill1 its compon5ts weigh+ at lea/ #ge & #fc times z mu* z ! sun1 & probably m2 ! exact weights are n kn[n 7see p4 #ee bel[74 ,! sy/em #bg ,canis ,majoris consi/s ( f\r />s1 ^: comb9$ weight1 accord+ to ! evid5ce at pres5t available1 appe>s to be at lea/ #idj times t ( ! sun1 b we may prop]ly ex]cise a c]ta9 am\nt ( caution be=e accept+ a figure s f> outside ! usual run ( /ell> weights4 ,! av]age con/itu5t /> 9 ! above v %ort table has #jid times ! weight ( ! sun1 s t our sun appe>s to be ( r m ?an av]age weight1 & ?is is confirm$ by a m ext5sive /udy ( /ell> weights4 ,we might h expect$ a priori t ! />s w\ld prove to h all sorts ( weights1 = !re is no obvi\s reason :y />s %\ld n exi/ ) weights millions ( times t ( ! sun1 or aga9 ) weights only equal to t ( ! e>? or less4 ,actually we f9d t ! weights ( ! />s are mo/ly fairly equal1 v few />s hav+ weights greatly dissimil> f t ( ! sun4 ,?is seems to indicate t a /> is a def9ite species ( a/ronomical product1 n a m]e r&om *unk ( lum9\s matt]4 ,,lum9osity4 ,! la/ column ( ! table on p4 #dh gives ! 8lum9osities0 ( ! />s1 :i* means _! c&le-p[] z lights1 t ( ! sun be+ tak5 z unity4 ,= in/ance ! entry ( #bfc = ,sirius means t ,sirius1 reg>d$ z a ligh?\se 9 space1 has #bfc times ! c&le-p[] ( ! sun4 ,! lum9osities ( ! />s %ew an enorm\sly great] range ?an _! weights4 ,9 a g5]al way ! heavie/ />s are f\nd to be ! mo/ lum9\s1 z we %\ld naturally expect1 b _! lum9osity is out ( all proportion to _! weight4 ,! heavi] compon5t ( ,sirius has only #bi times ! weight ( ! light] compon5t1 b #aj1jjj times its lum9osity4 ,aga91 9 ! sy/em ( ,procyon ! heavi] compon5t has #cb times ! weight1 b #ahj1jjj times ! lum9osity1 ( ! light] compon5t4 ,x appe>s to be an almo/ univ]sal law t ! c&le-p[] p] ton is f> great] 9 heavy />s ?an 9 light4 ,?is is "o ( ! c5tral &1 at fir/ sight1 "o ( ! mo/ p]plex+ facts ( physical a/ronomy3 x is s fundam5tal & s p]vad+ t no view ( /ell> me*anism c be accept$ :i* fails to expla9 x4 ,,spectroscopic ,,velocities4 ,:5 a />'s di/ance is kn[n1 its motion across ! sky tells u its spe$ 9 a direction at "r angles to ! l9e along :i* we look at x--i4e4 across ! l9e ( sight--b provides no means ( discov]+ its spe$ along ?is l9e4 ,we _c see ! motion ( a body :i* is com+ /raight t[>ds u1 & a /> mov+ at a million miles a second 9 a direction exactly along ! l9e ( sight w\ld yet appe> to be /&+ /ill 9 ! sky4 ,to evaluate velocities along ! l9e ( sight1 ! a/ronom] calls 9 ! aid ( ! spectroscope4 ,all light is a bl5d ( lights ( diff]5t col\rs1 & j z ,newton1 ) 8 fam\s prism1 analys$ sunlight into all ! col\rs ( ! ra9b[1 s ! spectroscope analyses ! light f a />1 or inde$ f any s\rce :atev]1 into its v>i\s con/itu5t col\rs4 ,! in/rum5t spreads out ! analys$ light into a /rip ( light ( cont9u\sly graduat$ col\r1 :i* is describ$ z a 8spectrum40 ,9 ?is ! col\rs are ! same1 & are f\nd to be arrang$ 9 ! same ord]1 z 9 ! ra9b[1 runn+ f violet ?r\gh gre5 & orange to r$4 ,!re is a physical reason = ?is4 ,we %all see lat] 7p4 #aad7 t light consi/s ( tra9s ( waves--l ! ripples :i* ! w9d bl[s up on a pond--& t ! diff]5t col\rs ( light result f waves ( diff]5t l5g?s1 r$ light be+ produc$ by ! longe/ waves1 & violet light by ! %orte/4 ,! col\rs 9 ! spectrum occur 9 ! ord] ( _! wave-l5g?s1 f ! longe/ 7r$7 to ! %orte/ 7violet74 ,9 ! typical /ell> spectrum c]ta9 %ort ranges ( col\r or wave-l5g? are g5]ally miss+1 = reasons we %all discuss lat] 7p4 #abf71 s t ! spectrum appe>s to be cross$ by a numb] ( d>k l9es or b&s1 ?us =m+ a patt]n r ?an a cont9u\s gradation ( col\rs4 ,examples ( /ell> spectra are %ewn 9 ,plate ,,viii4 ,illu/ration3 ,,plate ,,viii ,b #j ,orionis ,a #j ,sirius ,f #j ,gem9orum ,g #j ,capella ,k #j ,arcturus ,m #j ,betelgeux ,/ell> ,spectra 7,! spectral types are indicat$ on ! left7 ,x is frequ5tly conv5i5t to classify />s by ! type ( spectra !y emit4 ,x is n[ kn[n t a />'s spectrum dep5ds prim>ily ^u ! temp]ature ( its surface4 ,z a consequ5ce1 /ell> spectra c1 9 ! ma91 be arrang$ 9 a s+le cont9u\s sequ5ce1 & _! usual classification is by a sequ5ce ( lett]s1 ,o1 ,b1 ,a1 ,f1 ,g1 ,k1 ,m ) decimal subdivisions1 ! temp]ature fall+ z we pass along ! sequ5ce1 s t ,o-type />s h ! highe/ surface-temp]atures & ,m-type />s ! l[e/4 ,spectral types are indicat$ on ! left 9 ,plate ,,viii4 ,:5 ! light receiv$ f a /> is analys$ 9 a spectroscope1 ! patt]n ( l9es or b&s may be f\nd to be %ift$ bodily 9 "o direction or ! o!r4 ,if ! %ift is t[>ds ! r$ end ( ! spectrum1 ! light emitt$ by ! /> is rea*+ u 9 a r$d] /ate ?an t 9 :i* x ought normally to be1 & z r$ light has ! longe/ wave-l5g?1 ?is means t e wave ( light is long]--m drawn out--?an normal4 ,we conclude t ! /> is rec$+ f u4 ,9 ! same way1 if ! spectral patt]n is %ift$ t[>d ! violet end ( ! spectrum1 we "k t ! /> mu/ be approa*+ u4 ,! %ift ( a spectrum result+ f ! motion ( ! body :i* emits x is g5]ally describ$ z ! 8,doppl] ,effect40 ,f its am\nt we c calculate a />'s actual spe$ along ! l9e ( sight1 & ! calculation is surpris+ly simple4 ,if ea* l9e or b& 9 a spectrum is f\nd to repres5t a wave-l5g? a hundr$? ( "o p] c5t4 long] ?an t usually associat$ ) x1 !n ! />'s spe$ ( recession is a hundr$? ( "o p] c5t4 ( ! velocity ( light1 or #ahf miles a second--& simil>ly = all o!r displacem5ts4 ,,spectroscopic ,,b9>ies4 ,z ! two compon5ts ( a b9>y sy/em are g5]ally mov+ ) diff]5t spe$s1 ! normal spectrum ( a b9>y sy/em consi/s ( two di/9ct sup]pos$ spectra1 ! two spectra %ew+ diff]5t %ifts :i* correspond to ! spe$s ( ! two compon5ts4 ,f ! obs]v$ orbits ( ! two compon5ts ( a b9>y sy/em1 an a/ronom] might proce$ to calculate ) :at spe$s ^! compon5ts w\ld move 9 ! direction ( ! l9e ( sight1 & c\ld !n pr$ict to :at ext5t ! two spectra ought to be displac$ if ! light f ! sy/em 7 analys$ 9 a spectroscope2 ! spectroscope w\ld ( c\rse confirm 8 pr$iction4 ,x is m in/ructive to imag9e ! rev]se process4 ,suppose t on analys+ ! light f a />1 ! a/ronom] obta9s a composite spectrum 9 :i* two di/9ct spectra %ift rhy?mically backw>ds & =w>ds ab\t _! normal position4 ,! fact t !re are two spectra tells him t he is deal+ ) a b9>y sy/em2 if ! rhy?mic %ift repeats itself e two ye>s1 he kn[s t its orbit takes two ye>s to complete4 ,he /udies ! /> by direct vision & f9ds x is a b9>y sy/em 9 :i* ! con/itu5ts revolve ab\t "o ano!r e two ye>s4 ,he exam9es ano!r spectrum1 & f9ds t x %ifts rhy?mically e two days4 ,on look+ directly at ?is /> he c only see a s+le po9t ( light4 ,!re mu/1 ( c\rse1 be two />s1 b ! m]e fact t !y get ar\nd "o ano!r 9 s %ort a "t z two days proves t !y mu/ be v close to "o ano!r1 & he ne$ feel no surprise t 8 telescope has fail$ to sep>ate ! image into two di/9ct po9ts ( light4 ,sy/ems ( ?is k9d1 :i* ! spectroscope %ews to be b9>y1 b ! telescope usually %ews z a s+le po9t ( light1 are call$ 8spectroscopic b9>ies40 ,ov] a ?\s& su* sy/ems are kn[n4 ,if ! a/ronom] tries to con/ruct ! orbit ( su* a sy/em f ! spectroscopic obs]vations alone1 he f9ds himself 9 difficulties4 ,8 obs]vations only tell him ! velocities along ! l9e ( sight1 & ^! dep5d bo? on ! actual spe$ & on ! degree ( =e%ort5+2 ! same velocity may arise ei!r f a big orbit 9 a plane ne>ly at "r angles to ! l9e ( sight1 or f a mu* =e%ort5$ little orbit4 ,x is impossible to calculate ! actual orbit or ! weights ( ! />s f spectroscopic obs]vation alone4 ,illu/ration3 ,fig4 #e4 ,! little orbit ,,aa & ! big orbit ,,bb give ! same velocities along ! l9e ( sight ,,ce4 ,,eclips+ ,,b9>ies4 ,!re is "o exception4 ,suppose t a />'s light is se5 to dim9i% 9 am\nt at regul> int]vals & subsequ5tly to return to its orig9al /r5g?4 ,! obvi\s int]pretation ( ! dim9ution ( light is t "o compon5t ( ! sy/em is eclips+ ! o!r1 & ?is c only happ5 if ! orbit is s completely =e%ort5$ t its plane passes ?r\gh1 or at lea/ v close to1 ! e>?4 ,9 su* a case x is possible to recon/ruct ! :ole orbit1 & !nce to calculate ! weights ( ! two compon5ts4 ,n only s1 b ! l5g? ( "t dur+ :i* ! eclipses la/ tells u ! actual sizes ( ! two compon5ts1 s t x is possible to draw a complete picture ( ! sy/em4 ,diagrams ( ! dim5sions & orbits ( two typical eclips+ b9>ies are %ewn 9 fig4 #f2 ^! are drawn to ! same scale1 ?is be+ indicat$ by ! small circle repres5t+ ! sun4 ,illu/ration3 ,fig4 #f4 ,compon5ts & orbits ( ,eclips+ ,b9>ies4 ,:5 no eclipse occurs 9 a spectroscopic b9>y1 we d n "k h[ mu* =e%ort5+ to all[ =1 b we c obta9 a g5]al idea ( ! weights ( ! compon5ts by assum+ an av]age degree ( =e%ort5+4 ,if we assume diff]5t degrees ( =e%ort5+ 9 turn1 we %all f9d t ! comput$ weights come out lea/ :5 ! plane ( ! orbit is assum$ to pass ?r\gh ! e>?--i4e4 :5 ! orbits are comput$ z ?\gh ! sy/em 7 an eclips+ "o4 ,?us al?\gh we _c discov] ! actual weights ( ! compon5ts ( a non-eclips+ b9>y1 we c always /ate limits above :i* !y mu/ lie1 namely ! weights comput$ z ?\gh ! sy/em 7 an eclips+ "o4 ,9 ?is way1 we "k t ! two compon5ts ( ,plaskett's /> mu/ h m ?an #ge & #fc times ! weight ( ! sun4 ,,v>iable ,,/>s ,! majority ( />s %9e ) a p]fectly /eady light1 s t we c say t a /> is ( s _m c&le-p[]4 ,! sun1 = in/ance1 emits a light ( #cbc #aj c&le-p[]4 ,yet !re are classes ( exceptional />s 9 :i* ! light flick]s up & d[n4 ,9 "s1 z 9 ! eclips+ b9>ies j describ$1 ! light-fluctuations are q regul>1 repeat+ !mselves ) su* precision t ! />s might well be us$ z "t-keep]s4 ,9 o!rs ! fluctuations1 ?\gh n p]fectly regul>1 are ne>ly s1 :ile /ill o!rs exi/ 9 :i* ! fluctuations appe> at pres5t to be completely irregul>1 al?\gh no d\bt ! *anges 9 ^! w be r$uc$ to law & ord] 9 due c\rse4 ,= our pres5t discussion1 ! v>i\s types ( irregul> v>iables are n ( great importance4 ,,cepheid ,,v>iables4 ,! really int]e/+ />s are ^? ( a c]ta9 class ( regul> v>iable1 g5]ally call$ 8,cepheid v>iables10 aft] _! prototype ,cephei4 ,! physical nature ( ^! />s & ! me*anism ( _! light-fluctuation is /ill f> f be+ und]/ood2 compet+ !ories are 9 ! field :i* we ne$ n discuss at ?is /age 7see p4 #bbc bel[74 ,:atev] _! me*anism may be1 obs]vation %ews t ^! />s possess a c]ta9 def9ite prop]ty1 :i* proves to be ( ! utmo/ value4 ,?is be+ s1 we may accept x gratefully )\t tr\bl+ z to its :y & :]e=e4 ,! p]fectly regul> light-fluctuations ( ! eclips+ b9>ies w\ld make !m suitable = "t-keep]s ev5 ?\gh we did n und]/& ! me*anism beh9d ^! fluctuations4 ,9 ! same way ! fluctuations ( ,cepheid v>iables h a quality :i* makes !m valuable z measur+-rods ) :i* to survey ! di/ant p>ts ( ! univ]se4 ,9 brief1 ?is prop]ty is t we c d$uce ! intr9sic brightness ( ^! />s1 & s _! di/ances1 f _! obs]v$ light-fluctuations4 ,! light-fluctuations are s di/9ctive z to make ! />s easy ( detection4 ,!re is a rapid increase ( light1 foll[$ by a sl[ gradual decl9e2 !n aga9 ! same rapid increase & sl[ decl9e z be=e4 ,x is z ?\gh someone 7 ?r[+ armfuls ( fuel on to a bonfire at p]fectly regul> int]vals4 ,"o o!r class ( v>iable />s1 g5]ally kn[n z 8long-p]iod v>iables10 %ews some:at simil> light-fluctuations1 b ! two classes are easily di/+ui%$ by _! v diff]5t p]iods ( light-fluctuation4 ,! ,cepheid v>iable completes its cycle 9 a "t :i* may be a few h\rs1 or may be days or weeks1 b is nev] m ?an ab\t a mon?1 :]eas ! long-p]iod v>iable g5]ally requires ab\t a ye>4 ,fig4 #g %ews ! light curves ( typical v>iable />s ( ! diff]5t classes4 ,9 ea* diagram ! progress ( "t is repres5t$ by motion across ! page f left to "r2 ! high] ! fluctuat+ curve is above ! horizontal l9e at any in/ant1 ! bright] ! /> at t in/ant4 ,out ne> ! b\nd>y ( ! galactic sy/em is a clu/] ( />s kn[n z ! ,less] ,magellanic ,cl\d 7,plate ,,xxi1 p4 #bad71 9 :i* ,cepheid v>iables occur 9 great pr(usion4 ,9 #aiab1 ,miss ,leavitt ( ,h>v>d f\nd t ! light ( ! bright] ,cepheids 9 ?is cl\d fluctuat$ m sl[ly ?an ! light ( ! fa9t] ones4 ,:atev] 0 responsible = turn+ ! /ell> lights up & d[n1 act$ m rapidly = feeble ?an = brilliant lights4 ,! app>5t brightnesses ( a numb] ( ,cepheids at v>y+ di/ances w\ld ( c\rse dep5d only 9 "p on _! intr9sic brightness or c&le-p[]1 b ! />s 9 ! ,magellanic ,cl\d are all1 ne>ly en\gh1 at ! same di/ance f ! e>?4 ,?us diff]5ces 9 ! app>5t brightnesses ( />s 9 ?is cl\d mu/ repres5t real diff]5ces ( intr9sic brightness1 & ,miss ,leavitt's discov]y c\ld be /at$ 9 ! =m t ! p]iod ( light-fluctuation ( a ,cepheid dep5d$ on its c&le-p[]4 ,al?\gh ?is 0 only prov$ = ! ,cepheids 9 ! ,magellanic ,cl\d1 x mu/ be true = all ,cepheids :]ev] !y are1 = x is inconceivable t we c\ld make a />'s light fluctuate m sl[ly or m rapidly m]ely by alt]+ its di/ance f u--by ourselves rec$+ f x1 9 fact4 ,illu/ration3 ,light ,curve ( ,eclips+ ,b9>y 7 ,aurigae7 ,illu/ration3 ,light ,curve ( ,irregul> ,v>iable 7,,rs ,ophiu*i7 ,illu/ration3 ,light ,curve ( ,cepheid ,v>iable7 ,lac]bae7 ,illu/ration3 ,light ,curve ( ,long-,p]iod ,v>iable 7 ,ceti7 ,fig4 #g4 ,light ,curves ( typical ,v>iable ,/>s ( diff]5t classes4 ,pr(essor ,h]tzsprung ( ,leid5 & ,dr ,%apley1 !n ( ,m\nt ,wilson ,obs]vatory1 7 quick to seize ^u ! implications ( ?is discov]y4 ,if two ,cepheids ,a1 ,b 9 diff]5t p>ts ( ! sky are f\nd to fluctuate ) equal rapidities1 !n _! intr9sic c&le-p[]s mu/ be equal4 ,?us any diff]5ce 9 _! app>5t brightness mu/ be traceable to a diff]5ce 9 _! di/ances f u4 ,if ,a looks a hundr$ times z bright z ,b1 !n ,b mu/ be at t5 times ! di/ance ( ,a4 ,9 ! same way1 a ?ird ,cepheid ,c may prove to be at t5 times ! di/ance ( ,b4 ,we n[ "k t ,c is a hundr$ times z remote z ,a4 ,& if ,d c be f\nd t5 times z di/ant z ,c1 we "k t ,d is a ?\s& times z remote z ,a4 ,s we c g on con/ruct+ & ev] ext5d+ our measur+-rod2 !re is no limit until we rea* di/ances s great t ev5 ,cepheid v>iables1 :i* are exceptionally bright />s1 fade into invisibility4 ,s f> we h only consid]$ ! comp>ative di/ances ( ,cepheids4 ,! absolute di/ances ( _m ( ! ne>] ,cepheids h1 h[ev]1 be5 det]m9$ by ! p>allactic me?od already expla9$--i4e4 by measur+ _! app>5t motion 9 ! sky1 result+ f ! e>?'s motion r\nd ! sun4 ,tak+ any "o ( ^! />s z our orig9al ,cepheid ,a1 we c /ep cont9ually f "o ,cepheid to ano!r1 & s calculate ! absolute di/ances ( all ! ,cepheid v>iables 9 ! sky4 ,9 ?is way ! obs]v$ relation betwe5 ! p]iod ( fluctuation & ! brightness ( ,cepheid v>iables--commonly kn[n z ! 8p]iod-lum9osity law0--c be made to provide a scale on :i* ! absolute lum9osity1 or c&le-p[]1 ( a ,cepheid c be read (f directly f ! obs]v$ p]iod ( its light-fluctuations4 ,! ,cepheid v>iables may be reg>d$ z ligh?\ses set up 9 di/ant p>ts ( ! univ]se4 ,we c recognise !m1 j z a sailor recognises ligh?\ses1 by ! quality ( _! light4 ,we c read (f _! c&le-p[] f ! p]iod ( _! obs]v$ light-fluctuations z easily z ! sailor c\ld read (f ! c&le-p[] ( a ligh?\se f an ,admiralty *>t4 ,! app>5t brightness ( ! ,cepheid in=ms u z to its di/ance f u#g4 #g ,= in/ance1 ,cepheids ^: light fluctuates 9 a p]iod ( #dj h\rs h approximately a lum9osity #bej times t ( ! sun1 & s are ( #h #aj c&le-p[]2 a p]iod ( t5 days indicates a lum9osity #afjj times t ( ! sun1 or a c&le-p[] ( #eag #aj1 & s on4 ,if a /> 9 a di/ant a/ronomical object is obs]v$ to fluctuate ) a p]iod ( t5 days1 & ! quality ( its fluctuations %ew x to be a ,cepheid v>iable1 we "k t its actual c&le-p[] mu/ be #eag #aj4 ,its app>5t brightness is obs]v$ to be t ( a /> (1 say1 magnitude #af1 :i*1 /ripp$ ( te*nicalities1 means t we receive z mu* light f x z f a s+le c&le at a di/ance ( #egj miles4 ,! diff]5ce betwe5 "o c&le & #eag #aj c&les accord+ly corresponds to ! diff]5ce betwe5 #egj miles & ! di/ance ( ! object 9 "q1 :5ce1 s9ce light falls (f z ! inv]se squ>e ( ! di/ance1 we calculate t ! di/ance ( ! object mu/ be #eag #aj #egj miles or ab\t #bbj1jjj light-ye>s4 ,x w\ld be difficult to ov]-e/imate ! importance ( all ?is to mod]n a/ronomical sci5ce4 ,x means t a me?od has be5 f\nd = survey+1 if n ! :ole ( ! univ]se1 at lea/ ^? p>ts ( x 9 :i* ,cepheid v>iables are visible4 ,actually ?is la/ res]vation is unimportant1 = ,cepheid v>iables are v freely scatt]$ 9 space4 ,naturally ! me?od is ( mo/ value = ! exploration ( ! mo/ di/ant p>ts ( ! univ]se2 "h x a*ieves triumphant success :]e o!r me?ods fail completely4 ,! p>allactic me?od beg9s to fail :5 we try to s\nd di/ances ( m ?an ab\t a hundr$ light-ye>s4 ,! app>5t pa? 9 ! sky1 :i* a /> at ?is di/ance describes1 9 consequ5ce ( ! e>?'s motion r\nd ! sun1 is ( ! size ( a p9-head two miles away4 ,) all _! ref9em5ts1 mod]n in/rum5ts f9d x difficult en\gh to detect s small a motion z ?is1 & x is practically impossible to measure x ) accuracy4 ,! 8p]iod-lum9osity0 law measures ! di/ances ( objects up to a million light-ye>s away1 ) a small] p]c5tage ( error ?an is to be expect$ 9 ! p>allactic measures ( />s only a hundr$ light-ye>s away4 ,,s\nd+ ,,space ,?is by no means exhau/s ! li/ ( mod]n me?ods ( survey+ space4 ,any /&>d type ( a/ronomical object1 :i* is easily recognisable & emits ! same am\nt ( light no matt] :]e x occurs1 provides an obvi\s means ( measur+ a/ronomical di/ances1 = :5 once ! intr9sic lum9osity ( su* an object has be5 det]m9$1 ! di/ance ( e example ( x c be e/imat$ f its app>5t brightness4 ,cepheid v>iables ( assign$ p]iods provide ! mo/ /rik+ in/ance ( su* /&>d objects1 b ?ree o!rs are available1 al?\gh !y are n s g5]ally useful z ,cepheids4 ,fir/ comes ano!r type ( v>iable />1 ! 8long-p]iod v>iables0 already m5tion$1 :i* are g5]ally simil> to ,cepheids except t _! light fluctuates mu* m sl[ly4 ,^! />s are intr9sically f> m lum9\s ev5 ?an ,cepheids1 _m ( !m be+ #aj1jjj times z lum9\s z ! sun4 ,!y are accord+ly visible at enorm\s di/ances1 & may ultimately be f\nd to provide a means ( s\nd+ dep?s ( space at :i* ev5 ,cepheids are lo/ to sight4 ,next come 8novae0 or new />s4 ,e n[ & !n an ord9>y /> 9 ! sky sudd5ly bur/s out 9 a ph5om5al blaze ( light1 %9+ ) p]haps a ?\s& times its orig9al brilliance4 ,! cause ( ^! viol5t outbur/s is /ill a matt] = debate1 & no ?or\ghly conv9c+ explanation has z yet be5 giv54 ,a /udy ( comp>atively ne> novae has1 h[ev]1 provid$ in=mation z to ! lum9osity ( ! av]age nova :5 at its brighte/1 & z novae appe> 9 v>i\s p>ts ( ! sky1 & p>ticul>ly 9 ! extra-galactic nebulae1 !y provide a r\gh means ( measur+ /ell> & nebul> di/ances4 ,blue />s provide yet ano!r me?od4 ,^! are exce$+ly lum9\s1 & !y v>y b little 9 intr9sic lum9osity4 ,moreov]1 ! lum9osity ( any p>ticul> /> c g5]ally be e/imat$ fairly closely f ! quality ( ! light x emits1 by me?ods :i* w be expla9$ lat]4 ,?is makes x possible to det]m9e ! di/ances ( blue />s1 & s ( c\rse ( ! a/ronomical objects 9 :i* !y occur4 ,/ill two o!r me?ods ( a diff]5t k9d may be briefly m5tion$4 ,dr ,w4 ,s4 ,adams1 ,director ( ,m\nt ,wilson ,obs]vatory1 & o!rs h f\nd t c]ta9 def9ite peculi>ities 9 ! spectra ( c]ta9 classes ( />s convey in=mation z to ! intr9sic brightness ( ! /> emitt+ !m2 ) ?is in=mation x is easy to e/imate ! />'s di/ance f its app>5t brightness4 ,?is is commonly describ$ z ! me?od ( ,spectroscopic ,p>allaxes4 ,f9ally ! diffuse cl\d ( nebul> matt] :i* is spread ?r\gh int]/ell> space 7p4 #cj7 is f\nd to affect ! quality ( light travell+ ?r\gh x1 s t a />'s spectrum gives an indication ( ! am\nt ( cl\d ?r\gh :i* ! light ( ! /> has travell$1 & ?is aga9 provides a r\gh means ( e/imat+ di/ances inside ! galactic sy/em4 ,illu/ration3 ,,plate ,,ix ,dom9ion ,a/rophysical ,obs]vatory1 ,b4 ,c4 ,! ,globul> ,clu/] ,m #ac 9 ,h]cules ,,globul> ,,clu/]s4 ,! law ( ,cepheid lum9osity 0 fir/ us$ by ,h]tzsprung to e/imate ! di/ance ( ! ,less] ,magellanic ,cl\d1 ! /udy ( :i* _h be5 responsible = ! orig9al discov]y ( ! law4 ,%apley subsequ5tly us$ x to det]m9e ! di/ances ( ! r my/]i\s gr\ps ( />s kn[n z 8,globul> ,clu/]s40 ,a typical example ( ^! is %ewn 9 ,plate ,,ix4 ,ab\t #ajj ( ^! clu/]s are kn[n & !y all look pretty mu* alike1 except = diff]5ces 9 app>5t size4 ,ev5 ^! latt] c be trac$ ma9ly to diff]5ces ( di/ance1 s t ! globul> clu/]s are probably almo/ id5tical objects1 & ,plate ,,ix might almo/ be reg>d$ z a picture ( any "o ( !m4 ,cepheid v>iables ab\nd 9 !m all4 ,%apley f\nd ! ne>e/ globul> clu/]1 ,c5tauri1 to lie at a di/ance ( ab\t #bb1jjj light-ye>s1 ! fur!/1 ,n4,g4,c4 #gjjf1 be+ ab\t t5 times z remote1 at a di/ance ( #bbj1jjj light-ye>s4 ,at su* di/ances ! p>allactic me?od ( measur+ di/ances w\ld ( c\rse fail hopelessly4 ,! p>allactic orbit ( a /> at #bbj1jjj light-ye>s' di/ance is ab\t ! size ( a p9-head held at a di/ance ( #djjj miles2 no telescope on e>? c\ld detect1 /ill less measure1 su* an orbit4 ,! m]e figure ( #bbj1jjj light-ye>s c convey b little conception ( ! di/ance ( ?is remote/ ( />-clu/]s f u4 ,we may appreh5d x bett] if we reflect t ! light by :i* we see ! clu/] />t$ on its long j\rney f x to u some:]e ab\t ! "t :5 primaeval man fir/ appe>$ on e>?4 ,?r\gh ! *ildhood1 y\? & age ( c\ntless g5]ations ( m51 ?r\gh ! long prehi/oric ages1 ?r\gh ! sl[ dawn ( civilisation & ?r\gh ! :ole span ( "t :i* hi/ory records1 ?r\gh ! rise & fall ( dyna/ies & empires1 ?is light has travell$ /eadily on its c\rse1 cov]+ #ahf1jjj miles e second1 & is only j rea*+ u n[4 ,& yet ?is enorm\s /ret* ( space does n c>ry u to ! conf9es ( ! univ]se2 we %all n[ see t 9 all probability x has b>ely c>ri$ u to ! conf9es ( ! galactic sy/em4 ,illu/ration3 ,fig4 #h4 ,! arrangem5t ( ! ,globul> ,clu/]s4 ,%apley has mapp$ out ! complete sy/em ( ! globul> clu/]s1 & f9ds t !y occupy an oblong region1 ly+ on bo? sides ( ! plane ( ! ,milky ,way1 its greate/ diamet] ( ab\t #bej1jjj light-ye>s ly+ 9 ?is plane1 & its two transv]se diamet]s be+ consid]ably %ort]4 ,! sun is ne>] to ! edge ( ?is oblong region ?an to its c5tre1 :i* expla9s :y all ! globul> clu/]s appe> 9 "o half ( ! sky1 z ,h9ks fir/ not$ 9 #aiaa4 ,! g5]al arrangem5t is %ewn 9 fig4 #h4 ,! page ( ! book repres5ts ! plane ( ! ,milky ,way1 ! v>i\s dots repres5t+ ! po9ts 9 ?is plane :i* are ne>e/ to ! diff]5t clu/]s1 s t ! diagram exhibits ! sy/em ( globul> clu/]s z !y w\ld appe> to an obs]v] out 9 space :o view$ ! galactic plane 8full-on40 ,all ! globul> clu/]s except ,n4,g4,c4 #gjjf lie )9 a circle ( ab\t #abe1jjj light-ye>s' radius1 hav+ its c5tre at ab\t #ej1jjj light-ye>s f ! sun4 ,illu/ration3 ,,plate ,x ,e4 ,e4 ,b>n>d ,! ,region ( ,ophiu*i ,,! ,,arrangem5t ,,( ,,! ,,galactic ,,sy/em4 ,al?\gh ! matt] has long be5 "o ( vigor\s controv]sy1 x is n[ becom+ cle> t ! region ( space mapp$ out by ^! globul> clu/]s approximately co9cides ) t occupi$ by ! galactic sy/em itself4 ,h]s*el & ,kapteyn appe> to h be5 9 error 9 suppos+ ! c5tre ( ! galactic sy/em to be 9 ! neighb\rhood ( ! sun2 a consid]able accumulation ( evid5ce indicates t x lies 9 a massive />-cl\d 9 ! con/ellations ( ,ophiu*us & ,scorpio4 ,dr ,%apley & ,miss ,swope1 at ,h>v>d ,obs]vatory1 h rec5tly det]m9$ ! di/ance ( ?is />-cl\d f ! sun z #dg1jjj light-ye>s1 :i* places x almo/ exactly at ! c5tre ( ! sy/em ( globul> clu/]s1 z %ewn 9 fig4 #h4 ,!re is :at ,%apley describes z a 8local sy/em0 ( fairly bright />s surr\nd+ ! sun1 & ! error ( id5tify+ ?is ) ! ma9 galactic sy/em has app>5tly be5 responsible = a l>ge "p ( ! confusion :i* has hi!rto beset ! problem ( ! ar*itecture ( ! galaxy4 ,?is local sy/em has ! same flatt5$ %ape z ! ma9 sy/em1 b x does n lie exactly 9 ! plane ( ! ,milky ,way1 be+ incl9$ at an angle ( ab\t #ab degrees to x4 ,! sun appe>s to lie v ne> to ! plane ( ! c5tral plane ( ! sy/em2 rec5t det]m9ations place x ab\t #ajj light-ye>s to ! nor? ( ?is plane4 ,fig4 #i %ews a cross-section ( ! sy/em1 z x is n[ imag9$ to lie4 ,illu/ration3 ,fig4 #i4 ,diagrammatic s*eme ( cross-section ( ! ,galactic ,sy/em4 ,! sun is at ! head ( ! arr[4 ,we h already comp>$ ! %ape ( ! galactic sy/em to t ( a :eel4 ,x obvi\sly c\ld n reta9 ?is %ape if ! />s :i* =m$ x 7 /&+ /ill 9 space4 ,= ! gravitational pull ( ! inn] />s w\ld cause ! out]mo/ />s--! rim ( ! :eel--to fall inw>ds1 & ! sy/em w\ld end z a confus$ jumble ( />s some:]e 9 ! vic9ity ( ! hub ( ! :eel4 ,9 #aiac1 ,h5ri ,po9c>1 ,pr(essor ( ,ma!matics at ! ,sorbonne1 sugge/$ t ! galactic 8:eel0 might escape ?is fate if x 7 9 a /ate ( rotation4 ,j z ! e>?'s motion saves x f fall+ into ! sun1 & ! moon's motion saves x f fall+ on to ! e>?1 s1 ,po9c> sugge/$1 ! />s :i* =m ! rim ( ! :eel might be sav$ f fall+ into ! hub1 by a motion ( rotation ( ! :ole :eel4 ,a r\gh calculation sugge/$ t x w\ld be necess>y = ! :eel to rotate at ! rate ( a complete revolution ab\t e #ejj million ye>s4 ,naturally x is no simple matt] to detect s sl[ a rotation4 ,x 0 fir/ suspect$ to occur 9 ! foll[+ way4 ,we "k t :5 a sp9n+-top or gyroscope is set 9 rapid rotation1 a consid]able =ce is ne$$ to twi/ ! top or gyroscope ab\t 9 space4 ,?is is ! pr9ciple ( ! gyroscopic compass su* z is us$ to /e] %ips4 ,a gyroscope1 a sort ( big /eel sp9n+-top1 is />t$ sp9n+ ) its two ends pivot$ 9 a sw++ frame4 ,no matt] h[ ! %ip turns1 ! motion ( ! gyroscope keeps ! frame po9t+ away 9 ! same direction1 & by ! help ( ?is fix$ direction ! %ip is kept on its c\rse4 ,n[ ! sol> sy/em has _m ( ! prop]ties ( a huge sp9n+-top1 ! revolutions ( ! planets correspond+ to ! sp9 ( ! top4 ,z !re is no twi/ impress$ on ?is 8sp9n+-top0 f outside1 its axis ( rotation mu/ always po9t 9 ! same direction1 ?us provid+ a sort ( 8gyroscopic compass0 to give u our be>+s 9 space4 ,9 #aiac ,*>li] believ$ he _h f\nd t ?is 8gyroscopic compass0 0 turn+ r\nd aga9/ ! di/ant backgr\nd ( ! ,milky ,way1 at ! rate ( a complete rotation e #cgj million ye>s1 a p]iod :i* subsequ5t measurem5ts increas$ to #ecj million ye>s4 ,edd+ton !n sugge/$ t x might be ! backgr\nd r ?an ! gyroscopic compass t 0 turn+1 ! ,milky ,way actually rotat+ 9 ! way imag9$ by ,po9c>1 & at j ab\t ! rate :i* ,po9c> _h calculat$4 ,rec5t inve/igations by ,oort1 ,plaskett1 ,l9dblad & o!rs prove beyond d\bt t su* a rotation really occurs1 al?\gh x is n ( ! simple 8c>t-:eel type0 we h s f> discuss$4 ,9 ! sol> sy/em ! inn]mo/ planets move m rapidly ?an ! out]mo/3 !y mu/ necess>ily d s if ! motion ( ea* planet is to c\nt]act ! sun's attraction4 ,9 ! same way1 if ! rotational motion ( ! galaxy is to c\nt]act ! gravitational attraction ( its inn]mo/ />s1 its inn] p>ts mu/ rotate m rapidly ?an its out]mo/4 ,?us ! sun ought to be ov]tak+ ^? />s :i* lie outside x on ! galactic :eel1 :ile be+ itself ov]tak5 by ^? :i* lie inside x4 ,su* an ov]tak+ motion is fairly easy to detect4 ,a c>eful analysis ( obs]v$ /ell> motions has disclos$ su* a motion1 %ew+ t ! galaxy z a :ole is 9 rotation 9 precisely ! way j describ$1 ! inn] p>ts rotat+ mo/ rapidly4 ,! hub ( ?is gigantic :eel lies almo/ exactly 9 ! direction :i* ,%apley assign$ to ! c5tre ( ! galaxy f 8 /udy ( ! globul> clu/]s4 ,its di/ance f ! sun1 :i* _c yet be det]m9$ ) any great accuracy1 is probably some:]e ab\t #cg1jjj light-ye>s4 ,to )9 ! limits ( accuracy :i* are at pres5t atta9able1 ?is places ! c5tre ( ! galactic :eel at ! c5tre ( ! sy/em ( globul> clu/]s 7see fig4 #h1 p4 #fd74 ,9 ! vic9ity ( ! sun1 ! galactic :eel p]=ms a complete revolution 9 a p]iod ( ab\t #bcj million ye>s1 & ?is end[s ! />s ne> ! sun ) a motion ?r\gh space at a spe$ ( ne>ly #bjj miles a second1 aris+ f ! rotation ( ! galaxy alone4 ,) ^! data1 x is possible to weigh ! />s ( ! galactic sy/em en masse4 ,individual />s f> away f ! c5tre ( ! galactic sy/em mu/ be describ+ orbits "u ! gravitational pull ( ! sy/em z a :ole1 ! pull :i* prev5ts ! />s f scatt]+ away into space1 & s keeps ! galactic sy/em 9 be+4 ,! aggregate ( ^! orbital motions produces ! g5]al rotation ( ! galaxy :i* we h j discuss$4 ,& f ! figures j m5tion$1 x c be calculat$ t ! total weight ( matt] inside ! sun's orbit mu/ be ab\t t ( #bdj1jjj million suns4 ,"p ( ?is may ( c\rse arise f int]/ell> du/ or gas4 ,nev]!less1 z ! av]age /> weighs consid]ably less ?an ! sun1 ! total numb] ( />s 9 ! galactic sy/em may well be ( ! ord] ( #djj1jjj million4 ,?is e/imate ( c\rse includes all />s1 d>k z well z lum9\s1 b !re are reasons = believ+ t ! numb] ( d>k />s is comp>atively small 7see p4 #bfi bel[74 ,o!r e/imates ( ! numb] ( />s 9 ! galaxy h be5 made1 g5]ally l[] ?an ! =ego+4 ,two e/imates by ,l9dblad1 = in/ance1 give ! total weight ( ! galaxy z #aaj1jjj & #ahj1jjj million suns respectively4 ,aga9 we are confront$ ) ! difficulty ( visualis+ su* l>ge numb]s4 ,) p]fect eyesight on a cle> moonless night we c see ab\t #cjjj />s4 ,imag9e ea* ( ^! #cjjj />s to spread out into a complete sky-full ( #cjjj new />s1 & we are contemplat+ #i million />s1 :i* is /ill only ! numb] visible 9 a telescope ( #e in*es ap]ture4 ,we probably _c ask our imag9ation to play ! same trick = u a second "t1 b if x c be p]suad$ to d s1 & if we c ?9k ( ea* ( ^! #i million />s z aga9 g5]at+ a :ole sky-full ( />s1 we /ill h only #bg1jjj million />s )9 our purview--a numb] :i* is /ill f> bel[ any p]missible e/imate ( ! total numb] ( />s 9 ! galactic sy/em4 ,or aga91 let u notice t ! numb] ( />s photographically visible 9 ! #ajj-;in* telescope1 namely #aejj million1 is ab\t equal to ! numb] ( m51 wom5 & *ildr5 9 ! _w4 ,ea* inhabitant ( ! e>?--ea* man1 woman & *ild liv+ 9 ! five cont95ts or travell+ on ! sev5 seas--c be all[$ to *oose 8 own p>ticul> />1 & c !n repeat ! process t5s1 & m probably hundr$s1 ( times )\t go+ outside ! galactic sy/em4 ,aft] ?is we c /ill g explor+ outside ! galactic sy/em & f9d m & ev] m />s4 ,! galactic sy/em1 ) its hundr$s ( millions ( />s1 no m conta9s all ! />s 9 space ?an "o h\se conta9s all ! inhabitants ( ,great ,brita94 ,!re are millions ( o!r h\ses & millions ( o!r families ( />s4 ,,! ,,extra-,,galactic ,,nebulae4 ,we h already spok5 ( ! fa9t nebul\s objects :i* ,h]s*el describ$1 some:at conjecturally1 z 8isl& univ]ses40 ,^! are ! o!r h\ses 9 :i* o!r families ( />s are to be f\nd4 ,! mo/ p[]ful ( mod]n telescopes %ew t !y consi/1 9 "p at lea/1 ( huge cl\ds ( />s4 ,j z a p[]ful microscope %ews t a puff ( cig>ette smoke1 9 spite ( its appe>ance ( cont9uity1 consi/s ( a cl\d ( m9ute b q di/9ct p>ticles1 s a p[]ful mod]n telescope breaks up ! light f ! out] regions ( ^! nebulae into di/9ct spots ( light2 ! nebula is resolv$ into a cl\d ( %9+ p>ticles1 j z ! ,milky ,way 0 9 ,galileo's t9y telescope ( ?ree c5turies ago4 ,plate ,,xi %ews an example2 x repres5ts a magnification ( a small area 9 ! top left-h& corn] ( ! ,great ,nebula ,m #ca 9 ,&rom$a already %ewn 9 ,plate ,,iv 7p4 #cj71 & ! resolution into di/9ct spots ( light is unmi/akable4 ,we "k t "s at lea/ ( ^! spots ( light are />s1 because we recognise !m z ,cepheid v>iables1 _! light %ew+ ! unmi/akable *>act]i/ic fluctuations ( ! famili> ,cepheid v>iables ne>] home4 ,! o!r %9+ p>ticles are ( comp>able brightness & %ew ab\t ! range ( brightness above & bel[ t ( ! ,cepheids :i* is ne$$ to ju/ify u 9 suppos+ t !y are ord9>y />s4 ,illu/ration3 ,,plate ,,xi ,mt ,wilson ,obs]vatory ,magnification ( a "p 7left-h& top corn]7 ( ! ,great ,nebula ,m #ca 9 ,&rom$a1 :i* is %ewn complete 9 ,plate ,,iv 7p4 #cj7 ,illu/ration3 ,,plate ,,xii ,mt ,wilson ,obs]vatory ,magnification ( ! c5tral region ( ! ,great ,nebula ,m #ca 9 ,&rom$a ,f ! obs]v$ p]iods ( fluctuation ( _! ,cepheid v>iables1 9 comb9ation ) ! o!r me?ods j expla9$1 ,dr ,hubble ( ,m\nt ,wilson ,obs]vatory has rec5tly f\nd t ev5 ! ne>e/ ( ^! nebulae1 namely ! nebula ,m #cc %ewn 9 ,plate ,,xx 7p4 #bac71 is s remote t light takes "s #hej1jjj ye>s to travel f x to u4 ,! ,great ,nebula ,m #ca 9 ,&rom$a 7p4 #cj7 is at ! slightly great] di/ance ( ab\t #ijj1jjj light-ye>s4 ,?is abundantly proves t ^! nebulae lie "r outside ! galactic sy/em1 ju/ify+ ! t]m 8extra-galactic0 nebulae4 ,"o might attempt to e/imate ! total numb] ( />s 9 ^! nebulae by c\nt+ ^? visible 9 a select$ av]age small area1 b m precise me?ods are available4 ,j z we h suppos$ t ! out]mo/ />s 9 ! galactic sy/em are describ+ orbits "u ! gravitational attraction ( ! galaxy z a :ole1 s we mu/ suppose t ! out]mo/ />s 9 a nebula are describ+ orbits "u ! gravitational attraction ( ! ma9 mass ( ! nebula2 ! =ces :i* keep !m f runn+ away f ! nebula are simil> to ^? :i* keep ! e>? mov+ 9 its orbit r\nd ! sun4 ,if s1 we c weigh ! nebulae1 precisely 9 ! same way z we weigh ! sun 7p4 #dd7 or ! galactic sy/em 7p4 #fi74 ,dr ,hubble 9 ?is way e/imates t ! weight ( ! ,great ,nebula ,m #ca 9 ,&rom$a1 %ewn 9 ,plate ,,iv1 mu/ be ab\t #cejj million times t ( ! sun1 :ile ! nebula ,n4,g4,c4 #deid 9 ,virgo1 %ewn 9 ,plate ,,xv 7p4 #bjd71 mu/ h ab\t #bjjj million times ! weight ( ! sun4 ,9 g5]al x seems likely t ea* ( ! extra-galactic nebulae conta9s ab\t en\gh matt] to make "s #bjjj million />s4 ,?is is n ! same ?+ z say+ t ea* nebula already conta9s #bjjj million />s4 ,:ile _m ( ^! nebulae appe> to consi/ l>gely ( cl\ds ( />s1 yet mo/ ( !m conta9 also a l>ge c5tral region :i* no telescopic p[] has s f> succe$$ 9 resolv+ into di/9ct po9ts4 ,= in/ance1 ,plate ,,xii %ews ! c5tral region ( ! ,great ,nebula 9 ,&rom$a magnifi$ to ! same degree z ! left-h& top corn] %ewn 9 ,plate ,,xi1 & ?is is cle>ly n resolv$ into />s 9 ! same way z ! out] regions %ewn 9 ,plate ,,xi4 ,! :ole ( ! nebula ,n4,g4,c4 #deid 9 ,virgo1 %ewn 9 ,plate ,,xv1 also refuses to be resolv$ into sep>ate />s4 ,we %all f9d reasons lat] 7,*apt] ,,iv7 = int]pret+ ^! c5tral regions z masses ( gas :i* are de/9$ 9 "t to =m />s1 b h n yet done s4 ,we %all 9 fact f9d t ! nebulae are ! bir?places ( ! />s1 s t ea* nebula consi/s ( />s born & />s n yet born4 ,x is ! total weight ( />s already born & ( matt] :i* is de/9$ to =m />s t aggregates #bjjj million suns4 ,ab\t #b1jjj1jjj ( ^! extra-galactic nebulae are visible 9 ! great #ajj-;in* telescope4 ,9 g5]al1 !y appe> to be scatt]$ ) a tol]able approa* to uni=mity ?r\gh space1 _! av]age di/ance ap>t be+ some?+ ( ! ord] ( #b1jjj1jjj light-ye>s1 al?\gh "h & !re ?is uni=mity is brok5 by cl\ds & clu/]s ( nebulae4 ,= in/ance1 ! sky is rem>kably ri* 9 nebulae 9 ! con/ellations ( ,virgo & ,coma ,b]5ices4 ,"h a cl\d ( ab\t #cjj nebulae is collect$1 accord+ to ,%apley1 )9 a space hav+ only f #e to #aj times ! dim5sions ( ! galactic sy/em1 at a di/ance ( "s t5 million light-ye>s f ! sun4 ,! same region ( ! sky appe>s also to conta9 ?ree o!r & m remote cl\ds4 ,%apley has sugge/$ t our galactic sy/em1 ! ,&rom$a nebula & o!r ne> nebulae may con/itute a simil> cl\d4 ,,! ,,remote/ ,,dep?s ,,( ,,space4 ,hubble e/imates t ! mo/ di/ant ( ! #b1jjj1jjj nebulae reveal$ by ! #ajj-;in* telescope mu/ be ab\t #adj million light-ye>s away f u4 ,?is is ! greate/ di/ance :i* ! human eye has s f> se5 into space4 ,! #bbj1jjj light-ye>s :i* =m$ ! diamet] ( ! galactic sy/em seem$ /agg]+ly l>ge at fir/1 b we are n[ speak+ ( di/ances "s #fjj times great]4 ,= all b a #ejj? "p ( its long j\rney1 ! light by :i* we see ?is remote/ ( visible nebulae travell$ t[>ds an e>? un9habit$ by man4 ,j z x 0 ab\t to arrive1 man came into be+ on e>?1 & built telescopes to receive x4 ,s at lea/ x appe>s :5 view$ on ! a/ronomical scale4 ,yet ev5 ?is la/ #ejj? "p ( ! j\rney cov]s ! lives ( #aj1jjj g5]ations ( m51 ?r\gh all ( :i*1 z well z ?r\gh #ejj times z great a span ( "t1 ! light has be5 travell+ /eadily onw>d at #ahf1jjj miles a second4 ,!re are s _m fa9t nebulae at ! v limit ( vision ( ! #ajj-;in* telescope1 t x seems c]ta9 t a /ill l>g] telescope w\ld reveal a great _m m4 ,! #bjj-;in* telescope1 :i* x is hop$ w %ortly be built1 hav+ twice ! ap]ture ( ! pres5t #ajj-;in*1 ought to probe twice z f> into space1 & s may p]haps be expect$ to %ew ab\t eight times z _m1 or #af million1 nebulae4 ,,! ,,/ructure ,,( ,,! ,,univ]se ,s f> e increase ( telescopic p[] has c>ri$ u deep] & deep] into space1 & space has seem$ to exp& at an ev]-increas+ rate4 ,we may well ask :e!r ?is expansion is de/9$ to g on = ev]3 are !re any limits at all to ! ext5t ( space8 ,ev5 a g5]ation ago1 ,i ?9k mo/ sci5ti/s w\ld h answ]$ ?is la/ "q 9 ! negative4 ,!y w\ld h argu$ t space c\ld be limit$ only by ! pres5ce ( some?+ :i* is n space4 ,we1 or r our imag9ations1 c\ld only be prev5t$ f j\rney+ = ev] ?r\gh space by runn+ up aga9/ a wall ( some?+ diff]5t f space4 ,&1 h>d ?\gh x may be to imag9e space ext5d+ = ev]1 x is f> h>d] to imag9e a b>ri] ( some?+ diff]5t f space :i* c\ld prev5t our imag9ations f pass+ into fur!r space beyond4 ,! argum5t is n a s\nd "o4 ,= in/ance1 ! e>?'s surface is ( limit$ ext5t1 b !re is no b>ri] :i* prev5ts u f travell+ on & on z f> z we please4 ,a travell] :o did n und]/& t ! e>?'s surface is sph]ical1 w\ld naturally expect t long] & long] j\rneys f home w\ld = ev] op5 up new tracts ( c\ntry await+ exploration4 ,yet1 z we "k1 he w\ld necess>ily be r$uc$ 9 "t to repeat+ 8 own tracks4 ,z a result ( its curvature1 ! e>?'s surface1 al?\gh unlimit$1 is f9ite 9 ext5t4 ,,! ,,!ory ,,( ,,relativity ,?r\gh 8 !ory ( relativity1 ,e9/e9 claims to h e/abli%$ t space also1 al?\gh unlimit$1 is f9ite 9 ext5t4 ,! total volume ( space 9 ! univ]se is ( f9ite am\nt j z ! surface ( ! e>? is ( f9ite am\nt1 & = ! same reason2 bo? b5d back on !mselves & close up4 ,! analogy is valid & useful only s long z we are c>eful to comp>e ! :ole ( space to ! surface ( ! e>?1 & n to its volume4 ,! volume ( ! e>? is also f9ite 9 am\nt1 b = q diff]5t reasons4 ,a mole :i* burr[$ on & on ?r\gh ! e>? 9 a /raight l9e w\ld come 9 "t to some?+ :i* is n e>?--x w\ld em]ge into ! op5 air2 b we c g on & on ov] ! surface ( ! e>? )\t ev] com+ to any?+ :i* is n ! surface ( ! e>?4 ,! prop]ties ( space are ^? ( ! surface1 n ( ! volume1 ( ! e>?4 ,z a consequ5ce ( space b5d+ back into itself1 a projectile or a ray ( light c travel on = ev] )\t go+ outside space into some?+ :i* is n space1 & yet x _c g on = ev] )\t repeat+ its own tracks4 ,= ?is reason x is probable t light c travel r\nd ! :ole ( space & return to its />t+ po9t1 s t if we po9t$ a suffici5tly p[]ful telescope 9 ! "r direction 9 ! midnight sky1 we %\ld see ! sun & its neighb\rs 9 space by light :i* _h made ! circuit ( ! univ]se4 ,we %\ld n see !m z !y n[ are1 b z !y 7 _m millions ( ye>s ago4 ,light :i* _h left ! sun s long ago w\ld h travell$ r\nd almo/ ! :ole ( space & !n1 j z x 0 ab\t to complete ! circle1 x w\ld be caught 9 our telescope in/ead ( be+ all[$ to />t on its second j\rney r\nd space4 ,?is curvature ( space has o!r functions ?an t :i* x p]=ms on ! gr& scale1 ( limit+ ! total volume ( space4 ,be=e ,e9/e9's day ! curvatures ( ! pa?s ( planets1 cricket balls & projectiles 9 g5]al 7 all attribut$ to ! pull ( a 8=ce0 ( gravitation4 ,! !ory ( relativity dismisses ?is suppos$ =ce z a pure illusion1 & attributes ! curv$ pa?s ( projectiles ( all k9ds to _! ef=ts to keep a /raight track ?r\gh a curv$ space4 ,?is curv$ space is n1 x is true1 ! ord9>y space ( ! a/ronom]4 ,x is a purely ma!matical & probably :olly fictiti\s space1 9 :i* ! a/ronom]s' space & ! a/ronom]s' "t are inextricably b\nd toge!r & ent] z equal p>tn]s4 ,to be absolutely exact1 !re are f\r equal p>tn]s4 ,! fir/ ?ree are ! ?ree dim5sions ( ord9>y space--bread?1 wid?1 & height1 or1 if we pref]1 nor?-s\?1 ea/-we/ & up-d[n4 ,! f\r? is ord9>y "t measur$ 9 a way appropriate to ! way 9 :i* we h measur$ our space 7a ye> ( "t correspond+ to a light-ye> ( space1 & s on71 & !n multipli$ by ! squ>e-root ( -#a4 ,?is la/ multiplication by ! squ>e-root ( -#a is ( c\rse ! rem>kable feature ( ! :ole affair4 ,= ! squ>e-root ( -#a has no real exi/5ce2 x is :at ! ma!matician describes z an 8imag9>y0 numb]4 ,no real numb] c be multipli$ by itself & give -#a z ! product4 ,yet x is only :5 "t is measur$ 9 t]ms ( an imag9>y unit ( 7-#a7 ye>s t !re is true equal p>tn]%ip betwe5 space & "t4 ,?is %ews t ! equal p>tn]%ip is purely =mal--x is no?+ b a conv5i5t fiction ( ! ma!matician4 ,inde$ _h x be5 any?+ m1 our intuitive conviction t "t is some?+ ess5tially diff]5t f space c\ld h _h no basis 9 exp]i5ce & s w\ld h vani%$ ere n[4 ,^! complications ) respect to "t ne$ n conc]n u "h2 ! ess5tial po9t is t ,e9/e9's !ory ( relativity tea*es t space ultimately b5ds back on itself l ! e>?'s surface1 s t ! total am\nt ( space is f9ite4 ,,! ,,cosmology ,,( ,,e9/e94 ,accord+ to ,e9/e9's orig9al !ory1 ! dim5sions ( space are det]m9$ by ! am\nt ( matt] x conta9s4 ,! m matt] !re is1 ! small] space mu/ be1 & conv]sely2 space c\ld only be ( lit]ally inf9ite ext5t if x conta9$ no matt] at all4 ,! problem ( det]m9+ ! ext5t ( space accord+ly r$uces to t ( det]m9+ h[ mu* matt] x conta9s4 ,we h no means ( e/imat+ h[ mu* matt] may exi/ outside ^? regions ( space :i* are )9 ! rea* ( our telescopes1 b )9 ^! regions matt] seems to be fairly uni=mly di/ribut$ 9 ! =m ( extra-galactic nebulae4 ,f ! kn[n weights ( ^!1 ,hubble e/imates t ! mean d5sity ( matt] 9 space mu/ be ab\t #ae #aj times t ( wat]4 ,on ! assumption t matt] is di/ribut$ ) ?is d5sity ?r\gh ! :ole ( space1 includ+ ^? p>ts :i* our telescopes h n yet p5etrat$1 we c calculate q def9itely t ! radius ( space is #hd1jjj million light-ye>s1 or #fjj times ! di/ance ( ! fur!/ visible nebula4 ,! j\rney r\nd space w\ld take #ejj1jjj million light-ye>s1 & if ev] our telescopes %ew u ! sol> sy/em f beh9d1 we %all see x z x 0 #ejj1jjj million ye>s ago4 ,?us1 accord+ to ,e9/e9's orig9al !ory1 ev5 ! #adj million light-ye>s ?r\gh :i* we c range ) our telescopes =m only a small fraction ( ! :ole ( space--some?+ l "o "p 9 a ?\s& million4 ,!re is pl5ty ( space /ill await+ exploration4 ,x is p]haps n surpris+4 ,mank9d1 :o has be5 possess$ ( telescopes = only #cjj ye>s out ( ! #cjj1jjj ( 8 resid5ce on e>?1 c\ld h>dly hope to discov] ! :ole ( space 9 s %ort a "t4 ,our a/ronom]-explor]s are mov+ f isl& to isl& 9 ! small ar*ipelago :i* surr\nds _! home 9 space1 b !y are /ill f> f circumnavigat+ ! globe4 ,&1 j z ! e>lie/ geograph]s tri$ to e/imate ! size ( ! e>?1 long be=e !y ?\ght ( circumnavigat+ x1 f ! curvature ( a small "p ( its surface1 s a/ronom]s are n[ try+ to =m e/imates1 al?\gh necess>ily vague1 ( ! size ( ! :ole univ]se f ! curvature ( t "p ( x ) :i* !y are already acqua9t$4 ,! g5]al !ory ( relativity has long pass$ ! /age ( be+ reg>d$ z an int]e/+ speculation4 ,x n only acc\nts = ph5om5a ( planet>y motion be=e :i* ,newton's law ( gravitation fail$1 b x has pr$ict$ o!r ph5om5a--! app>5t displacem5ts ( />s ne> ! sun at an eclipse1 result+ f ! light by :i* we see !m be+ b5t z x passes ?r\gh ! sun's gravitational field1 & a c]ta9 displacem5t ( /ell> spectra t[>ds ! r$ end--:i* 7 entirely unsuspect$ :5 ! pr$ictions 7 fir/ made1 b h subsequ5tly be5 fully confirm$ by obs]vation4 ,inde$ ! !ory has by n[ qualifi$ z "o ( ! ord9>y work+ tools ( a/ronomy4 ,x has be5 us$ to measure ! diamet] ( ! small fa9t /> ,sirius ,b1 ! companion to ,sirius 7p4 #bfb71 z well z to discuss ! nature ( ! />s at ! c5tres ( ! 8planet>y nebulae0 7p4 #cbc74 ,nev]!less1 ! g5]al !ory ( relativity does n lead up to ,e9/e9's cosmology 9 a unique way4 ,x is p]fectly possible = ! =m] to be true & ! latt] false4 ,! g5]al !ory ( relativity fixes ! attributes ( any small fraction ( ! univ]se q def9itely1 b leaves op5 sev]al alt]native ways 9 :i* ^! small fractions c be piec$ toge!r to =m a :ole4 ,e9/e9's p>ticul> view ( ! cosmos _c !re=e claim ! pre/ige :i* atta*es to ! g5]al !ory ( relativity z a :ole4 ,& inde$ = "s ye>s x fell some:at into disfav\r1 & appe>$ likely to be sup]s$$ by an alt]native cosmology :i* de ,sitt] ( ,leid5 prop\nd$ & develop$ 9 "s detail 9 #aiag4 ,,! ,,cosmology ,,( ,,de ,,sitt]4 ,let u fir/ try to und]/& ! ess5tial diff]5ces betwe5 ^! two cosmologies4 ,e9/e9's cosmology supposes t ! size ( ! cosmos is det]m9$ by ! am\nt ( matt] x conta9s4 ,if x 0 decid$1 at ! creation1 to create a univ]se conta9+ a c]ta9 am\nt ( matt] :i* 0 to obey c]ta9 natural laws1 !n space mu/ at once h adju/$ itself to ! size suit$ = conta9+ j ?is am\nt ( matt] & no m4 ,or1 if ! size ( ! univ]se & ! natural laws 7 decid$ ^u1 ! creation ( a c]ta9 def9ite am\nt ( matt] became an inevitable necessity4 ,de ,sitt]'s univ]se is less simple1 or1 if we pref] s to put x1 all[$ m fre$om ( *oice 9 its creation4 ,aft] ! laws ( nature _h be5 fix$1 x 0 /ill possible to make a univ]se ( any size1 & to put any am\nt ( matt]1 )9 limits1 into x4 ,look$ at f ! /rictly sci5tific po9t ( view1 ,e9/e9's univ]se has "o elem5t ( arbitr>9ess few] ?an de ,sitt]'s univ]se1 & to ?is ext5t x has ! advantage ( simplicity4 ,on ! o!r h& ?is simplicity is acquir$ at a price4 ,! fundam5tal corn]-/one ( ! :ole !ory ( relativity is ! equal p>tn]%ip ( space & "t 9 ! s5se already expla9$4 ,e9/e9's cosmology ga9s its simplicity only at ! exp5se ( suppos+ t ?is equality ( p>tn]%ip disappe>s :5 we view ! cosmos z a :ole4 ,x supposes t space & "t are indi/+ui%able 79 ! purely =mal s5se already indicat$7 only to a be+ ^: exp]i5ce is limit$ to a small fraction ( ! univ]se2 !y become utt]ly di/9ct = a be+ :o c range ?r\gh ! :ole ( space & "t4 ,x is n altoge!r cle> h[ mu* weight ought to be atta*$ to ?is objection1 if objection x is4 ,real space & real "t und\bt$ly are di/9ct4 ,ev5 if we d5y ! reality ( bo?1 !y /ill rema9 di/+ui%able z modes ( p]ception4 ,:at reproa*1 !n1 c x be to a cosmology t x admits t1 9 ! la/ resort1 :5 ! univ]se is contemplat$ on ! gr& scale1 space & "t resolve !mselves into di/9ct types ( entity8 ,someh[ we knew x already1 be=e ev] we began to contemplate ! univ]se on ! gr& scale4 ,:atev] ! answ] to ?is la/ "q may be1 de ,sitt]'s cosmology avoids all possible reproa* by ma9ta9+ ! equal p>tn]%ip ( space & "t1 n only 9 individual fractions ( ! cosmos1 b ?r\gh\t ! cosmos z a :ole4 ,x w ( c\rse be und]/ood t we are /ill speak+ ( equal p>tn]%ip 9 ! purely =mal s5se already expla9$1 a light-ye> ent]+ ! cosmology on ! same foot+ z ! squ>e-root ( -#a ye>s4 ,ev5 de ,sitt]'s cosmology does n pret5d t a light-ye> 7#idf million million kilometres7 is ! same ?+ z twelve mon?s4 ,al?\gh ,e9/e9's ma9 !ory ( relativity has be5 amply confirm$ by obs]vation1 ! cosmological "p ( x did n pr$ict any special features su* z p]mitt$ ( a direct obs]vational te/4 ,de ,sitt]'s cosmology1 on ! o!r h&1 pr$ict$ t ! spectra ( all di/ant objects mu/ %ew a displacem5t t[>ds ! r$1 ( am\nt dep5d+ on ! di/ance ( ! object4 ,! equal p>tn]%ip ( space & "t results 9 ! vibrations ( ! light-waves emitt$ by any specifi$ s\rce be+ sl[] 9 di/ant ?an 9 ne> p>ts ( ! univ]se2 ! /ream ( "t rolls m rapidly j :]e we happ5 to be ?an any:]e else4 ,?is s\nds p>adoxical at fir/1 b exam9ation %ews t x is n2 de ,sitt] is n ask+ u to return to a geoc5tric univ]se1 because he %ews t ! inhabitant ( a di/ant /> w\ld also f9d t t]re/rial atoms 7 keep+ sl[] "t ?an 8 own4 ,! p>adox is completely resolv$ by ! concept ( ! relativity ( all measures ( space & "t4 ,?is displacem5t to ! r$ z a result ( m]e di/ance is peculi> to de ,sitt]'s cosmology4 ,x is additional to ! displacem5t :i*1 z all cosmologies agree1 ! spectrum ( a mov+ body mu/ %ew z ! result ( its motion1 ?is latt] be+ t[>ds ! r$ only if ! body is rec$+ f ! e>? 7p4 #ea74 ,on de ,sitt]'s cosmology1 ! two displacem5ts are n entirely indep5d5t1 = x is an ess5tial feature ( ?is cosmology t ne> bodies %\ld t5d to move fur!r ap>t f "o ano!r4 ,j z bits ( /raw ?r[n toge!r into a /ream t5d to get sep>at$ z !y float d[n ! /ream1 s objects 9 de ,sitt]'s univ]se move fur!r ap>t z !y float d[n ! /ream ( "t4 ,?us on de ,sitt]'s !ory a displacem5t ( spectral l9es to ! r$ _c be int]pret$ z evid5ce ei!r ( motion or ( di/ance2 x is a mixture ( bo?4 ,?is does n mean t we h be5 altoge!r wrong 9 d$uc+ ! velocities ( />s 9 ! galactic sy/em f ! obs]v$ displacem5ts ( _! spectral l9es4 ,no appreciable displacem5t is produc$ by di/ance alone1 unless ?is di/ance =ms an appreciable fraction ( ! radius ( ! univ]se4 ,sy/ematic displacem5ts to ! r$ are1 x is true1 obs]v$ 9 ! spectra ( ! mo/ di/ant />s1 b !y are ( v small am\nt4 ,x is only :5 we look to ! remote extra-galactic nebulae t we c expect to obs]ve ! effect 9 appreciable /r5g?4 ,n[ x has long be5 "o ( ! out/&+ puzzles ( a/ronomy t ! spectra ( ! di/ant nebulae are uni=mly displac$ t[>ds ! r$4 ,! obs]v$ displacem5ts are n small4 ,int]pret$ z velocities1 _m ( !m w\ld repres5t spe$s ( ov] #ajjj miles a second4 ,humason has f\nd t two fa9t nebulae ,n4,g4,c4 #dhfj & #dhec %ew app>5t spe$s ( recession ( #dijj & #dfjj miles a second respectively4 ,!y are bo? memb]s ( a cl\d ( nebulae 9 ,coma ,b]5ices 7p4 #gb71 :i* is probably at a di/ance ( ab\t #ej million light-ye>s4 ,q rec5tly ! spectrum ( ano!r v fa9t nebula 9 ,ursa ,major has be5 f\nd to indicate an app>5t motion ( recession ) a spe$ ( #gbjj miles a second4 ,if de ,sitt]'s !ory is reject$1 almo/ all ! extra-galactic nebulae mu/ be runn+ away f u ) t]rific1 almo/ unimag9able1 spe$s4 ,& ! fur!r away !y are ! m precipitately !y are increas+ _! di/ance4 ,yet we c h>dly re9troduce simplicity by adopt+ de ,sitt]'s !ory1 & treat+ ! :ole app>5t /amp$e ( nebulae z spuri\s1 s9ce ?is !ory involves t ! nebulae may well1 9 actual fact1 be runn+ away f u1 scatt]+ be+ an inh]5t prop]ty ( objects 9 a de ,sitt] univ]se4 ,! fact t ! spectra ( ! mo/ di/ant nebulae %ew ^! l>ge displacem5ts provides a c]ta9 presumption 9 fav\r ( ! tru? ( de ,sitt]'s cosmology2 ?is at lea/ expla9s !m twice ov]1 :ile no o!r cosmology expla9s !m at all4 ,if we t5tatively accept ?is cosmology1 !n ea* obs]v$ spectral %ift mu/ be reg>d$ z ! sum ( two p>ts1 "o aris+ 9 ! ord9>y way f a recession ( ! nebula1 & ! o!r aris+ m]ely f its di/ance4 ,a prelim9>y /udy by ,dr ,hubble has %ewn t on ! :ole ! spectral displacem5ts are l>ge/ = ! mo/ di/ant nebulae1 & t _! am\nts are r\ghly proportional to ! di/ances ( ! nebulae f u4 ,if we int]pret ! :ole ( ! obs]v$ displacem5ts purely z evid5ce ( recession1 we c calculate t ! radius ( ! univ]se is ab\t #bjjj million light-ye>s1 or "s f\rte5 times ! di/ance ( ! fur!/ visible nebula4 ,) s l>ge a radius ( ! univ]se1 ! fur!r displacem5t result+ f ! m]e di/ance ( ev5 remote nebulae is negligible1 s t our assumption t ! displacem5ts arise almo/ entirely f velocities ( recession receives po/]iori v9dication4 ,if ! obs]v$ displacem5ts ( ! nebul> spectra _h be5 /rictly proportional to _! di/ances f u1 we %\ld h obta9$ a consi/5t explanation ( ! obs]v$ facts by assum+ t we liv$ 9 a de ,sitt] univ]se hav+ a radius ( ab\t #bjjj million light-ye>s4 ,,! ,,exp&+ ,,univ]se4 ,x us$ to be ?\ght t ! cosmologies ( ,e9/e9 & de ,sitt] 7 antagoni/ic to "o ano!r1 s9ce obvi\sly no "o univ]se c\ld be an ,e9/e9 univ]se & a de ,sitt] univ]se at ! same "t4 ,a rec5t inve/igation by a ,belgian ma!matician1 ! ,abb ,g4 ,lematre1 has put a diff]5t complexion on ! problem4 ,9 brief ,lematre has %ewn t no univ]se c\ld /ay p]man5tly 9 ! /ate consid]$ by ,e9/e94 ,a univ]se 9 ?is /ate is an un/able /ructure2 imm$iately x came into be+ x w\ld />t to exp&1 & w\ld n cease f exp&+ until x _h become a de ,sitt] univ]se4 ,ev5 aft] ?is ! expansion w\ld cont9ue1 b x w\ld n[ become m]g$ 9 ! normal expansion ( ! de ,sitt] univ]se1 su* z we h already consid]$4 ,9 ! light ( ^! results1 ! "q at issue is n :e!r our univ]se is an ,e9/e9 univ]se or a de ,sitt] univ]se1 b r h[ f> x has travell$ along ! road :i* beg9s ) an ,e9/e9 univ]se & ends ) a de ,sitt] univ]se4 ,:atev] ! answ] may be1 we are l$ to suppose t at ! beg9n+ ( "t ! nebulae 7 mu* ne>] to "o ano!r ?an !y n[ are1 t ev] s9ce !n !y h obey$ _! inh]5t t5d5cy to scatt]1 or r ! t5d5cy ( ! fl[+ /ream ( "t to scatt] !m1 & t !y are n[ mov+ away f u1 & f "o ano!r1 ) spe$s :i* are proportional to _! di/ances4 ,?is is 9 accordance ) ,hubble's conclusion1 t ! app>5t spe$s ( recession ( ! nebulae are r\ghly proportional to _! di/ances4 ,f ,hubble's data ,edd+ton has calculat$ t ! orig9al ,e9/e9 univ]se mu/ h _h a radius ( ab\t #abjj million light-ye>s4 ,if ! app>5t spe$s ( recession ( ! nebulae _h be5 f\nd to be /rictly proportional to _! di/ances1 we c\ld h expla9$ ev]y?+ by suppos+ t we liv$ 9 an exp&+ univ]se1 :i* _h />t$ z an ,e9/e9 univ]se ( #abjj million light-ye>s' radius1 _h n[ exp&$ to some?+ ( ! ord] ( #bjjj million light-ye>s' radius1 & 0 de/9$ to g on exp&+ to all et]nity4 ,?is provides a simple & r fasc9at+ picture ( ! univ]se1 b !re are _m reasons aga9/ suppos+ t x is a true "o4 ,9 ! fir/ place1 if we int]pret ! spectral displacem5ts z evid5ce ( velocity alone1 ! spe$s ( ! nebulae are probably v f> f be+ 7z ! =ego+ picture w\ld require7 accurately proportional to _! di/ances f u4 ,a gr\p ( ?ree nebulae1 all believ$ to be at ! same di/ance ( ab\t #ej million light-ye>s1 diff] by ne>ly #bjjj miles a second 9 _! spe$s1 :i* av]age ab\t #ejjj miles a second4 ,oort has f\nd a g5]al t5d5cy = ! spe$s ( v di/ant nebulae n to be /rictly proportional to _! di/ances4 ,at f #bj to #dj million light-ye>s ! app>5t div]g5ces av]age #gej miles a second1 b x is n cle> h[ f> ^! result m]ely f inaccurate e/imates ( ! di/ances ( ^! remote nebulae4 ,9 ! second place1 if ! obs]v$ spectral %ifts repres5t m]e scatt]+1 we c calculate ! "t s9ce ?is scatt]+ began2 x proves to be _m ?\s&s ( millions ( ye>s4 ,enorm\s ?\gh su* a l5g? ( "t is1 x does n appe> to be en\gh4 ,we %all see lat] 7,*apt] ,,iii7 h[ "t leaves its m>k1 its wr9kles & its grey hairs1 on ! />s1 s t we c guess _! ages tol]ably well1 & ! evid5ce is all 9 fav\r ( /ell> lives1 n ( ?\s&s ( millions1 b ( millions ( millions1 ( ye>s4 ,if ! nebulae owe _! pres5t motions to m]e scatt]+1 !n ! />s mu/ h liv$ ! great] p>ts ( _! lives be=e ?is scatt]+ began4 ,su* a hypo!sis seems too artificial = acceptance1 at any rate s long z any alt]native is op54 ,( c\rse we mu/ frankly admit t our e/imates ( /ell> ages may be f\nd to ne$ revision4 ,inde$ !y h be5 calculat$ on ! supposition t no appreciable scatt]+ ( ! type requir$ by de ,sitt]'s cosmology has ev] tak5 place4 ,if n only ! nebulae1 b also ! />s compos+ ! galactic sy/em1 7 huddl$ toge!r at ! beg9n+ ( "t1 our e/imates ( ! lives ( ! />s w\ld h to be sub/antially %ort5$1 & x is conceivable1 al?\gh ,i ?9k v unlikely1 t !y c\ld be r$uc$ to l5g?s ( ! k9d we h j consid]$2 !y c]ta9ly c\ld n be s r$uc$ if ! orig9al univ]se _h a radius any:]e ne> to ,edd+ton's e/imate ( #abjj million light-ye>s4 ,nev]!less ! cosmologies ( de ,sitt] & ,lematre und\bt$ly require t ! pres5t-day univ]se mu/ be exp&+1 t ! nebulae mu/ be retreat+ bo? f "o ano!r1 & f u1 & t _! spectra mu/1 z a consequ5ce1 %ew displacem5ts to ! r$4 ,b !re is no?+ to compel u to id5tify ^! displacem5ts ) ^? actually obs]v$4 ,_m causes1 o!r ?an motions ( recession1 are capable ( r$d5+ spectral l9es1 & only aft] we h d$uct$ all ! r$d5+ due to ^! v>i\s o!r causes %all we be 9 a position to say t ! residue repres5ts a true motion ( recession4 ,q rec5tly ,dr ,zwicky ( ,pasad5a has sugge/$ t gravitat+ matt] diffus$ ?r\gh space may r$d5 all light :i* passes ?r\gh ! space4 ,he gives dynamical reasons = 8 sugge/ion1 calculates ! am\nt ( spectral %ift to be anticipat$ 9 ! light rea*+ u f ! nebulae1 & f9ds t x w\ld acc\nt = practically ! :ole ( ! obs]v$ %ift4 ,x is possible t ! great] "p ( ! obs]v$ r$d5+ ( nebul> light may be due to ?is or "s simil> cause1 only a small fraction repres5t+ true motions ( recession4 ,if s1 we c ext5d ! age ( ! univ]se indef9itely1 & are free to assign to ! />s ! v great ages :i* ! evid5ce ( g5]al a/ronomy seems to dem&4 ,?is we %all discuss fully 9 ,*apt] ,,iii4 ,9 de ,sitt]'s orig9al =m ( ?is cosmology1 light w\ld take an inf9ite "t to travel r\nd ! univ]se1 & ?is w\ld prev5t any object be+ se5 by light :i* _h travell$ ! long way r\nd4 ,?is results f de ,sitt] hav+ consid]$ only ! ideal case ( a univ]se entirely empty ( all matt]4 ,) ev5 a little matt] 9 ! univ]se1 ! pa? ( a ray ( light w\ld presumably b5d back on itself & return to its />t+ po9t aft] a f9ite "t4 ,x has be5 q s]i\sly sugge/$ t two fa9t nebulae 7h #cdcc & ,m #hc7 may actually be our two ne>e/ neighb\rs 9 ! sky1 ,m #cc & ,m #ca1 se5 ! long way r\nd space4 ,if s1 we see ! fronts ( two objects :5 we look at ,m #cc & ,m #ca1 & ! backs ( ! same two objects :5 we po9t our telescopes 9 exactly ! opposite directions & look at h #cdcc & ,m #hc4 ,no d\bt ?is is only a conjecture1 & p]haps r a wild "o1 b _m m />tl+ conjectures h be5 made 9 a/ronomy1 & subsequ5tly prov$ to be true4 ,all ^! discussions ( ! /ructure ( space are ( c\rse highly speculative1 b !y agree 9 sugge/+ ! g5]al conclusion t1 if we _c yet see ! :ole ( space1 we c at lea/ survey an appreciable fraction ( x4 ,our a/ronom]-explor]s may n z yet h circumnavigat$ ! globe1 b !y are p]haps discov]+ ,am]ica1 & we c well imag9e t ev5 ! next g5]ation w h complet$ ! circumnavigation ( space1 & w ?9k ( a f9ite b unb\nd$ space 9 ! same way1 & ) ! same ease1 z we ?9k ( ! f9ite b unb\nd$ surface ( ! e>?4 ,a ,,model ,,( ,,! ,,univ]se ,we f\nd x difficult en\gh to visualise ! #d light-ye>s :i* con/itute ! di/ance to ! ne>e/ />1 s we may be well advis$ n ev5 to attempt to visualise ?is la/ di/ance ( ?