,,/>gaz+3 ,,pa/ ,,& ,,pres5t ,illu/ration ,illu/ration3 ,r4 ,s4 ,,newall',s ,,telescope4 ,,/>gaz+3 ,,pa/ ,,& ,,pres5t4 ,,by ,j4 ,,norman ,,locky]1 ,f4,r4,s41 ,,correspond5t ,,( ,,! ,,in/itute ,,( ,,france4 ,,exp&$ ,,f ,,%or?& ,,notes ,,( ,a ,,c\rse ,,( ,,royal ,,in/itution ,,lectures1 ,,) ,,! ,,assi/ance ,,( ,g4 ,m4 ,,seabroke1 ,f4,r4,a4,s4 ,london3 ,,macmillan ,,& ,,co4 #ahgh4 ,! ,"r ( ,translation & ,reproduction is ,res]v$4 ,,london3 ,r4 ,,clay1 ,,sons1 ,,& ,,taylor1 ,,bread ,,/reet ,,hill1 ,e4,c4 ,,preface4 ,9 ! ye> #ahgj ,i gave a c\rse ( eight ,lectures on ,in/rum5tal ,a/ronomy at ! ,royal ,in/itution4 ,! ,lectures 7 tak5 d[n by a %or?& writ]1 my int5tion be+ to publi% !m imm$iately4 ,9 ?is1 h[ev]1 ,i 0 prev5t$ by o!r calls ^u my "t4 ,9 #ahge my fri5d ,mr4 ,seabroke g5]\sly (f]$ to take ! burd5 ( prep>+ ! notes = ! press (f my %\ld]s2 ,i avail myself ( ?is opportunity ( express+ my v great obligations to him = 8 valuable s]vices 9 ?is p>ticul> z well z = important help 9 ! f9al revision ( ! pro(s4 ,on look+ ov] ! s complet$ ,,mss41 h[ev]1 ,i saw t ! eight h\rs at my disposal _h n p]mitt$ me to t\* ^u _m po9ts ( int]e/ :i* c\ld h>dly be omitt$ f ! book4 ,besides ?is1 ! progress made 9 ! v>i\s in/rum5tal me?ods 9 ! int]val1 & ! results obta9$ by !m1 _h be5 v rem>kable4 ,i felt1 !re=e1 t ! object ,i _h 9 view1 namely1 to fur!r ! cause ( physical a/ronomy1 by creat+ & fo/]+1 s f> z 9 me lay1 a g5]al int]e/ 9 x1 & by %[+ h[ all dep>tm5ts ( physical inquiry 7 gradually be+ utiliz$ by ! a/ronom]1 w\ld only be half atta9$ unless ! acc\nt 7 m complete4 ,i h1 !re=e1 endeav\r$ to fill up ! gaps1 & h ref]r$ briefly to ! new in/rum5ts & me?ods4 ,! autotype ( ! tw5ty-five in* refractor is ! gift ( my fri5d ,mr4 ,newall1 & ,i take ?is opportunity ( express+ my obligation to him1 z also to ,messrs4 ,cooke1 ,grubb & ,br[n+ = sev]al ( ! woodcuts ) :i* ! *apt]s on ! ,equatorial are illu/rat$2 & to ,mr4 ,h4 ,d5t-,g>dn] = "s ( ^? illu/rat+ ,clock & ,*ronomet] ,escapem5ts1 & = revis+ my acc\nt ( !m4 ,nor c ,i omit to ?ank ,mr4 ,coop] = ! pa9s he has tak5 ) ! woodcuts1 especially ^? copi$ f ,ty*o ,brahe's description ( 8 ,obs]vatory1 & ,messrs4 ,clay = ! c>eful mann] 9 :i* !y h pr9t$ ! book4 ,j4 ,,norman ,,locky]4 ,novemb] #af?1 #ahgg4 ,,cont5ts4 ,,book ,i4 ,,! ,,pre-,,telescopic ,,age4 ,,*ap4 ,,page ,i4-- ,,! ,,dawn ,,( ,,/>gaz+ #a ,,ii4-- ,,! ,,fir/ ,,in/rum5ts #af ,,iii4-- ,,hipp>*us ,,& ,,ptolemy #be ,,iv4-- ,,ty*o ,,brahe #cg ,,book ,,ii4 ,,! ,,telescope4 ,v4-- ,,! ,,refraction ,,( ,,light #ee ,,vi4-- ,,! ,,refractor #gc ,,vii4-- ,,! ,,reflection ,,( ,,light #ij ,,viii4-- ,,! ,,reflector #ajj ,,ix4-- ,,eyepieces #aji ,x4-- ,,production ,,( ,,l5ses ,,& ,,specula #aag ,,xi4-- ,,! 8,,optick ,,tube0 #aci ,,xii4-- ,,! ,,mod]n ,,telescope #aeb ,,book ,,iii4 ,,"t ,,& ,,space ,,measur]s4 ,,xiii4-- ,,! ,,clock ,,& ,,*ronomet] #age ,,xiv4-- ,,circle ,,read+ #baa ,,xv4-- ,,! ,,micromet] #bah ,,book ,,iv4 ,,mod]n ,,m]idional ,,obs]vations4 ,,xvi4-- ,,! ,,transit ,,circle #bcc ,,xvii4-- ,,! ,,transit ,,clock ,,& ,,*ronograph #bec ,,xviii4-- 8,,gre5wi* ,,"t10 ,,& ,,! ,,use ,,made ,,( ,,x #bga ,,xix4-- ,,o!r ,,in/rum5ts ,,us$ ,,9 ,,a/ronomy ,,( ,,precision #bhd ,,book ,v4 ,,! ,,equatorial4 ,,xx4-- ,,v>i\s ,,me?ods ,,( ,,m\nt+ ,,l>ge ,,telescopes #bic ,,xxi4-- ,,! ,,adju/m5ts ,,( ,,! ,,equatorial #cbh ,,xxii4-- ,,! ,,equatorial ,,obs]vatory #ccg ,,xxiii4-- ,,! ,,sid]o/at #cdc ,,xxiv4-- ,,! ,,ord9>y ,,"w ,,( ,,! ,,equatorial #cdi ,,book ,,vi4 ,,a/ronomical ,,physics4 ,,xxv4-- ,,! ,,g5]al ,,field ,,( ,,physical ,,inquiry #cga ,,xxvi4-- ,,det]m9ation ,,( ,,! ,,light ,,& ,,heat ,,( ,,! ,,/>s #cgg ,,xxvii4-- ,,! ,,*emi/ry ,,( ,,! ,,/>s3 ,,con/ruction ,,( ,,! #chf ,,spectroscope ,,xxviii4-- ,,! ,,*emi/ry ,,( ,,! ,,/>s 7,,cont9u$73 ,,pr9ciples ,,( #dja ,,spectrum ,,analysis ,,xxix4-- ,,! ,,*emi/ry ,,( ,,! ,,/>s 7,,cont9u$73 ,,! #dbb ,,telespectroscope ,,xxx4-- ,,! ,,telepol>iscope #dda ,,xxxi4-- ,,cele/ial ,,photography4--,,! ,,ways ,,& ,,means #ded ,,xxxii4-- ,,cele/ial ,,photography 7,,cont9u$73 ,,"s ,,results #dfc ,,xxxiii4-- ,,cele/ial ,,photography 7,,cont9u$73 ,,rec5t ,,results #dfi ,,li/ ,,( ,,illu/rations4 ,,fig4 ,,page #a4 ,! heav5s accord+ to ,ptolemy #c #b4 ,! zodiac ( ,d5d]ah #g #c4 ,illu/ration ( ,euclid's /atem5ts #aj #d4 ,! plane ( ! ecliptic #ac #e4 ,! plane ( ! ecliptic1 %[+ ! incl9ation ( ! #ad e>?'s axis #f4 ,! fir/ m]idian circle #bj #g4 ,! fir/ in/rum5t graduat$ into #cfj 7we/ side7 #ba #h4 ,a/rolabe 7armill quatori ( ,ty*o ,brahe7 simil> to ! #bf "o contriv$ by ,hipp>*us #i4 ,ecliptic a/rolabe 7! armill zodiacales ( ,ty*o ,brahe71 #bh simil> to ! "o us$ by ,hipp>*us #aj4 ,diagram illu/rat+ ! precession ( ! equ9oxes #ca #aa4 ,revolution ( ! pole ( ! equator r\nd ! pole ( ! #cb ecliptic caus$ by ! precession ( ! equ9oxes #ab4 ,! v]nal equ9ox among ! con/ellations1 ,b4,c4 #bagj #cd #ac4 ,%[+ h[ ! v]nal equ9ox has n[ pass$ f ,taurus & #cd ,aries #ad4 ,in/rum5t = measur+ altitudes #ce #ae4 ,portrait ( ,ty*o ,brahe 7f orig9al pa9t+ 9 ! #ci possession ( ,dr4 ,crompton1 ( ,man*e/]7 #af4 ,ty*o ,brahe's obs]vatory on ! isl& ( ,hu5 #dc #ag4 ,ty*o ,brahe's sy/em #df #ah4 ,! quadrans maximus reproduc$ f ,ty*o's plate #dh #ai4 ,ty*o's sextant #ej #bj4 ,view & section ( a prism #ef #ba4 ,deviation ( light 9 pass+ at v>i\s incid5ces ?r\gh #eg prisms ( v>i\s angles #bb4 ,conv]g5ce ( light by two prisms base to base #ei #bc4 ,=mation ( a l5s f sections ( prisms #fj #bd4 ,front view & section ( a d\ble convex l5s #fa #be4 ,d\ble concave1 plane concave1 & concavo-convex l5ses #fa #bf4 ,d\ble convex1 plane convex1 & concavo-convex l5ses #fb #bg4 ,conv]g5ce ( rays by convex l5s to pr9cipal focus #fb #bh4 ,conjugate foci ( convex l5s #fc #bi4 ,conjugate images #fd #cj4 ,diagram expla9+ ,fig4 #bi #fd #ca4 ,disp]sion ( rays by a d\ble concave l5s #fe #cb4 ,horizontal section ( ! eyeball #ff #cc4 ,action ( eye 9 =mation ( images #fh #cd4 ,action ( a long-sight$ eye #fi #ce4 ,diagram %[+ pa? ( rays :5 view+ an object at an #gj easy di/ance #cf4 ,action ( %ort-sight$ eye #ga #cg4 ,galilean telescope #gc #ch4 ,telescope #ge #ci4 ,diagram expla9+ ! magnify+ p[] ( object-glass #gf #dj4 ,s*e9]'s telescope #gh #da4 ,disp]sion ( light by prism #hj #db4 ,diagram %[+ ! am\nt ( col\r produc$ by a l5s #ha #dc4 ,decomposition & recomposition ( light by two prisms #hc #dd4 ,diagram expla9+ ! =mation ( an a*romatic l5s #hd #de4 ,comb9ation ( fl9t- & cr[n-glass l5ses 9 an a*romatic #hf l5s #df4 ,diagram illu/rat+ ! irrationality ( ! spectrum #hg #dg4 ,diagram illu/rat+ ! action ( a reflect+ surface #ia #dh4 ,exp]im5tal pro( t ! angle ( incid5ce angle ( #ib reflection #di4 ,conv]g5ce ( light by concave mirror #id #ej4 ,conjugate foci ( convex mirror #id #ea4 ,=mation ( image ( c&le by reflection #ie #eb4 ,diagram expla9+ ,fig4 #ea #if #ec4 ,reflection ( rays by convex mirror #ih #ed4 ,reflect+ telescope 7,gregorian7 #aja #ee4 ,newton's telescope #ajb #ef4 ,reflect+ telescope 7,cassegra97 #ajc #eg4 ,front view telescope 7,h]s*el7 #ajc #eh4 ,diagram illu/rat+ sph]ical ab]ration #aje #ei4 ,diagram %[+ ! prop] =m ( reflector to be an ellipse #ajf #fj4 ,huygh5s' eyepiece #aaj #fa4 ,diagram expla9+ ! a*romaticity ( ! ,huygh5ian #aaa eyepiece #fb4 ,ramsd5's eyepiece #aab #fc4 ,erect+ or day eyepiece #aac #fd4 ,images ( planet produc$ by %ort & long focus l5ses1 c4 #abc #fe4 ,%[+ 9 an exagg]at$ =m h[ ! edge ( ! speculum #abh is worn d[n by poli%+ #fe994 ,section ( ,"l ,rosse's poli%+ ma*9e #aca #ff4 ,mr4 ,lassell's poli%+ ma*9e #acb #fg4 ,simple telescope tube1 %[+ arrangem5t ( object-glass #adj & eyepiece #fh4 ,appe>ance ( diffraction r+s r\nd a /> :5 ! #ada object-glass is prop]ly adju/$ #fi4 ,appe>ance ( same object :5 object-glass is out ( #ada adju/m5t #gj4 ,optical "p ( a ,newtonian reflector ( t5 in*es ap]ture #adc #ga4 ,optical "p ( a ,melb\rne reflector #adc #gb4 ,mr4 ,br[n+'s me?od ( support+ small specula #add #gc4 ,support ( ! mirror :5 v]tical #adf #gd4 ,division ( ! speculum into equal areas #adg #ge4 ,prim>y1 second>y1 & t]ti>y sy/ems ( lev]s %[n #adh sep>ately #gf4 ,complete sy/em consolidat$ into ?ree screws #adh #gg4 ,support ( diagonal plane mirror 7,front view7 #aej #gh4 ,support ( diagonal plane mirror 7,side view7 #aej #gi4 ,a portion ( ! con/ellation ,gem9i se5 ) ! nak$ eye #aed #hj4 ,! same region1 z se5 ?r\gh a l>ge telescope #aee #ha4 ,orion & ! neighb\r+ con/ellations #aef #hb4 ,nebula ( ,orion #aeg #hc4 ,saturn & 8 moons #afj #hd4 ,details ( ! r+ ( ,saturn #afa #he4 ,anci5t clock escapem5t #agg #hf4 ,! cr[n :eel #agh #hg4 ,! clock tra9 #ahj #hh4 ,w9d+ arrangem5ts #aha #hi4 ,! cycloidal p5dulum #ahe #ij4 ,graham's1 ,h>rison's1 & ,gre5wi* p5dulums #ahh #ia4 ,gre5wi* clock3 arrangem5t = comp5sation = b>ometric #aid pressure #ib4 ,! an*or escapem5t #aig #ic4 ,graham's dead beat #aii #id4 ,gravity escapem5t 7,mudge7 #bjj #ie4 ,gravity escapem5t 7,bloxam7 #bjb #if4 ,gre5wi* clock escapem5t #bjd #ig4 ,comp5sat+ balance #bjg #ih4 ,deta*$ lev] escapem5t #bjh #ii4 ,*ronomet] escapem5t #bji #ajj4 ,! fusee #bji #aja4 ,diggs' diagonal scale #bac #ajb4 ,! v]ni] #bad #ajc4 ,sy/em ( wires 9 a transit eyepiece #bbj #ajd4 ,wire micromet] #bba #aje4 ,images ( ,jupit] #bbd #ajf4 ,object-glass cut into two p>ts #bbe #ajg4 ,! p>ts sep>at$1 & giv+ two images ( any object #bbe #ajh4 ,d\ble images se5 ?r\gh ,icel& sp> #bbg #aji4 ,diagram %[+ ! ord9>y & extraord9>y rays 9 a #bbg cry/al ( ,icel& sp> #aaj4 ,cry/als ( ,icel& sp> #bbh #aaa4 ,d\ble image micromet] #bbi #aab4 ,ty*o ,brahe's mural quadrant #bce #aac4 ,transit in/rum5t 7,transit ( ,v5us ,exp$ition7 #bcf #aad4 ,transit in/rum5t 9 a fix$ obs]vatory #bcg #aae4 ,diagram expla9+ ?ird adju/m5t #bci #aaf4 ,! mural circle #bda #aag4 ,transit circle1 %[+ ! addition ( circles to ! #bdb transit in/rum5t #aah4 ,p]spective view ( ,gre5wi* transit circle #bdc #aai4 ,plan ( ! ,gre5wi* transit circle #bde #abj4 ,cambridge 7,u4,s47 m]idian circle #bdh #aba4 ,diagram illu/rat+ h[ ! pole is f\nd #bdi #abb4 ,diagram illu/rat+ ! diff]5t l5g?s ( sol> & #bee sid]eal day #abc4 ,sy/em ( wires 9 transit eyepiece #beg #abd4 ,! ,gre5wi* *ronograph4 7,g5]al view7 #bfa #abe4 ,details ( ! travell+ c>riage :i* c>ries ! magnets #bfb & prick]s4 7,side view & view f above7 #abf4 ,%[+ h[ on ! passage ( a curr5t r\nd ! s(t iron #bfc ! prick] is made to make a m>k on ! spiral l9e on ! cyl9d] #abg4 ,side view ( ! c>riage c>ry+ ! magnets & ! #bfc po9t] t draws ! spiral #abh4 ,:eel ( ! sid]eal clock1 & arrangem5t = mak+ #bff contact at ea* second #abi4 ,arrangem5t = correct+ mean sol> "t clock at ,gre5wi* #bfh #acj4 ,! *ronoph] #bgf #aca4 ,reflex z5i? tube #bhf #acb4 ,!odolite #bhh #acc4 ,portable alt-azimu? #bhi #acd4 ,! #dj-;feet at ,sl\gh #bid #ace4 ,"l ,rosse's #f-;feet #bie #acf4 ,refractor m\nt$ on alt-azimu? tripod = ord9>y #bif />-gaz+ #acg4 ,simple equatorial m\nt+ #bih #ach4 ,cooke's =m = refractors #cjj #aci4 ,mr4 ,grubb's =m appli$ to a ,cassegra9 reflector #cja #adj4 ,grubb's =m = ,newtonians #cjc #ada4 ,br[n+'s m\nt+ = ,newtonians #cjd #adb4 ,! ,wa%+ton great equatorial #cji #adc4 ,g5]al view ( ! ,melb\rne reflector #cab #add4 ,! m\nt+ ( ! ,melb\rne telescope #cac #ade4 ,great silv]-on-glass reflector at ! ,p>is obs]vatory #caf #adf4 ,clock gov]nor #cai #adg4 ,bond's spr+ gov]nor #cbj #adh4 ,f\cault's gov]nor #cbc #adi4 ,illum9at+ lamp = equatorial #cbe #aej4 ,cooke's illum9at+ lamp #cbf #aea4 ,dome #cch #aeb4 ,drum #cch #aec4 ,new ,c9c9nati obs]vatory--7,font elevation7 #cch #aed4 ,cambridge 7,u4,s47 equatorial #cci #aee4 ,section ( ma9 build+--,unit$ ,/ates naval obs]vatory #cda #aef4 ,f\cault's sid]o/at #cdd #aeg4 ,! sid]o/at at ,"l ,l9dsay's obs]vatory #cdh #aeh4 ,position circle #cec #aei4 ,h[ ! l5g? ( a %ad[ ?r[n by a lun> hill is measur$ #ced #afj4 ,! det]m9ation ( ! angle ( position ( ! axis ( #ceh ,saturn's r+ #afa4 ,measurem5t ( ! angle ( position ( ! axis ( a figure #cei ( a comet #afb4 ,d\ble /> measurem5t #cfj #afc4 ,r+ micromet] #cfh #afd4 ,!rmopile & galvanomet] #cgd #afe4 ,rum=d's photomet] #cgh #aff4 ,b\gu]'s photomet] #cgi #afg4 ,kepl]'s diagram #chg #afh4 ,newton's exp]im5t1 %[+ ! diff]5t refrangibilities #chh ( col\rs #afi4 ,fir/ obs]vation ( ! l9es 9 ! sol> spectrum #cia #agj4 ,sol> spectrum #cib #aga4 ,/ud5t's spectroscope #cic #agb4 ,section ( spectroscope #cid #agc4 ,spectroscope ) f\r prisms #cif #agd4 ,automatic spectroscope 7,grubb's =m7 #cig #age4 ,automatic spectroscope 7,br[n+'s =m7 #cig #agf4 ,la/ prism ( tra9 = return+ ! rays #cih #agg4 ,spectroscope ) return+ beam #cii #agh4 ,direct-vision prism #cii #agi4 ,electric lamp #djd #ahj4 ,electric lamp arrang$ = ?r[+ a spectrum on a scre5 #dje #aha4 ,comp>ison ( ! l9e spectra ( iron1 calcium1 & #djf alum9ium1 ) common impurities #ahb4 ,col\r$ flame ( salts 9 ! flame ( a ,buns5's burn] #djh #ahc4 ,spectroscope arrang$ = %[+ absorption #dji #ahd4 ,geissl]'s tube #dac #ahe4 ,spectrum ( sun-spot #dae #ahf4 ,diagram expla9+ long & %ort l9es #daf #ahg4 ,comp>ison ( ! absorption spectrum ( ! sun ) ! #dah radiation spectra ( iron & calcium1 ) common impurities #ahh4 ,comp>ison prism #dbc #ahi4 ,comp>ison prism #dbc #aij4 ,f\cault's helio/at #dbd #aia4 ,object-glass prism #dbf #aib4 ,! eyepiece end ( ! ,newall refractor #dbg #aic4 ,sol> telespectroscope 7,br[n+'s =m7 #dbh #aid4 ,sol> telespectroscope 7,grubb's =m7 #dbh #aie4 ,side view ( spectroscope #dbi #aif4 ,plan ( spectroscope #dbi #aig4 ,cambridge /> spectroscope elevation #dcj #aih4 ,cambridge spectroscope plan #dcj #aii4 ,direct-vision /> spectroscope 7,sec*i7 #dca #bjj4 ,types ( /ell> spectra #dcc #bja4 ,"p ( sol> spectrum ne> ,f #dcf #bjb4 ,di/ortions ( ,f l9e on sun #dch #bjc4 ,displacem5t ( ,f l9e on edge ( sun #dci #bjd4 ,diagram %[+ ! pa? ( ! ord9>y & extraord9>y #dde ray 9 cry/als ( ,icel& sp> #bje4 ,appe>ance ( ! spots ( light on ! scre5 %[n 9 ! #ddf prec$+ figure1 all[+ ! ord9>y ray to pass & rotat+ ! second cry/al #bjf4 ,appe>ance ( spots ( light on scre5 on rotat+ ! second #ddg cry/al1 :5 ! extraord9>y ray is all[$ to pass ?r\gh ! fir/ scre5 #bjg4 ,in/rum5t = %[+ pol>ization by reflection #ddh #bjh4 ,section ( plate-hold] #def #bji4 ,enl>g+ cam]a #deh #baj4 ,in/antane\s %utt] #dfj #baa4 ,photoheliograph z erect$ 9 a tempor>y obs]vatory = #dfa photograph+ ! transit ( ,v5us 9 #ahgd #bab4 ,copy ( photograph tak5 dur+ ! eclipse ( #ahfi #dgd #bac4 ,"p ( ,be] & ,mdl]'s map ( ! moon #dgf #bad4 ,! same region copi$ f a photograph by ,de ,la ,rue #dgg #bae4 ,comp>ison betwe5 ,kir*h(f's map & ,ru!rfurd's #dhj photograph #baf4 ,arrangem5t = photographically det]m9+ ! co9cid5ce #dha ( sol> & metallic l9es #bag4 ,telespectroscope ) cam]a = obta9+ photographs ( ! #dhb sol> prom95ces ,,book ,i4 ,,! ,,pre-,,telescopic ,,age4 ,,/>gaz+3 ,,pa/ ,,& ,,pres5t ,,*apt] ,i4 ,,! ,,dawn ,,( ,,/>gaz+4 ,"s sci5ces are ( ye/]day2 o!rs /ret* f> back into ! y\? ( "t4 ,among ^! !re is "o ( ! beg9n+s ( :i* we h lo/ all trace1 s coeval 0 x ) ! comm5cem5t ( man's hi/ory2 & t sci5ce is ! "o ( :i* we h to trace ! in/rum5tal developm5ts4 ,al?\gh our *ief task is to enl>ge ^u ! mod]n1 x w n be well1 inde$ x is impossible1 to neglect ! old1 because1 if = no o!r reason1 ! weld+ ( old & new has be5 s p]fect1 ! conque/ ( ! unkn[n s gradual4 ,! be/ c\rse !re=e w be to di/ribute ! diff]5t fields ( ?\ght & "w into some?+ l m>k$ divisions1 & to comm5ce by divid+ ! :ole "t dur+ :i* man has be5 obs]v+ ! heav5s into two p]iods1 :i* we w call ! ,pre-telescopic & ! ,telescopic ,ages4 ,! "w ( ! ,pre-telescopic age ( c\rse includes all ! e>ly obs]vations made by ! unaid$ eye1 :ile t ( ! ,telescopic age includes ^? ( va/ly diff]5t k9ds1 :i* t in/rum5t _h r5d]$ possible2 s t x divides itself naturally into "s ?ree or f\r sub-ages ( extreme importance4 ,x is unnecess>y to say "o ^w "h on ! importance ( ! inv5tion ( ! telescope2 x is well = ! pres5t purpose1 h[ev]1 to emphasize ! fur!r di/9ctions we obta9 :5 we consid] ! v>i\s additions made f "t to "t to ! telescope4 ,! ,telescope1 9 fact1 0 comp>atively little us$ until a/ronomy annex$ t important bran* ( physics to its aid :i* gave u a ,clock--a means ( divid+ "t 9 ! mo/ accurate mann]4 ,9 q rec5t times ! addition ( ! ,cam]a to ! ,telescope m>ks an important advance2 inde$ ! importance ( photography is n yet recognis$ 9 ! way x %\ld be4 ,!n1 aga91 !re is ! addition ( ! ,spectroscope1 :i*1 ?\gh x is only n[ beg9n+ to yield u ri* fruit1 really dates f ! beg9n+ ( ! pres5t c5tury4 ,?is is an ally to ! telescope ( su* p[] t he w\ld be a bold man :o w\ld v5ture to set b\nds to ! conque/s _! comb9$ =ces w make4 ,n[ n only is x ess5tial = ! prop] und]/&+ ( ! in/rum5ts us$ n[adays 9 e obs]vatory1 by e />gaz]1 to g back to ! orig9 ( ! sci5ce ( obs]vation1 b 9 no o!r way c "o fully see 9 :at way ! new in/rum5tal me?ods h add$ !mselves to ! old ones4 ,fur!r1 x is ( importance to g back to ! actual old field ( "w 9 :i* ! geometric conceptions :i* grew up 9 ! m9ds ( ! m5 ( anci5t "t--conceptions :i* we are n[ utiliz+ & ext5d+--7 gradually elaborat$4 ,to d ?is1 !re is no bett] way ?an to dwell v briefly on ! "w actually done by ! old a/ronom]s4 99 99 99 99 99 ,?is programme1 !n1 be+ agre$ to1 ! fir/ po9t is to trace ! progress ( a/ronomical in/rum5ts d[n to ! "t ( ,cop]nicus & ,galileo4 ,dur+ all ?is p]iod ! mo/ g5]ally receiv$ doctr9e 01 t ! e>? 0 ! c5tre ( ! visible heav5s2 & al?\gh !re 7 _m v>iations ( ?is1 /ill ! arrangem5t ( ,ptolemy1 ,fig4 #a1 is a good type ( ! ideas ( ! anci5ts4 ,illu/ration3 ,,fig4 #a4--,! ,heav5s accord+ to ,ptolemy4 ,we beg9 ) man's fir/ feeble ef=ts1 ! "w :i* man 0 enabl$ to d by 8 unaid$ eye2 & we end ) ! trem5d\s addition :i* he got to 8 obs]v+ p[]s by ! inv5tion ( ! telescope4 ,! fir/ in/rum5t us$ = a/ronomical obs]vations 0 none ( man's mak+4 ,9 ! old "t ! only in/rum5t 0 ! horizon2 &1 tru? to tell1 9 a l& ( ext5d$ pla9s & isolat$ hills1 x 0 n a bad "o4 ,h5ce x 01 d\btless1 t obs]vations 9 ! fir/ in/ance 7 limit$ to c]ta9 occurr5ces su* z ! ris+s & sett+s ( ! />s & ! relative app>5t di/ances ( ! heav5ly bodies f ea* o!r4 ,s f> z we are able to le>n f anci5t au?ors1 ! obs]vations next add$ 7 ^? ( ! conjunctions ( ! planets & ( eclipses4 ,! ,egyptians are /at$ to h record$ #cgc sol>1 & #hcb lun> eclipses2 & ?is /atem5t is probably correct1 z ! proportions are exact1 & !re %\ld be ! above numb] ( ea* 9 f #a1bjj to #a1cjj ye>s4 ,! ,*9ese also record an obs]vation1 made betwe5 ! ye>s #bead & #bdcf ,b4,c41 ( five planets be+ 9 conjunction4 ,! ,*aldeans appe> to h obs]v$ ! motions ( ! moon1 & an obs]vation 9 #bbbg ,b4,c4 is record$2 b ^! old dates are probably fictiti\s4 ,x is impossible to reg>d )\t surprise ! g5]al att5tion giv5 to a/ronomical inve/igation 9 ^? e>ly days comp>$ ) :at we f9d n[4 ,yet if we attempt to build up = ourselves any idea z to ! problems ( :i* ! anci5ts attempt$ ! solution1 x is difficult if n impossible to d x2 we _c realize ! blank :i* ! heav5s pres5t$ to !m1 s _m great m5 h liv$ betwe5 _! "t & our own1 by ^: lab\rs we1 ev5 if unconsci\sly1 h pr(it$4 ,! fir/ idea seems to h be5 to obs]ve :i* />s 7 ris+ or sett+ at se$ or h>ve/ "t1 to divide ! heav5s into ,moon ,/ations1 & !n to m>k a/ronomically _! mon?ly & ye>ly fe/ivals4 ,if "o looks into ! old records we f9d t all ! lab\rs ( man :i* _h to be p]=m$ 9 ! c\ntry or else:]e 7 det]m9$1 by ! ris+ or sett+ ( ! />s4 ,all ! ex]tions ( ! navigator & ! agriculturi/ 7 ?us regulat$4 ,( ! planets 9 ^? e>ly times we he> little1 except f ! ,*9ese annals :i* record conjunctions4 ,?is 0 be=e man began to use ! sun z a /&po9t1 & h5ce x is t !re are s _m ref]5ces 9 ! anci5t writ]s to ! ris+ & sett+ ( ! mo/ /rik+ /> clu/]--! ,pleiades1 & ! mo/ /rik+ con/ellation--,orion4 ,x is kn[n t ! ye>1 9 lat] times at all ev5ts1 began 9 ,egypt :5 ! brighte/ /> 9 ! heav5s1 ,sirius1 ! dog-/>1 rose ) ! sun1 ?is day be+ call$ ! #a/ ( ! mon? ,?o?1#a :i* 0 ! comm5cem5t ( ! ,so?iac p]iod ( #adfa ye>s4 ,x w\ld appe> t obs]vations ( culm9ations1 t is1 ( ! highe/ po9ts rea*$ by ! />s1 7 n made till long aft] horizon obs]vations 7 9 full vig\r2 & "h x is a "q :e!r pyramids & ! l 7 n ! fir/ a/ronomical in/rum5ts con/ruct$ by man1 because = great nicety 9 su* obs]vations--a nicety1 let u say1 suffici5t to det]m9e a/ronomically by means ( culm9ations ! "t = hold+ a fe/ival--a fix$ in/rum5t ( "s k9d 0 ess5tial4 ,! ri* m9e rec5tly op5$ up by ,mr4 ,haliburton & ,mr4 ,erne/ de ,buns5 conc]n+ ! survival 9 all nations--9 our own "o takes ! "n ! ,fea/ ( ,all ,s\ls'--( anci5t fe/ivals gov]n$ by ! midnight culm9ation ( ! ,pleiades w d\btless ere long call g5]al att5tion to ?is e>lie/ =m ( accurate a/ronomical obs]vation1 & ! det]m9ation by ,pr(essor ,piazzi ,smy? ( ! fact t 9 #bagj ,b4,c41 :5 ! ,pleiades culm9at$ at midnight at ! v]nal equ9ox1 ! passages 9 ! nor? & s\? faces ( ! pyramid ( ,gizeh 7 direct$1 ! s\!rn "o to ?is culm9ation1 & ! nor!rn "o to ! !n pole />1 ,draconis1 at its transit1 ab\t #d f ! pole4 ,h5ce "o may reg>d ! pyramid z ! next a/ronomical in/rum5t to ! horizon4 ,:ile !n x is possible t su* culm9ation obs]vations soon replac$ 9 "s measure t class ( obs]vations :i* h]et(ore _h be5 made on ! horizon1 ano!r tea*+ ( horizon obs]vations became app>5t4 ,by & by travell]s obs]v$ t z !y travell$ nor?w>ds ! />s t 7 j visible on ! s\!rn horizon1 :5 culm9at+1 gradually disappe>$ bel[ x4 ,^! obs]vations 7 at once seiz$ on1 & ,anaxim&] acc\nt$ = !m by suppos+ t ! e>? 