\s&s ( millions ( light-ye>s1 ! conjectur$ circumf]5ce ( ! univ]se4 ,yet we may try to see all ^! di/ances 9 prop] proportion relative to "o ano!r by ! help ( a model drawn to scale4 ,we c escape ! ef=t ( try+ to imag9e unimag9ably great di/ances by keep+ ! scale v small4 ,! e>?1 travell+ #abjj times fa/] ?an an express tra91 makes a j\rney ( #fjj million miles ar\nd ! sun e ye>4 ,let u repres5t ?is j\rney by a p9-head _/ ( an in* 9 diamet]4 ,?is fixes ! scale ( our model2 ! sun has %runk to a m9ute speck ( du/ _/ ( an in* 9 diamet]1 :ile ! e>? is a /ill m m9ute speck :i* is too small to be se5 at all ev5 9 ! mo/ p[]ful ( microscopes4 ,on ?is scale ! ne>e/ /> 9 ! sky1 ,proxima ,c5tauri1 mu/ be plac$ ab\t #bbe y>ds away1 & to conta9 ev5 ! hundr$ />s ne>e/ to our sun 9 space1 ! model mu/ be a mile high1 a mile long & a mile wide4 ,let u g on build+ ! model4 ,we may ?9k ( />s indiscrim9ately z specks ( du/1 because _! sizes v>y ab\t z mu* z ! sizes ( specks ( du/4 ,9 ! vic9ity ( ! sun we mu/ place specks ( du/ at av]age di/ances ( ab\t a qu>t] ( a mile ap>t4 ,9 o!r regions ( space !y are g5]ally ev5 f>!r ap>t1 =1 ow+ to ! pres5ce ( ! 8local clu/]10 ! imm$iate neighb\rhood ( ! sun happ5s to be a r cr[d$ "p ( ! sky4 ,we g on build+ ! model = hundr$s ( miles 9 e direction1 & !n1 if we are build+ 9 a direction well away f ! galactic plane1 ! specks ( du/ beg9 to ?9 out2 we are approa*+ ! conf9es ( ! galaxy4 ,9 ! galactic plane itself we build out = ab\t #gjjj miles be=e we come to ! f>!/ globul> clu/]1 & /ill we are inside ! galactic sy/em4 ,) our e>?'s long ye>ly j\rney r\nd ! sun z a p9-head ! :ole galactic sy/em is ab\t ! size ( ! ,am]ican cont95t4 ,x may be well to pause & try to visualise ! relative sizes ( a p9-head & ( ! ,am]ican cont95t1 be=e we g on ) our m5tal model-build+4 ,aft] we h f9i%$ ! galactic sy/em1 we mu/ travel ab\t #cj1jjj miles be=e we beg9 to set up ! next bit ( our model1 at any rate if we are keep+ x to scale4 ,at ?is di/ance we place ! next family ( />s1 a family :i* is probably sub/antially small] & m compact ?an our own galactic family1 b is comp>able ) x bo? 9 size & 9 numb]s4 ,s we g on build+ our model--a family ( ?\s&s ( millions ( />s e #cj1jjj miles or s--until we h two million su* families4 ,! model n[ /ret*es = ab\t f\r million miles 9 e direction4 ,?is repres5ts z f> z we c see into space ) a telescope2 we c imag9e ! model go+ on1 al?\gh we "k n h[ nor :]e--all we "k is t ! "p s f> built repres5ts only a fraction ( ! univ]se4 ,e galactic sy/em or isl& univ]se or extra-galactic nebula conta9s ?\s&s ( millions ( />s1 or gase\s matt] de/9$ ultimately to =m ?\s&s ( millions ( />s1 & we "k ( two million su* sy/ems4 ,!re are1 !n1 ?\s&s ( millions ( millions ( />s )9 ! range cov]$ by ! #ajj-;in* telescope1 & ?is numb] mu/ be fur!r multipli$ to all[ = ! p>ts ( ! univ]se :i* are /ill unexplor$4 ,at a mod]ate computation1 ! total numb] ( />s 9 ! univ]se mu/ be some?+ l ! total numb] ( specks ( du/ 9 ,london4 ,?9k ( ! sun z some?+ less ?an a s+le speck ( du/ 9 a va/ city1 ( ! e>? z less ?an a million? "p ( su* a speck ( du/1 & we h p]haps z vivid a picture z ! m9d c really grasp ( ! relation ( our home 9 space to ! re/ ( ! univ]se4 ,an alt]native proc$ure w\ld h be5 to con/ruct our scale-model by tak+ all ! specks ( du/ 9 ,london & spread+ !m out to ! "r di/ances to repres5t ! v>i\s />s 9 space4 ,! av]age actual di/ances betwe5 specks ( du/ 9 ,london is a q small fraction ( an in*2 to get our model to correct scale1 ?is di/ance mu/ be increas$ to ab\t a qu>t] ( a mile1 ev5 :5 we are build+ ! "p :i* repres5ts ! cr[d$ "p ( space r\nd ! sun4 ,if we build our model 9 ?is way1 we obta9 a vivid picture ( ! empt9ess ( space4 ,empty ,wat]loo ,/ation ( ev]y?+ except six specks ( du/1 & x is /ill f> m cr[d$ ) du/ ?an space is ) />s4 ,?is is true ev5 ( ! comp>atively cr[d$ region inside ! galactic sy/em2 x takes no acc\nt ( ! imm5se empty /ret*es betwe5 "o sy/em ( />s & ! next4 ,on av]ag+ ?r\gh\t ! :ole ( ! model1 ! mean di/ance ( a speck ( du/ f its ne>e/ neighb\r proves to be some?+ l #hj miles4 ,! univ]se consi/s 9 ! ma9 n ( />s b ( desolate empt9ess--inconceivably va/ /ret*es ( des]t space 9 :i* ! pres5ce ( a /> is a r>e & exceptional ev5t4 ,let u 9 imag9ation take up a position 9 space some:]e ne> ! sun1 & wat* ! />s mov+ pa/ ) spe$s ab\t #ajjj times t ( an express tra94 ,if space 7 really cr[d$ ) />s our position w\ld be z un5viable z if we sat d[n 9 ! middle ( ,reg5t ,/reet to wat* ! traffic g by--our life1 ?\gh ?rill+1 w\ld be brief4 ,yet1 z exact calculation %ews1 ! /ell> traffic is s little cr[d$ t we w\ld h to wait ab\t a million million million ye>s be=e a /> ran into u4 ,put 9 ano!r =m1 ! calculation %ews t any "o /> may expect to move = some?+ ( ! ord] ( a million million million ye>s be=e collid+ ) a second />4 ,! />s move bl9dly ?r\gh space1 & ! play]s 9 ! /ell> bl9d-man's-buff are s few & f> betwe5 t ! *ance ( enc\nt]+ ano!r /> is almo/ negligible4 ,we %all see lat] t ?is concept is ( ! pr(\nde/ significance 9 our int]pretation ( ! univ]se4 ,,*apt] ,,ii ,explor+ ! ,atom ,s f> our exploration ( ! univ]se has be5 9 ! direction f man to bigg] ?+s ?an man2 we h be5 explor+ ranges ( space :i* dw>f man & 8 home 9 space into utt] insignificance4 ,yet we h explor$ only ab\t half ! total range ( ! univ]se2 an almo/ equal range awaits exploration 9 ! direction ( ! inf9itely small4 ,we appreciate only half ( ! inf9ite ri*ness ( ! _w ar\nd u until we ext5d our survey d[n to ! smalle/ units ( matt]4 ,?is survey has be5 fir/ ! task1 & n[ ! brilliant a*ievem5t1 ( mod]n physics4 ,x may p]haps be ask$ :y an acc\nt ( mod]n a/ronomy %\ld conc]n itself ) ?is o!r end ( ! univ]se4 ,! answ] is t ! />s are some?+ m ?an huge in]t masses2 !y are ma*9es 9 action1 g5]at+ & emitt+ ! radiation by :i* we see !m4 ,we %all be/ und]/& _! me*anism by /udy+ ! ways 9 :i* radiation is g5]at$ & emitt$ on e>?1 & ?is takes u "r into ! he>t ( mod]n atomic physics4 ,9 ! pres5t book we naturally _c attempt to cov] ! :ole ( ?is new field ( k2 we %all conc]n ourselves only ) ^? p>ts :i* are important = ! int]pretation ( a/ronomical results4 ,,atomic ,,!ory ,z f> back z ! fif? c5tury be=e ,*ri/1 ,greek philosophy 0 greatly ex]cis$ by ! "q ( :e!r 9 ! la/ resort ! ultimate sub/ance ( ! univ]se 0 cont9u\s or discont9u\s4 ,we /& on ! sea-%ore1 & all ar\nd u see /ret*es ( s& :i* appe> at fir/ to be cont9u\s 9 /ructure1 b :i* a clos] exam9ation %ews to consi/ ( sep>ate h>d p>ticles or gra9s4 ,9 front rolls ! ocean1 :i* also appe>s at fir/ to be cont9u\s 9 /ructure1 & ?is we f9d we _c divide into gra9s or p>ticles no matt] h[ we try4 ,we c divide x into drops1 b !n ea* drop c be subdivid$ into small] drops1 & !re seems to be no reason1 on ! face ( ?+s1 :y ?is process ( subdivision %\ld n be cont9u$ = ev]4 ,! "q :i* agitat$ ! ,greek philosoph]s 01 9 effect1 :e!r ! wat] ( ! ocean or ! s& ( ! sea-%ore gave ! true/ picture ( ! ultimate /ructure ( ! sub/ance ( ! univ]se4 ,! s*ool ( ,democritus1 ,leucippus & ,lucretius believ$ 9 ! ultimate discont9uity ( matt]2 !y taught t any sub/ance1 aft] x _h be5 subdivid$ a suffici5t numb] ( times1 w\ld be f\nd to consi/ ( h>d discrete p>ticles :i* did n admit ( fur!r subdivision4 ,= !m ! s& gave a bett] picture ( ultimate /ructure ?an ! wat]1 because1 or s !y ?\ght1 suffici5t subdivision w\ld cause ! wat] to display ! granul> prop]ties ( s&4 ,& ?is intuitional conjecture is amply confirm$ by mod]n sci5ce4 ,! "q is1 9 effect1 settl$ z soon z a ?9 lay] ( a sub/ance is f\nd to %ew qualities ess5tially diff]5t f ^? ( a slightly ?ick] lay]4 ,a lay] ( yell[ s& swept uni=mly ov] a r$ floor w make ! :ole floor appe> yell[ if !re is en\gh s& to make a lay] at lea/ "o gra9 ?ick4 ,if1 h[ev]1 !re is only half ?is mu* s&1 ! r$ness ( ! floor inevitably %ews ?r\gh2 x is impossible to spread s& 9 a uni=m lay] only half a gra9 ?ick4 ,?is sudd5 *ange 9 ! prop]ties ( a lay] ( s& is ( c\rse a consequ5ce ( ! granul> /ructure ( s&4 ,simil> *anges are f\nd to occur 9 ! prop]ties ( ?9 lay]s ( liquid4 ,a teaspoonful ( s\p w cov] ! bottom ( a s\p plate1 b a s+le drop ( s\p w only make an untidy spla%4 ,9 "s cases x is possible to measure ! exact ?ickness ( lay] at :i* ! prop]ties ( liquids beg9 to *ange4 ,9 #ahij ,"l ,rayleigh f\nd t ?9 films ( olive oil float+ on wat] *ang$ _! prop]ties entirely z soon z ! ?ickness ( ! film 0 r$uc$ to bel[ a million? ( a millimetre 7or a #be1jjj1jjj? "p ( an in*74 ,! obvi\s int]pretation1 :i* is confirm$ 9 innum]able ways1 is t olive oil consi/s ( discrete p>ticles--analog\s to ! 8gra9s0 9 a pile ( s&--ea* hav+ a diamet] some:]e 9 ! neighb\rhood ( a #be1jjj1jjj? "p ( an in*4 ,e sub/ance consi/s ( su* 8gra9s40 ,!y are call$ molecules1 & ! famili> prop]ties ( matt] are ^? ( lay]s _m molecules ?ick2 ! prop]ties ( lay]s less ?an a s+le molecule ?ick are kn[n only to ! physici/ 9 8 laboratory4 ,,molecules ,h[ are we to break up a piece ( sub/ance into its ultimate gra9s1 or molecules8 ,x is easy = ! sci5ti/ to say t1 by subdivid+ wat] = long en\gh1 we %all come to gra9s :i* _c be subdivid$ any fur!r2 ! pla9 man w\ld l to see x done4 ,=tunately ! process is "o ( extreme simplicity4 ,take a glass ( wat]1 apply g5tle heat und]nea?1 & ! wat] beg9s to evaporate4 ,:at does ?is mean8 ,x means t ! wat] is be+ brok5 up into its sep>ate ultimate gra9s or molecules4 ,if ! glass ( wat] c\ld be plac$ on a suffici5tly s5sitive spr+ balance1 we %\ld see t ! process ( evaporation does n proce$ cont9u\sly1 lay] aft] lay]1 b j]kily1 molecule by molecule4 ,we %\ld f9d ! weight ( ! wat] *ang+ by jumps1 ea* jump repres5t+ ! weight ( a s+le molecule4 ,! glass may conta9 any integral numb] ( molecules b nev] fractional numb]s--if ! fractions ( a molecule exi/1 at any rate !y d n come into play 9 ! evaporation ( a glass ( wat]4 ,,! ,,gase\s ,,/ate4 ,! molecules :i* break loose f ! surface ( ! wat] z x evaporates =m a gas--wat]-vap\r or /eam4 ,a gas consi/s ( a va/ numb] ( molecules :i* fly ab\t entirely indep5d5tly ( "o ano!r1 except at ! r>e in/ants at :i* two collide1 & s int]f]e ) ea* o!r's motion4 ,! ext5t to :i* ! molecules int]f]e ) "o ano!r mu/ obvi\sly dep5d on _! sizes2 ! l>g] !y are1 ! m frequ5t _! collisions w be1 & ! m !y w int]f]e ) "o ano!r's motion4 ,actually ! ext5t ( ?is int]f]5ce provides ! be/ means ( e/imat+ ! sizes ( molecules4 ,!y prove to be exce$+ly small1 be+ = ! mo/ "p ab\t a hundr$-million? ( an in* 9 diamet]1 &1 z a g5]al rule1 ! simpl] molecules h ! small] diamet]s1 z we %\ld expect4 ,! molecule ( wat] has a diamet] ( #ah hundr$-million?s ( an in* 7#df #aj cms471 :ile t ( ! simpl] hydrog5 molecule is only j ov] a hundr$-million? ( an in* 7#bg #aj cms474 ,! fact t a numb] ( diff]5t l9es ( inve/igation all attribute ! same diamet]s to ^! molecules provides an excell5t pro( ( ! reality ( _! exi/5ce4 ,z molecules are s exce$+ly small1 !y mu/ also be exce$+ly num]\s4 ,a p9t ( wat] conta9s #ahi #aj molecules1 ea* weigh+ #ajf #aj ounces4 ,if ^! molecules 7 plac$ end to end1 !y w\ld =m a *a9 capable ( encircl+ ! e>? ov] #bjj million times4 ,if !y 7 scatt]$ ov] ! :ole l& surface ( ! e>?1 !re w\ld be ne>ly #ajj million molecules to e squ>e in* ( l&4 ,if we ?9k ( ! molecules z t9y se$s1 ! total am\nt ( se$ ne$$ to s[ ! :ole e>? at ! rate ( #ajj million molecules to ! squ>e in* c\ld be put into a p9t pot4 ,^! molecules move ) v high spe$s2 9 ! ord9>y air ( an ord9>y room1 ! av]age molecul> spe$ is ab\t #ejj y>ds a second4 ,?is is r\ghly ! spe$ ( a rifle-bullet1 & is r m ?an ! ord9>y spe$ ( s\nd4 ,z we are famili> ) ?is latt] spe$ f ev]yday exp]i5ce1 x is easy to =m "s conception ( molecul> spe$s 9 a gas4 ,x is n a m]e accid5t t molecul> spe$s are comp>able ) ! spe$ ( s\nd4 ,s\nd is a di/urbance :i* "o molecule passes on to ano!r :5 x collides ) x1 r l relays ( mess5g]s pass+ a message on to "o ano!r1 or ,greek tor*-be>]s h&+ on _! lights4 ,betwe5 collisions ! message is c>ri$ =w>d at exactly ! spe$ at :i* ! molecules travel4 ,if ^! all travell$ ) precisely ! same spe$ & 9 precisely ! same direction1 ! s\nd w\ld ( c\rse travel ) j ! spe$ ( ! molecules4 ,b _m ( !m travel on oblique c\rses1 s t al?\gh ! av]age spe$ ( individual molecules 9 ord9>y air is ab\t #ejj y>ds a second1 ! net =w>d velocity ( ! s\nd is only ab\t #cgj y>ds a second4 ,at high temp]atures ! molecules may h ev5 great] spe$s2 ! molecules ( /eam 9 a boil] may move at #ajjj y>ds a second4 ,x is ! high spe$ ( molecul> motion t is responsible = ! great pressure ex]t$ by a gas2 any surface 9 contact ) ! gas is expos$ to a hail ( molecules ea* mov+ ) ! spe$ ( a rifle-bullet4 ,= in/ance1 ! pi/on 9 a locomotive cyl9d] is bomb>d$ by ab\t #ad #aj molecules e second4 ,?is incessant fusillade ( innum]able t9y bullets urges ! pi/on =w>d 9 ! cyl9d]1 & s propels ! tra94 ,) ea* brea? we take1 sw>ms ( millions ( millions ( millions ( molecules ent] our bodies1 ea* mov+ at ab\t #ejj y>ds a second1 & no?+ b _! incessant hamm]+ on ! walls ( our lungs keeps our *e/s f collaps+4 ,p]haps ! be/ g5]al m5tal picture we c =m ( a gas is t ( an incessant hail ( %ot or rifle-bullets fly+ indiscrim9ately 9 all directions1 & runn+ into "o ano!r at frequ5t int]vals4 ,9 ord9>y air ea* molecule collides ) "s o!r molecule ab\t #cjjj million times e second1 & travels an av]age di/ance ( ab\t #a_/afj1jjj in* betwe5 successive collisions4 ,if we compress a gas to a great] d5sity1 m molecules are cr[d$ into a giv5 space1 s t collisions become m frequ5t & ! molecules travel %ort] di/ances betwe5 collisions4 ,if1 on ! contr>y1 we r$uce ! pressure ( ! gas1 & s less5 its d5sity1 collisions become less frequ5t & ! di/ance ( travel ( a molecule betwe5 successive collisions--! 8free-pa?0 z x is call$--is increas$4 ,9 ! l[e/ vacua :i* are at pres5t obta9able 9 ! laboratory1 a molecule c travel ov] #ajj y>ds )\t collid+ ) any o!r molecule1 al?\gh !re are /ill #fjj1jjj million molecules to ! cubic in*4 ,"u a/ronomical conditions /ill l[] vacua may occur4 ,9 "s nebulae molecules ( gas may travel millions ( miles )\t a collision1 s few are ! molecules to a giv5 volume ( space4 ,x might be ?\ght t ! fly+ molecules w\ld soon be br\ght to re/ by _! collisions2 rifle-bullets und\bt$ly w\ld1 b n ! molecule bullets ( a gas1 = reasons n[ to be expla9$4 ,,en]gy4 ,! am\nt ( ! *>ge ( p[d] us$ to fire a rifle-bullet gives a measure ( ! 8en]gy ( motion0 :i* is imp>t$ to ! bullet4 ,to fire a bullet ( d\ble weight requires twice z mu* p[d]1 because ! en]gy ( motion ( a bullet1 or inde$ ( any o!r mov+ body1 is proportional to its weight4 ,b to fire ! same bullet ) d\ble spe$ does n m]ely require d\ble ! *>ge ( p[d]4 ,f\r times z mu* p[d] is ne$$1 because ! en]gy ( motion ( a mov+ body is proportional to ! squ>e ( its spe$4 ,! exp]i5c$ motori/ is famili> ) ?is2 if our brakes /op our c> 9 #bj feet :5 we are travell+ #bj miles an h\r1 !y w n /op x 9 #dj feet :5 travell+ at #dj miles an h\r2 we ne$ #hj feet4 ,d\ble spe$ requires f\r times ! di/ance to pull up 91 because d\ble spe$ repres5ts f\rfold en]gy ( motion4 ,9 g5]al1 ! en]gy ( motion ( any mov+ body :atev] is proportional bo? to ! weight ( ! body & to ! squ>e ( its spe$#h4 #h ,?is is express$ 9 ! ma!matical =mula mv = ! en]gy ( motion ( a body ( weight m mov+ ) a spe$ v4 ,if m is measur$ 9 grammes1 & v 9 c5timetres p] second1 ! en]gy ( motion ( ! body is said to be mv 8ergs40 ,?us an 8erg0 is ! en]gy ( motion ( a body ( #b grammes weight 7s t m #a7 mov+ ) a spe$ ( "o c5timetre a second4 ,z an example1 ! en]gy ( an express tra9 ( #cjj tons' weight 7#c #aj gms47 mov+ at #fj miles an h\r 7#bfhb cms4 a second7 is #ajgi #aj ergs2 a cannon-ball or %ell weigh+ a ton & mov+ at #aebj feet a second has precisely ! same en]gy4 ,"o ( ! great a*ievem5ts ( n9ete5?-c5tury physics 0 to e/abli% ! g5]al pr9ciple kn[n z ! 8cons]vation ( en]gy40 ,en]gy c exi/ 9 a numb] ( =ms1 & c *ange ab\t almo/ endlessly f "o =m to ano!r1 b x c nev] be utt]ly de/roy$4 ,! en]gy ( a mov+ body is n lo/ :5 ! body is br\ght to re/1 x m]ely takes "s o!r =m4 ,:5 a bullet is br\ght to re/ by hitt+ a t>get1 "p ( its en]gy ( motion goes into heat+ up ! t>get1 & "p into heat+ up1 or p]haps ev5 melt+1 ! bullet4 ,9 its new guise ( heat1 !re is j z mu* en]gy z !re 0 9 ! orig9al motion ( ! bullet4 ,9 accordance ) ! same pr9ciple1 en]gy _c be creat$2 all exi/+ en]gy mu/ h exi/$ f all "t1 al?\gh possibly 9 "s =m entirely diff]5t f its pres5t =m4 ,= in/ance1 gunp[d] conta9s a l>ge am\nt ( en]gy /or$ up 9 ! =m ( *emical en]gy2 we h to take precautions to prev5t ?is bottl$-up en]gy sudd5ly break+ free & do+ damage1 z1 = in/ance1 by explod+ ! vessel 9 :i* x is conta9$1 kick+ ?+s up into ! air1 & s =?4 ,a rifle is 9 effect a device = sett+ free ! en]gy conta9$ 9 a measur$ *>ge ( gunp[d]1 & direct+ z mu* z possible ( x into ! =m ( en]gy ( motion ( a bullet4 ,:5 we fire a bullet at a t>get1 a specifi$ am\nt ( en]gy 7det]m9$ by ! *>ge ( p[d] we h us$7 is trans=m$ f *emical en]gy1 resid+ 9 ! p[d]1 fir/ into en]gy ( motion1 resid+ 9 ! bullet 7& to a m9or degree 9 ! recoil ( ! rifle71 & !n f9ally into heat-en]gy1 resid+ p>tly 9 ! sp5t bullet & p>tly 9 ! t>get4 ,"h we h en]gy tak+ ?ree diff]5t =ms 9 rapid succession4 ,all ! life ( ! univ]se may be reg>d$ z manife/ations ( en]gy masqu]ad+ 9 v>i\s =ms1 & all ! *anges 9 ! univ]se z en]gy runn+ ab\t f "o ( ^! =ms to ! o!r1 b always )\t alt]+ its total am\nt4 ,su* is ! great law ( cons]vation ( en]gy4 ,among ! common] =ms ( en]gy may be m5tion$ electric en]gy1 z exemplifi$ by ! en]gy ( a *>g$ accumulator or ( a ?und]cl\d3 me*anical en]gy1 z exemplifi$ 9 ! coil$ spr+ ( a wat* or ! rais$ weight ( a clock3 *emical en]gy1 z exemplifi$ by ! en]gy /or$ up 9 gunp[d] or 9 coal1 wood & oil3 en]gy ( motion1 z exemplifi$ by ! motion ( a bullet1 & f9ally heat-en]gy1 :i*1 z we h se51 is exemplifi$ by ! heat :i* appe>s :5 ! motion ( a rifle-bullet is *eck$4 ,,heat4 ,let u exam9e fur!r into heat z a possible =m ( en]gy4 ,:5 we want to w>m a room1 we light a fire & set free "s ( ! *emical en]gy :i* is /or$ up 9 coal or wood1 or we turn on an electric heat] & let ! electric curr5t transport to u "s ( ! en]gy :i* is be+ set free by ! burn+ ( coal 9 a di/ant p[]-/ation4 ,b :at1 9 ! la/ resort1 is heat1 & h[ does x come to be a mode ( en]gy8 ,heat1 :e!r ( a gas1 a liquid or a solid1 is m]ely ! en]gy ( motion ( individual molecules4 ,:5 we heat up ! air ( a room we simply make its molecules move fa/]1 & ! total heat ( ! sub/ance is ! total en]gy ( all ! molecules ( :i* x is compos$4 ,9 pump+ up a bicycle tyre1 we drive ! pi/on ( ! pump =w>d 9 opposition to ! impact ( innum]able millions ( molecules ( air inside ! pump4 ,9 kick+ ! oppos+ molecules out ( its way1 ! pi/on increases _! spe$ ( motion4 ,! result+ increase 9 ! en]gy ( motion ( ! molecules is simply an increase ( heat4 ,we c\ld v]ify ?is by ins]t+ a !rmomet]1 or1 /ill m simply1 by putt+ our h& on ! pump2 x feels hot4 ,! molecules ( a solid are n possess$ ( mu* en]gy1 & s d n move v fa/--s sl[ly inde$ t !y seldom *ange _! relative positions1 ! neighb\r+ molecules gripp+ !m s firmly t _! feeble en]gy ( motion _c extricate !m4 ,if we w>m ! solid up1 ! molecules acquire m en]gy1 & s beg9 to move fa/]4 ,aft] a "t !y are mov+ ) su* spe$s t !y c laugh at ! re/ra9+ pulls f _! neighb\rs2 ea* molecule has en\gh en]gy ( motion to g :]e x pleases1 & we h a cr[d ( molecules mov+ freely z indep5d5t units1 jo/l+ "o ano!r & pu%+ _! way pa/ "o ano!r2 ! sub/ance has assum$ ! liquid /ate4 ,to make ! picture def9ite1 ice has melt$ & become wat]2 ! froz5 grip is relax$1 & ! molecules fl[ freely pa/ "o ano!r4 ,ea* /ill ex]ts =ces on its neighb\rs1 b ^! are no long] /rong en\gh to preclude all motion4 ,heat ! liquid fur!r1 ?us fur!r increas+ ! en]gy ( motion ( ! molecules1 & ^! beg9 to break loose entirely f _! bonds & fly ab\t freely 9 space =m+ a gas or vap\r4 ,if we g on supply+ heat1 ! :ole sub/ance w 9 "t assume ! gase\s /ate4 ,heat+ ! gas /ill fur!r m]ely causes ! molecule-bullets to fly fa/]2 x increases _! en]gy ( motion4 ,! av]age en]gy ( motion ( ! molecules 9 a gas is proportional to ! temp]ature ( ! gas--inde$1 ?is is ! way 9 :i* temp]ature is def9$4 ,! temp]ature mu/ n1 h[ev]1 be measur$ on ! ,fahr5heit or ,c5tigrade scale 9 ord9>y use1 b on :at is call$ ! 8absolute0 scale1 :i* has its z]o at -#bgc ,c5tigrade1 or -#dfi ,fahr5heit4 ,?is 8absolute0 z]o1 be+ ! temp]ature ( a body :i* has no fur!r heat to lose1 is ! l[e/ temp]ature possible4 ,we c approa* to )9 ab\t "o degree ( x 9 ! laboratory1 & f9d t x freezes air1 hydrog5 & ev5 helium1 ! mo/ refractory gas ( all1 solid4 ,a !rmomet] plac$ out 9 int]/ell> space1 f> f any />1 w\ld probably %ew a temp]ature ( only ab\t f\r degrees above absolute z]o1 :ile /ill l[] temp]atures mu/ be rea*$ out beyond ! limits ( ! galactic sy/em4 ,,molecul> ,,collisions4 ,we may n[ try to picture a collision betwe5 two molecule-bullets 9 a gas4 ,lead bullets collid+ on a battlefield w\ld probably *ange mo/ ( _! en]gy ( motion into heat-en]gy2 !y w\ld become hott]1 or p]*ance ev5 melt4 ,b h[ c ! molecule-bullets trans=m _! en]gy ( motion into heat-en]gy8 ,= !m heat & en]gy ( motion are n two diff]5t =ms ( en]gy1 !y are "o & ! same ?+2 _! heat is _! en]gy ( motion4 ,! total en]gy mu/ be cons]v$1 & !re is no new disguise t x c assume4 ,s x comes ab\t t :5 two molecule-bullets collide1 ! mo/ t c happ5 is t !y may ex*ange a c]ta9 am\nt ( en]gy ( motion4 ,if _! en]gies ( motion be=e collision 71 say1 #g & #e respectively1 _! en]gies aft] collision may be #f & #f1 or #h & #d1 or #i & #c1 or any o!r comb9ation :i* adds up to #ab4 ,x is ! same at e collision2 en]gy c nei!r be lo/ nor trans=m$1 & s ! bullets on ! molecul> battlefield g on fly+ = ev]1 happily hitt+ only "o ano!r1 & do+ no h>m to "o ano!r :5 !y hit4 ,_! en]gies ( motion g up & d[n1 d[n & up1 accord+ z !y make lucky hits or ! rev]se1 b ! mo/ !y h to fe> are fluctuations & nev] total loss ( en]gy2 _! motion is p]petual4 ,,atoms ,9 ! gase\s /ate1 ea* sep>ate molecule reta9s all ! *emical prop]ties ( ! solid or liquid sub/ance f :i* x orig9at$2 molecules ( /eam1 = in/ance1 moi/5 salt or sug>1 or comb9e ) ?ir/y sub/ances su* z unslak$ lime or potassium *loride1 j z wat] does4 ,is x possible to break up ! molecules /ill fur!r8 ,lucretius & 8 pr$ecessors w\ld1 ( c\rse1 h said3 8,no40 ,a simple exp]im5t1 :i*1 h[ev]1 0 q beyond _! range1 w spe$ily %ew t !y 7 wrong4 ,on slid+ ! two wires ( an ord9>y electric bell circuit into a tumbl] ( wat]1 d[n opposite sides1 bubbles ( gas w be f\nd to collect on ! wires1 & *emical exam9ation %ews t ! two lots ( gas h entirely diff]5t prop]ties4 ,!y _c1 !n1 bo? be wat]-vap\r1 & 9 po9t ( fact nei!r ( !m is2 "o proves to be hydrog5 & ! o!r oxyg54 ,!re is f\nd to be twice z mu* hydrog5 z oxyg51 :5ce we conclude t ! electric curr5t has brok5 up ea* molecule ( wat] into two p>ts ( hydrog5 & "o ( oxyg54 ,^! small] units into :i* a molecule is brok5 are call$ 8atoms40 ,ea* molecule ( wat] consi/s ( two atoms ( hydrog5 7,h7 & "o atom ( oxyg5 7,o72 ?is is express$ 9 its *emical =mula ,h,o4 ,all ! innum]able sub/ances :i* occur on e>?--%oes1 %ips1 seal+-wax1 cabbages1 k+s1 c>p5t]s1 walruses1 oy/]s1 ev]y?+ we c ?9k (--c be analys$ into _! con/itu5t atoms1 ei!r 9 ?is or 9 o!r ways4 ,x might be ?\ght t a q incr$ible numb] ( diff]5t k9ds ( atoms w\ld em]ge f ! ri* v>iety ( sub/ances we f9d on e>?4 ,actually ! numb] is q small4 ,! same atoms turn up aga9 & aga91 & ! great v>iety ( sub/ances we f9d on e>? result1 n f any great v>iety ( atoms ent]+ into _! composition1 b f ! great v>iety ( ways 9 :i* a few types ( atoms c be comb9$--j z 9 a col\r-pr9t ?ree col\rs c be comb9$ s z to =m almo/ all ! col\rs we meet 9 nature1 n to m5tion o!r weird hues su* z nev] 7 on l& or sea4 ,analysis ( all kn[n t]re/rial sub/ances has1 s f>1 reveal$ only #ij diff]5t k9ds ( atoms4 ,probably #ib exi/1 !re be+ reasons = ?9k+ t two1 or possibly ev5 m1 /ill rema9 to be discov]$4 ,ev5 ( ! #ij already kn[n1 ! majority are exce$+ly r>e1 mo/ common sub/ances be+ =m$ out ( ! comb9ations ( ab\t #ad diff]5t atoms1 say hydrog5 7,h71 c>bon 7,c71 nitrog5 7,n71 oxyg5 7,o71 sodium 7,na71 magnesium 7,mg71 alum9ium 7,al71 silicon 7,si71 phosphorus 7,p71 sulphur 7,s71 *lor9e 7,cl71 potassium 7,k71 calcium 7,ca71 & iron 7,fe74 ,9 ?is way1 ! :ole e>?1 ) its endless div]sity ( sub/ances1 is f\nd to be a build+ built ( /&>d bricks--! atoms4 ,& ( ^! only a few types1 ab\t #ad1 occur at all abundantly 9 ! /ructure1 ! o!rs appe>+ b r>ely4 ,,spectroscopy4 ,j z a bell /ruck ) a hamm] emits a *>act]i/ic note1 s e atom put 9 a flame or 9 an electric arc or dis*>ge-tube1 emits a *>act]i/ic light4 ,:5 ,newton pass$ sunlight ?r\gh a prism1 he f\nd x to be a bl5d ( all ! col\rs ( ! ra9b[4 ,9 ! same way ! mod]n spectroscopi/1 ) inf9itely m ref9$ in/rum5ts1 c analyse any light into all ! con/itu5t col\rs :i* ent] into its composition4 ,! ra9b[ ( col\rs s produc$--! 8spectrum0--is cross$ by ! patt]n ( light or d>k l9es or b&s :i* ! a/ronom] utilises to det]m9e ! spe$s ( recession or approa* ( ! />s4 ,f an exam9ation ( ?is patt]n ! skill$ spectroscopi/ c at once ann\nce ! type ( atom f :i* ! light emanates1 s mu* s t "o ( ! mo/ delicate te/s = ! pres5ce ( c]ta9 sub/ances is ! spectroscopic te/4 ,?is spectroscopic me?od ( analysis is by no means conf9$ to t]re/rial sub/ances4 ,9 #ahad ,fraunh(] repeat$ ,newton's analysis ( sunlight1 & f\nd its spectrum to be cross$ by c]ta9 d>k l9es1 /ill kn[n z ,fraunh(] l9es4 ,! spectroscopi/ has no difficulty 9 int]pret+ ^! d>k l9es2 !y indicate ! pres5ce 9 ! sun ( ! common t]re/rial elem5ts1 hydrog51 sodium1 calcium1 & iron4 ,= reasons :i* we %all see lat] 7p4 #abe bel[71 ! atoms ( ^! sub/ances dr9k up ! light ( precisely ^? col\rs :i* ! ,fraunh(] l9es %ew to be abs5t f ! sol> spectrum4 ,?is spectrum is n[ kn[n to be incomp>ably m intricate ?an ,fraunh(] ?\ght1 b practically all ! l9es :i* occur 9 x c be assign$ to atoms kn[n on e>?1 & ! same is true ( ! spectra ( all ! />s 9 ! sky4 ,x is tempt+ to jump to ! g5]alisation t ! :ole univ]se is built solely ( ! #ij or #ib types ( atoms f\nd on e>?1 b at pres5t !re is no ju/ification = ?is4 ,! light we receive f ! sun & />s comes only f ! out]mo/ lay]s ( _! surfaces1 & s conveys no in=mation at all z to ! types ( atoms to be f\nd 9 ! />s' int]iors4 ,inde$ we h no k ( ! types ( atoms :i* occur 9 ! int]ior ( our own e>?4 ,,! ,,/ructure ,,( ,,! ,,atom4 ,until q rec5tly1 atoms 7 reg>d$ z ! p]man5t bricks ( :i* ! :ole univ]se 0 built4 ,all ! *anges ( ! univ]se 7 suppos$ to am\nt to no?+ m dra/ic ?an a re-arrangem5t ( p]man5t inde/ructible atoms2 l a *ild's box ( bricks1 ^! built _m build+s 9 turn4 ,! /ory ( tw5tie?-c5tury physics is prim>ily ! /ory ( ! %att]+ ( ?is concept4 ,x 0 t[>ds ! end ( ! la/ c5tury t ,crookes1 ,l5>d1 &1 above all1 ,sir ,j4 ,j4 ,?omson fir/ began to break up ! atom4 ,! /ructures :i* _h be5 deem$ ! unbreakable bricks ( ! univ]se = m ?an #bjjj ye>s1 7 sudd5ly %[n to be v susceptible to hav+ fragm5ts *ipp$ (f4 ,a mile-/one 0 rea*$ 9 #ahie1 :5 ,?omson %ew$ t ^! fragm5ts 7 id5tical1 no matt] :at type ( atom !y came f2 !y 7 ( equal weight & !y c>ri$ equal *>ges ( negative electricity4 ,on acc\nt ( ?is la/ prop]ty !y 7 call$ 8electrons40 ,! atom _c1 h[ev]1 be built up ( electrons & no?+ else1 = z ea* electron c>ries a negative *>ge ( electricity1 a /ructure :i* consi/$ ( no?+ b electrons w\ld also c>ry a negative *>ge4 ,two negative *>ges ( electricity repel "o ano!r1 z also d two positive *>ges1 :ile two *>ges1 "o ( positive & "o ( negative electricity1 attract "o ano!r4 ,?is makes x easy to det]m9e :e!r any body or /ructure c>ries a positive or a negative *>ge ( electricity1 or no *>ge at all4 ,obs]vation %ews t a complete atom c>ries no *>ge at all1 s t some:]e 9 ! atom !re mu/ be a positive *>ge ( electricity1 ( am\nt j suffici5t to neutralise ! comb9$ negative *>ges ( all ! electrons4 ,9 #aiaa exp]im5ts by ,sir ,erne/ ,ru!r=d & o!rs reveal$ ! ar*itecture ( ! atom4 ,z we %all soon see 7p4 #aab bel[71 nature h]self provides an endless supply ( small p>ticles *>g$ ) positive electricity1 & mov+ ) v high spe$s1 9 ! -p>ticles %ot (f f radio-active sub/ances4 ,ru!r=d's me?od 0 9 brief to fire ^! into atoms & obs]ve ! result4 ,& ! surpris+ result he obta9$ 0 t ! va/ majority ( ^! bullets pass$ /raight ?r\gh ! atom z ?\gh x simply did n exi/4 ,x 0 l %oot+ at a gho/4 ,yet ! atom 0 n all gho/ly4 ,a t9y fraction--p]haps "o 9 #aj1jjj--( ! bullets 7 deflect$ f _! c\rses z if !y _h met some?+ v sub/antial inde$4 ,a ma!matical calculation %ew$ t ^! ob/acles c\ld only be ! miss+ positive *>ges ( ! atoms4 ,a detail$ /udy ( ! pa?s ( ^! projectiles prov$ t ! :ole positive *>ge ( an atom mu/ be conc5trat$ 9 a s+le v small space1 hav+ dim5sions ( ! ord] ( only a million? ( a million? ( an in*4 ,9 ?is way1 ,ru!r=d 0 l$ to prop\nd ! view ( atomic /ructure :i* is g5]ally associat$ ) 8 "n4 ,he suppos$ ! *emical prop]ties & nature ( ! atom to reside 9 a weighty1 b excessively m9ute1 c5tral 8nucleus0 c>ry+ a positive *>ge ( electricity1 ar\nd :i* a numb] ( negatively *>g$ electrons describ$ orbits4 ,x 0 ( c\rse necess>y to suppose ! electrons to be 9 motion 9 ! atom1 o!rwise ! attraction ( positive = negative electricity w\ld imm$iately draw !m into ! c5tral nucleus--j z gravitational attraction w\ld cause ! e>? to fall into ! sun1 7 x n = ! orbital motion ( ! =m]4 ,9 brief ,ru!r=d suppos$ ! atom to be con/ruct$ l ! sol> sy/em1 ! heavy c5tral nucleus play+ ! "p ( ! sun & ! electrons act+ ! p>ts ( ! planets4 ,! spe$s ) :i* ^! electrons fly r\nd _! t9y orbits are t]rific4 ,! av]age electron revolves ar\nd its nucleus sev]al ?\s& million million times e second1 ) a spe$ ( hundr$s ( miles a second4 ,?us ! smallness ( _! orbits does n prev5t ! electrons mov+ ) high] orbital spe$s ?an ! planets1 or ev5 ! />s !mselves4 ,by cle>+ a space ar\nd ! c5tral nucleus1 & s prev5t+ o!r atoms f com+ too ne> to x1 ^! electronic orbits give size to ! atom4 ,! volume ( space kept cle> by ! electrons is enorm\sly great] ?an ! total volume ( ! electrons2 r\ghly1 ! ratio ( volumes is t ( ! battlefield to ! bullets4 ,! atom1 ) a radius ( ab\t #b #aj cms41 has ab\t #ajj1jjj times ! diamet]1 & s ab\t a ?\s& million million times ! volume1 ( a s+le electron1 :i* has a radius ( only ab\t #b #aj;cms4 ,! nucleus1 al?\gh x g5]ally weighs #cjjj or #djjj times z mu* z all ! electrons 9 ! atom toge!r1 is at mo/ comp>able 9 size )1 & may be ev5 small] ?an1 a s+le electron4 ,we h already comm5t$ on ! extreme empt9ess ( a/ronomical space4 ,*oose a po9t 9 space at r&om1 & ! odds aga9/ its be+ occupi$ by a /> are enorm\s4 ,ev5 ! sol> sy/em consi/s ov]:elm+ly ( empty space2 *oose a spot inside ! sol> sy/em at r&om1 & !re are /ill imm5se odds aga9/ its be+ occupi$ by a planet or ev5 by a comet1 meteorite or small] body4 ,& n[ we see t ?is empt9ess ext5ds also to ! space ( physics4 ,ev5 inside ! atom we *oose a po9t at r&om1 & ! odds aga9/ !re be+ any?+ !re are imm5se2 !y are ( ! ord] ( at lea/ millions ( millions to "o4 ,we saw h[ six specks ( du/ inside ,wat]loo ,/ation repres5t$--or r ov]-repres5t$--! ext5t to :i* space 0 cr[d$ ) />s4 ,9 ! same way a few wasps--six = ! atom ( c>bon--fly+ ar\nd 9 ,wat]loo ,/ation w repres5t ! ext5t to :i* ! atom is cr[d$ ) electrons--all ! re/ is empt9ess4 ,z we pass ! :ole /ructure ( ! univ]se "u review1 f ! giant nebulae & ! va/ int]/ell> & int]nebul> spaces d[n to ! t9y /ructure ( ! atom1 little b vacant space passes be=e our m5tal gaze4 ,we live 9 a gossam] univ]se2 patt]n1 plan & design are !re 9 abundance1 b solid sub/ance is r>e4 ,,atomic ,,numb]s4 ,! numb] ( electrons :i* fly r\nd 9 orbits 9 an atom is call$ ! 8atomic numb]0 ( ! atom4 ,atoms ( all atomic numb]s f #a to #ib h be5 f\nd1 except = two miss+ numb]s #he & #hg4 ,z already m5tion$1 x is highly probable t ^! also exi/1 & t !re are #ib 8elem5ts0 ^: atomic numb]s occupy ! :ole range ( atomic numb]s f #a to #ib cont9u\sly4 ,! atom ( atomic numb] unity is ( c\rse ! simple/ ( all4 ,x is ! hydrog5 atom1 9 :i* a solit>y electron revolves ar\nd a nucleus ^: *>ge ( positive electricity is exactly equal 9 am\nt1 al?\gh opposite 9 sign1 to ! *>ge on ! negative electron4 ,next comes ! helium atom ( atomic numb] #b1 9 :i* two electrons revolve ab\t a nucleus :i* has f\r times ! weight ( ! hydrog5 nucleus1 al?\gh c>ry+ only twice its electric *>ge4 ,aft] ?is comes ! li?ium atom ( atomic numb] #c1 9 :i* ?ree electrons revolve ar\nd a nucleus hav+ six times ! weight ( ! hydrog5 atom & ?ree times its *>ge4 ,& s x goes on1 until we rea* uranium1 ! heavie/ ( all atoms kn[n on e>?1 :i* has #ib electrons describ+ orbits ab\t a nucleus ( #bch times ! weight ( ! hydrog5 nucleus4 ,,radio-,,activity ,:ile x 0 /ill engag$ 9 break+ up ! atom into its compon5t factors1 physical sci5ce 0 beg9n+ to discov] t ! nuclei !mselves 7 nei!r p]man5t nor inde/ructible4 ,9 #ahif1 ,becqu]el _h f\nd t v>i\s sub/ances conta9+ uranium possess$ ! rem>kable prop]ty1 z x !n appe>$1 ( spontane\sly affect+ photographic plates 9 _! vic9ity4 ,?is obs]vation l$ to ! discov]y ( a new prop]ty ( matt]1 namely radio-activity4 ,all ! results obta9$ f ! /udy ( radio-activity 9 ! few foll[+ ye>s 7 co-ord9at$ 9 ! hypo!sis ( 8spontane\s dis9tegration0 :i* ,ru!r=d & ,soddy advanc$ 9 #aijc4 ,accord+ to ?is hypo!sis 9 its pres5t =m1 radio-activity indicates a spontane\s break-up ( ! nuclei ( ! atoms ( radio-active sub/ances4 ,^! atoms are s f> f be+ p]man5t & inde/ructible t _! v nuclei crumble away ) ! m]e lapse ( "t1 s t :at 0 once ! nucleus ( a uranium atom is trans=m$1 aft] suffici5t "t1 into ! nucleus ( a lead atom4 ,! process ( trans=mation is n in/antane\s2 x proce$s gradually & by di/9ct /ages4 ,dur+ its progress1 ?ree types ( product are emitt$1 :i* are designat$ -rays1 -rays1 & -rays4 ,^! 7 orig9ally describ$ z rays because !y h ! p[] ( p5etrat+ ?r\gh a c]ta9 ?ickness ( air1 metal1 or o!r sub/ance4 ,_! true nature 0 discov]$ lat]4 ,x is well kn[n t magnetic =ces su* z1 = in/ance1 occur 9 ! space betwe5 ! poles ( a magnet1 cause a mov+ p>ticle *>g$ ) electricity to deviate f a /raight c\rse2 x deviates 9 "o direction or ! o!r accord+ z x is *>g$ ) positive or negative electricity4 ,on pass+ ! v>i\s rays emitt$ by radio-active sub/ances ?r\gh ! space betwe5 ! poles ( a p[]ful magnet1 ! -rays 7 f\nd to consi/ ( p>ticles *>g$ ) positive electricity1 & ! -rays to consi/ ( p>ticles *>g$ ) negative electricity4 ,b ! mo/ p[]ful magnetic =ces :i* c\ld be employ$ fail$ to cause ! slighte/ deviation 9 ! pa?s ( ! -rays1 f :i* x 0 conclud$ t ei!r ! -rays 7 n mat]ial p>ticles at all1 or t1 if !y 71 !y c>ri$ no electric *>ges4 ,! =m] ( ^! alt]natives 0 subsequ5tly prov$ to be ! true "o4 -,,p>ticles4 ,! positively *>g$ p>ticles :i* con/itute -rays are g5]ally describ$ z -p>ticles4 ,9 #aiji ,ru!r=d & ,royds all[$ -p>ticles to p5etrate ?r\gh a ?9 glass wall ( less ?an a hundr$? ( a millimetre ?ickness into a *amb] f :i* !y c\ld n escape--a sort ( m\se-trap = -p>ticles4 ,!y f\nd t s long z ! numb] ( -p>ticles 9 ! vessel w5t on increas+1 an accumulation ( helium 0 =m+4 ,9 ?is way x 0 e/abli%$ t ! positively *>g$ -p>ticles are simply nuclei ( helium atoms4 ,^! p>ticles move ) enorm\s spe$s1 :i* dep5d ^u ! nature ( ! radio-active sub/ance f :i* !y h be5 %ot out4 ,! fa/e/ ( all1 ^? emitt$ by ,?orium ,c1 move ) a spe$ ( #ab1hjj miles a second2 ev5 ! sl[e/1 ^? f ,uranium #a1 h a spe$ ( #hhjj miles a second1 :i* is ab\t #cj1jjj times ! ord9>y molecul> velocity 9 air4 ,p>ticles mov+ ) ^! spe$s knock all ord9>y molecules out ( _! way2 ?is expla9s ! great p5etrat+ p[] ( ! -rays4 -,,p>ticles4 ,by exam9+ _! motion "u magnetic =ces1 ! -rays 7 f\nd to consi/ ( negatively *>g$ electrons1 exactly simil> to ^? :i* revolve orbitally 9 all atoms4 ,z an -p>ticle c>ries a positive *>ge equal 9 am\nt to t ( two electrons1 an atom :i* has eject$ an -p>ticle is left ) a defici5cy ( positive *>ge1 or :at comes to ! same ?+1 ) a negative *>ge1 equal to t ( two electrons4 ,consequ5tly x is natural1 & inde$ almo/ inevitable1 t ! ejections ( -p>ticles %\ld alt]nate ) an ejection ( negatively *>g$ electrons1 s t ! balance ( positive & negative electricity 9 ! atom may be ma9ta9$4 ,! -p>ticles move ) ev5 great] spe$s ?an ! -p>ticles1 _m approa*+ to )9 a few p] c5t4 ( ! velocity ( light 7#ahf1jjj miles a second74 ,illu/ration3 ,,plate ,,xiii ,c4 ,t4 ,r4 ,wilson ,! tracks ( - & -p>ticles ,"o ( ! mo/ beautiful devices kn[n to physical sci5ce1 ! inv5tion ( ,pr(essor ,c4 ,t4 ,r4 ,wilson1 makes x possible to /udy ! motions ( ! - & -p>ticles z !y ?read _! way ?r\gh a gas1 collid+ ) its molecules on _! way4 ,a *amb] ?r\gh :i* ! p>ticles are made to travel is fill$ ) wat]-vap\r 9 su* a condition t ! passage ( an electrically *>g$ p>ticle leaves beh9d x a trail ( cond5sations :i* c be photograph$4 ,z an example1 ,plate ,,xiii %ews a photograph tak5 by ,pr(essor ,wilson himself1 9 :i* ! trails ( bo? - & -p>ticles appe> on ! same plate4 ,z ! -p>ticles weigh ab\t #gdjj times z mu* z ! -p>ticles1 !y naturally create m di/urbance 9 ! gas1 & s leave broad] & m pron\nc$ tracks2 also !y pursue a comp>atively /raight c\rse :ile ! light] -p>ticles are deflect$ f _! c\rses by _m ( ! molecules !y meet4 ,! plate %ews f\r -p>ticle tracks & "o 7mu* fa9t]7 -ray track4 ,! knobby-look+ projections :i* may be se5 on "o ( ! -ray tracks are ( int]e/2 !y repres5t ! %ort pa?s ( electrons knock$ out ( atoms by ! passage ( ! -p>ticle#i4 #i ,^! 7 call$ -rays by ,bum/ead4 -,,rays4 ,! -rays are n mat]ial p>ticles at all2 !y prove to be m]ely radiation ( a v special k9d1 :i* we %all n[ discuss4 ,,radiation ,di/urb ! surface ( a pond ) a /ick & a s]ies ( ripples />ts f ! /ick & travels1 9 a s]ies ( ev]-exp&+ circles1 ov] ! surface ( ! pond4 ,z ! wat] resi/s ! motion ( ! /ick1 we h to "w to keep ! pond 9 a /ate ( agitation4 ,! en]gy ( ?is "w is trans=m$1 9 "p at lea/1 into ! en]gy ( ! ripples4 ,we c see t ! ripples c>ry en]gy ab\t ) !m1 because !y cause a float+ cork or a toy boat to rise up aga9/ ! e>?'s gravitational pull4 ,?us ! ripples provide a me*anism = di/ribut+ ov] ! surface ( ! pond ! en]gy t we put into ! pond ?r\gh ! m$ium ( ! mov+ /ick4 ,light & all o!r =ms ( radiation are analog\s to wat]-ripples or waves1 9 t !y di/ribute en]gy f a c5tral s\rce4 ,! sun's radiation di/ributes ?r\gh space ! va/ am\nt ( en]gy :i* is g5]at$ inside ! sun4 ,we h>dly "k :e!r !re is any actual wave-motion 9 light or n1 b we "k t bo? light & all o!r types ( radiation are propagat$ 9 su* a =m t !y h "s ( ! prop]ties ( a succession ( waves4 ,we h se5 h[ ! diff]5t col\rs ( light :i* 9 comb9ation con/itute sunlight c be sep>at$ out by pass+ ! light ?r\gh a prism4 ,an alt]native in/rum5t1 ! diffraction grat+1 analyses light into its con/itu5t wave-l5g?s#aj1 & ^! are f\nd to correspond to ! diff]5t col\rs ( ! ra9b[4 ,?is %ews t diff]5t col\rs ( light repres5t diff]5t wave-l5g?s1 & at ! same "t provides a means ( measur+ ! actual wave-l5g?s ( light ( diff]5t col\rs4 ,^! prove to be v m9ute4 ,! r$de/ light we c see1 :i* is t ( longe/ wave-l5g?1 has a wave-l5g? ( only #c_/ajj1jjj in* 7#ge #aj cms472 ! mo/ violet light we c see has a wave-l5g? only half ( ?is1 or #jjjjjae in*4 ,light ( all col\rs travels ) ! same uni=m spe$ ( #ahf1jjj miles1 or #c #aj c5timetres1 a second4 ,! numb] ( waves ( r$ light :i* pass any fix$ po9t 9 a second is accord+ly no few] ?an f\r hundr$ million million4 ,?is is call$ ! 8frequ5cy0 ( ! light4 ,violet light has ! /ill high] frequ5cy ( eight hundr$ million million2 :5 we see violet light1 eight hundr$ million million waves ( light ent] our eyes ea* second4 #aj ,! wave-l5g? 9 a sy/em ( ripples is ! di/ance f ! cre/ ( "o ripple to t ( ! next1 & ! t]m may be appli$ to all ph5om5a ( an undulatory nature4 ,! spectrum ( analys$ sunlight appe>s to ! eye to /ret* f r$ light at "o end to violet light at ! o!r1 b ^! are n its true limits4 ,if c]ta9 *emical salts are plac$ beyond ! violet end ( ! visible spectrum1 !y are f\nd to %9e vividly1 %ew+ t ev5 out "h en]gy is be+ transport$1 al?\gh 9 invisible =m4 ,regions ( invisible radiation /ret* indef9itely f bo? ends ( ! visible spectrum4 ,f "o end--! r$--we c pass cont9u\sly to waves ( ! type us$ = wireless transmission1 :i* h wave-l5g?s ( ! ord] ( hundr$s1 or ev5 ?\s&s1 ( y>ds4 ,f ! violet end1 we pass ?r\gh waves ( %ort] & ev] %ort] wave-l5g?--all ! v>i\s =ms ( ultra-violet radiation4 ,at wave-l5g?s ( f ab\t a hundr$? to a ?\s&? ( ! wave-l5g? ( visible light1 we come to ! famili> ,x-rays1 :i* p5etrate ?r\gh in*es ( our fle%1 s t we c photograph ! bones inside4 ,f> out ev5 beyond ^!1 we come to ! type ( radiation :i* con/itutes ! -rays1 its wave-l5g? be+ ( ! ord] ( #a_/aj1jjj1jjj1jjj in*1 or only ab\t a hundr$-?\s&? "p ( ! wave-l5g? ( visible light4 ,?us ! -rays may be reg>d$ z invisible radiation ( extremely %ort wave-l5g?4 ,we %all discuss ! exact function !y s]ve lat]4 ,= ! mom5t let u m]ely rem>k t 9 ! fir/ in/ance !y s]v$ ! extremely useful function ( fogg+ ,becqu]el's photographic plates1 ?us lead+ to ! detection ( ! radio-active prop]ty ( matt]4 ,?us we see t ! break-up ( a radio-active atom may be comp>$ to ! dis*>ge ( a gun2 ! -p>ticle is ! %ot fir$1 ! -p>ticles are ! smoke1 & ! -rays are ! fla%4 ,! atom ( lead :i* f9ally rema9s is ! unload$ gun1 & ! orig9al radio-active atom1 ( uranium or :at n1 0 ! load$ gun4 ,& ! special peculi>ity ( radio-active guns is t !y g (f spontane\sly & ( _! own accord4 ,all attempts to pull ! trigg] h s f> fail$1 or at lea/ h l$ to inconclusive results2 we c only wait1 & ! gun w be f\nd to fire itself 9 "t4 ,illu/ration3 ,,plate ,,xiv ,fig4 #a ,illu/ration3 ,p4 ,m4 ,s4 ,blackett ,fig4 #b ,collisions ( -p>ticles ) ,nitrog5 ,atoms ,9 fig4 #a ! -p>ticle m]ely reb\nds f a nitrog5 atom4 ,9 fig4 #b x drives out a proton & !n jo9s itself to ! atom ,,atomic ,,nuclei ,) ! unimportant exceptions ( potassium & rubidium 7( atomic numb]s #ai & #cg71 ! prop]ty ( radio-activity occurs only 9 ! mo/ complex & massive ( atoms1 be+ inde$ conf9$ to ^? ( atomic numb]s above #hc4 ,yet1 al?\gh ! light] atoms are n liable to spontane\s dis9tegration 9 ! same way z ! heavy radio-active atoms1 _! nuclei are ( composite /ructure1 & c be brok5 up by artificial means4 ,9 #aibj1 ,ru!r=d1 us+ radio-active atoms z guns1 fir$ -p>ticles at light atoms & f\nd t direct hits broke up _! nuclei4 ,!re is1 h[ev]1 f\nd to be a significant diff]5ce betwe5 ! spontane\s dis9tegration ( ! heavy radio-active atoms1 & ! artificial dis9tegration ( ! light atoms2 9 ! =m] case1 ap>t f ! ev]-pres5t -rays & -rays1 only -p>ticles are eject$1 :ile 9 ! latt] case -p>ticles 7 n eject$ at all1 b p>ticles ( only ab\t a qu>t] _! weight1 :i* prov$ to be id5tical ) ! nuclei ( hydrog5 atoms4 ,^! s5sational ev5ts 9 ! atomic "u-_w c be photograph$ by ,pr(essor ,c4 ,t4 ,r4 ,wilson's cond5sation me?od already expla9$4 ,plate ,,xiv %ews two collisions ( an -p>ticle ) a nitrog5 atom photograph$ by ,mr ,p4 ,m4 ,s4 ,blackett4 ,! /raight l9es are m]ely ! q unev5tful tracks ( ord9>y -p>ticles simil> to ^? already %ewn 9 ,plate ,,xiii4 ,b "o -p>ticle track 9 ea* photograph sudd5ly bran*es1 s t ! complete figure is ( a ,y-%ape4 ,!re is little room = d\bt t 9 fig4 #a ! bran* occurs because ! -p>ticle has collid$ ) a nitrog5 atom2 ! /em ( ! ,y is ! track ( ! -p>ticle be=e ! collision2 ! two upp] bran*es are ! tracks ( ! -p>ticle & ! nitrog5 atom aft] ! collision1 ! latt] n[ mov+ ) enorm\s spe$ & hitt+ ev]y?+ out ( its way4 ,by tak+ simultane\s photographs 9 two directions at "r angles1 z %ewn 9 ! ,plate1 ,mr ,blackett 0 able to recon/ruct ! :ole collision1 & ! angles 7 f\nd to agree exactly ) ^? :i* dynamical !ory w\ld require on ?is int]pretation ( ! photograph4 ,! occurr5ce photograph$ 9 fig4 #b is ( a diff]5t type f t se5 9 fig4 #a1 = ! angles d n agree ) ^? :i* dynamical !ory w\ld require if ! upp] bran*es ( ! ,y 7 ! tracks ( ! -p>ticles & ! nitrog5 atom z 9 fig4 #a4 ,! /em ( ! ,y is /ill an ord9>y -p>ticle track1 b ! long fa9t upp] bran* is ! track ( a p>ticle small] ?an an -p>ticle1 namely a p>ticle ( qu>t]-weight %ot out ( ! nucleus1 :il/ ! %ort] & cle>] bran* is t ( ! nitrog5 atom mov+ along 9 company ) ! -p>ticle1 :i* x has captur$4 ,x w\ld take too mu* space to describe 9 full ! beautiful me?od by :i* ,blackett has e/abli%$ ?is int]pretation ( 8 photographs1 b !re is little room = d\bt t 9 fig4 #b he has actually succe$$ 9 photograph+ ! break-up ( ! nucleus ( an atom ( nitrog54 ,,isotopes4 ,two atoms h ! same *emical prop]ties if ! *>ges ( positive electricity c>ri$ by _! nuclei are ! same4 ,! am\nt ( ?is *>ge fixes ! numb] ( electrons :i* c revolve ar\nd ! nucleus1 ?is numb] be+ ( c\rse exactly t ne$$ to neutralise ! electric field ( ! nucleus1 & ?is 9 turn fixes ! atomic numb] ( ! elem5t4 ,b ,dr ,a/on has %ewn t atoms ( ! same *emical elem5t1 say neon or *lor9e1 may h nuclei ( diff]5t weights4 ,! v>i\s =ms :i* ! atoms ( ! same *emical elem5t c assume are kn[n z isotopes1 be+ ( c\rse di/+ui%$ by _! diff]5t weights4 ,a/on fur!r made ! highly significant discov]y t ! weights ( all atoms are1 to a v close approximation1 multiples ( a s+le def9ite weight4 ,?is unit weight is approximately equal to ! weight ( ! hydrog5 atom1 b is m ne>ly equal to a sixte5? ( ! weight ( ! oxyg5 atom4 ,! weight ( any type ( atom1 measur$ 9 t]ms ( ?is unit1 is call$ ! 8atomic weight0 ( ! atom4 ,,protons ,,& ,,electrons4 ,9 conjunction ) ! results ( ,ru!r=d's artificial dis9tegration ( atomic nuclei1 ,a/on's results h l$ to ! g5]al acceptance ( ! hypo!sis t ! :ole univ]se is built up ( only two k9ds ( ultimate bricks1 namely1 electrons & protons4 ,ea* proton c>ries a positive *>ge ( electricity exactly equal 9 am\nt to ! negative *>ge c>ri$ by an electron1 b has ab\t #ahdj times ! weight ( ! electron4 ,protons are suppos$ to be id5tical ) ! nucleus ( ! hydrog5 atom1 all o!r nuclei be+ composite /ructures 9 :i* bo? protons & electrons are closely pack$ toge!r4 ,= in/ance1 ! nucleus ( ! helium atom1 or -p>ticle1 consi/s ( f\r protons & two electrons1 ^! giv+ x approximately f\r times ! weight ( ! hydrog5 atom1 & a resultant *>ge equal to twice t ( ! nucleus ( ! hydrog5 atom4 ,yet ?is is n q ! :ole /ory4 ,if x 71 e complete atom w\ld consi/ ( a c]ta9 numb] ,n ( protons1 toge!r ) j en\gh electrons1 namely ,n1 to neutralise ! electric *>ges on ! ,n protons1 s t its +r$i5ts w\ld be precisely ! same z ^? ( ,n hydrog5 atoms4 ,?us ! weight ( e atom w\ld be an exact multiple ( ! weight ( a hydrog5 atom4 ,exp]im5t %ews ?is n to be ! case4 ,,electromagnetic ,,en]gy4 ,to get at ! :ole tru?1 we h to recognise t1 9 addition to conta9+ mat]ial electrons & protons1 ! atom conta9s yet a ?ird +r$i5t :i* we may describe z electromagnetic en]gy4 ,we may ?9k ( ?is1 al?\gh ) some?+ %ort ( absolute sci5tific accuracy1 z bottl$ radiation4 ,x is a commonplace ( mod]n electromagnetic !ory t radiation ( e k9d c>ries weight ab\t ) x1 weight :i* is 9 e s5se z real z ! weight ( a ton ( coal4 ,a ray ( light causes an impact on any surface on :i* x falls1 j z a jet ( wat] does1 or a bla/ ( w9d1 or ! fall ( a ton ( coal2 ) a suffici5tly /rong light "o c\ld knock a man d[n j z surely z ) ! jet ( wat] f a fire-hose4 ,?is is n a m]e !oretical pr$iction4 ,! pressure ( light on a surface has be5 bo? detect$ & measur$ by direct exp]im5t4 ,! exp]im5ts are extraord9>ily difficult because1 judg$ by all ord9>y /&>ds1 ! weight c>ri$ by radiation is exce$+ly small2 all ! radiation emitt$ f a #ej horse-p[] se>*light work+ cont9u\sly = a c5tury weighs only ab\t a tw5tie? ( an ounce4 ,x foll[s t any sub/ance :i* is emitt+ radiation mu/ at ! same "t be los+ weight4 ,9 p>ticul>1 ! dis9tegration ( any radio-active sub/ance mu/ involve a decrease ( weight1 s9ce x is accompani$ by ! emission ( radiation 9 ! =m ( -rays4 ,! ultimate fate ( an ounce ( uranium may be express$ by ! equation3 #jhfec ounce lead1 #a ounce uranium #jacde 0 helium1 #jjjjb 0 radiation4 ,! lead & helium toge!r conta9 j z _m electrons & j z _m protons z did ! orig9al ounce ( uranium1 b _! comb9$ weight is %ort ( ! weight ( ! orig9al uranium by ab\t "o "p 9 #djjj4 ,:]e #djjj ounces ( matt] orig9ally exi/$1 only #ciii n[ rema92 ! miss+ ounce has gone (f 9 ! =m ( radiation4 ,?is makes x cle> t we mu/ n expect ! weights ( ! v>i\s atoms to be exact multiples ( ! weight ( ! hydrog5 atom2 any su* expectation w\ld ignore ! weight ( ! bottl$-up electromagnetic en]gy :i* is capable ( be+ set free & go+ (f into space 9 ! =m ( radiation z ! atom *anges its make up4 ,! weight ( ?is en]gy is relatively small1 s t ! weights ( ! atoms may be expect$ to be approximately integral multiples ( t ( ! hydrog5 atom1 & ?is expectation is confirm$1 b !y w n be s exactly4 ,! exact weight ( our atomic build+ is n simply ! total weight ( all its bricks2 some?+ mu/ be add$ = ! weight ( ! mort>--! electromagnetic en]gy--:i* keeps ! bricks b\nd toge!r4 ,?us ! normal atom consi/s ( protons1 electrons1 & en]gy1 ea* ( :i* contributes some?+ to its weight4 ,:5 ! atom re-arranges itself1 ei!r spontane\sly or "u bomb>dm5t1 protons & electrons may be %ot (f 9 ! =m ( mat]ial p>ticles 7- & -rays7 & en]gy may also be set free 9 ! =m ( radiation4 ,?is radiation may ei!r take ! =m ( -rays1 or1 z we %all %ortly see1 ( o!r =ms ( visible & invisible radiation4 ,! f9al weight ( ! atom w be obta9$ by d$uct+ f its orig9al weight n only ! weight ( all ! eject$ electrons & protons1 b also ! weight ( all ! en]gy :i* has be5 set free z radiation4 ,,quantum ,,!ory ,! s]ies ( concepts :i* we n[ approa* are difficult to grasp & /ill m difficult to expla91 l>gely1 no d\bt1 because our m9ds receive no assi/ance f our ev]yday exp]i5ce ( nature#aa4 ,x becomes necess>y to speak ma9ly 9 t]ms ( analogies1 p>ables & models :i* c make no claim to repres5t ultimate reality2 inde$ x is ra% to haz>d a guess ev5 z to ! direction 9 :i* ultimate reality lies4 #aa ,! read] ^: int]e/ is limit$ to a/ronomy may pref] to proce$ at once to ,*apt] ,,iii4 ,! laws ( electricity :i* 7 9 vogue up to ab\t ! end ( ! n9ete5? c5tury--! fam\s laws ( ,maxwell & ,f>aday--requir$ t ! en]gy ( an atom %\ld cont9ually decrease1 ?r\gh ! atom scatt]+ en]gy abroad 9 ! =m ( radiation1 & s hav+ less & less left = itself4 ,^! same laws pr$ict$ t all en]gy set free 9 space %\ld rapidly trans=m itself into radiation ( almo/ inf9itesimal wave-l5g?4 ,yet ^! ?+s simply did n happ51 mak+ x obvi\s t ! !n prevail+ electrodynamical laws _h to be giv5 up4 ,,cavity-,,radiation4 ,a crucial case ( failure 0 provid$ by :at is kn[n z 8cavity-radiation40 ,a body ) a cavity 9 its int]ior is heat$ up to inc&esc5ce2 no notice is tak5 ( ! light & heat emitt$ by its out] surface1 b ! light imprison$ 9 ! int]nal cavity is let out ?r\gh a small w9d[ & analys$ into its con/itu5t col\rs by a spectroscope or diffraction grat+4 ,x is ?is radiation t is kn[n z 8cavity-radiation40 ,x repres5ts ! mo/ complete =m ( radiation possible1 radiation f :i* no col\r is miss+1 & 9 :i* e col\r figures at its full /r5g?4 ,no kn[n sub/ance ev] emits q su* complete radiation f its surface1 al?\gh _m approximate to do+ s4 ,we speak ( su* bodies z 8full radiators40 ,! n9ete5?-c5tury laws ( electromagnetism pr$ict$ t ! :ole ( ! radiation emitt$ by a full radiator or f a cavity ought to be f\nd at or beyond ! extreme violet end ( ! spectrum1 indep5d5tly ( ! precise temp]ature to :i* ! body _h be5 heat$4 ,9 actual fact ! radiation is usually f\nd pil$ up at exactly ! opposite end ( ! spectrum1 & 9 no case does x ev] con=m to ! pr$ictions ( ! n9ete5?-c5tury laws1 or ev5 beg9 to ?9k ( do+ s4 ,9 ! ye> #aijj1 ,pr(essor ,planck ( ,b]l9 discov]$ exp]im5tally ! law by :i* 8cavity-radiation0 is di/ribut$ among ! diff]5t col\rs ( ! spectrum4 ,he fur!r %ew$ h[ 8 newly discov]$ law c\ld be d$uc$ !oretically f a sy/em ( electromagnetic laws :i* diff]$ v s5sationally f ^? !n 9 vogue4 ,planck imag9$ all k9ds ( radiation to be emitt$ by sy/ems ( vibrators :i* emitt$ light :5 excit$1 mu* z tun+ =ks emit s\nd :5 !y are /ruck4 ,! old electrodynamical laws pr$ict$ t ea* vibration %\ld gradually come to re/ & !n /op1 z ! vibrations ( a tun+ =k d1 until ! vibrator 0 9 "s way excit$ aga94 ,reject+ all ?is1 ,planck suppos$ t a vibrator c\ld *ange its en]gy by sudd5 j]ks1 & 9 no o!r way2 x might h "o1 two1 ?ree1 f\r or any o!r integral numb] ( units ( en]gy1 b no int]m$iate fractional numb]s1 s t gradual *anges ( en]gy 7 r5d]$ impossible4 ,! vibrator1 s to speak1 kept no small *ange1 & c\ld only pay out its en]gy a %ill+ at a "t until x _h none left4 ,n only s1 b x refus$ to receive small *ange1 al?\gh x 0 prep>$ to accept complete %ill+s4 ,?is concept1 s5sational1 revolution>y & ev5 ridicul\s1 z _m ?\ght x at ! "t1 0 f\nd to lead exactly to ! di/ribution ( col\rs actually obs]v$ 9 cavity-radiation4 ,9 #aiag1 ,e9/e9 put ! concept into ! m precise =m :i* n[ prevails4 ,accord+ to a !ory previ\sly advanc$ by ,pr(essor ,niels ,bohr ( ,cop5hag51 an atomic or molecul> /ructure does n *ange its configuration1 or dissipate away its en]gy1 by gradual /ages4 ,gradualness is driv5 out ( physics1 & discont9uity takes its place4 ,an atomic /ructure has a numb] ( possible /ates or configurations :i* are entirely di/9ct & deta*$ "o f ano!r1 j z a weight plac$ on a /aircase has only a possible numb] ( positions2 x may be #c /airs up1 or #d or #e1 b _c be #c or #c /airs up4 ,! *ange f "o position to ano!r is g5]ally effect$ ?r\gh ! m$ium ( radiation4 ,! sy/em c be pu%$ up/airs by absorb+ en]gy f radiation :i* falls on x1 or may move d[n/airs to a /ate ( l[] en]gy & emit en]gy 9 ! =m ( radiation 9 s do+4 ,only radiation ( a c]ta9 def9ite col\r1 & s ( a c]ta9 precise wave-l5g?1 is ( any acc\nt = effect+ a p>ticul> *ange ( /ate4 ,! problem ( %ift+ an atomic sy/em is l t ( extract+ a box ( mat*es f a p5ny-9-!-slot ma*9e2 x c only be done by a special implem5t1 to wit a p5ny1 :i* mu/ be ( precisely ! "r size & weight--a co9 :i* is ei!r too small or too l>ge1 too light or too heavy1 is doom$ to fail4 ,if we p\r radiation ( ! wrong wave-l5g? on to an atom1 we may reproduce ! com$y ( ! millionaire ^: total weal? w n procure him a box ( mat*es because he has n a loose p5ny1 or we may reproduce ! trag$y ( ! *ild :o _c obta9 a slab ( *ocolate because its ho>d$ weal? consi/s ( f>?+s & half-p5ce1 b we %all n di/urb ! atom4 ,:5 mix$ radiation is p\r$ on to a collection ( atoms1 ^! absorb ! radiation ( j ^? wave-l5g?s :i* are ne$$ to *ange _! int]nal /ates1 & none o!r2 radiation ( all o!r wave-l5g?s passes by unaffect$4 ,?is selective action ( ! atom on radiation is put 9 evid5ce 9 a v>iety ( ways2 x is p]haps mo/ simply %ewn 9 ! spectra ( ! sun & />s4 ,d>k l9es simil> to ^? :i* ,fraunh(] obs]v$ 9 ! sol> spectrum are obs]v$ 9 ! spectra ( practically all />s 7see ,plate ,,viii1 p4 #ea71 & we c n[ und]/& :y ?is mu/ be4 ,light ( e possible wave-l5g? /reams out f ! hot int]ior ( a />1 & bomb>ds ! atoms :i* =m its atmosph]e4 ,ea* atom dr9ks up t radiation :i* is ( precisely ! "r wave-l5g? = x1 b has no int]action ( any k9d ) ! re/1 s t ! radiation :i* is f9ally emitt$ f ! /> is defici5t 9 j ! p>ticul> wave-l5g?s :i* suit ! atoms4 ,?us ! /> %ews an absorption spectrum ( f9e l9es4 ,! positions ( ^! l9es 9 ! spectrum %ew :at types ( radiation ! /ell> atoms h swall[$1 & s enable u to id5tify ! atoms f our laboratory k ( ! ta/es ( diff]5t k9ds ( atoms = radiation4 ,b :at ultimately decides :i* types ( radiation an atom w swall[1 & :i* x w reject8 ,planck _h already suppos$ t radiation ( ea* wave-l5g? has associat$ ) x a c]ta9 am\nt ( en]gy1 call$ ! 8quantum10 :i* dep5ds on ! wave-l5g? & on no?+ else4 ,! quantum is suppos$ to be proportional to ! 8frequ5cy0 7p4 #aae71 or numb] ( vibrations ( ! radiation p] second#ab1 & s is inv]sely proportional to ! wave-l5g? ( ! radiation--! %ort] ! wave-l5g?1 ! great] ! en]gy ( ! quantum1 & conv]sely4 ,r$ light has feeble quanta1 violet light has en]getic quanta1 & s on4 #ab ,to be precise1 if v is ! frequ5cy ( ! radiation1 its quantum ( en]gy is hv1 :]e h is a univ]sal con/ant ( nature1 kn[n z ,planck's con/ant4 ,?is con/ant is ( ! physical nature ( en]gy multipli$ by "t2 its num]ical value is3 #fee #aj ergs seconds4 ,e9/e9 n[ supposes t radiation ( a giv5 type c effect an atomic or molecul> *ange1 only if ! en]gy ne$$ = ! *ange is precisely equal to t ( a s+le quantum ( ! radiation4 ,?is is commonly kn[n z ,e9/e9's law2 x det]m9es ! precise type ( radiation ne$$ to "w any atomic or molecul> p5ny-9-!-slot me*anism#ac4 #ac ,9 ! =m ( an equation3 ,e - ,e h1 :]e ,e1 ,e are ! en]gies ( ! mat]ial sy/em be=e & aft] ! *ange1 is ! frequ5cy ( ! radiation1 & h is ,planck's con/ant already specifi$4 ,we notice t "w :i* dem&s "o p[]ful quantum _c be p]=m$ by two1 or inde$ by any numb] :atev]1 ( feeble quanta4 ,a small am\nt ( violet 7high-frequ5cy7 light c accompli% :at no am\nt ( r$ 7l[-frequ5cy7 light c effect--a circum/ance ) :i* e photograph] is pa9fully famili>2 we c admit z mu* r$ light z we please )\t any damage be+ done1 b ev5 ! t9ie/ gleam ( violet light spoils our plates4 ,! law prohibits ! kill+ ( two birds ) "o /one1 z well z ! kill+ ( "o bird ) two /ones2 ! :ole quantum is us$ up 9 effect+ ! *ange1 s t no en]gy f ?is p>ticul> quantum is left ov] to contribute to any fur!r *ange4 ,?is aspect ( ! matt] is illu/rat$ by ,e9/e9's photo*emical law3 89 any *emical reaction :i* is produc$ by ! incid5ce ( light1 ! numb] ( molecules :i* are affect$ is equal to ! numb] ( quanta ( light :i* are absorb$40 ,^? :o manage p5ny-9-!-slot ma*9es are famili> ) a simil> law3 8! numb] ( articles sold is exactly equal to ! numb] ( co9s 9 ! ma*9e40 ,if we ?9k ( en]gy 9 t]ms ( its capacity = do+ damage1 we see t radiation ( %ort wave-l5g? c "w m de/ruction 9 atomic /ructures ?an radiation ( long wave-l5g?4 ,radiation ( suffici5tly %ort wave-l5g? may n only re-arrange molecules or atoms2 x may break up any atom on :i* x happ5s to fall1 by %oot+ out "o ( its electrons1 giv+ rise to :at is kn[n z photoelectric action4 ,aga9 !re is a def9ite limit ( frequ5cy1 su* t light ^: frequ5cy is bel[ ?is limit does n produce any effect at all1 no matt] h[ int5se x may be2 :]eas z soon z we pass to frequ5cies above ?is limit1 light ( ev5 ! feeble/ int5sity />ts photoelectric action at once4 ,aga9 ! absorption ( "o quantum breaks up only "o atom1 & fur!r ejects only "o electron f ! atom4 ,if ! radiation has a frequ5cy above ?is limit1 s t its quantum has m en]gy ?an ! m9imum necess>y to remove a s+le electron f ! atom1 ! :ole quantum is /ill absorb$1 ! excess en]gy n[ be+ us$ 9 end[+ ! eject$ electron ) motion4 ,,electron ,,orbits4 ,^! concepts are bas$ ^u ,bohr's supposition t only a limit$ numb] ( orbits are op5 to ! electrons 9 an atom1 all o!rs be+ prohibit$ = reasons :i* we /ill d n fully und]/&1 & t an electron is free to move f "o p]mitt$ orbit to ano!r "u ! /imulus ( radiation4 ,bohr himself inve/igat$ ! way 9 :i* ! v>i\s p]mitt$ orbits are arrang$4 ,mod]n inve/igations indicate ! ne$ = a good deal ( revision ( 8 simple concepts1 b we %all discuss ^! 9 "s detail1 p>tly because ,bohr's picture ( ! atom /ill provides ! be/ work+ me*anical model we h1 & p>tly because an und]/&+ ( 8 simple !ory is absolutely ess5tial to ! und]/&+ ( ! f> m intricate !ories :i* are beg9n+ to replace x4 ,! hydrog5 atom1 z we h already se51 consi/s ( a s+le proton z c5tral nucleus1 ) a s+le electron revolv+ ar\nd x4 ,! nucleus1 ) ab\t #ahdj times ! weight ( ! electron1 /&s practically at re/ unagitat$ by ! motion ( ! latt]1 j z ! sun rema9s practically undi/urb$ by ! motion ( ! e>? r\nd x4 ,! nucleus & electron c>ry *>ges ( positive & negative electricity1 & !re=e attract "o ano!r2 ?is is :y ! electron describes an orbit in/ead ( fly+ (f 9 a /raight l9e1 aga9 l ! e>? & sun4 ,fur!rmore1 ! attraction betwe5 electric *>ges ( opposite sign1 positive & negative1 foll[s1 z x happ5s1 precisely ! same law z gravitation1 ! attraction fall+ (f z ! inv]se squ>e ( ! di/ance betwe5 ! two *>ges4 ,?us ! nucleus-electron sy/em is simil> 9 all respects to a sun-planet sy/em1 & ! orbits :i* an electron c describe ar\nd a c5tral nucleus are precisely id5tical ) ^? :i* a planet c describe ab\t a c5tral sun2 !y consi/ ( a sy/em ( ellipses ea* hav+ ! nucleus 9 "o focus 7p4 #df74 ,yet ! g5]al concepts ( quantum-dynamics prohibit ! electron f mov+ 9 all ^! orbits indiscrim9ately4 ,accord+ to ,bohr1 ! electron ( ! hydrog5 atom c move 9 a c]ta9 numb] ( circul> orbits ^: diamet]s are proportional to ! squ>es ( ! natural numb]s #a1 #d1 #i1 #af1 #be1 4442 x c also move 9 a s]ies ( elliptic orbits ^: greate/ diamet]s are respectively equal to ! diamet]s ( ! possible circul> orbits1 al?\gh ^! elliptic orbits are /ill fur!r limit$ by ! condition t _! ecc5tricities mu/ h c]ta9 def9ite values4 ,all o!r orbits are 9 "s way prohibit$4 ,! smalle/ orbits :i* ! electron c describe 9 ! hydrog5 atom are %ewn 9 fig4 #aj4 ,! smalle/ orbit ( all1 ( diamet] #a1 is m>k$ #a2 beyond ?is come two orbits ( diamet] #d m>k$ #b #b2 !n ?ree orbits ( diamet] #i m>k$ #c1 #c1 #c2 & f\r orbits ( diamet] #af m>k$ #d1 #d1 #d1 #d4 ,! diagram /ops "h = want ( space1 b ! available orbits g on indef9itely4 ,ev5 "u laboratory conditions1 electrons may move 9 orbits ( a hundr$ times ! diamet] ( t m>k$ #a4 ,"u ! m r>efi$ conditions ( /ell> atmosph]es ! hydrog5 atom may swell out to ev5 great] dim5sions1 & /ell> spectra provide evid5ce ( orbits hav+ ov] a ?\s& times ! dim5sions ( ! #a orbit4 ,su* an orbit w\ld be repres5t$ 9 fig4 #aj by a circle f\r y>ds 9 diamet]4 ,illu/ration3 ,fig4 #aj4 ,! arrangem5t ( electron orbits 9 ! hydrog5 atom 7,bohr's model74 ,all orbits1 :e!r elliptic or circul>1 :i* h ! same diamet]1 h also ! same en]gy1 b ! en]gy *anges :5 an electron crosses ov] f any orbit to ano!r ( a diff]5t diamet]4 ,?us1 to a c]ta9 limit$ ext5t1 ! atom con/itutes a res]voir ( en]gy4 ,its *anges ( en]gy are easily calculat$2 = example1 ! two orbits ( smalle/ diamet]s 9 ! hydrog5 atom diff] 9 en]gy by #af #aj ergs4 ,if we p\r radiation ( ! appropriate wave-l5g? on to an atom 9 :i* ! electron is describ+ ! smalle/ orbit ( all1 x crosses ov] to ! next orbit1 absorb+ #af #aj ergs ( en]gy 9 ! process1 & s becom+ tempor>ily a res]voir ( en]gy hold+ #af #aj ergs4 ,if ! atom is 9 any way di/urb$ f outside1 x may ( c\rse dis*>ge ! en]gy at any "t1 or x may absorb /ill m en]gy & s increase its /ore4 ,if we "k all ! orbits :i* are possible = an atom ( any type1 x is easy to calculate ! *anges ( en]gy involv$ 9 ! v>i\s transitions betwe5 !m4 ,z ea* transition absorbs or releases exactly "o quantum ( en]gy1 we c imm$iately d$uce ! frequ5cies ( ! light emitt$ or absorb$ 9 ^! transitions4 ,9 brief1 giv5 ! arrangem5t ( atomic orbits1 we c calculate ! spectrum ( ! atom4 ,9 practice ! problem ( c\rse takes ! conv]se =m3 giv5 ! spectrum1 to f9d ! /ructure ( ! atom :i* emits x4 ,bohr's model ( ! hydrog5 atom is a good model at lea/ to ?is ext5t--t ! spectrum x w\ld emit reproduces ! hydrog5 spectrum almo/ exactly4 ,yet ! agreem5t is n q p]fect1 & x is n[ g5]ally accept$ t ,bohr's s*eme ( orbits is inadequate to acc\nt = actual spectra4 ,we cont9ue to discuss ,bohr's s*eme1 n because ! atom is actually built t way1 b because x provides a good en\gh work+ model = our pres5t purpose4 ,an ess5tial1 al?\gh at fir/ sight some:at unexpect$1 feature ( ! :ole !ory is t ev5 if ! hydrog5 atom *>g$ ) its #af #aj ergs ( en]gy is left entirely undi/urb$1 ! electron mu/1 aft] a c]ta9 "t1 lapse back spontane\sly to its orig9al small] orbit1 eject+ its #af #aj ergs ( en]gy 9 ! =m ( radiation 9 s do+4 ,e9/e9 %ew$ t1 if ?is 7 n s1 !n ,planck's well-e/abli%$ 8cavity-radiation0 law c\ld n be true4 ,?us a collection ( hydrog5 atoms 9 :i* ! electrons describe orbits l>g] ?an ! smalle/ possible orbit is simil> to a collection ( uranium or o!r radio-active atoms1 9 t ! atoms spontane\sly fall back to _! /ates ( l[] en]gy z ! result m]ely ( ! passage ( "t4 ,! electron orbits 9 m complicat$ atoms h mu* ! same g5]al arrangem5t z 9 ! hydrog5 atom1 b are diff]5t 9 size4 ,9 ! hydrog5 atom ! electron normally falls1 aft] suffici5t "t1 to ! orbit ( l[e/ en]gy & /ays !re4 ,x might be ?\ght by analogy t 9 m complicat$ atoms 9 :i* sev]al electrons are describ+ orbits1 all ! electrons w\ld 9 "t fall into ! orbit ( l[e/ en]gy & /ay !re4 ,su* does n prove to be ! case4 ,!re is nev] room = m ?an "o electron 9 ! same orbit4 ,?is is a special aspect ( a g5]al pr9ciple :i* appe>s to dom9ate ! :ole ( physics4 ,x has a "n--8! exclusion-pr9ciple0--b ?is is ab\t all z yet2 we h h>dly begun to und]/& x4 ,9 ano!r ( its special aspects x becomes id5tical ) ! old famili> corn]-/one ( sci5ce :i* ass]ts t two diff]5t pieces ( matt] _c occupy ! same space at ! same "t4 ,)\t und]/&+ ! und]ly+ pr9ciple1 we c accept ! fact t two electrons n only _c occupy ! same space1 b _c ev5 occupy ! same orbit4 ,x is z ?\gh 9 "s way ! electron spread itself out s z to occupy ! :ole ( its orbit1 ?us leav+ room = no o!r4 ,no d\bt ?is mu/ n be accept$ z a lit]al picture ( ?+s1 & yet x seems n improbable t ! orbits ( l[e/ en]gy 9 ! hydrog5 atom are possible orbits j because ! electron c completely fill !m1 & t adjac5t orbits are impossible because ! electron w\ld fill !m or #a times ov]1 & simil>ly = m complicat$ atoms4 ,9 ?is connection x is p]haps significant t no s+le kn[n ph5om5on ( physics makes x possible to say t at a giv5 in/ant an electron is at su* or su* a po9t 9 an orbit ( l[e/ en]gy2 su* a /atem5t appe>s to be q mean+less1 & ! condition ( an atom is app>5tly specifi$ ) all possible precision by say+ t at a giv5 in/ant an electron is 9 su* an orbit1 z x w\ld be1 = in/ance1 if ! electron _h spread itself out into a r+4 ,we _c say ! same ( o!r orbits4 ,z we pass to orbits ( high] en]gy1 & s ( great] diamet]1 ! indet]m9at5ess gradually assumes a diff]5t =m1 & f9ally becomes ( b little importance4 ,:atev] =m ! electron may assume :ile x is describ+ a little orbit ne> ! nucleus1 by ! "t x is describ+ a v big orbit f> out x has become a pla9 mat]ial p>ticle *>g$ ) electricity4 ,?us1 :atev] ! reason may be1 electrons :i* are describ+ orbits 9 ! same atom mu/ all be 9 diff]5t orbits4 ,! electrons 9 _! orbits are l m5 on a ladd]2 j z no two m5 c /& on ! same rung1 s no two electrons c ev] foll[ "o ano!r r\nd 9 ! same orbit4 ,! neon atom1 = in/ance1 ) #aj electrons1 is 9 its normal /ate ( l[e/ en]gy :5 its #aj electrons ea* occupy "o ( ! #aj orbits ^: en]gy is l[e/4 ,= reasons :i* ! quantum !ory has at la/ succe$$ 9 elucidat+1 !re are1 9 e atom1 two orbits 9 :i* ! en]gy is equal & l[] ?an 9 any o!r orbit4 ,aft] ?is come eight orbits ( equal b sub/antially high] en]gy1 !n #ah orbits ( equal b /ill high] en]gy1 & s on4 ,z ! electrons 9 ea* ( ^! v>i\s gr\ps ( orbits all h equal en]gy1 !y are commonly spok5 (1 9 a graphic b mislead+ phraseology1 z r+s ( electrons4 ,!y are designat$ ! ,k-r+1 ! ,l-r+1 ! ,m-r+ & s on4 ,! ,k-r+1 :i* is ne>e/ to ! nucleus1 has room = two electrons only4 ,any fur!r electrons are pu%$ out into ! ,l-r+1 :i* has room = eight electrons1 all describ+ orbits :i* are diff]5t b ( equal en]gy4 ,if /ill m electrons rema9 to be accommodat$ !y mu/ g into ! ,m-r+ & s on4 ,9 _! normal /ates1 ! hydrog5 atom has "o electron 9 its ,k-r+1 :ile ! helium atom has two1 ! ,l1 ,m1 & high] r+s be+ unoccupi$4 ,! atom ( next high] complexity1 ! li?ium atom1 has ?ree electrons1 & z only two c be accommodat$ 9 its ,k-r+1 "o has to w&] r\nd 9 ! out] spaces ( ! ,l-r+4 ,9 b]yllium ) f\r electrons1 two are driv5 out into ! ,l-r+4 ,& s x goes on1 until we rea* neon ) #aj electrons1 by :i* "t ! ,l-r+ z well z ! inn] ,k-r+ is full up4 ,9 ! next atom1 sodium1 "o ( ! #aa electrons is driv5 out into ! /ill m remote ,m-r+1 & s on4 ,provid$ ! electrons are n be+ excit$ by radiation or o!r /imulus1 ea* atom s9ks 9 "t to a /ate 9 :i* its electrons are occupy+ its orbits ( l[e/ en]gy1 "o 9 ea*4 ,s f> z our exp]i5ce goes1 an atom1 z soon z x rea*es ?is /ate1 becomes a true p]petual motion ma*9e1 ! electrons cont9u+ to move 9 _! orbits 7at any rate on ,bohr's !ory7 )\t any ( ! en]gy ( _! motion be+ dissipat$ away1 ei!r 9 ! =m ( radiation or o!rwise4 ,x seems a/oni%+ & q incompreh5sible t an atom 9 su* a /ate %\ld n be able to yield up its en]gy /ill fur!r1 b1 s f> z our exp]i5ce goes1 x _c4 ,& ?is prop]ty1 little ?\gh we und]/& x1 is1 9 ! la/ resort1 responsible = keep+ ! univ]se 9 be+4 ,if no re/riction ( ?is k9d int]v5$1 ! :ole mat]ial en]gy ( ! univ]se w\ld disappe> 9 ! =m ( radiation 9 a few ?\s&-million? p>ts ( a second4 ,if ! normal hydrog5 atom 7 capable ( emitt+ radiation 9 ! way dem&$ by ! n9ete5?-c5tury laws ( physics1 x w\ld1 z a direct consequ5ce ( ?is emission ( radiation1 beg9 to %r9k at ! rate ( ov] a metre a second1 ! electron cont9ually fall+ to orbits ( l[] & l[] en]gy4 ,aft] ab\t a ?\s&-million? "p ( a second ! nucleus & ! electron w\ld run into "o ano!r1 & ! :ole atom w\ld probably disappe> 9 a fla% ( radiation4 ,by prohibit+ any emission ( radiation except by complete quanta1 & by prohibit+ any emission at all :5 !re are no quanta available = dissipation1 ! quantum !ory succe$s 9 keep+ ! univ]se 9 exi/5ce z a go+ conc]n4 ,x is difficult to =m ev5 ! remote/ conception ( ! realities und]ly+ all ^! ph5om5a4 ,! rec5t bran* ( physics kn[n z 8wave-me*anics0 is at pres5t grop+ aft] an und]/&+1 b s f> progress has be5 9 ! direction ( co-ord9at+ obs]v$ ph5om5a r ?an 9 gett+ d[n to realities4 ,inde$ x may be d\bt$ :e!r we %all ev] prop]ly und]/& ! realities ultimately involv$2 !y may well be s fundam5tal z to be beyond ! grasp ( ! human m9d4 ,x is j = ?is reason t mod]n !oretical physics is s difficult to expla91 & s difficult to und]/&4 ,x is easy to expla9 ! motion ( ! e>? r\nd ! sun 9 ! sol> sy/em4 ,we see ! sun 9 ! sky2 we feel ! e>? "u our feet1 & ! concept ( motion is famili> to u f ev]yday exp]i5ce4 ,h[ diff]5t :5 we try to expla9 ! analog\s motion ( ! electron r\nd ! proton 9 ! hydrog5 atom6 ,nei!r y nor ,i h any direct exp]i5ce ( ei!r electrons or protons1 & no "o has s f> any inkl+ ( :at !y are really l4 ,s we agree to make a sort ( model 9 :i* ! electron & proton are repres5t$ by ! simple/ ?+s kn[n to u1 t9y h>d sph]es4 ,! model works well = a "t & !n sudd5ly breaks 9 our h&s4 ,9 ! new light ( ! wave-me*anics1 ! h>d sph]e is se5 to be hopelessly inadequate to repres5t ! electron4 ,a h>d sph]e has always a def9ite position 9 space2 ! electron app>5tly has n4 ,a h>d sph]e takes up a v def9ite am\nt ( room1 an electron--well1 x is probably z mean+less to discuss h[ mu* room an electron takes up z x is to discuss h[ mu* room a fe>1 an anxiety or an unc]ta9ty takes up1 b if we are press$ to say h[ mu* room an electron takes up1 p]haps ! be/ answ] is t x takes up ! :ole ( space4 ,a h>d sph]e moves f "o po9t to ! next2 our model electron1 jump+ f orbit to orbit 9 ! model hydrog5 atom c]ta9ly does n behave l any h>d sph]e ( our wak+ exp]i5ce1 & ! real electron--if !re is any su* ?+ z a real electron 9 an atom--probably ev5 less4 ,yet z our m9ds h s f> fail$ to conceive any bett] picture ( ! atom ?an ?is v imp]fect model1 we c only proce$ by describ+ ph5om5a 9 t]ms ( x4 ,,! ,,me*anical ,,effects ,,( ,,radiation ,! m compact an electrical /ructure is1 ! great] ! am\nt ( en]gy necess>y to di/urb x2 &1 z ?is en]gy mu/ be suppli$ 9 ! =m ( a s+le quantum1 ! great] ! en]gy ( ! quantum mu/ be1 & s ! %ort] ! wave-l5g? ( ! radiation4 ,a v compact /ructure c only be di/urb$ by radiation ( v %ort wave-l5g?4 ,a %ip head+ into a r\gh sea runs mo/ risk ( damage1 & its pass5g]s mo/ risk ( discom=t1 :5 its l5g? is ab\t equal to ! l5g? ( ! waves4 ,%ort waves di/urb a %ort %ip & long waves a long %ip1 b a long swell does little h>m to ei!r4 ,b ?is provides no real analogy ) ! effects ( radiation1 s9ce ! wave-l5g? ( radiation :i* breaks up an electrical /ructure is hundr$s ( times ! size ( ! /ructure4 ,! nautical analogy to su* radiation is a v long swell inde$4 ,z a r\gh work+ guide we may say t an electrical /ructure w only be di/urb$ by radiation ^: wave-l5g? is ab\t equal to #hfj times ! dim5sions ( ! /ructure1 & w only be brok5 up by radiation ^: wave-l5g? is bel[ ?is limit#ad4 ,9 brief1 ! reason :y blue light affects photographic plates1 :ile r$ light does n1 is t ! wave-l5g? ( blue light is less1 & t ( r$ light is great]1 ?an #hfj times ! diamet] ( ! molecule ( silv] bromide2 we mu/ get bel[ ! 8#hfj-limit0 be=e any?+ beg9s to happ54 #ad ,! ma!matician w readily see ! reason = ?is rule1 :i* is1 9 brief1 z foll[s3 ! en]gy ne$$ to sep>ate two electric *>ges e & - e1 at a di/ance r ap>t1 is e_/r1 & ! en]gy ne$$ to re-arrange or break up a /ructure ( electrons & protons ( l9e> dim5sions r w g5]ally be comp>able ) ?is4 ,if is ! wave-l5g? ( ! requisite radiation1 ! en]gy made available by ! absorption ( ?is radiation is ! quantum h,c_/4 ,comb9+ ?is ) ! circum/ance t ! value ( h is v approximately e #hfj ----------1 ,c we f9d t ! requisite wave-l5g? ( radiation is ab\t #hfj times ! dim5sions ( ! /ructure to be brok5 up4 ,:5 an atom dis*>ges its res]voir ( /or$ en]gy1 ! light x emits has necess>ily ! same wave-l5g? z ! light :i* x absorb$ 9 orig9ally /or+ up ?is en]gy2 ! two quanta ( en]gy be+ equal1 _! wave-l5g?s are ! same4 ,x foll[s t ! light emitt$ by any electrical /ructure w also h a wave-l5g? ( ab\t #hfj times ! dim5sions ( ! /ructure4 ,ord9>y visible light is emitt$ ma9ly by atoms1 & s has a wave-l5g? equal to ab\t #hfj atomic diamet]s4 ,inde$ x is j because x has ?is wave-l5g? t ! light acts on ! atoms ( our ret9a1 & s is visible4 ,radiation ( ?is wave-l5g? di/urbs only ! out]mo/ electrons 9 an atom1 b radiation ( mu* %ort] wave-l5g? may h mu* m deva/at+ effects2 ,x-radiation1 = in/ance1 may break up ! f> m compact inn] r+s ( electrons1 ! ,k-r+1 ,l-r+1 etc41 ( ! atomic /ructure4 ,radiation ( /ill %ort] wave-l5g? may ev5 di/urb ! protons & electrons ( ! nucleus4 ,= ! nuclei1 l ! atoms !mselves1 are /ructures ( positive & negative electrical *>ges1 & s mu/ behave simil>ly ) respect to ! radiation fall+ ^u !m1 except = ! wide diff]5ce 9 ! wave-l5g? ( ! radiation4 ,ellis & o!rs h f\nd t ! -radiation emitt$ dur+ ! dis9tegration ( ! atoms ( ! radio-active elem5t radium-,b has wave-l5g?s ( #ceb1 #dbj1 #dhj1 #eac1 & #bc #aj cms4 ,^! wave-l5g?s are only ab\t a hundr$-?\s&? "p ( ^? ( visible light1 ! reason be+ t ! atomic nucleus has only ab\t a hundr$-?\s&? "p ! dim5sions ( ! complete atom4 ,radiation ( su* wave-l5g?s ought to be j z effective 9 re-arrang+ ! nucleus ( radium-,b z t ( #ajj1jjj times long] wave-l5g? is effective 9 re-arrang+ ! hydrog5 atom4 ,s9ce ! wave-l5g? ( ! radiation absorb$ or emitt$ by an atom is inv]sely proportional to ! quantum ( en]gy1 ! quantum ne$$ to 8"w0 ! atomic nucleus mu/ h some?+ l #ajj1jjj times ! en]gy ( t ne$$ to 8"w0 ! atom4 ,if ! hydrog5 atom is a p5ny-9-!-slot ma*9e1 no?+ less ?an five-hundr$-p\nd notes w "w ! nuclei ( ! radio-active atoms4 ,! radio-active nuclei1 l ^? ( nitrog5 & oxyg51 c\ld probably be brok5 up by a suffici5tly int5se bomb>dm5t1 al?\gh ! exp]im5tal evid5ce on ?is po9t is n v def9ite4 ,if s1 ea* bomb>d+ p>ticle w\ld h to br+ to ! attack an en]gy ( motion equal at lea/ to t ( "o quantum ( ! radiation 9 "q1 ?is requir+ x to move ) an enorm\sly high spe$4 ,matt] at suffici5tly high temp]atures conta9s an abundant supply bo? ( quanta ( high en]gy1 & ( p>ticles mov+ ) high spe$s4 ,,temp]ature-,,radiation4 ,we speak 9 ord9>y life ( a r$-heat or a :ite-heat1 mean+ ! heat to :i* a sub/ance mu/ be rais$ to emit r$ or :ite light respectively4 ,! filam5t 9 a c>bon-filam5t lamp is said to be rais$ to a r$-heat1 t 9 a gas-fill$ lamp to a yell[-heat4 ,x is n necess>y to specify ! sub/ance we are deal+ )2 if c>bon emits a r$ light at a temp]ature ( #cjjj1 !n tung/5 or any o!r sub/ance1 rais$ to ?is same temp]ature1 w emit exactly ! same r$ light z ! c>bon1 & ! same is true = o!r col\rs ( radiation4 ,?us ea* col\r1 & s also ea* wave-l5g? ( radiation1 has a def9ite temp]ature associat$ ) x1 ?is be+ ! temp]ature at :i* ?is p>ticul> col\r is mo/ abundant 9 ! spectroscopic analysis ( ! light emitt$ by a hot body4 ,z soon z ?is p>ticul> temp]ature beg9s to be approa*$1 b n be=e1 radiation ( ! wave-l5g? 9 "q becomes pl5tiful2 at temp]atures well bel[ ?is x is q inappreciable#ae4 #ae ,! wave-l5g? ( ! radiation & ! associat$ temp]ature ,t 7measur$ 9 ,c5tigrade degrees absolute7 are connect$ ?r\gh ! well-kn[n relation3 ,t #jbhee cm4 degree4 ,j z we speak ( a r$-heat or a :ite-heat1 we might1 al?\gh we d n d s1 q legitimately speak ( an ,x-ray heat or a -ray heat4 ,! %ort] ! wave-l5g? ( ! radiation1 ! high] ! temp]ature specially associat$ ) x4 ,?us z we make a sub/ance hott] & hott]1 x emits light ( ev] %ort] wave-l5g?1 & runs 9 succession ?r\gh ! :ole ra9b[ ( col\rs--r$1 orange1 yell[1 gre51 blue1 indigo1 violet4 ,we _c comm& a suffici5t range ( temp]ature to p]=m ! complete exp]im5t 9 ! laboratory1 b nature p]=ms x = u 9 ! />s4 ,,! ,,effects ,,( ,,heat4 ,we h already se5 t radiation ( %ort wave-l5g? is ne$$ to break up an electric /ructure ( small dim5sions4 ,z %ort wave-l5g?s are associat$ ) high temp]atures1 x n[ appe>s t ! small] an electrical /ructure is1 ! great] ! heat ne$$ to break x up4 ,& we c calculate ! temp]ature at :i* an electric /ructure ( giv5 dim5sions w fir/ beg9 to break up "u ! influ5ce ( heat#af4 #af ,on comb9+ ! relation j giv5 betwe5 ,t & ) t impli$ 9 ! r\gh law ( ! 8#hfj-limit10 we f9d t a /ructure ^: dim5sions are r cms4 w beg9 to be brok5 up by temp]ature-radiation :5 ! temp]ature fir/ approa*es _/r degrees4 ,= in/ance1 an ord9>y atom ) a diamet] ( ab\t #d #aj cms4 w fir/ be brok5 up at temp]atures ( ! ord] ( ?\s&s ( degrees4 ,to take a def9ite example1 yell[ light ( wave-l5g? #jjjjjf cm4 is specially associat$ ) ! temp]ature #dhjj degrees2 ?is temp]ature repres5ts an av]age 8yell[-heat40 ,at temp]atures well bel[ ?is1 yell[ light only occurs :5 x is artificially creat$4 ,b />s1 & all o!r bodies1 at a temp]ature ( #dhjj degrees emit yell[ light naturally1 & %[ l9es 9 ! yell[ region ( _! spectrum1 because yell[ light removes ! out]mo/ electron f ! atoms ( calcium & simil> elem5ts4 ,! electrons 9 ! calcium atom beg9 to be di/urb$ :5 a temp]ature ( #dhjj degrees beg9s to be approa*$1 b n be=e4 ,?is temp]ature is n approa*$ on e>? 7except 9 ! electric arc & o!r artificial conditions71 s t t]re/rial calcium atoms are g5]ally at re/ 9 _! /ates ( l[e/ en]gy4 ,to take ano!r in/ance1 ! %orte/ wave-l5g? ( radiation emitt$ 9 ! trans=mation ( uranium is ab\t #je #aj cms41 & ?is corresponds to ! enorm\sly high temp]ature ( #e1hjj1jjj1jjj degrees4 ,:5 "s su* temp]ature beg9s to be approa*$1 b n be=e1 ! con/itu5ts ( ! radio-active nuclei ought to beg9 to re-arrange !mselves1 j z ! con/itu5ts ( ! calcium atom d :5 a temp]ature ( #dhjj degrees is approa*$#ag4 ,?is ( c\rse expla9s :y no temp]ature we c comm& on e>? has any appreciable effect 9 exp$it+ or inhibit+ radio-active dis9tegration4 #ag ,if we suppose t re-arrangem5ts ( an electric /ructure c also be effect$ by bomb>d+ x ) mat]ial p>ticles1 ! temp]ature at :i* bomb>dm5t by electrons1 nuclei1 or molecules fir/ becomes effective is ab\t ! same z t at :i* radiation ( ! effective wave-l5g? w\ld fir/ beg9 to be appreciable2 ! two processes beg9 at approximately ! same temp]ature4 ,! table on p4 #add %ews ! wave-l5g?s ( ! radiation necess>y to effect v>i\s atomic trans=mations4 ,! la/ two columns %ew ! correspond+ temp]atures1 & ! k9d ( place1 s f> z we "k1 :]e ?is temp]ature is to be f\nd1 ^! latt] entries anticipat+ c]ta9 results :i* w be giv5 9 detail 9 ,*apt] ,v bel[ 7p4 #bhh74 ,9 places :]e ! temp]ature is f> bel[ t m5tion$ 9 ! la/ column b "o1 ! trans=mation 9 "q _c be affect$ by heat1 & s c only occur spontane\sly4 ,?us x is entirely a "o-way process4 ,! available radiation n be+ ( suffici5tly %ort wave-l5g? to "w ! atomic slot ma*9e1 ! atoms absorb no en]gy f ! surr\nd+ radiation & s are cont9ually slipp+ back into /ates ( l[] en]gy1 if su* exi/4 ,,highly ,,p5etrat+ ,,radiation ,! %orte/ wave-l5g?s we h s f> _h "u discussion are ^? ( ! -rays1 b ! la/ l9e ( ! table ref]s to radiation ) a wave-l5g? ( only ab\t a f\r-hundr$? "p ( t ( ! %orte/ ( -rays4 ,s9ce #aijb1 v>i\s inve/igators1 ,ru!r=d1 ,cooke1 ,mc,lennan1 ,burton1 ,kolhr/] & ,millikan 9 p>ticul>1 h f\nd t ! e>?'s atmosph]e is cont9ually be+ trav]s$ by radiation :i* has enorm\sly high] p5etrat+ p[] ?an any kn[n -rays4 ,by s5d+ up balloons to great heights1 ,hess1 ,kolhr/]1 & lat] ,millikan & ,b[51 h %ewn t ! radiation is noticeably m int5se at great heights1 ?us prov+ t x comes into ! e>?'s atmosph]e f outside4 ,if ! radiation _h its orig9 9 ! sun & />s1 ! ma9 "p ( ! radiation receiv$ on e>? w\ld come f ! sun1 & ! radiation w\ld be m int5se by day ?an by night4 ,?is is f\nd n to be ! case1 s t ! radiation _c come f ! />s1 & s mu/ orig9ate 9 nebulae or cosmic masses o!r ?an />s4 ,millikan is confid5t t its s\rces lie outside ! galactic sy/em4 ,! ,me*anical ,effects ( ,radiation ---------------------------------------- ----------------------- ,wave-l5g?s ,nature ( ,effect on ,atom ,temp]ature ,:]e 7cms47 ,radiation 7deg4 abs47 f\nd ---------------------------------------- ----------------------- #gejj #aj ,visible ,di/urbs #c1hej ,/ell> to light out]mo/ to atmosph]es #cgej #aj electrons #g1gjj #bej #aj ,x-rays ,di/urbs inn] #aae1jjj ,/ell> to electrons to int]iors #aj #bi1jjj1jjj #e #aj ,s(t ,/rip (f all #eh1jjj1jjj ,c5tral to -rays or ne>ly all to regions ( #aj electrons #bij1jjj1jjj;d5se />s #d #aj -rays ( ,di/urbs nucle> #gbj1jjj1jjj 8 radium-,b arrangem5t #e #aj ,%orte/ ---- #e4h #aj -rays #ac #aj ,highly ,annihilation or #b4b #aj p5etrat+ creation ( radiation proton & 787 accompany+ electron ---------------------------------------- ----------------------- ,! am\nt ( ! radiation is v great4 ,ev5 at sea-level1 :]e x is lea/1 ,millikan & ,cam]on f9d t x breaks up ab\t #ad atoms 9 e cubic c5timetre ( air ea* second4 ,x mu/ break up millions ( atoms 9 ea* ( our bodies e second--& we d n "k :at its physiological effects may be4 ,! total en]gy ( ! radiation receiv$ on e>? is j ab\t a t5? ( t ( ! total radiation1 light & heat toge!r1 receiv$ f all ! />s4 ,?is does n mean t light & heat are t5 times z abundant z ?is radiation 9 ! univ]se z a :ole4 ,= if ! radiation orig9ates 9 extra-galactic regions1 !n ! />s :i* s5d u light & heat are comp>atively ne>1 :ile ! s\rces ( ! highly p5etrat+ radiation are f> m remote4 ,on tak+ an av]age ?r\gh ! :ole ( space1 includ+ ! va/ /ret*es ( int]nebul> space1 x seems likely t ! highly p5etrat+ radiation is f> m pl5tiful ?an /ell> light & heat1 & s is ! mo/ abundant =m ( radiation 9 ! :ole univ]se4 ,x is ! mo/ p5etrat+ =m ( radiation kn[n4 ,ord9>y light w h>dly pass ?r\gh metals or solid sub/ances at all2 only a t9y fraction em]ges ?r\gh ! ?9ne/ ( gold-leaf4 ,on acc\nt ( _! %ort] wave-l5g?1 & s ( _! m en]getic quanta1 ,x-rays w pass ?r\gh foils ( a few millimetres ?ickness ( gold or ( lead4 ,! mo/ highly p5etrat+ -rays f radium-,b w pass ?r\gh in*es ( lead4 ,! radiation we h j be5 discuss+ v>ies 9 p5etrat+ p[]2 ! mo/ p5etrat+ "p ( x w pass ?r\gh #af feet ( lead4 ,x is n altoge!r cle> :e!r ! radiation is ( ! nature ( v %ort -radiation or is ( a corpuscul> nature1 l -radiation2 x may ev5 be a mixture ( bo?4 ,its p5etrat+ p[] f> exce$s t ( any kn[n -radiation1 s t if x is corpuscul>1 ! corpuscles mu/ be mov+ ) v ne>ly ! velocity ( light4 ,if1 z seems f> m likely1 ! radiation is1 9 "p at lea/1 ( ! nature ( -radiation1 !n x ought to be possible to det]m9e its wave-l5g? f its p5etrat+ p[]4 ,until q rec5tly diff]5t !ories on ! relation betwe5 ! two h be5 9 ! field4 ,! late/ !ory ( all1 t ( ,kle9 & ,ni%9a1 :i* is m p]fect & m complete ?an any ( ! e>li] !ories1 assigns to ! mo/ p5etrat+ "p ( ! radiation ! amaz+ly %ort wave-l5g? ( #ac #aj cms41 z indicat$ 9 ! table on p4 #add4 ,we p]haps get ! cle>e/ conception ( :at ?is means if we apply ! #hfj-rule2 ?is %ews t ! radiation w\ld break up an electric /ructure ^: dim5sions are only ab\t #aj cms4 ,no /ructure =m$ ( electrons & protons c possibly be z small z ?is1 = ! radius ( a s+le electron is ab\t #b #aj cms4 ,! radiation is ( ab\t ! wave-l5g? ne$$ to break up ! proton itself1 ! smalle/ & mo/ compact /ructure kn[n to sci5ce4 ,approa*+ ! problem f ano!r angle1 ! num]ical relations already giv5 %ew t a quantum ( radiation ( ?is wave-l5g? mu/ h en]gy equal to #jjjae erg1 & s mu/ h a weight ( ab\t #aff #aj grammes4 ,e physici/ recognises ?is weight at once1 = ! be/ det]m9ations give ! weight ( ! hydrog5 atom z #affb #aj grammes4 ,! quantum ( highly p5etrat+ radiation has1 !n1 j ab\t ! weight1 & j ab\t ! en]gy1 t w\ld result f a complete hydrog5 atom sudd5ly be+ annihilat$ & hav+ all its en]gy set free z radiation4 ,x c h>dly be suppos$ t all ! highly p5etrat+ radiation receiv$ on e>? has its orig9 9 ! annihilation ( hydrog5 atoms4 ,if = no o!r reason1 !re are probably n en\gh hydrog5 atoms 9 ! univ]se = su* a hypo!sis to be t5able4 ,! hydrog5 atom consi/s ( a proton & an electron1 & its weight is r\ghly ! same z ! comb9$ weight ( a proton & an electron select$ f any atom 9 ! univ]se1 s t1 to a ne> en\gh approximation1 ! quantum ( highly p5etrat+ radiation has ! wave-l5g? & en]gy :i* w\ld result f a proton & electron 9 any atom :atev] coalesc+ & annihilat+ "o ano!r4 ,we h se5 h[ ! weights ( ! diff]5t kn[n types ( atoms approximate to integral multiples ( ! weight ( ! hydrog5 atom1 or to be m precise1 diff] by almo/ exactly equal /eps1 ea* ( :i* is ab\t equal to ! weight ( ! hydrog5 atom4 ,! weight ( ! quantum ( highly p5etrat+ radiation is equal to ! *ange ( weight repres5t$ by a s+le /ep1 s t ! quantum c\ld be produc$ by any trans=mation :i* degrad$ ! weight ( an atom by a s+le /ep4 ,9 ! mo/ g5]al case possible1 ?is degradation ( weight mu/1 s f> z we c see1 arise f ! coalesc5ce ( a proton & electron1 ) ! result+ annihilation ( bo?4 ,:ile ?is seems f> & away ! mo/ probable s\rce ( ?is radiation1 x is n ! only conceivable s\rce4 ,= in/ance1 ! mo/ abundant isotope ( x5on1 ( atomic numb] #ed & atomic weight #abi1 is built up ( #abi protons1 #ge nucle> electrons & #ed orbital electrons4 ,! sudd5 build+ up ( su* an atom out ( #abi protons & #abi electrons w\ld involve a loss ( weight j ab\t equal to ! weight ( ! hydrog5 atom4 ,if ! build+ took place absolutely simultane\sly1 s t ! :ole ( ! lib]at$ en]gy 0 emitt$ cata/rophically z a s+le quantum1 ?is quantum w\ld h ab\t ! same wave-l5g? & p5etrat+ p[] z ! obs]v$ highly p5etrat+ radiation4 ,"s "t ago ,millikan sugge/$ ! =mation ( o!r complex atoms out ( simpl] con/itu5ts z a possible s\rce ( ! radiation1 b x n[ appe>s t ! s*emes he prop\nd$ w\ld n result 9 radiation ( suffici5tly %ort wave-l5g?1 at any rate if ! mod]n ,kle9-,ni%9a !ory is correct4 ,on ! physical evid5ce alone1 su* s*emes _c be dismiss$ z impossible1 b !y mu/ be treat$ z suspect on acc\nt ( _! high improbability4 ,! x5on atom ) its #beh con/itu5t p>ts is a highly complicat$ /ructure1 & x is exce$+ly h>d to believe t all ^! #beh p>ts c\ld be hamm]$ into a fully-=m$ atom by a s+le in/antane\s act1 accompani$ by ! cata/rophic emission ( only "o quantum ( radiation4 ,if atoms ev] are built up out ( simpl] con/itu5ts--& !re is no evid5ce :atev] t ?is process ev] occurs 9 nature--x seems s mu* m likely t ! aggregation w\ld take place by di/9ct /ages1 & t ! radiation w\ld be emitt$ 9 a numb] ( small quanta r ?an 9 "o l>ge quantum4 ,moreov]1 any su* hypo!sis has to expla9 ! num]ical agreem5t ( ! calculat$ weight ( ! obs]v$ quanta ( radiation ) ! kn[n weight ( ! hydrog5 atom z a pure co9cid5ce4 ,n only s1 b also we h to suppose t atoms ( x5on1 & possibly o!rs ( approximately ! same atomic weight1 are =m$ f> m frequ5tly ?an atoms ( o!r atomic weights4 ,inde$ ! am\nt ( ! highly p5etrat+ radiation receiv$ on e>? is s great t if x 7 evid5ce ( ! creation ( x5on1 a l>ge "p ( ! univ]se ought already to consi/ ( x5on1 mix$ p]haps ) elem5ts ( ne>ly equal atomic weight4 ,s f> is ?is f be+ ! case1 t x5on & its neighb\rs 9 ! atomic weight table are among ! r>e/ ( elem5ts4 ,= ^! reasons1 & on ! g5]al pr9ciple t ! simpl] & m natural hypo!sis is always to be giv5 pref]5ce 9 sci5ce1 we may say t ! annihilation ( electrons & protons =ms a m probable & m acceptable orig9 = ! obs]v$ highly p5etrat+ radiation4 ,we may leave ! problem 9 ?is /ate ( unc]ta9ty = ! pres5t1 because x w appe> lat] t a/ronomy has "s evid5ce to give on ! "q4 ,,*apt] ,,iii ,explor+ 9 ,"t ,we h explor$ space to ! fur!/ dep?s to :i* our telescopes c probe2 we h explor$ into ! intricacies ( ! m9ute /ructures we call atoms1 ( :i* ! :ole mat]ial univ]se is built2 we n[ wi% to g explor+ 9 "t4 ,man's individual span ( life1 & inde$ ! :ole span ( "t cov]$ by our hi/orical records--"s few ?\s&s ( ye>s at mo/--are bo? f> too %ort to be ( any s]vice = our purpose4 ,we mu/ f9d f> long] measur+ rods ) :i* to s\nd ! dep?s ( pa/ "t & to probe =w>d into ! future4 ,our g5]al me?od w be "o :i* ! /udy ( geology has already made famili>4 ,undet]r$ by ! abs5ce ( direct hi/orical evid5ce1 ! geologi/ insi/s t life has exi/$ on e>? = millions ( ye>s1 because fossil rema9s ( life are f\nd to occur "u deposits :i*1 he e/imates1 mu/ h tak5 millions ( ye>s to accumulate4 ,z he digs d[n ?r\gh diff]5t /rata 9 succession1 he is explor+ 9 "t j z truly z ! geograph] :o travels ov] ! surface ( ! e>? is explor+ 9 space4 ,a simil> me?od c be us$ by ! a/ronom]4 ,we f9d "s a/ronomical effect1 quality1 or prop]ty1 :i* exhibits a cont9ual accumulation or decrease1 l ! s& 9 ! bottom or top half ( ! h\r-glass2 we e/imate ! rate at :i* ?is increase or decrease is occurr+ at ! pres5t mom5t1 & also1 if we c1 ! rate at :i* x mu/ h occurr$ "u ! diff]5t conditions prevail+ 9 ! pa/4 ,x !n becomes a "q1 p]haps ( m]e ari?metic1 al?\gh possibly ( m complicat$ ma!matics1 to e/imate ! "t :i* has elaps$ s9ce ! process fir/ />t$4 ,,! ,,age ,,( ,,! ,,e>? ,! me?od is well exemplifi$ 9 ! comp>atively simple problem ( ! age ( ! e>?4 ,! fir/ sci5tific attempt to fix ! age ( ! e>? 0 made by ,halley1 ! a/ronom]1 9 ! ye> #agae4 ,ea* day ! riv]s c>ry a c]ta9 am\nt ( wat] d[n to ! sea1 & ?is conta9s small am\nts ( salt 9 solution4 ,! wat] evaporates & 9 due c\rse returns to ! riv]s2 ! salt does n4 ,z a consequ5ce ! am\nt ( salt 9 ! oceans goes on increas+2 ea* day !y conta9 a little m salt ?an !y did on ! prec$+ day1 & ! pres5t sal9ity ( ! oceans gives an indication ( ! l5g? ( "t dur+ :i* ! salt has be5 accumulat+4 8,we are ?us furni%$ ) an argum5t10 said ,halley1 some:at optimi/ically1 8= e/imat+ ! duration ( all ?+s40 ,?is l9e ( argum5t does n lead to v precise e/imates ( ! e>?'s age1 b calculations bas$ on mod]n data sugge/ t x mu/ be _m hundr$s ( millions ( ye>s4 ,m valuable in=mation c be obta9$ f ! accumulation ( s$im5t wa%$ d[n by ! ra94 ,e ye> t passes witnesses a levell+ ( ! e>?'s surface4 ,soil :i* 0 high up on ! slopes ( hills & m\nta9s la/ ye> has by n[ be5 wa%$ d[n to ! bottoms ( muddy riv]s by ! ra9 & is cont9ually be+ c>ri$ out to sea4 ,! ,?ames alone c>ries betwe5 "o & two million tons ( soil out to sea e ye>4 ,= h[ long w ,engl& la/ at ?is rate1 & = h[ long c x h already la/$8 ,9 our own lifetimes we h se5 l>ge masses ( l& r\nd our coa/s =m l&slides1 & ei!r fall :olly into ! sea or slip d[n ne>] to sea-level4 ,su* conspicu\s l&m>ks z ! ,ne$les1 & inde$ a l>ge "p ( ! s\!rn coa/ ( ! ,isle ( ,wight1 are disappe>+ be=e our eyes4 ,! geologi/ c =m an e/imate ( ! rapidity ) :i* ^! & simil> processes are happ5+1 & s c e/imate h[ long s$im5tation has be5 9 progress to produce ! obs]v$ ?ickness ( geological lay]s4 ,^! ?icknesses are v great2 ,pr(essor ,ar?ur ,holmes#ah gives ! obs]v$ maximum ?icknesses z foll[s3 ,pre-,cambrian at lea/ #ahj1jjj feet ,palaeozoic ,era 7,anci5t life7 #ahe1jjj 0 ,mesozoic ,era 7,m$iaeval life7 #ia1jjj 0 ,ca9ozoic ,era 7,mod]n life7 #gc1jjj 0 #ah ,9 discuss+ ! e>?'s age1 ,i h borr[$ ext5sively f ,pr(essor ,holmes' book1 ,! ,age ( ! ,e>?4 ,we c =m a g5]al idea ( ! rate at :i* ^! s$im5ts h be5 deposit$4 ,s9ce ,rameses ,,ii reign$ 9 ,egypt ov] #cjjj ye>s ago1 s$im5t has be5 deposit$ at ,memphis at ! rate ( a foot e #djj or #ejj ye>s2 ! excavator mu/ dig d[n #f or #g feet to rea* ! surface ( ,egypt z x /ood :5 ,rameses ,,ii 0 k+4 ,! pres5t rate ( d5udation 9 ,nor? ,am]ica is e/imat$ to be "o foot 9 #hfjj ye>s2 simil> e/imates = ,great ,brita9 indicate a rate ( "o foot 9 #cjjj ye>s4 ,) geological /rata deposit$ at an av]age rate ( "o foot p] #ajjj ye>s1 ! total #ebi1jjj feet ( /rata li/$ above w\ld require ov] #ejj million ye>s = _! deposition4 ,at a rate ( "o foot p] #djjj ye>s1 ! "t w\ld be ab\t #bajj million ye>s4 ,?is me?od ( e/imat+ geological "t has be5 describ$ z ! 8,geological h\r-glass40 ,we see h[ mu* s& has already run1 we notice h[ fa/ x is runn+ n[1 & a calculation tells u h[ long x is s9ce x fir/ />t$ to run4 ,! me?od suff]s f ! usual defect ( h\r-glasses1 t !re is no gu>antee t ! s& has always run at a uni=m rate4 ,geological me?ods suffice to %ew t ! e>? mu/ be hundr$s ( millions ( ye>s old1 b to obta9 m def9ite e/imates ( its age1 ! m precise me?ods ( physics & a/ronomy mu/ be call$ 94 ,=tunately ! radio-active atoms discuss$ 9 ! previ\s *apt] provide a p]fect sy/em ( clocks1 ^: rate s f> z we "k does n v>y by a hair's bread? f "o age to ano!r4 ,we h se5 h[1 ) ! lapse ( suffici5t "t1 an ounce ( uranium dis9tegrates into #jhfe ounce ( lead & #jace ounce ( helium4 ,! process ( dis9tegration is absolutely spontane\s2 no physical ag5cy kn[n 9 ! :ole univ]se c ei!r inhibit or exp$ite x 9 ! t9ie/ degree4 ,! foll[+ table %ews ! rate at :i* x progresses3 ,hi/ory ( ,"o ounce ( ,uranium ,initially3 #a oz4 uranium ,no lead ,aft] #ajj million ye>s #jihe oz4 uranium #jjac oz4 lead 0 #ajjj 0 #jhfe 0 0 #jaaf 0 0 0 #bjjj 0 #jgdg 0 0 #jbai 0 0 0 #cjjj 0 #jfdf 0 0 #jcjf 0 0 & s on4 ,?us a small am\nt ( uranium provides a p]fect clock1 provid$ we are able to measure ! am\nt ( lead x has =m$1 & also ! am\nt ( uranium /ill surviv+1 at any "t we please4 ,:5 ! e>? fir/ solidifi$1 _m fragm5ts ( uranium 7 imprison$ 9 its rocks1 & may n[ be us$ to disclose ! age ( ! e>?4 ,we are n entitl$ to assume t all ! lead :i* is f\nd associat$ ) uranium has be5 =m$ by radio-active integration4 ,b1 by a =tunate *ance1 lead :i* has be5 =m$ by ! dis9tegration ( uranium is j a bit diff]5t f ord9>y lead2 ! latt] has an atomic weight ( #bjgb1 :ile ! =m] is ( atomic weight only #bjfj4 ,?us a *emical analysis ( any sample ( radio-active rock %ews exactly h[ mu* ( ! lead pres5t is ord9>y lead1 & h[ mu* has be5 =m$ by radio-active dis9tegration4 ,! proportion ( ! am\nt ( lead ( ?is latt] k9d to ! am\nt ( uranium /ill surviv+ tells u exactly = h[ long ! process ( dis9tegration has be5 go+ on4 ,9 g5]al all ! samples ( rock :i* are exam9$ tell mu* ! same /ory1 & ! radio-active clock is f\nd to fix ! "t s9ce ! e>? solidifi$ at #adjj million ye>s or m4 ,! clock _c tell u = h[ long be=e ?is ! e>? _h exi/$ 9 a pla/ic or fluid /ate1 s9ce 9 ?is e>li] /ate ! products ( dis9tegration 7 liable to become sep>at$ f "o ano!r4 ,a/on has rec5tly discov]$ a new isotope 7see p4 #aah7 ( uranium1 call$ act9o-uranium4 ,z uranium & its isotope h diff]5t p]iods ( decay1 ! relative abundance ( ! two is cont9ually *ang+4 ,f ! ratio ( ! am\nts ( ^! sub/ances n[ surviv+ on e>?1 ,ru!r=d has calculat$ t ! age ( ! e>? _c exce$ #cdjj million ye>s1 & is probably sub/antially less4 ,^! two physical e/imates ( ! "t :i* has elaps$ s9ce ! e>? solidifi$ /& z foll[s3 ,age ( ! ,e>? by ! ,radio-active ,clock #a4 ,f ! lead-uranium ratio 9 radio-active ,m ?an #adjj million ye>s4 rocks #b4 ,f ! relative abundance ( uranium & ,less ?an #cdjj million ye>s4 act9o-uranium ,v>i\s a/ronomical me?ods are also available = det]m9+ ! "t s9ce ! sol> sy/em came into be+4 ,"h ! 8clocks0 are provid$ by ! %apes ( ! orbits ( v>i\s planets & satellites4 ,! orbits d n *ange at uni=m rates1 b _! *anges are det]m9$ by kn[n laws1 s t ! ma!matician c calculate ! rates at :i* *ange occurr$ "u pa/ conditions1 & h5ce1 by totall+ up1 c d$uce ! "t ne$$ to e/abli% pres5t conditions4 ,! foll[+ two e/imates are bo? due to ,dr ,h4 ,jeffreys3 ,age ( ! ,sol> ,sy/em by ! ,a/ronomical ,clock #a4 ,f ! orbit ( ,m]cury 444 ,f #ajjj to #aj1jjj million ye>s4 #b4 0 0 ! ,moon 444 ,r\ghly ab\t #djjj million ye>s4 ,:ile ^! v>i\s figures d n admit ( any v exact e/imate ( ! e>?'s age1 !y all indicate t ?is mu/ be measur$ 9 ?\s&s ( millions ( ye>s4 ,if we wi% to fix our ?\ghts on a r\nd numb]1 probably #bjjj million ye>s is ! be/ to select4 ,,! ,,ages ,,( ,,! ,,/>s ,we n[ turn to ! f> m difficult problem ( det]m9+ ! ages ( ! />s4 ,we %all n approa* x by a direct frontal attack1 b />t f> away f our real objective4 ,let u 9 fact />t at ! extreme o!r end ( ! univ]se1 & delve a bit fur!r into ! prop]ties ( a gas4 ,,equip>tition ,,( ,,en]gy ,,9 ,a ,,gas4 ,we h pictur$ a gas z an indiscrim9ate flight ( molecule-bullets4 ,^! fly equally 9 all directions1 occasionally cra%+ into "o ano!r1 & 9 s do+1 *ang+ bo? _! spe$s & directions ( flight4 ,we h se5 t ! total en]gy ( motion und]goes no decrease :5 su* collisions occur4 ,if "o ( ! molecules tak+ "p 9 a collision has its spe$ *eck$1 ! o!r has its spe$ increas$ by su* an am\nt t ! en]gy lo/ by "o molecule is ga9$ by ! o!r4 ,total en]gy ( motion is 8cons]v$40 ,into ?is r&om hail ( bullets1 let u imag9e t we project a f> heavi] projectile1 :i* we may call a cannon-ball1 ) a spe$ equal to ab\t ! av]age spe$ ( ! bullets4 ,! en]gies ( ! v>i\s projectiles are proportional jo9tly to _! weights & to ! squ>es ( _! spe$s1 s t 9 ! pres5t case1 9 :i* ! spe$s are all mu* ! same1 ! big projectile has m en]gy ?an ! bullets simply on acc\nt ( its great] weight4 ,if x weighs z mu* z a ?\s& bullets1 x has a ?\s& times z mu* en]gy z ea* s+le bullet4 ,yet ! heavy projectile _c = long cont9ue swagg]+ ?r\gh its less] companions ) a ?\s& times its fair %>e ( en]gy4 ,its fir/ exp]i5ce is to enc\nt] a hail ( bullets on its *e/4 ,v few bullets hit x 9 ! back1 = !y are only mov+ at ab\t its own spe$1 & s c h>dly ov]take x f beh9d4 ,moreov]1 ev5 if !y d1 _! bl[s on its back are v feeble because !y are h>dly mov+ fa/] ?an x4 ,b ! %[] ( bl[s on its *e/ is s]i\s2 e "o ( ^! t5ds to *eck its spe$1 & s to less5 its en]gy4 ,& z ! total en]gy ( motion is cons]v$ at e collision1 x foll[s t1 :ile ! big projectile is los+ en]gy all ! "t1 ! little ones mu/ be ga9+ en]gy at its exp5se4 ,= h[ long w ?is int]*ange ( en]gy g on8 ,w x1 = in/ance1 cont9ue until ! big projectile has lo/ all its en]gy1 & be5 br\ght completely to re/8 ,! problem is "o = ! ma!matician1 & x admits ( a p]fectly exact ma!matical solution1 :i* ,maxwell gave z f> back z #ahei4 ,! big projectile is n depriv$ ( all its en]gy4 ,z its spe$ gradually decreases1 conditions *ange 9 all sorts ( ways4 ,:5 we all[ = ?is *ange ( conditions1 we f9d t ! en]gy ( ! big projectile goes on decreas+1 n until x has lo/ all its en]gy1 b until x has no m en]gy ?an ! av]age bullet4 ,:5 ?is /age is rea*$1 ! hits ( ! bullets are z likely on ! av]age to increase ! en]gy ( ! big projectile z to decrease x1 s t ?is ends up by fluctuat+ ar\nd an am\nt equal to ! av]age en]gy ( ! little projectiles4 ,maxwell1 & o!rs aft] him1 fur!r %ew$ t no matt] h[ _m k9ds ( molecules !re may be mix$ toge!r 9 a gas1 & no matt] h[ widely _! weights may diff] f "o ano!r1 _! repeat$ collisions mu/ ultimately e/abli% a /ate ( ?+s 9 :i* big molecules & little1 light & heavy1 all h ! same av]age en]gy4 ,?is is kn[n z ! !orem ( equip>tition ( en]gy4 ,x does n mean t at any s+le in/ant all ! molecules h precisely ! same en]gy2 obvi\sly su* a /ate ( ?+s c\ld n cont9ue = a mom5t1 s9ce ! fir/ collision betwe5 any pair ( molecules w\ld upset x imm$iately4 ,b on av]ag+ ! en]gy ( ea* molecule ov] a suffici5tly long p]iod ( "t--say a second1 :i* is a v long "t inde$ 9 ! life ( a molecule1 be+ ! "t 9 :i* at lea/ a hundr$ million collisions occur--we %all f9d t ! av]age en]gy ( all ! molecules is ! same1 reg>dless ( _! weights4 ,! same !orem c be /at$ 9 a slightly diff]5t =m4 ,air consi/s ( a mixture ( molecules ( diff]5t k9ds & ( diff]5t weights--molecules ( helium :i* are v light1 molecules ( nitrog5 :i* are f> heavi]1 ea* weigh+ z mu* z sev5 molecules ( helium1 & ! /ill heavi] molecules ( oxyg51 ea* ) ! weight ( eight molecules ( helium4 ,9 its alt]native =m1 ! !orem tells u t at any in/ant ! av]age en]gy ( all ! molecules ( helium1 9 spite ( _! light weights1 is exactly equal to ! av]age en]gy ( ! molecules ( nitrog51 & aga9 ea* ( ^! is exactly equal to ! av]age en]gy ( ! molecules ( oxyg54 ,! light] types ( molecule make up = _! small weights by _! high spe$s ( motion4 ,simil> /atem5ts are ( c\rse true = any o!r mixture ( gases4 ,! tru? ( ! !orem is confirm$ obs]vationally 9 a great v>iety ( ways4 ,9 #ahdf1 ,graham measur$ ! relative spe$s ) :i* ! molecules ( diff]5t k9ds ( gas mov$1 by obs]v+ ! rates at :i* !y /ream$ ?r\gh an orifice into a vacuum2 ^! prov$ to be su* t ! av]age en]gies ( ! v>i\s types ( molecules 7 precisely equal to "o ano!r4 ,ev5 e>li] ?an ?is1 ,leslie & o!rs _h us$ ?is me?od to det]m9e ! relative weights ( diff]5t molecules1 al?\gh )\t fully und]/&+ ! und]ly+ !ory4 ,?us x may be accept$ z a well-e/abli%$ law ( nature t no molecule is all[$ p]man5tly to reta9 m en]gy ?an 8 fell[s2 9 respect ( _! en]gies ( motion1 a gas =ms a p]fectly organis$ communi/ic /ate 9 :i* a law1 :i* !y _c evade1 compels ! molecules to %>e _! en]gies equally & fairly4 ,subject to c]ta9 slight modifications1 ! same law applies also to liquids & solids4 ,9 liquids & gases1 we c actually p]=m an exp]im5t analog\s to t ( project+ our imag9>y cannon-ball into ! hail ( molecule-bullets1 & wat* ev5ts4 ,we may take a few gra9s ( v f9e p[d]1 p[d]$ gamboge or lycopodium se$1 = in/ance1 & let ^! play ! "p ( sup]-molecules among/ ! ord9>y molecules ( a gas or liquid4 ,a p[]ful microscope %ews t ^! sup]-molecules are n br\ght completely to re/1 b reta9 a c]ta9 livel9ess ( movem5t1 z !y are cont9ually hit ab\t by ! small] & q invisible true molecules4 ,x looks = all ! _w z ?\gh !y 7 affect$ by a *ronic ,/ ,vitus' dance1 :i* %ews no signs ( dim9i%+ z "t goes on4 ,^! movem5ts are call$ 8,br[nian movem5ts10 aft] ,rob]t ,br[n1 ! botani/1 :o fir/ obs]v$ !m 9 ! sap ( plants4 ,br[n at fir/ int]pret$ !m z evid5ce ( real life 9 ! small p>ticles affect$ by !m1 an int]pretation :i* he _h to ab&on :5 he f\nd t p>ticles ( wax %ew$ ! same movem5ts4 ,9 a s]ies ( exp]im5ts ( amaz+ delicacy1 ,p]r9 n only obs]v$1 b also measur$1 ! ,br[nian movem5ts ( small solid p>ticles z !y 7 hit ab\t by ! molecules ( air & o!r gases1 & d$uc$ ! weights ( ! molecules ( ^! gases ) great accuracy4 ,,/ell> ,,equip>tition ,,( ,,en]gy4 ,we c n[ get back to ! />s4 ,! !orem ( equip>tition ( en]gy is true n only ( ! molecules ( a gas1 & ( a solid1 & ( a liquid2 x is true also ( ! />s ( ! sky4 ,! processes ( ma!matics are applicable to ! v great z well z to ! v small1 & a !orem :i* is prov$ true = ! m9ute/ ( atoms is equally true = ! mo/ /up5d\s ( />s1 provid$ ( c\rse t ! premisses on :i* x is bas$ rema9 true1 & d n suff] by transf]5ce f ! small to ! great end ( ! univ]se4 ,n[ ! conditions :i* are necess>y = ! !orem ( equip>tition ( en]gy to be true happ5 to be amaz+ly simple2 inde$ x is difficult to believe t su* wide consequ5ces c foll[ f su* simple conditions4 ,!y am\nt to practically no?+ beyond a law ( cont9uity & a law ( causation2 9 o!r words1 t ! /ate ( ! sy/em at any in/ant %all foll[ inevitably f its /ate at ! prec$+ in/ant1 or if y l1 t !re %all be no free-w among ! molecules or />s or o!r bodies ^: motions are "u discussion4 ,9 ! pres5t turmoil z to ! fundam5tal laws ( physics1 we _c be entirely c]ta9 z to h[ f> ^! v simple conditions are fulfill$ 9 ! molecul> problem1 al?\gh abundant obs]vational evid5ce makes x cle> t ! law ( equip>tition holds1 at any rate to an exce$+ly good approximation1 9 an ord9>y gas4 ,on ! o!r h&1 !re is n ! slighte/ d\bt z to :at det]m9es ! motions ( ! />s2 x is ! law ( gravitation1 e /> attract+ e o!r /> ) a =ce :i* v>ies inv]sely z ! squ>e ( _! di/ance ap>t4 ,?is is ,newton's =m ( ! law1 b x is a matt] ( complete indiff]5ce = our pres5t purpose :e!r we use ! law 9 ,newton's or 9 ,e9/e9's =m2 = /ell> problems ! two are practically indi/+ui%able1 & !re is abundant evid5ce1 p>ticul>ly f ! obs]v$ orbits ( b9>y />s1 9 fav\r ( ei!r4 ,! ess5tial po9t is t1 f ! s+le supposition t ! motions ( ! />s are gov]n$ by ei!r ( ^! laws ( gravitation--or1 = ! matt] ( t1 by any o!r n entirely dissimil> law--we c prove ! !orem ( equip>tition ( en]gy to be true = ^! motions4 ,no subtle /atem5t ( exact conditions is requir$2 ! m]e law ( gravitation1 toge!r ) ! supposition t ! />s _c ex]cise free-w z to :e!r !y obey x or n1 is en\gh4 ,x is important to und]/& q cle>ly :at precisely ! !orem ass]ts :5 appli$ to ! />s4 ,x does n ( c\rse ass]t t all ! />s 9 ! sky h equal en]gies4 ,x does n ev5 ass]t t on ! av]age ! heavy-weight />s 9 ! sky h ! same en]gy z ! light-weight />s4 ,:at x ass]ts is t if we put any miscellane\s assortm5t ( />s into space1 !n1 aft] !y h int]act$ ) "o ano!r = a suffici5t l5g? ( "t 7?is is ! ess5tial po9t71 ^? :i* />t$ ) m ?an _! fair %>e ( en]gy w h be5 compell$ to h& ov] _! excess to />s ) less] en]gy1 s t ! av]age en]gy ( all ! diff]5t types ( />s mu/ necess>ily become r$uc$ to equality 9 ! long run4 ,9 ! molecul> problem1 ! int]action betwe5 ! molecules takes place ?r\gh ! m$ium ( collisions1 & equip>tition ( en]gy is e/abli%$1 to a v good approximation1 aft] "s eight or t5 collisions h happ5$ to ea* molecule4 ,9 ord9>y air1 ?is requires a p]iod ( only ab\t a hundr$-million? "p ( a second4 ,9 ! /ell> problem1 we are deal+ ) v diff]5t l5g?s ( "t2 collisions only occur at int]vals ( ?\s&s ( millions ( millions ( ye>s4 ,if ! />s only r$i/ribut$ _! en]gy :5 actual collisions occurr$1 we might surmise t a close approximation to equip>tition ( en]gy w\ld n be atta9$ until aft] ea* /> _h exp]i5c$ eight or t5 collisions1 & ?is w\ld require a really /up5d\s l5g? ( "t4 ,actually no su* l5g? ( "t is ne$$ because ! num]\s gravitational pulls1 ev5 betwe5 />s :i* are at a consid]able di/ance ap>t1 equalise en]gy f> m effici5tly & exp$iti\sly ?an ! v r>e direct hits4 ,e "t t two />s happ5 to pass ev5 fairly ne> to "o ano!r 9 _! w&]+s1 ea* pulls ! o!r a bit out ( its c\rse1 & ! directions & spe$s ( motion ( bo? />s are *ang$--by mu* or little accord+ z ! />s pass q close to "o ano!r or keep at a sub/antial di/ance ap>t4 ,9 brief1 ea* approa* ( />s causes an int]*ange ( en]gy1 & aft] suffici5t "t1 ^! repeat$ int]*anges ( en]gy result 9 ! total en]gy be+ %>$ equally1 on ! av]age1 betwe5 ! />s1 reg>dless ( diff]5ces 9 _! weights4 ,n[ ! crux ( ! situation1 to :i* all ?is has be5 lead+ up1 is t obs]vation %ews t />s ( diff]5t weights are mov+ ) diff]5t av]age spe$s1 ^! av]age spe$s be+ su* t equip>tition ( en]gy already prevails among ! />s--n absolutely exactly1 b to a tol]ably good approximation4 ,! "q ( h[ long ! />s mu/ h int]act$ to rea* su* a condition n[ becomes "o ( absolutely fundam5tal importance1 = ! answ] tells u ! ages ( ! />s4 ,,/ell> ,,velocities4 ,we h already se5 7p4 #dh7 h[ />s :i* =m b9>y sy/ems c be weigh$1 su* weigh+s disclos+ weights rang+ f ab\t a hundr$ times ! weight ( ! sun to only a fif? ( its weight4 ,! spe$s ( motion ( b9>y sy/ems c be measur$ 9 precisely ! same way z ! spe$s ( s+le />s4 ,z f> back z #aiaa1 ,halm1 ) an accumulation ( su* measurem5ts be=e him1 po9t$ out t ! heavie/ />s mov$ ! mo/ sl[ly4 ,he f\nd t1 on ! av]age1 ! heavie/ ( kn[n />s _h approximately ! same en]gy ( motion z ! lighte/1 ! high spe$s ( ! latt] j ab\t mak+ up = ! smallness ( _! weights1 & s sugge/$ t ! velocities ( ! />s1 l ^? ( ! molecules ( a gas1 might be f\nd to con=m to ! law ( equip>tition ( en]gy4 ,x appe>$ to be a case ( ,br[nian movem5ts on a /up5d\s scale4 ,s9ce !n a great deal m obs]vational evid5ce has accumulat$1 & an exhau/ive inve/igation made by ,dr ,se>es ( ,m\nt ,wilson 9 #aibb leaves v little room = d\bt t ! motions ( ! />s %ew a real1 & fairly close1 approximation to equip>tition ( en]gy4 ,! table ov]leaf %ews ! f9al result ( ,se>es' discussion4 ,! />s are fir/ classifi$ accord+ to ! diff]5t types ( spectrum _! light %ews :5 analys$ 9 a spectroscope4 ,equip>tition ( ,en]gy 9 ,/ell> ,motions ---------------------------------------- ---------------------- ,av]age ,av]age ,av]age ,correspond+ weight spe$ en]gy temp]ature ,type ( /> ,m ,c ,,mc 7degrees7 7grammes7 7cms4_/sec47 7ergs7 ---------------------------------------- ---------------------- ,spectral type ,b #c #aih #ajadh #aj #aie #ajaj #aj 0 ,b #heabi #aeh #afb #jh 0 ,a #j #aba #bde #cfc #ah 0 ,a #b #ajj #bgb #cgb #ah 0 ,a #e #hj #bii #cee #ag 0 ,f #j #ej #cei #cbd #af 0 ,f #e #ca #dgi #cee #ag 0 ,g #j #bj #fdf #djg #bj 0 ,g #e #ae #ggf #deg #bb 0 ,k #j #ad #gid #dbg #ba 0 ,k #e #ab #gda #cci #ag 0 ,m #j #ab #ggf #cee #ag ---------------------------------------- ---------------------- ,^! diff]5t types ( />s h v diff]5t av]age weights2 ! second column ( ! table %ews t !y exhibit a range ( ov] #af to #a4 ,! ?ird column1 :i* gives ! av]age spe$s ( ^! diff]5t types ( />s1 %ews t ! heavie/ />s move ! mo/ sl[ly1 & ! lighte/ on ! :ole ! mo/ rapidly4 ,! next column gives ! av]age en]gy ( motion ( ! diff]5t types ( />s4 ,?is %ews t ! v>iation 9 spe$s is j ab\t t ne$$ to make ! av]age en]gies ( all types ( />s equal4 ,an exception c]ta9ly occurs 9 ! fir/ two l9es1 :i* ref] to ! heavie/ />s ( all4 ,ap>t f ^!1 ! rema9+ t5 l9es %ew a ratio ( #aj to #a 9 weight1 :]eas ! av]age deviation ( en]gy f ! mean is only "o ( #i p] c5t4 ,f ?is we see t ! motions ( ! />s %ew a real approa*1 & ev5 a fairly close approa*1 to equip>tition ( en]gy4 ,! "q :i* naturally pres5ts itself is :e!r ?is approximate equality ( en]gy c be attribut$ to any o!r cause ?an long-cont9u$ gravitational int]action betwe5 ! />s4 ,?is latt] ag5cy c\ld und\bt$ly produce x1 b c\ld any?+ else produce a simil> result8 ,! la/ column ( ! table provides ! answ]4 ,x %ews ! temp]atures to :i* a gas w\ld h to be rais$1 9 ord] t ea* ( its molecules %\ld h ! same en]gy z ! diff]5t types ( />s4 ,?is may well seem an absurd calculation4 ,a /> weigh+ millions ( millions ( millions ( tons goes hurtl+ ?r\gh space at a spe$ ( ab\t #a1jjj1jjj miles an h\r2 are we s]i\sly sett+ out to inquire h[ hot a gas mu/ be = e s+le "o ( its t9y molecules to h ! same en]gy ( motion1 ! same p[] ( do+ damage--= t is :at en]gy ( motion really am\nts to--z ! />8 ,! calculation is und\bt$ly absurd1 & x is meant to be1 because x is lead+ up to a r$uctio ad absurdum4 ,if ! obs]v$ equip>tition ( en]gy 7 br\ght ab\t by any physical ag5cy1 su* z pressure ( radiation1 bomb>dm5t by molecules1 by atoms or by high spe$ electrons1 ?is ag5cy w\ld h to be at a temp]ature1 or 9 equilibrium ) matt] at a temp]ature1 ( ! ord] ( ^? giv5 9 ! la/ column4 ,^! are temp]atures ( ! ord] ( #aj degrees4 ,we c be pretty sure no su* temp]ature exi/s 9 nature1 :5ce ! argum5t runs t ! obs]v$ equip>tition ( en]gy _c h be5 br\ght ab\t by physical means1 & s mu/ be ! result ( gravitational int]action betwe5 ! />s4 ,! age ( ! />s is1 !n1 simply ! l5g? ( "t ne$$ = gravitational =ces to br+ ab\t z good an approximation to equip>tition ( en]gy z is obs]v$4 ,! calculation ( ?is l5g? ( "t pres5ts a complicat$ b by no means intractable problem4 ,all ! necess>y data are available1 & z ! me?od ( calculation is well und]/ood f previ\s exp]i5ce 9 ! !ory ( gases1 ! ma!matician may be tru/$ to supply a reliable & reasonably exact answ] :5 we ask him1 b ev5 )\t 8 help we c see t ! "t mu/ be v long inde$4 ,leav+ actual figures aside = ! mom5t1 we may f9d x easi] to ?9k 9 t]ms ( ! scale-model we con/ruct$ 9 ! fir/ *apt] 7p4 #hh74 ,we took our scale s small t ! />s 7 r$uc$ to t9y specks ( du/2 we notic$ t space is s little cr[d$ ) />s t 9 our model ! specks ( du/ _h to be plac$ ov] #bjj y>ds ap>t2 to put x all 9 a concrete =m1 we f\nd t ,wat]loo ,/ation ) only six specks ( du/ left 9 x is m cr[d$ ) du/ ?an space is ) />s4 ,n[ let ! model come to life1 s z to repres5t ! motions ( ! />s4 ,to keep ! proportions "r1 ! spe$ ( ! />s mu/ ( c\rse be r$uc$ 9 ! same proportion z ! l9e> dim5sions ( ! model4 ,9 ?is ! e>?'s ye>ly j\rney r\nd ! sun ( #fjj million miles _h become r$uc$ to a p9-head a sixte5? ( an in* 9 diamet]1 or1 say1 a fif? ( an in* 9 circumf]5ce4 ,z ! />s move ?r\gh space ) r\ghly ! same spe$ z ! e>? 9 its orbit1 we may suppose ! ye>ly j\rney ( ea* speck ( du/ 9 our model also to be ab\t a fif? ( an in*4 ,?us ea* speck ( du/ w move ab\t an in* 9 five ye>s1 r\ghly #af feet 9 a ?\s& ye>s--or say a t5-million? "p ( a snail's pace4 ,ev5 if two specks />t$ mov+ directly t[>ds "o ano!r x w\ld take !m ab\t #bj1jjj ye>s to meet4 ,= h[ long mu/ six p>ticles ( du/1 float+ bl9dly ab\t 9 ,wat]loo ,/ation1 move at ?is pace be=e ea* has _h en\gh close meet+s ) o!r specks ( du/ = _! en]gy ( motion to become ?or\ghly r$i/ribut$8 ,! ma!matician1 c>ry+ out exact calculations ) respect to ! actual weights1 spe$s & di/ances ( ! />s1 f9ds t ! obs]v$ degree ( approximation to equip>tition ( en]gy %ews t gravitational int]action mu/ h cont9u$ ?r\gh millions ( millions ( ye>s1 mo/ probably f #e to #aj millions ( millions ( ye>s4 ,?is1 !n1 mu/ be ! l5g? ( life ( ! />s4 ,x is a /up5d\s l5g? ( "t1 & be=e f9ally accept+ x we may well look = confirmation f o!r s\rces4 ,9 e/imat+ ! age ( ! e>? we 7 able to invoke assi/ance f all k9ds ( clocks1 a/ronomical1 geological & physical2 happily !y all told mu* ! same /ory4 ,9 ! pres5t problem only a/ronomical clocks are available1 b =tunately !re are no few] ?an ?ree ( ^!1 & aga9 !y agree 9 say+ mu* ! same ?