0 a cyl9d]4#b ,! idea ( a sph]e did n come till lat]2 :5 x did come !n came ! circle z an a/ronomical in/rum5t4 ,= let u consid] t a p]son on ! e>? /&s1 say1 at ! equator2 !n he w j be able to see along 8 nor? & s\? horizon ! />s po9t$ to by ! axis ( ! globe3 if n[ he is transport$ nor?w>ds1 8 horizon w *ange ) him2 he w no long] be able to see ! s\!rn />s1 b ! nor!rn ones w gradually rise above 8 horizon till he gets to ! nor? pole1 :5 ! nor? pole />1 in/ead ( be+ on 8 horizon1 z 0 ! case :5 he 0 at ! equator1 w be ov] 8 head4 ,s by mov+ f ! equator to ! pole 7or a qu>t] ( ! di/ance r\nd ! e>?7 ! />s h mov$ f ! horizon to ! po9t ov]head1 or ! z5i?1 t is also a qu>t] ( a circle4 ,s x appe>s t if an obs]v] moves to su* a di/ance t ! />s appe> to move ov] a c]ta9 division ( a circle ) ref]5ce to ! horizon1 he mu/ h mov$ ov] an equal division on ! e>?'s surface4 ,!n1 z n[1 ! circle 9 ! ,we/]n _w 0 divid$ into #cfj1 s t ! obs]v] 9 mov+ #a by ! />s w\ld h mov$ ov] #a_/cfj ( ! di/ance r\nd ! e>?1 on ! assumption t ! e>? is a globe2 & if ! di/ance ov] :i* ! obs]v] has mov$ be multipli$ by #cfj1 ! result w be ! di/ance r\nd ! e>?4 ,illu/ration3 ,,fig4 #b4--,! ,zodiac ( ,d5d]ah4 ,n[ let u see h[ ,posidonius a long "t aft]w>ds 7he 0 born ab\t #ace ye>s ,b4,c47 appli$ ?is conception4 ,he obs]v$ t at ,rhodes ! /> ,canopus graz$ ! horizon at culm9ation1 :ile at ,alex&ria x rose above x #g4 ,n[ #g is #a_/dh ( ! :ole circle2 s he f\nd t f ! latitude ( ,rhodes to t ( ,alex&ria 0 #a_/dh ( ! circumf]5ce ( ! e>?4 ,he !n e/imat$ ! di/ance1 gett+ #e1jjj /adia z ! result2 & ?is multipli$ by #dh gave him #bdj1jjj /adia1 8 measure ( ! circumf]5ce ( ! e>?4 ,:5 ! sun's ye>ly c\rse 9 ! heav5s _h be5 det]m9$1 x 0 f\nd t x 0 re/rict$ to t b& ( />s call$ ! ,zodiac1 ,fig4 #b2 ! sun's position 9 ! zodiac at any "o "t ( ! ye> be+ f\nd by ! midnight culm9ation ( ! />s opposite ! sun2 ?is & ! app>5t & heliacal ris+s & sett+s 7 alone ! subjects ( obs]vation4 ,x is obvi\s1 !n1 t :5 obs]vations ( ?is nature _h gone on = "s "t1 m5 w\ld be anxi\s to map ! />s1 to make a *>t ( ! field ( heav52 & su* a "w 0 produc$ by ,autolycus ?ree & a half c5turies be=e ,*ri/4 ,we also owe to ,autolycus & ,euclid1 :o fl\ri%$ ab\t ! same "t 7#cjj ,b4,c471 ! fir/ geometrical conceptions connect$ ) ! app>5t motions ( ! />s4 ,9 ! !orems ( ,autolycus !re is a p>ticul> ref]5ce to ! twelve p>ts ( ! zodiac1 z d5ot$ by con/ellations4 ,! foll[+ are ! mo/ important propositions :i* he lays d[n3-- #a4 8,! zodiacal sign occupi$ by ! sun nei!r rises nor sets1 b is ei!r conceal$ by ! e>? or lo/ 9 ! sun's rays4 ,! opposite sign nei!r rises nor sets1 i4e41 visibly1 i4e41 aft] sund[n1 b x is visible dur+ ! :ole night4 #b4 8,( ! twelve signs ( ! zodiac1 t :i* prec$es ! sign occupi$ by ! sun rises visibly 9 ! morn+2 t :i* succe$s ! same sign sets visibly 9 ! ev5+4 #c4 8,elev5 signs ( ! zodiac are se5 e night4 ,six signs are visible1 & ! five o!rs1 n occupi$ by ! sun1 aft]w>ds rise4 #d4 8,e /> has an int]val ( five mon?s betwe5 its morn+ & its ev5+ ris+1 dur+ :i* "t x is visible4 ,x has an int]val ( at lea/ ?irty days--betwe5 its ev5+ sett+1 & its morn+ ris+--dur+ :i* "t x is invisible40 7,t is1 ! space pass$ ov] by ! sun 9 its annual pa? is su* t a /> :i* y see on "o side ( ! sun1 :5 ! sun rises at "o "t1 w\ld be se5 a mon? aft]w>ds on ! o!r side ( ! sun47 ,autolycus makes no m5tion ( ! planets4 ,_! irregul> movem5ts r5d]$ !m unsuit$ to ! practical object :i* he _h 9 view4 ,he is1 h[ev]1 /at$ by ,simplicius1 z quot$ by ,sir ,g4 ,c4 ,lewis to h propos$ "s hypo!sis = expla9+ _! anomal\s motions1 & to h fail$ 9 8 attempt4 ,euclid c>ries ! results arriv$ at 9 ?is e>ly pre-telescopic age mu* fur!r2 9 a little-kn[n treatise1 ! ,ph5om5a1#c he ?us sums up ! k !n acquir$3-- 8,! fix$ />s rise at ! same po9t1 & set at ! same po9t2 ! same />s always rise toge!r1 & set toge!r1 & 9 _! c\rse f ! ea/ to ! we/ !y always pres]ve ! same di/ance f "o ano!r4 ,n[1 z ^! appe>ances are only consi/5t ) a circul> movem5t1 :5 ! eye ( ! obs]v] is equally di/ant f ! circumf]5ce ( ! circle 9 e direction 7z has be5 demon/rat$ 9 ! treatise on ,optics71 x foll[s t ! />s move 9 a circle & are atta*$ to a s+le body1 & t ! vision is equally di/ant f ! circumf]5ce4 ,illu/ration3 ,,fig4 #c4--;,illu/ration ( ,euclid's /atem5ts4 ,p ! /> betwe5 ! ,be>s4 ,d ,d ! region ( ! always visible4 ,c ,b ,a ! regions ( ! />s :i* rise & set4 8,a /> is visible betwe5 ! ,be>s1 n *ang+ its place1 b always revolv+ ^u itself4 ,s9ce ?is /> appe>s to be equally di/ant f e "p ( ! circumf]5ce ( ea* circle describ$ by ! o!r />s1 x mu/ be assum$ t all ! circles are p>allel1 s t all ! fix$ />s move along p>allel circles1 hav+ ?is /> z _! common pole4 8,"s ( ^! nei!r rise nor set1 on acc\nt ( _! mov+ 9 elevat$ circles1 :i* are call$ ! #8always visible4' ,!y are ! />s :i* ext5d f ! visible pole to ! ,arctic circle4 ,^? :i* are ne>e/ ! pole describe ! smalle/ circle1 & ^? ^u ! ,arctic circle ! l>ge/4 ,! latt] appe>s to graze ! horizon4 8,! />s to ! s\? ( ?is circle all rise & set1 on acc\nt ( _! circles be+ p>tly above & p>tly bel[ ! e>?4 ,! segm5ts above ! e>? are l>ge & ! segm5ts bel[ ! e>? are small 9 proportion z !y approa* ! ,arctic circle1 because ! motion ( ! />s ne>e/ ! circle above ! e>? is made 9 ! longe/ "t1 & ( ^? bel[ ! e>? 9 ! %orte/4 ,9 proportion z ! />s rec$e f ?is circle1 _! motion above ! e>? is made 9 less "t1 & t bel[ ! e>? 9 great]4 ,^? t are ne>e/ ! s\? are ! lea/ "t above ! e>?1 & ! longe/ bel[ x4 ,! />s :i* are ^u ! middle circle make _! times above & bel[ ! e>? equal2 :5ce ?is circle is call$ ! ,equ9octial4 ,^? :i* are ^u circles equally di/ant f ! equ9octial make ! alt]nate segm5ts 9 equal times4 ,= example1 ^? above ! e>? to ! nor? correspond ) ^? bel[ ! e>? to ! s\?2 & ^? above ! e>? to ! s\? correspond ) ^? bel[ ! e>? to ! nor?4 ,! jo9t times ( all ! circles above & bel[ ! e>? are equal4 ,! circle ( ! milky way & ! zodiacal circle be+ oblique to ! p>allel circles1 & cutt+ ea* o!r1 always h a semicircle above ! e>?4 8,h5ce x foll[s t ! heav5 is sph]ical4 ,= if x 7 cyl9drical or conical1 ! />s ^u ! oblique circles1 :i* cut ! equator1 w\ld n 9 ! revolution ( ! heav5 always appe> to be divid$ into semicircles2 b ! visible segm5t w\ld sometimes be great] & sometimes less ?an a semicircle4 ,= if a cone or a cyl9d] 7 cut by a plane n p>allel to ! base1 ! section is t ( an acute-angl$ cone1 :i* resembles a %ield 7an ellipse74 ,x is1 !re=e1 evid5t t if a figure ( ?is description is cut 9 ! middle bo? 9 l5g? & brea?1 its segm5ts w be unequal4 ,b ! appe>ances ( ! heav5 agree ) none ( ^! results4 ,!re=e ! heav5 mu/ be suppos$ to be sph]ical1 & to revolve equally r\nd an axis ( :i* "o pole above ! e>? is visible & ! o!r bel[ ! e>? is invisible4 8,! ,horizon is ! plane rea*+ f our /ation to ! heav51 & b\nd+ ! hemisph]e visible above ! e>?4 ,x is a circle2 = if a sph]e be cut by a plane ! section is a circle4 8,! ,m]idian is a circle pass+ ?r\gh ! poles ( ! sph]e1 & at "r angles to ! horizon4 8,! ,tropics are circles :i* t\* ! zodiacal circle1 & h ! same poles z ! sph]e4 ,! zodiacal & ! equ9octial are bo? great circles1 = !y bisect "o ano!r4 ,= ! beg9n+ ( ,aries & ! beg9n+ ( ! ,claws 7or ,scorpio7 are ^u ! same diamet]2 & :5 !y are bo? ^u ! equ9octial1 !y rise & set 9 conjunction1 hav+ betwe5 _! beg9n+s six ( ! twelve signs & two semicircles ( ! equ9octial2 inasmu* z ea* beg9n+1 be+ ^u ! equ9octial1 p]=ms its movem5t above & bel[ ! e>? 9 equal times4 ,if a sph]e revolves equally r\nd its axis1 all ! po9ts on its surface pass ?r\gh simil> axes ( ! p>allel circles 9 equal times4 ,!re=e ^! signs pass ?r\gh equal axes ( ! equ9octial1 "o above & ! o!r bel[ ! e>?2 consequ5tly ! axes are equal1 & ea* is a semicircle2 = ! circuit f ea/ to ea/ & f we/ to we/ is an entire circle4 ,consequ5tly ! zodiacal & equ9octial circles bisect "o ano!r2 ea* w be a great circle4 ,!re=e ! zodiacal & equ9octial are great circles4 ,! horizon is likewise a great circle2 = x bisects ! zodiacal & equ9octial1 bo? great circles4 ,= x always has six ( ! twelve signs above ! e>?1 z well z a semicircle ( ! equator4 ,! />s above ! horizon :i* rise & set toge!r reappe> 9 equal times1 "s mov+ f ea/ to we/1 & "s f we/ to ea/40 ,we h giv5 ?is long extract 9 ju/ice to ! m5 ( old1 conta9+ z x does _m ( ^? geometrical pr9ciples :i* all our mod]n in/rum5ts mu/ & actually d fulfil4 ,x is true t ! pres5t idea ( ! e>?'s place 9 ! sy/em is diff]5t4 ,euclid imag9$ ! e>? to be at ! c5tre ( ! univ]se4 ,x is n[ kn[n t ! e>? is "o ( v>i\s planets :i* revolve r\nd ! sun1 & fur!r1 t ! j\rney ( ! e>? r\nd ! sun is s ev5 & beautifully regulat$ t its motion is conf9$ to a s+le plane4 ,ye> aft] ye> ! e>? goes on revolv+ r\nd ! sun1 nev] dep>t+1 except to a v small ext5t1 f ?is plane1 :i* is "o ( ! fundam5tal planes ( ! a/ronom] & call$ ! ,plane ( ! ,ecliptic4 ,illu/ration3 ,,fig4 #d4--,! ,plane ( ! ,ecliptic4 ,suppose ?is plane to be a tangible ?+1 l ! surface ( an inf9ite ocean1 ! sun w occupy a c]ta9 position 9 ?is inf9ite ocean1 & ! e>? w travel r\nd x e ye>4 ,if ! axis ( ! e>? 7 upright1 "o w\ld repres5t ! position ( ?+s by hold+ a globe ) its axis upright1 s t ! equator ( ! e>? is 9 e "p ( its revolution on a level ) ?is ecliptic sea4 ,b x is kn[n t ! e>?1 in/ead ( float+1 z x 71 upright1 z 9 ,fig4 #d1 has its axis incl9$ to ! plane ( ! ecliptic1 z 9 ,fig4 #e4 ,x is also kn[n t by turn+ a globe r\nd1 di/ant objects w\ld appe> to move r\nd an obs]v] on ! globe 9 an opposite direction to 8 own motion1 & ^! di/ant objects w\ld describe circles r\nd a l9e jo9+ ! places po9t$ to by ! poles ( ! e>?1 i4e41 r\nd ! e>?'s axis4 ,illu/ration3 ,,fig4 #e4--,! ,plane ( ! ,ecliptic1 %[+ ! ,incl9ation ( ! ,e>?'s ,axis4 ,x is n[ easy to expla9 ! obs]vations ref]r$ to by ,euclid by suppos+ ! surface ( ! wat] 9 ! tub to repres5t ! plane ( ! ecliptic1 t is1 ! plane ( ! pa? :i* ! sun app>5tly takes 9 go+ r\nd ! e>?2 & exam9+ ! relative positions ( ! sun & e>? repres5t$ by two float+ balls1 ! latt] hav+ a wire ?r\gh x incl9$ to ! upright position2 x w be se5 at once by turn+ ! ball on ! wire z an axis to repres5t ! diurnal motion ( our e>?1 h[ ,euclid f9ds ! ,be> :i* nev] sets1 be+ ! place 9 ! heav5s po9t$ to by ! e>?'s pole2 & h[ all ! />s 9 diff]5t portions ( ! heav5s appe> to move 9 complete circles r\nd ! pole-/> :5 !y d n set1 & 9 p>ts ( circles :5 !y pass bel[ ! horizon4 ,by mov+ ! ball repres5t+ ! e>? r\nd ! sun & s exam9+ _! relative positions1 dur+ ! c\rse ( a ye> x w be se5 h[ ! sun appe>s to travel ?r\gh all ! signs ( ! zodiac 9 succession 9 8 ye>ly c\rse1 rema9+ a long] or %ort] "t above ! horizon at diff]5t times ( ! ye>4 ,= x w be se5 t if ! spectator on ! globe1 :5 9 ! position t its incl9$ axis1 z %[n 9 ,fig4 #e1 po9ts t[>ds ! sun1 7 look+ at ! sun f a place :]e "o c imag9e ,engl& to be at midday1 ! sun w\ld appe> to be v high up above ! horizon2 & if he look$ at x f ! e>? 9 ! opposite "p ( its orbit x w\ld be v l[ & ne> ! horizon4 ,:5 ! e>?1 !re=e1 occupi$ ! int]m$iate positions1 ! sun w\ld be half way betwe5 ! extreme upp] position & ! extreme l[] position z ! e>? moves r\nd ! sun1 & 9 ?is way ! sol/ices1 equ9oxes1 & ! seasonal *anges on ! surface ( our planet1 are easily expla9$4 ----- ,footnote #a3 ,correspond+ to #bj? ,july1 #aci ,b4,c4 ,footnote #b3 ,anaxim&] fl\ri%$ ab\t #edg ,b4,c4 ,footnote #c3 ,quot$ by ,sir ,g4 ,c4 ,lewis 9 8 ,a/ronomy ( ! ,anci5ts1 p4 #ahg4 ,,*apt] ,,ii4 ,,! ,,fir/ ,,in/rum5ts4 ,! anci5ts call$ ! places occupi$ by ! sun :5 highe/ & l[e/ ! ,sol/ices1 & ! int]m$iate positions ! ,equ9oxes4 ,! fir/ in/rum5t made 0 = ! det]m9ation ( ! sun's altitude 9 ord] to fix ! sol/ices4 ,?is in/rum5t 0 call$ ! ,gnomon4 ,x consi/$ ( an upright rod1 %>p at ! end & rais$ p]p5dicul>ly on a horizontal plane1 & its %ad[ c\ld be measur$ 9 ! plane ( ! m]idian by a nor? & s\? l9e on ! gr\nd4 ,:5ev] ! %ad[ 0 longe/ ! sun 0 naturally l[e/ d[n at ! w9t] sol/ice1 & vice v]s = ! summ] sol/ice4 ,"h !n we leave obs]vations on ! horizon & come to ^? made on ! m]idian4 ,! ,gnomon is said to h be5 kn[n to ! ,*9ese 9 ! "t ( ! ,emp]or ,yao's reign 7#bcjj ,b4,c471 b x 0 n us$ by ! ,greeks#d till ! "t ( ,?ales1 ab\t #ehe ,b4,c41 :o fix$ ! dates ( ! sol/ices & equ9oxes1 & ! l5g? ( ! tropical ye>--t is1 ! "t tak5 by ! sun to travel f ! v]nal equ9octial po9t r\nd to ! same po9t aga94 ,! next problem 0 to discov] ! incl9ation ( ! ecliptic1 or1 :at is ! same ?+1 ! am\nt t ! e>?'s equator is incl9$ to ! ecliptic plane 7repres5t$ by ! surface ( ! wat] 9 our tub74 ,n[ 9 ord] to asc]ta9 ?is1 ! angul> di/ance betwe5 ! positions occupi$ by ! sun :5 at ! sol/ices mu/ be measur$2 or1 s9ce "o sol/ice is j z mu* bel[ ! equ9octial l9e z ! o!r is above x1 we might take half ! angle betwe5 ! sol/ices z be+ ! obliquity requir$4 ,! fir/ me?od ( measur+ ! angle 0 to measure ! l5g? ( ! sun's %ad[ at ea* sol/ice1 & s1 by comp>ison ( ! l5g? ( ! %ad[ ) ! height ( ! gnomon1 calculate ! diff]5ce 9 altitude1 ! half ( :i* 0 ! angle s\ght4 ,& ?is 0 probably ! me?od ( ! ,*9ese1 :o obta9$ a result ( #bc #ch #aa 9 ! "t ( ,yao2 & also ( ,anaxim&] 9 8 e>ly days1 :o obta9$ a result ( #bd4 ,b be=e trigonometrical tables1 ! fir/ ( :i* seem to h be5 con/ruct$ by ,hipp>*us & ,ptolemy1 7 kn[n1 9 ord] to f9d ?is angle x 0 con/ruct$ geometrically1 & !n :at aliquot "p ( ! circumf]5ce x 01 or h[ mu* ( ! circumf]5ce x conta9$ 0 det]m9$2 = ! division ( ! circle into #cfj is subsequ5t to ! fir/ beg9n+ ( a/ronomy--& h5ce x 0 t ,erato/h5es said t ! di/ance f ! tropics 0 #aa_/hc ( ! circumf]5ce1 & n t x 0 #dg #df #bf4 ,! gnomon is1 )\t exception1 ( all in/rum5ts ! "o ) :i* ! anci5ts 7 able to make ! be/ obs]vations ( ! sun's altitude4 ,b !y did n give suffici5t att5tion to x to enable x to be us$ ) accuracy4 ,! %ad[ project$ by a po9t :5 ! sun is %9+ is n well def9$1 s t !y c\ld n be q c]ta9 ( its extremity1 & x w\ld seem t ! anci5t obs]vations ( ! height ( ! sun made 9 ?is mann] ought to be correct$ by ab\t half ! app>5t diamet] ( ! sun2 = x is probable t ! anci5ts took ! /rong %ad[ = ! true %ad[2 & s !y _h only ! height ( ! upp] "p ( ! sun & n t ( ! c5tre4 ,!re is no pro( t !y did n make ?is correction1 at lea/ 9 ! lat] obs]vations4 ,9 ord] to obviate ?is inconv5i5ce1 !y subsequ5tly t]m9at$ ! gnomon by a b[l or disc1 ! c5tre ( :i* answ]$ to ! summit2 s t1 tak+ ! c5tre ( ! %ad[ ( ?is b[l1 !y _h ! height ( ! c5tre ( ! sun4 ,su* 0 ! =m ( ! "o t ,manlius ! ma!matician erect$ at ,rome "u ! auspices ( ,augu/us4 ,b 9 comp>atively mod]n times a/ronom]s h rem$i$ ?is defect 9 a /ill m happy mann]1 by us+ a v]tical or horizontal plate pi]c$ ) a circul> hole :i* all[s ! rays ( ! sun to ent] into a d>k place1 & 9 fact to =m a true image ( ! sun on a floor or o!r conv5i5t receptacle1 z we f9d is ! case 9 _m cont95tal *ur*es4 ,( c\rse at ?is e>ly p]iod ! ref]5ce ( any p>ticul> ph5om5on to true "t 0 out ( ! "q4 ,! anci5ts at ! p]iod we are consid]+ us$ twelve h\rs to repres5t a day1 irrespective ( ! "t ( ! ye>--! day always be+ reckon$ z ! "t betwe5 sunrise & sunset4 ,s t 9 summ] ! h\rs 7 long & 9 w9t] !y 7 %ort4 ,! idea ( equal h\rs did n occur to !m till lat]2 b no obs]vations are clos] ?an an h\r1 & ! smalle/ division ( space ( :i* !y took notice 0 some?+ l equal to a qu>t] or half ( ! moon's diamet]4 ,:5 we come d[n1 h[ev]1 to ?ree c5turies be=e ,*ri/1 we f9d t a diff]5t /ate ( ?+s is com+ ab\t4 ,! magnific5t museum at ,alex&ria 0 beg9n+ to be built1 & a/ronomical obs]vations 7 among ! mo/ important ?+s to be done 9 t va/ e/abli%m5t4 ,! fir/ a/ronomical work]s !re seem to h be5 ,timo*>is & ,ari/illus1 :o began ab\t #bie ,b4,c41 & work$ = tw5ty-six ye>s4 ,we are told t !y made a catalogue ( />s1 giv+ _! positions ) ref]5ce to ! sun's pa? or ecliptic4 ,x 0 soon aft] ?is t ! gnomon gave way to ! inv5tion ( ! ,sc>phie4 ,x is really a little gnomon on ! summit ( :i* is a sph]ical segm5t4 ,an arc ( a circle pass+ out ( ! foot ( ! /yle 0 divid$ into p>ts1 & we ?us _h ! angle :i* ! sol> ray =m$ ) ! v]tical4 ,nev]!less ! sc>phie 0 subject to ! same inconv5i5ces1 & x requir$ ! same corrections1 z ! gnomon2 9 %ort1 x 0 less accurate ?an x4 ,t did n1 h[ev]1 h9d] ,erato/h5es f mak+ use ( x to measure ! size ( ! e>? & ! incl9ation ( ! ecliptic to ! equator4 ,! me?od ,erato/h5es foll[$ 9 asc]ta9+ ! size ( ! e>? 0 to measure ! arc betwe5 ,sy5e & ,alex&ria by obs]v+ ! altitude ( ! sun at ea* place4 ,he f\nd x to be #a_/ej ( ! circumf]5ce & #e1jjj /adia1 s t if #a_/ej ( ! circumf]5ce ( ! e>? is #e1jjj /adia1 ! :ole circumf]5ce mu/ be #ej times #e1jjj1 or #bej1jjj /adia4#e ,illu/ration3 ,,fig4 #f4--,! ,fir/ ,m]idian ,circle4 ,& n[ /ill ano!r in/rum5t is introduc$1 & we beg9 to f9d ! horizon altoge!r disreg>d$ 9 fav\r ( obs]vations made on ! m]idian4 ,! in/rum5t 9 "q 0 probably ! inv5tion ( ,erato/h5es4 ,x consi/$ ( two circles ( ne>ly ! same size cross+ ea* o!r at "r angles1 7,fig4 #f72 "o circle repres5t$ ! equator & ! o!r ! m]idian1 & x 0 employ$ z foll[s3-- ,! circle ,a 0 fix$ p]fectly upright 9 ! m]idian1 s t ! greate/ altitude ( ! sun ea* day c\ld be obs]v$2 ! circle ,b 0 !n plac$ exactly 9 ! plane ( ! e>?'s equator by adju/+ ! l9e jo9+ ,c & ,d to ! "p ( ! heav5s betwe5 ! ,be>s1 ab\t :i* ! />s appe> to revolve4 ,?is done1 ! occurr5ce ( ! equ9ox 0 wait$ =1 at :i* "t ! %ad[ ( ! "p ( ! circle ,e mu/ fall ^u ! "p m>k$ ,f1 s z exactly to cov] x4 ,illu/ration3 ,,fig4 #g4--,! ,fir/ ,in/rum5t ,graduat$ into #cfj 7,we/ ,side74 ,we n[ come to ! "t :5 ! circle began to be divid$ into #cfj divisions or degrees--ab\t ! "t ( ,hipp>*us 7#afj ,b4,c474 ,!re are two in/rum5ts describ$ by ,ptolemy = measur+ ! altitude ( ! sun 9 degrees in/ead ( 9 fractions ( a circle4 ,!y1 l ! gnomon1 7 us$ = det]m9+ ! altitude ( ! sun4 ,! fir/1 ,fig4 #g1 consi/$ ( two circles ( copp]1 "o1 ,c ,d1 l>g] ?an ! o!r1 hav+ ! small] "o1 ,b1 s fitt$ inside x z to turn r\nd :ile ! l>g] rema9$ fix$4 ,! l>g] 0 divid$ into #cfj1 & ! small] "o c>ri$ two po9t]s4 ,?is in/rum5t 0 plac$ p]fectly upright & 9 ! plane ( ! m]idian1 & ) a fix$ po9t1 ,c1 always at ! top by means ( a plumb-l9e hang+ f ,c ov] a m>k1 ,d4 ,on ?is small circle are two squ>e knobs project+ on ! side1 ,e & ,f4 ,:5 ! sun 0 on ! m]idian ! small circle 0 turn$ s z to br+ ! %ad[ ( ! knob ,e ov] ! knob ,f1 & !n ! degree to :i* ! po9t] po9t$ 0 read (f on ! l>g] circle4 ,& ( c\rse1 z ! position ( ! knobs _h to be *ang$ z ! sun mov$ 9 altitude1 ! angle ?r\gh :i* ! sun mov$ 0 measur$1 & ! circle be+ fix$1 ! sun's