+4 ,,! ,,orbits ,,( ,,b9>y ,,sy/ems4 ,we h already se5 7p4 #dg7 h[ ! two con/itu5ts ( a b9>y sy/em p]man5tly describe clos$ elliptical orbits ab\t "o ano!r1 because nei!r c escape f ! gravitational hold ( its companion4 ,en]gy c reside 9 ! orbital motion ( ^! sy/ems1 z well z 9 _! motion ?r\gh space4 ,& /rict ma!matical analysis %ews t a long succession ( gravitational pulls f pass+ />s mu/ f9ally result 9 equip>tition ( en]gy1 n only betwe5 ! en]gies ( motion ( "o sy/em & ano!r ?r\gh space1 b also betwe5 ! v>i\s orbital motions ( :i* ea* b9>y sy/em is capable4 ,:5 ?is f9al /ate ( equip>tition is ultimately rea*$1 ! orbits ( ! sy/ems w n all be simil>1 b x c be %ewn t _! %apes w be di/ribut$ accord+ to a q simple /ati/ical law#ai4 ,z ! orbits ( actual sy/ems are n f\nd to con=m to ?is law1 x is cle> t ! />s h n yet liv$ long en\gh to atta9 equip>tition ( en]gy 9 respect ( _! orbital motions4 ,x is impossible to discuss h[ f> !y h travell$ along ! road to equip>tition )\t kn[+ ! po9t1 or po9ts1 f :i* !y />t$4 #ai ,! ecc5tricity ( orbit e is di/ribut$ 9 su* a way t all values ( e f e #j to e #a are equally probable4 ,! "q ( ! orig9 ( b9>y sy/ems w be discuss$ m fully 9 ! next *apt]4 ,= ! mom5t x may be said t !y appe> to come into be+ 9 two di/9ct ways4 ,practically all a/ronomical bodies are 9 a /ate ( rotation ab\t an axis4 ,! e>? rotates ab\t its axis once e #bd h\rs1 & ,jupit] once e #aj h\rs1 z is %ewn by ! motion ( ! r$ spot & o!r m>k+s on its surface4 ,! surface ( ! sun rotates e #bf days or s2 we c foll[ its rotation by wat*+ sun-spots1 faculae & o!r features mov+ r\nd & r\nd its equator4 ,!re are !oretical gr\nds = suppos+ t ! sun's c5tral core rotates consid]ably fa/] ?an ?is1 mo/ probably p]=m+ a complete rotation 9 comp>atively few days4 ,& x is likely t all ! o!r />s 9 ! sky are also 9 rotation1 "s fa/ & "s sl[4 ,we %all see lat] h[1 ) advanc+ age1 a /> is likely to %r9k 9 size1 & ?is %r9kage g5]ally causes its spe$ ( rotation to increase4 ,n[ ma!matical !ory %ews t !re is a critical spe$ ( rotation :i* _c be exce$$ ) safety4 ,if ! /> rotates too fa/ = safety1 x simply bur/s into two1 mu* z a rotat+ fly-:eel may bur/ if x is driv5 at too high a spe$4 ,x is 9 ?is way t "o class ( b9>y />s come into be+4 ,) a few exceptions ?is class is id5tical ) ! class ( spectroscopic b9>ies describ$ 9 ,*apt] ,i 7p4 #eb72 ! two compon5t />s are g5]ally too close toge!r to appe> z di/9ct spots ( light 9 ! telescope1 only spectroscopic evid5ce tell+ u t we are deal+ ) two di/9ct bodies4 ,ano!r class ( b9>ies1 ! visual b9>ies1 :i* appe> q def9itely z pairs ( spots ( light 9 ! telescope1 probably h a diff]5t orig94 ,we %all see lat] h[ ! />s fir/ come into be+ z cond5sations ( nebul\s gas1 a :ole %oal be+ born :5 a s+le great nebula breaks up4 ,x mu/ (t5 happ5 t adjac5t cond5sations are s ne> z to be unable to elude ea* o!r's gravitational grip4 ,9 "t ^! %r9k d[n into normal />s1 :ile ! gravitational =ces rema9 j z p[]ful z be=e1 & we are left ) a pair ( />s :i* mu/ p]man5tly j\rney ?r\gh space 9 d\ble h>ness1 because !y h n en]gy ( motion en\gh ev] to get cle> ( "o ano!r's gravitational hold4 ,?is me*anism produces a class ( b9>ies :i* is precisely simil> to t =m$ by ! break-up ( s+le />s1 except = an enorm\s diff]5ce 9 scale4 ,! di/ance betwe5 ! two compon5ts ( su* a sy/em mu/ be comp>able ) ! orig9al di/ance betwe5 sep>ate cond5sations 9 ! primaeval nebula out ( :i* ! />s 7 born1 & s is enorm\sly great] ?an ! correspond+ di/ance 9 spectroscopic b9>ies1 :i* is comp>able only ) ! diamet] ( an ord9>y /> :i* has brok5 into pieces4 ,?is expla9s :y visual b9>ies appe> z di/9ct pairs ( spots ( light1 :ile spectroscopic b9>ies d n4 ,9 ! f9al /ate ( equip>tition ( en]gy1 ! %apes ( ! orbits w1 z we h se51 be di/ribut$ accord+ to a def9ite /ati/ical law4 ,?is law ( di/ribution is ! same = all sizes ( orbit4 ,on ! o!r h&1 ! "t ne$$ = equip>tition ( en]gy to br+ ?is law ab\t is n ! same = all sizes ( orbit2 x is f> great] = ! compact orbits ( ! spectroscopic b9>ies ?an = ! m op5 orbits ( ! visual b9>ies4 ,! reason = ?is is t *anges 9 ! %ape ( an orbit are caus$ m]ely by ! diff]5ce ( ! gravitational pulls ( a pass+ /> on ! two compon5ts ( ! b9>y4 ,if ! two compon5ts are v close toge!r1 ! pass+ /> ex]ts practically ! same =ces on bo?4 ,^! =ces affect ! motions ( ! two compon5ts 9 precisely ! same way1 ) ! result t ! motion ( ! b9>y sy/em z a :ole ?r\gh space is *ang$1 b ! %ape ( orbit rema9s unalt]$4 ,! pass+ /> gets a grip on ! motion ( ! b9>y z a :ole1 b none on ! orbits ( ! compon5ts4 ,on ! o!r h&1 :5 ! compon5ts are f> ap>t1 ! gravitational =ces act+ on ! two may be widely diff]5t1 s t a sub/antial *ange 9 ! %ape ( ! orbit may result1 ev5 if ! enc\nt] is n a v close "o4 ,9 visual b9>ies1 9 :i* ! compon5ts are usually hundr$s ( millions ( miles ap>t1 ! "t necess>y to e/abli% ! f9al di/ribution ( ! 8ecc5tricities10 by :i* ! %apes ( elliptical orbits are measur$1 is once aga9 f\nd to be ( ! ord] ( millions ( millions ( ye>s1 b x is some?+ l a hundr$ times z great z ?is = ! f> m compact spectroscopic b9>ies4 ,! foll[+ table1 compil$ f mat]ial giv5 by ,dr ,aitk5 ( ,lick ,obs]vatory1 %ews ! obs]v$ di/ribution ( ecc5tricities 9 ! orbits ( ^? b9>ies = :i* accurate in=mation is available3 ,! ,approa* to ,equip>tition ( ,en]gy 9 ,b9>y ,orbits ---------------------------------------- ------------------ ,obs]v$ ,obs]v$ ,numb] to be expect$ ,ecc5tricity numb] ( numb] ( !oretically ( ,orbits spectroscopic visual :5 ! b9>ies b9>ies f9al /ate is atta9$ ---------------------------------------- ------------------ #j to #jb #gh #g #f #jb 0 #jd #ah #ah #ah #jd 0 #jf #af #bh #cj #jf 0 #jh #f #aa #db #jh 0 #aj #a #d #ed ---------------------------------------- ------------------ ,let u look fir/ at ! spectroscopic b9>ies4 ,9 ! obs]v$ orbits1 we see t l[ ecc5tricities pr$om9ate1 no few] ?an #gh out ( #aai hav+ an ecc5tricity ( less ?an "o-fif?4 ,9 o!r words1 mo/ spectroscopic b9>ies h ne>ly circul> orbits4 ,bo? !ory & obs]vation %ew t :5 a /> fir/ divides up into a spectroscopic b9>y1 ! orbits ( ! two compon5ts mu/ be ne>ly circul>1 s t ! table ( obs]v$ orbits provides v little evid5ce ( any progressive *ange ( %ape 9 ! orbits z a :ole4 ,9 contra/ to ?is1 ! la/ column ( ! table %ews ! proportion ( orbits ( diff]5t ecc5tricities :i* is to be expect$ :51 if ev]1 equip>tition ( en]gy is f9ally atta9$4 ,"h high ecc5tricities1 repres5t+ v elongat$ orbits1 pr$om9ate2 only "o orbit 9 tw5ty-five is s ne>ly circul> z to h an ecc5tricity less ?an a fif?4 ,9 g5]al ! obs]v$ numb]s tabulat$ 9 ! second column %ew no resemblance at all to ! !oretical numb]s tabulat$ 9 ! f\r? column4 ,9 o!r words1 ! spectroscopic b9>ies %ew no sugge/ion ( any ne> approa* to ! f9al /ate1 mo/ ( !m reta9+ ! l[ ecc5tricity ( orbit ) :i* !y />t$ life4 ,we %\ld naturally expect ?is1 s9ce we h se5 t hundr$s or ev5 ?\s&s ( millions ( millions ( ye>s w\ld be ne$$ = ^! orbits to atta9 a f9al /ate ( equip>tition1 & ! />s _c be z old z ?is1 = if !y 71 _! motions ?r\gh space ought to %ew absolutely p]fect equip>tition1 :i* !y c]ta9ly d n4 ,turn+ n[ to ! ?ird column1 we see t ! visual b9>ies %ew a good approa* to ! !oretical f9al /ate up to an ecc5tricity ( ab\t #jf1 b n beyond4 ,! defici5cy ( orbits ( high ecc5tricity may mean t gravitational =ces h n _h suffici5t "t to produce ! highe/ ecc5tricities ( all1 b "p1 & p]haps all1 ( x mu/ be ascrib$ to ! simple fact t orbits ( high ecc5tricity are exce$+ly difficult to detect obs]vationally & to measure accurately4 ,cle>ly1 !n1 ! /udy ( orbital motions1 l t ( motions ?r\gh space1 po9ts to gravitational action ext5d+ ov] millions ( millions ( ye>s4 ,9 ea* case !re is an exception to 8prove ! rule40 ,9 ! case we h j consid]$ x is provid$ by ! spectroscopic b9>ies1 :i* are s compact t _! con/itu5ts c defy ! pull+-ap>t action ( gravitation2 9 ! =m] case x 0 provid$ by ! ,b-type />s1 :i* are s massive1 possibly also s "y1 t ! gravitational =ces f less weighty />s h n yet greatly affect$ _! motion4 ,:5 ^! two l9es ( evid5ce are discuss$ 9 detail1 !y agree 9 sugge/+ t ! g5]al age ( ! />s is ab\t t already /at$1 namely1 f five to t5 millions ( millions ( ye>s4 ,,mov+ ,,clu/]s4 ,a ?ird l9e ( evid5ce1 :i* also tells mu* ! same /ory1 may be briefly m5tion$4 ,! conspicu\s gr\ps ( bright />s 9 ! sky1 su* z ! ,great ,be>1 ! ,pleiades & ,orion's ,belt1 consi/ = ! mo/ "p ( exceptionally massive />s :i* move 9 regul> ord]ly =mation ?r\gh a jumble ( slight] />s1 l a flight ( swans ?r\gh a confus$ cr[d ( rooks & />l+s4 ,swans cont9ually adju/ _! flight s z to pres]ve _! =mation4 ,! />s _c1 s t _! ord]ly =mation mu/ 9 "t be brok5 by ! gravitational pull ( o!r />s4 ,! light] />s are naturally knock$ out ( =mation fir/1 :ile ! mo/ massive />s reta9 _! =mation longe/4 ,obs]vation sugge/s t ?is is :at actually happ5s to a mov+ />-clu/]2 at any rate ! />s :i* rema9 9 =mation g5]ally h weights f> above ! av]age4 ,&1 z we c calculate ! "t necess>y to knock out ! light] />s1 we c at once d$uce ! ages ( ^? :i* are left 94 ,! result ( ! calculation confirms ^? already m5tion$1 s t we f9d t ! ?ree available a/ronomical clocks all tell mu* ! same "t4 ,!y agree 9 indicat+ an age ( ! ord] ( five to t5 millions ( millions ( ye>s = ! />s z a :ole4 ,ano!r l9e ( inve/igation1 to be m5tion$ lat] 7p4 #ahh7 aga9 po9ts to a simil> age4 ,x is p]haps a little surpris+ t ?is age %\ld prove to be s mu* long] ?an ! age ( ! e>?1 al?\gh !re is ( c\rse no positive reason :y ! e>? %\ld n h be5 born dur+ ! la/ few mom5ts ( ! lives ( ! />s4 ,x is p]haps also a little surpris+ t x %\ld prove to be mu* long] ?an ! age sugge/$1 v vaguely x is true1 by ! cosmologies ( de ,sitt] & ,lematre4 ,if we accept ! app>5t velocities ( recession ( ! mo/ di/ant nebulae z real1 we f9d t "s ?\s&s ( millions ( ye>s ( motion at _! pres5t spe$s w\ld j ab\t acc\nt = _! pres5t di/ances f u1 s t a few ?\s&s ( millions ( ye>s ago1 ! nebulae mu/ h be5 f> m huddl$ toge!r ?an !y n[ are4 ,?is is ( c\rse v diff]5t f say+ t ! "t :i* has elaps$ s9ce ! creation ( ! nebulae c only be a few ?\s&s ( millions ( ye>s1 yet we might reasonably h expect$ priori t ! two p]iods w\ld be at lea/ comp>able4 ,to /ate ! difficulty 9 a slightly diff]5t =m1 a p]iod ( two ?\s& million ye>s seems to h made a great deal ( diff]5ce to ! e>?1 & if ! app>5t spe$s ( nebul> motion are real1 x has made a great deal ( diff]5ce to ! g5]al arrangem5t 9 space ( ! great nebulae1 s t x is odd t x %\ld make s little diff]5ce to ! />s t we ne$ to po/ulate an age a ?\s& times z great be=e we c expla9 _! pres5t condition4 ,^! consid]ations may seem to sugge/ t ! e/imate j made ( /ell> ages %\ld be accept$ ) caution & p]haps ev5 ) suspicion4 ,yet if we reject x1 s _m facts ( a/ronomy are left up 9 ! air )\t any explanation1 & s mu* ( ! fabric ( a/ronomy is ?r[n into disord] 7see p4 #ahg1 bel[71 t we h little option b to accept x1 & suppose t ! />s h actually liv$ ?r\gh times ( ! ord] ( millions ( millions ( ye>s4 ,,! ,,sun',s ,,radiation ,dur+ ! :ole ( "s su* va/ p]iod ( "t1 ! sun has 9 all probability be5 p\r+ out light & heat at lea/ z pr(usely z at pres5t4 ,inde$ a mass ( evid5ce1 to :i* we %all return lat]1 %ews t "y />s emit m radiation ?an old] />s1 s t dur+ mo/ ( its long life ! sun mu/ h be5 p\r+ out en]gy ev5 m lavi%ly ?an n[4 ,if our ance/ors ?\ght ab\t ! matt] at all1 !y probably saw no?+ rem>kable 9 ?is pr(use outp\r+ ( light & heat1 p>ticul>ly z !y _h no conception ( ! /up5d\s l5g? ( "t dur+ :i* x _h la/$4 ,x 0 only 9 ! middle ( la/ c5tury1 :5 ! pr9ciple ( cons]vation ( en]gy fir/ began to be cle>ly und]/ood1 t ! s\rce ( ! sun's en]gy 0 se5 to con/itute a sci5tific puzzle ( really fir/-class difficulty4 ,! sun's radiation obvi\sly repres5t$ a loss ( en]gy to ! sun1 &1 z ! pr9ciple ( cons]vation %ew$ t en]gy c\ld n orig9ate out ( no?+1 ?is en]gy necess>ily came f "s s\rce or /ore adequate to supply va/ outp\r+s ( en]gy ov] a v long p]iod ( "t4 ,:]e 0 su* a /ore to be f\nd8 ,! sun at pres5t p\rs out radiation at su* a rate t if ! necess>y en]gy 7 g5]at$ 9 a p[]-/ation outside ! sun1 ?is /ation w\ld h to burn coal at ! rate ( _m ?\s&s ( millions ( millions ( tons a second4 ,!re is ( c\rse no su* p[]-/ation4 ,! sun is entirely dep5d5t on its own res\rces2 x is a %ip on an empty ocean4 ,& if1 l su* a %ip1 ! sun c>ri$ its own /ore ( coal1 or if1 z ,kant imag9$1 its :ole sub/ance 7 its /ore ( coal1 s t its light & heat came f its own combu/ion1 ! :ole w\ld be burnt into a%es & c9d]s 9 a few ?\s& ye>s at mo/4 ,! hi/ory ( sci5ce records "o solit>y attempt to expla9 ! sun's en]gy z com+ 9 f outside4 ,we h se5 h[ ! en]gy ( motion ( a bullet is trans=m$ into heat :5 ! spe$ ( ! bullet is *eck$4 ,an a/ronomical example ( ! same effect is provid$ by ! famili> ph5om5on ( %oot+-/>s4 ,^! are bullet-l bodies :i* fall into ! e>?'s atmosph]e f out] space4 ,s long z su* a body is travell+ ?r\gh empty space1 its fall t[>ds ! e>? cont9ually increases its spe$1 b1 z x ent]s ! e>?'s atmosph]e1 its spe$ is *eck$ by air-resi/ance1 & ! en]gy ( its motion is gradually trans=m$ into heat4 ,! %oot+-/> becomes fir/ hot & !n inc&esc5t1 emitt+ ! bright light by :i* we recognise x4 ,f9ally1 ! heat completely vaporises x1 & x disappe>s f sight1 leav+ only a mom5t>y trail ( lum9\s gas beh9d4 ,! orig9al en]gy ( motion ( ! %oot+-/> has be5 trans=m$ into light & heat--! light by :i* we see x1 & ! heat by :i* x is ultimately vaporis$4 ,9 #ahdi1 ,rob]t ,may] sugge/$ t ! en]gy :i* ! sun emitt$ z radiation might accrue to x f a cont9u\s fall ( %oot+-/>s or simil> bodies into ! sol> atmosph]e4 ,! sugge/ion is unt5able1 because a simple calculation %ews t a mass ( su* bodies equal to ! weight ( ! :ole e>? w\ld h>dly ma9ta9 ! sun's radiation = a c5tury1 & t ! infall ne$$ to ma9ta9 ! sun's radiation = #cj million ye>s w\ld d\ble its weight4 ,z x is q impossible to admit t ! sun's weight c be increas+ at any su* rate1 ,may]'s hypo!sis has to be ab&on$4 ,9 #ahec ,helmholtz put =w>d a v simil> !ory1 ! fam\s 8contraction-hypo!sis10 accord+ to :i* ! sun's own %r9kage sets free ! en]gy :i* ultimately appe>s z radiation4 ,if ! sun's radius %r9ks by a mile1 its out] atmosph]e falls ?r\gh a height ( a mile & sets free z mu* en]gy 9 s do+ z w\ld be yield$ up by an equal weight ( %oot+-/>s fall+ ?r\gh a mile & hav+ _! motion *eck$4 ,on ,helmholtz's !ory1 ! diff]5t p>ts ( ! sun's own body p]=m$ ! rles :i* ,may] _h allott$ to %oot+-/>s fall+ 9 f outside2 !y p]=m$ ^! same p>ts aga9 & aga91 until ultimately ! sun _h %runk s f> t x c\ld %r9k no fur!r4 ,yet ,helmholtz's !ory1 l t ( ,may]1 fail$ to survive ! te/ ( num]ical computation4 ,9 #ahfb ,"l ,kelv9 calculat$ t ! %r9kage ( ! sun to its pres5t size c\ld h>dly h provid$ en]gy = m ?an ab\t #ej million ye>s ( radiation 9 ! pa/1 :]eas ! geological evid5ce already notic$ 7p4 #aea7 %ews t ! sun mu/ h be5 %9+ = a p]iod enorm\sly long] ?an ?is4 ,to track d[n ! actual s\rce ( ! sun's en]gy ) any hope ( success1 we mu/ give up guess+1 & approa* ! problem f a new angle4 ,we h se5 7p4 #abj7 h[ radiation c>ries weight ab\t ) x1 s t any body :i* is emitt+ radiation is necess>ily los+ weight2 ! radiation emitt$ by a se>*light ( #ej horse-p[] w\ld1 we saw1 c>ry away weight at ! rate ( ab\t a tw5tie? ( an ounce a c5tury4 ,n[ ea* squ>e in* ( ! sun's surface is 9 effect a se>*light ( j ab\t #ej horse-p[]1 :5ce we conclude t weight is /ream+ away f e squ>e in* ( ! sun's surface at ! rate ( ab\t a tw5tie? ( an ounce a c5tury4 ,su* a loss ( weight seems small en\gh1 until we multiply x by ! total numb] ( squ>e in*es :i* con/itute ! :ole surface ( ! sun4 ,x !n appe>s t ! sun z a :ole is los+ weight at ! rate ( r ov] #d million tons a second1 or ab\t #bej million tons a m9ute--some?+ l #fej times ! rate at :i* wat] is /ream+ ov] ,niag>a4 ,,! ,,pa/ ,,hi/ories ,,( ,,! ,,sun ,,& ,,/>s4 ,let u c>ry on ! multiplication4 ,two hundr$ & fifty million tons a m9ute is #cfj1jjj million tons a day4 ,?us ! sun mu/ h weigh$ #cfj1jjj million tons m ?an n[ at ?is "t ye/]day1 & w weigh #cfj1jjj million tons less at ?is "t to-morr[4 ,& #cfj1jjj million tons a day is #aca million million tons a ye>4 ,we c dig z f> into ! pa/ z we l 9 ?is way & c probe z f> z we l into ! future4 ,b soon we enc\nt] ! usual tr\ble :i* besets all calculations ( ?is k9d--! s& does n always run ?r\gh ! h\r-glass at ! same rate4 ,! rate at :i* ! sun loses weight w n v>y appreciably betwe5 to-day & to-morr[1 or ev5 ov] a c5tury or a million ye>s1 b we mu/ be on our gu>d aga9/ go+ too f>4 ,if ! sun cont9u$ to radiate at precisely its pres5t rate1 a simple sum 9 division %ews t x w\ld la/ = j ab\t #ae million million ye>s1 by :i* "t its la/ ounce ( weight w\ld be disappe>+4 ,incid5tally ?is gives u a vivid conception ( ! enorm\s weight ( ! sun2 x c\ld g on p\r+ away its sub/ance into space at #fej times ! rate at :i* wat] is p\r+ ov] ,niag>a = #ae million million ye>s be=e becom+ exhau/$4 ,obvi\sly1 h[ev]1 we _c c>ry out our calculations 9 ?is simple light-he>t$ way2 x w\ld be absurd to suppose t ! sun's la/ ton ( sub/ance w radiate en]gy at ! same rate z 8 pres5t /up5d\s mass ( two ?\s& million million million million tons4 ,a s]ies ( inve/igations :i* culm9at$ 9 a pap] publi%$ by ,edd+ton 9 #aibd1 disclos$ t1 9 a g5]al sort ( way1 a />'s lum9osity dep5ds ma9ly on its weight4 ,! dep5d5ce is n v precise1 & nei!r is x univ]sal1 b :5 we are told a />'s weight we c say t its lum9osity is likely1 ) a high degree ( probability1 to lie )9 c]ta9 fairly n>r[ limits4 ,= in/ance mo/ />s ^: weight is ne>ly equal to ! sun are f\nd to h ab\t ! same lum9osity z ! sun4 ,9 g5]al1 z might be expect$1 />s ( light weight radiate less ?an heavy />s1 b also--& ?is c\ld n h be5 =ese5--! diff]5ces 9 _! radiations are f> great] ?an ! diff]5ces 9 _! weights4 ,! law :i* we h already notic$ to hold = a few />s 9 ! neighb\rhood ( ! sun is true1 al?\gh 9 a some:at diff]5t s5se1 = ! />s z a :ole--! c&le-p[] p] ton is greate/ 9 ! heavie/ />s4 ,= example1 ! av]age /> ( half ! weight ( ! sun does n radiate any?+ l half z mu* en]gy z ! sun3 ! fraction is m l an eigh?4 ,?is consid]ation ext5ds ! future life ( ! sun1 & inde$ ( all ! />s1 almo/ indef9itely4 ,a sort ( p>simony seems to creep ov] ! />s 9 _! old age2 s long z !y h pl5ty ( weight to squ&]1 !y squ&] x lavi%ly1 b !y contract _! scale ( exp5diture :5 !y h little left to sp5d4 ,! s& runs sl[ly ?r\gh ! h\r-glass :5 !re is little left to run4 ,9 ! same way1 ! av]age /> ( d\ble ! sun's weight does n m]ely radiate twice z mu* en]gy z ! sun2 x radiates ab\t eight times z mu*4 ,we mu/ keep ?is 9 view 9 e/imat+ ! pa/ life ( ! sun2 x %ort5s ! sun's pa/ life j z surely z ! opposite effect l5g!ns its future life4 ,obs]vation tells u at :at rate ! av]age /> ( any giv5 weight sp5ds its weight 9 ! =m ( radiation1 &1 on ! supposition t ! sun has behav$ l ?is typical av]age /> at ! correspond+ /age ( its own pa/ hi/ory1 we c draw up a table exhibit+ its gradual *ange ( weight z its life progress$4 ,select$ entries f ?is table w\ld read some:at z foll[s3 #b #aj ye>s ago1 ! sun _h #ajjjac times its pres5t weight #a1jjj #aj 0 0 #ajg 0 0 #b1jjj #aj 0 0 #aaf 0 0 #e1gjj #aj 0 0 d\ble 0 #g1ajj #aj 0 0 #d times 0 #g1djj #aj 0 0 #h 0 0 #g1ejj #aj 0 0 #bj 0 0 #g1fjj #aj 0 0 #ajj 0 0 ,! fir/ entry repres5ts r\ghly ! "t s9ce ! e>? 0 born4 ,x %ews t1 dur+ ! :ole exi/5ce ( ! e>?1 ! sun's weight has *ang$ by only an inappreciable fraction ( ! :ole4 ,consequ5tly1 x seems likely1 al?\gh naturally we _c be c]ta91 t :5 ! e>? 0 born ! sun 0 mu* ! same z x n[ is1 & t x has be5 ! same1 9 all ess5tial respects1 ?r\gh\t ! :ole life ( ! e>?4 ,to come to appreciably diff]5t conditions we h to g back to remote aeons f> beyond ! "t ( ! e>?'s bir?4 ,we are free to d ?is1 = we h se5 t ! e>?'s :ole life is only a mom5t 9 ! lives ( ! />s4 ,we h e/imat$ ! latt] z be+ some?+ ( ! ord] ( #e to #aj million million ye>s1 & x is only :5 we g back an appreciable fraction ( ^! long p]iods t we f9d ! sun's weight diff]+ appreciably f its pres5t weight4 ,we h1 = in/ance1 to g back m ?an #e million million ye>s to f9d ! sun ) d\ble its pres5t weight4 ,:5 we g back mu* fur!r ?an ?is a new ph5om5on appe>s2 ! weight ( our hypo!tical pa/ sun beg9s to g up by leaps & b\nds4 ,9 "t x beg9s to d\ble & m ?an d\ble e #ajj1jjj million ye>s1 & we _c g back z f> z #h million million ye>s )\t po/ulat+ a sun ( q impossibly high weight4 ,! sun mu/1 !n1 h be5 born "s "t )9 ! la/ #h million million ye>s4 ,! exact figures ( our table may be op5 to suspicion1 b z a g5]al fact ( obs]vation !re is no d\bt t v massive />s radiate away _! en]gy1 & !re=e also _! weight1 ) extraord9>y rapidity4 ,inde$ ! process is s rapid t we may disreg>d all t "p ( a />'s life 9 :i* x has m ?an ab\t #aj times ! weight ( ! sun--?is is liv$ at lightn+ spe$4 ,ap>t f all detail$ calculations1 ?is g5]al pr9ciple fixes a def9ite limit to ! ages1 n only ( ! sun1 b also ( e o!r />4 ,! upp] limit to ! age ( ! sun is c]ta9ly some:]e 9 ! neighb\rhood ( #h million million ye>s4 ,?is agrees well en\gh ) ! g5]al age ( f #e to #aj million million ye>s t o!r calculations h assign$ to ! />s 9 g5]al4 ,! calculations ?us re9=ce "o ano!r1 & x looks z if at lea/ two ( ! pieces ( ! puzzle 7 beg9n+ to fit satisfactorily toge!r4 ,if all ! />s 9 ! sky 7 simil> to ! sun1 we might feel a good deal ( confid5ce 9 ! conclusions we h rea*$4 ,un=tunately1 difficulties em]ge z soon z we discuss ! ages ( />s :i* at pres5t h _m times ! weight ( ! sun4 ,! table on p4 #afd %ews t a class ( />s 7spectral type ,a #j7 ( six times ! weight ( ! sun h motions 9 space :i* con=m well en\gh to ! law ( equip>tition ( en]gy4 ,unless ?is is a pure co9cid5ce 7& ?is is unlikely1 9 view ( ! fact t o!r gr\ps ( only slightly less weight con=m equally well71 we mu/ assign an age ( f #e to #aj million million ye>s to ^! v massive />s4 ,yet ! av]age /> ( ?is weight is emitt+ ab\t a hundr$ times z mu* radiation z ! sun1 :i* means t x is halv+ its weight e #aej1jjj million ye>s4 ,cle>ly ?is process _c h gone on = any?+ l #e or #aj million million ye>s4 ,/ill m lum9\s />s pres5t ! problem 9 an ev5 m acute =m4 ,! /> ,s ,doradus 9 ! ,less] ,magellanic ,cl\d is at pres5t emitt+ #cjj1jjj times z mu* radiation z ! sun4 ,:]eas ! sun is p\r+ its weight out into space at ! rate ( #fej ,niag>as1 ,s ,doradus is p\r+ x out at ! rate ( #bjj1jjj1jjj ,niag>as2 e #ej million ye>s x loses a weight equal to ! total weight ( ! sun4 ,x is obvi\sly absurd to imag9e t ?is /> c h be5 los+ weight at ?is rate = millions ( millions ( ye>s4 ,= su* a /> z ,s ,doradus only two alt]natives seem op54 ,ei!r x 0 creat$ q rec5tly 7on ! a/ronomical "t-scale71 & s is /ill at ! v beg9n+ ( its prodigal y\?1 or else its loss ( weight has 9 "s way be5 inhibit$ ?r\gh ! great] "p ( its life4 ,a good _m argum5ts weigh aga9/ ! hypo!sis ( rec5t creation4 ,! /> is a memb] ( a />-cl\d 9 :i* we %\ld naturally expect all ! memb]s to be ( approximately equal age4 ,x is 9 a region ( space 9 :i* !re are no indications t />s are /ill be+ born4 ,&1 ev5 if we accept ! hypo!sis ( rec5t creation = ?is p>ticul> />1 we are /ill at a loss to expla9 h[ ! o!r massive />s1 :i* figure 9 ! table on p4 #afd1 c be old en\gh = equip>tition ( en]gy to h become already e/abli%$4 ,= _m reasons x seems pref]able1 & inde$ almo/ inevitable1 to suppose t ^! highly lum9\s & v weighty />s h 9 "s way be5 sav$ f en]getic radiation1 ) its consequ5tial rapid wa/+ ( weight1 ?r\gh\t ! great] "p ( _! lives4 ,9 brief1 we suppose t !y are cases ( arre/$ developm5t1 ^: weight & g5]al appe>ance equally belie _! true ages4 ,lat] 7p4 #cah7 we %all come ^u a physical me*anism :i* expla9s v simply & naturally h[ ?is c\ld happ54 ,if ?is hypo!sis c be accept$1 x cle>s up ! :ole situation4 ,z soon z we accept x1 we become free to assign any age we please to ! />s1 & naturally select t indicat$ by ! law ( equip>tition ( en]gy1 at any rate = ^? classes ( />s :i* are f\nd to con=m to ?is law4 ,! exceptionally lum9\s />s :i* we h j _h "u discussion are comp>atively r>e objects 9 ! sky4 ,! va/ majority ( />s h lum9osities & weights comp>able )1 or di/9ctly less ?an1 ^? ( ! sun1 & = ^! ! difficulty does n exi/4 ,inde$ ! hypo!sis ( arre/$ developm5t w\ld break d[n "u its own weight if we _h to invoke its help = _m />s2 x is t5able j because we seldom ne$ to use x4 ,we may accept ! table on p4 #ahj z giv+ ! pa/ hi/ory ( ! sun ) tol]able accuracy1 ?us fix+ its age at some?+ "u #h million million ye>s1 & a g5]ally simil> table w\ld apply to mo/ ( ! />s 9 ! sky4 ,,! ,,s\rce ,,( ,,/ell> ,,en]gy ,! ages ( #e million million ye>s or m :i* we h be5 l$ to assign to ! />s imply t at bir? ! sun mu/ h _h at lea/ d\ble1 & m probably sev]al times1 its pres5t weight4 ,= e ton :i* exi/$ 9 ! sun at its bir? only a few hundr$-weight rema9 to-day4 ,! re/ ( ! ton has be5 trans=m$ into radiation &1 /ream+ away into space1 has left ! sun = ev]4 ,9 ! prec$+ *apt]1 we _h occasion to discuss ! trans=mation ( weight into radiation :i* accompanies ! spontane\s dis9tegration ( radio-active atoms4 ,! mo/ en]getic in/ance ( ?is ph5om5on kn[n on e>? is ! trans=mation ( uranium into lead1 9 :i* ab\t "o "p 9 #djjj ( ! total weight is trans=m$ into radiation4 ,9 ! sun1 ! correspond+ fraction may be half1 or n9e-t5?s1 or ev5 #ii p] c5t41 b1 :atev] x is1 x c]ta9ly exce$s "o "p 9 #djjj4 ,?us ! process by :i* ! sun g5]ates its light & heat mu/ involve a f> m en]getic trans=mation ( mat]ial weight into radiation ?an any process kn[n on e>?4 ,p]r9 & ,edd+ton at "o "t sugge/$ t ?is process may be ! build+ up ( complex atomic nuclei out ( protons & electrons4 ,! simple/1 & mo/ fav\rable example ( ?is1 :i* 0 especially consid]$ by ,edd+ton1 is to be f\nd 9 ! build+ up ( ! helium nucleus4 ,! con/itu5ts ( a helium atom are precisely id5tical ) ^? ( f\r hydrog5 atoms1 namely1 f\r electrons & f\r protons4 ,if ^! con/itu5ts c\ld be re>rang$ )\t any trans=mation ( mat]ial weight into radiation1 ! helium atom w\ld h precisely f\r times ! weight ( ! hydrog5 atom4 ,9 actual fact ,a/on f9ds t ! ratio ( weights is only #cigj4 ,! diff]5ce betwe5 ?is & #djjj mu/ repres5t ! weight ( ! radiation :i* goes (f :51 if ev]1 ! helium atom is built up by ! coalesc5ce ( f\r hydrog5 atoms4 ,! loss ( weight1 "o "p 9 #acj1 is v mu* great] ?an occurs 9 radio-active trans=mations1 b ev5 s x does n provide adequate lives = ! />s4 ,! trans=mation ( a sun :i* orig9ally consi/$ ( pure hydrog5 into "o consi/+ :olly ( helium w\ld only provide radiation at ! sun's pres5t rate ( radiation = ab\t #ajj1jjj million ye>s1 & ! dynamical evid5ce ( equip>tition ( en]gy1 etc41 z well z o!r evid5ce :i* we %all consid] lat] 7p4 #ahh bel[71 dem&s f> long] lives = ! />s ?an ?is4 ,,! ,,annihilation ,,( ,,matt]4 ,mod]n physics is only able to sugge/ "o process capable ( provid+ a suffici5tly long life = a radiat+ />2 x is ! actual annihilation ( matt]4 ,v>i\s l9es ( evid5ce g to %ew t ! atoms 9 v massive />s are n1 = ! mo/ "p1 fundam5tally diff]5t f ^? 9 less massive />s4 ,?us ! prim>y cause ( ! diff]5ce 9 weight betwe5 a heavy /> & a light /> is n a diff]5ce 9 ! quality ( ! atoms2 x is a diff]5ce 9 _! numb]4 ,a heavy /> c only *ange into a light /> ?r\gh ! actual disappe>ance ( atoms2 ^! mu/ be annihilat$1 & _! weight trans=m$ into radiation4 ,i fir/ drew att5tion 9 #aijd to ! l>ge am\nt ( en]gy capable ( be+ lib]at$ by ! annihilation ( matt]1 positive & negative electric *>ges ru%+ toge!r1 annihilat+ "o ano!r & sett+ _! en]gy loose 9 space z radiation4 ,! next ye> ,e9/e9's !ory ( relativity provid$ a means = calculat+ ! am\nt ( en]gy :i* w\ld be produc$ by ! annihilation ( a giv5 am\nt ( matt]2 x %ew$ t en]gy is set free at ! rate ( #i #aj ergs p] gramme1 reg>dless ( ! nature or condition ( ! sub/ance :i* is annihilat$4 ,i subsequ5tly calculat$ ! l5g? ( lives :i* ?is s\rce ( en]gy p]mitt$ to ! />s1 b ! calculat$ lives ( millions ( millions ( ye>s seem$ great] ?an 7 ne$$ by ! a/ronomical evid5ce available at ! "t4 ,s9ce !n a cont9ual accumulation ( new evid5ce1 p>ticul>ly t discuss$ 9 ! pres5t *apt]1 has be5 se5 to dem& /ell> lives ( precisely ^! l5g?s1 ) ! result t ! majority ( a/ronom]s n[ reg>d annihilation ( matt] z ! mo/ probable s\rce ( /ell> en]gy4 ,o!r consid]ations 9 addition to ^? j m5tion$ po9t to ! annihilation ( matt] z ! fundam5tal process go+ on 9 ! />s4 ,if !re 7 no annihilation ( matt]1 a /> c\ld only *ange its weight by "s small fraction ( ! :ole1 su*1 = example1 z ! "o "p 9 #djjj :i* accompanies radio-active dis9tegration1 or z ! "o "p 9 #acj :i* w\ld result f ! build+ up ( helium atoms out ( hydrog54 ,a /> w\ld reta9 its weight practically unalt]$ ?r\gh its life4 ,?is w\ld ( c\rse necess>ily impose f> %ort] lives on ! />s ?an we believe !m to h _h1 = no?+ c alt] ! fact t ! sun loses #cfj1jjj million tons ( weight e day 9 radiation1 s t if its weight _c *ange mu*1 x _c h radiat$ = long4 ,we h se5 t 9 ! pres5t univ]se1 a />'s lum9osity dep5ds ma9ly on its weight4 ,if we imag9e t ! same condition ( ?+s has always prevail$1 !n />s :i* reta9$ ! same weight ?r\gh\t _! lives w\ld h to reta9 approximately ! same lum9osity1 at any rate until _! capacity = radiation became exhau/$4 ,o!rwise1 contr>y to obs]vation1 we %\ld f9d />s ) weights equal to ! sun hav+ all possible degrees ( lum9osity4 ,?us if we disc>d ! hypo!sis ( ! annihilation ( matt]1 x becomes necess>y to imag9e "s controll+ me*anism1 ( a k9d :i* w\ld compel />s hav+ ! weight ( ! sun always to radiate at ab\t ! same rate z ! sun1 at lea/ until %e] exhau/ion prev5ts !m f radiat+ any m1 & simil>ly = />s ( all o!r weights4 ,!re does n seem to be any g5]al objection aga9/ suppos+ su* a controll+ me*anism to exi/1 & inde$ su* me*anisms h be5 advocat$ by ,russell & ,edd+ton4 ,b :5 we consid] su* a me*anism 9 detail1 we enc\nt] v>i\s objections :i* we %all consid] 9 ,*apt] ,v 7p4 #bid71 ! pr9cipal ( :i* is t />s controll$ by x w\ld1 s f> z we c see1 be 9 a highly explosive /ate4 ,& imm$iately we ab&on ! hypo!sis ( su* a controll+ me*anism1 ! obs]v$ close dep5d5ce ( lum9osity on weight compels u to suppose t a />'s weight decreases z its lum9osity dim9i%es1 :i* leads u back imm$iately to ! annihilation ( matt]4 ,a fur!r consid]ation :i* po9ts 9 ! same direction may be m5tion$ "h4 ,we h se5 h[ ! 8c&le-p[] p] ton ( weight0 is greate/ 9 ! heavi] />s4 ,z an imm$iate consequ5ce ! loss ( weight p] ton is greate/ 9 ! heavie/ />s4 ,9 ! "t 9 :i* a massive /> loses a hundr$-weight p] ton1 a /> ( light weight may lose only a few p\nds p] ton4 ,! consequ5ce is t ! passage ( "t t5ds to equalise ! weights ( ! />s4 ,?is pr9ciple no d\bt expla9s 9 l>ge "p :y ! pres5t />s %ew no v great range ( weight4 ,x also leads to int]e/+ consequ5ces :5 appli$ to ! two compon5ts ( a b9>y sy/em4 ,x %ews t z a b9>y sy/em ages1 its two compon5ts ought cont9ually to become m ne>ly equal 9 weight4 ,?us ! two compon5ts ought to diff] less 9 weight 9 old b9>ies ?an 9 "y4 ,?is la/ conclusion c be te/$ obs]vationally4 ,z reg>ds spectroscopic b9>ies1 ,aitk5 f9ds t ! ratio ( weights ( ! two con/itu5ts ( a b9>y increases f ab\t #jgj = "y sy/ems ( l>ge weight to #jij = old] sy/ems 9 :i* ! con/itu5ts are ab\t simil> to ! sun4 ,! direction ( *ange is t pr$ict$ by !ory2 ! am\nt ( *ange indicates a "t-int]val ( ! ord] ( millions ( millions ( ye>s betwe5 ! two /ates conc]n$4 ,o!r a/ronom]s h /udi$ ! correspond+ problems pres5t$ by eclips+ & visual b9>ies1 & h rea*$ almo/ id5tical conclusions4 ,! pr$ictions ( !ory seem to be confirm$ by ea* type ( b9>y sy/em sep>ately4 ,on ! :ole1 9 :atev] direction we try to escape f ! hypo!sis ( annihilation ( matt]1 ! alt]native hypo!sis we set up to expla9 ! facts seems to lead back 9 "t to ! annihilation ( matt]4 ,we mu/ n ov]look ! revolution>y nature ( ! *ange :i* ?is hypo!sis introduces into physical sci5ce4 ,! two fundam5tal corn]-/ones ( n9ete5?-c5tury physics1 ! cons]vation ( matt] & ! cons]vation ( en]gy1 are bo? aboli%$1 or r are replac$ by ! cons]vation ( a s+le entity :i* may be matt] & en]gy 9 turn4 ,matt] & en]gy cease to be inde/ructible & become int]*angeable1 accord+ to ! fix$ rate ( ex*ange ( #i #aj ergs p] gramme4 ,yet1 look$ at f ano!r angle1 ! hypo!sis only c>ries physics "o /age fur!r along ! road x has already trodd5 9 ! pa/4 ,heat1 light1 electricity h all 9 turn prov$ to be =ms ( en]gy2 ! annihilation hypo!sis only proposes to add ano!r to ! li/1 s t matt] itself also becomes a =m ( en]gy4 ,accord+ to ?is hypo!sis all ! en]gy :i* makes life possible on e>?1 ! light & heat :i* keep ! e>? w>m & gr[ our food1 & ! /or$ up sunlight 9 ! coal & wood we burn1 if trac$ f> en\gh back1 are f\nd to orig9ate out ( ! annihilation ( electrons & protons 9 ! sun4 ,! sun is de/roy+ its sub/ance 9 ord] t we may live1 or1 p]haps we %\ld r say1 ) ! consequ5ce t we are able to live4 ,! atoms 9 ! sun & />s are1 9 effect1 bottles ( en]gy1 ea* capable ( be+ brok5 & hav+ its en]gy spill$ ?r\gh\t ! univ]se 9 ! =m ( light & heat4 ,mo/ ( ! atoms ) :i* ! sun & />s />t$ _! lives h already met ?is fate2 ! rema9d] are d\btless de/9$ to meet x 9 "t4 ,sci5tific writ]s ( half a c5tury ago delight$ 9 ! picturesque description ( coal z 8bottl$ sun%9e02 !y ask$ u to ?9k ( ! sun%9e z be+ bottl$-up z x fell on ! vegetation ( ! primaeval jungle1 & /or$ = use 9 our fireplaces aft] millions ( ye>s4 ,on ! mod]n view we mu/ ?9k ( x z re-bottl$ sun%9e1 or r re-bottl$ en]gy4 ,! fir/ bottl+ took place millions ( millions ( ye>s ago1 be=e ei!r sun or e>? 0 9 be+1 :5 ! en]gy 0 fir/ p5n$ up 9 protons & electrons4 ,in/ead ( ?9k+ prosaically ( our sun z a m]e collection ( atoms1 let u ?9k ( x = a mom5t z a va/ /oreh\se ( bottles ( en]gy :i* h already la9 9 /orage = millions ( millions ( ye>s4 ,s enorm\s is ! sun's supply ( ^! bottles1 & s great ! am\nt ( en]gy /or$ 9 ea* t1 ev5 aft] radiat+ light & heat = #g or #h million million ye>s1 x /ill has en\gh left to provide light & heat = millions ( millions ( ye>s yet to come4 ,two quantitative consid]ations may help to %ew ^! processes 9 a cle>] light4 ,we h se5 t ! sun's pres5t /ore ( atoms w\ld1 at ! pres5t rate ( breakage1 la/ = #ae million million ye>s4 ,?is means t e ye> only "o atom 9 #ae million million is brok51 a fraction :i* may seem absurdly small to produce ! sun's va/ cont9u\s outp\r+s ( en]gy4 ,let u1 h[ev]1 reflect t ! en]gy :i* is cont9ually p\r+ out ( ! sun's surface at ! rate ( ab\t #ej horse-p[] p] squ>e in* is g5]at$ ?r\gh\t ! va/ int]ior ( ! sun's body2 ! /ream ( en]gy :i* em]ges f a squ>e in* ( surface is ! conc5tration ( all ! en]gy g5]at$ 9 a cone ( a squ>e in* cross-section1 b ( #dcc1jjj miles dep?4 ,su* a cone conta9s ab\t #aj atoms1 & al?\gh only "o 9 #ae million million is brok5 ea* ye>1 !re are /ill ab\t two million million atoms de/roy$ ea* second4 ,ev5 s1 ! am\nt ( en]gy set free by ! annihilation ( matt] is r surpris+2 x is ( an entirely diff]5t ord] ( magnitude f t made available by any o!r treatm5t4 ,! combu/ion ( a ton ( ! be/ coal 9 pure oxyg5 lib]ates ab\t #e #aj ergs ( en]gy2 ! annihilation ( a ton ( coal lib]ates #i #aj ergs1 :i* is #ah1jjj million times z mu*4 ,9 ! ord9>y combu/ion ( coal we are m]ely skimm+ (f ! topmo/ cream ( ! en]gy conta9$ 9 ! coal1 ) ! consequ5ce t #iiiiiiiiiid p] c5t4 ( ! total weight rema9s beh9d 9 ! =m ( smoke1 c9d]s or a%4 ,annihilation leaves no?+ beh9d2 x is a combu/ion s complete t nei!r smoke1 a%1 nor c9d]s is left4 ,if we on e>? c\ld burn our coal z completely z ?is1 a s+le p\nd w\ld keep ! :ole ,briti% nation go+ = a =tnight1 dome/ic fires1 factories1 tra9s1 p[]-/ations1 %ips & all2 a piece ( coal small] ?an a pea w\ld take ! ,mauretania across ! ,atlantic & back4 ,purely a/ronomical evid5ce has l$ to ! conclusion t atoms are cont9ually be+ annihilat$ 9 ! sun & />s4 ,"h we h a piece ( ! puzzle :i* fits p]fectly on to ^? we t5tatively fitt$ toge!r 9 ! la/ *apt]4 ,z we !re saw1 rec5t inve/igations 9 ma!matical physics sugge/ t ! highly p5etrat+ radiation receiv$ on e>? has its orig9 9 ! annihilation ( matt] out 9 space4 ,& ! am\nt ( ?is radiation receiv$ on e>? is s great t we _h to suppose ! und]ly+ annihilation ( matt] to be "o ( ! fundam5tal processes ( ! univ]se2 we n[ discov] t x is 9 all probability ! process :i* keeps ! sun & />s %9+ & ! univ]se alive4 ,,physical ,,int]pretation4 ,x is p]haps wor? try+ to probe /ill "o /age fur!r into ! physical nature ( ?is process ( annihilation ( matt]1 al?\gh x mu/ be premis$ t :at foll[s is speculative 9 ! s5se t no direct obs]vational confirmation is at pres5t available4 ,we saw 7p4 #ace7 h[ ! electrodynamical !ory curr5t 9 ! la/ c5tury requir$ t ! nucleus & electron ( ! hydrog5 atom %\ld approa* ev] clos] & clos] to "o ano!r ) ! m]e passage ( "t1 until f9ally !y ru%$ toge!r & coalesc$4 ,:5 ?is happ5$1 ! negative *>ge ( ! electron & ! positive *>ge ( ! nucleus w\ld neutralise "o ano!r & _! en]gy w\ld g (f 9 a fla% ( radiation simil> to ! fla% ( lightn+ :i* indicates t ! negative & positive *>ges 9 two oppos+ ?und]cl\ds h met & neutralis$ "o ano!r4 ,! m rec5t quantum !ory calls a halt to ?is motion z soon z ! nucleus & electron h approa*$ to )9 a di/ance ( #jec #aj c5timetres ( "o ano!r1 & by s do+ keeps ! univ]se 9 be+ z a go+ conc]n 7p4 #ace74 ,o!r halts are also e/abli%$ at #d1 #i1 #af1 etc4 times ?is di/ance1 b "h ! prohibition on fur!r progress is n absolute4 ,at ^! long] di/ances ! dem& ( ! quantum !ory 8?us f> %alt ?\ g & no fur!r0 seems to be replac$ by 8?\ %alt g no fur!r until aft] a long "t40 ,& x n[ seems possible1 on ! a/ronomical evid5ce1 t ! prohibition at ! %ort] di/ance may n be absolute ei!r4 ,f ! physical end no?+ is kn[n = c]ta91 al?\gh "h aga9 x seems contr>y to ! new] conceptions ( physics1 z embodi$ 9 ! wave-me*anics1 t any su* absolute prohibition %\ld exi/1 ei!r = ! hydrog5 atom or = o!r m complex atoms4 ,p]haps aft] wait+ a long "t 9 ! orbit ne>e/ to ! nucleus1 ! electron is p]mitt$1 or ev5 enc\rag$ or compell$1 to proce$2 x m]ges itself into ! nucleus & a fla% ( radiation is born 9 a />4 ,?is provides ! mo/ obvi\s me*anism = ! annihilation ( electrons & protons :i* ! evid5ce ( a/ronomy seems to dem&4 ,x w1 h[ev]1 be cle>ly und]/ood t ?is is a purely conjectural conception ( ! me*anism2 we %all return to a fur!r consid]ation ( ?is v intricate problem 9 ,*apt] ,v4 ,if ?is conjecture %\ld prove to be s\nd1 n only ! atoms :i* provide /ell> light & heat1 b also e atom 9 ! univ]se1 are doom$ to de/ruction1 & mu/ 9 "t dissolve away 9 radiation4 ,! solid e>? & ! et]nal hills w melt away z surely1 al?\gh n z rapidly1 z ! />s3 ,! cl\d-capp$ t[]s1 ! gorge\s palaces1 ,! solemn temples1 ! great globe itself1 ,yea1 all :i* x inh]it1 %all dissolve1 ,& 444 leave n a rack beh9d4 ,& if ! univ]se am\nts to no?+ m ?an ?is1 %all we c>ry on ! quotation3 ,we are su* /uff ,z dreams are made on2 & our little life ,is r\nd$ ) a sleep1 --or %all we n8 ,,*apt] ,,iv ,c>v+ out ! ,univ]se ,we h comm5t$ on ! surpris+ empt9ess ( space3 six specks ( du/ 9 ,wat]loo ,/ation ab\t repres5t ! ext5t to :i* x is occupi$ by />s 9 its mo/ cr[d$ p>ts4 ,! comm5t might well h tak5 ano!r =m4 ,six specks ( du/ conta91 let u say1 a ?\s& million million molecules4 ,our model ( space is empty because ?is great numb] ( molecules happ5s all to be aggregat$ into z few z six lumps4 ,9 real space ! unit ( aggregation is ! />1 & an av]age /> conta9s ab\t #aj molecules--a numb] s l>ge t x is q useless to try to imag9e x4 ,! empt9ess ( space does n orig9ate f any paucity ( molecules2 x orig9ates f ! circum/ance t1 ap>t f ^? :i* =m ! t5u\s cl\ds ( gas /ret*+ f /> to />1 ! molecules are aggregat$ toge!r 9 ! huge colonies we call />s1 ) ab\t #aj memb]s to ea*4 ,:y %\ld ! molecules 9 space h]d toge!r 9 ?is way1 :5 ! molecules 9 ! rooms 9 :i* ,i am writ+ & y are read+ d n8 ,foll[+ a well-tri$ sci5tific me?od1 we may attempt to discov] :y ^! aggregates h =m$1 by fir/ exam9+ :at keeps !m toge!r n[ t !y h =m$4 ,! e>?'s atmosph]e consi/s ( ab\t #aj molecules4 ,:y d !y /ay press$ d[n into an atmosph]e in/ead ( spread+ out ?r\gh space8 ,! answ] is ( c\rse provid$ by ! e>?'s gravitation4 ,a bullet fir$ f ! e>?'s surface ) a spe$ ( #fic miles a second or m w fly (f into space1 because ! e>?'s gravitational pull is inadequate to hold x back :5 x moves ) s high a spe$4 ,b a bullet fir$ ) a spe$ ( less ?an #fic miles a second does n leave ! e>?2 its spe$ is inadequate to take x cle> ( ! e>?'s pull4 ,?us ! molecule-bullets :i* =m ! e>?'s atmosph]e1 fly+ ) spe$s less ?an a ?ird ( a mile a second1 h no *ance at all ( gett+ away4 ,! e>?'s gravitation cont9ually pulls !m back to e>?1 s t ! e>? reta9s its cov]+ ( air4 ,at r>e int]vals a molecule may exp]i5ce a succession ( exceptionally lucky collisions ) o!r molecules1 & s atta9 a spe$ ( m ?an #fic miles a second4 ,a molecule :i* arrives at ! outside ( ! e>?'s atmosph]e ) su* a spe$ w leave ! e>? altoge!r1 & jo9 ! int]/ell> cr[d ( /ray molecules4 ,! e>? is cont9ually %$d+ its atmosph]e 9 ?is way1 b calculation %ews t ! loss1 ev5 9 millions ( millions ( ye>s1 is q insignificant1 s t we may reg>d ! e>?'s atmosph]e z p]man5t4 ,x is ! same ) ! sun4 ,! sun's heat has brok5 up ! molecules ( its atmosph]e into _! con/itu5t atoms1 & ^! move ) an av]age spe$ ( ab\t #b miles a second4 ,b an atom-bullet w\ld h to move at ab\t #chj miles a second to escape altoge!r f ! sun1 s t ! sol> atoms rema9 to =m an atmosph]e4 ,if all ! molecules ( air 9 an ord9>y room 7 collect$ into a bun* at ! c5tre ( ! room1 ! ball ( air s =m$ w\ld ( c\rse ex]t a gravitational pull on its out]mo/ molecules1 ( ! same k9d z ! e>? & sun ex]t on ! molecules ( _! atmosph]es4 ,b1 because ! weight ( ?is ball ( air is s small1 ! int5sity ( its gravitational pull w\ld also be small2 inde$ x w\ld be s feeble t a spe$ ( ab\t a y>d a c5tury w\ld be en\gh to take ! out]mo/ molecules cle> ( x4 ,z ! molecules ( ord9>y air move at ab\t #ejj y>ds a second1 su* a ball ( air w\ld imm$iately scatt] ?r\gh ! :ole room4 ,on ! o!r h&1 if ! room 7 big en\gh to conta9 ! sun1 all its molecules c\ld /ay 9 a ball at ! c5tre1 j z !y d 9 ! sun4 ,! out]mo/ molecules w\ld ne$ a spe$ ( at lea/ #chj miles a second to escape1 s t _! actual spe$s ( #ejj y>ds a second or s w\ld be ( no s]vice to !m4 ,,planet>y ,,atmosph]es4 ,9 g5]al ! "q ( escape or no escape dep5ds on ! outcome ( a battle betwe5 ! molecul> spe$s ( ! out]mo/ molecules1 & ! int5sity ( ! gravitational hold :i* ! rema9d] ( ! mass ex]ts on !m4 ,! sol> sy/em provides _m examples ( ?is4 ,! moon has only a six? z mu* gravitational hold ov] ! molecules ( an atmosph]e z ! e>? has1 ) ! result t any atmosph]e ! moon may ev] h _h1 has escap$ by n[4 ,m]cury has two-fif?s ( ! e>?'s gravitational hold1 b1 ow+ to its ne>ness to ! sun1 its sunw>d surface is v hot1 ) ! consequ5ce t its atmosph]e also has escap$4 ,! gravitational hold ( ,m>s on its molecules is only a fif? ( ! e>?'s1 b its surface is cool]4 ,calculation %ews t wat]-vap\r & heavi] molecules ought to rema91 :ile ! light] molecules ( helium & hydrog5 ought to h escap$4 ,?is probably repres5ts :at has actually happ5$4 ,! l>ge/ satellite ( ,saturn & ! two l>ge/ satellites ( ,jupit] w\ld ex]cise ab\t ! same gravitational hold z ! moon1 b z _! surfaces mu/ be enorm\sly cold] ?an t ( ! moon1 !y ought to be able to reta9 atmosph]es4 ,"s obs]v]s claim to h se5 indications ( atmosph]es on all ?ree satellites4 ,all ! f\r major planets ex]t /rong] gravitational holds ov] _! molecules ?an ! e>?1 & s reta9 _! atmosph]es ) ease1 :ile ,v5us1 ) approximately ! same gravitational hold z ! e>?1 also reta9s an atmosph]e4 ,^! consid]ations amply expla9 :y ! molecules ( ! />s mu/ necess>ily rema9 aggregat$ n[ t ! aggregates h once be5 =m$1 b ! "q ( h[ & :y ^! aggregates =m$ 9 ! fir/ in/ance is f> m complex4 ,:at1 = in/ance1 det]m9$ t !re %\ld be ab\t #aj molecules 9 ea* /> r ?an #aj or #aj8 ,,gravitational ,,in/ability ,x is natural to enquire :e!r ! =ces :i* n[ keep a /> toge!r may n also h be5 responsible = its fall+ toge!r 9 ! fir/ in/ance4 ,?is leads u to /udy ! aggregat+ p[] ( gravitation 9 "s detail4 ,five ye>s aft] ,newton _h publi%$ 8 law ( gravitation1 ,b5tley1 ! ,ma/] ( ,tr9ity ,college1 wrote him1 rais+ ! "q ( :e!r ! newly discov]$ =ce ( gravitation w\ld n acc\nt = ! aggregation ( matt] into />s1 & we f9d ,newton reply+1 9 a lett] ( date ,decemb] #aj1 #afib3 ,x seems to me1 t if ! matt] ( our sun & planets1 & all ! matt] ( ! univ]se1 7 ev5ly scatt]$ ?r\gh\t all ! heav5s1 & e p>ticle _h an innate gravity t[>ds oil ! re/1 & ! :ole space ?r\gh\t :i* ?is matt] 0 scatt]$1 0 f9ite1 ! matt] on ! outside ( ?is space w\ld by its gravity t5d t[>ds all ! matt] on ! inside1 & by consequ5ce fall d[n into ! middle ( ! :ole space1 & !re compose "o great sph]ical mass4 ,b if ! matt] 7 ev5ly dispos$ ?r\gh\t an inf9ite space1 x c\ld nev] conv5e into "o mass2 b "s ( x w\ld conv5e into "o mass & "s into ano!r1 s z to make an inf9ite numb] ( great masses1 scatt]$ great di/ances f "o to ano!r ?r\gh\t all t inf9ite space4 ,& ?us might ! sun & fix$ />s be =m$1 suppos+ ! matt] 7 ( a lucid nature4 ,an exact ma!matical inve/igation on :i* ,i emb>k$ 9 #aija1 n only confirms ,newton's conjecture 9 g5]al t]ms1 b also provides a me?od = calculat+ :at size ( aggregates w\ld be =m$ "u ! action ( gravitation4 ,,! ,,=mation ,,( ,,cond5sations4 ,y /& 9 ! middle ( a room & clap y\r h&s4 ,9 common language y are mak+ a noise2 ! physici/1 9 8 pr(essional capacity1 w\ld say y are creat+ waves ( s\nd4 ,z !y approa* "o ano!r1 y\r h&s expel ! int]v5+ molecules ( air4 ,^! /amp$e out1 collid+ ) ! molecules ( out] lay]s ( air1 :i* are 9 turn driv5 away to collide ) /ill m remote lay]s2 ! di/urbance orig9ally creat$ by ! motion ( y\r h&s is c>ri$ on 9 ! =m ( a wave4 ,al?\gh ! individual molecules h an av]age spe$ ( #ejj y>ds a second1 ! zig-zag quality ( _! motions r$uces ! spe$ ( ! di/urbance1 z we h already se51 to ab\t #cgj y>ds a second--! ord9>y velocity ( s\nd4 ,z ! di/urbance rea*es any po9t ! numb] ( molecules !re becomes abnormally high1 = ! /amp$+ molecules add to ! normal quota ( molecules at ! po9t4 ,?is ( c\rse produces an excess ( pressure4 ,x is ?is excess pressure act+ on my e>-drum t transmits a s5sation to my bra91 s t ,i he> ! noise ( y\r clapp+ y\r h&s4 ,?is excess ( pressure _c ( c\rse p]si/ = long1 s t ! excess ( molecules :i* produces x mu/ rapidly dissipate4 ,x is ?us t ! wave passes on4 ,yet !re is "o factor :i* militates aga9/ its dissipation4 ,ea* molecule ex]ts a gravitational pull on all its neighb\rs1 s t :]e !re is an excess ( molecules1 !re is also an excess ( gravitational =ce4 ,9 an ord9>y s\nd wave ?is is ( absolutely inappreciable am\nt1 yet su* z x is1 x provides a t9y =ce hold+ ! molecules back1 & prev5t+ !m scatt]+ z freely z !y o!rwise w\ld d4 ,:5 ! same ph5om5on occurs on ! a/ronomical scale1 ! correspond+ =ces may become ( ov]:elm+ importance4 ,let u speak ( ! gas 9 any region ( space :]e ! numb] ( molecules is above ! av]age ( ! surr\nd+ space1 z a 8cond5sation40 ,!n x c be prov$ t1 if a cond5sation is ( suffici5t ext5t1 ! excess ( gravitational =ce may be suffici5t to inhibit scatt]+ altoge!r4 ,9 su* a case1 ! cond5sation may cont9ually gr[ ?r\gh attract+ molecules into x f outside1 ^: molecul> spe$s are !n inadequate to c>ry !m away aga94 ,:e!r ?is happ5s or n w dep5d ( c\rse on ! spe$ ( molecul> motion 9 ! gas1 z well z on ! size ( ! cond5sation4 ,b x w n dep5d at all on ! ext5t to :i* ! process ( cond5sation has proce$$4 ,by d\bl+ ! excess numb] ( molecules 9 any cond5sation1 we d\ble ! ext5t to :i* cond5sation has proce$$4 ,9 s do+1 we d\ble ! gravitational pull t5d+ to increase ! cond5sation1 b we also d\ble ! excess pressure :i* t5ds to dissipate x2 we d\ble ! weights on ea* side ( ! balance1 b ! balance /ill sw+s 9 ! same direction4 ,if once conditions are fav\rable to its gr[?1 a cond5sation goes on gr[+ automatically until !re are no fur!r molecules left = x to absorb4 ,! great] ! ext5t 9 space ( a cond5sation1 ! m fav\rable conditions are to its cont9u$ gr[?4 ,o!r ?+s be+ equal1 a cond5sation two million miles 9 diamet] w ex]t twice ! gravitational =ce ( a cond5sation "o million miles 9 diamet]1 b ! excess pressures are ! same 9 ! two cases4 ,?us1 ! l>g] a cond5sation is ! m likely x is to g on gr[+1 & by pass+ 9 imag9ation to l>g] & l>g] cond5sations we mu/ 9 "t come to cond5sations ( su* a size t !y are b\nd to keep on gr[+4 ,nature's law "h is "o ( unre/rict$ competition4 ,no?+ succe$s l success1 & s we f9d t cond5sations :i* are big to />t ) h ! capacity ( increas+ /ill fur!r1 :ile ^? :i* are small m]ely dissipate away4 ,suppose n[ t an enorm\s mass ( uni=m gas ext5ds ?r\gh space = millions ( millions ( miles 9 e direction4 ,any di/urbance :i* de/roys its uni=mity may be reg>d$ z sett+ up cond5sations ( e conceivable size4 ,?is may n seem obvi\s at fir/2 x may be ?\ght t a di/urbance :i* only affect$ a small area ( gas w\ld only produce a cond5sation ( small ext5t4 ,su* an argum5t ov]looks ! way 9 :i* ! gravitational pull ( a small body acts ?r\gh\t ! univ]se4 ,! moon raises tides on ! di/ant e>?1 & also tides1 al?\gh incomp>ably less 9 am\nt1 on ! mo/ di/ant ( />s4 ,ea* "t ! *ild ?r[s its toy out ( its baby-c>riage1 x di/urbs ! motion ( e /> 9 ! univ]se4 ,s long z gravitation acts1 no di/urbance c be conf9$ to any area less ?an ! :ole ( space4 ,! m viol5t ! di/urbance :i* creates !m1 ! m int5se ! cond5sations w be to beg9 )1 b ev5 ! smalle/ di/urbance mu/ set up cond5sations1 al?\gh ^! may be ( extremely feeble int5sity4 ,& we h se5 t ! fate ( a cond5sation is n det]m9$ by its int5sity b by its size4 ,no matt] h[ feeble _! orig9al int5sity may h be51 ! big cond5sations g on gr[+1 ! small ones disappe>4 ,9 "t no?+ is left b a collection ( big cond5sations4 ,! ma!matical analysis already ref]r$ to %ews t !re is a def9ite m9imum weight su* t all cond5sations bel[ ?is weight m]ely dissipate away into space4 ,to a good en\gh approximation = our pres5t purpose1 ?is m9imum weight is su* t if a t5? ( ?is weight ( gas 7 isolat$ 9 space1 & all ! re/ ( ! gas annihilat$1 ! molecules w\ld j & only j fail to escape f its surface#bj4 #bj ,?is is ne> en\gh1 b n absolutely accurate4 ,exact ma!matical analysis %ews t ! weight ( ! m9imum cond5sation ,m is giv5 by ,c ,m --------------1 :]e ,c1 1 1 are ! molecul> velocity1 gravitation con/ant1 initial d5sity1 & ratio ( specific heats1 :]eas ! weight f :i* molecules mov+ ) velocity ,c j fail to escape is giv5 by #c ,c ,m ---- ------------------4 #d ,) #a ! m9imum weight ( cond5sation is #ig times ! weight :i* is j adequate to reta9 ! molecules4 ,we may say t ! orig9al uni=mly di/ribut$ mass ( gas 0 8un/able0 because any di/urbance1 h[ev] slight1 causes x to *ange its configuration entirely2 x _h ! dynamical attributes ( a /ick balanc$ on its po9t1 or ( a soap-bubble :i* is j ready to bur/4 ,,primaeval ,,*aos4 ,^! g5]al !oretical results may n[ be appli$ to any mass ( gas we please4 ,let u beg9 by apply+ !m to ,newton's hypo!tical 8matt] ev5ly dispos$ ?r\gh\t an inf9ite space40 ,we return 9 imag9ation to a "t :5 all ! sub/ance ( ! pres5t />s & nebulae 0 spread uni=mly ?r\gh\t space2 9 brief1 we />t f ! primaeval *aos f :i* mo/ sci5tific !ories ( cosmogony h />t$4 ,hubble has e/imat$ t if ! :ole ( ! matt] 9 ^? p>ts ( ! univ]se we "k 7 r$i/ribut$ ev5ly ?r\gh\t space1 ! gas s =m$ w\ld h only ab\t #ae #aj times ! d5sity ( wat]4 ,?is e/imate is almo/ c]ta9ly on ! l[ side1 ev5 z repres5t+ pres5t conditions1 & 9 try+ to recon/ruct ! primaeval gas we mu/ add some?+ to all[ = ! molecules & atoms :i* h melt$ away into radiation 9 ! int]v5+ p]iod4 ,on ! :ole1 p]haps #aj is n an unreasonable d5sity to assign to ! hypo!tical primaeval nebula4 ,x is almo/ inconceivably l[4 ,9 ord9>y air1 at a d5sity ( "o eight-hundr$? t ( wat]1 ! av]age di/ance betwe5 adjo9+ molecules is ab\t an eight-million? "p ( an in*2 9 ! primaeval gas we are n[ consid]+1 ! correspond+ di/ance is two or ?ree y>ds4 ,! contra/ aga9 leads back to ! !me ( ! extreme empt9ess ( space4 ,:at is ! m9imum weight ( cond5sation t w\ld p]si/ 9 ?is primaeval gas8 ,calculation %ews t if ord9>y air 7 att5uat$ to ?is extraord9>y degree1 no cond5sation c\ld p]si/ & cont9ue to gr[ unless x _h at lea/ #fb million times ! weight ( ! sun2 any small] weight ( gas w\ld ex]t s slight a gravitational pull on its out]mo/ molecules1 t _! normal molecul> spe$s ( #ejj y>ds a second w\ld lead to ! prompt dissipation ( ! :ole cond5sation4 ,we c c>ry out simil> calculations ) ref]5ce to o!r assum$ d5sities ( gas1 & o!r molecul> velocities4 ,! foll[+ table %ews ! weights ( cond5sations :i* w\ld be =m$ 9 primaeval masses ( *aotic gas hav+ ! d5sities %ewn 9 ! fir/ column1 & ! v>i\s molecul> velocities m5tion$ at ! heads ( ! rema9+ columns4 ,9 ea* case ! weights ( ! cond5sations are giv5 9 t]ms ( ! weight ( ! sun3 ---------------------------------------- ----------------------- ,d5sity ,mol4 vel4 ,mol4 vel4 ( ,mol4 vel4 ( ,mol4 vel4 ( 9 t]ms #ejj y>ds #ajjj y>ds #bjjj y>ds #cjjj y>ds ( wat] a sec4 a sec4 a sec4 a sec4 ---------------------------------------- ----------------------- #aj #be1jjj1jjj #bjj1jjj1jjj #a1ejj1jjj1jjj #e1jjj1jjj1jjj #aj #fb1ejj1jjj #ejj1jjj1jjj #d1jjj1jjj1jjjac1jjj1jjj1jjj #ae #ajafj1jjj1jjja1cjj1jjj1jjjaj1jjj1jjj1jj jcj1jjj1jjj1jjj ---------------------------------------- ----------------------- ,all kn[n />s h weights comp>able ) t ( ! sun4 ,?us if1 z ,newton conjectur$1 ! />s fir/ came into be+ z cond5sations ( ?is k9d1 !n ! entries 9 ?is table ought to be comp>able ) unity4 ,newton's conjecture1 9 ! =m 9 :i* we h j consid]$ x1 is cle>ly unt5able1 s9ce all ! calculat$ weights are _m millions ( times t ( ! sun4 ,if !re ev] exi/$ a primaeval *aos ( ! k9d we are n[ consid]+1 x w\ld n cond5se into />s1 b into enorm\sly m massive cond5sations1 ea* hav+ ! weight ( millions ( />s4 ,,! ,,bir? ,,( ,,! ,,great ,,nebulae ,n[ x is significant t bodies are kn[n 9 space hav+ weights equal to ^? j calculat$1 namely ! great extra-galactic nebulae4 ,!re are two nebulae ^: weights c be det]m9$ ) fair accuracy1 namely ! ,great ,nebula 9 ,&rom$a 7,plate ,,iv1 p4 #cj7 & ! nebula ,n4,g4,c4 #deid 9 ,virgo 7,plate ,,xv74 ,hubble e/imates ^! to be z foll[s3 ,nebula ,m #ca3 weight #cejj million times t ( sun 0 ,n4,g4,c4 #deid3 0 #bjjj 0 0 ,^! e/imates are aga9 probably bo? on ! l[ side1 b _! g5]al ord] ( magnitude is su* z to sugge/ t ! cond5sations :i* w\ld fir/ be =m$ out ( ! primaeval nebula mu/ h be5 ! great extra-galactic nebulae1 & n m]e />s4 ,x is ( c\rse at be/ only a conjecture t ! great nebulae 7 =m$ 9 ?is mann]--if = no o!r reason because we c nev] "k :e!r ! hypo!tical primaeval nebula ev5 exi/$--b x seems ! mo/ reasonable hypo!sis we c frame to expla9 ! fact t ! pres5t nebulae exi/4 ,^! nebulae are s g5]ally simil> to "o ano!r t x seems likely t !y mu/ all h be5 produc$ by ! action ( ! same ag5cy1 & t :i* we h j consid]$ provides a reasonable explanation :i*1 ap>t f ! po/ulat$ exi/5ce ( ! cont9u\s primaeval nebula1 is bas$ on v]ae causae4 ,! great nebulae are ( c\rse n exactly simil>1 & our next inquiry mu/ be z to ! orig9 ( _! diff]5ces4 ,illu/ration3 ,,plate ,,xv ,! ,nebula ,n4,g4,c4 #deid 9 ,virgo ,illu/ration3 ,mt ,wilson ,obs]vatory ,! ,nebula ,n4,g4,c4 #gbag ,if ! cond5sations 9 ! primaeval gase\s nebula _h =m$ & contract$ 9 an absolutely regul> fa%ion1 ! f9al product w\ld be an array ( p]fectly equal & simil> masses ( gas spac$ ) p]fect regul>ity4 ,b nature is seldom z regul> z ?is2 & we ne$ n be surpris$ t ! obs]v$ nebul> array is n ev5ly spac$1 or t its memb]s are nei!r equal 9 weight1 nor symmetrically arrang$4 ,z ! orig9al cond5sations 9 ! primaeval gas contract$1 !y mu/ h produc$ curr5ts1 & ^! w\ld h>dly be likely to occur absolutely symmetrically4 ,if ! motion 9 ea* mass ( cond5s+ gas _h be5 directly t[>ds ! c5tre ( ! cond5sation at e po9t1 ! f9al result w\ld h be5 a sph]ical nebula devoid ( all motion1 b any less symmetrical sy/em ( curr5ts w\ld result 9 a sp9 be+ giv5 to ea* contract+ mass4 ,?is sp9 w\ld no d\bt be v sl[ at fir/1 b ! well-kn[n pr9ciple ( 8cons]vation ( angul> mom5tum0 requires t1 z a sp9n+ body contracts1 its rate ( sp9 mu/ increase4 ,?us :5 ! process ( cond5sation 0 complete1 ! f9al product w\ld be a s]ies ( nebulae rotat+ at diff]5t rates4 ,,nebul> ,,rotation4 ,& ?is is exactly :at is obs]v$2 s f> z our evid5ce goes ! nebulae are 9 rotation1 & at diff]5t rates4 ,! v>i\s p>ts ( ! surface ( any rotat+ mass necess>ily h diff]5t spe$s 9 space4 ,! sun = in/ance rotates ab\t its axis 9 su* a direction t ! surface we see is mov+ always f ea/ to we/2 z a result ! ea/]n limb is always advanc+ t[>ds ! e>?1 :ile ! we/]n limb is rec$+ f u4 ,a spectroscope turn$ on to diff]5t p>ts ( ! sun's surface 9 succession at once reveals ^! diff]5ces ( spe$2 !y n only assure u ( ! sun's rotation1 b enable u to measure its am\nt4 ,! nebulae may be exam9$ 9 ! same way1 & ! exam9ation %ews t a l>ge numb] ( !m are rotat+ ) ! p]fectly regul> motion ( a solid body--a sp9n+-top1 = in/ance4 ,measur$ by t]re/rial /&>ds _! rates ( rotation seem extraord9>ily sl[2 = in/ance ! ,great ,nebula ,m #ca 9 ,&rom$a requires ab\t #ai1jjj1jjj ye>s to make a complete rotation1 b ?is app>5t sl[ness is an inevitable result ( ! huge size ( ! nebula4 ,ev5 to get r\nd once 9 #ai1jjj1jjj ye>s1 ! out] p>ts ( ! nebula h to move ) spe$s ( hundr$s ( miles a second4 ,a few ( ! nebulae are q irregul> 9 %ape1 b ! majority h regul> %apes1 & x is highly significant t ^! are precisely ! %apes :i*1 x c be calculat$ ma!matically1 w\ld be exhibit$ by rotat+ masses ( gas4 ,actually !re is a f> /rong] case ?an ?is = suppos+ ! nebulae to be rotat+ masses ( gas4 ,f ! purely obs]vational evid5ce ( surface-brightness & o!r *>act]i/ics1 ,hubble f\nd t ne>ly all ( ^! nebulae c\ld be arrang$ 9 a s+le l9e> sequ5ce--!y c\ld be arrang$ 9 ord] l beads on a /r+4 ,& ?is ord] prov$ to be practically id5tical ) ! sequ5ce :i* _h previ\sly be5 calculat$1 by purely !oretical me?ods1 = ! configurations ( masses ( gas rotat+ at gradually increas+ rates ( spe$4 ,let u exam9e ?is sequ5ce ( !oretical configurations 9 _! natural ord]4 ,a mass ( gas :i* 0 n rotat+ at all w\ld ( c\rse assume a sph]ical %ape "u its own gravitation4 ,a numb] ( p]fectly sph]ical nebulae are kn[n2 a typical example is %ewn 9 fig4 #a on ,plate ,,xvi4 ,illu/ration3 ,,plate ,,xvi ,fig4 #a ,n4,g4,c4 #ccgi ,illu/ration3 ,fig4 #b ,n4,g4,c4 #dfba ,illu/ration3 ,fig4 #c ,n4,g4,c4 #caae ,illu/ration3 ,fig4 #d ,n4,g4,c4 #deid 9 ,virgo ,illu/ration3 ,fig4 #e ,n4,g4,c4 #defe 9 ,b]5ice's hair ,mt ,wilson ,obs]vatory ,a sequ5ce ( ,nebul> ,configurations ,) slight rotation ! mass assumes ! %ape ( a slightly flatt5$ orange1 l ! e>? or ,jupit]4 ,nebulae ( ?is %ape are also kn[n 9 abundance2 an example is %ewn 9 fig4 #b on ! same plate4 ,) a high] degree ( rotation ! degree ( flatt5+ increases1 b !oretical calculation %ews t ! orange %ape is soon dep>t$ f4 ,! equator fir/ beg9s to %ew a pron\nc$ bulge1 until f9ally1 ) suffici5t rotation1 ?is develops into a %>p edge1 ! rotat+ mass n[ be+ %ap$ l a d\ble-convex l5s4 ,?is pr$iction ( !ory is abundantly confirm$ by obs]vation1 a l>ge numb] ( ^! l5s-%ap$ nebulae be+ obs]v$ 9 ! sky4 ,an example is %ewn 9 fig4 #c on ,plate ,,xvi4 ,! next /ep is some:at s5sational4 ,fur!r rotation does n1 z might be expect$1 result 9 /ill fur!r flatt5+4 ,up to n[1 ea* increase 9 rotation has made ! bulge on ! equator %>p]1 b ?is is n[ z %>p z x c be4 ,!ory %ews t ! flatt5+ has also proce$$ to ! utmo/ possible limit1 & t ! next /age mu/ consi/ 9 matt] be+ eject$ ?r\gh ! %>p edge ( ! equator & spread ?r\gh\t ! equatorial plane4 ,"h aga9 obs]vation confirms !ory2 figs4 #d & #e 7,plate ,,xvi7 %ew types ( nebulae actually obs]v$1 ! =m] be+ ! nebula 9 ,virgo :i* we h already _h "u discussion4 ,! comp>atively ?9 lay] ( gas :i* n[ lies 9 ! equatorial plane is simil> 9 "o respect at lea/ to ,newton's matt] 8ev5ly dispos$ ?r\gh\t an inf9ite space40 ,di/urbances c be set up 9 x 9 a v>iety ( ways1 & any di/urbance1 no matt] h[ slight1 mu/ result 9 ! creation ( a s]ies ( cond5sations4 ,z be=e1 ^? bel[ a c]ta9 limit ( size disappe> ( !mselves1 :ile ^? above ?is limit cont9ually increase 9 int5sity until !y h absorb$ all ! gas 9 ! equatorial plane4 ,aga91 z ) ! hypo!tical primaeval *aos1 we c calculate ! m9imum size ( cond5sation :i* c be expect$ to h a p]man5t exi/5ce1 & once aga9 ! result proves to be highly significant4 ,hubble's e/imates ( ! total weights ( two conspicu\s nebulae h already be5 giv54 ,z ! di/ances1 & !re=e also ! sizes1 ( bo? ^! nebulae are kn[n1 x is an easy matt] to calculate ! av]age d5sity ( ! gas ?r\gh\t ! :ole nebula4 ,! av]age d5sity 9 ,m #ca is f\nd to be ab\t #e #aj ( t ( wat]2 ! correspond+ numb] = ,n4,g4,c4 #deid is #b #aj4 ,^! figures give u "s idea ( ! d5sity ( matt] 9 ! out] regions ( ! nebulae4 ,al?\gh ^! d5sities are ab\t a ?\s& million times z great z ! e/imat$ d5sity ( ! orig9al primaeval nebula ( space1 !y are /ill almo/ inconceivably l[4 ,!re is /ill only ab\t "o molecule to ! cubic in*1 & a s+le brea? f ! lungs ( a fly c\ld fill a l>ge ca!dral ) air ( ?is d5sity4 ,on proce$+ to calculate ! weights ( ! smalle/ cond5sations :i* c\ld =m & p]si/ 9 a gas ( ?is l[ d5sity1 we obta9 ! results %ewn 9 ! foll[+ table4 ,! molecul> velocities are tak5 r l[1 s z to all[ = ! cool+ :i* mu/ occur :5 ! gas is spread out 9 ! equatorial plane ( ! nebula4 ,aga9 ! weights ( ! cond5sations are giv5 9 t]ms ( ! weight ( ! sun4 ,& ! significant fact em]ges t mo/ ( ! entries 9 ! table repres5t weights comp>able ) t ( ! sun4 ,we are deal+ ) /ell> weights at la/2 ! cond5sations :i* mu/ =m 9 ! out] regions ( ! great nebulae w h weights comp>able ) ^? ( ! />s4 ---------------------------------------- ---------------------- ,d5sity 9 ,mol4 vel4 ( ,mol4 vel4 ( ,mol4 vel4 ( t]ms ( wat]#ajj y>ds a sec4#cjj y>ds a sec4#ejj y>ds a sec4 ---------------------------------------- ---------------------- #aj #ag #cf #bbj #aj #e #acj #fbe #aj #ag #cfj #bbjj ---------------------------------------- ---------------------- ,,! ,,bir? ,,( ,,/>s ,& inde$ !re c be b little d\bt t ! process we h j be5 consid]+ is t ( ! bir? ( />s4 ,ev5 a casual glance at photographs ( nebulae suffices to %ew t ! matt] :i* has be5 eject$ into ! equatorial plane ( a nebula does n lie uni=mly spread out 9 t plane2 x is se5 to h fall5 into bun*es1 knots or cond5sations4 ,^! are app>5t en\gh 9 _m ( ! nebul> photographs already %ewn1 b !y c be se5 /ill m cle>ly 9 nebulae :i* are view$ ne>ly full-on1 su* z = in/ance ! two /rik+ nebulae %ewn 9 ,plates ,,xvii & ,,xviii4 ,^! bun*es are inv>iably too l>ge to be int]pret$ z s+le />s2 !y are m probably gr\ps ( />s4 ,9 ! l>ge/ telescopes !y break up into great numb]s ( po9ts ( light 9 ! way already exhibit$ 9 ,plate ,,xi 7p4 #gj74 ,we h already m5tion$ ! reasons :i* compel u to reg>d ^! po9ts ( light z actual />s1 ! pr9cipal be+ t "s ( !m %ew ! *>act]i/ic light-fluctuations ( ! ,cepheid v>iables4 ,x is n altoge!r cle> :e!r ! />s are =m$ directly z cond5sations 9 ! equatorial plane ( ! nebula1 or :e!r l>g] cond5sations =m fir/1 namely ! bun*es obs]vable 9 nebul> photographs1 :i* subsequ5tly =m small] cond5sations1 ! />s4 ,on ! :ole x seems likely t !re are two processes involv$--fir/ ! break-up ( ! nebul> matt] into big cond5sations1 & !n ! break-up ( ^! big cond5sations into />s4 ,su* a succession ( processes might well accompany a gradual cool+ ( ! matt]1 & x is ( c\rse possible t !re are ev5 m ?an two processes involv$4 ,!re is no ne$ to =m a f9al op9ion on ?is at pres5t1 z x is 9 no way ess5tial to ! progress ( ! ma9 argum5t4 ,a collection ( nebul> photographs enables u to foll[ nebul> evolution f ! e>lie/ /ages %ewn 9 ,plate ,,xvi 7p4 #bjg71 ?r\gh ! fir/ appe>ance ( granul> bun*es1 su* z are %ewn 9 ,plate ,,xvii1 & ! fir/ di/9ct appe>ance ( />s %ewn 9 ,plate ,,xviii1 d[n to ! lat] /ages1 su* z are %ewn 9 ,plates ,,xix & ,,xx1 9 :i* ! nebula appe>s to be b little m ?an a cl\d ( />s4 ,hubble has f\nd x possible to foll[ ! sequ5ce /ill fur!r1 & c trace a cont9u\s transition f ! nebulae ( ?is la/ type to pure />-cl\ds su* z ! ,great] & ,less] ,magellanic ,cl\ds %ewn 9 ,plate ,,xxi4 ,illu/ration3 ,,plate ,,xvii ,mt ,wilson ,obs]vatory ,! 8,:irlpool0 ,nebula ,m #ea 9 ,canes ,v5atici ,illu/ration3 ,,plate ,,xviii ,mt ,wilson ,obs]vatory ,! ,nebula ,m #ha 9 ,ursa ,major ,?us ! />s appe> to h be5 born 9 mu* ! same way z we h conjectur$ t _! p>5ts1 ! great nebulae1 _h be5 born be=e !m1 namely1 ?r\gh ! ag5cy ( :at is g5]ally kn[n z 8,gravitational ,in/ability40 ,?is causes any mass ( *aotic gas to break up into deta*$ cond5sations1 &1 ! m t5u\s ! orig9al gas1 ! great] ! weights ( ! cond5sations =m$ out ( x4 ,! orig9al primaeval nebula 0 ( su* l[ d5sity t ! cond5sations :i* =m$ 9 x weigh$ ?\s&s ( millions ( times z mu* z ! sun4 ,^! increas$ _! d5sity s mu* 9 contract+ t :5 _! rotation caus$ !m to eject gase\s matt]1 ?is cond5s$ into masses ( /ell> weight :i* we believe actually to be />s4 ,we h less c]ta9 k ( ! =m] process ?an ( ! latt]4 ,our only reason = ?9k+ t ! =m] process ev] occurr$ is t ! extra-galactic nebulae n[ exi/4 ,!re is no evid5ce t ! primaeval *aotic nebula ev] exi/$1 beyond ! fact t ! hypo!sis ( its previ\s exi/5ce leads to a v satisfactory explanation ( ! pres5t nebulae exi/+ z !y n[ d4 ,on ! o!r h&1 we n only "k t ! />s exi/3 we also "k t ! masses ( gas exi/ out ( :i* !ory %ews t />s mu/ necess>ily be born4 ,!y are ! t5u\s equatorial fr+es ( ! great nebulae4 ,our telescopes %ew u bo? ! nebul> fr+es & ! />s1 & we c almo/ /udy ! actual process ( bir?4 ,,! ,,galactic ,,sy/em ,,( ,,/>s4 ,if ?is is ! true acc\nt ( ! bir? ( ! />s1 !n our sun & its companions 9 space mu/ h be5 born out ( a rotat+ nebula4 ,obs]vation gives /rong support to ?is conclusion4 ,s9ce ! "t ( ! ,h]s*els1 x has be5 a matt] ( frequ5t comm5t t ! galactic sy/em has ! g5]al %ape ( ! extra-galactic nebulae1 ! galactic plane ( c\rse repres5t+ ! equatorial plane ( ! orig9al nebula4 ,on purely obs]vational gr\nds1 pres5t-day a/ronomical ?\ght is mov+ rapidly t[>ds reg>d+ ! :ole galactic sy/em ei!r z a rotat+ nebula or ! rema9s ( "o4 ,x is ev5 possible t ?is may /ill reta9 a c5tral region :i* is z yet uncond5s$ into />s4 ,9 ! direction ( ! con/ellations ,scorpio & ,ophiu*us are d>k cl\ds :i* may ei!r veil ! c5tre ( ! sy/em or may conceivably be ! c5tre itself4 ,9 #aijd1 ,kapteyn f\nd t ! directions ( motion ( ! />s 9 ! vic9ity ( ! sun 7 n di/ribut$ at r&om4 ,! />s appe>$ to pref] to move to & fro along a c]ta9 direction 9 ! galactic plane r ?an 9 o!r directions--8/>-/ream+10 he call$ x4 ,?is peculi>ity 9 ! motion ( ! />s may be expect$ to ?r[ "s light on _! orig94 ,ea* /> moves 9 a complicat$ orbit "u ! gravitational attraction ( all ! o!r />s ( ! galactic sy/em4 ,x is n possible to calculate ?is orbit 9 detail4 ,! orbit ( a planet r\nd ! sun is easily calculat$ because only two bodies are involv$1 ! planet & ! sun4 ,b ev5 :5 !re are only ?ree bodies involv$1 x is impossible to calculate ! orbits t ea* describes "u ! attractions ( ! o!r two jo9tly3 ?is is ! fam\s problem ( ?ree bodies1 :i* has nev] be5 solv$4 ,:51 z 9 ! galactic sy/em1 ?\s&s ( millions ( />s are involv$1 x is naturally useless to try to calculate ! orbit ( ea* />--x w\ld be z futile z try+ to calculate ! pa? ( ea* molecule 9 a gas4 ,yet ! same /ati/ical me?ods :i* give u useful in=mation z to ! prop]ties ( a gas may be appli$ to /udy+ ! motions ( ! />s4 ,!re are s _m />s t we d n tr\ble ab\t individuals at all1 we j treat !m all toge!r z a cr[d4 ,to treat !m z individuals w\ld be z ?\gh ! railway company tri$ to =eca/ ! ,bank ,holiday traffic f ,london to ,brighton by consid]+ ! f9ances1 habits & psy*ology ( ea* individual ,london]4 ,illu/ration3 ,,plate ,,xix ,mt ,wilson ,obs]vatory ,! ,nebula ,m #aja 9 ,ursa ,major ,illu/ration3 ,,plate ,,xx ,mt ,wilson ,obs]vatory ,! ,nebula ,m #cc 9 ,triangulum ,)\t go+ into individual details1 we c see t ea* /> mu/ describe an orbit :i*1 aft] t\r+ r\nd a l>ge "p ( ! galaxy1 comes back to some:]e ne> its />t+ po9t4 ,calculation %ews t ea* su* circuit mu/ take hundr$s ( millions ( ye>s to complete4 ,ev5 s1 ! />s w mo/ly h p]=m$ sev]al complete circuits :ile ! e>? has be5 9 exi/5ce1 & if we are "r 9 suppos+ ! ages ( ! />s to be millions ( millions ( ye>s1 ea* /> mu/ h t\r$ r\nd ! galaxy sev]al ?\s&s ( times4 ,we %\ld accord+ly expect ! galaxy to h assum$ a def9ite p]man5t %ape by n[2 ! di/ribution ( />s 9 its diff]5t p>ts ought to h become some?+ l /eady1 & ! />s ought to h settl$ d[n to a /ate approximat+ to "o ( /eady motion4 ,/ati/ical me?ods ( inve/igation %ew t !re is n a great numb] ( possible arrangem5ts = a sy/em ( />s :i* has liv$ long en\gh to atta9 a /eady /ate4 ,if ! sy/em z a :ole has no rotation at all1 !re is only "o arrangem5t2 ! />s =m a globul> mass ) p]fect symmetry 9 all directions4 ,! obs]v$ globul> clu/]s 7,plate ,,ix1 p4 #fc7 provide good approximations to ?is type ( =mation1 al?\gh ,%apley has f\nd t ! majority are n absolutely sph]ical 9 %ape4 ,if ! sy/em z a :ole is end[$ ) rotation1 ! possible configurations are all ( a flatt5$ symmetrical %ape1 l a co91 a wat* or a r\nd biscuit--9 o!r words a sy/em ( />s 9 rotation mu/ be %ap$ pretty mu* z we believe ! galaxy to be %ap$4 ,fur!rmore ! motions ( ^! />s mu/ %ew 8/>-/ream+0 ( precisely ! k9d discov]$ by ,kapteyn4 ,?us bo? ! %ape ( ! galaxy & ! peculi>ities ( motion ( its />s indicate t ! galactic sy/em z a :ole mu/ be 9 a /ate ( rotation4 ,&1 z we h se5 7p4 #fg71 rec5t obs]vational rese>*es by ,oort1 ,plaskett & o!rs make x fairly c]ta9 t ! rotation requir$ by !ory is an actual fact4 ,! motions ( ! />s indicate t ! :ole galactic sy/em is rotat+ at a rate :i* v>ies f "o region to ano!r1 be+ ab\t "o revolution e #bcj million ye>s 9 ! vic9ity ( ! sun4 ,& ! hub ( ?is gigantic :eel is f\nd to co9cide v closely ) ! spot :i* ,%apley _h previ\sly fix$ z ! geometrical c5tre ( ! galactic sy/em f 8 rese>*es on ! di/ribution ( ! globul> clu/]s4 ,?us1 s9ce rotation _c be g5]at$ out ( no?+1 all ! ph5om5a agree 9 %ew+ t ! galactic sy/em mu/ h be5 born out ( a rotat+ body4 ,we are acqua9t$ ) only "o type ( a/ronomical body :i* is ( suffici5t size to turn into a galactic sy/em1 namely ! great nebulae1 & z ! majority ( ^! are believ$1 & "s are kn[n ) c]ta9ty1 to be 9 rotation1 x seems reasonable to conclude t ! galactic sy/em mu/ h be5 born out ( a nebula1 unless inde$ its /ructure is /ill su* t we %\ld ev5 n[ describe x z a nebula if we saw x f ! great di/ance f :i* we view ! o!r great nebulae4 ,! obs]v$ p]iod ( rotation ( ! galactic sy/em1 ( ! ord] ( #bcj million ye>s1 is sub/antially long] ?an ! p]iod1 ei!r kn[n or suspect$1 ( any ( ! nebulae1 b ! dim5sions ( ! galactic sy/em are also great] ?an ^? ( any kn[n nebula1 & ! two facts hang toge!r4 ,aga91 ! numb] ( />s 9 ! galactic sy/em is probably sub/antially high] ?an 9 any nebula1 z also is ! total weight ( ^! />s#ba4 ,all ?is makes x cle> t if ! galaxy is1 or ev] has be51 "o ( ! great nebulae1 x mu/ h be5 "o ( unusual size & weight4 #ba ,! foll[+ e/imates h already be5 m5tion$3 ,weight ( ,galaxy 9 t]ms ( sun #bdj1jjj1jjj1jjj 0 nebula ,m #ca 9 t]ms ( sun #c1ejj1jjj1jjj 0 0 ,n4,g4,c4 #deid 9 t]ms ( sun #b1jjj1jjj1jjj ,illu/ration3 ,,plate ,,xxi ,h>v>d 7,arequipa7 ,obs]vatory ,! ,less] ,magellanic ,cl\d ,illu/ration3 ,frankl9-,adams ,*>t ,! ,great] ,magellanic ,cl\d ,we h se5 h[ ! sun & all ! />s are cont9ually los+ weight z ! result ( _! emission ( radiation4 ,x foll[s t ! total weight ( ! galactic sy/em is = ev] decreas+1 & z a consequ5ce its gravitational hold on its con/itu5t />s is cont9ually weak5+4 ,if ?is gravitational hold 7 sudd5ly to vani% altoge!r1 ea* /> w\ld replace its pres5t curv$ pa? by a p]fectly /raight l9e1 along :i* x w\ld travel at its pres5t spe$1 undeflect$ by any gravitational =ces f o!r />s1 s t ! />s :i* n[ con/itute ! galactic sy/em w\ld soon be scatt]$ ?r\gh ! :ole ( space4 ,9 brief1 if ! gravitational pull ( ! />s 7 sudd5ly aboli%$1 ! galaxy w\ld beg9 to exp& at a great rate4 ,al?\gh ?is is n likely to happ51 ! gradual abolition ( ! gravitational pull ( ! />s1 z !y turn _! weight into radiation1 mu/ cause ! galaxy to exp& all ! "t at a sl[ rate3 calculation sugge/s t its pres5t rate ( expansion w\ld d\ble its size 9 ab\t #cj million million ye>s4 ,! expansion mu/ h be5 f> m rapid 9 ! pa/1 :5 ! />s 7 full ( y\?ful vig\r & squ&]$ _! sub/ance m lavi%ly ?an n[1 s t x seems probable t ! galactic sy/em 0 sub/antially small] & m compact 9 ! pa/ ?an n[1 & ! orig9al nebula probably small] /ill4 ,we h se5 h[ ! />s 9 ! great nebulae appe> to be congregat$ 9 bun*es or clu/]s4 ,! globul> clu/]s 9 ! galactic sy/em may possibly be bun*es ( />s ( ! same g5]al type1 :i* h rema9$ undi/urb$ by o!r gr\ps ( />s & s h assum$ ! globul> =m "u _! own attraction--j z a mass ( gas w\ld d4 ,%apley f9ds t ^! clu/]s lie some:at outside ! galactic plane2 x looks z ?\gh !y 7 brok5 up or disorganis$ 9 travell+ ?r\gh ?is plane1 :]e !y w\ld enc\nt] o!r />s4 ,by contra/ gr\ps ( />s ( ! type g5]ally describ$ z mov+ clu/]s--! ,pleiades1 ! ,hyades1 ! />s ( ! ,great ,be> & a cr[d ( o!rs voyag+ 9 company ) !m ?r\gh space--are g5]ally f\nd to move 9 ! galactic plane4 ,^! may q possibly repres5t ! f9al ve/iges ( globul> clu/]s :i* h be5 brok5 up by int]action ) o!r />s1 all except ! mo/ massive memb]s hav+ be5 knock$ out ( =mation4 ,ma!matical analysis %ews t ! int]action betwe5 ! />s ( su* mov+ clu/]s & o!r />s 9 ! galactic plane w\ld cause ea* clu/] to assume ! %ape ( a flat biscuit or wat*1 ( diamet] equal to #b times its ?ickness4 ,x is significant t ! majority ( ! mov+ clu/]s %ew a flatt5+ ( ?is k9d1 its am\nt agree+ tol]ably well ) ! calculat$ value4 ,x is ev5 conceivable t ! 8local clu/]0 surr\nd+ ! sun 7p4 #fe7 may be ! rema9s ( su* a bun* ( />s4 ,! motions ( ^! clu/]s may also induce a fur!r flatt5+1 9 a direction p]p5dicul> to _! motion4 ,"s clu/]s %ew ?is fur!r flatt5+1 ! ,ursa ,major clu/] be+ a /rik+ example4 ,,! ,,bir? ,,( ,,b9>y ,,sy/ems ,9 discuss+ ! way 9 :i* nebulae might be born out ( *aos1 we notic$ t ! exi/5ce ( curr5ts 9 ! primordial m$ium w\ld end[ ! result+ nebulae ) v>y+ am\nts ( rotation4 ,= ! same reason ! *ildr5 ( ! nebulae1 ! />s1 mu/ also be end[$ ) rotation at _! bir?4 ,!re is a fur!r reason = su* rotation4 ,! g5]al pr9ciple ( ! 8cons]vation ( angul> mom5tum0 requires t rotation1 l en]gy1 _c entirely disappe>4 ,its total am\nt is cons]v$1 s t :5 a nebula breaks up into />s1 ! orig9al rotation ( ! nebula mu/ be cons]v$ 9 ! rotations ( ! />s4 ,?us ! />s1 z soon z !y come into be+1 are end[$ ) rotations transmitt$ to !m by _! p>5t nebula1 9 addition to ! rotations result+ f ! curr5ts set up 9 ! process ( cond5sation4 ,_! cont9ual loss ( weight causes ! physical conditions ( ! />s to *ange1 & we %all f9d 9 ! next *apt] t ?is *ange g5]ally involves a %r9kage ( ! />'s diamet]4 ,! same pr9ciple ( 8cons]vation ( angul> mom5tum0 n[ requires t1 z a /> %r9ks1 its spe$ ( rotation %all increase4 ,9 brief1 z a /> ages1 x sp9s fa/] & fa/]4 ,n[ rotation 0 ! ess5tial factor 9 ! bir? ( ! />s out ( ! p>5t nebula4 ,a nebula p]fectly devoid ( rotation w\ld n1 s f> z we c see1 break up into />s at all1 & ?is pr$iction ( !ory appe>s to be confirm$ by obs]vation1 s9ce nebulae ( ! p]fectly sph]ical type %ewn 9 fig4 #a ( ,plate ,,xvi c nev] be resolv$ into />s 9 ! telescope4 ,on ! o!r h& we saw h[ nebulae :i* 7 initially end[$ ) rotation w\ld cont9ually increase _! spe$ ( rotation "u %r9kage1 until f9ally _! rotation broke !m up & produc$ a family ( />s out ( ea*4 ,! "q n[ obvi\sly arises :e!r1 z ! spe$ ( rotation ( ! />s increases1 ^! are likely to break up 9 _! turn1 & produce yet a ?ird g5]ation ( a/ronomical bodies4 ,aga9 we might expect t ma!matical analysis w\ld apply to l>ge & small bodies equally1 irrespective ( scale4 ,& a detail$ exam9ation ( ! problem %ews t 9 actual fact ! process we h _h "u consid]ation w\ld repeat itself1 & aga9 br+ a fur!r g5]ation ( small] bodies into be+1 provid$ ! physical conditions 7 suitable4 ,! physical conditions1 h[ev]1 prove n to be suitable2 !y c]ta9ly fail 9 "o respect at lea/4 ,al?\gh a rotat+ /> may eject gase\s matt] 9 its equatorial plane1 ! :ole process w be on a mu* small] scale ?an 9 ! nebulae4 ,we might expect ! eject$ matt] to =m cond5sations z be=e1 b calculation %ews t1 unless ! molecul> velocity is extraord9>ily l[1 no cond5sation c survive unless x has a weight great] ?an ! :ole weight ( ! />6 ,?is means t ) any reasonable molecul> velocity1 ! eject$ gas w\ld n =m cond5sations at all4 ,x w\ld m]ely scatt] into ! surr\nd+ space1 =m+ an atmosph]e )\t any di/9ct cond5sations4 ,su* is ! c\rse ( ev5ts if ! />s1 l ! nebulae be=e !m1 are treat$ z pure masses ( gas4 ,ano!r alt]native mu/1 h[ev]1 be consid]$4 ,,! ,,fission ,,( ,,liquid ,,/>s4 ,we h se5 h[ a gase\s nebula devoid ( rotation w\ld assume a /rictly sph]ical %ape "u its own gravitational attraction1 :ile slight rotation w\ld cause x to flatt5 into an orange %ape1 l ! e>?4 ,! e>? also has assum$ ?is %ape on acc\nt ( its rotation1 al?\gh its int]nal /ructure is v diff]5t f t ( a gase\s nebula4 ,/rict ma!matical inve/igation %ews t ?is flatt5$-orange %ape mu/ be common to all sl[ly rotat+ bodies1 reg>dless ( _! int]nal composition2 gases1 liquids1 & pla/ic bodies assume x equally4 ,b ! %ape ( a rapidly rotat+ body mu/ dep5d v greatly on its int]nal arrangem5t & con/itution1 be+ especially affect$ by ! ext5t to :i* ! weight ( ! body is conc5trat$ ne> its c5tre4 ,z a consequ5ce ( ! high compressibility ( gases1 ?is c5tral conc5tration ( weight rea*es its extreme limit 9 a purely gase\s mass4 ,! opposite extreme is rea*$ 9 a mass ( uni=m incompressible liquid su* z wat]1 9 :i* !re c be no c5tral conc5tration at all4 ,z a mass ( ?is latt] type increases its spe$ ( rotation1 ! slightly flatt5$-orange %ape m]ely gives place to ! %ape ( a m flatt5$ orange4 ,! t5d5cy ( a gase\s mass to =m a %>p edge r\nd ! equator is entirely abs5t1 & ! cross-section ( its figure rema9s elliptical ?r\gh\t4 ,at a /ill high] spe$ ( rotation1 ! equator loses its circul> %ape & x too becomes elliptical4 ,! figure has n[ ?ree unequal diamet]s1 b e cross-section is /rictly elliptical2 ! figure is an 8ellipsoid40 ,aft] ?is1 its longe/ diamet] beg9s to elongate until ! mass1 /ill ellipsoidal 9 %ape1 has =m$ a cig>-%ap$ figure ) a l5g? ne>ly ?ree times its %orte/ diamet]4 ,a new s]ies ( ev5ts n[ beg9s4 ,! mass ( liquid gradually conc5trates ab\t two di/9ct po9ts on its longe/ diamet]1 a wai/ or furr[ =m+ across its middle4 ,?is furr[ gets deep] & deep] until x has cut ! body into two di/9ct deta*$ masses1 :i* n[ rotate 9 orbital motion ab\t "o ano!r & =m a b9>y />4 ,! sequ5ce ( ev5ts is %ewn 9 fig4 #aa2 diagrams ( ! f9al /age z repres5t$ by actual b9>y />s h already be5 giv5 on p4 #ed4 ,= comp>ison ! sequ5ce ( %apes assum$ by a rotat+ mass ( gas is %ewn 9 fig4 #ab1 ?is be+ id5tical ) ! sequ5ce ( obs]v$ nebul> %apes :i* is actually obs]v$1 & is illu/rat$ photographically 9 ,plate ,,xvi 7p4 #bjg74 ,! two *a9s ( configurations %ewn 9 figs4 #aa & #ab repres5t1 x w be rememb]$1 ! two extreme cases ( a rotat+ body ^: sub/ance is di/ribut$ ) complete uni=mity1 & ( a rotat+ body ^: sub/ance is v highly cond5s$ t[>ds its c5tre4 ,z ! con/itutions ( actual a/ronomical bodies mu/ lie some:]e betwe5 ^! two extremes1 we might naturally expect su* a body to foll[ a s]ies ( configurations int]m$iate betwe5 ! two %ewn 9 figs4 #aa & #ab4 ,!ory %ews t z a matt] ( fact x does n4 ,all bodies hav+ less ?an a c]ta9 critical degree ( c5tral cond5sation foll[ ! sequ5ce %ewn 9 fig4 #aa1 or a sequ5ce diff]+ only immat]ially f ?is2 all bodies hav+ m ?an ?is critical am\nt ( c5tral cond5sation foll[ ! sequ5ce %ewn 9 fig4 #ab4 ,?us :5 ?is critical degree ( c5tral cond5sation is rea*$ !re is a sudd5 sw+ ov] f fig4 #aa to fig4 #ab4 ,9 brief1 e rotat+ body conducts itself ei!r z if x 7 purely liquid1 or z if x 7 purely gase\s2 !re are no int]m$iate possibilities4 ,illu/ration3 ,fig4 #aa4 ,! sequ5ce ( configurations ( a rotat+ mass ( liquid4 ,illu/ration3 ,fig4 #ab4 ,! sequ5ce ( configurations ( a rotat+ mass ( gas4 ,obs]vational a/ronomy leaves no room = d\bt t a great numb] ( />s1 possibly ev5 all />s1 foll[ ! sequ5ce %ewn 9 fig4 #aa4 ,no o!r me*anism1 s f> z we "k1 is available = ! =mation ( ! num]\s spectroscopic b9>y sy/ems1 9 :i* two con/itu5ts describe small orbits ab\t "o ano!r4 ,9 ^! />s1 !n1 ! c5tral cond5sation ( mass mu/ be bel[ ! critical am\nt j m5tion$2 to ?is ext5t !y behave l liquids r ?an gases4 ,we h reli$ entirely on ma!matical analysis 9 trac+ out ! details ( ! process ( fission j describ$4 ,& we are totally unable to *eck our !oretical results by obs]vation4 ,!re is n a s+le /> 9 ! sky ( :i* we c say3 "h is a /> :i* has c]ta9ly />t$ to break up by fission1 & w c]ta9ly end z a b9>y sy/em4 ,x is p]haps n altoge!r surpris+4 ,! break+ up process is 9 all probability ( v %ort duration by comp>ison ) ! lives ( ! />s1 s t 9 any case we %\ld h to inve/igate a great _m />s be=e cat*+ "o 9 ! act ( break+ into two4 ,on ! o!r h&1 a /> 9 ! act ( break+ up ought to be v easily diff]5tiat$ f ord9>y />s4 ,ma!matical analysis %ews t its int]ior w\ld be 9 a /ate ( consid]able turmoil1 s t x w\ld h>dly be likely to %9e ) a /eady light3 x w\ld be a 8v>iable0 />4 ,fur!r1 its condition ought to %ew a progressive *ange1 al?\gh x is an op5 "q :e!r ?is w\ld be rapid en\gh to be detect$ 9 a few ye>s ( obs]vation4 ,f9ally1 if any gr\p or class ( />s 7 suspect$ ( be+ />s 9 process ( fission1 x ought to be possible to arrange !m 9 an ord] correspond+ to ! ext5t to :i* ! fissional process _h advanc$1 & ! sequ5ce s =m$ ought to end ) />s 9 ! physical condition ( newly =m$ b9>ies4 ,i h rec5tly sugge/$ t ! ,cepheid v>iables1 ^: unkn[n me*anism ( light-v>iation r5d]s su* valuable s]vice to ! a/ronom]1 are m]ely />s 9 ! act ( fission4 ,want ( space prev5ts our ent]+ "h into ! intricate "q ( h[ f> !y exhibit ! peculi>ities :i* ma!matical analysis requires ( />s 9 process ( fission1 b x is easily se5 t !y satisfy ! ?ree simple te/s outl9$ above4 ,!y are c]ta9ly v>iable />s1 & ! light-v>iations ( diff]5t />s are s simil> z to sugge/ v /rongly t !y all arise f ! same cause4 ,! p]iods ( a numb] ( ,cepheids are suspect$ ( *ange1 & ,h]tzsprung has e/imat$ t ! prototype />1 ,cephei1 :i* has n[ be5 obs]v$ = #abf ye>s1 is decreas+ its p]iod ( light-fluctuation at ! rate ( ab\t a t5? ( a second p] annum2 ?us a million ye>s w\ld r$uce its pres5t p]iod ( #e days by ov] a day4 ,f9ally ,dr ,otto ,/ruve has f\nd t ! sequ5ce ( ,cepheids fits almo/ p]fectly on to t ( newly =m$ b9>ies4 ,?us ! prospects = ! 8fission !ory0 ( ,cepheid v>iables seem hopeful1 b ! !ory mu/ be v ?or\ghly te/$ be=e x c be accept$1 & x _c be claim$ t x has be5 s f> ei!r te/$ ?or\ghly or accept$ ext5sively4 ,an alt]native view1 fir/ prop\nd$ by ,plumm] & ,%apley1 reg>ds ,cepheid v>iables z pulsat+ sph]es ( gas4 ,! behavi\r ( su* masses ( gas has be5 inve/igat$ ma!matically by ,edd+ton & o!rs1 b x does n appe> t x c be reconcil$ ) ! obs]v$ behavi\r ( ,cepheid v>iables4 ,,! ,,developm5t ,,( ,,b9>y ,,sy/ems ,:atev] ! process ( =mation ( b9>y sy/ems may be1 we exp]i5ce fairly pla9 sail+ 9 attempt+ to trace out ! subsequ5t developm5t ( su* sy/ems4 ,?ree factors are simultane\sly 9 op]ation4 ,,tidal ,,friction4 ,! fir/ ( ^! ?ree factors1 :i* is only ( brief duration1 0 designat$ 8tidal friction0 by ,sir ,george ,d>w91 :o fir/ drew att5tion to x1 & inve/igat$ ! mann] ( its op]ation4 ,:5 fir/ a rotat+ mass breaks up & =ms a b9>y sy/em1 ! two compon5ts are s ne> t !y necess>ily raise trem5d\s tides on "o ano!r2 ,d>w9 %ew$ t ^! drive ! two bodies ap>t1 & equalise _! rates ( rotation 9 s do+4 ,aft] ^! processes h be5 9 op]ation = millions ( ye>s1 ! rates ( rotation ( ! two bodies & _! rate ( revolution ab\t "o ano!r mu/ all become equal1 s t ea* body p]petually turns ! same face to its companion1 & ! two rotate ab\t "o ano!r l ! two masses ( a dumb-bell jo9$ by an invisible arm4 ,al?\gh a sun & planet d n =m a b9>y sy/em 9 ! /rict te*nical s5se1 !y are necess>ily subject to ! same =ces z true b9>y sy/ems4 ,?us we c see ! op]ation ( tidal friction 9 ! fact t ,m]cury always turns ! same face to ! sun1 & t ,v5us rotates s sl[ly on its axis t x turns ! same face to ! sun day aft] day1 & probably also week aft] week4 ,z we pass fur!r out into space ! effects ( tidal friction rapidly dim9i%1 b x is probably significant t ! ne>] planets1 ,e>? & ,m>s1 h days ( ab\t #bd h\rs ea*1 :ile ! remote planets ,jupit]1 ,saturn & ,uranus ea* h days ( only ab\t #aj h\rs4 ,! p]iods ( rotation ( ,neptune & ,pluto are unkn[n4 ,ap>t f ^! we f9d1 9 a g5]al way1 t ! fur!r we rec$e f ! sun ! m rapidly ! planets rotate1 :i* is precisely ! effect t ought to be produc$ by tidal friction4 ,9 ! same way1 tidal friction has 9 all probability be5 ma9ly responsible = ! pres5t configuration ( ! e>?-moon sy/em1 driv+ ! moon away to its pres5t di/ance f ! e>? & caus+ x always to turn ! same face t[>ds u4 ,tidal friction mu/ ( c\rse /ill be 9 op]ation4 ,! moon is responsible = ! great] "p ( ! tides rais$ 9 ! oceans ( ! e>?2 ^!1 ex]t+ a pull on ! solid e>? und]nea?1 sl[ d[n its spe$ ( rotation1 ) ! result t ! day is cont9ually l5g!n+1 & w cont9ue to d s until ! e>? & moon are rotat+ & revolv+ 9 complete unison4 ,:51 if ev]1 t "t arrives1 ! e>? w cont9ually turn ! same face to ! moon1 s t ! inhabitants ( "o ( ! hemisph]es ( ! e>? w nev] see ! moon at all1 :ile ! o!r side w be light$ by x e night4 ,by ?is "t ! l5g? ( ! day & ! mon? w be id5tical1 ea* be+ equal to ab\t #dg ( our pres5t days4 ,jeffreys has calculat$ t ?is /ate ( ?+s is likely to be atta9$ aft] ab\t #ej1jjj million ye>s4 ,aft] ?is1 tidal friction w no long] op]ate 9 ! s5se ( driv+ ! moon fur!r away f ! e>?4 ,! jo9t effect ( sol> & lun> tides w be to sl[ d[n ! e>?'s rotation /ill fur!r1 ! moon at ! same "t gradually less5+ its di/ance f ! e>?4 ,:5 x has f9ally1 aft] un?9kable ages1 be5 dragg$ d[n to )9 ab\t #ab1jjj miles ( ! e>?1 ! tides rais$ by ! e>? 9 ! solid body ( ! moon w %att] ! latt] into fragm5ts 7p4 #bej bel[71 :i* w =m a sy/em ( t9y satellites revolv+ ar\nd ! e>? 9 ! same way z ! p>ticles ( ,saturn's r+s revolve ar\nd ,saturn1 or z ! a/]oids revolve ar\nd ! sun4 ,we h already notic$ h[ ! pres5t arrangem5t ( ! e>?-moon sy/em enables u to calculate ! e>?'s age2 ,jeffreys e/imates t ! sy/em mu/ h tak5 some?+ ( ! ord] ( #djjj million ye>s to rea* its pres5t configuration 7p4 #aee74 ,?is p]iod1 :i* seems s long :5 judg$ by t]re/rial /&>ds1 is only a mom5t 9 ! life ( a />4 ,! compon5ts ( ! true b9>y /> atta9 a configuration l t ( ! e>?-moon sy/em 9 a brief fraction ( _! lives1 &1 pass+ on1 rea* 9 "t ! configuration 9 :i* ea* p]petually turns ! same face to ! o!r4 ,up to n[1 tidal friction has be5 driv+ ! masses ev] fur!r ap>t1 b z soon z ?is /age is atta9$1 ! tides become /ation>y on bo? compon5ts1 s t tidal friction goes out ( op]ation4 ,?us ! sep>ation produc$ by tidal friction has n[ rea*$ its limit1 &1 s f> z tidal friction is conc]n$1 ! two bodies might rotate 9 ! way j describ$ to all et]nity4 ,,loss ,,( ,,weight4 ,z tidal friction becomes inop]ative1 a new ag5cy takes hold4 ,we h calculat$ t ! sun is los+ weight at ! rate ( #bej million tons a m9ute1 t x has be5 los+ weight at ?is rate1 or "s comp>able rate1 = millions ( millions ( ye>s1 & w cont9ue s to d = millions ( millions ( ye>s yet to come4 ,! e>? is at its pres5t di/ance f ! sun because ?is di/ance is exactly suit$ to ! pres5t weight ( ! sun4 ,if ! sun's weight 7 sudd5ly r$uc$ to half1 its gravitational pull on ! e>? w\ld also be r$uc$ to half1 & ! e>? w\ld move to a great] di/ance f ! sun#bb4 #bb ,al?\gh ! details are unimportant1 ! actual c\rse ( ev5ts w\ld be t ! e>? w\ld beg9 to describe an elliptic in/ead ( a circul> orbit ab\t ! sun1 ! e>?'s av]age di/ance be+ great] ?an n[4 ,! sun's weight is n likely to be sudd5ly r$uc$ to half1 b x has be5 r$uc$ by a ?\s& million tons 9 ! la/ f\r m9utes1 ) ! result t its gravitational grip on ! e>? has be5 weak5$ & ! e>? has mov$ out to a wid] orbit2 at ?is mom5t ! radius ( ! e>?'s orbit is great] ?an x 0 f\r m9utes ago4 ,! details c be trac$ out ma!matically ) complete precision4 ,x appe>s t ! e>?'s orbit r\nd ! sun is n a circle1 or ev5 an ellipse ( small ecc5tricity2 x is a spiral curve1 l an uncoil$ wat* spr+4 ,e ye> ! e>? moves a t9y /ep fur!r out into ! out] cold & d>kness2 exact calculation %ews t its av]age di/ance f ! sun increases at ! rate ( ab\t a metre 7#cicg in*es7 a c5tury4 ,! effect is ( c\rse ( precisely ! same k9d z we h se5 mu/ be produc$ 9 ! galactic sy/em by ! loss ( weight ( ! />s4 ,! only diff]5ce is t 9 ! galaxy a sy/em ( ?\s&s ( millions ( />s is exp&+1 :]eas ! sun-e>? sy/em consi/s ( only two memb]s4 ,precisely simil> effects mu/ be produc$ by ! loss ( weight 9 ! two compon5ts ( a b9>y />4 ,"h bo? compon5ts are radiat+ away en]gy1 & s are simultane\sly los+ weight4 ,detail$ calculation %ews t !y mu/ cont9ually rec$e f "o ano!r1 b t ! %ape ( _! orbit w und]go no *ange4 ,nei!r sep>ately nor 9 comb9ation d ! two effects j describ$ expla9 ei!r ! %apes or ! sizes ( ! obs]v$ orbits ( b9>y />s z a :ole4 ,to int]pret ^! we mu/ call on yet a ?ird ag5cy1 ! gravitational =ces f pass+ />s4 ,we h already se5 h[ ^! acc\nt = ! /ati/ical di/ribution ( orbits :i* is actually obs]v$4 ,! comb9ation ( all ?ree ag5cies1 tidal friction1 ext5d+ ov] millions ( ye>s1 loss ( weight1 ext5d+ ov] millions ( millions ( ye>s1 & di/urbance f pass+ />s1 ext5d+ ov] a simil> p]iod1 is responsible = ! evolution ( b9>y /> sy/ems4 ,_! aggregate effect is to wid5 ! di/ance betwe5 ! two />s1 :ile at ! same "t knock+ ! orbit out ( %ape4 ,,subdivision4 ,:ile ^! *anges are go+ on 9 ! orbital arrangem5t ( a b9>y sy/em1 ! two compon5ts are !mselves *ang+ _! physical condition on acc\nt ( _! cont9ual loss ( weight1 &1 z ) ! p>5t />s1 ?is loss ( weight w g5]ally result 9 a %r9kage 9 ! size ( ! />4 ,! %r9kage ( ei!r compon5t ( ! sy/em causes its %ape to run ?r\gh ! sequ5ce ( configurations we h already enum]at$1 & if ! %r9kage cont9ues = long en\gh1 ! compon5t may end by fur!r divid+ into two sep>ate masses4 ,ei!r or bo? ( ! con/itu5ts ( a b9>y sy/em may subdivide into b9>y sub-sy/ems 9 ?is way1 result+ 9 a sy/em ( ei!r ?ree or f\r />s4 ,h4 ,n4 ,russell has %ewn ma!matically t :5 a b9>y sy/em ,p1 ,q divides into a triple sy/em1 ,p1 q1 q1 ?r\gh ,q break+ up into two con/itu5ts q1 q1 ! di/ance betwe5 q & q _c be m ?an ab\t a fif? ( ! orig9al di/ance ,,pq4 ,?is !oretical law is well confirm$ by obs]vation4 ,fig4 #ac %ews a typical multiple sy/em1 & we notice t ! sep>ations 9 ea* ( ! v>i\s sub-sy/ems are all q small 9 comp>ison ) ^? ( ! ma9 sy/ems4 ,illu/ration3 ,fig4 #ac4 ,a typical multiple />4 ,! developm5t ( ! hypo!tical primitive *aos has n[ be5 trac$ ?r\gh five g5]ations ( a/ronomical bodies1 *aos--nebulae--/>s--b9>y sy/ems--sub-sy/ems1 to :i* a six? g5]ation mu/ be add$ if ! />s ( ! sub-sy/em happ5 to fission fur!r1 z1 = in/ance1 !y h done 9 ! /> %ewn 9 fig4 #ac4 ,! g5ealogy ( ! />s beg9s ) a va/ t5u\s nebula fill+ all space2 ! la/ g5]ation consi/s ( small1 %runk51 dy+ />s ) no capacity = fur!r subdivision4 ,! g5ealogy has be5 trac$ out prim>ily on !oretical gr\nds alone1 b we ne$ h no d\bts z to its g5]al accuracy1 s9ce obs]vation confirms x repeat$ly & at almo/ e /ep4 ,inde$ x is h>dly too mu* to say t ! evolution>y sequ5ce c\ld h be5 discov]$ almo/ equally well f obs]vational evid5ce alone1 except = ! hypo!tical primaeval *aos1 ab\t :i*1 f ! nature ( ! case1 obs]vation _c h any?+ to say4 ,,! ,,orig9 ,,( ,,! ,,sol> ,,sy/em ,almo/ all obs]v$ a/ronomical =mations c be plac$ 9 ! evolution>y sequ5ce we h j discuss$1 ei!r ) fair c]ta9ty or ) reasonable plausibility1 except = "o out/&+ & conspicu\s exception--! ,sol> ,sy/em4 ,cosmogony came into be+ z an attempt to discov] ! orig9 ( ! sol> sy/em4 ,! reasons :y x limit$ its ef=ts to ?is p>ticul> problem are *ronological2 9 ! e>ly days ( cosmogony1 a/ronomy 0 b>ely consci\s ( any?+ outside ! sol> sy/em4 ,! sket* j giv5 ( ! f9d+s ( mod]n sci5tific cosmogony has be5 rem>kable 9 t x has exhibit$ cosmogony tak+ u a t\r r\nd ! :ole univ]se1 expla9+ ! orig9 & life-hi/ory ( practically e object we enc\nt] on ?is t\r1 & !n becom+ spee*less :5 x is br\ght back home & confront$ ) its bir?place1 ! sol> sy/em4 ,,laplace',s ,,nebul> ,,hypo!sis4 ,! fir/ s]i\s sci5tific cosmogony 0 t embodi$ 9 ! fam\s ,nebul> ,hypo!sis ( ,laplace4 ,9 #agee ,kant _h pictur$ a primaeval *aos cond5s+ into sp9n+ nebulae1 &1 id5tify+ "o ( ^! nebulae ) ! sun1 _h imag9$ ! planets to be =m$ by ! solidification ( masses ( gas %$ f ! nebula1 mu* 9 ! way 9 :i* we h suppos$ ! />s to be born4 ,9 #agif1 ,laplace advanc$ simil> ideas1 :i* he develop$ 9 detail ) a ma!matical precision q beyond ! capacities ( ,kant4 ,he %ew$ h[1 z its %r9kage made x sp9 ev] fa/] & fa/]1 a rotat+ mass ( gas w\ld flatt5 out1 develop ! l5ticul> =m we h already discuss$ 7fig4 #c ( ,plate ,,xvi71 & !n proce$ to eject matt] 9 its equatorial plane1 or r to leave x beh9d z ! %r9kage ( ! ma9 mass cont9u$4 ,at ?is /age x w\ld look some:at l ! nebulae %ewn 9 figs4 #d & #e ( ,plate ,,xvi1 al?\gh ,laplace1 be+ unacqua9t$ ) nebulae ( ?is type1 adduc$ ,saturn surr\nd$ by its r+s z an example ( ! =mation to be expect$ at ?is /age 7,plate ,,xxiv1 p4 #bej74 ,laplace imag9$ t ! fr+e ( ab&on$ gas w\ld !n cond5se & =m a s+le planet4 ,z ! ma9 mass %runk fur!r1 m gas 0 ab&on$ 9 ! equatorial plane1 :i* 9 due c\rse cond5s$ into ano!r planet1 & s on1 until ! sun left (f %r9k+ & no m planets 7 born4 ,a repetition ( ! same process1 b on a f> small] scale1 result$ 9 ! satellites be+ born out ( ! planets4 ,t ! hypo!sis is prima facie plausible1 is evid5t f its hav+ surviv$1 & inde$ be5 g5]ally accept$1 = ne>ly a c5tury be=e x enc\nt]$ any s]i\s opposition4 ,rec5tly criticisms h accumulat$1 ( s vital a nature z to make x cle> t ! hypo!sis mu/ be ab&on$4 ,! sun1 accord+ to ,laplace1 broke up & gave bir? to planets ?r\gh excess ( rotation4 ,yet bo? !ory & obs]vation indicate q cle>ly ! fate 9 /ore = a /> :i* rotates too fa/ = safety2 x does n f\nd a family1 b m]ely bur/s1 l an ov]driv5 fly-:eel1 into p>ts ( ne>ly equal size4 ,spectroscopic b9>y & multiple sy/ems are ! relics ( />s :i* h brok5 up ?r\gh excess ( rotation1 & !y d n 9 ! lea/ resemble ! sol> sy/em4 ,aga91 ! pr9ciple ( 8cons]vation ( angul> mom5tum0 requires t ! rotation ( ! primaeval sun %all p]si/ 9 ! rotation ( ! pres5t sun1 & 9 ! revolutions ( ! planets ar\nd x4 ,on add+ toge!r ! contributions f all ( ^!1 we obta9 a total :i* ought to repres5t ! angul> mom5tum ( ! primaeval sun4 ,9 /rictness a fur!r contribution ought to be add$ on acc\nt ( ! weight ( all ! radiation :i* ! sun has emitt$ s9ce ! planets 7 born4 ,we c calculate ! am\nt ( ?is contribution1 because we "k ! age ( ! e>? ) tol]able accuracy1 b x proves to be entirely negligible4 ,! total angul> mom5tum ( ! primaeval sun c be calculat$ ) v fair accuracy1 because m ?an #ie p] c5t4 ( ! total angul> mom5tum ( ! pres5t sol> sy/em resides 9 ! orbital motion ( ,jupit]4 ,?is contribution c be calculat$ ) great exactness1 s t "s unc]ta9ty 9 ! m9or contributions :i* make up ! rema9+ #e p] c5t4 c h b little influ5ce on ! total4 ,:5 ?is total is calculat$ ! />tl+ fact em]ges t ! primaeval sun _c h _h en\gh rotation to cause break-up at all4 ,cle>ly ! sun is v f> f be+ brok5 up by its pres5t rotation4 ,flatt5+ ( figure is ! fir/ /ep t[>ds break-up1 & ! sun's figure is s little flatt5$ by its pres5t rotation t ! mo/ ref9$ measurem5ts h s f> fail$ to detect any flatt5+ at all4 ,on add+ ! fur!r angul> mom5tum n[ repres5t$ 9 ! motions ( ,jupit] & all ! o!r memb]s ( ! sol> sy/em1 we arrive at a primaeval sun rotat+ ab\t z fa/ z ,jupit] n[ rotates1 & %ew+ ab\t ! same degree ( flatt5+ ( figure z ,jupit]--en\gh to measure q easily 9 a telescope1 or ev5 to detect ) ! eye alone1 b no?+ l en\gh to cause break-up4 ,! sun is h>dly likely to h alt]$ mu* s9ce its planets 7 born1 = ! int]v5+ #bjjj million ye>s or s repres5t b a m9ute fraction ( ! sun's total life4 ,if1 h[ev]1 we imag9e x to h %runk appreciably 9 ! int]val1 !n ! available am\nt ( angul> mom5tum w\ld h be5 ev5 m unable to break up ! l>ge primaeval sun ?an x is to break up ! pres5t %runk5 sun4 ,:i*ev] way we look at x1 we rea* ! conclusion t ! sun _c h brok5 up1 z ,laplace imag9$1 ?r\gh excess ( rotation2 inde$ x c nev] h possess$ m ?an a q t9y fraction ( ! am\nt ( rotation ne$$ to break x up4 ,a ?ird objection is ( a some:at diff]5t "*4 ,laplace 0 a v great ma!matician1 & !re 0 no?+ ! matt] ) 8 ab/ract ma!matical !ory1 s f> z x w5t4 ,m ref9$ mod]n analysis has confirm$ x at e /ep1 & obs]vation does ! same1 z photographs ( rotat+ nebulae 7,plate ,,xvi7 be> witness4 ,^! photographs exhibit a process tak+ place be=e our eyes1 :i* is ess5tially id5tical ) t imag9$ by ,laplace1 except = a colossal diff]5ce ( scale4 ,ev]y?+ happ5s qualitatively z ,laplace imag9$1 b on a scale incomp>ably gr&] ?an he ev] dream$ (4 ,9 ^! photographs ! primitive nebula is n a s+le sun 9 ! mak+1 b conta9s sub/ance suffici5t to =m hundr$s ( millions ( suns2 ! cond5sations d n =m puny planets ( ! size ( our e>?1 b are !mselves suns2 !y are n eight or s 9 numb]1 b mu/ be c\nt$ 9 millions4 ,we may ask :y ! same ?+ _c happ5 on ! small] scale imag9$ by ,laplace--= are n ! conclusions ( ma!matics applicable indep5d5tly ( ! size ( ! body ) :i* we are deal+8 ,! answ] has 9 effect be5 giv5 already 7p4 #bah74 ,ev]y?+ happ5s on ! small] scale accord+ to plan until we come to ! =mation ( ! cond5sations2 "h ! "q ( scale proves to be vital4 ,we h se5 7p4 #aif7 h[ ! molecules :i* =m ! sun h cond5s$ into a /> because ( _! great numb]2 ! molecules 9 a room d n cond5se into any?+ at all because !y are too few4 ,9 ! same way1 ! molecules left beh9d by ! sl[ %r9kage ( a sun 7assum+ ?is = ! mom5t to rotate rapidly en\gh to leave molecules beh9d7 w\ld n cond5se1 because at any in/ant !re w\ld be too few ( !m available = cond5sation4 ,!y w\ld be %$ by driblets1 & a driblet ( gas does n cond5se b scatt]s into space4 ,a ma!matical calculation decides ! "q def9itely1 & ! decision is entirely adv]se to ! hypo!sis ( ,laplace4 ,ap>t f m9or details1 ! process imag9$ by ,laplace expla9s ! bir? ( suns out ( nebulae2 x _c expla9 ! bir? ( planets out ( suns4 ,,second ,,body ,,!ories4 ,laplace imag9$ 8 sun to be alone 9 space1 ev5 its ne>e/ neighb\rs be+ too remote to influ5ce x 9 any way4 ,x 0 ! natural supposition to make2 we h already rem>k$ h[ exce$+ly r>e an ev5t x mu/ be = two />s to approa* ne> en\gh to influ5ce "o ano!r4 ,yet no possible mode ( evolution ( a /> :i* rema9s alone 9 space seems able to expla9 ! orig9 ( ! sol> sy/em4 ,z f> back z #agej1 ,buffon _h sugge/$ t ! sol> sy/em might h be5 produc$ ?r\gh ! disruption ( ! sun by ano!r body1 :i* he describ$ z a 8comet40 ,9 prop\nd+ 8 ,nebul> ,hypo!sis1 ,laplace m5tion$ ,buffon's idea1 b dismiss$ x some:at curtly on ! gr\nds t x seem$ unable to acc\nt = ! ne>ly circul> orbits ( ! planets--an ill-f\nd$ objection1 z we %all soon see4 ,yet :5 we f9d t a s+le /> _c ( itself give bir? to a sol> sy/em1 x becomes natural to inve/igate :at happ5s on ! r>e occasions on :i* ! evolution ( a /> is direct$ along o!r pa?s by ! ne> approa* ( a second />4 ,9 #ahhj1 ,bick]ton ( ,new ,zeal&1 reviv+ ,buffon's idea1 suppos$ t ! sol> sy/em _h be5 =m$ by ! collision ( ! sun ) ano!r />4 ,he imag9$ ! dbris ( ! collision to =m a ?ird nebul\s body1 cond5sations 9 :i* =m$ ! planets4 ,he %ew$ h[ ! resi/ance :i* ! planets w\ld enc\nt] z !y mov$ ?r\gh ! surr\nd+ nebula w\ld gradually make _! orbits m circul>1 & s acc\nt = _! pres5t ne>ly circul> %apes4 ,t5 ye>s e>li]1 ! ,engli% writ]1 ,r4 ,a4 ,proctor1 _h advanc$ simil> ideas1 al?\gh ) less precision4 ,9 #aije ,pr(essors ,*amb]l9 & ,m\lton ( ,*icago advanc$ a modification ( ! same ideas1 "u ! "n ( ! 8,planetesimal ,hypo!sis40 ,disc>d+ ! idea ( mat]ial collision1 !y suppos$ t a pass+ /> ex]t$ a p[]ful tidal pull on ! sun1 ) ! result t ! ord9>y sol> prom95ces tempor>ily atta9$ an extraord9>y viol5ce2 ! eject$ matt] 0 suppos$ to rise to unusual heights & cond5se into small solid bodies1 ! 8planetesimals10 out ( ! aggregation ( :i* ! planets 7 ultimately =m$4 ,^! v>i\s !ories 7 all purely speculative4 ,!y h %ewn v little capacity ei!r = surviv+ ! acid te/ ( ma!matical analysis1 or = expla9+ ! m sali5t features ( ! sol> sy/em2 none ( !m1 = in/ance1 expla9s :y ! l>g] planets 9 ! sol> sy/em are accompani$ by families ( satellites4 ,?ree ye>s be=e ,*amb]l9 & ,m\lton advanc$ _! planetesimal !ory1 ,i _h speculat$ z to ! possibility ( tidal =ces break+ up a />1 & g5]at+ a sol> sy/em4 ,9 #aiaf1 ,i inve/igat$ ma!matically :at w\ld actually happ5 :5 "o /> rais$ viol5t tidal =ces on ano!r4 ,! results ,i obta9$ seem$ to me to demoli% ! planetesimal !ory ( ,*amb]l9 & ,m\lton1 & l$ me to put =w>d ! pres5t-day 8,tidal ,!ory10 :i* ,i believe a l>ge proportion ( a/ronom]s n[ accept z giv+ ! mo/ probable orig9 ( ! sol> sy/em2 x c ( c\rse make no claim to f9ality or c]ta9ty4 ,,tidal ,,!ory4 ,:5 two />s or o!r bodies pass close to "o ano!r )\t collision1 ! prim>y effect mu/ be t ea* raises tides 9 ! o!r4 ,! clos] ! approa*1 ! high] ! tides 9 g5]al1 al?\gh some?+ mu/ dep5d also on ! spe$ ) :i* ! bodies pass "o ano!r1 because ?is det]m9es ! l5g? ( "t dur+ :i* !y influ5ce "o ano!r4 ,x is likely t ! two spiral arms :i* give _! "n & *>act]i/ic appe>ance to ! spiral nebulae may owe _! inception to a some:at simil> tidal action4 ,conditions "h are diff]5t 9 t ! rotation ( ! nebulae 9 any case causes !m to emit matt] 9 _! equatorial planes1 s t ev5 small tidal =ces %\ld !n cause ?is matt] to conc5trate 9 two symmetrical arms4 ,"u /ell> conditions a f> clos] approa* is necess>y to draw matt] out f ! />1 & x is !n mo/ likely t !re w be two unequal & dissimil> arms1 or possibly only "o arm4 ,illu/ration3 ,,plate ,,xxii ,mt ,wilson ,obs]vatory ,two ,nebulae 7,n4,g4,c4 #dcie1 #ddja7 sugge/ive ( ,tidal ,action ,illu/ration3 ,,plate ,,xxiii ,! tw9 ,nebulae ,n4,g4,c4 #defg-h ,illu/ration3 ,mt ,wilson ,obs]vatory ,! ,nebula ,n4,g4,c4 #gdgi ,if ! approa* is v close inde$1 ! tides may assume an entirely diff]5t aspect f ! feeble tides :i* ! sun & moon raise 9 our oceans2 !y may take ! exagg]at$ =ms ( high m\nta9s ( matt] mov+ ov] ! surface ( ! />4 ,an ev5 clos] approa* may trans=m ^! m\nta9s into long arms ( gas drawn out f ! body ( ! />4 ,if1 z w g5]ally be ! case1 ! two />s are ( unequal weights1 ! less] w 9 g5]al suff] m di/urbance ?an ! weighti]4 ,,! ,,bir? ,,( ,,planets4 ,! long arm or filam5t ( matt] drawn out ( a /> by tidal action is at fir/ cont9u\s 9 its /ructure1 b analysis %ews t x provides a fit subject = ! op]ation ( :at we h call$ 8,gravitational ,in/ability40 ,cond5sations beg9 to =m 9 ?is long arm ( gas1 9 ! way already describ$4 ,z be=e1 ! small] cond5sations are dissipat$1 :ile ! l>g] increase 9 int5sity until f9ally ! filam5t breaks up into a numb] ( deta*$ masses--planets h be5 born out ( ! small] />4 ,! pairs ( nebulae %ewn 9 ,plate ,,xxii & ! upp] half ( ,plate ,,xxiii are v probably "u "o ano!r's tidal influ5ce1 & may s]ve to sugge/ ! g5]al nature ( ! process we are n[ consid]+1 al?\gh x mu/ be rememb]$ t :atev] is happ5+ "h is on an enorm\sly great] scale ?an t ( ! sol> sy/em--if x 7 n1 ! telescope w\ld be utt]ly unable to %ew x to u4 ,:5 ! new-born planets fir/ beg9 to move z sep>ate & indep5d5t bodies1 !y are act$ on by ! gravitational pulls ( bo? />s1 & s describe highly complicat$ orbits4 ,gradually ! bigg] /> rec$es until its gravitational effect becomes negligible1 & ! planets are left describ+ orbits ar\nd ! small] /> alone4 ,if ! planets mov$ 9 a cle> field ( empty space1 ^! orbits w\ld be exact ellipses4 ,b ! great cataclysm :i* has j occurr$ mu/ h left all sorts ( dbris beh9d4 ,comets1 meteors & o!r m9or bodies :i* /ill survive 9 ! sol> sy/em may repres5t a small "p ( x1 b probably ! ma9 "p 0 left 9 ! =m ( du/ or gas1 s t ! new-born planets _h at fir/ to pl\gh _! way ?r\gh a m$ium :i* (f]$ "s resi/ance to _! motions4 ,"u ^! circum/ances _! orbits w\ld n be /rict ellipses4 ,x c be prov$ t a resi/ance ( ! k9d j describ$ w\ld *ange ! %ape ( ! orbits1 & t ) ! progress ( "t !y w\ld become m circul>1 f9ally becom+ absolutely circul> if ! m$ium %\ld la/ long en\gh4 ,! dbris ( gas & du/ w\ld1 h[ev]1 cont9ually be swept up by ! planets & w\ld disappe> completely 9 "t1 probably leav+ ! planet>y orbits some?+ %ort ( absolute circles4 ,assum+ t all ?is has happ5$ 9 ! sol> sy/em1 v little ( ! orig9al dbris c n[ rema91 its la/ ve/iges be+ probably repres5t$ by ! p>ticles ( du/ :i* are responsible = ! zodiacal light4 ,nev]!less1 ! resi/+ m$ium appe>s to h exi/$ = long en\gh to make ! orbits1 bo? ( ! planets & ( _! satellites1 v ne>ly circul> = ! mo/ "p4 ,! exceptional cases are fully z significant z ! cases ( con=mity4 ,comp>atively elongat$ orbits /ill exi/ 9 j ^? regions :]e we %\ld expect ! primaeval resi/+ m$ium to h be5 mo/ sp>sely spread 9 space1 namely on ! out]mo/ conf9es ( ! sol> sy/em & ( ! v>i\s satellite sy/em4 ,pluto1 ! out]mo/ planet ( all1 has a m elongat$ orbit ?an any o!r planet4 ,aga91 9 ! sy/ems ( ,jupit] & ,saturn1 ! satellites ) ! mo/ elongat$ orbits are ^? :i* are fur!/ away f _! prim>ies4 ,9 addition to ?is1 a g5]al t5d5cy may be disc]n$ = elongat$ orbits to be associat$ ) small weights1 bo? 9 planets & _! satellites4 ,m]cury1 ) a weight ( only a tw5ty-fif? t ( ! e>?1 has a q elongat$ orbit1 z also to a less degree has ,m>s ) a n9? ( ! weight ( ! e>?4 ,an explanation ( ?is has be5 sugge/$ by ,jeffreys4 ,massive planets su* z ,jupit] & ,saturn mu/ h collect$ a l>ge mass ( ! resi/+ m$ium r\nd !m1 & c>ri$ x ?r\gh space ) !m z a f>-rea*+ envelope4 ,! massive planets w\ld h _! motion *eck$ by ! int]action ( ! :ole ( ?is big envelope ) ! rema9d] ( ! m$ium1 & s w\ld atta9 circul> orbits m rapidly ?an ! light] planets :i* _h accumulat$ envelopes ( v mu* small] dim5sions4 ,& ! same1 ) ! appropriate modifications1 is true ( ! satellite sy/ems4 ,jeffreys has calculat$ ! rate at :i* planet>y orbits w\ld *ange _! %ape "u ! action ( ?is resi/+ m$ium4 ,! data ( ! problem are necess>ily unc]ta91 & ?is unc]ta9ty naturally affects 8 conclusions1 b 8 /udy has yield$ a valuable confirmation ( o!r e/imates ( ! l5g? ( "t :i* has elaps$ s9ce ! planets 7 born4 ,we may next turn our att5tion to ! physical *anges :i* mu/ all ?is "t be affect+ ! v>i\s planets4 ,! long filam5t ( matt] pull$ out ( ! sun is likely to h be5 ri*e/ 9 matt] 9 its middle p>ts1 ^! p>ts hav+ be5 pull$ out :5 ! second /> 0 ne>e/ & its gravitational pull 0 /ronge/4 ,diagrammatically at lea/1 we may ?9k ( ?is filam5t z %ap$ l a cig>--?ick ne> ! middle1 ?9 at ! ends--s t :5 cond5sations beg9 to =m1 ^? ne> ! middle are likely to be ri*] 9 matt] ?an ^? at ! ends4 ,?is probably expla9s :y ! two mo/ massive planets1 ,jupit] & ,saturn1 occupy ! middle positions 9 ! sequ5ce ( planets4 ,illu/ration3 ,fig4 #ad4 ,diagrammatic s*eme %ew+ ! bir? ( planets out ( a cig>-%ap$ filam5t ( gas4 ,! numb] ( satellites is indicat$ "u ea* planet 7see p4 #bdc74 ,fig4 #ad %ews ! planets arrang$ 9 ! ord] ( _! di/ances f ! sun1 ) _! sizes drawn r\ghly to scale4 ,! ?\s&s ( a/]oids ^: orbits n[ fill ! space betwe5 ! orbits ( ,m>s & ,jupit] are repres5t$ z a s+le planet1 x be+ g5]ally suppos$ t ^! a/]oids 7 =m$ by ! break-up ( :at 0 orig9ally a s+le planet 9 a way we %all %ortly describe4 ,if we surr\nd ! planets by a cont9u\s outl9e1 z 9 ! diagram1 we c recon/ruct 9 imag9ation ! cig>-%ap$ filam5t out ( :i* !y 7 produc$1 & we see at once h[ ! bigge/ planets 7 produc$ :]e matt] 0 mo/ abundant4 ,! tidal !ory :i* pr$icts all ^! features _h be5 prop\nd$1 & its consequ5ces work$ out1 _m ye>s be=e ! new planet ,pluto _h be5 discov]$4 ,valuable support = ! !ory may ?us be f\nd 9 ! circum/ance t ,pluto behaves 9 e way accord+ to ! requirem5ts ( ! tidal !ory4 ,,! ,,bir? ,,( ,,satellites4 ,we h already notic$ h[ ! great disp>ity ( weight betwe5 ! sun & planets di/+ui%es ! sun-planet =mation f t ( ! normal b9>y />1 & s sugge/s entirely diff]5t orig9s = ! two =mations4 ,exactly ! same disp>ity repeats itself 9 ! planet-satellite sy/ems4 ,j z ! p>5t sun is enorm\sly m massive ?an its *ildr5 ! planets1 s ^! 9 turn are f> m massive ?an _! satellite *ildr54 ,! sun has #ajdg times ! weight ( its mo/ massive planet & _m millions ( times ! weight ( ! smalle/4 ,9 ! sy/em ( ,saturn ! correspond+ figures are #daej & ab\t #af1jjj1jjj4 ,! ne>e/ approa* to equality ( weights is provid$ by ! e>?-moon sy/em1 ! e>? hav+ only #ha times ! weight ( ! moon4 ,&1 l ! planet>y sy/em ( ! sun1 ! satellite sy/ems ( ,saturn &1 to a less] degree1 ( ,jupit] %ew a g5]al t5d5cy = ! weights ( ! v>i\s satellites to increase up to a maximum z we pass outw>ds f ! planet1 & !n to decrease aga94 ,?is aga9 sugge/s =mation out ( a cig>-%ap$ filam5t ) matt] occurr+ mo/ ri*ly ne> ! middle4 ,9 conjunction ) ! repetition ( ! great disp>ity ( weights betwe5 prim>y & second>ies1 ?is indicates v =cibly t ! satellites ( ! planets mu/ h be5 born by ! same type ( process z _h previ\sly result$ 9 ! bir? ( _! p>5ts4 ,we c imag9e ! process 9 a g5]al way4 ,imm$iately aft] _! bir?1 ! planets mu/ beg9 to cool d[n4 ,! l>ge/ planets1 ,jupit] & ,saturn1 naturally cool mo/ sl[ly & ! smalle/ mo/ rapidly4 ,! latt] may lose heat s spe$ily t !y liquefy1 & p]haps ev5 solidify1 almo/ imm$iately aft] _! bir?4 ,:ile ^! ev5ts are 9 progress1 ! planets are /ill pursu+ some:at erratic orbits1 9 describ+ :i* !y may pass s ne> to ! sun t a second s]ies ( tidal disruptions occurs4 ,9 ^! ! sun itself plays ! rle orig9ally play$ by ! pass+ /> f space1 ! planets play+ ! "p orig9ally tak5 by ! sun4 ,! sun may n[ te> long filam5ts ( matt] out ( ! surfaces ( ! planets1 & ^!1 =m+ cond5sations1 may give bir? to yet ano!r g5]ation ( a/ronomical bodies1 ! satellites ( ! planets4 ,9 "s su* way ! tidal !ory imag9es ! planet>y satellites to h come into be+4 ,ma!matical inve/igation %ews t ! m liquid a planet 0 at bir?1 ! less likely x w\ld be to be brok5 up by ! /ill gase\s sun4 ,if1 h[ev]1 su* a break-up occurr$1 ! weights ( prim>y & satellites w\ld be m ne>ly equal ?an if ! planet _h be5 m gase\s4 ,?us1 on pass+ f :olly gase\s planets to planets :i* liquefi$ at or imm$iately aft] _! bir?1 we %\ld expect at fir/ to f9d planets ) l>ge numb]s ( relatively small satellites1 & !n1 aft] pass+ ?r\gh ! bord]-l9e cases ( planets ) small numb]s ( relatively l>ge satellites1 we %\ld expect to come to planets hav+ no satellites at all4 ,we h already se5 t ! big c5tral planets1 ,jupit] & ,saturn1 ought to h rema9$ gase\s = longe/ & ! small] planets to h liquefi$ e>lie/2 we n[ see t ?is pr$iction ( !ory exactly describes :at is actually f\nd 9 ! sol> sy/em4 ,/>t+ f ,jupit] & ,saturn1 ea* ) n9e relatively small satellites1 we pass ,m>s ) only two satellites1 & come to ! e>? ) its "o relatively l>ge satellite1 foll[$ by ,v5us & ,m]cury :i* h no satellites at all4 ,proce$+ 9 ! o!r direction we leave ,jupit] & ,saturn ea* ) _! n9e t9y satellites1 to discov] ,uranus ) f\r small satellites & ,neptune ) "o comp>atively big satellite4 ,! numb] plac$ "u ea* planet 9 fig4 #ad gives ! numb] ( its satellites4 ,:5 ! numb]s are exhibit$ 9 ?is way1 ! law & ord] 9 ! arrangem5t ( ! satellite sy/ems becomes v app>5t1 & ?is arrangem5t is se5 to be exactly 9 accordance ) ! pr$iction ( ! tidal !ory4 ,! cig>-%ap$ arrangem5t applies n only to ! sizes ( ! planets1 b also1 z x ought1 to ! numb]s ( _! satellites4 ,! e>? & ,neptune1 ) only "o satellite ea*1 & ^? comp>atively l>ge ones1 =m ! obvi\s l9es ( dem>cation betwe5 planets :i* 7 orig9ally liquid & ^? :i* 7 orig9ally gase\s4 ,?is leads u to conjecture t ,m]cury1 ,v5us & ,pluto mu/ h become liquid or solid imm$iately aft] bir?1 t ! e>? & ,neptune 7 p>tly liquid & p>tly gase\s1 & t ,m>s1 ,jupit]1 ,saturn & ,uranus 7 born gase\s & rema9$ gase\s at lea/ until aft] ! bir? ( _! families ( satellites4 ,we may p]haps f9d fur!r evid5ce confirmatory ( ! tidal !ory 9 ! circum/ance t ! weights ( ,m>s & ,uranus are abnormally small = _! positions 9 ! sequ5ce ( planets4 ,if1 z we h suppos$1 ! planets 7 all born out ( a cont9u\s filam5t ( matt]1 ! weight ( ,m>s at bir? w\ld 9 all probability h be5 int]m$iate betwe5 ^? ( ! e>? & ,jupit]1 & ! weight ( ,uranus int]m$iate betwe5 ^? ( ,neptune & ,saturn4 ,b if1 z we h already be5 l$ to suppose1 ! two anomal\s planets ,m>s & ,uranus 7 ! two smalle/ planets to be born 9 ! gase\s /ate1 !y w\ld be likely to lose m ( _! sub/ance ?an ! o!r planets ?r\gh _! out]mo/ lay]s ( molecules dissipat+ away into space be=e !y _h cool$ d[n into ! liquid /ate4 ,if ,m>s & ,uranus are suppos$ to be m]e relics ( planets :i* 7 initially f> m massive ?an !y n[ are1 ! anomalies beg9 to disappe> & ! pieces ( ! puzzle to fit toge!r 9 a v satisfactory mann]4 ,,orbital ,,planes4 ,e rotat+ mass1 :e!r gase\s1 liquid or solid1 has a def9ite axis ( rotation1 &1 p]p5dicul> to ?is1 a def9ite equatorial plane :i* divides ! mass symmetrically into two exactly equal & simil> halves4 ,:5 a mass breaks up "u its own rotation1 ! equatorial plane & ! symmetry /ill p]si/4 ,illu/rations ( ?is c be f\nd 9 any set ( photographs ( rotat+ nebulae1 z1 = in/ance1 ^? %ewn 9 ,plates ,,xv & ,,xvi4 ,9 m humble life an illu/ration is provid$ by ! spla%es ( mud ?r[n (f by a sp9n+ bicycle-:eel1 :i* all keep 9 ! plane 9 :i* ! :eel is sp9n+4 ,if ! sun's equatorial plane _h prov$ to be a plane ( symmetry = ! sol> sy/em1 s t ! :ole sy/em 0 simil>ly arrang$ z reg>ds ! two sides ( ?is plane1 x might h be5 possible to expla9 ! sy/em z ! result ( a rotational break-up4 ,b ! sun's equatorial plane is n a plane ( symmetry4 ,! planets d n move 9 x1 mo/ ( !m mov+ 9 a plane :i* makes an angle ( #e or #f degrees ) x4 ,9 t]ms ( our humble analogy1 ! spla%es ( mud are n fly+ ab\t 9 ! plane 9 :i* ! bicycle-:eel is sp9n+4 ,! hypo!sis t ! planets came into be+ ?r\gh a rotational break-up ( ! sun fails completely be=e ?is fact1 b ! tidal !ory provides a simple explanation ( x at once4 ,! sun is /ill rotat+ mu* z x 0 be=e ! planets 7 born1 & s reta9s its orig9al equatorial plane4 ,! q diff]5t plane 91 or v close to1 :i* ! planets are describ+ orbits mu/ cle>ly be ! plane 9 :i* ! long tidal filam5t 0 orig9ally drawn out by ! pass+ />4 ,?us ! plane 9 :i* ! out] planets n[ move mu/ record ! position ( ! plane 9 :i* ! two />s1 ! sun & ! w&]+ />1 ! second p>5t ( ! sun's family ( *ildr51 describ$ orbits ab\t "o ano!r #bjjj million ye>s ago4 ,x is ! only clue ! latt] has left ( 8 id5tity1 & is ( c\rse f> too slight to make id5tification possible aft] ?is long lapse ( "t4 ,to sum up1 we h se5 t ! normal me*anism by :i* ! great] "p ( ! univ]se has be5 c>v$ out is ! bir? ( successive g5]ations ( a/ronomical bodies ?r\gh ! action ( 8gravitational in/ability40 ,! normal g5ealogy runs some:at z foll[s3 *aos--nebulae--/>s--b9>y sy/ems--sub-sy/ems4 ,n all />s h pass$ on to ! la/ two g5]ations2 :]e only a small am\nt ( rotation 0 pres5t1 a /> might well live its :ole life )\t fur!r subdivision4 ,our sun w\ld h provid$ an in/ance ( ?is _h x n be5 = ! r>e accid5t ( ! close approa* ( a second />4 ,f ! int]action ( ^!1 two o!r g5]ations came into be+1 /ill ?r\gh ! me*anism ( gravitational in/ability4 ,= our sol> sy/em1 z = any o!r simil> sy/ems !re may be 9 ! sky1 ! g5ealogy runs z foll[s3 *aos--nebula--sun--planets--satellites4 ,bo? types ( g5ealogy %ew five g5]ations1 ea* born f its p>5t ?r\gh ! action ( gravitational in/ability1 & betwe5 !m ! two g5ealogies include practically all ! l>ge size a/ronomical objects ) :i* we are acqua9t$4 ,x is !n fair to say t 8gravitational in/ability0 appe>s to be ! ag5cy prim>ily responsible = ! ma9 ar*itecture ( ! univ]se4 ,,ro*e',s ,,limit4 ,! reign ( gravitational in/ability mu/ end ) ! bir? ( planet>y satellites1 s9ce gase\s bodies ( less weight ?an ^! c\ld n hold toge!r4 ,ev5 "u ! mo/ fav\rable circum/ances _! feeble gravitational pulls w\ld be unable to re/ra9 _! out]mo/ molecules f escap+1 s t ! :ole mass w\ld spe$ily scatt] into space4 ,yet a/ronomy provides _m in/ances ( small] bodies2 we h already m5tion$ ! a/]oids1 meteors or %oot+-/>s1 & ! p>ticles ( ,saturn's r+s4 ,z all ^! are too small to h be5 born 9 ! gase\s /ate1 we mu/ suppose !m to be ! brok5-up fragm5ts ( l>g] masses4 ,?is accords ) ! circum/ance t ^! small bodies z a rule d n occur individually b 9 sw>ms4 ,! a/]oids occur z a s+le sw>m4 ,if ^! 