altitude c\ld always be obta9$4 ,! o!r in/rum5t consi/$ ( a block ( wood or /one1 "o side ( :i* 0 plac$ 9 ! plane ( ! m]idian2 & on ! top corn] ( ?is side 0 fix$ a /ud2 & r\nd x z a c5tre a qu>t] ( a circle 0 describ$1 divid$ into #ij4 ,bel[ ?is /ud 0 ano!r1 & by means ( a plumb-l9e "o /ud c\ld always be br\ght ov] ! o!r2 s t ! in/rum5t c\ld always be plac$ 9 a true position4 ,at midday !n1 :5 ! sun 0 %9+1 ! %ad[ ( ! upp] /ud w\ld fall across ! scale ( degrees1 & at once give ! altitude ( ! sun4 ,ptolemy1 :o us$ ?is in/rum5t1 f\nd t ! arc includ$ betwe5 ! tropics 0 #dg4 ,! result ( all ^! accurate det]m9ations ( ! sol/ices & equ9oxes 0 ! fix+ ( ! l5g? ( ! ye>4 ,we h s f> dealt ) ! me?ods ( obs]vation :i* dep5d ^u ! use ( ! horizon & ( ! m]idian2 we w n[ turn our att5tion to extra-m]idional obs]vations1 or ^? made 9 any "p ( ! sky4 ,be=e we discuss !m1 let u consid] ! pr9ciples on :i* we dep5d = fix+ ! position ( a place on a globe4 ,on a t]re/rial globe !re are l9es drawn f pole to pole1 call$ m]idians ( longitude2 & if a place is on any "o m]idian x is said to be 9 s _m degrees ( longitude1 ea/ or we/ ( a c]ta9 fix$ m]idian1 z !re are degrees int]cept$ betwe5 ?is m]idian & ! "o on :i* ! place is situat$4 ,!re are also circles at "r angles to ! above & p>allel to ! equator2 ^! are circles ( latitude1 & a place is said to h s _m degrees ,n4 or ,s4 latitude z ! circle :i* passes ?r\gh x int]cepts on a m]idian betwe5 itself & ! equator1 s t ! latitude ( a place is its angul> di/ance f ! equator1 & ! longitude is its angul> di/ance ,e4 or ,w4 ( a fix$ m]idian--t ( ,gre5wi* be+ ! "o us$ = ,engli% calculation2 & ea* l>ge c\ntry takes ! m]idian ( its c5tral obs]vatory = its />t+-po9t4 ,! di/ance r\nd ! equator is sometimes express$ 9 h\rs in/ead ( degrees2 = z ! e>? turns r\nd 9 tw5ty-f\r h\rs1 s ! equator c be divid$ into h\rs1 m9utes1 & seconds4 ,s t if a /> be j ov] ! m]idian ( ,gre5wi*1 :i* is #j #j #j1 or #j;h #jm #js longitude at a c]ta9 "t1 9 an h\r aft] x w be ov] a m]idian #ae or "o h\r we/ ( ,gre5wi*1 & s on1 till at ! end ( tw5ty-f\r h\rs x w\ld be ov] ,gre5wi* aga94 ,n[ let u turn to ! cele/ial globe4 ,:at we call latitude & longitude on a t]re/rial globe is call$ decl9ation & "r asc5sion on ! cele/ial globe1 because 9 ! heav5s !re is a latitude & longitude :i* does n correspond to our latitude & longitude on ! e>?4 ,if we imag9e ! l9es ( latitude & longitude on ! e>? to be project$1 say z %ad[s ?r[n on ! heav5s by a light 9 ! c5tre ( ! e>?1 ! l9es ( "r asc5sion 7g5]ally writt5 ,r4,a47 & decl9ation 7writt5 ,dec4 or ,d47 w be p]fectly depict$4 ,b !re is ano!r me?od ( co-ord9at+ ! />s1 9 :i* we h ! words latitude & longitude us$ also1 z we h said1 = ! heav5s2 mean+ ! di/ance ( a /> f ! ecliptic in/ead ( ! equator1 & its di/ance ea/ or we/ measur$ by m]idians at "r angles to ! ecliptic4 ,?is premis$1 we are 9 a position to see ! enorm\s advance r5d]$ possible by ! me?ods ( obs]vation introduc$ by ,hipp>*us & ,ptolemy4 ----- ,footnote #d3 ,?is in/rum5t is also report$ to h be5 us$ by ! ,*aldeans 9 #hej ,b4,c42 ! inv5tion ( x be+ attribut$ to ,anaxim&]4 ,?is philosoph]1 says ,diog5es ,la]tes1 obs]v$ ! revolution ( ! sun1 t is to say1 ! sol/ices1 ) a gnomon2 & probably he measur$ ! obliquity ( ! ecliptic to ! equator1 :i* 8 ma/] _h already discov]$4 ,footnote #e3 #bh1bgi miles4 ,,*apt] ,,iii4 ,,hipp>*us ,,& ,,ptolemy4 ,among ! a/ronom]s ( antiquity !re are two figures :o /& out 9 full relief--,hipp>*us & ,ptolemy4 ,! =m]1 8! fa!r ( a/ronomy10 is especially ! fa!r ( in/rum5tal a/ronomy4 ,z he 0 ! fir/ to place obs]vation on a sure basis1 & left beh9d him ! g]ms ( _m ( our mod]n in/rum5ts & me?ods1 x is desirable to ref] some:at at l5g? to 8 "w & t ( 8 successor1 ,ptolemy4 ,hipp>*us introduc$ extra-m]idional obs]vations4 ,he foll[$ ,meton1 ,anaxim&]1 & o!rs 9 obs]v+ on ! m]idian in/ead ( on ! horizon1 & !n x /ruck him t x 0 n necess>y to keep to ! m]idian1 & he conceiv$ an in/rum5t1 call$ an ,a/rolabe1 fix$ on an axis s t ! axis w\ld po9t to ! pole-/>1 l ! "o repres5t$ 9 ,fig4 #h4 ,?is engrav+ is ( "o ( ,ty*o ,brahe's in/rum5ts1 :i* is simil> to b m elaborate ?an t ( ,hipp>*us no draw+ ( :i* is extant4 ,c1 ,d1 is ! axis ( ! in/rum5t po9t$ to ! pole ( ! heav5s2 ,e1 ,b1 ,c1 ! circle plac$ ,nor? & ,s\? repres5t+ ! m]idian2 ,r1 ,q1 ,n1 ! circle plac$ at "r angles to ! pol> axis1 repres5t+ ! equator1 b 9 ! in/rum5t ( ,hipp>*us x 0 fix$ to ! circle ,e1 ,b1 ,c1 & n movable 9 its own plane z ?is "o is4 ,m1 ,l1 ,k1 is a circle at "r angles to ! equator1 & mov+ r\nd ! poles1 be+ a sort ( movable m]idian4 ,?us1 !n1 if ! altitude ( a /> f ! equator 7or its decl9ation7 0 requir$ to be obs]v$1 ! circle 0 turn$ r\nd on ! axis1 & ! sights1 ,q1 ,m1 mov$ on ! circle till !y1 toge!r ) ! sight ,a1 po9t$ to ! />2 ! numb] ( degrees betwe5 "o ( ! sights & ! equator1 0 !n read (f1 giv+ ! decl9ation requir$4 ,! numb] ( degrees1 or h\rs & m9utes1 ( ,"r ,asc5sion1 f ,k to ,e c\ld be !n read (f along ! circle ,r1 ,q1 ,n1 giv+ ! di/ance ( ! object f ! m]idian4 ,z ! />s h an app>5t motion1 ! diff]5ce 9 "r asc5sion betwe5 two />s only c\ld be obta9$ by obs]v+ !m directly aft] ea* o!r1 & all[+ = ! motion dur+ ! int]val betwe5 ! two obs]vations4 ,illu/ration3 ,,fig4 #h4--;,a/rolabe 7,armill quatori ( ,ty*o ,brahe7 simil> to ! "o contriv$ by ,hipp>*us4 ,9 ?is mann]1 !n1 ,hipp>*us c\ld po9t to any "p ( ! heav5s & obs]ve1 on ei!r side ( ! m]idian1 ! sun1 moon1 planets or any ( ! />s1 & obta9 _! di/ance f ! equatorial plane2 b ano!r fix$ plane 0 requir$2 & ,hipp>*us1 no long] cont5t ) be+ limit$ to measur+ di/ances f ! equator1 ?\ght x might be possible to get ano!r />t+-po9t = di/ances along ! equator4 ,x 0 ! det]m9ation ( ?is plane1 or />t+-po9t f :i* to reckon "r asc5sion1 t 0 "o ( ! difficulties ,hipp>*us _h to enc\nt]4 ,?is po9t he decid$ %\ld be ! place 9 ! heav5s :]e ! sun crosses ! equator at ! spr+ equ9ox4 ,b ! />s c\ld n be se5 :5 ! sun 0 %9+2 h[1 !n1 0 he to fix t po9t s t he c\ld measure f x at night8 ,illu/ration3 ,,fig4 #i4--;,ecliptic ,a/rolabe 7! ,armill ,zodiacales ( ,ty*o ,brahe71 simil> to ! "o us$ by ,hipp>*us4 ,he f\nd x at fir/ a trem5d\s problem1 & at la/ hit ^u ?is happy way ( solv+ x4 ,he reason$ 9 ?is way3 8,z an eclipse ( ! moon is caus$ by ! e>?'s %ad[ be+ ?r[n by ! sun on ! moon1 if ?is happ5 ne> ! equ9ox1 ! sun & moon mu/ !n be v ne> ! equator1 & v ne> ! ecliptic--9 fact1 ne> ! int]section ( ! two fundam5tal planes :i* are suppos$ to cross ea* o!r4 ,if ,i c obs]ve ! di/ance1 measur$ along ! equator1 betwe5 ! moon & a />1 ,i %all h obta9$ ! />'s actual place1 because1 ( c\rse1 if ! moon is exactly opposite ! sun1 ! sun w be #ahj degrees ( "r asc5sion f ! moon1 & ! "r asc5sion ( ! sun be+ kn[n x w give me ! position ( ! />40 ,?is me?od ( obs]vation 0 an extremely good "o = ! "t1 b x c\ld only h be5 us$ dur+ an eclipse ( ! moon1 & :5 ! sun 0 s ne> ! equator t its di/ance f ! equ9octial po9t along ! ecliptic1 z calculat$ by ! "t elaps$ s9ce ! equ9ox1 diff]$ little f ! same di/ance measur$ along ! equator1 or its "r asc5sion1 s t ! "r asc5sion ( ! sun 0 v ne>ly correct4 ,hipp>*us hit ^u a v happy alt]ation ( ! same in/rum5t to enable him to measure latitude & longitude in/ead ( decl9ation & "r asc5sion--9 fact1 to measure along ! ecliptic in/ead ( ! equator4 ,in/ead ( hav+ ! axis ( ! inn] r+s p>allel to ! axis ( ! e>?1 z 9 ,fig4 #i1 he s arrang$ matt]s t ! axis ( ?is sy/em 0 sep>at$ f ! e>?'s axis to ! ext5t ( ! obliquity ( ! ecliptic1 ! circle ,r1 ,q1 ,n1 !re=e in/ead ( be+ 9 ! plane ( ! equator1 0 9 t ( ! ecliptic4 ,!n x 0 pla9 to ,hipp>*us t he w\ld1 in/ead ( be+ limit$ to obs]ve dur+ eclipses ( ! moon1 be able to reckon f ! sun at all times2 because ! sun moves always along ! ecliptic & ! latitude ( ! sun is no?+4 ,we w n[ describe ! details ( ! in/rum5t4 ,!re is fir/ a l>ge circle1 ,e1 ,b1 ,c1 ,fig4 #i 7:i* is tak5 f a draw+ ( ?is k9d ( in/rum5t z con/ruct$ subsequ5tly by ,ty*o ,brahe71 fix$ 9 ! plane ( ! m]idian1 hav+ its poles1 ,d1 ,c1 po9t+ to ! poles ( ! heav5s2 inside ?is !re is ano!r circle1 ,f1 ,i1 ,h1 turn+ on ! pivots ,d1 ,c1 & c>ry+ fix$ to x ! circle1 ,o1 ,p1 arrang$ 9 a plane at "r angles to ! po9ts ,i1 ,k1 :i* are plac$ at a di/ance f ,c & ,d equal to ! obliquity ( ! ecliptic2 s t ,i & ,k repres5t ! poles ( ! ecliptic1 & ! circle1 ,o1 ,p1 ! ecliptic itself4 ,!re is !n ano!r circle1 ,r1 ,m1 turn+ on ! pivots ,i & ,k1 repres5t+ a m]idian ( latitude1 & along :i* x is measur$4 ,!n1 z ! sun is on t "p ( ! ecliptic ne>e/ ! nor? pole1 9 summ]1 its position is repres5t$ by ! po9t ,f on ! ecliptic1 & by ,n at ! w9t] sol/ice2 s1 kn[+ ! "t ( ! ye>1 ! sight ,q c be plac$ ! same numb] ( degrees f ,f z ! sun is f ! sol/ice1 or 9 a simil> position on ! circle ,o ,p z ! sun occupies on ! ecliptic4 ,! circle c !n be turn$ r\nd ! axis ,c1 ,d1 till ! sight ,q1 & ! sight opposite to x1 ,q1 are 9 l9e ) ! sun4 ,! circle1 ,o1 ,r1 w !n be 9 ! plane ( ! ecliptic1 or ( ! pa? ( ! e>? r\nd ! sun4 ,! circle1 ,r1 ,m1 is !n turn$ on its axis1 ,i1 ,k1 & ! sights1 ,r1 ,r1 mov$ until !y po9t to ! moon4 ,! di/ance ,q1 ,l1 measur$ along ,o1 ,p1 w !n be ! diff]5ce 9 longitude ( ! moon & sun1 & its latitude1 ,l1 ,r1 measur$ along ! circle ,r1 ,m4 ,b :y %\ld he use ! moon8 ,8 object 0 to det]m9e ! longitude ( ! />s1 b 8 only me?od 0 to ref] to ! motion ( ! sun1 :i* c\ld be laid d[n 9 tables1 s t its longitude or di/ance f ! v]nal equ9ox 0 always kn[n4 ,b we d n see ! />s & ! sun at ! same "t2 !re=e 9 ! day "t1 :ile ! moon 0 above ! horizon1 he det]m9$ ! diff]5ce ( longitude betwe5 ! sun & ! moon1 ! longitude ( ! sun or its di/ance f ! v]nal equ9ox be+ kn[n by ! "t ( ! ye>2 & aft] ! sun _h set he det]m9$ ! diff]5ce ( longitude betwe5 ! moon & any p>ticul> />2 & s he got a fair repres5tation ( ! longitude ( ! />s1 & succe$$ 9 tabulat+ ! position ( #a1jbb ( !m4 ,x is to ! use ( ?is in/rum5t t we owe ! discov]y ( ! precession ( ! equ9oxes4 ,illu/ration3 ,,fig4 #aj4--;,diagram ,illu/rat+ ! ,precession ( ! ,equ9oxes4 ,aft] ,hipp>*us _h fix$ ! position ( a numb] ( />s1 he f\nd t on comp>+ ! place among/ !m ( ! sun at ! equ9oxes 9 8 day ) its place 9 ! "t ( ,ari/illus t ! positions diff]$--t ! sun got to ! equ9ox1 or po9t :]e x cross$ ! equator1 a %ort "t be=e x got to ! place among/ ! />s :]e x cross$ 9 ! "t ( ,ari/illus2 9 fact1 he f\nd t ! equ9octial po9ts retrograd$ along ! equator1 & ,ptolemy 7,b4,c4 #ace7 appe>s to h e/abli%$ ! fact t ! :ole heav5s _h a sl[ motion ( "o degree 9 a c5tury :i* acc\nt$ = ! motion ( ! equ9oxes4 ,illu/ration3 ,,fig4 #aa4--,revolution ( ! ,pole ( ! ,equator r\nd ! ,pole ( ! ,ecliptic caus$ by ! ,precession ( ! ,equ9oxes4 ,let u see :at we h le>n$ f ! obs]vation ( ?is motion1 = motion !re is1 & ! anci5ts mu/ be look$ on ) rev]5ce = _! skill 9 det]m9+ x ) _! comp>atively rude in/rum5ts4 ,9 ,fig4 #aj1 ,a repres5ts ! e>? at ! v]nal equ9ox1 & at ?is "t ! sun appe>s ne> a c]ta9 />1 ,s1 :i* 0 fix$ by ,ari/illus2 b 9 ! "t ( ,hipp>*us ! equ9ox happ5$ :5 ! sun 0 ne> a />1 ,s1 & be=e x got to ,s4 ,n[ we "k t ! sun has no motion r\nd ! e>?1 & t ! equ9ox simply dep5ds on ! position ( ! e>?'s equator 9 ref]5ce to ! ecliptic2 s t 9 ord] to produce ! equ9ox :5 ! e>? is at ,e & be=e x get to ,a1 its usual place1 all we h to d is to turn ! pole ( ! e>? ?r\gh a small arc ( ! dott$ circle1 & s alt] its position to t %[n at ,f1 :5 its equator & poles w h ! same position z reg>ds ! sun z !y h at ,a1 s ! equ9ox w happ5 :5 ! e>? is at ,e1 & be=e x rea*es ,a4 ,?is may be practically repres5t$ by tak+ an orange & putt+ a knitt+-ne$le ?r\gh x1 & draw+ a l9e repres5t+ ! equator r\nd x1 & half imm]s+ x 9 a tub ( wat]1 ! surface ( :i* repres5ts ! ecliptic4 ,we are !n able to exam9e ^! motions by mov+ ! orange r\nd ! tub to repres5t ! e>?'s annual motion1 & at ! same "t mak+ ! orange sl[ly :obble l a sp9n+-top j be=e x falls1 by mov+ ! top ( ! knitt+-ne$le ?r\gh a small arc ( a circle 9 ! same direction z ! h&s ( a clock at e revolution ( ! orange r\nd ! c5tre ( ! tub4 ,! po9ts :]e ! equator is cut by ! surface ( ! wat] 7or ecliptic7 w !n *ange1 z ! orange :obbles1 & ! l9e jo9+ !m1 w rotate1 & z ! equ9ox happ5s :5 ?is l9e passes ?r\gh ! sun1 x w be se5 t ?is w take place e>li] at ea* revolution ( ! orange r\nd ! tub4 ,! equ9ox w !re=e appe> to happ5 e>li] ea* ye>1 s t ! tropical ye>1 or ! "t f equ9ox to equ9ox1 is a little %ort] ?an ! sid]eal ye>1 or ! "t t ! e>? takes to travel f a c]ta9 place 9 its orbit to ! same aga92 = if ! e>? />t f an equ9octial po9t1 ! equ9ox w happ5 be=e x gets to ! same place :]e ! equ9octial po9t 0 at />t+4 ,?is is call$ ! precession ( ! equ9oxes4 ,illu/ration3 ,,fig4 #ab4--,! ,v]nal ,equ9ox among ! ,con/ellations1 ,b4,c4 #bagj4 ,illu/ration3 ,,fig4 #ac4--,%[+ h[ ! ,v]nal ,equ9ox has n[ pass$ f ,taurus & ,aries4 ,?is discov]y mu/ be reg>d$ z ! greate/ triumph obta9$ by ! e>ly />gaz]s1 & !re is mu* evid5ce to %[ t :5 ! zodiac 0 fir/ m>k$ out among ! c5tral zone ( />s1 ! ,bull & n ! ,ram 0 ! fir/ ( ! tra94 ,ev5 ! ,ram1 ow+ to precession1 is no long] ! lead]1 = ! sign ,aries is n[ 9 ! con/ellation ,pisces4 ,! two accompany+ draw+s by ,pr(essor ,piazzi ,smy? ( ! position ( ! v]nal equ9ox among ! />s 9 ! ye>s #bagj ,b4,c4 & #ahhc ,a4,d4 w %[ h[ precession has br\ght ab\t cele/ial *anges :i* h n be5 unaccompani$ by *anges ( religi\s ideas & obs]vances 9 orig9 connect$ ) ! />s4 ,illu/ration3 ,,fig4 #ad4--;,in/rum5t = ,measur+ ,altitudes4 ,we n[ come to ,ptolemy4 ,!re 0 ano!r in/rum5t us$ by ,ptolemy1 & describ$ by him1 :i* we may m5tion "h2 x 0 call$ ! ,p>allactic ,rules1 s nam$ p]haps because t anci5t a/ronom] us$ x fir/ = ! obs]vation ( ! p>allax ( ! moon4 ,x consi/s ( ?ree rods1 ,d ,e1 ,d ,f1 ,e ,f1 ,fig4 #ad1 two ( :i* =m$ equal sides ( an isosceles triangle2 & ! ?ird1 :i* _h divisions on x1 made ! "o at ! base1 or 0 ! *ord ( ! angle at ! summit4 ,"o ( ! equal sides1 ,d ,f1 0 furni%$ ) po9t]s1 ov] :i* a p]son obs]v$ ! />1 :il/ ! o!r1 ,d ,e1 0 plac$ v]tically1 s t !y read (f ! divisions on ,e ,f1 & !n1 by means ( a table ( *ords1 ! angle 0 f\nd2 ?is angle 0 ! di/ance ( ! /> f ! z5i?4 ,ptolemy1 wi%+ to obs]ve ) great accuracy ! position ( ! moon1 made himself an in/rum5t ( ?is k9d ( a consid]able size2 = ! equal rul]s 7 f\r cubits long1 s t its divisions might be m obvi\s4 ,he rectifi$ its position by means ( a plumb-l9e4 ,purba*1 ,regiomontanus1 & ,wal!r1 a/ronom]s ( ! fifte5? c5tury1 employ$ ?is mann] ( obs]v+1 :i*1 consid]+ ! y\? ( a/ronomy1 0 by no means to be despis$4 ,?is in/rum5t1 con/ruct$ ) great c>e1 w\ld h suffici5tly be5 useful z f> z conc]ns c]ta9 measurem5ts & w\ld h furni%$ results suffici5tly exact2 b ! "p ( anci5t a/ronomy t fail$ 0 ! way ( measur+ "t ) any precision4 ,!re 7 a/ronom]s :o propos$ clepsydras = ?is purpose2 b ,ptolemy reject$ !m z v likely to introduce errors2 & inde$ ?is me?od is subject to mu* inconv5i5ce & to irregul>ities difficult to prev5t4 ,h[ev]1 z ! measurem5t ( "t is ! s\l ( a/ronomy1 ,ptolemy _h rec\rse to ano!r exp$i5t :i* 0 v +5i\s4 ,x consi/$ 9 obs]v+ ! height ( ! sun if x 7 day1 or ( a fix$ /> if x 7 night1 at ! in/ant ( a ph5om5on ( :i* he wi%$ to "k ! "t ( occurr5ce1 = ! place ( ! sun or /> be+ kn[n to "s m9utes ( decl9ation & "r asc5sion z also 0 ! latitude ( ! place1 he 0 able to calculate ! h\r2 ?us :5 !y obs]v$1 = example1 an eclipse ( ! moon1 x 0 only necess>y to take c>e to get ! height ( "s rem>kable /> at ea* phase ( ! eclipse1 say at ! comm5cem5t & at ! end1 9 ord] to be able to conclude ! true "t at :i* x took place4 ,?is 0 ! me?od adopt$ by a/ronom]s until ! introduction ( ! p5dulum4 ,,*apt] ,,iv4 ,,ty*o ,,brahe4 ,leav+ beh9d u ! results ( ! rese>*es ( ,ptolemy1 :o succe$$ ,hipp>*us & ^: me?ods h be5 describ$1 & pass+ ov] ! a/ronomy ( ! ,arabs & ,p]sians z be+ little 9 advance ( ,hipp>*us & ,ptolemy1 we come d[n to ! sixte5? c5tury ( our era4 ,"h we f9d ourselves 9 pres5ce ( ! improvem5ts 9 in/rum5ts effect$ by a man ^: "n is conspicu\s--,ty*o ,brahe--a ,dani% nobleman :o1 9 ! ye> #aegf1 e/abli%$ a magnific5t obs]vatory at ,hu51 :i* may be look$ ^u z ! next build+ ( importance aft] t great edifice at ,alex&ria :i* has already be5 ref]r$ to4 ,:at ,hipp>*us 0 to ! a/ronomy ( ! ,anci5ts su* 0 ,ty*o to ! a/ronomy ( ! ,middle ,ages4 ,z su* 8 life m]its a brief notice be=e we proce$ to 8 "w4 ,he 0 born at ,knud/horp1 ne> ,hels+borg1 9 ,sw$51 9 #aedf1 & w5t to ! ,univ]sity ( ,cop5hag5 to prep>e to /udy law2 :ile !re he 0 s /ruck ) ! pr$iction ( an eclipse ( ! sun by ! a/rological almanacks t he gave all 8 sp>e "t to ! /udy ( a/ronomy4 ,9 #aefe 8 uncle di$ & ,ty*o ,brahe fell into possession ( "o ( 8 uncle's e/ates2 & z a/ronomy1 or a/rology z x 0 !n call$1 0 ?\ght degrad+ to a man 9 8 position by 8 fri5ds1 :o took (f5ce at 8 pursuits & made !mselves v objectionable1 he left = a %ort /ay at ,witt5b]g1 !n he w5t to ,ro/ock & aft]w>ds to ,augsburg1 :]e he con/ruct$ 8 l>ge quadrant4 ,he return$ to 8 old c\ntry 9 #aega2 :ile !re1 ,fr$]ick ,,ii41 ,k+ ( ,d5m>k1 reque/$ him to deliv] a c\rse ( lectures on a/ronomy & a/rology & became 8 mo/ lib]al patron4 ,! ,k+ grant$ to ,ty*o ,brahe = life ! isl& ( ,hu51 ly+ betwe5 ,d5m>k & ,sw$51 & built !re a magnific5t obs]vatory & ap>tm5ts = ,ty*o1 8 assi/ants & s]vants4 ,! ma9 build+ 0 sixty feet squ>e1 ) obs]v+ t[]s on ! nor? & s\?1 & a libr>y & museum4 ,ty*o call$ ?is ,uranib]g--! city ( ! heav5s2 & he aft]w>ds built a small] obs]vatory ne> call$ by him ,/]nb]g--city ( ! />s1 ! =m] be+ insuffici5tly l>ge to conta9 all 8 in/rum5ts4 ,! foll[+ is a li/ ( ^! in/rum5ts z giv5 9 ,sir ,david ,brew/]'s excell5t memoir ( ,brahe1 9 ,m>tyrs ( ,sci5ce3-- ,9 ! ,s\? & great] ,obs]vatory4 #a4 ,a semicircle ( solid iron1 cov]$ ) brass1 f\r cubits radius4 #b4 ,a sextant ( ! same mat]ials & size4 #c4 ,a quadrant ( "o & a half cubits radius1 & an azimu? circle ( ?ree cubits4 #d4 ,ptolemy's p>allactic rules1 cov]$ ) brass1 f\r cubits 9 ! side4 #e4 ,ano!r sextant4 #f4 ,ano!r quadrant1 l ,no4 #c4 ,illu/ration3 ,,fig4 #ae4--,portrait ( ,ty*o ,brahe 7f orig9al pa9t+ 9 ! possession ( ,dr4 ,crompton1 ( ,man*e/]74 #g4 ,zodiacal armill>ies ( melt$ brass1 & turn$ out ( ! solid1 ( ?ree cubits 9 diamet]4 ,ne> ?is obs]vatory !re 0 a l>ge clock ) "o :eel two cubits 9 diamet]1 & two small] ones :i*1 l x1 indicat$ h\rs1 m9utes1 & seconds4 ,9 ! ,s\? & less] ,obs]vatory4 #h4 ,an armill>y sph]e ( brass1 ) a /eel m]idian1 ^: diamet] 0 ab\t f\r cubits4 ,9 ! ,nor? ,obs]vatory4 #i4 ,brass p>allactic rules1 :i* revolv$ 9 azimu? above a brass horizon1 twelve feet 9 diamet]4 #aj4 ,a half sextant1 ( f\r cubits radius4 #aa4 ,a /eel sextant4 #ab4 ,ano!r half sextant ) /eel limb1 f\r cubits radius4 #ac4 ,! p>allactic rules ( ,cop]nicus4 #ad4 ,equatorial armill>ies4 #ae4 ,a quadrant ( a solid plate ( brass1 five cubits 9 radius1 %[+ e t5 seconds4 #af4 ,9 ! museum 0 ! l>ge globe made at ,augsburg4 ,9 ! ,/]nb]g ,obs]vatory4 #ag4 ,9 ! c5tral "p1 a l>ge semicircle1 ) a brass limb1 & ?ree clocks1 %[+ h\rs1 m9utes1 & seconds4 #ah4 ,equatorial armill>ies ( sev5 cubits1 ) semi-armill>ies ( n9e cubits4 #ai4 ,a sextant ( f\r cubits radius4 #bj4 ,a geometrical squ>e ( iron1 ) an int]cept$ quadrant ( five cubits1 & divid$ into fifte5 seconds4 #ba4 ,a quadrant ( f\r cubits radius1 %[+ t5 seconds1 ) an azimu? circle4 #bb4 ,zodiacal armill>ies ( brass1 ) /eel m]idians1 ?ree cubits 9 diamet]4 #bc4 ,a sextant ( brass1 kept toge!r by screws1 & capable ( be+ tak5 to pieces = travell+ )4 ,its radius 0 f\r cubits4 #bd4 ,a movable armill>y sph]e1 ?ree cubits 9 diamet]4 #be4 ,a quadrant ( solid brass1 "o cubit radius1 & divid$ into m9utes by ,nonian circles4 #bf4 ,an a/ronomical radius ( solid brass1 ?ree cubits long4 #bg4 ,an a/ronomical r+ ( brass1 a cubit 9 diamet]4 #bh4 ,a small brass a/rolabe4 ,ty*o ,brahe c>ri$ on 8 "w at ,uranib]g = tw5ty-"o ye>s1 & appe>s to h be5 visit$ by _m ( ! pr9ces ( ! p]iod & by /ud5ts anxi\s to le>n f s great a man4 ,9 ,fr$]ick's treatm5t ( ,ty*o ,brahe we h an e>ly & munific5t &1 9 its results1 mo/ successful in/ance ( ! end[m5t ( rese>*4 ,on ! dea? ( ,fr$]ick ,,ii41 9 #aehh1 ,*ri/ian ,,iv4 came to ! ?rone4 ,! successor c>$ little = a/ronomy1 & 8 c\rti]s1 :o 7 jeal\s ( ,ty*o's position1 s act$ ^u him t ! p5sion1 e/ate & canonry ) :i* ,ty*o _h be5 end[$ 7 tak5 away4 ,unable to put up ) ^! insults & loss ( 8 money1 he left = ,w&esburg 9 #aeig1 :]e he 0 ent]ta9$ by ,c\nt ,h5ry ,rantzau4 ,x 0 n[ t he wrote & publi%$ ! ,a/ronomi in/aurat ,me*anica1 a copy ( :i*1 toge!r ) 8 catalogue ( #ajjj />s1 0 s5t to ! ,emp]or ,rudolph ,,ii41 :o invit$ him to g to ,prague4 ,?is he accept$1 & he & 8 family w5t to ! ca/le ( ,b5a* 9 #aeii1 & a p5sion ( #cjjj cr[ns 0 giv5 to him4 ,t5 ye>s aft]w>ds he remov$ ) 8 in/rum5ts into ,prague to a h\se pur*as$ & pres5t$ to him by ! ,emp]or2 "h he di$ 9 ! same ye>4 ,! wond]ful assi/ance :i* ,ty*o ,brahe 0 able to br+ to a/ronomy %[s t !n1 z n[1 any consid]able advance 9 physical inve/igation 0 m or less a matt] ( money1 & :e!r t money be f\nd by individuals or corporations1 n[ or !n1 we _c expect any consid]able advance )\t su* a necess>y adjunct4 ,illu/ration3 ,,fig4 #af4--,ty*o ,brahe's ,obs]vatory on ! ,isl& ( ,hu54 ,! pr9cipal in/rum5ts us$ at fir/ by ,ty*o ,brahe resembl$ ! ,greek ones1 except t !y 7 mu* l>g]4 ,hipp>*us 0 enabl$ to e/abli% ! position ( a heav5ly body )9 some?