7 f\nd scatt]$ ?r\gh\t ! sol> sy/em1 _! orig9 might pres5t a difficult problem4 ,z ?+s are1 ! :ole sw>m c be expla9$ q simply z ! brok5 fragm5ts ( a primaeval planet4 ,saturn's r+s aga9 admit ( a natural explanation z ! fragm5ts ( a =m] %att]$ moon ( ,saturn4 ,comets1 :i* we h h>dly _h occasion to m5tion s f>1 are 9 all probability sw>ms ( m9ute bodies :i* are j held toge!r suffici5tly by _! mutual gravitational attraction to describe a common orbit 9 space4 ,at its app>ition 9 #aiji1 ,halley's comet 0 e/imat$ to reflect z mu* ( ! sun's light z a s+le body #be miles 9 diamet]4 ,yet its app>5t surface 0 #cjj1jjj times t ( su* a body1 & 0 q transp>5t4 ,x is difficult to resi/ ! conclusion t ! comet consi/$ ( a widely-spac$ sw>m ( small bodies1 & su* a sw>m aga9 admits ( a simple explanation z ! brok5 fragm5ts ( a s+le mass4 ,%oot+-/>s1 or meteors1 also are enc\nt]$ 9 sw>ms4 ,z we %all see lat]1 ! motion ( _m ( ^! sw>ms makes x possible to id5tify !m z brok5-up comets4 ,?us ! brok5 fragm5ts :i* compose a comet are id5tical ) ! meteors :i* we see z %oot+-/>s :5 !y p5etrate into ! e>?'s atmosph]e4 ,%apley has e/imat$ t ! e>?'s atmosph]e mu/ cat* ?\s&s ( millions ( %oot+-/>s e day1 ( :i* at mo/ only "o 9 a hundr$ is bright en\gh to be visible to ! nak$ eye4 ,g5]ally !y dissolve into vap\r be=e !y rea* ! e>?'s surface 7see p4 #agf72 occasionally "o is s big t ! e>?'s atmosph]e fails to dissipate x entirely1 & :at rema9s ( x /rikes ! e>? z a solid body--a meteorite4 ,e %oot+-/> & meteorite may be reg>d$ z a m9iature comet1 consi/+ ( only a s+le fragm5t4 ,on occasions a :ole gr\p ( fragm5ts1 mov+ 9 p>allel pa?s at only small di/ances ap>t1 may /rike ! e>?'s atmosph]e & appe> z a 8fireball40 ,g5]ally speak+ all ! small fry ( ! sol> sy/em move 9 sw>ms1 & c be naturally int]pret$ z ! brok5-up fragm5ts ( l>g] bodies4 ,if ! meteorites are brok5 fragm5ts ( bodies :i* 7 born out ( ! sun at ! same "t z ! planets1 !y mu/ h solidifi$ at ab\t ! same "t z ! e>?1 at an epo* :i* we h plac$ at ab\t #bjjj million ye>s ago4 ,b if !y _h be5 born out ( "s o!r />1 ! "t ( _! solidification might h be5 any:]e up to millions ( millions ( ye>s ago4 ,pr(essor ,pane? & two colleagues at ,knigsb]g h rec5tly e/imat$ ! ages ( v>i\s meteoric /ones by me?ods simil> to ^? employ$ to fix ! age ( ! e>? 7p4 #aed74 ,!y obta9 ages :i* range f a few million ye>s up to #bijj million ye>s1 b !re is no?+ beyond ?is la/ figure4 ,n a s+le /one sugge/s an age ev5 approa*+ millions ( millions ( ye>s4 ,?is provides v /rong evid5ce t ^! /ones 7 products ( ! same cataclysm z produc$ ! e>?1 & incid5tally provides valuable confirmation ( our previ\s e/imate ( ! e>?'s age4 ,we c easily see h[ l>g] bodies might be brok5 up into sw>ms ( meteors4 ,we h suppos$ ! sun to h be5 brok5 up1 at lea/ to ! ext5t ( eject+ a family ( planets1 by ! tidal pull ( a pass+ />4 ,:at w\ld h happ5$ if ! pass+ /> _h n pass$1 b _h come to /ay8 ,s long z x rema9$ )9 a c]ta9 di/ance ( ! sun1 its tidal =ces 7 pull+ ! sun to pieces4 ,we c imag9e h[ a long] visit f x w\ld h result$ 9 a great] upheaval 9 ! sun1 & ! bir? ( a l>g] family ( planets4 ,f9ally a visit ( unlimit$ duration w\ld h %att]$ ! sun into fragm5ts4 ,9 #ahej ,ro*e gave a ma!matical inve/igation ( ?is process ( tidal break-up4 ,8 discussion dealt only ) solid or liquid bodies1 b ! und]ly+ me*anism is ! same :e!r ! bodies are solid1 liquid or gase\s4 ,we h se5 t ! small] ( ! two bodies involv$ 9 a tidal enc\nt] suff]s ! mo/4 ,ro*e dealt only ) ! case 9 :i* "o body 0 v small 9 comp>ison ) ! o!r2 9 su* a case ! small body 0 completely brok5 up1 :ile ! l>g] "o rema9$ unsca!d4 ,ro*e imag9$ ! small body to describe an orbit ( gradually decreas+ size ar\nd ! big body4 ,if ! two bodies 7 ( equal d5sity1 he calculat$ t ! small body w\ld be brok5 up z soon z ! radius ( its orbit fell to #bde times ! radius ( ! l>ge body4 ,if ! bodies are ( diff]5t d5sity ! matt] is slightly m complicat$4 ,we mu/ imag9e ! l>g] body to exp& or contract until x has ! same av]age d5sity z ! small] body2 ! critical di/ance is !n #bde radii ( ! l>g] body 9 its imag9>y exp&$ or contract$ /ate4 ,?is di/ance is g5]ally kn[n z ,ro*e's limit4 ,a satellite c ) safety describe a circul> orbit ab\t its prim>y s long z ?is orbit lies beyond ,ro*e's limit1 b x is brok5 into fragm5ts z soon z x trespasses )9 ! limit4 ,! foll[+ figures confirm ,ro*e's ma!matical analysis3 ,radius ( ,saturn's out]mo/ r+ #bcj radii ( ,saturn ,ro*e's limit #bde radii ( prim>y ,radius ( orbit ( ,saturn's inn]mo/ satellite #caa radii ( ,saturn ,radius ( orbit ( ,jupit]'s inn]mo/ satellite #bed radii ( ,jupit] ,radius ( orbit ( ,m>s' inn]mo/ satellite #bgi radii ( ,m>s ,at ! same "t !y sugge/ v =cibly t ,saturn's r+s are ! brok5-up fragm5ts ( a =m] satellite :i* v5tur$ into ! dang]-zone m>k$ out by ,ro*e's limit4 ,we h se5 h[ our own moon is de/9$ 9 "t to contract its orbit1 until x is f9ally drawn )9 ! ,ro*e's limit surr\nd+ ! e>? & brok5 into fragm5ts4 ,aft] ?is ! e>? w h no moon1 b w be surr\nd$ by r+s l ,saturn4 ,we speak ( ,saturn's r+s 9 ! plural1 because two di/9ct circul> gaps cause an appe>ance ( ?ree deta*$ r+s4 ,!re is a t5d5cy to jump to ! ha/y inf]5ce t ! r+s are ! %att]$ rema9s ( ?ree di/9ct satellites1 b x is n s4 ,goldsbr\gh has %ewn h[ c]ta9 orbits ar\nd ,saturn are r5d]$ un/able by ! motions ( ! l>g] satellites ( ,saturn1 s t no p>ticle c\ld p]man5tly rema9 9 su* an orbit4 ,he has calculat$ positions = ^! un/able orbits1 & ^! are f\nd to agree exactly ) ! positions ( ! obs]v$ divisions betwe5 ! r+s4 ,?us ,saturn's r+s 7 9 all probability produc$ by ! breakage ( a s+le satellite4 ,! r+ ( small satellites :i* our moon w ultimately =m r\nd ! e>? w conta9 no divisions1 because ! e>? has no o!r moons to r5d] c]ta9 orbits un/able4 ,illu/ration3 ,,plate ,,xxiv ,saturn 9 #aiaf ,illu/ration3 ,saturn 9 #aiag ,illu/ration3 ,l[ell ,obs]vatory ,saturn 9 #aiba ,saturn & its ,sy/em ( ,r+s ,ro*e's fundam5tal idea c be ext5d$ 9 _m directions & admits ( v>i$ applications4 ,!re mu/1 = in/ance1 be a dang]-zone1 m>k$ (f by a ,ro*e's limit1 surr\nd+ ! sun4 ,! di/ance ( ?is dang]-zone f ! sun dep5ds on ! d5sity ( ! body = :i* x is dang]\s 7p4 #bdi74 ,= a body hav+ ! l[ d5sity ( a comet ! di/ance w be v great inde$4 ,:atev] ! di/ances ( _! dang]-zones1 comets mu/ occasionally pass ?r\gh !m & become brok5 up 9 s do+4 ,two comets1 ,biela's comet 7#ahdf7 & ,taylor's comet 7#aiaf71 7 obs]v$ actually to break 9 two :ile at ab\t ! e>?'s di/ance f ! sun1 & 9 #ahhb a comet 0 se5 to divide into f\r p>ts4 ,biela's comet return$ 9 due c\rse 7#aheb7 9 ! =m ( two di/9ct comets a million & a half miles ap>t1 s9ce :i* "t nei!r "p ( ! orig9al comet has be5 se5 aga94 ,! orbit ( ?is comet 0 id5tical ) t ( ! ,&rom$id meteors1 :i* make a display ( %oot+-/>s 9 ! e>?'s atmosph]e on fav\rable #bg?s ( ,novemb]1 s t x is likely t ^! %oot+-/>s are ! brok5 rema9s ( ,biela's comet4 ,o!r conspicu\s sw>ms ( %oot+-/>s also move 9 ! tracks ( comets--! ,leonids :i* us$ to make a magnific5t %[ e #cc ye>s move 9 ! track ( ,comet #ahff ,i1 ! ,p]seids 9 ! track ( ano!r ,comet 7#ahfb ,,ii71 & ! ,aqu>ids 9 ! track ( ,halley's fam\s comet4 ,9 ea* case1 !re c be little d\bt t ! %oot+-/>s are scatt]$ fragm5ts ( ! comets4 ,besides ?is !re are sev]al families ( comets ^: memb]s foll[ "o ano!r r\nd & r\nd 9 ! same orbit1 z ?\gh !y _h orig9ally =m$ a s+le mass4 ,9 ! same way a ,ro*e's limit mu/ surr\nd ! planet ,jupit]1 s t comets & o!r bodies may be brok5 up ?r\gh gett+ inside ! dang]-zone m>k$ (f by ?is limit4 ,jupit]'s inn]mo/ satellite is already p]il\sly ne> x4 ,b ! greate/ int]e/ ( ?is p>ticul> dang]-zone is t x probably acc\nts = ! exi/5ce ( ! a/]oids4 ,9 ! e>ly days ( ! sol> sy/em1 :5 ! orbits ( ! planets 7 less ne>ly circul> ?an !y n[ are1 a primaeval planet betwe5 ,m>s & ,jupit] may well h describ$ an orbit s elongat$ z to take x repeat$ly )9 ! dang]-zone ( ,jupit]4 ,if s1 we ne$ look no fur!r = ! orig9 ( ! a/]oids4 ,x is significant t ! av]age orbit ( all ! a/]oids agrees almo/ exactly ) t ( ! planet :i* ,bode's law 7p4 #ai7 w\ld require to exi/ betwe5 ,m>s & ,jupit]4 ,,*apt] ,v ,/>s ,! process ( c>v+ out ! univ]se :i* we consid]$ 9 ! la/ *apt] ends normally ) a simple />1 al?\gh special accid5ts may h o!r consequ5ces4 ,z ! result ( close approa*es ) o!r />s1 a t9y fraction ( ! total numb] ( ! />s1 p]haps ab\t "o /> 9 #ajj1jjj 7p4 #cda bel[71 may be att5d$ by a ret9ue ( planets4 ,ano!r fraction1 /ill small1 al?\gh f> great] ?an ! =ego+1 appe>s to h brok5 up z ! result ( excessive rotation1 & =m$ b9>y or p]*ance multiple sy/ems4 ,b ! de/9y ( ! majority ( />s is to pursue _! pa?s solit>y ?r\gh space1 nei!r break+ up ( !mselves nor be+ brok5 up by o!r />s4 ,! only contact su* />s h ) ! out] univ]se is t !y are incessantly p\r+ away radiation into space4 ,?is outp\r+ ( radiation is almo/ entirely a "o-way process1 any radiation a /> may receive f o!r />s be+ q inappreciable 9 comp>ison ) ! am\nt x is itself emitt+4 ,! radiation is accompani$ by a loss ( weight1 & ?is aga9 is all give & no take1 ! weight ( any /ray matt] ! /> may sweep up out ( space1 l t ( any radiation x receives1 be+ q inappreciable 9 comp>ison ) ! weight x loses by radiation4 ,)\t unduly /ra9+ ! facts1 ! normal object 9 ! sky may be idealis$ z a solit>y body1 alone 9 endless space1 :i* cont9ually p\rs out radiation & receives no?+ 9 return4 ,9 ! pres5t *apt] we %all consid] ! sequ5ce ( *anges :i* su* a /> may be expect$ to exp]i5ce dur+ ! c\rse ( its life4 ,hav+ already discuss$ ! me*anical accid5ts to :i* />s are liable1 namely1 fission ?r\gh rotation & break-up ?r\gh ! tidal action ( a pass+ />1 we n[ turn to consid] ! life ( a normal /> :i* escapes all accid5ts until x f9ally becomes ext9ct ?r\gh m]e old age4 ,x w be necess>y 9 ! fir/ place to describe ! physical /ates ( ! v>i\s types ( />s obs]v$ 9 ! sky1 & z a prelim9>y to ?is we mu/ expla9 h[ ! obs]vations ( ! a/ronom] are translat$ into a =m :i* gives u direct in=mation z to ! condition ( ! />4 ,,surface-,,temp]ature4 ,9 ,*apt] ,,ii 7p4 #adj7 we saw h[ ea* col\r ( light or wave-l5g? ( radiation has a special temp]ature associat$ ) x1 light ( ?is col\r pr$om9at+ :5 a body is heat$ up to ! temp]ature 9 "q4 ,= in/ance1 a body rais$ to :at we call a r$-heat emits m r$ light ?an light ( any o!r col\r1 & s looks r$ to ! eye4 ,?us if a /> looks r$1 x is legitimate to inf] t its surface is at ! temp]ature we describe z a r$-heat4 ,if ano!r /> has ! col\r ( ! c>bon ( an arc-light1 we may conclude t its surface is at ab\t ! same temp]ature z ! arc4 ,9 ?is way we c e/imate ! temp]atures ( ! surfaces ( ! />s4 ,9 practice ! proc$ure is n s crude z ! =ego+ description might seem to imply4 ,! a/ronom] passes ! light f a /> ?r\gh a spectroscope1 ?us analys+ x into its diff]5t col\rs4 ,by a process ( exact measurem5t1 he !n det]m9es ! proportions 9 :i* ! diff]5t col\rs ( light occur4 ,?is %ews at once :i* col\r ( light is mo/ pl5tiful 9 ! spectrum ( ! />4 ,ei!r f ?is or f ! g5]al di/ribution ( col\rs1 he c d$uce ! temp]ature ( ! />'s surface4 ,illu/ration3 ,fig4 #ae4 ,di/ribution ( radiation ( diff]5t wave-l5g?s at v>i\s temp]atures4 ,we h already se5 7p4 #abc7 h[ ,planck discov]$ ! law accord+ to :i* ! radiation emitt$ by a full radiator is di/ribut$ among/ ! diff]5t col\rs or wave-l5g?s ( ! spectrum4 ,! f\r curves %ewn 9 fig4 #ae repres5t ! !oretical di/ribution = ! radiation emitt$ by surfaces at ! f\r temp]atures #cjjj1 #djjj1 #ejjj & #fjjj degrees respectively4 ,! diff]5t wave-l5g?s ( light are repres5t$ by po9ts on ! horizontal axis1 ! m>k$ wave-l5g?s be+ measur$ 9 ! unit ( a hundr$-million? "p ( a c5timetre1 :i* is usually call$ an ,ang/rom4 ,! height ( ! curve above su* a po9t repres5ts ! abundance ( radiation ( ! wave-l5g? 9 "q4 ,! two me?ods ( det]m9+ /ell> temp]ature w be easily und]/ood by ref]5ce to ^! curves4 ,! #fjjj degrees curve rea*es its greate/ height at a wave-l5g? ( #dhjj ,ang/roms1 s t if light ( wave-l5g? #dhjj ,ang/roms proves to be mo/ abundant 9 ! spectrum ( any />1 we "k t ! />'s surface has a temp]ature ( #fjjj degrees4 ,! second me?od consi/s m]ely 9 exam9+ to :i* ( ! !oretical curves %ewn 9 fig4 #ae ! obs]v$ curve c be fitt$ mo/ closely4 ,ei!r ( ^! me?ods indicates t ! temp]ature ( ! sun's surface is ab\t #fjjj degrees absolute1 :i* is ne>ly twice ! temp]ature ( ! hotte/ "p ( ! electric arc4 ,! total am\nt ( light & heat receiv$ on e>? f ! sun %ews t ! sun's radiation mu/ be v ne>ly1 al?\gh n q1 ! 8full temp]ature radiation0 7p4 #abc7 ( a body at ?is temp]ature4 ,?is is also %ewn by ! sun's radiation be+ di/ribut$ among ! v>i\s col\rs 9 a way :i* con=ms v closely to ! !oretical curve = a full radiator at #fjjj degrees %ewn 9 fig4 #ae4 ,! surface-temp]ature ( a /> c also be e/imat$ f its spectral type4 ,_m ( ! l9es 9 /ell> spectra are emitt$ by atoms f :i* "o or m electrons h be5 torn (f by ! heat ( ! />'s atmosph]e4 ,we "k ! temp]atures at :i* ! electrons 9 "q are fir/ /ripp$ (f _! atoms1 & s c d$uce ! />'s temp]ature4 ,! temp]atures :i* correspond to ! diff]5t types ( /ell> spectra z %ewn 9 ,plate ,,viii 7p4 #ea71 are approximately z foll[s3 ------------------------ ,spectral type,temp]ature ------------------------ ,b #bc1jjj ,a #aa1jjj ,f #g1djj ,g #f1jjj ,k #e1ajj ,m #c1djj ------------------------ ,! la/ ?ree entries 9 ! table ref] only to normal />s hav+ diamet]s comp>able ) t ( ! sun4 ,we %all f9d 7p4 #bgf7 t a second class ( />s 7giants7 exi/1 ^: diamet]s are enorm\sly great] ?an ! sun's4 ,^! h ! sub/antially l[] temp]atures %ewn bel[3 ------------------------ ,spectral type,temp]ature ------------------------ ,g #efjj ,k #dbjj ,m #cbjj ------------------------ ,9 /udy+ /ell> /ructure & me*anism1 we are less conc]n$ ) ! heat ( ! />'s surface z measur$ by its temp]ature1 ?an ) ! am\nt ( radiation x p\rs out p] squ>e in*4 ,?is ( c\rse dep5ds on ! temp]ature2 ! hott] a surface1 ! m radiation x emits4 ,b ! temp]ature does n measure ! quantity ( radiation emitt$4 ,if we d\ble ! temp]ature ( a surface x emits #af times1 n twice1 its previ\s am\nt ( radiation2 ! radiation f ea* squ>e in* ( surface v>ies z ! f\r? p[] ( ! temp]ature4 ,z a consequ5ce1 a /> ) a surface-temp]ature ( #cjjj degrees1 or half t ( ! sun1 emits only a sixte5? "p z mu* radiation p] squ>e in* z ! sun#bc4 ,! radiation ( ea* /> is a comp\nd ( light1 heat & ultra-violet radiation1 & ! proportions ( ^! are n ! same 9 diff]5t />s2 ! cool] a />'s surface ! great] ! fraction ( its radiation :i* is emitt$ z heat4 ,?us ! /> at #cjjj degrees w emit no?+ l z mu* z a sixte5? ( ! sun's light p] squ>e in*1 b w emit m ?an a sixte5? ( ! sun's heat4 #bc ,?is is %ewn 9 fig4 #ae1 ! area ( ! #cjjj degree curve be+ only a sixte5? ( ! area ( ! #fjjj degree curve4 ,?is %ews t ! total emission ( radiation ( a /> _c be e/imat$ f its visual brightness alone2 a sub/antial all[ance mu/ always be made = invisible radiations1 bo? = ! invisible heat at ! r$ end ( ! spectrum & = ! invisible ultra-violet radiation at ! o!r end4 ,! importance ( ^! corrections is %ewn 9 fig4 #af4 ,! f\r ?ick curves are id5tical ) ^? already giv5 9 fig4 #ae1 & %ew h[ ! radiation f a /> ( giv5 surface-temp]ature is di/ribut$ ov] ! diff]5t wave-l5g?s4 ,! total radiation emitt$ at any temp]ature is ( c\rse repres5t$ by ! :ole area enclos$ betwe5 ! correspond+ curve & ! horizontal axis4 ,! eye is only s5sitive to radiation ( wave-l5g?s ly+ betwe5 #cgej & #gejj ,ang/roms1 s t ( all ?is radiation only t "p 9 ! %ad$ /rip is visible1 all ! re/ repres5t+ invisible radiation4 ,we see at once t a fair proportion ( ! radiation emitt$ by a /> at #fjjj degrees comes )9 ! range ( visibility1 b only a small fraction ( t emitt$ by a /> at #cjjj degrees4 ,tak+ ! />s z a :ole1 />-light =ms only a small "p ( ! total radiation ( ! />s4 ,illu/ration3 ,fig4 #af4 ,di/ribution ( radiation into visible & invisible4 ,if our eyes 7 sudd5ly to become s5sitive to all k9ds ( radiation1 & n to visual light alone1 ! appe>ance ( ! sky w\ld und]go a /range metamorphosis4 ,! r$ />s ,betelgeux & ,ant>es1 :i* are at pres5t only #ab? & #af? 9 ord] ( brightness1 w\ld fla% out z ! two brighte/ />s 9 ! sky1 :ile ,sirius1 at pres5t ! brighte/ ( all1 w\ld s9k to ?ird place4 ,a /> 9 ! v undi/+ui%$ con/ellation ( ,h]cules w\ld be se5 z ! six? brighte/ /> 9 ! sky4 ,x is ! /> ,h]culis1 at pres5t out%one by ab\t #bej />s4 ,z a consequ5ce ( its extremely l[ temp]ature ( #bfej degrees1 ?is /> emits its radiation almo/ entirely 9 ! =m ( invisible heat4 ,= in/ance x emits #fj times z mu* heat z ! blue /> ,aurigae1 ^: temp]ature is ab\t #bj1jjj degrees1 b only f\r-fif?s z mu* light4 ,all[ances = invisible radiation h be5 made 9 all ! calculations ref]r$ to 9 ! pres5t book1 al?\gh x has n be5 ?\ght necess>y cont9ually to re/ate ?is4 ,,/ell> ,,diamet]s4 ,x is easy to measure ! diamet] ( a planet1 because ?is appe>s 9 ! telescope z a disc ( f9ite size4 ,b ! />s are too remote = _! diamet]s to be measur$ 9 ! same way4 ,no /> appe>s l>g] 9 ! sky ?an a p9-head held at a di/ance ( six miles1 & no telescope yet built c %ew an object ( ?is size z a disc4 ,all />s1 ev5 ! ne>e/ & l>ge/1 appe> z m]e po9ts ( light#bd1 s t _! diamet]s c only be measur$ by r\ndab\t me?ods4 #bd ,! l>ge r\nd images ( />s %ewn 9 ! frontispiece result m]ely f ov]-exposure1 & h no?+ to d ) ! sizes ( ! />s4 ,:5 a />'s di/ance is kn[n1 we c tell its lum9osity f its app>5t brightness4 ,f ?is1 aft] all[+ = invisible radiation1 we c d$uce ! />'s total outp\r+ ( en]gy--s _m million million million million horse-p[]4 ,we also "k its outp\r+ ( en]gy p] squ>e in* ( surface1 because ?is dep5ds only on its surface-temp]ature :i* we d$uce directly f spectroscopic obs]vation4 ,kn[+ ^! two data1 x is a m]e matt] ( simple division to calculate ! numb] ( squ>e in*es :i* make up ! />'s surface1 & ?is imm$iately tells u ! diamet] ( ! />4 ,! diamet]s ( exceptionally l>ge />s may be measur$ m directly by an in/rum5t kn[n z ! int]f]omet]4 ,:5 we focus a telescope on a /> we d n1 /rictly speak+1 see only a po9t ( light1 b a po9t ( light surr\nd$ by a r elaborate sy/em ( r+s ( alt]nat+ light & d>kness1 call$ a diffraction patt]n4 ,x might be ?\ght t ! size ( ^! r+s w\ld tell u ! size ( ! />1 b ! two h no?+ to d ) "o ano!r4 ,! r+s repres5t a m]e in/rum5tal defect1 _! size dep5d+ solely on ! size & optical arrangem5t ( ! telescope4 ,foll[+ a me?od sugge/$ by ,fizeau 9 #ahfh1 ,pr(essor ,mi*elson has %ewn h[ ev5 ?is defect c be turn$ to useful ends1 & by its aid has produc$ :at is p]haps ! mo/ +5i\s & s5sational in/rum5t 9 ! s]vice ( mod]n a/ronomy--! int]f]omet]4 ,9 effect1 ?is in/rum5t sup]poses two sep>ate diffraction patt]ns ( ! same />1 & sets "o (f aga9/ ! o!r 9 su* a way z to disclose ! size ( /> produc+ !m4 ,! diamet]s ( a few ( ! l>ge/ />s h be5 measur$ 9 ?is way1 s t we may say t we "k _! sizes f direct obs]vation4 ,9 e case ! directly measur$ diamet] agrees fairly well1 al?\gh n p]fectly1 ) t calculat$ indirectly 9 ! way already expla9$4 ,! discrepancies1 :i* are n s]i\s1 appe> to result f r$ />s n be+ accurate 8full radiators0 9 ! s5se expla9$ on p4 #abc4 ,! int]f]omet] me?od is only available = ! l>ge/ />s1 b at ! extreme o!r end ( ! scale ! !ory ( relativity has come to ! rescue4 ,e9/e9 %ew$ x to be a necess>y consequ5ce ( 8 !ory ( relativity t ! spectrum ( a /> %\ld be %ift$ t[>ds ! r$ end by an am\nt dep5d+ on bo? ! weight & ! diamet] ( ! />4 ,if1 !n1 a />'s weight is kn[n1 ! obs]v$ spectral %ift ought imm$iately to tell u its diamet]4 ,?is spectral %ift has rec5tly be5 obs]v$ 9 ! light receiv$ f ! companion ( ,sirius1 & measurem5ts ( its am\nt lead to a value = ! />'s diamet] :i* agrees exactly ) t calculat$ f its lum9osity4 ,?us at bo? ends ( ! scale1 = ! v l>ge/ z well z = ! v smalle/ ( />s1 direct obs]vation confirms ! values calculat$ = ! diamet]s ( ! />s4 ,we may accord+ly feel e confid5ce 9 ! calculat$ diamet]s ( all />s1 ev5 :5 ^! _c be *eck$ by direct measurem5t4 ,inde$ a discrepancy betwe5 ! true & calculat$ diamet]s c\ld only arise 9 "o way4 ,! diamet]s are calculat$ on ! assumption t ! />s emit _! full temp]ature-radiation4 ,if ! />s _h be5 p>tially transp>5t l ! nebulae1 or solid bodies l ! moon1 ?is assumption w\ld h be5 false1 & its falsity w\ld at once h be5 %ewn by discordances betwe5 ! calculat$ & measur$ diamet]s ( ! />s4 ,! fact t no l>ge discordances appe> sugge/s t ! />s emit ne>ly full temp]ature-radiation ?r\gh\t ! :ole range ( size f ! l>ge/ to ! smalle/4 ,,! ,,v>iety ,,( ,,/>s ,obs]vation %ews t ! physical *>act]i/ics ( ! />s v>y enorm\sly1 s t x is easy1 z we %all soon see1 to tell a s5sational /ory by contra/+ extremes1 sett+ ! brighte/ aga9/ ! dimme/1 ! bigge/ aga9/ ! smalle/1 & s on4 ,?is w\ld1 h[ev]1 give a v unfair impression ( ! inhabitants ( ! sky2 x w\ld be l judg+ a nation f ! giants & dw>fs1 ! /rong m5 & ! fa/+ m51 se5 inside ! %[man's t5t4 ,we %all obta9 a m balanc$ impression ( ! actual degree ( div]sity %ewn by ! />s z a :ole if we consid] ! physical /ates ( ^? />s :i* are ne>e/ ! sun4 ,by tak+ ^! precisely 9 ! ord] 9 :i* !y come1 we avoid any suspicion ( go+ out ( our way to introduce />s m]ely because !y are biz>re or exceptional4 ,! small gr\p ( />s obta9$ 9 ?is way may be expect$ to =m a fair sample ( ! />s 9 ! sky1 al?\gh ( c\rse x w n be a l>ge en\gh sample to include extremes4 ,we ne$ n discuss ! sun itself 9 detail because x w figure z our /&>d />1 ) ref]5ce to :i* all comp>isons are made4 ,! ,sy/em ( ,c5tauri4 ,?is sy/em consi/s ( ?ree con/itu5t />s1 :i* are believ$ to be our ?ree ne>e/ neighb\rs 9 space4 ,! brighte/1 ,c5tauri ,a1 is v simil> to ! sun4 ,x is ( ! same col\r & spectral type1 b weighs #ad p] c5t4 m & is ab\t #ab p] c5t4 m lum9\s4 ,be+ ( ! same col\r z ! sun1 x emits ! same am\nt ( radiation p] squ>e in*4 ,?us its #ab p] c5t4 great] lum9osity %ews t x mu/ h a surface #ab p] c5t4 great]1 & !re=e a diamet] #f p] c5t4 great]1 ?an ! sun4 ,! second con/itu5t1 ,c5tauri ,b1 is consid]ably r$d] ?an ! sun1 its surface-temp]ature be+ only ab\t #ddjj degrees aga9/ ! sun's #fjjj degrees or s4 ,x has #ig p] c5t4 ( ! sun's weight1 b only ab\t a ?ird ( its lum9osity4 ,yet1 z a consequ5ce ( its l[ temp]ature1 x ne$s #ej p] c5t4 m area ?an ! sun to dis*>ge a ?ird ( ! sun's radiation2 ?is makes its diamet] #bb p] c5t4 great] ?an t ( ! sun4 ,c5tauri ,a & ,c5tauri ,b toge!r =m a visual b9>y1 ! two compon5ts revolv+ ab\t "o ano!r 9 a p]iod ( #gi ye>s4 ,nei!r ( ^! two con/itu5ts is v dissimil> f ! sun1 b ! ?ird /> ( ! sy/em1 ,proxima ,c5tauri1 is ( an altoge!r diff]5t type4 ,x is r$ 9 col\r1 ) a surface-temp]ature ( only ab\t #cjjj degrees4 ,x is exce$+ly dim1 emitt+ only a t5-?\s&? "p z mu* light z ! sun1 & has only a f\rte5? "p ( ! sun's diamet]4 ,its weight is unkn[n4 ,illu/ration3 ,fig4 #ag4 ,! ,sy/em ( ,c5tauri1 ) ! ,sun = comp>ison4 ,! sizes ( ! ?ree />s ( ?is sy/em1 ) t ( ! sun = comp>ison1 are %ewn 9 fig4 #ag4 ,muni* #aejdj4 ,?is is a s+le fa9t /> ab\t :i* little is kn[n4 ,its surface is r$1 ) a temp]ature probably little above #bejj degrees1 & x emits only _/? ( ! light ( ! sun4 ,wolf #cei4 ,?is is ! fa9te/ /> yet discov]$1 b beyond ?is v little is kn[n ab\t x4 ,x is r$ 9 col\r & emits only ab\t #a_/ej1jjj? ( ! light ( ! sun4 ,lal&e #baahe4 ,ano!r fa9t r$ />1 emitt+ _/? ( ! light ( ! sun4 ,! ,sy/em ( ,sirius4 ,?is consi/s ( two v dissimil> />s1 !re be+ "s suspicion t a ?ird also may exi/4 ,! pr9cipal />1 ,sirius ,a1 :i* appe>s z ! brighte/ /> 9 ! sky 7! ,dog-/>71 is :ite 9 col\r & has a surface-temp]ature ( ab\t #aa1jjj degrees4 ,z ?is is ne>ly twice ! sun's temp]ature1 ,sirius ,a emits ne>ly #af times z mu* radiation p] squ>e in* z ! sun4 ,its lum9osity is ab\t #bf times t ( ! sun1 & ?is requires ! />'s diamet] to be #eh p] c5t4 great] ?an t ( ! sun4 ,x has ne>ly f\r times ! sun's volume1 b only #bde times its weight1 s t matt] is n z closely pack$ 9 ,sirius ,a z 9 ! sun4 ,an av]age cubic metre conta9s #adb ton 9 ! sun1 b only #jic ton 9 ,sirius ,a4 ,illu/ration3 ,fig4 #ah4 ,! ,sy/em ( ,sirius1 ) ! ,sun = comp>ison4 ,! fa9t companion ,sirius ,b is "o ( ! mo/ int]e/+ />s 9 ! sky4 ,x is ( ne>ly ! same col\r & spectral type z ,sirius ,a1 b emits only a t5-?\s&? "p z mu* light4 ,aft] all[+ = ! slight diff]5ce 9 surface-temp]ature1 we f9d t its surface is only _/?1 & its diamet] _/? ( t ( ,sirius ,a4 ,yet ,sirius ,a weighs only ?ree times z mu* z ,sirius ,b1 al?\gh hav+ #abe1jjj times its volume4 ,x is n ,sirius ,a b ,sirius ,b t is rem>kable2 ! av]age d5sity ( matt] 9 ! latt] is ab\t #fj1jjj times t ( wat]1 ! av]age cubic in* conta9+ ne>ly a ton ( matt]4 ,fig4 #ah %ews ! sizes ( ! two compon5ts ( ,sirius drawn to ! same scale z fig4 #ag4 ,b4,d4 #ab #debc & ,innes #aa h4 #ab m41 #egb4 ,two />s1 z to ! physical /ate ( :i* no?+ is kn[n1 except t !y are v fa9t1 emitt+ _/? & #a_/aj1jjj? ( ! sun's light respectively4 ,cordoba #e h4 #cdc & ,ceti4 ,two fa9t />s1 bo? ( r$di% col\r1 emitt+ _/? & a ?ird ( ! sun's light respectively4 ,illu/ration3 ,fig4 #ai4 ,! ,sy/em ( ,procyon1 ) ! ,sun = comp>ison4 ,! ,sy/em ( ,procyon4 ,?is is a b9>y sy/em1 simil> 9 _m respects to ,sirius4 ,! ma9 />1 ,procyon ,a1 is ( ! same g5]al type z ! sun1 b weighs #bd p] c5t4 m1 & emits #e times z mu* light4 ,its surface-temp]ature is ab\t #gjjj degrees1 & its diamet] is #ahj times t ( ! sun4 ,! fa9t companion1 ,procyon ,b1 is s fa9t t no?+ is kn[n z to its physical condition except t x emits only #a_/cj1jjj? ( ! light ( ! sun4 ,its weight is #ci p] c5t4 ( ! sun's weight4 ,fig4 #ai %ews ! sizes ( ! two compon5ts ( ,procyon on ! same scale z be=e4 ,next 9 ord]1 z we rec$e f ! sun1 come eight v undi/+ui%$ />s1 e "o ( :i* is r$d] & fa9t] ?an ! sun1 none ( !m hav+ a surface-temp]ature high] ?an #ejjj degrees1 & none ( !m emitt+ m ?an a qu>t] ( ! sun's light4 ,aft] ^! we come to3 ,! ,sy/em ( ,krug] #fj4 ,?is is a b9>y sy/em 9 :i* bo? compon5ts are small1 r$ & dim4 ,illu/ration3 ,fig4 #bj4 ,! ,sy/em ( ,krug] #fj1 ) ! ,sun = comp>ison4 ,! bright] compon5t1 ,krug] #fj ,a1 has a surface-temp]ature ( #cbjj degrees1 & emits _/? ( ! light ( ! sun4 ,its diamet] is a ?ird1 & its weight a qu>t] ( ! sun's2 s t its sub/ance mu/ be pack$ ab\t #g times z closely z t ( ! sun4 ,! fa9t] compon5t1 ,krug] #fj ,b1 has a simil> surface-temp]ature b emits only #a_/ad1jjj? ( ! sun's light4 ,its diamet] is a six?1 & its weight a fif? ( ! sun's2 s t its sub/ance mu/ be pack$ ab\t #dj times z closely z t ( ! sun4 ,! sy/em is illu/rat$ 9 fig4 #bj4 van ,maan5's />4 ,ano!r v fa9t />1 :i* has ! high surface-temp]ature ( #gjjj degrees4 ,not)/&+ ?is1 x only emits _/? ( ! sun's light4 ,consequ5tly its diamet] is only ab\t _/? ( ! sun's1 ! /> be+ if any?+ small] ?an ! e>?4 ,its weight is unkn[n1 b its sub/ance is 9 all probability pack$ ev5 m closely ?an 9 ,sirius ,b4 ,! discussion ( ?is sample ( />s sugge/s t ! majority ( />s 9 space are small]1 cool] & fa9t] ?an ! sun4 ,/>s exi/ :i* are f> bright] ?an ! sun1 b !y are exceptional1 ! av]age /> 9 ! sky be+ a small dull dim affair 9 comp>ison ) our sun4 ,) ?is sample ( ! av]age population ( ! sky be=e u1 we may proce$ to discuss ! v>i\s *>act]i/ics ( />s 9 a sy/ematic way1 )\t fe>+ to m5tion extremes4 ,let u beg9 ) _! weights4 ,,/ell> ,,weights4 ,! two />s ( smalle/ kn[n weight 9 ! :ole sky are ! fa9t con/itu5t ( ,krug] #fj1 j discuss$1 & ! fa9te/ con/itu5t ( ! triple sy/em ,eridani1 ea* ( :i* has a fif? ( ! sun's weight4 ,b ! />s ^: weights are kn[n are s few t !re c be no ju/ification = suppos+ ^! to be ! smalle/ weights :i* occur 9 ! :ole univ]se ( />s4 ,a g5]al survey ( ! situation1 on l9es to be indicat$ lat] 7p4 #bha71 sugge/s t !re may be _m />s ( /ill small] weight1 b t v few are likely to h weights :i* are enorm\sly small]4 ,probably v few />s weigh z little z a t5? ( ! sun's weight4 ,! va/ majority ( />s h weights int]m$iate betwe5 ?is & t5 times ! sun's weight4 ,/>s :i* weigh ev5 ?ree times z mu* z ! sun are r>e1 ^? :i* weigh t5 times z mu* are v r>e1 probably only ab\t "o /> 9 #ajj1jjj hav+ t5 times ! weight ( ! sun4 ,ev5 high] weights und\bt$ly occur--we h already m5tion$ ,plaskett's />1 ^: two con/itu5ts h m ?an #ge & #fc times ! sun's weight respectively1 & ! quadruple sy/em #bg ,canis ,majoris :i* to all appe>ances weighs #idj times z mu* z ! sun--b su* in/ances are v1 v unusual4 ,we may say t z a g5]al rule ! weights ( ! />s lie )9 ! range ( f a t5? to t5 times ! sun's weight1 & we %all f9d t />s diff] less 9 _! weights ?an 9 mo/ ( _! o!r physical *>act]i/ics4 ,,lum9osity4 ,a f> great] range is %ewn1 = in/ance1 9 ! lum9osities ( ! />s--9 _! c&le-p[]s measur$ 9 t]ms ( ! sun's c&le-p[] z unity4 ,! mo/ lum9\s /> kn[n is ,s ,doradus1 already m5tion$1 ) #cjj1jjj times ! lum9osity ( ! sun1 :ile ! lea/ lum9\s is ,wolf #cei ) only a fifty-?\s&? "p ( ! lum9osity ( ! sun4 ,! range ( /ell> lum9osities1 z ( /ell> weights1 ext5ds ab\t equally on ! two sides ( ! sun1 s t ! sun is r a m$ium /> 9 respect bo? ( weight & lum9osity4 ,x is m$ium 9 ! s5se ( be+ ab\t half-way betwe5 extremes1 b we h se5 t !re are _m m />s bel[ ?an above x4 ,9 comp>ison ) ! v mod]ate range ( /ell> weights1 ! range ( lum9osity is enorm\s2 ,s ,doradus is #ae1jjj1jjj1jjj times z lum9\s z ,wolf #cei4 ,if ,s ,doradus is a ligh?\se1 ,wolf #cei is some?+ less ?an a firefly1 ! sun be+ an ord9>y c&le4 ,if ! sun sudd5ly />t$ to emit z mu* light & heat z ,s ,doradus1 ! temp]ature ( ! e>? & ev]y?+ on x w\ld run up to ab\t #gjjj degrees1 s t bo? we & ! solid e>? w\ld disappe> into a cl\d ( vap\r4 ,on ! o!r h&1 if ! sun's emission ( light & heat 7 sudd5ly to s9k to t ( ,wolf #cei1 p at ! e>?'s equator w\ld f9d t _! new sun only gave z mu* light & heat at mid-day z a coal fire a mile away2 we %\ld all be froz5 solid1 :ile ! e>?'s atmosph]e w\ld surr\nd u 9 ! =m ( an ocean ( liquid air4 ,s f> z we "k1 !re is no possibility ( ! sun sudd5ly beg9n+ to behave l ,s ,doradus1 b we %all see lat] t ! possibility ( its behav+ l ,wolf #cei is n altoge!r a vision>y dream4 ,,surface-,,temp]ature ,,& ,,radiation4 ,sirius has be5 f\nd to h ! highe/ surface-temp]ature ( all ! />s ne> ! sun2 x is ab\t #aa1jjj degrees1 or ne>ly d\ble t ( ! sun4 ,go+ fur!r afield1 we f9d _m />s ) f> high] surface-temp]atures4 ,= in/ance1 ,plaskett's /> is cr$it$ ) a temp]ature ( #bh1jjj degrees1 al?\gh x mu/ be admitt$ t a sub/antial elem5t ( unc]ta9ty ent]s into all e/imates ( v high /ell> temp]atures4 ,at ! o!r extreme1 /ell> temp]atures rang+ d[n to ab\t #bejj degrees are comp>atively common4 ,! l[e/ temp]atures ( all are conf9$ to v>iable />s ( a v special type 7long p]iod v>iables7 9 :i* ! light-v>iation is accompani$ by1 & inde$ ma9ly arises f1 a v>iation 9 ! temp]ature ( ! />'s surface4 ,! temp]ature ( ^! />s :5 at ! l[e/1 ranges d[n to #afej degrees1 :i* is b little above ! temp]ature ( an ord9>y coal fire4 ,9 _m ( !m1 ! temp]ature v>ies ?r\gh a l>ge range1 b x nev] s9ks s l[ t ! /> becomes completely invisible4 ,?us !re is a range ( temp]ature bel[ ab\t #bejj degrees :i* no /> is kn[n to occupy1 except = ! long-p]iod v>iables :i* only ent] x at int]vals4 ,?is w\ld seem to sugge/ t ! numb] ( absolutely d>k />s 9 ! sky is relatively small4 ,o!r l9es ( evid5ce lead to ! same conclusion4 ,if a /> ceas$ to %9e1 its gravitational pull w\ld /ill betray its exi/5ce4 ,al?\gh we c\ld n detect a s+le d>k /> 9 ?is way1 we c\ld detect a multitude4 ,if a great proportion ( />s 7 d>k1 we %\ld probably suspect ! exi/5ce ( ! d>k />s f _! effects on ! motions ( ! rema9d]1 s t g5]al gravitational consid]ations preclude ! possibility ( !re be+ a great numb] ( d>k />s4 ,s f> z our pres5t k goes1 ! temp]ature ( /ell> surfaces ranges1 9 ! ma91 f ab\t #cj1jjj degrees d[n to ab\t #bejj1 ! l[] limit be+ ext5d$ to ab\t #afej = long-p]iod v>iables at _! l[e/ temp]atures4 ,ap>t f ! long-p]iod v>iables1 ?is is only a #ab to #a range1 s t ! temp]atures ( ! />s are m uni=m ?an ei!r _! lum9osities or _! weights4 ,we mu/1 h[ev]1 rememb] t a />'s radiation p] squ>e in* is f> m fundam5tal ?an its surface-temp]ature1 & t a #ab to #a range 9 ! latt] involves a range ( ov] #bj1jjj to #a 9 ! =m]4 ,if we include ! long-p]iod v>iables1 !re is a range ( ab\t #aaj1jjj to #a 9 ! emission ( radiation p] squ>e in*4 ,9 t]ms ( horse-p[]1 ! sun emits en]gy at ! rate ( #ej horse-p[] p] squ>e in*1 a /> ) a surface-temp]ature ( #afej degrees emits only #jce horse-p[] p] squ>e in*1 :ile ,plaskett's />1 ) a surface-temp]ature ( #bh1jjj degrees1 emits ab\t #bh1jjj horse-p[] p] squ>e in*4 ,9 pla9 ,engli%1 ea* squ>e in* ( ?is la/ /> p\rs out en\gh en]gy to keep an ,atlantic l9] go+ at full spe$1 h\r aft] h\r1 & c5tury aft] c5tury4 ,& ! en]gy emitt$ p] squ>e in* by ! surfaces ( v>i\s />s cov]s ! :ole range f ! p[] ( a l9] to t ( a man 9 a r[-boat4 ,,size4 ,! f\r />s ( l>ge/ kn[n diamet] are ! foll[+3 ---------------------------------------- -- ,/> ,diamet] 9 ,diamet] t]ms ( sun 9 miles ---------------------------------------- -- ,ant>es #dej #cij1jjj1jjj ,h]culis ab\t #djj #cdf1jjj1jjj ,ceti 7at max47 #cjj #bfj1jjj1jjj ,betelgeux 7av]age7 #bej #baf1jjj1jjj ---------------------------------------- -- ,all ^! diamet]s h be5 measur$ directly by ! int]f]omet]4 ,on ! scale us$ 9 figs4 #ag to #bj1 9 :i* ! sun is ab\t ! size ( a sixp5ce1 ! circle necess>y to repres5t ,ceti w\ld be z l>ge z ! floor ( a good-siz$ room1 :ile ! second /> ( ! sy/em 7= ,ceti is b9>y7 w\ld be ! size ( a gra9 ( s&4 ,we may obta9 "s idea ( ! imm5se size ( ^! />s by notic+ t e "o ( _! diamet]s is l>g] ?an ! diamet] ( ! e>?'s orbit1 s t if ! sun 7 to exp& to ! size ( any "o ( !m we %\ld f9d ourselves inside x4 ,^! />s mu/ be exce$+ly t5u\s4 ,ant>es1 = in/ance1 occupies #ij1jjj1jjj times z mu* space z ! sun1 s t if its sub/ance 7 z closely pack$1 x w\ld weigh #ij1jjj1jjj times z mu* z ! sun4 ,yet1 9 actual fact1 x probably has only ab\t #dj or #ej times ! sun's weight1 ! diff]5ce betwe5 ?is numb] & #ij1jjj1jjj aris+ f ! diff]5ce betwe5 ! d5sities ( ,ant>es & ! sun4 ,on ! av]age a ton ( matt] 9 ! sun occupies consid]ably less ?an a cubic y>d2 9 ,ant>es x occupies r m space ?an ! int]ior ( ,sa9t ,paul's ,ca!dral4 ,yet a detail$ /udy ( /ell> int]iors %ews t we c atta* b little mean+ to an av]age ( ?is sort4 ,x is q likely t matt] at ! c5tre ( ,ant>es is pack$ ne>ly 7b n q7 z closely z matt] at ! c5tre ( ! sun 7p4 #bia bel[74 ,! huge size ( ,ant>es is probably due ma9ly to an enorm\sly ext5d$ atmosph]e ( v t5u\s gas1 & !re is n mu* po9t 9 /rik+ an av]age betwe5 ?is & ! compact matt] at ! c5tre ( ! />4 ,! my/]i\s objects kn[n z planet>y nebulae1 ( :i* examples are %ewn 9 ,plate ,,ii 7p4 #bh71 ought p]haps to be reg>d$ z />s ( /ill l>g] diamet]4 ,at ! c5tre ( ea* ( ^! ! telescope discloses a comp>atively fa9t /> ) an extremely high surface-temp]ature4 ,surr\nd+ ?is is ! nebulosity f :i* ^! objects d]ive _! some:at un=tunate "n4 ,?is is 9 all probability m]ely an atmosph]e ( ev5 great] ext5t ?an t surr\nd+ ! f\r />s ( our table4 ,van ,maan5 e/imates ! diamet] ( ! nebulosity ( ! ,r+ ,nebula 9 ,lyra 7fig4 #b ( ,plate ,,ii7 to be #egj times t ( ! e>?'s orbit1 or ab\t #ajf1jjj1jjj1jjj miles4 ,?is nebulosity1 h[ev]1 diff]s f ! atmosph]e ( an ord9>y /> 9 be+ v ne>ly transp>5t2 we c see ?r\gh #ajf1jjj1jjj1jjj miles ( ! ,r+ ,nebula b c only see a few t5s or hundr$s ( miles into an ord9>y />4 ,at ! o!r extreme ( size1 ! smalle/ kn[n />1 van ,maan5's /> 7p4 #bfh7 is j ab\t z l>ge z ! e>?2 ov] a million su* />s c\ld be pack$ inside ! sun & /ill leave room to sp>e4 ,& yet its weight is 9 all probability comp>able1 n ) t ( ! e>?1 b ) t ( ! sun2 at a guess x may h ab\t a fif? ( ! sun's weight4 ,to pack a fif? ( ! sun's sub/ance inside a globe ( ! size ( ! e>?1 ! av]age ton ( matt] mu/ be pack$ into a space ( ab\t ! size ( a small *]ry--t5 tons or s to ! cubic in*4 ,! solidity ( ! e>? sugge/s t its atoms mu/ be pack$ pretty closely toge!r1 b ! atoms 9 van ,maan5's /> mu/ be pack$ #ff1jjj times m closely4 ,h[ is x done8 ,z we %all %ortly see1 !re is only "o possible answ]4 ,! atom consi/s mo/ly ( empt9ess--we comp>$ ! c>bon atom to six wasps buzz+ ab\t 9 ,wat]loo ,/ation4 ,let u break ! atom up into its con/itu5t p>ts1 pack ^! toge!r z closely z !y w g1 & we see ! way 9 :i* matt] is pack$ 9 van ,maan5's />4 ,six wasps :i* c roam ?r\gh\t ! :ole ( ,wat]loo ,/ation c nev]!less be pack$ inside a v small box4 ,,giants ,,& ,,dw>fs4 ,!re is a cont9u\s s]ies ( />s betwe5 ! limits ( weight we h m5tion$1 & ! same is true ( ! limits ( temp]ature 7& s also ( col\r7 & ( size4 ,illu/ration3 ,fig4 #ba4 ,/>s ( diff]5t col\rs arrang$ 9 ord] ( lum9osity4 ,)9 ^! specifi$ limits1 ,i c f9d y a /> ( any weight or ( any col\r or ( any size y l4 ,b ?is does n mean t y may specify ! weight & col\r & size ( ! /> y want1 & t ,i w und]take to f9d x = y2 if ! weight is "r ! col\r may be wrong1 & s on4 ,= in/ance1 if y ask = a r$ /> ,i c f9d y a v heavy "o or a v light "o1 b x is no good y\r ask+ = "o ( int]m$iate weight4 ,s f> z we "k1 r$ />s ( int]m$iate weight simply d n exi/4 ,! same is true z reg>ds size--!re are no r$ />s ( int]m$iate size4 ,h]tzsprung notic$ 9 #aije t ! r$ />s c\ld be divid$ %>ply into two di/9ct classes *>act]is$ by l>ge & small size--he call$ !m ,giants & ,dw>fs4 ,russell1 /udy+ ! "q fur!r 9 #aiac1 confirm$ ,h]tzsprung's e>li] conclusions1 & %ew$ t ! giant-dw>f division ext5d$ to />s ( o!r col\rs ?an r$4 ,imag9e t we h a s]ies ( col\r$ ladd]s1 "o = ea* col\r ( />--r$1 orange1 etc4 ,take all ! r$ />s & /& !m 79 imag9ation7 on ! diff]5t rungs ( ! r$ ladd]4 ,d n m]ely place !m on at r&om2 arrange !m 9 ord] ( _! lum9osities1 plac+ ^? ( highe/ lum9osity upp]-mo/4 ,fur!r let sev]al />s /& on ! same rung if _! lum9osities are ab\t equal4 ,to make ! arrangem5t def9ite1 let ea* rung ( ! ladd] repres5t #e times high] lum9osity ?an ! rung imm$iately bel[ x1 s t ea* rung has a def9ite lum9osity associat$ ) x#be4 #be ,= purely practical reasons ! height is n tak5 proportional to ! lum9osity b to its log>i?m2 )\t "s su* device z ?is x w\ld be impossible to repres5t ! range ( m ?an #a1jjj1jjj to #a 9 ! obs]v$ lum9osities ( r$ />s4 ,) ?is agreem5t we are n[ ready to proce$4 ,we take our r$ />s & place ea* on ! appropriate rung ( ! r$ ladd]1 & s on = ea* o!r col\r4 ,! result is %ewn diagrammatically 9 fig4 #ba1 ! diff]5t />s be+ repres5t$ by crosses4 ,! r$ />s w be f\nd to lie z on ! "r ( ! diagram1 ,h]tzsprung's division into giants & dw>fs be+ v cle>ly m>k$4 ,! orange />s lie z on ! next ladd] to ! left2 z ,russell f\nd1 ! division aga9 appe>s1 b is less m>k$4 ,,! ,,russell ,,diagram4 ,let u make ladd] diagrams ( ?is k9d = ea* col\r ( />1 & put !m side by side 9 _! prop] ord]1 s z to repres5t />s ( all possible col\rs4 ,we obta9 a diagram ( ! k9d %ewn 9 fig4 #bb4 ,?is type ( diagram 0 introduc$ by ,russell 9 #aiac1 & is n[ g5]ally kn[n z a ,russell diagram4 ,! lett]s at ! top ( ! diagram repres5t spectral types ( />s1 because ^! provide a bett] & m exact work+ classification ?an ! names ( col\rs4 ,! col\rs :i* approximately correspond to ! v>i\s spectral types are indicat$ at ! bottom ( ! diagram4 ,only a v few sample />s are %ewn1 b all kn[n />s are f\nd to be conc5trat$ ar\nd ! positions ( ^! few typical />s4 ,broadly speak+1 !re are two di/9ct & disconnect$ regions :i* are occupi$ by />s4 ,fir/1 & mo/ important1 is a region %ap$ r l a rev]s$ 3 ! c5tral l9e ( ?is region is m>k$ 9 by a cont9u\s ?ick l9e1 foll[+ a det]m9ation ( its position by ,r$man4 ,second1 !re is a small] region ne> ! left-h& bottom corn] ( ! diagram4 ,! />s :i* occupy ?is region are v fa9t1 & h f> high] surface-temp]atures ?an o!r />s ( simil> lum9osity4 ,we h already se5 h[ a />'s diamet] c be calculat$ f its surface-temp]ature & lum9osity4 ,?is am\nts to ! same ?+ z say+ t two />s :i* occupy ! same position 9 ! ,russell diagram mu/ h ! same diamet]4 ,?us !re is a def9ite diamet] associat$ ) ea* po9t 9 ! diagram1 & we c map out /ell> diamet]s 9 ! diagram1 j z we c map out heights above sea-level on a geographical map1 by a sy/em ( 8cont\r l9es40 ,9 ! pres5t case ! 8cont\r l9es0 prove to be a sy/em ( almo/ p>allel curves4 ,^! lie r\ghly z %ewn by ! brok5 l9es 9 fig4 #bb1 all />s ly+ on any "o l9e hav+ ! same diamet]4 ,illu/ration3 ,fig4 #bb4 ,! ,russell diagram4 ,?is diagram ?r[s a flood ( light on ! g5]al "q ( /ell> diamet]s4 ,we see at once t />s ( ! bigge/ diamet]s--#ajj times ! sun's diamet] or m--mu/ necess>ily be r$ />s ( high lum9osity4 ,& 9 actual fact ! />s ( l>ge diamet] %ewn 9 ! table on p4 #bgb are all r$ & h v high lum9osities2 !y are r$ giants4 ,! majority ( ! />s 9 ! sky lie 9 ! belt :i* runs across ! diagram ( fig4 #bb f top left-h& to bottom "r-h&4 ,?is is kn[n z ! 8ma9-sequ5ce40 ,! position ( ?is b& ) ref]5ce to ! 8cont\r l9es0 ( diamet]s %ews t ma9-sequ5ce />s are ( mod]ate diamet]s4 ,! brighte/ ( all may h tw5ty times ! diamet] ( ! sun1 :ile ! fa9te/ may h only ab\t a tw5tie? ( ! sun's diamet]1 b !y all h diamet]s :i* are at lea/ comp>able ) t ( ! sun4 ,! sample ( />s f ne> ! sun1 :i* we h already discuss$1 provides _m in/ances ( ma9-sequ5ce />s2 we h1 9 ord] ( decreas+ lum9osity3 ------------------------------------- ,/> ,lum9osity,diamet] 79 t]ms ( sun7 ------------------------------------- ,sirius ,a #bfc #aeh ,procyon ,a #ee #ahj ,c5tauri ,a #aab #ajg ,sun #ajj #ajj ,c5tauri ,b #jcb #abb ,ceti #jcb #jie ,indi #jae #jhb ,krug] #fj ,a #jjjbf #jcc 0 ,b #jjjjg #jag ,wolf #cei #jjjjjb #jjc ------------------------------------- ,?is table %ews cle>ly h[ /ell> lum9osity & diamet] decrease toge!r z we pass d[n ! ma9-sequ5ce4 ,! rema9+ gr\p ( />s 9 fig4 #bb1 ^? 9 ! bottom left-h& corn]1 are g5]ally kn[n z 8:ite dw>fs40 ,_! position 9 ! diagram %ews t _! diamet]s mu/ be excessively small4 ,! vic9ity ( ! sun provides ?ree examples ( ?is class ( />1 z %ewn 9 ! foll[+ table3 ---------------------------------------- --------- ,/> ,lum9osity ,diamet] 79 t]ms ( sun7 ---------------------------------------- --------- ,sirius ,b #jjjbf #jjc ,eridani ,b #jjjca #jjah van ,maan5's /> #jjjjaf #jjji ---------------------------------------- --------- ,9 addition to ^!1 ! fa9t companion ( ,ceti is c]ta9ly a :ite dw>f1 :ile ,procyon ,b may be4 ,^! are ! only kn[n examples ( :ite dw>fs1 b ! extreme fa9tness ( ^! />s makes !m v difficult ( detection1 s t x is q likely t !y are fairly frequ5t objects 9 space4 ,9 ! table on p4 #bgi1 ! ma9-sequ5ce />s 7 int5d$ to be arrang$ 9 ! ord] ( lum9osity1 b ?is happ5s also to be ! ord] ( weights4 ,! weights ( ?ree ( ! />s are unkn[n2 ^? ( ! rema9d] are z foll[s3 ---------------------------------------- --------- ,/> ,lum9osity ,weight 79 t]ms ( sun7 ---------------------------------------- --------- ,sirius ,a #bfc #bde ,procyon ,a #ee #abd ,c5tauri ,a #aab #aad ,sun #ajj #ajj ,c5tauri ,b #jcb #jig ,krug] #fj ,a #jjjbf #jbe 0 ,b #jjjjg #jbj ---------------------------------------- --------- ,l ! lum9osities1 ! weights fall (f /eadily z we pass d[n ! ma9-sequ5ce1 al?\gh1 z already rem>k$1 weight falls f> less rapidly ?an lum9osity4 ,! only />s ^: weights c be measur$ directly are ! compon5ts ( b9>y sy/ems1 & ^! are relatively few 9 numb]4 ,se>es f\nd1 h[ev]1 t ! weights ( b9>y sy/ems con=m$ to ! law ( equip>tition ( en]gy already expla9$ 9 ,*apt] ,,iii1 s t x is highly probable t o!r />s :i* are n b9>y also con=m1 = x is difficult to imag9e any reason :y b9>y sy/ems %\ld atta9 to a /ate ( equip>tition soon] ?an o!r />s4 ,x w be rememb]$ t ?is /ate is def9$ by a purely /ati/ical law connect+ ! weights & spe$s ( motion ( />s1 s t ! fact t a sy/em ( />s has atta9$ ?is /ate c give no in=mation z to ! weight ( an individual /> ^: spe$ is kn[n1 b x makes x possible to det]m9e ! av]age weight ( any gr\p ( />s 9 t]ms ( _! av]age spe$s ( motion4 ,9 ?is way ,se>es has det]m9$ ! av]age weights ( />s ( diff]5t assign$ lum9osities & spectral types--9 o!r words1 ! av]age weights ( ! />s repres5t$ at ! v>i\s po9ts 9 ! diagram ( fig4 #bb4 ,! results he obta9$ are %ewn by ! ?ick curv$ l9es 9 fig4 #bc4 ,! arrangem5t ( ^! curves confirms ! inf]5ce we h drawn f a few select$ />s2 ! weight ( ma9-sequ5ce />s falls (f /eadily z we pass d[n ! sequ5ce f high lum9osity to l[4 ,^! curv$ l9es specify ! av]age weight ( ! />s repres5t$ at ea* po9t 9 ! ,russell diagram1 & ! diamet]s are already kn[n f fig4 #bb4 ,f ^! two data ! mean d5sity ( ! /> c ( c\rse be calculat$4 ,! mean d5sities z calculat$ by ,se>es are %ewn by ! brok5 l9es 9 fig4 #bc4 ,illu/ration3 ,fig4 #bc4 ,/ell> weights & d5sities 9 ! ,russell diagram1 accord+ to ,se>es4 ,?is completes our collection ( obs]vational mat]ial4 ,we n[ turn to ! f> m difficult problem ( discuss+ :at x all means4 ,"h we leave ! firm gr\nd ( asc]ta9$ fact1 to ent] ! %ad[y morasses ( conjecture1 hypo!sis & speculation4 ,! que/ions we %all discuss are "s ( ! mo/ int]e/+ 9 ! :ole ( a/ronomy1 to :i* x mu/ be admitt$ t sci5ce has s f> obta9$ only lam5tably du/y answ]s4 ,! read] :o is hot = c]ta9ties may pref] to read some?+ o!r ?an ! rema9d] ( ! pres5t *apt]4 ,,! ,,physical ,,condition ,,( ,,! ,,/>s ,! =ego+ collection ( obs]vational data has provid$ abundant pro( t />s to c]ta9 specifications d n exi/ at all4 ,to put ! same ?+ 9 ano!r way1 !re are c]ta9 regions 9 ! ,russell diagram :i* are :olly unoccupi$ by />s4 ,to take ! mo/ conspicu\s in/ance ( all1 !re are no />s at all to ! left ( ! ma9-sequ5ce 9 ! ,russell diagram 7fig4 #bb71 until we come to ! q deta*$ gr\p ( :ite dw>fs4 ,:y are !re no />s 9 int]m$iate conditions8 ,:y1 to make ! example /ill m precise1 does no /> exi/ ( ! same col\r z ,sirius b ) only a t5? ( its lum9osity8 ,:y d we h to g d[n to ! :ite dw>f ,eridani ,b1 ) a lum9osity ( only a t5-?\s&? ( t ( ,sirius1 be=e we c f9d a /> to mat* ,sirius 9 col\r8 ,a hypo!sis :i* occurs naturally to ! m9d is t ! ma9-sequ5ce />s & ! :ite dw>fs may =m di/9ct gr\ps because !y are ( entirely diff]5t ages--!y may repres5t di/9ct creations4 ,z />s age !y decrease 9 weight & 9 lum9osity1 s t x is natural to int]pret ! small weights & extremely l[ lum9osity ( ! :ite dw>fs z evid5ce ( an age f> great] ?an ! age ( ! normal ma9-sequ5ce />s4 ,yet ?is hypo!sis does n appe> to be t5able4 ,) ! s+le exception ( van ,maan5's />1 e /> :i* is ei!r kn[n or suspect$ to be a :ite dw>f =ms "o compon5t ( a b9>y sy/em1 & 9 e case its companion is a ma9-sequ5ce /> or 79 ! case ( ,ceti7 a r$ giant4 ,we h already se5 h[ r>e x is = two />s to approa* ne> to "o ano!r 9 space4 ,x mu/ be an almo/ inconceivably r>e ev5t = two />s1 orig9ally mov+ z indep5d5t bodies1 s to meet 9 _! r&om w&]+s1 t ! big "o 8captures0 ! little "o1 & !y h5ce=? j\rney toge!r ?r\gh space4 ,= x c be %ewn t1 = su* an ev5t to occur1 some?+ m ?an a close approa* is ne$$2 a close approa* mu/ take place 9 ! pres5ce ( yet a ?ird />1 s t no few] ?an ?ree />s mu/ *ance to come ne> "o ano!r simultane\sly 9 _! w&]+s ?r\gh ! va/ empt9esses ( space4 ,x is almo/ inconceivable t ?is %\ld happ5 9 a s+le in/ance1 b x is /ra9+ ! probabilities too f> to suppose t x has happ5$ 9 ! case ( e s+le kn[n :ite dw>f b "o4 ,?us we h to suppose t ! :ite dw>fs & _! m normal companions h be5 toge!r s9ce bir?1 & s 7 born at ! same "t out ( ! same nebula4 ,! diff]5ce betwe5 :ite dw>fs & ma9-sequ5ce />s _c1 !n1 be a m]e diff]5ce ( age1 & x w\ld seem z ?\gh !re mu/ be "s physical reason militat+ aga9/ ! exi/5ce ( />s 9 int]m$iate conditions4 ,tak+ a m g5]al view ( ! "q1 we are l$ to inve/igate :e!r ! abs5ce ( />s built to c]ta9 specifications c be attribut$ to su* />s ne$+ physical prop]ties :i* nature _c provide4 ,?is leads directly into ! g5]al "q ( ! /ructure & me*anism ( ! />s4 ,,! ,,int]nal ,,con/itution ,,( ,,! ,,/>s ,mo/ inve/igations on ! /ructure ( ! />s h proce$$ on ! supposition t _! int]iors are gase\s ?r\gh\t4 ,)\t accept+ ?is supposition z f9al tru?1 we may adopt x = ! mom5t1 = ! purely opportuni/ reason t x provides ! mo/ conv5i5t l9e ( approa* to an excessively difficult problem4 ,a ma!matical !orem1 g5]ally kn[n z ,po9c>'s !orem1 proves to be ( ! utmo/ s]vice 9 discuss+ ! int]nal /ate ( a gase\s />4 ,we h se5 h[ ,helmholtz ?\ght t ! en]gy ( ! sun's radiation might come f ! sun's contraction1 ea* lay] fall+ 9 ^u ! next inn] lay] z ! latt] %runk1 & trans=m+ ! en]gy set free by its fall into heat & light4 ,x is easy to e/imate h[ mu* en]gy w\ld be set free by a contraction ( ?is k9d4 ,= in/ance1 ,"l ,kelv9 calculat$ t ! contraction ( ! sun1 z x %runk f inf9ite size to its pres5t diamet] ( #hfe1jjj miles1 w\ld lib]ate ab\t z mu* en]gy z ! sun n[ radiates 9 #ej million ye>s4 ,9 t]ms ( ergs1 ! sun's %r9kage w\ld lib]ate #f #aj ergs ( en]gy4 ,po9c>'s !orem /ates t ! total en]gy ( motion ( all ! molecules 9 any gase\s /> :atev] is equal to precisely half ! total en]gy :i* ! /> w\ld h lib]at$ 9 %r9k+ d[n to its pres5t size4 ,! !orem is true q indep5d5tly ( :e!r ! /> ev] has s %runk or n3 no?+ is involv$ b ! pres5t /ate ( ! />4 ,"o int]e/+ consequ5ce is t ! fur!r a gase\s /> %r9ks1 ! hott] x becomes2 if a /> %r9ks to half its pres5t size1 ! total en]gy set free by its %r9kage f inf9ite size is d\bl$1 s t ! total en]gy ( motion ( its molecules is d\bl$1 & !re=e its av]age temp]ature is d\bl$4 ,?is is a special case ( :at is g5]ally kn[n z ,lane's law4 ,let u g on ) our calculation = ! special case ( ! sun4 ,po9c>'s !orem tells u t1 if ! sun is gase\s1 ! total en]gy ( motion ( all its molecules is #c #aj ergs4 ,! next ?+ we want to "k is h[ _m molecules !re are 9 ! sun4 ,! sun's weight is #b #aj grammes1 b h[ _m molecules are !re to a gramme8 ,! answ] ( c\rse dep5ds on ! type ( molecule conc]n$2 !re are #c #aj molecules 9 a gramme ( hydrog51 #b #aj 9 a gramme ( air & only #be #aj 9 a gramme ( uranium4 ,if we suppose ! sun to be made ( air1 x mu/ consi/ ( #d #aj molecules1 s t ! av]age en]gy ( motion ( ea* molecule mu/ be #ge #aj ergs1 & ?is repres5ts an av]age temp]ature1 = ! sun's int]ior1 ( #cge million degrees4 ,9 #aijg ,emd51 by a diff]5t calculation1 f\nd t if ! sun 7 made ( air1 ! temp]ature at its c5tre w\ld be #dee million degrees4 ,ap>t f details1 x is cle> t ! int]ior temp]ature ( a sun made ( air w\ld be "o ( hundr$s ( millions ( degrees4 ,s f> all /udy ( /ell> int]iors _h proce$$ on ! supposition t ! />s 7 =m$ ( complete atoms or ev5 molecules4 ,9 #aiag1 ,i made a simple calculation1 ( ! type already expla9$ on p4 #ada1 & f\nd t ! quanta ( radiation :i* fly ab\t at su* temp]atures w\ld be en]getic en\gh n m]ely to break up ! molecules ( air into atoms1 b also to /rip all1 or ne>ly all1 ( ! electrons f ! atoms4 ,at su* temp]atures ea* molecule ( air w\ld break up into its con/itu5t nuclei & electrons j z surely z1 on a hot day1 a lump ( ice breaks up into its con/itu5t molecules4 ,! electric =ces :i*1 9 quiet] surr\nd+s1 w\ld unite ! electrons & nuclei1 fir/ into atoms & !n into complete molecules1 f9d !mselves p[]less aga9/ ! incessant hail ( rapidly mov+ projectiles & ! %att]+ bl[s ( quanta ( high en]gy2 x w\ld be l try+ to build a h\se ( c>ds 9 a hurricane4 ,a sun consi/+ ( molecules ( air proves to be an inconsi/5cy1 a contradiction2 our hypo!sis has defeat$ itself1 & we mu/ />t aga9 f ! beg9n+4 ,we may />t :]ev] we l1 b ! conclusion :i* we mu/ f9ally rea* is t1 no matt] :at k9d ( molecules ! sun consi/s (1 ! heat at ! sun's c5tre w break !m up1 ei!r completely or ne>ly s1 into _! con/itu5t nuclei & electrons4 ,! same is true = all o!r />s1 & ?is introduces an extreme simplification into ! problem ( ! int]ior con/itution ( ! />s4 ,we _c say h[ _m complete molecules !re are to a gramme )\t kn[+ ! nature ( ! molecules1 b once let ^! molecules be brok5 up into _! con/itu5t p>ts1 & we "k at once ! total numb] ( con/itu5t p>ts1 nuclei & electrons1 :i* g to make up a gramme4 ,=1 ! atomic weights ( all elem5ts except hydrog5 are ne>ly d\ble _! atomic numb]s 7p4 #aaj74 ,h5ce1 z ,edd+ton fir/ po9t$ out1 ! total numb] ( nuclei & protons 9 a fully brok5-up atom ( any sub/ance except hydrog5 mu/ be equal to ab\t half ! atomic weight ( ! atom4 ,we may probably disreg>d ! possibility ( a /> consi/+ to any great ext5t ( hydrog54 ,if s1 ! numb] ( con/itu5t p>ts 9 a gramme ( fully brok5-up /ell> matt] mu/ be ab\t #c #aj1 reg>dless ( ! type ( molecule f :i* ^! p>ts orig9ate4 ,& :5 we "k ! total numb] ( su* p>ts 9 any />1 x becomes easy to calculate ! temp]ature ( ! />'s int]ior1 ei!r f ! !orem ( ,po9c> j m5tion$ or o!rwise4 ,! temp]ature w be ! same z ?\gh ! /> 7 made ( unbrok5 molecules ( hydrog54 ,emd5 calculat$ 9 #aijg t ! c5tral temp]ature ( a sun ( ?is k9d w\ld be ab\t #ca1ejj1jjj degrees4 ,lat] & m ref9$ calculations by ,edd+ton l$ to an almo/ id5tical temp]ature1 b "s /ill lat] calculations ( my own give ! sub/antially high] figure ( #ee1jjj1jjj degrees4 ,!re is no ne$ = ! mom5t to discuss :i* ( ^! figures is ne>e/ ! tru?4 ,_! div]sity w indicate :at k9d ( degree ( unc]ta9ty atta*es to all calculations ( ?is type4 ,x is easy to see ! physical necessity = ?is high temp]ature4 ,! heat :i* fl[s away f ! sun's surface mu/ fir/ h be5 br\ght !re f its int]ior4 ,heat only fl[s f a hott] to a cool] place1 & a vigor\s fl[ ( heat is evid5ce ( a /eep temp]ature gradi5t4 ,! temp]ature mu/ rise %>ply z we pass f ! sun's surface t[>ds its c5tre1 & ?is rise1 cont9u$ along ! :ole #dcc1jjj miles to ! c5tre1 mu/ result 9 a v high temp]ature inde$ be+ rea*$ !re4 ,! calculat$ c5tral temp]ature ( #cj to #fj million degrees s f> transc5ds our exp]i5ce t x is difficult to realise :at x means4 ,let u1 9 imag9ation1 keep a cubic millimetre ( ord9>y matt]--a piece ! size ( an ord9>y p9-head--at a temp]ature ( #ej1jjj1jjj degrees1 ! approximate temp]ature at ! c5tre ( ! sun4 ,incr$ible ?