+ less ?an "o degree ( space--"s say )9 t5 m9utes2 b !re 0 an imm5se improvem5t made 9 ?is direction 9 ! in/rum5ts us$ by ,ty*o4 ,"o ( ! in/rum5ts :i* he us$ 0 9 e way simil> to ! equatorial a/rolabe design$1 by ,hipp>*us1 & 0 call$ by ,ty*o1 ! #8armill equatori' 7,fig4 #h74 ,) t in/rum5t 9 connection ) o!rs ,ty*o 0 enabl$ to make an imm5se advance ^u ! "w done by ,hipp>*us4 ,ty*o1 l ,hipp>*us1 hav+ no clock1 9 ! mod]n s5se1 0 n able to det]m9e ! diff]5ce ( "t betwe5 ! transit ( ! sun or a p>ticul> /> ov] ! m]idian1 s t he 0 compell$ to ref] ev]y?+ to ! sun at ! in/ant ( obs]vation1 & he did t by means ( ! moon4 ,hipp>*us1 z we h se51 det]m9$ ! diff]5ce ( longitude1 or "r asc5sion1 betwe5 ! sun & ! moon & betwe5 ! moon & ! />s1 9 ! mann] already describ$1 & s us$ ! moon z a means ( det]m9+ diff]5ces betwe5 ! longitude or "r asc5sion ( ! sun & ! />s4 ,n[ ,ty*o1 us+ an in/rum5t simil> to t ( ,hipp>*us1 saw t he w\ld make an improvem5t if in/ead ( us+ ! ,moon he us$ ,v5us2 = ! measure ( ! surface ( ! moon 0 consid]able1 & c\ld n be easily reckon$1 & its app>5t position 9 ! heav5s 0 dep5d5t on ! position ( a p]son on ! e>?1--because x is s ne> ! e>? t x has a s5sible p>allax1 t is1 a p]son at ! equator ( ! e>? might see ! moon 9 ! direction ( a c]ta9 />2 b1 on go+ to ! pole1 ! moon w\ld appe> bel[ ! l9e ( ! />4 ,if "o 7 look+ at a kite 9 ! air to ! s\? & !n walk$ t[>ds ! s\?1 ! kite w\ld gradually get ov] head1 & on proce$+ fur!r x w\ld get nor?4 ,to p]sons at diff]5t /ations ! kite w\ld appe> 9 diff]5t positions1 & ! ne>] ! kite 0 to ! obs]v] ! less di/ance he w\ld h to g to make x *ange its place4 ,s also ) ! moon2 x is s ne> to u t a *ange ( place on ! e>? makes a consid]able diff]5ce 9 ! direction 9 :i* x is se54 ,in/ead1 !re=e1 ( us+ ! ,moon1 ,ty*o us$ ,v5us1 & s mapp$ #a1ejj />s aft] det]m9+ _! absolute "r asc5sions1 9 ?is mann] )\t ! use ( clocks4 ,fig4 #h %[s ! in/rum5t call$ ! 8armill equatori10 :i* he con/ruct$1 & :i* 0 bas$ ^u ! pr9ciple ( t :i* ,hipp>*us _h us$4 ,"h ! axis ( motion1 ,c1 ,d1 ( ^! circles is s arrang$ t x is absolutely p>allel to ! axis ( ! e>?2 b in/ead ( ! circle ,r1 ,q1 ,n1 repres5t+ ! equator1 be+ fix$1 x revolv$ 9 its own plane :ile held by ! circle ,g1 ,h1 ,i1 mak+ its use probably m easy1 b leav+ ! pr9ciples unalt]$4 ,ty*o ,brahe also us$ ano!r simil> in/rum5t ( mu* l>g] size = ! same purposes z ! "o we h j consid]$4 ,x consi/$ ( a l>ge circle1 :i* 0 sev5 cubits 9 diamet]1 correspond+ to ! circle ,k1 ,l1 ,m1 ,fig4 #h2 & c>ry+ ! sights 9 ! same mann]1 x 0 plac$ 9 a circul> pit 9 ! gr\nd1 ) its diamet] po9t+ t[>ds ! pole4 ,?is 0 us$ = measur+ decl9ations4 ,! circle ,r1 ,q1 ,n1 ,fig4 #i1 0 repres5t$ by a fix$ circle c>ri$ on pill>s surr\nd+ ! pit1 & along :i* ! "r asc5sion ( ! /> 0 measur$4 ,?is in/rum5t1 !re=e1 0 m simple ?an ! small] "o1 & probably mu* m accurate4 ,ty*o 0 n "o ( ^? :o 0 aw>e ( ! true sy/em ( ! univ]se2 he ?\ght ! e>? fix$1 z ,ptolemy & o!rs did2 b :e!r we suppose ! e>? to be movable 9 ! middle ( ! vault ( />s or /ation>y1 9 ei!r case t position is absolutely immat]ial 9 asc]ta9+ ! "r asc5sion ( />s4 ,if "o takes ! t]re/rial globe1 & looks ^u ! m]idians1 x is at once cle> t ! di/ance f m]idian to m]idian rema9s unalt]$1 :e!r ! globe is /ill or turn+ r\nd3 s ! />s ma9ta9 _! relative positions to ea* o!r1 :e!r we consid] ! e>? 9 motion or ! sph]e 9 :i* ! />s are plac$ to revolve r\nd x4 ,illu/ration3 ,,fig4 #ag4--,ty*o ,brahe's ,sy/em4 ,! introduction ( clocks gave ,ty*o ! inv5tion ( ! next in/rum5t1 :i* 0 ! transit circle4 ,at ?is "t ! p5dulum _h n be5 inv5t$2 b x /ruck him & o!rs t !re 0 no necessity = hav+ two or m circles rotat+ ab\t an axis p>allel to ! e>?'s axis1 z 9 ! a/rolabes or armill1 b only to h "o circle 9 ! plane ( ! m]idian ( ! place4 ,s t1 by ! diurnal movem5t ( ! e>? r\nd its own axis1 all ! />s 9 ! heav5s w\ld gradually & s]iatim be br\ght to be visible along ! arc ( ! circle1 s he arrang$ matt]s 9 ! foll[+ way4 ,! />s 7 obs]v$ ?r\gh a hole 9 a wall & ?r\gh an eyehole1 slid+ on a fix$ arc4 ,! numb] ( degrees m>k$ at ! eyehole on ! arc at once gave ! altitude ( ! heav5ly bodies z se5 ?r\gh t hole4 ,if a /> 0 v high1 x w\ld be necess>y = an obs]v] to place 8 eye l[ d[n to be able to see x4 ,if x 7 ne> ! horizon1 he w\ld h to travel up to ! top ( ?is circle to det]m9e its altitude1 & hav+ done t1 & kn[+ ! latitude ( ! place ( obs]vation1 ! obs]v] w be able to det]m9e ! position ( ! /> ) ref]5ce to ! cele/ial equator4 ,! actual mom5t at :i* ! /> 0 se5 0 not$ by ! clock1 & ! "t t ! sun _h pass$ ! hole be+ also previ\sly not$1 ! l5g? ( "t betwe5 ! transits 0 kn[n2 & z ! />s appe> to transit or pass ! m]idian e tw5ty-f\r h\rs1 x 0 at once kn[n :at "p ( ! heav5s 0 int]cept$ betwe5 ! sun & ! /> 9 degrees1 or1 z is usually ! case1 ! "r asc5sion ( ! /> 0 left express$ 9 h\rs & m9utes in/ead ( degrees2 ?us he _h a means ( det]m9+ ! two co-ord9ates ( any cele/ial body4 ,! places ( ! comet ( #afgg1 :i* ,ty*o discov]$1 & ( _m />s1 7 det]m9$ ) absolute c]ta9ty2 b a/ronom]s began to be ambiti\s4 ,x 0 necess>y 9 us+ ?is in/rum5t to wait till a cele/ial body got to ! m]idian4 ,if x 0 miss$1 !n !y _h to wait till ! next day2 & fur!r1 !y _h no opportunity :atev] ( obs]v+ bodies :i* set 9 ! ev5+4 ,illu/ration3 ,,fig4 #ah4--,! ,quadrans ,maximus reproduc$ f ,ty*o's plate4 ,see+1 !re=e1 t clocks 7 improv+1 x 0 sugge/$ by "o ( ,ty*o's compe]s1 ! ,l&grave ( ,hesse-,cassel1 t by an in/rum5t arrang$ some?+ l ,fig4 #ah1 x w\ld be possible to det]m9e ! exact position ( any body 9 ! heav5s :5 exam9$ out ( ! m]idian1 & s !y got aga9 to extra-m]idional obs]vations4 ,! in/rum5t us$ by ,ty*o ,brahe = ! purpose1 call$ ! ,quadrans ,maximus1 is repres5t$ 9 ,fig4 #ah4 ,9 ?is !re is ! quadrant ,b1 ,d1 "o po9t] be+ plac$1 z %[n at ! bottom1 ne> ,h1 & ! o!r at ! top1 ,c4 ,^! po9t]s or sights 7 direct$ at ! /> by mov+ ! arm ,c1 ,h1 on ! pivot ,a1 & turn+ ! :ole arm & divid$ arc r\nd on ! axis ,n1 ,r4 ,! altitude ( ! /> is !n read (f on ! quadrant ,b1 ,d1 & ! azimu?1 or numb] ( degrees ea/ or we/ ( ! nor? & s\? l9e1 is !n read (f on ! circle ,q1 ,r1 ,s4 ,! screws ,y1 ,y1 s]v$ to elevate ! horizontal circle1 & level x exactly ) ! horizon1 & ! plummets ,w & ,v1 hang+ f ,g1 7 to %[ :5 ! circle 0 level or n2 = ! "p ,a1 ,g1 be+ at "r angles to ! circle %\ld be upright :5 ! circle is level1 s t if ,a1 ,g1 is upright 9 all positions :5 mov$ r\nd ! circle 9 azimu?1 ! circle is horizontal4 ,"h1 !n1 is an in/rum5t v diff]5t 9 pr9ciple f :at we _h be=e4 ,9 ?is case ! heav5s are view$ f ! mo/ g5]al /&po9t we c obta9--! horizon2 b obs]vations su* z ^! ref] to ! position ( ! place ( obs]vation absolutely1 )\t any ref]5ce to ! position ( ! body ) respect to ! equator or ! ecliptic2 b kn[+ ! latitude ( ! place ( obs]vation & ! "t1 x 0 possible = a ma!matical a/ronom] to r$uce ! co-ord9ates to "r asc5sion & decl9ation1 & s actually to look at ! position ( ^! bodies ) ref]5ce to ! cele/ial sph]e4 ,ty*o also _h v>i\s o!r in/rum5ts ( ! same k9d1 diff]+ only 9 ! position ( ! quadrant ,d1 ,b1 & ( ! circle on :i* ! azimu? 0 measur$4 ,^! in/rum5ts are ! same 9 pr9ciple z our mod]n alt-azimu?1 :i* w be describ$ h]eaft]1 "o =m hav+ a telescope & ! o!r be+ )\t x4 ,illu/ration3 ,,fig4 #ai4--,ty*o's ,sextant4 ,fig4 #ai is yet ano!r v important in/rum5t inv5t$ by ,ty*o ,brahe2 x is ! prototype ( our mod]n mu* us$ sextant4 ,x 0 us$ by ,ty*o ,brahe = det]m9+ ! di/ance f "o body to ano!r 9 a direct l9e2 a /> or ! moon1 say1 0 obs]v$ by ! po9t]s ,c1 ,a1 :ile ano!r 0 obs]v$ by ! po9t]s ,n1 ,a1 by ano!r obs]v]4 ,! numb] ( degrees !n betwe5 ,n & ,c gave ! angul> di/ance ( ! two bodies obs]v$4 ,?is in/rum5t 0 m\nt$ at ,e1 s t x c\ld be turn$ into any position4 ,n only !n _h ?is in/rum5t its repres5tative 9 our pres5t sextant1 b x 0 us$ 9 ! same way1 n requir+ to be fix$ 9 any "o position4 ,we also f9d repres5t$ 9 ,ty*o ,brahe's book ano!r =m ( ! same in/rum5t1 ! sight ,a be+ next ! obs]v]1 in/ead ( away f him1 s t he c\ld obs]ve ! two />s ?r\gh ! sights ,n & ,c )\t mov+ ! eye4 ,9 ?is =m only "o obs]v] 0 requir$ in/ead ( two z 9 ! la/4 ,!re 0 also ano!r in/rum5t1 ,fig4 #f1 us$ by ?is great a/ronom]1 v simil> to ,ptolemy's p>allactic rules1 us$ = measur+ z5i? di/ances1 or ! di/ances ( />s f ! "p exactly ov]head4 ,! /> or moon 0 obs]v$ by ! sights ,h1 ,i1 & ! angle f ! upright /&>d ,d1 ,k1 giv5 by divisions on ! rod ,e1 ,f1 ,d1 ,e be+ plac$ exactly upright by a plummet1 & be+ also able to turn on h+es at ,b & ,c1 any "p ( ! sky c\ld be rea*$4 ,!re is "o m ( 8 in/rum5ts t ne$s notice--he _h s _m ( all k9ds t space w n all[ ref]5ce to m ?an a v few4 ,?is "o 0 = measur+ ! altitudes ( ! />s z !y pass$ ! m]idian2 x is a m conv5i5t =m ( ! mural quadrant1 & in/ead ( a hole 9 ! wall1 !re are sights on a movable arm1 work+ ov] a divid$ quadrant fix$ 9 ! plane ( ! m]idian1 j l ! quadrant outside ! horizontal circle1 s ! obs]v] _h no reason to move up or d[n accord+ z ! /> 0 high or l[4 ,"h !n ends ! pre-telescopic age4 ,ty*o 0 "o ( ! v la/ ( ! di/+ui%$ a/ronom]s :o us$ in/rum5ts )\t ! telescope4 ,we began ) ! horizon1 & we h n[ end$ ) ! m]idian4 ,we also end ) a p[] ( det]m9+ ! position ( a heav5ly body to t5 seconds ( space1 ! in/rum5t ( ! ,greeks read+ to #aj & ^? ( ,ty*o to #aj4 ,we began ) ! immovable e>? fix$ 9 ! mid/ ( ! vault ( ! sky1 & on ?is assumption ,ty*o ,brahe made all 8 obs]vations1 :i* end$ 9 enabl+ ,kepl] to give u ! true sy/em ( ! _w1 :i* 0 ! requisite basis = ! cr[n+ triumph ( ,newton4 ,,book ,,ii4 ,,! ,,telescope4 ,,*apt] ,v4 ,,! ,,refraction ,,( ,,light4 ,x is difficult to give ! cr$it ( ! inv5tion ( ! telescope to any "o p>ticul> p]son1 =1 z 9 ! case ( mo/ in/rum5ts1 its hi/ory has be5 a hi/ory ( improvem5ts2 & :e!r we %\ld give ! laurel to ,jans51 ,bapti/a ,porta1 ,galileo or to o!rs ^: names are unkn[n1 is an invidi\s task to decide2 we w !re=e n ent] 9 any way into ! "q1 int]e/+ ?