\gh x may seem1 m]ely to ma9ta9 ?is p9-head ( matt] at su* a temp]ature--i4e4 to repl5i% ! en]gy x loses by radiation f its six faces--w ne$ all ! en]gy g5]at$ by an eng9e ( ?ree ?\s& million million horse-p[]2 ! p9-head ( matt] w\ld emit en\gh heat to kill anyone :o v5tur$ )9 a ?\s& miles ( x4 ,high ?\gh ?is temp]ature is1 calculations %ew t x w\ld n suffice to break up ! /ell> molecules completely4 ,x w\ld /rip ! atoms ( all _! electrons d[n to ! ,k-r+s 7p4 #acd71 b ^! w\ld rema9 intact4 ,x ne$s temp]atures ev5 high] ?an ^? we are n[ consid]+ to /rip ! ,k-r+ electrons f ! nucleus ( an atom4 ,?is result is true = ! :ole range1 f ab\t #cj to #fj million degrees1 )9 :i* ! temp]ature ( ! sun's c5tre is at all likely to lie1 & x is true almo/ indep5d5tly ( ! atomic weight or atomic numb] ( ! atoms ( :i* we suppose ! sun to be built4 ,?us if ! sun is :olly gase\s1 its c5tral p>ts mu/ consi/ ( a collection ( atoms /ripp$ d[n to _! ,k-r+s1 b n beyond1 fly+ ab\t indep5d5tly l ! molecules ( a gas1 & ) !m1 also fly+ ab\t l ! molecules ( a gas1 all ! /ripp$-(f electrons :i* orig9ally =m$ ! ,l-r+1 ! ,m-r+1 etc41 ( ! atoms1 ! :ole be+ at a temp]ature ( some:]e betwe5 #cj & #fj million degrees4 ,z we pass outw>ds t[>ds ! sun's surface we come to l[] temp]atures1 at :i* ! atoms are less completely brok5 up4 ,f9ally1 close to ! sun's surface1 we may meet atoms :i* are completely =m$ except p]haps = "o or two ( _! out]mo/ electrons4 ,9 ! surfaces ( ! coole/ />s ( all1 we ev5 f9d complete molecules1 z1 = example1 ! molecules ( titanium oxide & magnesium hydride1 :i* %ew !mselves 9 ! spectra ( ! r$ />s4 ,:5 ! int]nal con/itution ( o!r />s is inve/igat$ 9 ! same way1 all ma9-sequ5ce />s are f\nd to h ab\t ! same c5tral temp]atures z ! sun4 ,moreov]1 ?is is n ! only prop]ty :i* !y h 9 common4 ,fig4 #bc1 :i* exhibits ,se>es' calculations ( mean /ell> d5sities1 %ews t ! mean d5sities ( ma9-sequ5ce />s are all approximately ! same1 except = comp>atively small deviations at ! two extremities4 ,! mean d5sity ( ! sun is #ad1 :i* means t ! av]age cubic metre 9 ! sun conta9s #ad ton ( matt]4 ,at ! sun's c5tre1 ! d5sity is ab\t #ajj times ?is1 s t a cubic metre !re conta9s ab\t #adj tons ( matt]4 ,= comp>ison1 a cubic metre ( lead conta9s only ab\t #aa tons4 ,if all />s 7 built on ! same model z ! sun1 any two />s :i* _h ! same mean d5sity w\ld also h equal d5sities at _! c5tres4 ,b 9 />s hav+ sev]al times ! weight ( ! sun1 a new factor comes into play1 namely pressure ( radiation--! pressure :i* radiation ex]ts 9 virtue ( ! weight x c>ries ab\t ) x4 ,9 mo/ />s ?is pressure is insignificant 9 comp>ison ) ! pressure produc$ by ! impact ( mat]ial atoms & electrons1 b 9 v massive />s x is l>ge en\gh to influ5ce ! /ructure ( ! />4 ,x is to ?is t ! v massive />s ^: diamet]s are tabulat$ on p4 #bgb owe _! abnormally l>ge size4 ,x is a g5]al consequ5ce ( ! di/urb+ effects ( radiation-pressure1 t ! weight ( a v massive /> is f> m conc5trat$ 9 its c5tral regions ?an t ( a light] />1 s t if a light & a massive /> h ! same av]age d5sity1 ! latt] w h by f> ! high] d5sity at its c5tre4 ,:5 ?is di/urb+ factor is all[$ =1 all />s 9 ! upp] "p ( ! ma9-sequ5ce are f\nd to h approximately ! same d5sities 9 _! c5tral regions1 a d5sity ab\t equal to t at ! c5tre ( ! sun1 :i* we may e/imate at #adj tons to ! cubic metre4 ,& we h already se5 t ! c5tral regions ( ^! />s h also approximately ! same temp]atures z ! c5tre ( ! sun1 :5ce x foll[s t _! physical conditions are all sub/antially ! same4 ,?us ! atoms 9 ! c5tral regions ( all ^! />s mu/ be brok5 d[n to ! same ext5t z ! atoms 9 ! c5tral regions ( ! sun4 ,! ,k-r+s ( electrons survive intact1 b ! out] r+s are trans=m$ into a hail ( electrons fly+ ab\t l indep5d5t molecules4 ,) suffici5t accuracy = our pres5t purpose1 all ! />s on ! ma9-sequ5ce1 except p]haps ^? at its extreme l[] end1 may be suppos$ to be 9 ! same physical condition4 ,on acc\nt ( ?is prop]ty1 ! ma9-sequ5ce =ms an admirable base-l9e f :i* to c>ry out a survey ( ! ,russell diagram 9 respect ( ! physical conditions ( /ell> int]iors4 ,fig4 #bb %ews t a /> to ! "r ( ! ma9-sequ5ce has a great] diamet] ?an a ma9-sequ5ce /> ( ! same weight4 ,consequ5tly ! en]gy x w\ld emit 9 %r9k+ to its pres5t diamet] is less1 & h5ce its molecul> en]gy ( motion is less 7by ,po9c>'s !orem74 ,x foll[s t its int]nal temp]atures are l[]1 & its atoms are less completely brok5 up4 ,r$ giants su* z ,ant>es are f\nd only to h c5tral temp]atures ( f "o to five million degrees1 & _! atoms probably reta9 intact n only _! ,k-r+s ( electrons1 b also _! ,l-r+s & "p at lea/ ( _! ,m-r+s4 ,to ! left ( ! ma9-sequ5ce we come to a region 9 :i* />s1 if !y occurr$ at all1 w\ld h %runk fur!r1 & s w\ld h high] temp]atures & m ?or\ghly brok5 atoms4 ,actually no />s are enc\nt]$ until we come to ! :ite dw>fs4 ,calculation %ews t ! c5tral temp]atures ( ^! mu/ be _m hundr$s ( millions ( degrees at lea/1 & t _! atoms mu/ be /ripp$ ( electrons "r d[n to ! nuclei4 ,except = a small numb] ( atoms :i* may h escap$ ?is g5]al fate1 ! /ell> matt] mu/ consi/ ( nuclei /ripp$ absolutely b>e1 & ( free electrons1 all fly+ indep5d5tly ?r\gh ! />4 ,! high d5sities ( ^! />s provide a conv9c+ pro( ( ! accuracy ( ?is result4 ,! mean d5sity ( ,sirius ,b is c]ta9ly ov] #ej1jjj1 :ile t ( van ,maan5's /> is probably ov] #cjj1jjj4 ,!re is no way 9 :i* matt] c be pack$ z closely z ?is1 except t ( /ripp+ ! atoms ( electrons "r d[n to _! b>e nuclei4 ,! cle>e/ g5]al impression we c =m ( ! ,russell diagram 9 t]ms ( physical condition is probably obta9$ z foll[s3 ,we ?9k fir/ ( two deta*$ b&s ( />s1 "o1 ! :ite dw>f gr\p1 =m$ by />s 9 :i* all ! electrons are torn (f ! atoms2 & ! o!r1 ! ma9-sequ5ce1 =m$ ( />s 9 :i* ! atoms are /ill surr\nd$ by _! ,k-r+s ( electrons1 :ile ! ext]ior r+s h be5 torn (f4 ,/>t+ f ab\t ! middle ( ! ma9-sequ5ce is ! spur bran* lead+ up to ! r$ giants1 z %ewn 9 fig4 #bb4 ,z we pass along ?is1 ! int]nal temp]atures ( ! />s decrease1 s t ! /ell> atoms are less brok5 up ?an 9 ma9-sequ5ce />s4 ,9 ! r$ giants at ! extreme end1 ev5 ,m-r+ electrons may /ill rema94 ,,russell',s ,,hypo!sis ,two entirely diff]5t explanations ( ?is di/ribution ( />s h be5 sugge/$4 ,9 #aibe ,russell put =w>d a !ory :i* c5tr$ prim>ily ar\nd ! fact t ! temp]atures at ! c5tres ( ! ma9-sequ5ce />s are all v ne>ly equal4 ,let u simplify ! situation = a mom5t by imag9+ x to be an asc]ta9$ fact t ! temp]atures at ! c5tres ( all />s are precisely ! same1 say #cb1jjj1jjj degrees4 ,if ?is 7 a sure fact1 x w\ld be natural to conjecture t ! />s _h "s sort ( controll+ me*anism by :i* !y cont9ually adju/$ _! c5tral temp]atures to ?is exact figure1 s t if ev] ! temp]ature fell bel[ #cb1jjj1jjj degrees ! me*anism w\ld come into play & raise ! temp]ature to precisely ?is am\nt1 :ile if x increas$ to above ?is figure1 ! me*anism w\ld come into play & depress x4 ,su* controll+ me*anisms are ( c\rse common 9 eng9e]+ practice2 !re are = in/ance ! safety-valves :i* keep ! pressure 9 a boil] always uni=m1 ! ,watts-gov]nor :i* keeps an eng9e go+ always at ! same rate ( spe$1 & ! !rmo/at :i* keeps ! temp]ature ( a room con/ant4 ,a me*anism is already kn[n = rais+ ! temp]ature at a />'s c5tre4 ,if a /> is n g5]at+ any en]gy at all 9 its int]ior1 ei!r by ! annihilation ( matt] or o!rwise1 its emission ( radiation causes x to %r9k1 & ?is1 z we h se5 7p4 #bhe71 causes its temp]ature to rise4 ,?us x is easy to keep a />'s c5tral temp]ature up to #cb1jjj1jjj degrees by arrang+ t no en]gy %all be g5]at$ s long z ! temp]ature at ! c5tre is bel[ #cb1jjj1jjj degrees1 & ?is is ! ma9 hypo!sis on :i* ,russell's !ory is bas$4 ,he supposes t no en]gy at all is g5]at$ by matt] at temp]atures bel[ #cb1jjj1jjj degrees1 b t1 z soon z ?is temp]ature is rea*$1 matt] beg9s to annihilate itself 9 suffici5t quantity to provide = ! radiation ( a />4 ,! tr\ble ) ! !ory is t x seems impossible to regulate ! temp]ature f ! o!r end4 ,a /> ^: c5tral temp]ature is bel[ #cb1jjj1jjj degrees mu/ be contract+ )\t g5]at+ heat4 ,! contraction w n /op dead ! mom5t ! critical temp]ature is atta9$2 its mom5tum w c>ry x on until ! c5tral temp]ature sub/antially exce$s #cb1jjj1jjj degrees4 ,z soon z ! temp]ature s]i\sly exce$s #cb1jjj1jjj degrees at ! c5tre1 t ( a sub/antial piece ( ! /> w be #cb1jjj1jjj degrees or high]4 ,! annihilation ( all ?is matt] mu/ produce a pr(usion ( heat :i* w\ld raise ! temp]ature ( ! /> /ill fur!r1 result+ 9 m & m annihilation ( matt]1 until f9ally ! :ole /> disappe>$ 9 a fla% ( radiation4 ,inde$ ,russell's !ory supposes t matt] at #cb1jjj1jjj degrees is 9 a simil> condition to gunp[d] at its fla% po9t4 ,ma!matical analysis !n %ews t a /> ^: c5tre is at a temp]ature ( #cb1jjj1jjj degrees w\ld be 9 ! /ate ( a keg ( gunp[d] ) a sp>k at its c5tre1 &--well1 8ohne ha/1 ohne ra/0 h>dly describes ! subsequ5t c\rse ( ev5ts4 ,edd+ton has sugge/$ t ! /ability ( ! />s might be sav$ by imag9+ a "t-lag betwe5 ! in/ant at :i* matt] atta9$ ! critical temp]ature necess>y = annihilation & ! in/ant at :i* ?is annihilation occurr$4 ,x has n yet be5 prov$ t ! propos$ rem$y c\ld be made effective1 b ev5 if x c\ld1 o!r difficulties rema94 ,z ! normal /> inhabits ! ma9-sequ5ce1 ,russell suppos$ x to be a prop]ty ( normal matt] to annihilate itself at a temp]ature ( ab\t #cb1jjj1jjj degrees1 ! suppos$ly uni=m c5tral temp]ature ( all ma9-sequ5ce />s4 ,x !n became necess>y to introduce fur!r special assumptions to expla9 ! lum9osity ( :ite dw>fs & ( />s on ! r$ giant spur l9e1 ^: c5tres are at temp]atures v diff]5t f #cb1jjj1jjj degrees4 ,he accord+ly suppos$ t su* />s conta9$ o!r types ( matt] :i* dissolv$ into radiation at temp]atures :i* 7 respectively high] & l[] ?an #cb1jjj1jjj degrees4 ,ev5 if ! /ability difficulty c\ld be ov]come1 ?is latt] s]ies ( assumptions seems to me to be s artificial z to compel ! ab&onm5t ( ?is int]e/+ !ory4 ,a discussion ( ! difficulties ( ,russell's !ory l$ me to und]take a ma!matical inve/igation ( ! /ability ( />s 9 g5]al1 & ?is 0 f\nd to provide a simple & some:at unexpect$ explanation ( ! o!rwise incompreh5sible di/ribution ( />s 9 ! ,russell diagram2 x is 9 brief t ! unoccupi$ regions ( ! diagram repres5t />s 9 an un/able condition4 ,i d n "k :at proportion ( a/ronom]s accept ?is explanation2 "s1 ^: op9ion ,i value1 d n4 ,i d n ?9k t mu* s f> writt5 9 ?is book w\ld be s]i\sly *all5g$ by compet5t critics1 b x is only fair to say t at ?is po9t we are ent]+ controv]sial gr\nd4 ,,! ,,hypo!sis ,,( ,,liquid ,,/>s ,let u beg9 by imag9+ an enorm\s numb] ( />s built on all possible plans1 out ( all k9ds ( sub/ances4 ,ma!matical inve/igation %ews t "s ( ^! />s may be unable to %9e ) a /eady light = ei!r or bo? ( two reasons--!y may explode1 l a heat$ keg ( gunp[d]1 or !y may h an inh]5t t5d5cy to contract or exp& )\t limit4 ,:e!r a /> escapes ! fir/ pitfall or n dep5ds ma9ly ^u ! prop]ties ( ! sub/ance ( :i* x is built2 :e!r x escapes ! second dep5ds ma9ly ^u ! way x is built4 ,! two pitfalls are n altoge!r di/9ct1 & :5 we consid] ! /ability ( :olly gase\s />s ( enorm\sly great weight1 we f9d t ! pits on ! two sides ( ! pa? m]ge into "o1 or at mo/ only a n>r[ /rip ( safe gr\nd is left betwe5 !m4 ,nev]!less />s ( enorm\sly great weight are kn[n to exi/1 & cont9ue %9+ /eadily4 ,if !n1 ^! />s are :olly gase\s1 !y mu/ occupy ! "o safe spot ( gr\nd betwe5 ! two pits1 & ?is in=ms u bo? z to ! way !y are built & z to ! prop]ties ( ! sub/ance ( :i* !y are built4 ,we f9d t su* />s only escape bo? pitfalls if _! sub/ance possesses prop]ties :i* appe> v improbable1 & contr>y to any?+ ( :i* we h any exp]i5ce or k 9 physics2 9 brief1 = su* a /> to rema9 /able1 ! annihilation ( its matt] mu/ proce$ at a rate :i* dep5ds on ! temp]ature4 ,su* a prop]ty seems 9 e way contr>y to ! physical pr9ciples expla9$ 9 ,*apt] ,,ii1 z x is to all our expectations ( atomic behavi\r4 ,! annihilation ( matt] is a f> m viol5t *ange1 & involves quanta ( f> high] en]gy1 ?an m]e radio-active dis9tegration1 & z ! latt] process is n affect$ by temp]ature *anges1 x h>dly seems possible t ! process ( annihilation %\ld be1 at any rate until we rea* temp]atures ( ! ord] ( ! #b1bjj1jjj1jjj1jjj degrees tabulat$ on p4 #addbf4 #bf ,?is provides a fur!r objection to ,russell's hypo!sis1 :i*1 to avoid confusion1 0 n m5tion$ on p4 #bie4 ,we h1 h[ev]1 already f\nd indications t ! />s are n purely gase\s1 s9ce purely gase\s masses c\ld n =m close b9>y sy/ems ( ! type obs]v$ 9 ! spectroscopic b9>ies 7p4 #bbb74 ,su* sy/ems c only be =m$ out ( a mass :i* simulates ! prop]ties ( a liquid r ?an ^? ( a gas2 ! mass ne$ n be :olly liquid1 b !re mu/ be a consid]able div]g5ce f ! /ate ( a pure gas1 at any rate 9 its c5tral regions4 ,additional evid5ce to ! same effect w also em]ge lat] 7pp4 #caj1 #caa74 ,z soon z we admit t ! int]iors ( ! />s ne$ n be 9 a completely gase\s /ate1 ! :ole situation *anges1 ev5 a slight dep>ture f ! gase\s /ate be+ f\nd to imp>t a great deal ( additional /ability to ! />4 ,if a /> ( great weight is purely gase\s 9 its /ructure1 ! region ( /ability betwe5 ! two pitfalls is r$uc$ to a n>r[ /rip1 & only by tread+ ?is c ! /> escape ! alt]native fates ( explod+ or collaps+4 ,b if ! /> has a liquid1 or p>tially liquid1 c5tre1 ?is /rip ( safe l& is s wide t1 consi/5tly ) /ability1 ! /ell> mat]ial may h exactly ! prop]ty t we %\ld priori expect to f9d1 namely1 t its annihilation proce$s1 l radio-active dis9tegration1 at ! same rate at all temp]atures4 ,if ! sub/ance ( ! /> has ?is prop]ty1 ! /> c be 9 no dang] ( explod+1 = a mass ( uranium or radium does n explode :atev] we d to x4 ,& ma!matical analysis %ews t if ! c5tre ( ! /> is ei!r liquid1 or p>tially s1 !re is no dang] ( collapse2 ! liquid c5tre provides s firm a basis = ! /> z to r5d] a collapse impossible4 ,^! consid]ations sugge/ ! two complem5t>y hypo!ses3 #a4 ,t ! annihilation ( /ell> matt] proce$s spontane\sly1 n be+ affect$ by ! temp]ature ( ! />4 #b4 ,t ! c5tral regions ( ! />s are n 9 a purely gase\s /ate2 _! atoms1 nuclei & electrons are s closely pack$ t !y _c move freely pa/ "o ano!r1 z 9 a gas1 b r jo/le "o ano!r ab\t l ! molecules ( a liquid4 ,if we h be5 "r 7p4 #adi7 9 attribut+ ! obs]v$ highly p5etrat+ radiation 9 ! e>?'s atmosph]e to ! annihilation ( matt] 9 di/ant a/ronomical bodies1 !n ! fir/ hypo!sis is confirm$4 ,= ! radiation c\ld n reta9 its obs]v$ high p5etrat+ p[] if x _h already p5etrat$ any great ?ickness ( matt]4 ,! /ruggle ( pass+ ?r\gh matt] l5g!ns ! wave-l5g? ( all k9ds ( radiation 7! quanta get weak] all ! "t71 & s dim9i%es its p5etrat+ p[]4 ,?us1 :]ev] ! highly p5etrat+ radiation orig9at$1 x mu/ h got out into empty space )\t mu* ( a /ruggle1 & ?is is ! same ?+ z say+ t x mu/ h orig9at$ 9 matt] at a comp>atively l[ temp]ature4 ,?us ! exi/5ce ( ! highly p5etrat+ radiation proves t matt] c be annihilat$ 9 great quantities at q l[ temp]atures2 ! high temp]atures ( /ell> int]iors are n ne$$1 z ,russell's !ory ass]ts1 = annihilation to occur4 ,a simple calculation %ews t !re c be no appreciable annihilation ( ! e>?'s sub/ance4 ,9 ! sun ab\t "o atom 9 e #aj is annihilat$ e m9ute2 if ev5 a t5-?\s&? "p z _m atoms z ?is 7 annihilat$ 9 ! e>?1 its surface w\ld be too hot = human habitation4 ,we c no long] expla9 ?is by say+ t ! sun is hot & ! e>? cool1 s t annihilation goes on 9 ! =m] b n 9 ! latt]4 ,we mu/ r suppose t ! atoms 9 ! sun are ( a diff]5t type f ^? on e>?4 ,sol> atoms spontane\sly annihilate !mselves1 t]re/rial atoms d n1 or at lea/ d n to any appreciable ext5t4 ,! second ( our hypo!ses1 t ! c5tral regions ( ! />s are m l a liquid ?an a gas1 is1 z we h se51 a necess>y consequ5ce ( ! fir/1 b indep5d5t evid5ce 9 its fav\r is f\nd 9 ! =mation ( b9>y sy/ems by fission4 ,= 9 ,*apt] ,,iv 7p4 #bbb7 we saw t a /> c\ld only break up by fission if x _h a liquid1 or a ne>ly liquid1 c5tre4 ,,! ,,/ability ,,( ,,/ell> ,,/ructures ,= ! pres5t1 let u t5tatively accept ! hypo!sis t ! g5]ation ( /ell> en]gy occurs spontane\sly1 l ! dis9tegration ( radio-active atoms4 ,! atoms :i* are responsible = ! light & heat ( ! />s may be reg>d$ z sup]-radio-active atoms :i* spontane\sly annihilate !mselves & s *ange _! sub/ance into radiation4 ,we h already se5 t1 on ?is view ( ! me*anism ( g5]ation ( /ell> en]gy1 a /> c only cont9ue to %9e /eadily if its c5tral regions are n 9 a purely gase\s condition4 ,a /> built on f\ndations ( highly compressible gas meets ! same fate z a h\se built on s&3 x collapses4 ,a purely gase\s /> is a dynamically un/able /ructure1 & mu/ cont9ually contract until ! atoms 9 its c5tral regions are s closely pack$ t _! /ate c no long] be reg>d$ z gase\s4 ,!n1 & !n only1 c ! /> exi/ p]man5tly z a /able /ructure4 ,?us ! c5tral regions ( any actual p]man5t />1 ! sun = in/ance1 mu/ be 9 a /ate :i* = brevity we may describe z liquid4 ,n[ let u imag9e ! sun to be exp&$ to t5 times its pres5t diamet]4 ,?is w\ld dim9i% its d5sity to a ?\s&? "p ( its orig9al value4 ,! actual sun is #dj p] c5t4 m d5se ?an wat]1 b ! exp&$ sun w\ld only be z d5se z ord9>y atmosph]ic air4 ,! atoms & electrons1 hav+ mov$ t5 times f>!r ap>t1 w\ld be s di/ant f "o ano!r t ! new sun might be reg>d$ z :olly gase\s4 ,?us x w\ld be dynamically un/able & c\ld n rema9 9 its :olly gase\s /ate4 ,our imag9>y exp&$ sun is ( c\rse no long] a ma9-sequ5ce /> 9 ! ,russell diagram4 ,9 exp&+ ! sun to t5 times its pres5t size we move x (f ! ma9-sequ5ce into a region entirely vacant ( />s--9 fact1 into ! great gulf :i* lies betwe5 ! r$ giants & ! r$ dw>fs 7see fig4 #bb1 p4 #bgh74 ,?us1 x appe>s t ev5 if we delib]ately place a /> 9 ?is region1 x does n /ay !re b imm$iately contracts until x gets on to ! ma9-sequ5ce4 ,may n ?is expla9 :y ! region 9 "q is unt5ant$ by />s8 ,next let u imag9e ! sun contract$ to a t5? ( its pres5t diamet]1 s t its atoms & electrons move t5 times ne>] to "o ano!r4 ,its mean d5sity is !reby increas$ f #ad to #adjj times t ( wat]1 & its c5tral d5sity f ab\t #adj to #adj1jjj4 ,y may *eck me "h by po9t+ out t if ! sun is already 9 a liquid /ate x _c be compress$ to any su* ext5t--a liquid _c usually h its d5sity increas$ a ?\s&-fold4 ,b we h already notic$ t halv+ a />'s diamet] d\bles its temp]ature ?r\gh\t4 ,9 ! same way r$uc+ a />'s diamet] to a t5? increases its temp]ature t5-fold1 s t ! sun's c5tral temp]ature w be increas$ f1 say1 #ej million degrees to #ejj million degrees4 ,& at ?is latt] temp]ature atoms h>dly exi/ any long] z su*--! /ell> matt] consi/s almo/ entirely ( free electrons & nuclei4 ,& ^! are s m9ute1 t ! increase ( ! sun's mean d5sity f #ad to #adjj times ! d5sity ( wat] is n only possible1 b leaves ! sun's sub/ance 9 a /ate :i* may be/ be describ$ z gase\s4 ,once aga91 !n1 ! new sun is dynamically un/able4 ,x w\ld be repres5t$ by a po9t well to ! left ( ! ma9-sequ5ce1 ne> ! middle ( ! unoccupi$ region betwe5 ! ma9-sequ5ce & ! :ite dw>fs1 b z x is un/able x _c ma9ta9 its position "h4 ,aga9 we see t ev5 if we place a /> 9 ?is region x _c /ay !re4 ,&1 aga9--may x n be t ! reason :y ?is region is unoccupi$ is t x repres5ts un/able />s8 ,once m y may *eck me4 ,if ,i h made my po9t1 x has be5 by ! help ( ! rise ( temp]ature :i* accompanies contraction4 ,:5 we imag9$ ! sun to exp&1 ought we n to h consid]$ ! fall ( temp]ature :i* accompanies expansion8 ,! answ] is t we ought1 b x w\ld h made no diff]5ce4 ,l[]+ ! temp]ature w cause a numb] ( ,l-r+s1 & possibly also ( ,m-r+s1 ( electrons to re-=m1 s t ! new atoms w be ( l>g] size1 b !y w n lose _! fre$om ( motion suffici5tly to make ! sun /able4 ,x w\ld h be5 diff]5t if we _h be5 discuss+ a /> ( #aj or #ej times ! sun's weight2 !n x c be %ewn t ! re-=mation ( ,k- & ,l-r+s w\ld h produc$ a s]ies ( /able configurations4 ,& ! spur bran* 9 ! ,russell diagram exi/s to provide a home = j su* />s4 ,! :ole problem is too complicat$ to be discuss$ satisfactorily 9 ?is fragm5t>y way2 its prop] discussion involves v complicat$ ma!matical analysis4 ,ma!matical discussion %ews t ! ,russell diagram c be divid$ into regions repres5t+ /able & un/able configurations 9 ! mann] %ewn 9 fig4 #bd4 ,illu/ration3 ,fig4 #bd4 ,/able & un/able configurations 9 ! ,russell diagram4 ,! un/able areas are s m>k$2 ! rema9+ areas are /able4 ,! dots :i* =m a sort ( backgr\nd to ! diagram repres5t #bajj />s ^: absolute magnitudes are kn[n ?r\gh _! p>allaxes hav+ be5 det]m9$ spectroscopically at ,m\nt ,wilson4 ,! obs]vational mat]ial is n p]fect1 = consid]able unc]ta9ty atta*es to all spectroscopic p>allaxes ( ,b-type />s1 & ,a-type />s are almo/ unrepres5t$ because x is practically impossible to obta9 _! p>allaxes by ! spectroscopic me?od4 ,! !oretical curves are probably /ill m imp]fect1 yet1 su* z !y are1 !y seem to sugge/ v =cibly t ! occupi$ & unoccupi$ regions co9cide ) ^? repres5t+ /able & un/able configurations2 aft] mak+ all possible all[ances = ! imp]fections bo? ( !ory & ( obs]vation1 too mu* agreem5t rema9s to be expla9$ away z m]e co9cid5ce4 ,?us ! conclusion to :i* ma!matical discussion seems to lead is t ! regions 9 ! ,russell diagram :i* are occupi$1 repres5t />s ^: c5tral regions are 9 a liquid1 or ne>ly liquid1 /ate4 ,all o!r />s are un/able1 s t ! correspond+ regions 9 ! ,russell diagram are necess>ily vacant4 ,to put x 9 less te*nical language1 all ! />s 9 ! sky mu/ h liquid1 or ne>ly liquid1 c5tres4 ,"h we h a piece ( ! puzzle :i* seems to fit on to ! piece we une>!d 9 ,*apt] ,,iv1 :]e we f\nd t a /> c\ld only break up by fission if x _h a liquid1 or ne>ly liquid c5tre4 ,evid5ce accumulates t ! />s h liquid r ?an gase\s c5tres4 ,criticism ( ! =ego+ hypo!sis--g5]ally describ$ z ! 8liquid-/>0 hypo!sis--has ma9ly tak5 ! =m t ! diamet]s ( ! ,k-r+s ( atoms are s small t ! ,k-r+ atoms 9 ! sun's c5tral regions _c possibly be pack$ closely en\gh to involve any sub/antial dep>ture f ! gase\s /ate4 ,x is difficult to discuss1 & /ill m to meet1 ?is criticism )\t kn[+ ! precise diamet]s ( ^! ,k-r+ atoms4 ,we ( c\rse "k ! diamet]s assign$ to ! ,k-r+ by ,bohr's !ory 7p4 #abi71 b no "o any long] cont5ds t ?is !ory gives a true picture ( ! atom4 ,x provides a good work+ model )9 limits1 b we d n "k :]e ! limits end4 ,! only practical exp]i5ce we h ( ,k-r+ atoms is ) helium atoms2 ,bohr's !ory assigns to ^! a diamet] ( #jed #aj cms4 ,yet solid & liquid helium provide a practical illu/ration ( ! clos5ess ) :i* helium atoms c be pack$2 9 ^! ea* atom occupies a sph]e ( diamet] #d #aj cms41 or ov] #djj times ! space allott$ to x by ,bohr's !ory4 ,x looks z ?\gh we are /ill f> f def9ite k ( ! dim5sions ( ,k-r+s ( electrons4 ,! new wave-me*anics ( ,s*rd+] draws a v diff]5t picture ( atomic int]iors f ! simpl] !ory ( ,bohr :i* x is rapidly sup]s$+4 ,ev5 ! electron is some?+ v diff]5t f ! electron ( ,bohr's old !ory4 ,x is ! old-fa%ion$ electron only :5 x is at an inf9ite di/ance f ! nucleus4 ,z x gradually approa*es ?is nucleus1 x und]goes a metamorphosis ( a k9d :i* no "o has yet succe$$ 9 describ+1 & x is utt]ly impossible to say :at =m x may h assum$ by ! "t x is do+ :at we call 8describ+ a ,k-r+ orbit40 ,all we "k ab\t ! ,k-r+ orbit is its en]gy1 & x seems impossible to pr$ict ! am\nt ( space occupi$ by su* an orbit until we h a bett] k ( ! qualities ( ! article :i* is describ+ x4 ,we h ( c\rse to admit t ! physical evid5ce1 su* z x is1 seems to po9t to ,k-r+ atoms be+ sub/antially small] ?an is ne$$ = ! liquid-/> hypo!sis4 ,b ! a/ronomical evid5ce seems to me /rong] & m reliable1 & to po9t 9 exactly ! opposite direction4 ,& "h we mu/ leave ! puzzle until fur!r pieces come to light4 ,until we "k ! k9d ( atoms ( :i* a p>ticul> /> is compos$1 we _c calculate ! ext5t to :i* !y w be brok5 up by ! temp]ature ( ! />'s int]ior4 ,z a consequ5ce1 ! !oretical curves ( dem>cation betwe5 /able & un/able configurations _c be calculat$ )\t assum+ def9ite atomic numb]s = ! /ell> atoms4 ,! curves %ewn 9 fig4 #bd h be5 drawn = an atomic numb] ( ab\t #ie1 ?is be+ slightly high] ?an ! atomic numb]1 #ib1 ( uranium4 ,?is atomic numb] 0 select$ because x 0 f\nd to produce ! be/ agreem5t betwe5 !ory & obs]vation1 b we %all see t o!r consid]ations ju/ify our *oice4 ,,/ell> ,,/ructure ,a />1 l a h\se or a pile ( s&1 is a /ructure :i* w\ld collapse "u its own weight 7 x n t ea* lay] is held up aga9/ gravity by ! pressure :i* ! next inn] lay] ( ! /> ex]ts ^u x4 ,?is pressure is n1 l ord9>y gas-pressure1 ! result ( ! impacts ( complete molecules4 ,x is produc$ 9 "p by ! impact ( a c]ta9 numb] ( atoms :i* h be5 /ripp$ ( electrons almo/ or q d[n to _! nuclei1 b to a f> great] ext5t by ! impact ( a hail ( free electrons4 ,9 massive />s1 an additional pressure is produc$ by ! impact ( radiation :i*1 z we h se51 c>ries weight ab\t ) x1 & s ex]ts pressure on any ob/acle x enc\nt]s4 ,! comb9$ impacts ( free electrons1 ( atoms 7or b>e nuclei71 & ( radiation prev5t ! /> f fall+ 9 "u its own gravitational attraction4 ,?is gives a reasonably good snap%ot picture ( a />'s /ructure4 ,! correspond+ picture ( its me*anism is obta9$ by ?9k+ ( ! nuclei z -ray p>ticles1 ( ! free electrons z -ray p>ticles1 & ( ! radiation z -rays 7al?\gh 9 mo/ />s ! ma9 bulk ( ! radiation has ! wave-l5g? ( ,x-rays74 ,all ^! ?read _! way ?r\gh ! />1 &1 precisely z 9 laboratory "w1 ! -rays are m p5etrat+ ?an ! -rays1 & ! -rays are m p5etrat+ ?an ei!r4 ,,! ,,transport ,,( ,,en]gy ,,9 ,a ,,/>4 ,we h se5 h[ ! heat ( a gas is m]ely ! en]gy ( its molecul> motion4 ,conduction ( heat 9 a gas is usually /udi$ by reg>d+ ea* molecule z a c>ri] ( en]gy2 :5 x collides ) a second molecule ! en]gy ( ! two collid+ molecules is r$i/ribut$ betwe5 !m1 & 9 ?is way heat is transport$ f hott] to cool] regions4 ,ea* molecule has a p[] ( transport :i* is jo9tly proportional to its en]gy ( motion1 its spe$ ( motion1 & its 8free-pa?0--! di/ance x travels betwe5 successive collisions4 ,9 ! int]ior ( a />1 !re are ?ree di/9ct types ( c>ri] 9 action--atoms 7or b>e nuclei71 free electrons1 & radiation4 ,we c comp>e _! relative capacities z c>ri]s by multiply+ up ! en]gy1 spe$s & free-pa?s ( ea*4 ,= ?is purpose ! 8free-pa?0 ( radiation may be tak5 to be ! di/ance ! radiation travels be=e #cg p] c5t4 ( x has be5 absorb$1 s9ce x c be %ewn t ?is is ! av]age di/ance x c>ries its en]gy4 ,on c>ry+ out ! calculation1 ! c>ry+ capacity ( bo? nuclei & electrons is f\nd to be insignificant 9 comp>ison ) t ( ! radiation4 ,! nuclei & electrons may h ! great] am\nt ( en]gy to c>ry1 b ow+ to _! feebl] p5etrat+ p[]s1 ! di/ance ov] :i* !y c>ry x1 _! free-pa?1 is f> less ?an t ( ! radiation4 ,_! spe$ ( transport is also less1 s9ce radiation transports its en]gy ) ! velocity ( light4 ,9 ?is way x comes ab\t t practically ! :ole transport ( en]gy f ! int]ior ( a /> to its surface is by ! vehicle ( radiation4 ,?is g5]al pr9ciple 0 fir/ cle>ly /at$ by ,sampson 9 #ahid4 ,he also %ew$ h[ ! temp]ature ( any small fragm5t ( a />'s int]ior mu/ be det]m9$ by ! condition t x receives j z mu* radiation z x emits1 b 8 detail$ applications 7 vitiat$ ?r\gh 8 us+ an errone\s law ( radiation4 ,twelve ye>s lat]1 ,s*w>zs*ild indep5d5tly advanc$ ! same idea1 & express$ x 9 ma!matical equations ( 8radiative equilibrium0 :i* h =m$ ! basis ( e subsequ5t discussion ( ! problem4 ,j because radiation completely out/rips atoms & electrons 9 c>ry+ en]gy f a />'s int]ior to its surface1 x foll[s t ! build ( a /> mu/ be det]m9$ by ! opacity ( ! matt] 9 its int]ior4 ,if ?is is alt]$1 ! c>ry+ p[] ( ! radiation is alt]$1 & ?is affects ! :ole /ructure ( ! />4 ,a /> ^: int]ior 0 entirely transp>5t c\ld n reta9 any heat at all2 its :ole int]ior w\ld be at a v l[ temp]ature & ! /> w\ld be ( enorm\s ext5t4 ,on ! o!r h&1 9 a v opaque />1 all en]gy w\ld rema9 accumulat$ at ! spot at :i* x 0 g5]at$1 s t ! int]ior temp]ature w\ld become v high & ! />'s diamet] w\ld be correspond+ly small4 ,x is1 ( c\rse1 ! int]m$iate cases :i* are ( practical int]e/1 b ! extreme in/ances j m5tion$ %ew h[ a />'s build dep5ds on its opacity4 ,un=tunately x is impossible to obta9 any sort ( direct measurem5t ( ! opacity ( /ell> matt]4 ,we _c ev5 measure ! opacity ( t]re/rial matt] "u /ell> conditions1 s9ce ! int]iors ( ! />s are at incomp>ably high] temp]atures ?an any available 9 ! laboratory4 ,h[ev]1 we "k t ! opacity ( /ell> matt] is due to ! atoms1 nuclei & free electrons ( :i* x is compos$ *eck+ ! onw>d j\rney ( radiation1 & al?\gh we _c obta9 a sample ( /ell> matt]1 we "k fairly def9itely h[ _m atoms1 nuclei & electrons su* a sample w\ld conta94 ,?us x becomes a matt] ( !oretical calculation to det]m9e its opacity4 ,su* a calculation 0 c>ri$ ?r\gh by ,dr ,kram]s ( ,cop5hag5 9 #aibc1 & 8 results ga9$ g5]al acceptance4 ,q rec5tly ,mr ,gaunt ( ,cambridge has made a mu* m ref9$ calculation1 & obta9$ results :i* agree v closely ) ^? orig9ally giv5 by ,kram]s4 ,9 s f> z ^! results c be te/$ 9 ! laboratory1 !y agree well ) obs]vation4 ,&1 al?\gh !re is a big gap betwe5 laboratory conditions & /ell> conditions1 x is difficult to see h[ ,kram]s' =mula c\ld fail 9 ! />s4 ,f ?is =mula we c det]m9e ! build ( ! />s completely1 or1 if ! build ( ! /> is suppos$ to be kn[n1 ,kram]s' =mula tells u ! rate at :i* en]gy fl[s to its surface 7?is dep5d+ entirely on ! opacity ( ! />'s sub/ance71 & ?is 9 turn tells u at :at rate en]gy mu/ be g5]at$ inside ! /> = x to be able to rema9 9 equilibrium 9 ! configuration 9 "q4 ,z might be expect$1 configurations ( diff]5t diamet]s are f\nd to require diff]5t rates ( g5]ation ( en]gy4 ,9 nature1 a /> mu/ adju/ its diamet] to suit ! rate at :i* x is g5]at+ en]gy2 9 s do+ x fixes n only its diamet] b also its surface-temp]ature1 col\r & spectral type4 ,if a />'s rate ( g5]ation ( en]gy 7 sudd5ly to *ange1 ! /> w\ld exp& or contract until x _h assum$ ! radius & temp]ature suit$ to its new rate ( g5]ation ( en]gy4 ,detail$ calculation %ews t1 = :olly gase\s />s1 l>ge diamet]s correspond to feeble g5]ation ( en]gy & vice v]sa4 ,?us1 if ! />s 7 :olly gase\s1 r$ giants w\ld be less lum9\s ?an ma9-sequ5ce />s ( ! same weight4 ,se>es' diagram1 reproduc$ on p4 #bhb1 %ews t ! rev]se is actually ! case1 a r$ giant emitt+ f #aj to #bj times z mu* total radiation z an equally massive ma9-sequ5ce />4 ,?is provides evid5ce aga9/ ! />s be+ :olly gase\s1 b !re is /rong] evid5ce ?an ?is4 ,= :olly gase\s />s1 ! ?ick l9es %ewn 9 ,se>es' diagram w\ld be /raight slant l9es1 slant+ upw>ds to ! left4 ,! wide div]g5ce betwe5 su* a sy/em ( slant l9es & ! curves %ewn 9 fig4 #bc gives "s indication ( ! ext5t to :i* ! condition ( /ell> matt] div]ges f ! purely gase\s /ate4 ,accord+ to ,kram]s' !ory1 ! opacity ( matt] dep5ds on ! atomic numb]s & atomic weights ( ! atoms ( :i* x is built1 a l>ge clot ( matt] 9 ! =m ( a massive atomic nucleus be+ f> m effective 9 absorb+ radiation ?an a l>ge numb] ( small clots ( ! same total weight4 ,ev]yday t]re/rial exp]i5ce %ews t ?is is s4 ,x is = ?is reason t ! physici/ & surgeon bo? select lead z ! mat]ial ) :i* to scre5 _! ,x-ray app>atus2 !y f9d t a ton ( lead is f> m effective 9 /opp+ unwant$ ,x-rays ?an a ton ( wood or ( iron4 ,if we knew ! /r5g? ( an ,x-ray app>atus1 & ! total weight ( %ield+ mat]ial r\nd x1 we c\ld =m a v fair e/imate ( ! atomic weight ( ! %ield+ mat]ial by measur+ ! am\nt ( ,x-radiation :i* escap$ ?r\gh x4 ,a v simil> me?od may be us$ to det]m9e ! atomic weights ( ! atoms ( :i* ! />s are compos$4 ,a /> is 9 effect no?+ b a huge ,x-ray app>atus4 ,we "k ! weights ( _m ( ! />s1 & ! rate at :i* !y are g5]at+ ,x-rays is m]ely ! rate at :i* !y are radiat+ en]gy away into space4 ,if we c\ld cut ea* atomic nucleus 9 a /> into two halves1 we %\ld halve ! opacity ( ! />1 s t radiation w\ld travel twice z f> ?r\gh ! /> be=e be+ absorb$4 ,if ! /> 7 :olly gase\s1 ?is w\ld result 9 its exp&+ to f\r times its orig9al diamet]1 & 9 its surface-temp]ature be+ halv$4 ,x foll[s t we c calculate ! atomic weight ( ! atoms ( :i* a /> is compos$ f ! weight1 lum9osity & surface-temp]ature ( ! />4 ,! atomic weights ( a numb] ( />s1 :i* ,i calculat$ on ! supposition t ! />s 7 :olly gase\s1 came out 9 practically e case high] ?an t ( uranium1 :i* is ! weightie/ atom kn[n on e>?4 ,!y n only prov$ to be high]1 b enorm\sly high]2 s high inde$1 z to seem utt]ly improbable4 ,aga9 ! explanation seems to be t ! />s are n :olly gase\s4 ,z soon z /ell> int]iors are suppos$ to be p>tially liquid1 ! calculat$ atomic weights are r$uc$ enorm\sly4 ,!y c no long] be det]m9$ exactly1 b ! atomic numb] ( ab\t #ie to :i* we 7 l$ f a consid]ation ( ! ,russell diagram seems to be entirely consi/5t ) all ! kn[n facts4 ,inde$ o!r consid]ations seem to sugge/ t ! atomic numb]s ( /ell> atoms mu/ be high] ?an #ib4 ,a priori /ell> radiation might ei!r orig9ate 9 types ( matt] kn[n to u on e>? or else 9 o!r & unkn[n types4 ,:5 once x is accept$ t high temp]ature & d5sity c d no?+ to accel]ate ! g5]ation ( radiation by ord9>y matt]1 x becomes cle> t /ell> radiation _c orig9ate 9 types ( matt] kn[n to u on e>?4 ,o!r types ( matt] mu/ exi/1 & z1 ) two exceptions1 all atomic numb]s up to #ib 7uranium7 are already occupi$ by t]re/rial elem5ts1 x seems probable t ^! o!r types mu/ be elem5ts ( high] atomic weight ?an uranium4 ,^! sup]-heavy atoms mu/ n be expect$ to disclose _! pres5ce 9 /ell> spectra1 = ^! only in=m u z to ! con/itution ( ! atmosph]es ( ! />s4 ,& z ! light] atoms float to ! top x is ^!1 9 ! ma91 :i* figure 9 /ell> spectra4 ,if ! sun's atmosph]e _h conta9$ any consid]able numb] ( sup]-heavy atoms :5 ! planets 7 born1 "s ( !m ought /ill to exi/ 9 ! e>?4 ,!re _c be any great numb]1 or _! high g5]ation ( en]gy w\ld betray !m4 ,! simple/ view seems to be t ! heavi] atoms s9k to ! c5tre 9 ! />s1 & t ! e>? 0 =m$ ma9ly or solely out ( ! light] atoms :i* _h float$ to ! sun's surface4 ,,/ell> ,,evolution ,we h suppos$ t ! />s 7 born initially z cond5sations 9 ! out] fr+es ( spiral nebulae4 ,^! cond5sations w\ld1 f ! mode ( _! =mation1 necess>ily be ( all sorts ( sizes1 & subject only to ! s+le re/riction t none ( !m c\ld be bel[ a c]ta9 limit ( weight4 ,?us we %\ld n expect ! />s1 ei!r at bir? or subsequ5tly1 to be all ( ! same size or weight1 or all 9 ! same physical condition4 ,! />s w\ld />t _! exi/5ces at diff]5t po9ts 9 ! ,russell diagram1 b we may imag9e t _! initial positions are limit$ to ^? p>ts ( ! diagram :i* c be occupi$ by />s--ei!r1 z ! liquid-/> hypo!sis w\ld sugge/1 because ^! are ! only /able configurations1 or else = "s o!r reason s f> undiscov]$4 ,ea* ye> a /> loses a c]ta9 am\nt ( weight1 & its rate ( g5]at+ en]gy1 & s also its lum9osity1 are correspond+ly r$uc$1 ) ! result t x moves to a new position 9 ! diagram4 ,turn+ to ,se>es' diagram ( /ell> weights on p4 #bhb1 we may ?9k ( ! curves ( equal weight z a flight ( /eps--v unev5 /eps1 x is true--ea* repres5t+ a l[] weight ?an ! "o above4 ,:atev] a />'s evolution may be1 x is ess5tial t x %\ld always be d[n ! /eps3 any upw>d /ep is impossible4 ,we c trace out two possible pa?s ( /ell> evolution 9 ! ,russell diagram :i* involve no entry into regions unoccupi$ by />s--two roads along :i* ! /ell> army may m>* z !y trans=m _! sub/ance into radiation4 ,! fir/ is ( c\rse ! 8ma9-sequ5ce10 :i* a great numb] ( consid]ations sugge/ to be ! ma9 l9e ( m>* ( ! /ell> army4 ,! bran* :i* />ts f ! r$ giants 9 ! ,russell diagram repres5ts a second possible l9e ( m>*1 a c]ta9 numb] ( />s travell+ along ?is bran* until !y rea* ! ma9-sequ5ce z blue or :ite />s1 & !n travell+ d[n ! l[] half ( ! ma9-sequ5ce to end z fa9t r$ />s pass+ on to ultimate ext9ction4 ,progress along ea* ( ^! roads is accompani$ by a cont9u\s %r9kage 9 ! size ( ! />1 its diamet] /eadily decreas+4 ,?is is n ! same ?+ z say+ t ! />'s d5sity cont9ually increases1 = ! /> is cont9ually dim9i%+ 9 weight1 s t ev5 if ! />'s d5sity rema9$ ! same1 its diamet] w\ld decrease4 ,nev]!less a /udy ( ,se>es' det]m9ations ( mean d5sities1 z %ewn 9 ! diagram on p4 #bhb1 sugge/s t !re is a cont9u\s increase ( d5sity1 al?\gh ?is becomes v slight 9 ! middle rea*es ( ! ma9-sequ5ce4 ,practically e !ory ( /ell> evolution :i* has ev] be5 prop\nd$ has imag9$ ! m>* ( ! /ell> army to be ( ! same g5]al type z t j describ$1 al?\gh p]haps pres5t-day op9ion is incl9$ to treat ! ma9-sequ5ce z ! pr9cipal l9e ( m>*1 :]eas e>li] !ories suppos$ ! y\nge/ />s to m>* solely along ! r$ giant bran*1 only jo9+ ! ma9-sequ5ce ) middle age4 ,! fir/ s]i\s !ory ( all1 t ( ,locky]1 0 express$ 9 t]ms ( bran*es ( asc5d+ & desc5d+ temp]ature1 ^! toge!r =m+ ! la/-m5tion$ l9e ( m>* 9 ! ,russell diagram4 ,a !ory :i* ,russell prop\nd$ 9 #aiac aga9 assign$ to ! />s ! l9es ( m>* j describ$4 ,x also attempt$ a physical explanation1 s9ce ab&on$1 z to :y ! />s foll[$ ^! p>ticul> pa?s r ?an o!rs4 ,8 m rec5t !ory ( #aibe only diff]$ f 8 e>li] !ory 9 giv+ ! new explanation1 :i* we h already discuss$ 7p4 #bic71 z to :y ! />s foll[$ ^! p>ticul> pa?s4 ,at pres5t1 x is probably fair to say t ne>ly1 & p]haps q1 all a/ronom]s are agre$ t ! evolution>y pa?s ( ! />s are ( ! g5]al type we h describ$4 ,"s />s />t z r$ giants1 "s z blue1 "s possibly 9 int]m$iate conditions4 ,z !y age1 all move d[nw>ds 9 ! ,russell diagram1 _! v>i\s pa?s conv]g+ to a po9t at ! =k ( ! rev]s$ %ewn 9 fig4 #bb1 & aft] pass+ ?is po9t !y move d[n ! ma9-sequ5ce4 ,on ! o!r h&1 !re is ! wide/ diff]5ce ( op9ion z to ! physical int]pretation :i* is to be assign$ to ^! pa?s4 ,mo/ a/ronom]s are probably susp5d+ judgm5t until "s def9ite obs]vational evid5ce is obta9$ to decide betwe5 conflict+ !ories4 ,:5 ! />s fir/ came into be+ z flecks ( fi]y spray ?r[n (f by sp9n+ nebulae1 !y w\ld consi/ ( mixtures ( atoms ( all k9ds1 "s p]haps be+ s %ort-liv$ z to trans=m !mselves almo/ at once into radiation1 & o!rs hav+ su* long lives t !y may prop]ly be describ$ z p]man5t4 ,except = a small numb] ( radio-active atoms1 ! e>? mu/ consi/ entirely ( atoms ( ?is latt] type4 ,calculation %ews t t]re/rial atoms mu/ h enorm\sly long] lives ?an ! av]age /ell> atom1 o!rwise _! self-annihilation w\ld make ! e>? too hot = habitation4 ,! p]man5t atoms 9 a /> contribute almo/ no?+ to its en]gy-g5]at+ capacity1 & s m]ely add to its weight4 ,! %orte/ liv$ atoms ( all contribute greatly to ! />'s g5]ation ( en]gy :ile add+ b little to its weight4 ,9 g5]al ! %ort] ! life ( any type ( atom1 ! great] ! proportion ( its numb]s annihilat$ p] ye>1 & s ! great] ! am\nt ( en]gy x g5]ates p] ton ( weight4 ,a /> beg9s life ) a l>ge proportion ( %ort-liv$ atoms1 & s at fir/ g5]ates en]gy furi\sly4 ,z x ages1 ! %orte/ liv$ atoms disappe> fir/1 & 9 s do+ r$uce ! av]age en]gy-g5]ation ( ! /> p] ton s t1 z a />'s weight decreases1 s also mu/ its rate ( g5]ation ( en]gy p] ton4 ,f9ally all ! atoms ) mu* en]gy-g5]at+ capacity h disappe>$1 & ! /> is left1 a %runk5 & dim9i%$ mass ( atoms :i* h v little capacity = g5]at+ radiation4 ,to put ! same ?+ 9 ano!r way1 ! rate at :i* a /> g5]ates en]gy p] ton is proportional to ! dea?-rate 9 its population ( atoms4 ,to say t ,sirius g5]ates #af times z mu* en]gy p] ton z ! sun is only ano!r way ( say+ t ! av]age atom 9 ,sirius has only a sixte5? ( ! expectation ( life ( ! sol> atoms2 _! dea?-rate is #af times z high4 ,z ^? types ( atoms :i* h ! highe/ dea?-rate gradually die (f 9 any />1 ! av]age dea?-rate ( ! population decreases1 or1 9 o!r words1 z a /> ages its capacity = en]gy-g5]ation p] ton decreases4 ,?is agrees ) ! f9d+s ( obs]vational a/ronomy4 ,! mo/ massive />s n only g5]ate m en]gy ?an less massive />s1 z is 9 any case to be expect$2 !y also g5]ate enorm\sly m en]gy p] ton4 ,?is is illu/rat$ by ! foll[+ li/ ( ma9-sequ5ce />s3 ---------------------------------------- -------------- ,/> ,weight ,g5]ation ( en]gy 79 t]ms ( sun7 7ergs p] gramme7 ---------------------------------------- -------------- ,pe>ce's ,/> ,a #cfc #ae1jjj ,v ,puppis ,a #aib #a1jjj ,sirius ,a #bde #bi ,sun #ajj #aij ,eridani 7#jde7 #jbf ,krug] #fj ,b #jbj #jjba ---------------------------------------- -------------- ,se>es' diagram ( /ell> weights 7p4 #bhb7 %ews t ?is is a g5]al prop]ty ( ! />s4 ,to repeat our =m] metaphor1 ! />s squ&] _! sub/ance lavi%ly 9 _! y\?1 :ile !y h pl5ty left to sp5d1 b p>simony comes ov] !m ) old age4 ,!oretical consid]ations h n[ giv5 u an explanation ( ?is ph5om5on4 ,! same diagram %ews t two />s ( ! same weight d n usually h ! same lum9osity4 ,9 g5]al1 giant />s on ! spur bran* lead+ out to ! r$ giants h sub/antially high] lum9osities ?an ! ma9-sequ5ce />s ( equal weight4 ,we h already notic$ h[ a r$ giant may emit z mu* z #aj or #bj times ! radiation ( an equally massive ma9-sequ5ce />4 ,! same /ory is repeat$ :5 we pass f ! ma9-sequ5ce />s to ! :ite dw>fs4 ,ma9-sequ5ce />s emit enorm\sly m radiation--any?+ up to #ejj times m--?an :ite dw>fs ( equal weight4 ,?is is illu/rat$ by ! ?ree foll[+ :ite dw>fs1 :i* may be comp>$ ) ! la/ ?ree />s ( ! prec$+ table3 ---------------------------------------- -------------- ,/> ,weight ,g5]ation ( en]gy 79 t]ms ( sun7 7ergs p] gramme7 ---------------------------------------- -------------- ,sirius ,b #jhe #jjjbg ,eridani ,b #jdd #jjjb van ,maan5's /> 7#jbj7 7#jjjjee7 ---------------------------------------- -------------- ,we h hi!rto suppos$ g5]ation ( en]gy to be spontane\s & s unaffect$ by *anges ( physical conditions4 ,yet ! facts j m5tion$ seem to sugge/ t ?is c h>dly be ! :ole tru? ( ! matt]4 ,to /ate ! objection 9 t]ms ( a concrete in/ance1 ,sirius ,a & its :ite dw>f companion ,sirius ,b mu/ 9 all probability h be5 born at ! same "t out ( ! same nebula 7p4 #bhd71 yet ! =m] g5]ates #djjj times z mu* en]gy p] ton z ! latt]4 ,x seems improbable t s great a diff]5ce c be attribut$ to diff]5t types ( atoms2 ! common orig9 ( ! two />s almo/ precludes ?is4 ,we "k t ! atoms are 9 diff]5t physical conditions 9 ! two />s2 9 ,sirius ,a !y h reta9$ _! ,k-r+s intact1 :ile 9 ,sirius ,b1 ! :ite dw>f1 !y are completely brok5 up into b>e nuclei & free electrons4 ,if ! two compon5ts ( ,sirius consi/ ( ess5tially ! same types ( atoms1 z _! common orig9 w\ld lead u to expect1 !n ! enorm\s diff]5ce 9 ! rates at :i* ^! atoms g5]ate en]gy w\ld seem to dep5d on ! diff]5t physical conditions ( _! atoms4 ,! consid]ations br\ght =w>d 9 ,*apt] ,,iii make x highly probable t a />'s rate ( g5]ation ( en]gy dep5ds on ! physical condition ( its atoms4 ,we !re suppos$ /ell> en]gy to be g5]at$ ?r\gh electrons coalesc+ ) protons2 protons exi/ only 9 atomic nuclei1 & purely physical consid]ations l$ to ! conjecture t ! only electrons :i* c coalesce ) a p>ticul> proton are ^? :i* are mom5t>ily describ+ orbits ar\nd ! nucleus 9 :i* ! proton resides4 ,a /udy ( /ell> /ructure supports ?is hypo!sis1 = if en]gy c\ld be g5]at$ by free electrons fall+ into nuclei1 x c be %ewn t ! :ole /> w\ld be un/able & w\ld explode 9 a fla% ( radiation4 ,on ?is hypo!sis1 a /> 9 :i* only a few atoms h any electrons left 9 orbital motion c ( c\rse g5]ate b little en]gy4 ,?is at once expla9s ! feeble en]gy-g5]at+ p[]s ( ! :ite dw>fs1 & also gives an inkl+ z to :y ! r$ giants1 9 :i* ,l- & ,m-r+s ( electrons survive1 g5]ate m en]gy ?an ma9-sequ5ce />s ( equal weights4 ,z a /> ages & its weight decreases1 x cont9ually has to pick out new configurations su* z make its emission ( en]gy equal to its int]nal rate ( g5]ation ( en]gy4 ,! same /> may be a r$ giant1 a ma9-sequ5ce /> & a :ite dw>f 9 turn4 ,/ripp$ ( te*nicalities ?is means t a /> cont9ually adju/s its diamet] to suit its v>y+ rate ( g5]ation ( en]gy4 ,on ! hypo!sis j consid]$1 a /> alt]s bo? its emission & its g5]ation ( en]gy on *ang+ its diamet]4 ,at e in/ant x has to select a diamet] = :i* ! two exactly balance4 ,! /> has s l>ge a range ( rates ( g5]ation1 accord+ z x has few or _m electrons left 9 orbital motion1 t x is likely always to be able to f9d a configuration ( equilibrium4 ,at any rate all ! />s 9 ! sky appe> to h done s1 ) ! exception ( ! long p]iod v>iables :i* are cont9ually exp&+ & contract+ z ?\gh !y c\ld n hit ^u a diamet] at :i* _! income & exp5diture ( en]gy w\ld j balance4 ,?is same hypo!sis imm$iately makes x possible = all ! great v>iety ( />s 9 ! galactic sy/em to be ( approximately ! same age1 & s to h be5 all born out ( ! same nebula4 ,! mo/ lum9\s galactic />s c h>dly h be5 g5]at+ en]gy at _! pres5t rate = m ?an ab\t #ajj1jjj million ye>s--any long] age w\ld require an impossibly high weight to />t )4 ,yet ! motions ( ! />s indicate t ev5 ^! highly lum9\s />s mu/ h be5 9 exi/5ce = at lea/ #ej times ?is p]iod4 ,! app>5t contradiction disappe>s if we admit t ! extreme lum9osity ( ! v brighte/ />s may be a rec5t developm5t1 & t = p]haps #ih p] c5t4 ( its life su* a /> 0 los+ b little en]gy because mo/ ( its atoms 7 /ripp$ b>e ( electrons & s 7 immune f annihilation4 ,! requisite proportion ( #ih p] c5t4 may seem suspici\sly l>ge1 b we h /at$ an extreme case2 we ne$ only dem& s l>ge a proportion 9 ! case ( a v r>e type ( />3 probably n m ?an "o /> 9 t5 million is ( su* a type4 ,9 _! e>li] dormant /ate1 ^! />s1 :i* are n[ s lum9\s1 w\ld 9 effect h be5 :ite dw>fs ( enorm\s weight4 ,obs]vational a/ronomy provides no evid5ce t any su* />s exi/1 b !re is c]ta9ly no evid5ce t !y d n exi/4 ,v massive />s are kn[n to be v r>e objects1 s t 9 all probability we %\ld h to travel a long di/ance f ! sun be=e f9d+ "o1 & !n x might be s di/ant z to be invisible f ! e>?4 ,9 any case1 a v di/ant /> ( feeble lum9osity w\ld be exce$+ly likely to escape detection4 ,we c\ld n inf] t no su* />s exi/$ f ! fact ( none hav+ yet be5 f\nd4 ,moreov]1 x is f> f absolutely c]ta9 t su* />s h n be5 f\nd4 ,v massive :ite dw>fs ought to h high] surface-temp]atures ?an ei!r massive ma9-sequ5ce />s or ?an ! kn[n :ite dw>fs1 all ( :i* are ( small weight4 ,a :ole gr\p ( />s is kn[n--! ,o-type />s--^: spectra indicate v high temp]atures inde$4 ,^! are usually int]pret$ z />s ( enorm\s lum9osity at enorm\s di/ances1 b x is possible t "s at lea/ ( !m may be />s ( feeble lum9osity at mod]ate di/ances4 ,9 p>ticul> ! c5tral />s ( ! planet>y nebulae are ( types ,o & ,b4 ,b :]eas ! normal ma9-sequ5ce /> ( ^! spectral types is g5]ally ab\t a ?\s& times z lum9\s z ! sun1 ! c5tral />s ( ! planet>y nebulae are f\nd to be consid]ably less lum9\s ?an ! sun4 ,dr ,g]asimovi has rec5tly %ewn t #eb ( ^! />s h an av]age lum9osity only ab\t two-?irds ( t ( ! sun4 ,o!r obs]v]s h f\nd ev5 l[] lum9osities4 ,z ! surface-temp]atures ( ^! />s mu/ be ( ! ord] ( #cj1jjj degrees1 !y mu/ be m9ute 9 size2 inde$ a simple calculation %ews t !y c h>dly h m ?an ab\t a t5? ( ! sun's radius4 ,n only are !y small 9 size1 b !re are indications t !y are ( great weight4 ,spectroscopic evid5ce %ews t 9 _m cases ! surr\nd+ nebulae are 9 rotation1 &1 j z ) ! galaxy 7p4 #fi7 & ! huge extra-galactic nebulae 7p4 #ga71 _! weights c be calculat$ f _! obs]v$ spe$s ( rotation4 ,^! seem to indicate av]age weights ( some?+ l #dj or #ej times ! weight ( ! sun4 ,campbell & ,moore1 ( ,lick ,obs]vatory1 h calculat$ t ! planet>y nebula ,n4,g4,c4 #gjji mu/ h #afb times ! weight ( ! sun1 b _m factors comb9e to make ?is e/imate r unc]ta94 ,all ?is goes to sugge/ t ! c5tral />s ( ! planet>y nebulae mu/1 9 all probability1 be reg>d$ z 8:ite dw>fs0 ( enorm\s weight4 ,x seems possible t !y are exactly ! type ( /> ne$$ by our !ory4 ,! #eb planet>y nebulae already m5tion$ h ! same av]age di/ance f ! sun1 & ! same di/ribution ) respect to ! galaxy1 z ! ,o-type />s1 s t x is possible t ,o-type />s & planet>y nebulae are =ms assum$ ei!r successively or alt]natively 9 ! c\rse ( evolution ( simil> bodies4 ,x %\ld be m5tion$ t ! planet>y nebulae exhibit spectral displacem5ts :i*1 if int]pret$ 9 ! ord9>y way1 w\ld indicate t !y are mov+ ) v high spe$s1 9 "s cases rea*+ hundr$s ( miles a second4 ,su* spe$s w\ld be entirely inappropriate to />s ( l>ge weight4 ,yet ?is objection r defeats itself1 = if ! spectral %ifts really arose f high spe$s ( motion1 ! highe/ ( ! obs]v$ spe$s w\ld suffice to c>ry ! planet>y nebulae possess+ !m cle> ( ! galactic sy/em altoge!r2 !y w\ld be r&om travell]s ?r\gh our sy/em ( />s1 :]eas _! ord]ly arrangem5t & conc5tration ne> ! galactic plane sugge/s v =cibly t !y are p]man5t memb]s ( x4 ,?us ! obs]v$ l>ge %ifts ( ! spectral l9es c h>dly indicate l>ge spe$s 9 space2 "s o!r int]pretation mu/ be f\nd4 ,pr(essor ,p]r9e consid]s t !y arise 9 ! ma9 f int]nal motions1 contraction1 expansion & rotation ( ! nebulae4 ,if s1 ! motions 9 space _c be det]m9$1 b at lea/ !y no long] pres5t any difficulty4 ,if ^! />s are1 z our hypo!sis requires1 :ite dw>fs ( v great weight & small radius1 _! spectra ought to exhibit a relativity displacem5t to ! r$ ( ! same type z t actually obs]v$ 9 ,sirius ,b4 ,x is possible t ?is may be f\nd to pres5t a m s]i\s difficulty1 al?\gh x is also possible t x aga9 may prove to be m]g$ 9 ! l>ge obs]v$ displacem5ts4 ,9 view ( all ?is1 x seems q possible t bo? ! planet>y nebulae1 & also o!r ,o- or ,b-type />s ( feeble lum9osity1 may be v massive />s 9 ! dormant condition contemplat$ by ! hypo!sis we h j be5 discuss+4 ,9 brief1 we imag9e t a massive /> may h its weight cons]v$ ?r\gh exi/+ z a planet>y nebula or a dw>f ,o-type /> = millions ( millions ( ye>s1 & !n bur/ out z a highly lum9\s /> ) all ! appe>ance ( extreme y\?4 ,b !re is at pres5t insuffici5t obs]vational evid5ce ei!r = or aga9/ su* a hypo!sis4 ,"s pieces ( ! puzzle are miss+1 & we c only wait until !y turn up4 ,,:ite ,,dw>fs4 ,ap>t f ^! hypo!tical massive :ite dw>fs1 a/ronom]s g5]ally reg>d ord9>y :ite dw>fs z ! f9al /age 9 /ell> evolution4 ,!re is g5]al agreem5t t !y are />s ) c5tral temp]atures s high t _! atoms are /ripp$ b>e ( electrons1 b !re is no g5]al cons5sus ( op9ion z to :y />s %r9k to ?is condition4 ,on ! liquid-/> hypo!sis1 ! unoccupi$ regions 9 ! ,russell diagram repres5t un/able configurations4 ,usually a slight loss ( weight by a /> m]ely moves x to a new position 9 ! diagram contigu\s to ! old "o4 ,sometimes1 h[ev]1 ?is slight move may happ5 to c>ry ! /> into an un/able region ( ! diagram1 9 :i* case x w hurri$ly trav]se ?is region1 until f9ally x ends up 9 "s entirely diff]5t /able configuration4 ,! liquid-/> hypo!sis expla9s ! :ite dw>f /ate q simply z ! f9al /ate to :i* a /> %r9ks cataclysmically :5 its g5]ation ( en]gy is no long] suffici5t to entitle x to a place 9 ! ma9-sequ5ce4 ,9 ?is /ate ! /> radiates s little en]gy t annihilation & decay are almo/ entirely *eck$4 ,we h se5 t if ! sun w5t on radiat+ at its pres5t rate = #ae million million ye>s1 its :ole weight w\ld be trans=m$ into radiation4 ,by contra/1 van ,maan5's /> c1 & probably w1 g on radiat+ at its pres5t rate = #ae million million ye>s )\t los+ m ?an ab\t a ?\s&? "p ( its pres5t weight4 ,we may ?9k ( ! :ite dw>f /ate z a f9al /ate f :i* *ange & decay h s ne>ly disappe>$ t a /> :i* %r9ks to ?is /ate acquires a new lease ( life = a p]iod ( ?\s&s ( millions ( millions ( ye>s--we c only wond] to :at purpose4 ,,*apt] ,,vi ,beg9n+s & ,end+s ,we h se5 h[ ! solid sub/ance ( ! mat]ial univ]se is cont9ually dissolv+ away into intangible radiation4 ,! sun weigh$ #cfj1jjj million tons m ye/]day ?an to-day1 ! diff]5ce be+ ! weight ( #bd-;h\rs' emission ( radiation :i* is n[ travell+ ?r\gh space1 &1 s f> z direct obs]vation goes1 is de/9$ to j\rney on ?r\gh space until ! end ( "t4 ,! same trans=mation ( mat]ial weight into radiation is 9 progress 9 all ! />s1 & to a less] degree on e>?1 :]e complex atoms su* z uranium are cont9ually *ang+ into ! simpl] atoms ( lead & helium1 & sett+ radiation free 9 ! process4 ,b aga9/ ! sun's daily loss ( weight ( #cfj1jjj million tons1 ! e>? is only los+ weight f ?is cause at ! rate ( ab\t n9ety p\nds a day4 ,,cyclic ,,processes4 ,x is natural to ask :e!r a /udy ( ! univ]se z a :ole reveals ^! processes z "p only ( a clos$ cycle1 s t ! wa/age :i* we see 9 progress 9 ! sun & />s & on ! e>? is made good else:]e4 ,:5 we /& on ! banks ( a riv] & wat* its curr5t ev] c>ry+ wat] out to sea1 we "k t ?is wat] is 9 due c\rse trans=m$ into cl\ds & ra9 :i* repl5i% ! riv]4 ,is ! physical univ]se a simil> cyclic sy/em1 or ought x r to be comp>$ to a /ream :i*1 hav+ no s\rce ( repl5i%m5t1 mu/ cease fl[+ aft] x has sp5t itself8 ,,!rmodynamics ,to ?is "q1 ! wide sci5tific pr9ciple kn[n z ! second law ( !rmodynamics provides an answ] 9 v g5]al t]ms4 ,if we ask :at is ! und]ly+ cause ( all ! v>i$ animation we see ar\nd u 9 ! _w1 ! answ] is 9 e case1 en]gy--! *emical en]gy ( ! fuel :i* drives our %ips1 tra9s & c>s1 or ( ! food :i* keeps our bodies alive & is us$ 9 muscul> ef=t1 ! me*anical en]gy ( ! e>?'s motion :i* is responsible = ! alt]nations ( day & night1 ( summ] & w9t]1 ( high tide & l[ tide1 ! heat-en]gy ( ! sun :i* makes our crops gr[ & provides u ) w9d & ra94 ,! fir/ law ( !rmodynamics1 :i* embodies ! pr9ciple ( 8cons]vation ( en]gy10 tea*es t en]gy is inde/ructible2 x may *ange ab\t f "o =m to ano!r1 b its total am\nt rema9s unalt]$ ?r\gh all ^! *anges1 s t ! total en]gy ( ! univ]se rema9s always ! same4 ,z ! en]gy :i* is ! cause ( all ! life ( ! univ]se is inde/ructible1 x might be ?\ght t ?is life c\ld g on = ev] undim9i%$ 9 am\nt4 ,,availability ,,( ,,en]gy4 ,! second law ( !rmodynamics rules out any su* possibility4 ,en]gy is inde/ructible z reg>ds its am\nt1 b x cont9ually *anges 9 =m1 & g5]ally speak+ !re are upw>d & d[nw>d directions ( *ange4 ,x is ! usual /ory--! d[nw>d j\rney is easy1 :ile ! upw>d is ei!r h>d or impossible4 ,z a consequ5ce1 m en]gy passes 9 "o direction ?an 9 ! o!r4 ,= in/ance1 bo? light & heat are =ms ( en]gy1 & a million ergs ( light-en]gy c be trans=m$ into a million ergs ( heat ) ! utmo/ ease2 let ! light fall on any cool1 black surface1 & ! ?+ is done4 ,b ! rev]se trans=mation is impossible2 a million ergs :i* h once assum$ ! =m ( heat1 c nev] aga9 assume ! =m ( a million ergs ( light4 ,?is is a special example ( ! g5]al pr9ciple t radiative en]gy t5ds always to *ange into a =m ( long]1 n %ort]1 wave-l5g?4 ,9 g5]al1 = in/ance1 fluoresc5ce increases ! wave-l5g? ( ! light2 x *anges blue light into gre51 yell[ or r$1 b n r$ light into yell[1 gre5 or blue4 ,exceptions to ! g5]al pr9ciple are kn[n1 b !y are ( special type1 admitt+ ( special explanations1 & d n affect ! g5]al pr9ciple4 ,x may be object$ t ! ev]yday act ( light+ a fire disproves all ?is4 ,has n ! sun's heat be5 /or$ up 9 ! coal we burn1 & _c we produce light by burn+ coal8 ,! answ] is t ! sun's radiation is a mixture ( bo? light & heat1 & inde$ ( radiation ( all wave-l5g?s4 ,:at is /or$ up 9 ! coal is prim>ily ! sun's light & o!r radiation ( /ill %ort] wave-l5g?4 ,:5 we burn coal we get "s light1 b n z mu* z ! sun orig9ally put into ! coal2 we also get "s heat1 & ?is is m ?an ! am\nt ( heat :i* 0 orig9ally put 94 ,on balance1 ! net result ( ! :ole transaction is t a c]ta9 am\nt ( light has be5 trans=m$ into a c]ta9 am\nt ( heat4 ,all ?is %ews t we mu/ le>n to ?9k ( en]gy1 n only 9 t]ms ( quantity1 b also 9 t]ms ( quality4 ,its total quantity rema9s always ! same2 ?is is ! fir/ law ( !rmodynamics4 ,b its quality *anges1 & t5ds to *ange always 9 ! same direction4 ,turn/iles are set up betwe5 ! diff]5t qualities ( en]gy2 ! passage is easy 9 "o direction1 impossible 9 ! o!r4 ,a human cr[d may contrive to f9d a way r\nd )\t jump+ ov] turn/iles1 b 9 nature !re is no way r\nd2 ?is is ! second law ( !rmodynamics4 ,en]gy fl[s always 9 ! same direction1 z surely z wat] fl[s d[nhill4 ,"p ( ! d[nw>d pa? consi/s1 z we h se51 ( ! transition f radiation ( %ort wave-l5g? into radiation ( long] wave-l5g?4 ,9 t]ms ( quanta 7p4 #abf7 ! transition is f a few quanta ( high en]gy to a l>ge numb] ( quanta ( l[ en]gy1 ! total am\nt ( en]gy ( c\rse rema9+ unalt]$4 ,! d[nfall ( ! en]gy accord+ly consi/s 9 ! break+ ( its quanta into small] units4 ,& :5 once ! fall & breakage h tak5 place1 x is z impossible to recon/itute ! orig9al l>ge quanta z x 0 to put ,humpty-,dumpty back on 8 wall4 ,al?\gh ?is is ! ma9 "p ( ! d[nw>d pa?1 x is n ! :ole ( x4 ,!rmodynamics tea*es t all ! diff]5t =ms ( en]gy h diff]5t degrees ( 8availability10 & t ! d[nw>d pa? is always f high] to l[] availability4 ,& n[ we may return to ! "q ) :i* we />t$ ! pres5t *apt]3 8,:at is x t keeps ! v>i$ life ( ! univ]se go+80 ,our orig9al answ] 8en]gy0 is se5 to be incomplete4 ,en]gy is no d\bt ess5tial1 b ! really complete answ] is t x is ! trans=mation ( en]gy f a m available to a less available =m2 x is ! runn+ d[nhill ( en]gy4 ,to argue t ! total en]gy ( ! univ]se _c dim9i%1 & !re=e ! univ]se mu/ g on = ev]1 is l argu+ t z a clock-weight _c dim9i%1 ! clock-h& mu/ g r\nd & r\nd = ev]4 ,,! ,,f9al ,,end ,,( ,,! ,,univ]se ,en]gy _c run d[nhill = ev]1 &1 l ! clock-weight1 x mu/ t\* bottom at la/4 ,& s ! univ]se _c g on = ev]2 soon] or lat] ! "t mu/ come :5 its la/ erg ( en]gy has rea*$ ! l[e/ rung on ! ladd] ( desc5d+ availability1 & at ?is mom5t ! active life ( ! univ]se mu/ cease4 ,! en]gy is /ill !re1 b x has lo/ all capacity = *ange2 x is z little able to "w ! univ]se z ! wat] 9 a flat pond is able to turn a wat]-:eel4 ,we are left ) a dead1 al?\gh possibly a w>m1 univ]se--a 8heat-dea?40 ,su* is ! tea*+ ( mod]n !rmodynamics4 ,!re is no reason = d\bt+ or *all5g+ x1 & inde$ x is s fully confirm$ by ! :ole ( our t]re/rial exp]i5ce1 t x is difficult to see at :at po9t x c\ld be op5 to attack4 ,x disposes at once ( any possibility ( a cyclic univ]se 9 :i* ! ev5ts we see are z ! p\r+ ( riv] wat] into ! sea1 :ile ev5ts we d n see re/ore ?is wat] back to ! riv]4 ,! wat] ( ! riv] c g r\nd & r\nd 9 ?is way1 j because x is n ! :ole ( ! univ]se2 some?+ extrane\s to ! riv]-cycle keeps x cont9ually 9 motion--namely1 ! heat ( ! sun4 ,b ! univ]se z a :ole _c s g r\nd & r\nd4 ,%ort ( po/ulat+ cont9u\s action f outside ! univ]se1 :atev] ?is may mean1 ! en]gy ( ! univ]se mu/ cont9ually lose availability2 a univ]se 9 :i* ! en]gy _h no fur!r availability to lose w\ld be dead already4 ,*ange c occur only 9 ! "o direction1 :i* leads to ! heat-dea?4 ,) univ]ses z ) mortals1 ! only possible life is progress to ! grave4 ,ev5 ! fl[ ( ! riv] to ! sea1 :i* we select$ z an obvi\s in/ance ( true cyclic motion1 is se5 to illu/rate ?is1 z soon z all ! relevant factors are tak5 into acc\nt4 ,z ! riv] p\rs seaw>d ov] its falls & cascades1 ! tumbl+ ( its wat]s g5]ates heat1 :i* ultimately passes (f into space 9 ! =m ( heat radiation4 ,b ! en]gy :i* keeps ! riv] p\r+ along comes ultimately f ! sun 9 ! =m ma9ly ( light2 %ut (f ! sun's radiation & ! riv] w soon /op fl[+4 ,! riv] fl[s only by cont9ually trans=m+ light-en]gy into heat-en]gy1 & z soon z ! cool+ sun ceases to supply en]gy ( suffici5tly high availability ! fl[ mu/ cease4 ,! same g5]al pr9ciples may be appli$ to ! a/ronomical univ]se4 ,!re is no "q z to ! way 9 :i* en]gy runs d[n "h4 ,x is fir/ lib]at$ 9 ! hot int]ior ( a /> 9 ! =m ( quanta ( extremely %ort wave-l5g? & excessively high en]gy4 ,z ?is radiant en]gy /ruggles out to ! />'s surface1 x cont9ually adju/s itself1 ?r\gh repeat$ absorption & re-emission1 to ! temp]ature ( t "p ( ! /> ?r\gh :i* x is pass+4 ,z long] wave-l5g?s are associat$ ) l[] temp]atures 7p4 #adj71 ! wave-l5g? ( ! radiation is cont9ually l5g!n$2 a few en]getic quanta are be+ trans=m$ into num]\s feeble quanta4 ,once ^! are free 9 space1 !y travel onw>d un*ang$ until !y meet du/ p>ticles1 /ray atoms1 free electrons1 or "s o!r =m ( int]/ell> matt]4 ,except 9 ! highly improbable ev5t ( ?is matt] be+ at a high] temp]ature ?an ! surfaces ( ! />s1 ^! enc\nt]s /ill fur!r increase ! wave-l5g? ( ! radiation1 & ! f9al result ( innum]able enc\nt]s is radiation ( v great wave-l5g?4 ,! quanta h increas$ enorm\sly 9 numb]s1 b h paid = _! increase by a correspond+ decrease 9 individual /r5g?4 ,9 all probability1 ! orig9al v en]getic quanta _h _! s\rce 9 ! annihilation ( protons & electrons1 s t ! ma9 process ( ! univ]se consi/s 9 ! en]gy ( exce$+ly high availability :i* is bottl$ up 9 electrons & protons be+ trans=m$ into heat-en]gy at ! l[e/ level ( availability4 ,_m1 giv+ re9 to _! fancy1 h speculat$ t ?is l[-level heat-en]gy may 9 due c\rse re-=m itself into new electrons & protons4 ,z ! exi/+ univ]se dissolves away into radiation1 _! imag9ation sees new heav5s & a new e>? com+ into be+ out ( ! a%es ( ! old4 ,b sci5ce c give no support to su* fancies4 ,p]haps x is z well2 x is h>d to see :at advantage c\ld accrue f an et]nal reit]ation ( ! same !me1 or ev5 f endless v>iations ( x4 ,! f9al /ate ( ! univ]se w1 !n1 be atta9$ :5 e atom :i* is capable ( annihilation has be5 annihilat$1 & its en]gy trans=m$ into heat-en]gy w&]+ = ev] r\nd space1 & :5 all ! weight ( any k9d :atev] :i* is capable ( be+ trans=m$ into radiation has be5 s trans=m$4 ,we h m5tion$ ,hubble's e/imate t matt] is di/ribut$ 9 space at an av]age rate ( #ae #aj grammes p] cubic c5timetre4 ,! annihilation ( a gramme ( matt] lib]ates #i #aj ergs ( en]gy1 s t ! annihilation ( #ae #aj grammes ( matt] lib]ates #ace #aj ergs ( en]gy4 ,x foll[s t ! total annihilation ( all ! sub/ance ( ! exi/+ univ]se w\ld only fill space ) en]gy at ! rate ( #ace #aj ergs p] cubic c5timetre4 ,?is am\nt ( en]gy is only en\gh to raise ! temp]ature ( space f absolute z]o to a temp]ature f> bel[ t ( liquid air2 x w\ld only raise ! temp]ature ( ! e>?'s surface by a #fjjj? "p ( a degree ,c5tigrade4 ,! reason :y ! effect ( annihilat+ a :ole univ]se is s extraord9>ily slight is ( c\rse t space is s extraord9>ily empty ( matt]2 try+ to w>m space by annihilat+ all ! matt] 9 x is l try+ to w>m a room by burn+ a speck ( du/ "h & a speck ( du/ !re4 ,z comp>$ ) any am\nt ( radiation t is ev] likely to be p\r$ into x1 ! capacity ( space is t ( a bottomless pit4 ,inde$1 s f> z sci5tific obs]vation goes1 x is entirely possible t ! radiation ( ?\s&s ( dead univ]ses may ev5 n[ be w&]+ r\nd space )\t our suspect+ x4 ,su* is ! f9al end ( ?+s to :i*1 s f> z pres5t-day sci5ce c see1 ! mat]ial univ]se mu/ inevitably come 9 "s f>-(f age1 unless ! c\rse ( nature is *ang$ 9 ! meantime4 ,let u n[ try to pe] back t[>ds ! beg9n+s ( ?+s4 ,,! ,,beg9n+s ,,( ,,! ,,univ]se ,z we g =w>ds 9 "t1 mat]ial weight cont9ually *anges into radiation4 ,conv]sely1 z we g backw>ds 9 "t1 ! total mat]ial weight ( ! univ]se mu/ cont9ually increase4 ,we h se5 h[ ! pres5t weights ( ! />s are incompatible ) _! hav+ exi/$ = m ?an "s #e or #aj million million ye>s1 & t !y w\ld ne$ approximately ! :ole ( ?is enorm\s p]iod to acquire c]ta9 signs ( age :i* _! pres5t arrangem5t & motions reveal4 ,we h se5 t ! break-up ( ! huge extra-galactic nebulae mu/ result 9 ! bir? ( />s1 & h f\nd t ! mo/ consi/5t acc\nt ( ! orig9 ( ! galactic sy/em ( />s is provid$ by ! supposition t ! :ole sy/em orig9at$ out ( ! break-up ( a s+le huge nebula "s #e to #aj million million ye>s ago4 ,let u pause = a mom5t to comp>e ?is ) an alt]native hypo!sis1 :i* "s a/ronom]s h fav\r$1 t />s are be+ creat$ all ! "t4 ,on ?is hypo!sis we picture ! />s z pass+ 9 an endless /eady /ream f creation to ext9ction1 j z m5 pass 9 an endless /eady /ream f _! cradles to _! graves1 a new g5]ation always com+ into be+ to /ep into ! place vacat$ by ! old4 ,on ?is view ,plaskett's />1 ) ab\t a hundr$ times ! weight ( ! sun1 mu/ be a rec5t creation1 :ile ,krug] #fj1 ) only a fraction ( ! sun's weight1 w\ld be v1 v old--p]haps #ajj million million ye>s old] ?an ,plaskett's />4 ,at pres5t direct obs]vation _c def9itely decide betwe5 ! two conflict+ hypo!ses1 b x r fr[ns ^u ! 8/eady /ream0 view ( ! />s4 ,9 a /eady population ! numb] ( p 9 any assign$ condition is exactly proportional to ! "t tak5 to pass ?r\gh t condition4 ,suppose = in/ance t human be+s possess infant tee? = a qu>t] z long z !y possess adult tee?4 ,if exam9ation ( ! tee? ( a population %ew$ t f\r times z _m _h adult tee? z infant tee?1 ?is w\ld create a prima facie expectation t we 7 deal+ ) a /eady population4 ,if1 on ! contr>y1 #ajj times z _m p 7 f\nd ) adult tee? z ) infant tee?1 we %\ld "k we 7 n deal+ ) a /eady population4 ,if o!r evid5ce po9t$ to ! population all be+ ( approximately ! same age1 we %\ld be incl9$ to accept ?is & reg>d ! #a p] c5t4 ( cases ( infant tee? z cases ( arre/$ developm5t4 ,we d n judge ! ages ( />s by _! tee? b by _! weights & lum9osities4 ,& ! lum9osities ( ! />s are n f\nd to con=m to ! /ati/ical laws :i* w\ld prevail 9 a /eady population ( />s4 ,!re appe> to be s _m middle-ag$ />s & s few infants & vet]ans z to make ! hypo!sis ( a /eady cont9u\s creation h>dly t5able4 ,inde$ !re is r di/9ct evid5ce ( a special creation ( />s at ab\t ! "t our sun 0 born4 ,?is leads back aga9 q naturally to ! view t ! galactic sy/em 0 born out ( a spiral nebula ^: ma9 activity z a p>5t ( />s occurr$ "s #e to #aj million million ye>s ago4 ,,pre-,,/ell> ,,exi/5ce4 ,on ! :ole x seems likely t we mu/ assign ages ( #e to #aj million million ye>s to mo/ or all ( ! />s 9 ! galactic sy/em4 ,?is is z f> z we c probe back into "t ) any reasonable plausibility4 ,! atoms :i* n[ =m ! sun & />s mu/ no d\bt h _h a previ\s exi/5ce z atoms ( a nebula1 b we _c say = h[ long4 ,! temp]atures at ! c5tres ( ! spiral nebulae may be1 & 9 all probability are1 s high t atoms are /ripp$ b>e ( electrons & s %ield$ f annihilation4 ,we may 9 fact reg>d ! gase\s c5tres ( nebulae z a sort ( 8:ite dw>fs0 built on a colossal scale4 ,?is fits on to ! fact t ! nebulae g5]ate v little en]gy = _! weights & s %9e v feebly4 ,we h se5 t ! weights ( two extra-galactic nebulae c be e/imat$ to a reasonable degree ( accuracy4 ,! great ,&rom$a nebula ,m #ca has ! weight ( #cejj million suns1 its total lum9osity be+ t ( #ffj million suns4 ,! nebula ,n4,g4,c4 #deid has ! weight ( #bjjj million suns1 & ! lum9osity ( #bfj million suns4 ,a simple calculation %ews t ! atoms 9 ! ,&rom$a nebula h an av]age expectation ( life ( #hj million million ye>s1 :ile ! correspond+ figure 9 ,n4,g4,c4 #deid is #aae million million ye>s4 ,f ^! two in/ances1 we may guess t ! av]age life1 be=e annihilation1 ( ! atoms 9 su* nebulae mu/ be ( ! ord] ( #ajj million million ye>s4 ,x _c be claim$ t ?is calculation is ei!r v conv9c+ or v exact1 b x supplies ! only evid5ce at pres5t available z to ! probable l5g? ( life ( matt] 9 ! nebul> /ate4 ,we c say t ! />s h exi/$ z su* = f #e to #aj million million ye>s1 & t _! atoms may h previ\sly exi/$ 9 nebulae = at lea/ a comp>able1 & possibly = a mu* long]1 "t4 ,ap>t f detail$ figures1 h[ev]1 x is cle> t we _c g backw>d 9 "t = ev]4 ,ea* /ep back 9 "t involves an increase 9 ! total weight ( ! matt] ( ! univ]se1 &1 j z ) individual />s1 we _c g s f> back t ?is total weight becomes inf9ite4 ,inde$ a limit may q possibly be set by consid]ations :i* we h already m5tion$4 ,! complete annihilation ( all ! matt] n[ 9 ! univ]se w\ld raise ! temp]ature ( ! e>?'s surface by ! six-?\s&? "p ( a degree2 ! annihilation ( a million times z mu* matt] w\ld raise x by #afj degrees4 ,we _c admit t z mu* radiation z ?is c be w&]+ ab\t space4 ,! e>?'s temp]ature is det]m9$ by ! am\nt ( radiation x receives f ! sun2 x adju/s its temp]ature s t x radiates away j z mu* en]gy z x receives4 ,a small correction is requir$ on acc\nt ( ! e>?'s own radio-activity1 b ?is ne$ n bo!r u4 ,:at w\ld bo!r u1 & w\ld inde$ upset ! balance entirely1 w\ld be ! radiation ( a million dead univ]ses if ?is 7 = ev] /ream+ on to u out ( space2 9 ?is ev5t ! e>?'s surface w\ld h to rise to a temp]ature well above t ( boil+ wat] be=e x c\ld re/ore ! balance betwe5 ! radiation x receiv$ & t x emitt$4 ,9 a ^w1 ! radiation ( a million dead univ]ses w\ld boil our seas1 riv]s & ourselves4 ,,! ,,creation ,,( ,,matt]4 ,all ?is makes x cle> t ! pres5t matt] ( ! univ]se _c h exi/$ = ev]3 inde$ we c probably assign an upp] limit to its age (1 say1 "s su* r\nd numb] z #bjj million million ye>s4 ,&1 :]ev] we fix x1 our next /ep back 9 "t leads u to contemplate a def9ite ev5t1 or s]ies ( ev5ts1 or cont9u\s process1 ( creation ( matt] at "s "t n inf9itely remote4 ,9 "s way matt] :i* _h n previ\sly exi/$1 came1 or 0 br\ght1 into be+4 ,if we want a naturali/ic int]pretation ( ?is creation ( matt]1 we may imag9e radiant en]gy ( any wave-l5g? less ?an #ac #aj cms4 be+ p\r$ into empty space2 ?is is en]gy ( high] 8availability0 ?an any kn[n 9 ! pres5t univ]se1 & ! runn+ d[n ( su* en]gy might well create a univ]se simil> to our own4 ,! table on p4 #add %ews t radiation ( ! wave-l5g? j m5tion$ might conceivably cry/allise into electrons & protons1 & f9ally =m atoms4 ,if we want a concrete picture ( su* a creation1 we may ?9k ( ! f+] ( ,god agitat+ ! e!r4 ,we may avoid ?is sort ( crude imag]y by insi/+ on space1 "t1 & matt] be+ treat$ toge!r & insep>ably z a s+le sy/em1 s t x becomes mean+less to speak ( space & "t z exi/+ at all be=e matt] exi/$4 ,su* a view is consonant n only ) anci5t metaphysical !ories1 b also ) ! mod]n !ory ( relativity 7p4 #gd74 ,! univ]se n[ becomes a f9ite picture ^: dim5sions are a c]ta9 am\nt ( space & a c]ta9 am\nt ( "t2 ! protons & electrons are ! /reaks ( pa9t :i* def9e ! picture aga9/ its space-"t backgr\nd4 ,travell+ z f> back 9 "t z we c1 br+s u n to ! creation ( ! picture1 b to its edge2 ! creation ( ! picture lies z mu* outside ! picture z ! arti/ is outside 8 canvas4 ,on ?is view1 discuss+ ! creation ( ! univ]se 9 t]ms ( "t & space is l try+ to discov] ! arti/ & ! action ( pa9t+1 by go+ to ! edge ( ! picture4 ,?is br+s u v ne> to ^? philosophical sy/ems :i* reg>d ! univ]se z a ?\ght 9 ! m9d ( its ,creator1 !reby r$uc+ all discussion ( mat]ial creation to futility4 ,bo? ^! po9ts ( view are impregnable1 b s also is t ( ! pla9 man :o1 recognis+ t x is impossible = ! human m9d to compreh5d ! full plan ( ! univ]se1 decides t 8 own ef=ts %all /op ?is side ( ! creation ( matt]4 ,?is la/ po9t ( view is p]haps ! mo/ ju/ifiable ( all f ! purely philosophic /&po9t4 ,x is n[ a full qu>t] ( a c5tury s9ce physical sci5ce1 l>gely "u ! lead]%ip ( ,po9c>1 left (f try+ to expla9 ph5om5a & resign$ itself m]ely to describ+ !m 9 ! simple/ way possible4 ,to take ! simple/ illu/ration1 ! ,victorian sci5ti/ ?\ght x necess>y to 8expla90 light z a wave-motion 9 ! me*anical e!r :i* he 0 = ev] try+ to con/ruct out ( jellies & gyroscopes2 ! sci5ti/ ( to-day1 =tunately = 8 sanity1 has giv5 up ! attempt & is well satisfi$ if he c obta9 a ma!matical =mula :i* w pr$ict :at light w d "u specifi$ conditions4 ,x does n matt] mu* :e!r ! =mula admits ( a me*anical explanation or n1 or :e!r su* an explanation corresponds to any ?9kable ultimate reality4 ,! =mulae ( mod]n sci5ce are judg$ ma9ly1 if n entirely1 by _! capacity = describ+ ! ph5om5a ( nature ) simplicity1 accuracy1 & complet5ess4 ,= in/ance1 ! e!r has dropp$ out ( sci5ce1 n because sci5ti/s z a :ole h =m$ a reason$ judgm5t t no su* ?+ exi/s1 b because !y f9d !y c describe all ! ph5om5a ( nature q p]fectly )\t x4 ,x m]ely cumb]s ! picture1 s !y leave x out4 ,if at "s future "t !y f9d !y ne$ x1 !y w put x back aga94 ,?is does n imply any l[]+ ( ! /&>ds or ideals ( sci5ce2 x implies m]ely a gr[+ conviction t ! ultimate realities ( ! univ]se are at pres5t q beyond ! rea* ( sci5ce1 & may be--& probably are--= ev] beyond ! compreh5sion ( ! human m9d4 ,x is priori probable t only ! arti/ c und]/& ! full significance ( ! picture he has pa9t$1 & t ?is w rema9 = ev] impossible = a few specks ( pa9t on ! canvas4 ,x is = ?is k9d ( reason t1 :51 z 9 ,*apt] ,,ii1 we try to discuss ! ultimate /ructure ( ! atom1 we are driv5 to speak 9 t]ms ( similes1 metaphors1 & p>ables4 ,!re is no ne$ ev5 to worry ov]mu* ab\t app>5t contradictions4 ,! high] unity ( ultimate reality mu/ no d\bt reconcile !m all1 al?\gh x rema9s to be se5 :e!r ?is high] unity is )9 our compreh5sion or n4 ,9 ! meantime a contradiction worries u ab\t z mu* z an unexpla9$ fact1 b h>dly m2 x may or may n disappe> 9 ! progress ( sci5ce4 ,if "s su* tra9 ( ?\ght may be appli$ to our ef=ts to und]/& ! mo/ m9ute processes ( ! univ]se 7& x is ! common ev]yday tra9 ( ?\ght ( ^? :o are work+ 9 ?is field71 !n x mu/ surely be /ill m applicable to our ef=ts to und]/& ! univ]se z a :ole4 ,ph5om5a come to u disguis$ 9 _! frameworks ( "t & space2 !y are messages 9 cyph] ( :i* we %all n und]/& ! ultimate significance until we h discov]$ h[ to decode !m out ( _! space-"t wrapp+s4 ,:atev] may be ?\ght ab\t our f9al ability to decode ! difficult messages we h rec5tly receiv$ ab\t ! ultimate /ructure ( ! m9ute/ p>ts ( matt]1 x seems natural t we %\ld feel "s appreh5sion ) reg>d to ^? ab\t ! /ructure ( ! univ]se z a :ole1 & p>ticul>ly ^? ab\t its beg9n+s & end+s4 ,(t5 en\gh ! message itself may help u to discov] ! code 9 :i* x rea*es u--) suffici5t skill we c (t5 d ?is--b we are n[ speak+ ( problems z to :51 by :om1 & = :at purpose1 ! code 0 devis$4 ,!re is no reason :y a code message %\ld ?r[ any light on ?is4 ,! a/ronom] mu/ leave ! problem at ?is /age4 ,! message ( a/ronomy is ( obvi\s conc]n to philosophy1 to religion & to humanity 9 g5]al1 b x is n ! bus9ess ( ! a/ronom] to decode x4 ,! obs]v+ a/ronom] wat*es & records ! dots & da%es ( ! ne$le :i* deliv]s ! message1 ! !oretical a/ronom] translates ^! into words--& accord+ z !y are f\nd to =m kn[n consi/5t words or n1 x is kn[n :e!r he has done 8 job well or ill--b x is = o!rs to try to und]/& & expla9 ! ultimate decod$ mean+ ( ! words he writes d[n4 ,,life ,,& ,,! ,,univ]se ,ab&on+ our ef=ts to und]/& ! univ]se z a :ole1 let u glance = a mom5t at ! relation ( life to ! univ]se we "k4 ,! old view t e po9t ( light 9 ! sky repres5t$ a possible home = life is q =eign to mod]n a/ronomy4 ,! />s !mselves h surface-temp]atures ( any?+ f #afej degrees to #cj1jjj degrees or m1 & are ( c\rse at f> high] temp]atures inside4 ,by f> ! great] "p ( ! matt] ( ! univ]se is at a temp]ature ( millions ( degrees1 s t its molecules are brok5 up into atoms1 & ! atoms are brok5 up1 p>tially at lea/1 into _! con/itu5t p>ts4 ,n[ ! v concept ( life implies duration 9 "t2 !re c be no life :]e atoms *ange _! make up millions ( times a second & no pair ( atoms c ev] /ay jo9$ toge!r4 ,x also implies a c]ta9 mobility 9 space1 & ^! two implications re/rict life to ! small range ( physical conditions 9 :i* ! liquid /ate is possible4 ,our survey ( ! univ]se has %ewn h[ small ?is range is 9 comp>ison ) t exhibit$ by ! univ]se z a :ole4 ,x is n to be f\nd 9 ! />s1 nor 9 ! nebulae out ( :i* ! />s are born4 ,we "k ( no type ( a/ronomical body 9 :i* ! conditions c be fav\rable to life except planets l our own revolv+ r\nd a sun4 ,n[1 to ! be/ ( our pres5t k1 planets are v r>e4 ,we h se5 h[ a s+le /> _c ( itself produce planets4 ,a family ( planets mu/ h two p>5ts2 x only comes into be+ z ! result ( ! close approa* ( two />s1 & />s are s sp>sely scatt]$ 9 space t x is an inconceivably r>e ev5t = "o to pass ne> to a neighb\r4 ,on ! ,tidal ,!ory1 expla9$ on p4 #bcf1 planets _c be born except :5 two />s pass )9 ab\t ?ree diamet]s ( "o ano!r4 ,z we "k h[ ! />s are scatt]$ 9 space1 we c e/imate fairly closely h[ (t5 two />s w approa* )9 ?is di/ance ( "o ano!r4 ,! calculation %ews t ev5 aft] a /> has liv$ its life ( millions ( millions ( ye>s1 ! *ance is /ill ab\t a hundr$ ?\s& to "o aga9/ its be+ a sun surr\nd$ by planets4 ,ev5 s1 if life is to obta9 a foot+1 ! planets mu/ n be too hot or too cold4 ,9 ! sol> sy/em1 = in/ance1 we _c imag9e life exi/+ on ,m]cury or on ,neptune2 liquids boil on ! =m] & freeze h>d on ! latt]4 ,^! planets are unsuitable = life because !y are too ne> to1 or too f> f1 ! sun4 ,we c imag9e o!r planets :i* are unsuitable because _! sub/ance itself g5]ates en]gy at su* a rate z to make !m unsuitable = habitation4 ,! in]t atoms :i* =m our e>? seem to be ! end products ( a long s]ies ( atomic *anges1 a sort ( f9al a% result+ f ! combu/ion ( ! univ]se4 ,we h se5 h[ su* atoms probably float to ! top 9 e />1 z be+ ! lighte/ 9 weight1 b x is by no means a =egone conclusion t all planets w consi/ ( no?+ b in]t atoms1 & s w cool d[n until life c obta9 a foot+ on !m4 ,?is has happ5$ ) our e>?1 b we d n "k h[ _m planets & planet>y sy/ems may be unsuit$ = life because x has n happ5$ ) !m4 ,all ?is sugge/s t only an inf9itesimally small corn] ( ! univ]se c be 9 ! lea/ suit$ to =m an abode ( life4 ,primaeval matt] mu/ g on trans=m+ itself into radiation = millions ( millions ( ye>s to produce a m9ute quantity ( ! in]t a% on :i* life c exi/4 ,!n by an almo/ incr$ible accid5t ?is a%1 & no?+ else1 mu/ be torn out ( ! sun :i* has produc$ x1 & cond5se into a planet4 ,ev5 !n1 ?is residue ( a% mu/ n be too hot or too cold1 or life w be impossible4 ,f9ally1 aft] all ^! conditions are satisfi$1 w life come or w x n8 ,we mu/ probably disc>d ! at "o "t widely accept$ view t once life _h come into ! univ]se 9 any way :atsoev]1 x w\ld rapidly spread f planet to planet & f "o planet>y sy/em to ano!r until ! :ole univ]se teem$ ) life2 space n[ seems too cold1 & planet>y sy/ems too f> ap>t4 ,our t]re/rial life mu/ 9 all probability h orig9at$ on ! e>? itself4 ,:at we w\ld l to "k is :e!r x orig9at$ z ! result ( /ill ano!r amaz+ accid5t or succession ( co9cid5ces1 or :e!r x is ! normal ev5t = inanimate matt] to produce life 9 due c\rse1 :5 ! physical environm5t is suitable4 ,we look to ! biologi/ = ! answ]1 :i* s f> he has n be5 able to produce4 ,! a/ronom] might be able to give a p>tial answ] if he c\ld f9d evid5ce ( life on "s o!r planet1 = we %\ld !n at lea/ "k t life _h occurr$ m ?an once 9 ! hi/ory ( ! univ]se1 b s f> no conv9c+ evid5ce has be5 =?com+4 ,"s a/ronom]s int]pret c]ta9 m>k+s on ,m>s z canals1 :i* !y believe to be ! h&iwork ( intellig5t be+s1 b ?is int]pretation is n g5]ally accept$4 ,aga91 seasonal *anges necess>ily occur on ,m>s z on ! e>?1 & c]ta9 ph5om5a accompany ^! :i* _m a/ronom]s are incl9$ to ascribe to ! gr[? & decl9e ( vegetation1 al?\gh !y may repres5t no?+ m ?an ra9s wat]+ ! des]t4 ,!re is no def9ite evid5ce ( life1 & c]ta9ly no evid5ce ( consci\s life1 on ,m>s--or inde$ any:]e else 9 ! univ]se4 ,x seems at fir/ some:at surpris+ t oxyg5 figures s l>gely 9 ! e>?'s atmosph]e1 9 view ( its read9ess to ent] into *emical comb9ation ) o!r sub/ances4 ,we "k1 h[ev]1 t vegetation is cont9ually dis*>g+ oxyg5 into ! atmosph]e1 & x has (t5 be5 sugge/$ t ! oxyg5 ( ! e>?'s atmosph]e may be ma9ly or entirely ( vegetable orig94 ,if s1 ! pres5ce or abs5ce ( oxyg5 9 ! atmosph]es ( o!r planets %\ld %ew :e!r vegetation simil> to t we h on e>? exi/s on ^! planets or n4 ,oxyg5 c]ta9ly exi/s 9 ! ,m>tian atmosph]e1 b its am\nt is small4 ,adams & ,/ ,john e/imate t !re _c be m ?an #ae p] c5t4 z mu*1 p] squ>e mile1 z on e>?4 ,on ! o!r h& x is ei!r completely abs5t1 or ( negligible am\nt1 9 ! atmosph]e ( ,v5us4 ,if any is pres5t at all1 ,/ ,john e/imates t ! am\nt above ! cl\ds :i* cov] ! surface ( ,v5us is less ?an #ja p] c5t4 ( ! t]re/rial am\nt4 ,! evid5ce1 = :at x is wor?1 goes to sugge/ t ,v5us1 ! only planet 9 ! sol> sy/em outside ,m>s & ! e>? on :i* life c\ld possibly exi/1 possesses no vegetation & no oxyg5 = high] =ms ( life to brea!4 ,ap>t f ! c]ta9 k t life exi/s on e>?1 we h no def9ite k :atev] except t1 at ! be/1 life mu/ be limit$ to a t9y fraction ( ! univ]se4 ,millions ( millions ( />s exi/ :i* support no life1 :i* h nev] done s & nev] w d s4 ,( ! r>e planet>y sy/ems 9 ! sky1 _m mu/ be entirely lifeless1 & 9 o!rs life1 if x exi/s at all1 is probably limit$ to a few planets4 ,! ?ree c5turies :i* h elaps$ s9ce ,giordano ,bruno suff]$ m>tyrdom = believ+ 9 ! plurality ( worlds h *ang$ our conception ( ! univ]se almo/ beyond description1 b !y h n br\ght u appreciably ne>] to und]/&+ ! relation ( life to ! univ]se4 ,we c /ill only guess z to ! mean+ ( ?is life :i*1 to all appe>ances1 is s r>e4 ,is x ! f9al climax t[>ds :i* ! :ole creation moves1 = :i* ! millions ( millions ( ye>s ( trans=mation ( matt] 9 un9habit$ />s & nebulae1 & ( ! wa/e ( radiation 9 des]t space1 h be5 only an incr$ibly extravagant prep>ation8 ,or is x a m]e accid5tal & possibly q unimportant by-product ( natural processes1 :i* h "s o!r & m /up5d\s end 9 view8 ,or1 to glance at a /ill m mode/ l9e ( ?\ght1 mu/ we reg>d x z some?+ ( ! nature ( a disease1 :i* affects matt] 9 its old age :5 x has lo/ ! high temp]ature & capacity = g5]at+ high-frequ5cy radiation ) :i* y\ng] & m vigor\s matt] w\ld at once de/roy life8 ,or1 ?r[+ humility aside1 %all we v5ture to imag9e t x is ! only reality1 :i* creates1 in/ead ( be+ creat$ by1 ! colossal masses ( ! />s & nebulae & ! almo/ inconceivably long vi/as ( a/ronomical "t8 ,aga9 x is n = ! a/ronom] to select betwe5 ^! alt]native guesses2 8 task is done :5 he has deliv]$ ! message ( a/ronomy4 ,p]haps x is ov]-ra% = him ev5 to =mulate ! que/ions ?is message sugge/s4 ,,! ,,e>? ,,& ,,its ,,future ,,prospects ,let u leave ^! r ab/ract regions ( ?\ght & come d[n to e>?4 ,we feel ! solid e>? "u our feet1 & ! rays ( ! sun ov]head4 ,someh[1 b we "k n h[ or :y1 life also is "h2 we ourselves are "p ( x4 ,& x is natural to enquire :at a/ronomy has to say z to its future prospects4 ,! c5tral facts :i* dom9ate ! :ole situation are t we are dep5d5t on ! light & heat ( ! sun1 & t ^! _c rema9 = ev] z !y n[ are4 ,s f> z we c at pres5t see1 sol> conditions c h>dly h *ang$ mu* s9ce ! e>? 0 born2 ! e>?'s #bjjj million ye>s =m s small a fraction ( ! sun's :ole life t we c almo/ suppose ! sun to h /ood /ill ?r\gh\t x4 ,?is ( itself sugge/s t1 9 s f> z a/ronomical factors are conc]n$1 life may look to a t5ancy ( ! e>? ( f> long] duration ?an ! total pa/ age ( ! e>?4 ,! e>?1 :i* />t$ life z a hot mass ( gas1 has gradually cool$1 until x has n[ ab\t t\*$ bottom1 & has almo/ no heat beyond t :i* x receives f ! sun4 ,?is j ab\t balances ! am\nt x radiates away into space1 s t x w\ld /ay at its pres5t temp]ature = ev] if ext]nal conditions did n *ange1 & any *anges 9 its condition w be =c$ on x by *anges occurr+ outside4 ,^! ext]nal *anges may be ( _m k9ds4 ,! sun's loss ( weight causes ! e>? to rec$e f x at ! rate ( ab\t a y>d a c5tury1 s t aft] a million million ye>s1 ! e>? w be #aj p] c5t4 fur!r away f ! s\rce ( its light & life ?an n[4 ,consequ5tly ev5 if ! sun !n radiat$ z mu* light & heat z n[1 ! e>? w\ld receive #bj p] c5t4 less ( ?is radiation1 & its mean temp]ature w\ld be "s #ae degrees ,c5tigrade or s l[] ?an at pres5t4 ,b aft] a million million ye>s ! sun w n radiate z mu* light & heat z n[2 x w h lo/ "s #f p] c5t4 ( its pres5t weight ?r\gh radiation1 &1 judg+ f o!r />s1 ?is loss w probably r$uce its en]gy-g5]at+ capacity by ab\t #bj p] c5t4 ,?is w r$uce ! e>?'s temp]ature by ab\t ano!r #ae degrees1 s t aft] a million million ye>s ! inevitable c\rse ( ev5ts w h r$uc$ ! e>?'s temp]ature by ab\t #cj degrees ,c5tigrade4 ,x w\ld be ra% to attempt to pr$ict h[ su* a fall ( temp]ature may affect t]re/rial life1 & human life 9 p>ticul>4 ,giv5 suffici5t "t1 life has su* an enorm\s capacity = adapt+ itself to its environm5t t x seems possible t1 ev5 ) a temp]ature #cj degrees ,c5tigrade l[] ?an n[1 life may /ill exi/ on e>? a million million ye>s h5ce4 ,if s1 ,i am glad t my life has n fall5 9 ?is f> di/ant future4 ,m\nta9s & seas1 :i* provide "s ( ! ke5e/ pleasures ( our pres5t life1 w exi/ only z traditions h&$ d[n f a remote & almo/ incr$ible pa/4 ,! d5udation ( a million million ye>s w h r$uc$ ! m\nta9s almo/ to pla9s1 :ile seas & riv]s w be froz5 packs ( solid ice4 ,we may well imag9e t man w h inf9itely m k ?an n[1 b he w no long] "k ! ?rill ( pleasure ( ! pione] :o op5s up new realms ( k4 ,disease1 & p]haps dea?1 w h be5 conqu]$1 & life w d\btless be saf] & incomp>ably bett]-ord]$ ?an n[4 ,x w seem incr$ible t a "t c\ld h exi/$ :5 m5 risk$1 & lo/1 _! lives 9 trav]s+ unexplor$ c\ntry1 9 climb+ hi!rto unclimb$ peaks1 9 fight+ wild bea/s = ! fun ( x4 ,life w be m ( a r\t9e & less ( an adv5ture ?an n[2 x w also be m purposeless :5 ! human race kn[s t )9 a measurable space ( "t x mu/ face ext9ction & ! et]nal de/ruction ( all its hopes1 endeav\rs1 & a*ievem5ts4 ,)\t lay+ too mu* /ress on ^! vision>y concepts ( life a million million ye>s h5ce1 we may nev]!less ?9k ( ?is z ! p]iod 9 r\nd numb]s aft] :i* ! inevitable wa/age ( ! sun's weight is likely to drive life (f ! e>?4 ,v5us1 ) a mean temp]ature "s #fj degrees high] ?an ! e>?1 is probably r too hot = life at pres5t4 ,b aft] a million million ye>s1 ! temp]ature ( ,v5us w h fall5 by #dj degrees1 & :at ! e>? is n[1 ,v5us may p]haps be some:]e betwe5 "o & two million million ye>s h5ce4 ,:e!r life w !n inhabit ,v5us we _c "k1 & x w\ld be futile to guess1 b !re is at lea/ a *ance t z ! e>? fails1 ,v5us may /ep into its place4 ,possibly ,v5us may be foll[$ by ,m]cury 9 due c\rse1 b ! pres5t evid5ce is t ,m]cury is devoid ( atmosph]e1 9 :i* case x is h>d to imag9e x z a home = life at all resembl+ t :i* n[ inhabits ! e>?4 ,s f> we h consid]$ only ! normal c\rse ( ev5ts2 a v>iety ( accid5ts may br+ ! human race to an end long be=e a million million ye>s h elaps$4 ,to m5tion only possible a/ronomical occurr5ces1 ! sun may run into ano!r />1 any a/]oid may hit any o!r a/]oid &1 z a result1 be s deflect$ f its pa? z to /rike ! e>?1 any ( ! />s 9 space may w&] into ! sol> sy/em &1 9 s do+1 upset all ! planet>y orbits to su* an ext5t t ! e>? becomes impossible z an abode ( life4 ,x is difficult to e/imate ! likelihood ( any ( ^! ev5ts happ5+ b !y all seem v improbable1 & ! fir/ & la/ highly s4 ,let u disreg>d !m all4 ,a dang] rema9s :i* _c be s lightly dismiss$4 ,let u fir/ /ate x 9 te*nical language4 ,! sun is a ma9-sequ5ce />1 & is moreov] v ne> to ! left-h& edge ( ! ma9-sequ5ce 9 ! ,russell diagram 7p4 #bgh74 ,beyond ?is edge is a region ( ! diagram :i* is completely unt5ant$ by />s4 ,we h suppos$ ?is region to be unt5ant$ by />s because ! /ell> configurations x repres5ts w\ld be un/able4 ,/>s pass ?r\gh x rapidly until !y f9d a /able configuration1 & s end up 9 a region :i* c be p]man5tly t5ant$ by />s4 ,n[ ! next /able configurations beyond ?is region are ^? ( ! :ite dw>fs1 & z ^! are less massive z a class ?an ! ma9-sequ5ce />s1 ! g5]al tr5d ( /ell> evolution appe>s to be f ma9-sequ5ce /> to :ite dw>f4 ,on ?is view ! :ite dw>fs mu/ h previ\sly be5 ma9-sequ5ce />s :i* w&]$ across ! left-h& edge ( ! b& ( /able configurations & !n fell ?r\gh ! un/able region until !y resum$ /ability z :ite dw>fs4 ,! dang] lies 9 ! fact t ! sun is already p]il\sly ne> to ! left-h& edge ( ! ma9-sequ5ce4 ,accord+ to ,r$man's det]m9ations1 :i* are probably by f> ! mo/ reliable at pres5t available1 ! ma9-sequ5ce belt ( /able configurations = />s ( ! same spectral type z ! sun 7,g #j7 ext5ds r\ghly betwe5 /ell> absolute magnitudes1 #dhh & #ced1 ! =m] m>k+ ! dang]\s left-h& edge4 ,! sun's pres5t absolute magnitude is e/imat$ z #dhe4 ,?us if ! sun 7 to become #jjc magnitudes fa9t]1 ?is repres5t+ a r$uction ( only #c p] c5t4 9 its lum9osity1 x w\ld arrive exactly at ! edge ( ! ma9-sequ5ce1 & w\ld proce$ to contract precipitately to ! :ite dw>f /ate4 ,9 s do+1 its light & heat w\ld dim9i% to su* an ext5t t life w\ld be bani%$ f ! e>?4 ,! kn[n :ite dw>f /> :i* x w\ld mo/ closely resemble is ! companion ( ,sirius1 & ?is emits only a f\r-hundr$? "p z mu* light & heat z ! sun4 ,to put ! same ?+ 9 non-te*nical language1 ! sun is 91 or is n f> f1 a prec>i\s /ate 9 :i* />s are liable to beg9 to %r9k & 9 s do+ to r$uce _! radiation to a t9y fraction ( t at pres5t emitt$ by ! sun4 ,! %r9kage ( ! sun to ?is /ate w\ld trans=m our oceans into ice & our atmosph]e into liquid air2 x seems impossible t t]re/rial life c\ld survive4 ,! va/ museum ( ! sky mu/ almo/ c]ta9ly conta9 examples ( %runk5 suns ( ?is type ) planets l our e>? revolv+ r\nd !m4 ,:e!r ^! planets c>ry on !m ! froz5 rema9s ( a life :i* 0 once z active z our pres5t life on e>? we c h>dly ev5 surmise4 ,?is may be ?\ght to op5 up a />tl+ prospect = ! e>?1 b we c take c\rage = sev]al reasons4 ,9 ! fir/ place a #c p] c5t4 decrease 9 ! sun's lum9osity c h>dly occur 9 less ?an ab\t #aej1jjj million ye>s4 ,?is 9 itself is n too bad1 b ! prospect becomes enorm\sly m hopeful :5 we reflect t ! evolution ( ! />s1 includ+ ! sun1 takes place 9 a direction almo/ p>allel to ! edge ( ! ma9-sequ5ce4 ,! sun is n head+ = ! precipice1 s mu* z skirt+ along its edge4 ,:e!r x is approa*+ ! edge1 & is ultimately de/9$ to fall ov]1 we d n "k1 b x is 9 any case unlikely to rea* ! edge )9 ! next million million ye>s4 ,f9ally1 ! sun's di/ance f ! edge ( ! ma9-sequ5ce _c be e/imat$ ) any?+ l ! degree ( accuracy assum$ 9 ! =ego+ calculations4 ,! figure ( #jjc appe>$ z ! diff]5ce ( two mu* l>g] numb]s1 & al?\gh bo? ( ^! c be e/imat$ ) fair accuracy1 nei!r c be e/imat$ ) suffici5t accuracy to ju/ify u 9 treat+ _! small diff]5ce ( #jjc z exact4 ,! mo/ we c say is t ! sun is q fairly ne> to ! dang]\s edge1 b t any appreciable motion t[>ds ?is edge is a matt] ( millions ( millions ( ye>s4 ,ano!r dang]1 ( a m speculative k9d1 mu/ also be m5tion$4 ,we h se5 7p4 #fa7 h[ e n[ & !n a new /> appe>s 9 ! sky1 %9es ) t]rific brilliancy = a %ort "t1 & !n ei!r fades away entirely or cont9ues to %9e z an ord9>y />4 ,^! app>itions are kn[n z 8novae0--new />s4 ,9 _m cases ! nova has be5 prov$ to be an ord9>y /> :i* 0 visible z a v fa9t /> long be=e x appe>$ z a nova1 fla%$ into brilliance = a brief span ( life1 & !n laps$ back into commonplac5ess1 & x seems reasonable to suppose t all novae are ( ?is k9d1 al?\gh ! /> may (t5 escape detection until x assumes its brilliant nova /ate4 ,^! app>itions are by no means r>e2 some?+ l six appe> e ye> 9 ! galactic sy/em alone4 ,n[ if we suppose ! galactic sy/em to consi/ ( #cjj1jjj million />s1 ?is means t1 on ! av]age1 ea* /> becomes a nova once 9 e #ej1jjj million ye>s4 ,:at we w\ld l to "k is :e!r our sun is 9 dang] ( becom+ a nova2 =1 if all k9ds ( />s run equal *ances1 x is likely to become a nova "s tw5ty times 9 ! next million million ye>s4 ,s f> !re is no agreem5t among a/ronom]s ei!r z to ! physical causes :i* turn an ord9>y /> into a nova1 or z to ! physical conditions :i* prevail 9 novae4 ,v>i\s sugge/ions are 9 ! field1 b none ( !m w9s g5]al acceptance4 ,x seems fairly c]ta9 t if our sun 7 sudd5ly to become a nova1 its emission ( light & heat w\ld s increase z to scor* all life (f ! e>?1 b we are completely 9 ! d>k z to :e!r our sun runs any risk ( ent]+ ! nova /age4 ,if x does1 ?is is probably ! greate/ ( all ! risks to :i* life on e>? is expos$4 ,ap>t f accid5ts1 we h se5 t if ! sol> sy/em is left to ! natural c\rse ( evolution1 ! e>? is likely to rema9 a possible abode ( life = some?+ ( ! ord] ( a million million ye>s to come4 ,?is is "s five hundr$ times ! pa/ age ( ! e>?1 & ov] ?ree million times ! p]iod ?r\gh :i* humanity has s f> exi/$ on e>?4 ,let u try to see ^! times 9 _! prop] proportion by ! help ( yet ano!r simple model4 ,take a po/age-/amp1 & /ick x on to a p5ny4 ,n[ climb ,cleopatra's ne$le & lay ! p5ny flat1 po/age-/amp upp]-mo/1 on top ( ! obelisk4 ,! height ( ! :ole /ructure may be tak5 to repres5t ! "t t has elaps$ s9ce ! e>? 0 born4 ,on ?is scale1 ! ?ickness ( ! p5ny & po/age-/amp toge!r repres5ts ! "t t man has liv$ on e>?4 ,! ?ickness ( ! po/age-/amp repres5ts ! "t he has be5 civilis$1 ! ?ickness ( ! p5ny repres5t+ ! "t he liv$ 9 an uncivilis$ /ate4 ,n[ /ick ano!r po/age-/amp on top ( ! fir/ to repres5t ! next #ejjj ye>s ( civilisation1 & keep /ick+ on po/age-/amps until y h a pile z high z ,mont ,blanc4 ,ev5 n[ ! pile =ms an inadequate repres5tation ( ! l5g? ( ! future :i*1 s f> z a/ronomy c see1 probably /ret*es be=e civilis$ humanity1 unless an accid5t cuts x %ort4 ,! fir/ po/age-/amp 0 ! pa/ ( civilisation2 ! column high] ?an ,mont ,blanc is its future4 ,or1 to look at x 9 ano!r way1 ! fir/ po/age-/amp repres5ts :at man has already a*iev$2 ! pile :i* outtops ,mont ,blanc repres5ts :at he may a*ieve1 if 8 future a*ievem5t is proportional to 8 "t on e>?4 ,yet we h se5 t we _c c\nt on su* a l5g? ( future ) any c]ta9ty4 ,accid5ts may happ5 to ! race z to ! individual4 ,cele/ial collisions may occur2 %r9k+ into a :ite dw>f1 ! sun may freeze t]re/rial life out ( exi/5ce2 bur/+ out z a nova x may scor* our race to dea?4 ,accid5t may replace our ,mont ,blanc ( po/age-/amps by a truncat$ column ( only a fraction ( ! height ( ,mont ,blanc4 ,ev5 s1 !re is a prospect ( t5s ( ?\s&s ( millions ( ye>s be=e our race4 ,& ! human m9d1 z ap>t f ! m9d ( ! ma!matician1 c h>dly di/+ui% cle>ly betwe5 su* a p]iod z ?is & ! million million ye>s to :i* we may look =w>d if accid5ts d n ov]take u4 ,= all practical purpose ! only /atem5t t conveys any real mean+ is t our race may look =w>d to occupy+ ! e>? = a "t incomp>ably long] ?an any we c imag9e4 ,look$ at 9 t]ms ( space1 ! message ( a/ronomy is at be/ "o ( melan*oly gr&eur & oppressive va/ness4 ,look$ at 9 t]ms ( "t1 x becomes "o ( almo/ endless possibility & hope4 ,z d5iz5s ( ! univ]se we may be liv+ ne> its end r ?an its beg9n+2 = x seems likely t mo/ ( ! univ]se _h melt$ into radiation be=e we appe>$ on ! sc5e4 ,b z inhabitants ( ! e>?1 we are liv+ at ! v beg9n+ ( "t4 ,we h come into be+ 9 ! fre% glory ( ! dawn1 & a day ( almo/ un?9kable l5g? /ret*es be=e u ) unimag9able opportunities = accompli%m5t4 ,our desc5dants ( f>-(f ages1 look+ d[n ?is long vi/a ( "t f ! o!r end1 w see our pres5t age z ! mi/y morn+ ( ! _w's hi/ory2 our contempor>ies ( to-day w appe> z dim h]oic figures :o f\ght _! way ?r\gh jungles ( ignorance1 error & sup]/ition to discov] tru?1 to le>n h[ to h>ness ! =ces ( nature1 & to make a _w wor?y = mank9d to live 94 ,we are /ill too mu* engulf$ 9 ! greyness ( ! morn+ mi/s to be able to imag9e1 h[ev] vaguely1 h[ ?is _w ( ours w appe> to ^? :o w come aft] u & see x 9 ! full light ( day4 ,b by :at light we h1 we seem to disc]n t ! ma9 message ( a/ronomy is "o ( hope to ! race & ( responsibility to ! individual--( responsibility because we are draw+ plans & lay+ f\ndations = a long] future ?an we c well imag9e4 ,,index ,aquil1 see ,altair ,canis ,majoris1 see ,sirius ,canis ,m9oris1 see ,procyon ,c5tauri1 di/ance1 #cc1 #ce lum9osity & weight1 #dh sy/em (1 #dj1 #bfc1 #bgi1 #bhj ,h]culis1 #bei1 #bgb ,lyrae1 #cc ,orionis1 see ,betelgeux -p>ticles1 #aab1 #aaf1 #aag1 #aah & ,plate ,,xiii 7p4 #aac7 -rays1 #aaa ,scorpii1 see ,ant>es ,absolute temp]ature1 #ajb ,absorption l9es & spectrum1 #ea1 #abf ,act9o-uranium1 #aed1 #aee ,adams1 ,j4 ,c41 #ah1 #ai ,adams1 ,w4 ,s41 #fb1 #cdc ,age ( e>?1 #ad1 #aea ff41 #bdh ( />s1 #aee ff4 ( sun1 #ahj1 #ahd ( univ]se1 #ccf ,aitk51 ,r4 ,g41 #aga1 #ahh ,altair 7 ,aquil71 #cc1 #bgh ,&rom$a1 ,great ,nebula ,m #ca 91 ,plate ,,iv 7p4 #cj71 #cj1 #gj1 #ga1 #gb1 #bjd1 #bjf1 #bjh1 #bae1 #cce age1 #cce di/ance1 #ga rotation1 #bjf size1 #cj weight1 #ga1 #bjh1 #bae ,&rom$id meteors1 #bea ,ang/rom unit1 def9$1 #bef ,angul> mom5tum1 cons]vation (1 #bje1 #bag1 #bcb ( sol> sy/em1 #bcb ,annihilation ( matt]1 #ahe1 #aia1 #aic1 #bih1 #cca ,ant>es 7 ,scorpii71 #bei1 #bgb1 #bgc1 #bgh int]nal con/itution (1 #bgc1 #bia ,aqu>id meteors1 #bea ,ari/>*us ( ,samos1 #b1 #ac ,ari/otle1 #b1 #e ,arrangem5t ( sol> sy/em1 #af1 #bdj ff4 ,bode's law1 #ai1 #bj ,cop]nican1 #c1 #e1 #f1 #bg1 #cb ,ptolemaic1 #b1 #d1 #f1 #h1 #ca ,a/]oids1 #ag1 #bbf1 #bdj1 #bdg1 #beb1 #cdh ,c]es1 #ag di/ance (1 #ai1 #bj1 #beb ,eros1 #cd orig9 (1 #bdg1 #beb ,a/on1 ,f4 ,w41 #aai1 #aed1 #ahe ,atmosph]e1 ( e>?1 #aie1 #cdc ( moon1 #aif ( planets1 #aif1 #cdc1 #cdd1 #cdh ( sun1 #aie ,atomic nuclei1 #ajh1 #aag dis9tegration (1 #aaa1 #aag size & weight (1 #aji /ructure (1 #aai1 #aci1 #adg ,atomic numb]s & weights1 #aaj1 #bhg 9 /ell> matt]1 #cjf1 #caa ,atomic !ory1 #ib1 #ajc ,atoms1 #ajc1 #cah /ructure (1 #ajf syn!sis (1 #adh1 #adi1 #ahe ,availability ( ,en]gy1 #cbf1 #cbi ,aurigae1 #ed1 #eh -p>ticles1 #aab1 #aac1 #aaf1 #ade & ,plate ,,xiii 7p4 #aac7 -rays1 #aaa1 #ade ,b4,d4 #f #acji1 see ,plaskett's /> ,bacon1 ,rog]1 #a ,becqu]el1 ,h41 #aaj ,b5tley1 ,r41 #aig ,b]5ice's hair1 #ci ,bessel1 ,f4 ,w41 #cc ,betelgeux 7 ,orionis71 #bei1 #bgb1 #bgh ,bick]ton1 ,a4 ,w41 #bce ,biela's comet1 #bea ,b9>y sy/ems1 #ci1 #dj1 #eb1 #ed bir? (1 #bag eclips+1 #ed1 #eh loss ( weight 91 #ahh1 #bbh orbits (1 #df1 #dg1 #afg orig9s (1 #afi1 #bai1 #big relative weights ( compon5ts 91 #ahh subdivision 91 #bbh weights (1 #dh1 #ee ,bir? ( b9>y sy/ems1 #bag ( nebulae1 #bjd ( planets1 #bcb1 #bcg ( satellites1 #bcb1 #bda ( />s1 #bji ,blackett4 ,p4 ,m4 ,s41 #aag1 #aah ,blue />s1 #fb ,bode's law1 #ai1 #bj1 #beb ,bohr1 ,niels1 #abd1 #abh1 #abi1 #aca1 #cjd1 #cje ,b[51 ,j4 ,s41 #adc ,boys1 ,c4 ,v41 #dd ,br[nian movem5ts1 #aei1 #afc ,bruno1 ,giordano1 #c1 #d1 #cdd ,buffon1 ,g4 ,l4 ,l41 #bce ,bum/ead1 ,h4 ,a41 #aac ,burton1 ,e4 ,f41 #adc -rays1 #aaa1 #aad1 #abb1 #aci1 #add1 #ade ,cam]on1 ,g4 ,h41 #adc ,campbell1 ,w4 ,w41 #cba ,c&le-p[] ( />s1 #di1 #ee1 #agi1 #ahh2 see ,lum9osity ,capella1 #bgh ,cass9i1 ,d41 #bc ,cavity-radiation1 #abc1 #bee ,cepheid v>iables1 #ee1 #ef1 #eg1 #ei1 #fj1 #gj1 #bji me*anism (1 #bbc ,c]es 7a/]oid71 #ag ,*amb]l91 ,t4 ,c41 #bce1 #bcf ,*aos1 primaeval1 d5sity (1 #bjb evolution f1 #bjb1 #bjd1 #bbi1 #bcj ,*>li]1 ,c4 ,v4 ,l41 #fg ,clu/]s1 globul>1 #fc1 #fd1 #fh1 #bac1 #baf mov+1 #ci1 #agc1 #baf1 #bag ,coal1 combu/ion (1 #age1 #aia ,coal sack1 #cj ,comets1 #bdg1 #bea orig9 (1 #bch ,cond5sation-*amb] ( ,c4 ,t4 ,r4 ,wilson1 #aac1 #aag ,cond5sations 9 a gas1 #aih1 #bjj1 #bjc1 #bji1 #bcg ,configurations ( rotat+ masses1 #bba ,cons]vation1 ( angul> mom5tum1 #bje1 #bag1 #bcb ( en]gy1 #ii1 #ahi1 #cbf1 #cbh ( matt]1 #ahi ,con/ellations1 #cf1 #ci ,cooke1 ,h4 ,l41 #adc ,cop]nican a/ronomy1 #c1 #e1 #f1 #bg1 #cb ,cop]nicus1 #c ,creation1 ( matt]1 #ccf ( univ]se1 #gi1 #ccg ,crookes1 ,sir ,w41 #ajf ,cycles & epicycles 7,ptolemaic71 #b1 #c1 #d ,cyclic processes 9 nature1 #cbe1 #cbi1 #cca ,cephei1 #ef1 #bbc -rays1 #aac ,d>w91 ,sir ,george1 #bbd de ,sitt]1 cosmology (1 #gi ff41 #hd1 #hf1 #agd ,democritus1 #ic ,d5sity1 ( matt] 9 space1 #gg1 #cca1 #ccb ( nebulae1 #bjh ( />s1 #bfe-h1 #bgc1 #bhb ,diamet]s ( />s1 #bfj1 #bfc-h1 #bgb1 #bgg-hj ,diffraction grat+1 #aad ,dim5sions1 ( e>?1 #cd ( galactic sy/em1 #fe ( sol> sy/em1 #bj1 #cd ( univ]se1 #gg1 #hc1 #hf1 #hg ,discont9uity1 9 physics1 #abd ff4 ( matt]1 #ic ,displacem5ts ( spectral l9es1 7de ,sitt]71 #ha 7,doppl]71 #eb 7,e9/e971 #gh1 #cbc ,di/ances1 ( globul> clu/]s1 #fc ( nebulae1 #ga1 #gc ( />s1 #cc1 #ce1 #cf1 #fa1 #fb1 #fc ,doppl] effect1 #eb ,dw>f & ,giant />s1 #bgf ,dw>fs1 :ite1 #bhj1 #bhc1 #bhd1 #bib1 #cag1 #cai1 #cbj1 #cbb1 #cbc1 #cce ,e>?1 age (1 #ad1 #aea1 #aee1 #agc1 #bdg z a planet1 #af1 #ai1 #bcj1 #bcg1 #bdc bir? (1 #bcg1 #bdc dim5sions (1 #cd future (1 #bbe1 #bbf1 #bej1 #cdf1 #ceb -moon sy/em1 #cd1 #bbe1 #bbf1 #bdj1 #bdc1 #bej orbit (1 #ce1 #cf1 #bbg1 #cdf ,ecc5tricity ( b9>y orbits1 #aga ( ellipse 7def9$71 #df ,eclips+ b9>ies1 #ed1 #ee1 #ef1 #eh ,edd+ton1 ,a4 ,s41 #fg1 #hd1 #agi1 #ahd1 #ahg1 #bbd1 #bhg1 #bhh1 #bie ,e9/e91 ,a41 7,cosmology71 #gd1 #gg1 #gi1 #hd 7,gravitation71 #de1 #ge1 #gi1 #afa 7,quantum !ory71 #abd1 #abf1 #abg 7,relativity71 #gd ff41 #ahf1 #bfa ,electricity1 positive & negative1 #ajg attraction & repulsion1 #ajg1 #abi ,electromagnetic en]gy1 #abj1 #aba ,electron1 #ajg1 #aab1 #aai1 #aba orbits 9 atom1 #ajh1 #abh ,ellipse1 def9$1 #df z atomic orbit1 #abi z gravitational orbit1 #df1 #dg1 #bbg ,ellis1 ,c4 ,d41 #aci ,emd51 ,r41 #bhf1 #bhh ,en]gy1 #ih1 #abj1 #ahi1 #cbf ff4 availability (1 #cbf1 #cbh cons]vation (1 #ii1 #ahi s\rce ( /ell>1 #ahd weight (1 #abj ,epicycles1 #b1 #c1 #d ,equip>tition ( en]gy1 9 a gas1 #aef /ell>1 #afj1 #afd1 #agj1 #agb ,eros1 #cd ,e!r1 exi/5ce (1 #cch ,evaporation1 #id ,ev5+ />s1 #ag ,evolution1 f primaeval *aos1 #bjb1 #bje1 #bbi1 #bcj /ell>1 #cac ff4 ,exp&+ univ]se1 #hd1 #hf ff4 ,extra-galactic nebulae1 #cj1 #gj1 #hb d5sities (1 #bjh di/ance (1 #ga1 #hb evolution (1 #bjd ff4 & ,plates ,,xvi to ,,xxi 9 ord] numb] (1 #gb rotation (1 #bje1 #bjf size (1 #ca velocities (1 #hb1 #hd1 #hf weights (1 #ga1 #bae ,f>aday1 ,m41 #abb ,f9al end ( univ]se1 #cbi ff4 ,fireball1 #bdh ,fission ( />s1 #afi1 #bag1 #bai1 #bbb1 #bbi ,fizeau1 ,h4 ,l41 #bfa ,fluoresc5ce1 #aae1 #cbg ,fraunh(]1 ,j4 von1 #aje ,free-pa? ( molecules1 #ih ,frequ5cy ( radiation1 #aae1 #abf1 #abg ,full radiator1 #abc1 #bee1 #bfa ,galactic latitude & longitude1 #bd1 #be ,galactic nebulae1 #bi1 ,plates ,,iii 7p4 #bi71 ,,vi 7p4 #cg71 ,,vii 7p4 #dd7 ,galactic sy/em ( />s1 #bc1 #be1 #fe ff41 #baa numb] (1 #fh1 #fi1 #bae rotation (1 #ff ff41 #bad weight (1 #fi1 #bae ,galileo1 #a1 #c1 #d1 #e1 #h1 #af1 #bd ,galle1 ,j4 ,g41 #ai ,gase\s masses 9 rotation1 #bjf1 #bba ,gase\s /ate1 nature (1 #ie equip>tition ( en]gy 91 #aef ,gaunt1 ,j4 ,a41 #cji ,geodesy1 #cd ,geology1 #aej1 #aeb ,g]asimovi1 ,b4 ,p41 #cba ,giant & ,dw>f />s 7def9$71 #bgf ,giant />s1 int]nal con/itution1 #bgc1 #bij1 #bia1 #caj1 #cai ,globul> clu/]s1 #fc1 #fe1 #bac1 #baf & ,plate ,,ix 7p4 #fc7 orig9 (1 #baf %ape (1 #bac ,goldsbr\gh1 ,g4 ,r41 #bej ,graham1 ,t41 #aeh ,gravitation1 law (1 #da1 #de1 #gh1 #afa cause (1 #gf ,gravitational in/ability1 #aig1 #baj1 #bcg1 #bde1 #bdf ,great ,be> 7clu/]71 #agc1 #baf1 #bag 7con/ellation71 #cb1 #ci ,great nebulae1 see ,extra-galactic nebulae ,h4,d4 #accg1 see ,pe>ce's /> ,halley1 ,e41 #aea ,halley's comet1 #bdg1 #bea ,halm1 ,j41 #afc ,hay=d1 ,j4 ,f41 #cd ,heat1 nature (1 #ajj effect (1 on electrical /ructures1 #ada1 #add transport (1 9 a />1 #cjg ,heat-dea?1 #cbi1 #ccj ,helium atom1 #aaj1 #aai1 #ahe1 #cje ,helmholtz1 ,h41 #agg1 #bhe ,h5d]son1 ,t41 #cc ,h]s*el1 ,sir ,john1 #bc1 #bd1 #baa ,h]s*el1 ,sir ,william1 #ah1 #bc1 #bd1 #be1 #bf1 #bh1 #fe1 #gj1 #baa ,h]tzsprung1 ,e41 #ei1 #bbc1 #bge ,hesp]us1 #ag ,hess1 ,v4 ,f41 #adc ,highly p5etrat+ radiation1 #adc1 #add1 #aia1 #bih1 #bii ,h9ks1 ,a4 ,r41 #fe ,holmes1 ,a41 #aeb ,hubble1 ,e41 #ga1 #gc1 #gg1 #hc1 #hd1 #bjb1 #bjd1 #bjf1 #bjh1 #baj ,humason1 ,m4 ,l41 #hb ,huygh5s1 ,c41 #bc ,hydrog5 atom1 #aaj1 #aai1 #acj1 #ace1 #adf annihilation (1 #adf1 #adg1 #aib electron orbits 91 #abh1 #acj1 #aib ,hyp]bola1 #df ,in/ability1 dynamical1 #bjb gravitational1 #aig1 #baj1 #bcg1 #bde1 #bdf ,int]f]omet]1 #bfa1 #bgb ,int]/ell> matt]1 #bi1 #cj1 #fc ,int]/ell> space1 temp]ature (1 #ajb ,inv]se squ>e law1 7electric71 #abi 7gravitational71 #dd1 #de1 #dg 7lum9osity71 #bd1 #cc ,invisible radiation1 #aae1 #beh1 #bei ,irregul> nebulae1 #bjf ,irregul> v>iables1 #ee1 #eh ,isl& univ]ses1 #bh1 #ca1 #fh ,isotopes1 #aah ,jeffreys1 ,h41 #aee1 #bbe1 #bbf1 #bci ,jupit]1 #d1 #af1 #ag1 #ai1 #bjg bir? (1 #bdj ff41 #bdc1 #bdd rotation (1 #afh1 #bbe satellites (1 #d1 #bc1 #aif1 #bdj1 #bda1 #bdc1 #bej size (1 #ag temp]ature (1 #ba weight (1 #de ,k-r+ ( electrons 9 atom1 #acd1 #ach1 #bhi1 #bia1 #bib1 #cjb1 #cjd1 #cah ,kant1 ,i41 #agf1 #bcj1 #bca ,kapteyn1 ,j4 ,c41 #bg1 #fe1 #bab1 #bad ,kelv91 ,"l1 #agg1 #bhe ,kepl]1 ,j41 #e1 #cc1 #df ,kle91 ,o41 #adf1 #adh ,kolhr/]1 ,w41 #adc ,kram]s1 ,h4 ,a41 #cji1 #caj ,krug] #fj1 #dh1 #bgh1 #bgi1 #bhj1 #cag sy/em (1 #bfg1 #bgi1 #bhj ,l-r+ ( electrons 9 atom1 #acd1 #ach1 #bhi1 #bib1 #cjb ,lal&e #baahe1 #cf1 #bfe ,lane's law1 #bhf ,laplace1 ,p4 ,s41 #bcj1 #bcc ff4 nebul> hypo!sis (1 #bcj1 #bca1 #bcb ff4 ,lead1 radio-active1 #aed ,leavitt1 ,miss1 #eg ,lematre1 ,g41 #hd1 #hf1 #agd ,l5>d1 ,p41 #ajf ,leonid %oot+-/>s1 #bej ,leslie1 ,sir ,john1 #aeh ,leucippus1 #ic ,lev]ri]1 ,u4 ,j4 ,j41 #ah1 #ai ,life 9 sol> sy/em1 #cda 9 univ]se1 #cdj1 #cdb1 #cde on ,e>?1 #ab1 #cdb1 #cde on ,m>s1 #cdc on ,v5us1 #cdd1 #cdg ,light1 nature & composition (1 #cg1 #ej1 #aad spe$ (1 #cg1 #aae wave-l5g? (1 #aae1 #ach ,light-ye>1 #cg ,l9dblad1 ,b41 #fg1 #fi ,lipp]%ey1 #a ,liquid masses 9 rotation1 #bai ff4 ,liquid />s1 #bbb1 #bif ff41 #cjj1 #cjd1 #caj ,lives ( />s1 see ,/>s ,locky]1 ,sir ,n41 #cad ,long-p]iod v>iables1 #ef1 #eh1 #fa1 #bga1 #cai ,l[ell1 ,p41 #ai ,lucif]1 #ag ,lucretius1 #ic ,lum9osity ( />s1 #dh1 #di1 #agi1 #bfi1 #bgh1 #bgi1 #bhj ,m-r+ ( electrons 9 atom1 #acd1 #bhi1 #bib1 #bic1 #cjb ,mc,lennan1 ,j4 ,c41 #adc ,magellanic cl\ds1 #eg1 #baj & ,plate ,,xxi 7p4 #bad7 ,ma9-sequ5ce />s1 #bgi1 #bia1 #bie ,major planets1 #af1 #ag atmosph]es on1 #aig ,man's life on e>?3 pa/1 #ab1 #af future1 #cde ff4 ,m>ius1 #ca ,m>s1 #ah1 #ai1 #ce atmosph]e (1 #aif1 #cdc bir? (1 #bdj1 #bdc1 #bdd life on1 #cdc orbit (1 #bj1 #bci rotation (1 #bbe satellites (1 #bdj1 #bdc1 #bej temp]ature (1 #ba ,matt]1 annihilation (1 #ahe1 #aia1 #aib1 #cae cons]vation (1 #ahi ,maxwell1 ,j4 ,c41 #abb1 #aeg ,may]1 ,r41 #agf ,m]cury1 #d1 #e1 #af1 #ag1 #ai1 #bb1 #ce abs5ce ( satellites1 #bdc atmosph]e (1 #aif1 #cdh bir? (1 #bdj1 #bdc life on1 #cdh orbit (1 #bj1 #de1 #bci rotation (1 #bb1 #bbd ,meteor1 #bch1 #bdg1 #bdh ,meteorite1 #bdh ,mi*elson1 ,a4 ,a41 #bfa ,milky way1 #c1 #bc1 #bf1 #bg1 #bh1 #cj ,millikan1 ,r4 ,a41 #adc1 #adh ,m9or planets1 #af ,molecule1 #id collisions (1 #ig1 #ih1 #ajb equip>tition ( en]gy1 #aef size (1 #ie spe$ (1 #if1 #aie ,moon1 #d1 #dc atmosph]e (1 #aif bir? (1 #bdc di/ance (1 #cd1 #dc eclipse (1 #cd future (1 #bbe1 #bbf1 #bea rotation (1 #bbe ,moore1 ,j4 ,h41 #cba ,morn+ />1 #ag ,m\lton1 ,f4 ,r41 #bce1 #bcf ,mov+ clu/]s1 #dj1 #agc1 #baf %ape (1 #baf1 #bag ,muni* #aejdj1 #cf1 #bfd ,nebulae1 classification (1 #bh ,nebulae1 di/ance & size (1 #ca1 #ga1 #gb extra-galactic1 #bh1 #cj1 #gj1 #gc1 #hb1 #bjd ff4 motions (1 #hb rotation (1 #bje weights (1 #ga1 #bjd1 #bjh1 #bae ,m #ca1 see ,&rom$a1 ,great ,nebula 9 ,m #cc1 #ga1 #baj & ,plate ,,xx 7p4 #bac7 ,n4,g4,c4 #deid1 #ga1 #gb1 #bjd1 #bjh & ,plate ,,xv 7p4 #bjd7 ,nebulae1 galactic1 #bi & ,plates ,,iii 7p4 #bi71 ,,vi 7p4 #cg71 ,,vii 7p4 #dd7 ,nebulae1 planet>y1 #bi1 #bgc1 #cba1 #cbc & ,plate ,,ii 7p4 #bh7 ,nebulae1 spiral1 #cj1 #bcf ,nebul> hypo!sis ( ,laplace1 #bcj1 #bca1 #bcb ff4 ,neptune1 #af1 #ag1 #ah1 #ai bir? (1 #bdj1 #bdc1 #bdd rotation (1 #bbe satellite (1 #bdj1 #bdc ,new />s 7novae71 #fa1 #cea ,newton1 ,sir ,isaac1 7cosmogony71 #aig1 #bjc 7di/ances ( />s71 #cc 7law ( gravitation71 #dd1 #de1 #df1 #afa1 #aig 7light & optics71 #ej1 #aje ,ni*olas ( ,cusa1 #c ,ni%9a1 ,y41 #adf1 #adh ,novae1 #fa1 #cea ,nucleus1 atomic1 see ,atomic ,ceti1 #eh1 #bgb1 #bhj ,eridani1 #bfh1 #bgh1 #bhj -type />s1 #ea1 #cba1 #cbc ,obscur+ matt] 9 galactic sy/em1 #bd1 #cj ,oort1 ,j4 ,h41 #fg1 #hd1 #bad ,opacity ( /ell> matt]1 #cji ,orbit1 ( b9>y sy/ems1 #dg1 #afg ff41 #bbd ff4 ( e>?1 #cd1 #cf1 #bbg ( moon1 #cd1 #dc1 #bbf1 #bej ( planets1 #de1 #df1 #bcg1 #bci1 #bde ( />s1 #baa1 #bac1 #baf ,oresme1 #b ,orion1 con/ellation (1 #cb1 #ci1 #agc ,pane?1 ,f41 #bdg ,p>allactic measures ( /ell> di/ances1 #cc1 #fa1 #fc ,p>allactic motion1 def9$1 #cc ,p>allax1 spectroscopic1 #fb1 #cjc ,pe>ce's /> 7,h4,d4 #accg71 #di1 #ed1 #cag ,p]iod-lum9osity law 7,cepheid v>iables71 #ei-fa ,p]r91 ,j41 #aei1 #ahd ,p]seid %oot+-/>s1 #bea ,phases ( moon & inn] planets1 #d1 #e ,philolaus1 #b ,phosphoros1 #ag ,photo-electric action1 #abh ,photography 9 a/ronomy1 #cg ,piazzi1 ,g41 #ag ,planck1 ,m41 #abc1 #abd1 #abf1 #bee 8,planet ,x10 #ai ,planet>y motions1 #cf1 #de1 #df1 #gh ,planet>y nebulae1 #bi1 #bgc1 #cba1 #cbc & ,plate ,,ii 7p4 #bh7 ,planet>y orbits1 #de1 #df1 #bcg1 #bde ,planetesimal ,hypo!sis1 #bce1 #bcf ,planets1 arrangem5t (1 #af1 #ai1 #bdj bir? ( 7,laplace71 #bca1 #bcd bir? ( 7,tidal ,!ory71 #bcg1 #bdj1 #bdd 9 ! univ]se1 #cda1 #cdi motions & orbits (1 #cf1 #de1 #df1 #gh1 #bcg1 #bci1 #bde ,plaskett1 ,j4 ,s41 #fg1 #bad ,plaskett's /> 7,b4,d4 #f #acji71 #di1 #ee1 #bfi1 #bgj1 #bgb ,pleiades1 #cb1 #ci1 #dj1 #agc1 #baf ,plumm]1 ,h4 ,c41 #bbc ,pluto1 #af1 #ah1 #ai1 #bj1 #bci1 #bdj1 #bda1 #bdc bir? (1 #bdj1 #bdc temp]ature (1 #bj ,po9c>1 ,h41 #ff1 #bhe1 #cch ,po9c>'s !orem1 #bhe1 #bia ,pressure 9 a gas1 #ig 9 a />1 #cjf ( radiation1 #abj ( radiation 9 a />1 #bij1 #cjf ,primaeval *aos1 evolution f1 #bjb1 #bje1 #bbi1 #bcj ,proctor1 ,r4 ,a41 #bce ,procyon1 #dh1 #bff1 #bgh1 #bgi1 #bhj ,proton1 #aai1 #aba ,proxima ,c5tauri1 #cf1 #dj1 #bfd1 #bgh ,ptolemy1 #b1 #c1 #d1 #e1 #f1 #h1 #ca ,py?agoras1 #b1 #c1 #e1 #ac ,quantum1 def9$1 #abf ,quantum !ory1 #abb ff41 #acg ff41 #bhf1 #ccj1 #cca ,quotations1 ,arnold1 ,mat!w1 #e ,b$e1 #g ,bruno1 ,giordano1 #c ,corn=d1 ,frances1 #aa ,cusa1 ,ni*olas (1 #c ,galileo1 #e ,m]$i?1 ,george1 #bhc ,newton1 ,sir ,isaac1 #aig ,sackville-,we/1 ,victoria1 #g ,%akespe>e1 #aic ,radiation1 #aad ff41 #acg ff41 #bed ff41 #cjg di/ribution by wave-l5g?1 #bec highly p5etrat+1 #adc1 #add1 #aia1 #bih1 #bii me*anical effects (1 #abj1 #acg1 #bij1 #cjf ( sun1 #ee1 #age1 #bef pressure (1 #abj2 9 a />1 #bij1 #cjf visible & invisible1 #beh1 #bei wave-l5g? (1 #abb1 #bee1 #beh weight (1 #abj1 #abb1 #acf ,radio-activity1 #aaj ff41 #aec1 #bih ,ra9b[1 #ej1 #ea1 #aje ,rayleigh1 ,"l1 #id ,r$man1 ,h4 ,o41 #bgg1 #cdi ,relativity1 !ory (1 #gd ff41 #ahf1 #bfa1 #cbc1 #ccg ,r+ nebula 9 ,lyra1 #bi1 #bgd & ,plate ,,ii 7p4 #bh7 ,r+s ( electrons1 9 atom1 #acd1 #ach1 #bhi1 #bia ff41 #cjb1 #cjd1 #cje ,ro*e1 ,e41 #bde1 #bdi ,ro*e's limit1 #bdf1 #bej1 #bea1 #beb ,rosse1 ,"l1 #cj ,rotat+ masses1 ( gas1 #bjf1 #bba ( liquid1 #bai1 #bba ,rotat+ nebulae1 #bje ,rotat+ sy/ems ( />s1 #afh1 #bac ,rotation1 ( a/ronomical bodies1 #afh1 #baf ( galaxy1 #ff ff41 #bad ( nebulae1 #bje ( />s1 #bag ,royds1 ,t41 #aab ,russell1 ,h4 ,n41 #ahg1 #bbi1 #bgf1 #bic1 #bii1 #cad ,russell diagram1 #bgf1 #bgg1 #bgh1 #bhb1 #bhc1 #bia1 #bie1 #cjb1 #cjc1 #cad1 #cch ,ru!r=d1 ,sir ,e41 #ajg1 #aaa1 #aab1 #aag1 #adc1 #aed ,s ,doradus1 #ahb1 #bfi1 #bgj ,/ ,john1 ,c4 ,e41 #cdc1 #cdd ,sal9ity ( oceans1 #aea ,sampson1 ,r4 ,a41 #ag1 #cjh ,satellites1 atmosph]es on1 #aif bir? ( 7,laplace71 #bca bir? ( 7,tidal ,!ory71 #bda1 #bdc1 #bdf discov]y (1 #bc ,saturn1 #af1 #ag1 #ah1 #ai1 #cb1 #de bir? (1 #bdj1 #bdb1 #bdc r+s (1 #bbf1 #bca1 #bdf1 #bdg1 #bej rotation (1 #bbe satellites (1 #bc1 #aif1 #bdj1 #bda ff41 #bej temp]ature (1 #ba ,s*rd+]1 ,e41 #cje ,s*w>zs*ild1 ,k41 #cjh ,se>es1 ,f4 ,h41 #bf1 #afc1 #bha1 #bhb ,s$im5tation1 #aea ,%apley1 ,h41 #bf1 #ei1 #fc1 #fe1 #bac1 #baf1 #bbc1 #bdg ,%oot+-/>s1 nature (1 #agf1 #bdg orig9 (1 #bch1 #bdg sw>ms (1 #bdg1 #bdh1 #bea ,sirius1 #cf1 #dh1 #bei1 #bgh1 #bgi1 #bhj1 #caf sy/em (1 #bfe ,sirius ,b1 #dh1 #bfb1 #bhj1 #bib ,soddy1 ,f41 #aaa ,sol> spectrum1 #ea1 #aje1 #abe1 #bef ,sol> sy/em1 arrangem5t (1 ,bode's law1 #ai arrangem5t ( 7,cop]nican71 #c1 #e1 #f1 #bg1 #cb arrangem5t ( 7,ptolemaic71 #b1 #d1 #f1 #h1 #ca atmosph]es 91 #aid ff41 #cdc1 #cdd1 #cdg orbits 91 #de1 #df1 #bbd ff41 #bch orig9 (1 #bcj ff4 ,s\nd1 #if1 #aih ,spectra1 /ell>1 #ej1 #abe1 #acj & ,plate ,,viii 7p4 #ea74 ,see also ,displacem5ts ,spectral types1 #ea relation to /ell> weights1 #afd relation to surface-temp]atures1 #beg ,spectroscope1 #ej ,spectroscopic b9>ies1 #eb orbits (1 #aga1 #agb orig9 (1 #afi1 #bbb1 #bbc ,spectroscopic p>allaxes1 #fb1 #cjc ,spectroscopic velocities1 #ej ,spectroscopy1 #aje ,spectrum1 #ej ( sun1 #ej1 #aje1 #abe1 #bef ,sph]ical nebulae1 #bjg1 #bah1 #bai ,spiral nebulae1 #cj1 #bcf arms (1 #bcf ,/ability ( /ell> /ructures1 #bie1 #bif1 #cjj ff4 ,/>s1 ages (1 #hd1 #aee1 #afg1 #agc1 #agd1 #ahf arrangem5t (1 #bd1 #fe bir? (1 #bji d5sity (1 #bfc ff41 #bgc1 #bhb1 #bib diamet]s (1 #bfj ff41 #bgg1 #bgh1 #cba di/ances (1 #ca1 #ce1 #cg evolution (1 #cac ff4 int]nal con/itution (1 #bhe ff4 int]nal temp]atures (1 #bhf liquid1 #bbb1 #bif ff41 #bih1 #cja1 #caj lum9osity (1 #di1 #agi1 #ahj1 #bfi motions (1 #cf1 #ej1 #ff ff41 #afd1 #bab1 #bac numb] (1 #fh1 #fi1 #hh spectra (1 #ea1 #abe1 #acj & ,plate ,,viii 7p4 #ea74 ,see also ,displacem5ts /ability (1 #bie1 #bif1 #cjj ff4 surface-temp]atures (1 #bed1 #beg1 #bfc ff41 #bgj1 #bga v>iable1 #ee ff41 #bbc weights (1 #df1 #dh1 #di1 #afd1 #agi1 #bfh1 #bhj ff4 ,/>-/ream+1 #bab1 #bad ,/ati/ical me?ods 9 a/ronomy1 #bab1 #bac ,/ell>1 see ,/>s ,/ruve1 ,otto1 #bbc ,/ruve1 ,w41 #cc ,sun1 age (1 #aha1 #ahd c&le-p[] (1 #ee di/ance f e>?1 #cd1 #bbg1 #cdf future (1 #cdh1 #cej int]nal con/itution (1 #bhf1 #bij int]nal temp]ature (1 #bhf1 #bhh loss ( weight (1 #agh1 #bbg1 #cdf pa/ hi/ory (1 #ahj position 9 galactic sy/em1 #bf1 #ff radiation (1 #ee1 #age1 #ahi1 #aij rotation (1 #afh1 #bje1 #bde surface-temp]ature (1 #bef ,surface-temp]atures ( planets1 #ba ff41 #cdf1 #cdg ,surface-temp]atures ( />s1 #bed1 #beg1 #bfc ff41 #bgj1 #bga ( sun1 #bef ,taylor's comet1 #bea ,telescope1 #a ,galileo's1 #b1 #ac ,h]s*els'1 #be ,"l ,rosse's1 #cj #ajj-;in*1 #b1 #bj1 #fh1 #gb1 #gc #bjj-;in*1 #b1 #gc ,temp]ature1 scale (1 #ajb ,temp]ature-radiation1 #adj1 #bee ,!rmodynamics1 #cbf ff4 fir/ & second laws (1 #cbf1 #cbh ,?omson1 ,sir ,j4 ,j41 #ajf ,tidal friction1 #bbd ff4 ,tidal !ory ( sol> sy/em1 #bcf ff4 ,tides 9 b9>y />s1 #bbd1 #bbf ,titan 7satellite ( ,saturn71 #bc1 #aif ,transit ( ,v5us1 #cd ,transport ( en]gy 9 a />1 #cjg ,ultra-violet radiation1 #aaf1 #adc1 #add ,univ]se1 age (1 #ccd1 #ccf app>5t expansion (1 #hd1 #hf ff4 beg9n+ (1 #gg1 #ccb ff4 f9al end (1 #cbi ff4 size (1 #gg1 #hd1 #hg /ructure (1 #gd ff41 #hg ,uranium atom1 #aaj dis9tegration (1 #aaf1 #aba1 #aec ,uranus1 #af1 #ag1 #ah1 #ai1 #bj bir? (1 #bdj1 #bdc1 #bdd rotation (1 #bbe satellites (1 #bc1 #bdj1 #bdc1 #bdd temp]ature (1 #ba ,v ,puppis1 #bgh1 #cag van ,maan51 ,a41 #bgc van ,maan5's />1 #bfh1 #bgd1 #bgh1 #bib van ,rhijn1 ,p4 ,j41 #bf ,v>iable />s1 #ee ff41 #bbb1 #bga1 #cai ,vega 7 ,lyrae71 #cc ,velocities ( />s1 #cf1 #fh1 #afc ff4 ,v5us1 #d1 #e1 #af1 #ag1 #ai1 #cd abs5ce ( satellites1 #bdc atmosph]e on1 #aig1 #cdd bir? (1 #bdj1 #bdc life on1 #cdd1 #cdg phases (1 #d1 #e rotation (1 #bbd temp]ature (1 #bb1 #cdg transit (1 #cd ,virgo1 nebula ,n4,g4,c4 #deid 91 #ga1 #gb1 #bjd1 #bjh & ,plate ,,xv 7p4 #bjd7 ,visual b9>ies1 orbits (1 #agj1 #aga orig9 (1 #afi1 #bhd ,wave-l5g? ( radiation1 #aae1 #abb ,wave-me*anics1 #acf1 #cje ,:ite dw>f />s1 #bhj1 #bhc1 #bhh1 #cag1 #cah1 #cai1 #cbj1 #cbc1 #cdh1 #cdi ,wilson1 ,c4 ,t4 ,r41 #aac1 #aag ,wireless transmission1 #aae ,wolf #cei1 #cf1 #bfd1 #bfi1 #bgj ,x-rays1 #aaf1 #ach1 #add1 #cjg1 #caa ,z]o 7absolute7 ( temp]ature1 #ajb ,zodiacal light1 #bch ,zwicky1 ,f41 #hg ,,cambridge3 ,,pr9t$ ,,by ,w4 ,,lewis1 ,m4,a4 ,,at ,,! ,,univ]sity ,,press