\gh x be1 z to :o 0 ! inv5tor ( ! 8optick tube10 z ! telescope 0 call$ by its fir/ us]s4 ,! telescope is n a ?+ 9 ! ord9>y s5se--x is a comb9ation ( ?+s1 ! ?+s be+ c]ta9 k9ds ( l5ses1 concave & convex1 kn[n & us$ z spectacles long be=e !y 7 comb9$ to =m ! telescope4 ,! fir/ telescopes dep5d$ on ! refraction ( light2 o!rs1 to :i* att5tion w be call$ 9 a future *apt]1 dep5d$ on reflection4 ,illu/ration3 ,,fig4 #bj4--,view & ,section ( a ,prism4 ,9 ord] to und]/& ! action ( a l5s1 x is necess>y to und]/& ! action ( a prism4 ,by ! aid ( ,fig4 #bj ! action ( ! l5ses ( :i* telescopes are con/ruct$ w be und]/ood4 ,a prism is a piece ( glass1 or o!r transp>5t sub/ance1 ! sides ( :i* are s incl9$ to ea* o!r t its section is a triangle1 & its action on light pass+ ?r\gh x is to *ange ! direction ( ! c\rse ( ! beam4 ,if we exam9e ,fig4 #ba we %all und]/& ! action cle>ly4 ,x is a kn[n law1 t :5 a beam ( light falls obliquely on ! surface ( a m$ium m d5se ?an t ?r\gh :i* x has be5 pass+1 its direction is *ang$ to a new "o1 ne>] ! l9e drawn at "r angles to t surface1 rail$ ! normal4 ,= in/ance1 ! ray ,s1 ,i1 fall+ on ! prism at ,i1 is b5t into ! c\rse ,i1 ,e1 :i* is 9 a direction ne>] to t ( ,n1 ,i1 produc$ inside ! prism4 ,on em]g+1 ! rev]se takes place1 & ! ray is b5t away f ! normal ,e1 ,n1 & takes ! c\rse ,e1 ,r4 ,9 ! second diagram1 ,fig4 #ba1 ! ray ,s1 ,i1 call$ ! incid5t ray1 co9cides ) ! normal to ! surface1 s x is n refract$ until x rea*es ! second surface1 :5 x has its pa? *ang$ to ,e1 ,r1 in/ead ( tak+ its direct c\rse %[n by ! dott$ l9e4 ,?is b5d+ ( ! ray is v pla9ly %[n ) an electric lamp & scre54 ,if a tr\gh ) p>allel sides be plac$ s z to int]cept "p ( ! light com+ f ! electric lamp1 s t "p %all pass ?r\gh x & "p above1 we h ! image ( ! hole 9 ! diaphragm ( ! lant]n on ! scre5 un*ang$4 ,n[1 if ! tr\gh be fill$ ) wat]1 no diff]5ce :atev] is made 9 ! position ( ! light on ! scre51 because ! wat]1 :i* is d5s] ?an ! air1 is conta9$ 9 a tr\gh ) p>allel sides2 b by op5+ ! sides l op5+ a book1 or by int]pos+ ano!r tr\gh ) incl9$ sides1 %ap$ l a ,v1 t p>allelism is de/roy$1 & !n ! light pass+ ?r\gh x w be deflect$ upw>ds f its orig9al c\rse1 & w fall high] on ! scre52 by op5+ ! sides m & m1 "o is able to alt] ! direction ( ! light pass+ ?r\gh ! prism1 :i* has be5 con/ruct$ by de/roy+ ! p>allelism ( ! two sides4 ,illu/ration3 ,,fig4 #ba4--;,deviation ( ,light 9 ,pass+ at ,v>i\s ,incid5ces ?r\gh ,prisms ( ,v>i\s ,angles4 ,! refraction ( light !n dep5ds ^u ! d5sity ( ! sub/ance ?r\gh :i* x passes1 on ! angle ( incid5ce ( ! ray1 on ! angle ( ! prism1 & also on ! col\r ( ! light1 ab\t :i* we %all h some?+ to say pres5tly4 ,let u n[ pass f ! prism to ! l5s2 = hav+ once grasp$ ! idea ( refraction !re w be no difficulty 9 see+ :at a l5s really is4 ,) ! prism j consid]$1 plac$ s t a v]tical section is repres5t$ by a ,v1 a ray is ?r[n upw>ds2 if ano!r simil> prism be plac$ ) its base 9 contact ) ! base ( ! o!r1 & its apex upw>ds1 s t its section w be repres5t$ by a ,v rev]s$1 1 x is cle> ?is w turn ! rays d[nw>ds1 s t ! rays1 on em]g+ f bo? prisms w t5d to meet ea* o!r1 z %[n1 9 ,fig4 #bb1 :]e "o ray is turn$ d[n to ! same ext5t t ! o!r is turn$ up2 s t by ! comb9ation ( two prisms ! two rays are br\ght to a po9t1 :i* is call$ a focus4 ,n[1 if in/ead ( putt+ ! prisms base to base1 !y are put apex to apex1 a contr>y action takes place1 & by ?is means "o is able to cause two rays ( light to div]ge in/ead ( conv]g+1 s t ! prisms1 plac$ apex to apex1 cause ! rays to div]ge1 & :5 plac$ base to base !y cause ! light to conv]ge4 ,illu/ration3 ,,fig4 #bb4--;,conv]g5ce ( ,light by ,two ,prisms ,base to ,base4 ,if in/ead ( hav+ two prisms m]ely1 !re be tak5 a sy/em hav+ diff]5t angles at _! apices1 & f ea* prism !re be cut a section1 beg9n+ by cutt+ (f ! apex ( ! mo/ p[]ful prism1 a slice f bel[ ! apex ( ! next1 & a slice bel[ ! correspond+ "p ( ! next1 & s on2 & !n if ^! slices be laid on ea* o!r s z to =m a comp\nd prism1 & ano!r simil> prism be plac$ ) its base to ?is "o1 we get :at is repres5t$ 9 ,fig4 #bc4 ,^! diff]5t slices ( prisms become m & m prismatic1 t is1 !y =m p>ts ( prisms ( great] angle1 z !y approa* ! ends4 ,we c imag9e a section ( su* a sy/em z ?9 z we please4 ,suppose we _h su* a section & put x 9 a la!1 rotat+ x on ! axis ,a ,b1 we %\ld describe a solid figure1 & if we suppose all ! angles r\nd$ (f1 s t x is made ?9n] & ?9n] z we rec$e f ! c5tre1 ! prism sy/em is turn$ into a l5s hav+ ! =m repres5t$ 9 ,fig4 #bd4 ,9 a simil> mann]1 l5ses ?9n] 9 ! middle ?an at ! edges1 call$ concave l5ses1 c he con/ruct$1 "s =ms ( :i* are repres5t$ 9 section 9 ,fig4 #be4 ,x is also obvi\s t convex l5ses ( all curves & comb9ations ( curves c be made1 "s ( :i* appe> 9 ,fig4 #bf4 ,illu/ration3 ,,fig4 #bc4--;,=mation ( a ,l5s f ,sections ( ,prisms4 ,illu/ration3 ,,fig4 #bd4--;,front ,view & ,section ( a ,d\ble ,convex ,l5s4 ,illu/ration3 ,,fig4 #be4--;,d\ble ,concave1 ,plane ,concave1 & ,concavo-,convex ,l5ses4 ,! action ( su* l5ses ^u ! light proce$+ f any s\rce may n[ be consid]$4 ,if !re is a p>allel beam proce$+ f a lamp1 or f ! sun1 & x falls on ! =m ( l5s1 call$ a convex l5s1 :i* bulges out 9 ! middle1 we le>n f ,fig4 #bg1 t ! upp] "p acts l ! upp] prism j consid]$ & turns ! light d[n1 & ! l[] acts 9 ! rev]se mann] & turns ! light up1 & ! sides act 9 a simil> mann]2 & z ! incl9ation ( ! surfaces ( ! l5s increases z we approa* ! edge1 ! rays fall+ on ! p>ts ne> ! edge are turn$ out ( _! c\rse m ?an ^? fall+ ne> ! c5tre1 s t we h ! rays conv]g$ to a po9t ,f1 call$ ! focus ( ! l5s2 & z ! rays f an electric lamp are g5]ally r5d]$ p>allel by means ( ! l5ses 9 ! lant]n1 call$ ! cond5s]s1 ! rays f su* a lamp fall+ on a convex l5s w come to a focus at j ! same di/ance f ! l5s1 call$ its pr9cipal focal l5g? z !y w\ld d if !y came f ! sun or />s4 ,illu/ration3 ,,fig4 #bf4--;,d\ble ,convex1 ,plane ,convex1 & ,concavo-,convex ,l5ses4 ,illu/ration3 ,,fig4 #bg4--;,conv]g5ce ( ,rays by ,convex ,l5s to ,pr9cipal ,focus4 ,s f> we h br\ght rays to a focus1 & on hold+ a piece ( pap] at ! focus ( ! convex l5s1 z j m5tion$1 !re appe>s on x a spot ( light2 & e "o kn[s t if ?is exp]im5t be p]=m$ ) ! sun1 "o br+s all ! rays fall+ on ! l5s almo/ to a po9t1 & ! long] waves ( light w set fire to ! pap]2 & on ?is pr9ciple burn+-glasses are con/ruct$4 ,if1 h[ev]1 ! rays are n p>allel :5 fall+ on ! l5s1 b div]g+1 !y are n br\ght to a focus s ne> ! l5s1 & ! ne>] ! lum9\s s\rce or object is1 ! fur!r (f w ! light be br\ght to a focus on ! o!r side4 ,if matt]s are rev]s$1 & ! lum9\s s\rce be plac$ 9 ! focus1 ! rays ( light1 :5 !y leave ! l5s1 w conv]ge to ! position ( ! orig9al s\rce2 s t !re are two po9ts1 "o on ei!r side ( ! l5s1 :i* are ! foci ( ea* o!r ,s1 ,s1 ,fig4 #bh1 call$ conjugate foci2 z "o approa*es ! l5s ! o!r rec$es1 & vice v]s1 & x is obvi\s t :5 ! "o approa*es ! l5s s z to co9cide ) ! pr9cipal focus1 ! o!r rec$es to an inf9ite di/ance1 & ! em]g5t rays are p>allel4 ,illu/ration3 ,,fig4 #bh4--;,conjugate ,foci or ,convex ,l5s4 ,illu/ration3 ,,fig4 #bi4--;,conjugate ,images4 ,illu/ration3 ,,fig4 #cj4--;,diagram expla9+ ,fig4 #bi4 ,n[ let u consid] h[ images are =m$4 ,if we take a c&le1 ,fig4 #bi1 & hold ! l5s a little di/ance away f x1 !n1 on plac+ a scre5 ( pap] j on ! o!r side ( ! l5s1 !re w be a small flame depict$ on x1 an exact repres5tation ( ! real flame3 & x is =m$ 9 ?is way3 ,consid] ! rays proce$+ f ! top ( ! flame1 :i* are repres5t$ sep>ately 9 ,fig4 #cj1 :]e ,a repres5ts ! top4 ,"o ( ^! rays1 ,a a1 pass+ ?r\gh ! c5tre ( ! l5s o1 w he unaffect$ because ! surfaces ?r\gh :i* x passes are p>allel to ea* o!r2 & we "k f ! prop]ty ( ! l5s t all ! o!r rays f ,a w1 on pass+ ?r\gh x1 be br\ght to a focus some:]e on ,a a1 dep5d+ on ! curvature ( ! l5s1 & 9 ! case ( our l5s x is at a4 ,illu/ration3 ,,fig4 #ca4--;,disp]sion ( ,rays by a ,d\ble ,concave ,l5s4 ,9 l mann] also all ! rays f ,b are br\ght to a focus at b1 & s on ) all o!r p>ts ( ,a1 ,b1 :i* 9 ?is case repres5ts ! flame1 ea* w h its correspond+ focus2 !re be+ cones ( rays f e po9t ( ! object & to e po9t ( ! image1 hav+ = _! bases ! convex l5s1 & we get an image or exact repres5tation ( our c&le flame4 ,x w fur!r be notic$ t ! image a b is small] ?an ,a ,b1 9 proportion z ! di/ance a b is less ?an ,a ,b2 s t if we increase ! focal l5g? ( ! l5s till a b is twice ! di/ance away f ! l5s1 x w become d\ble its pres5t size4 ,if n[ ! flame be br\ght ne>] ! l5s1 its image a b becomes indi/9ct2 & we mu/ move ! scre5 fur!r away 9 ord] to r5d] ! image aga9 cle>2 h5ce ! place ( ! focus dep5ds on ! di/ance ( ! object1 & ! c&le & its image mu/ correspond to two conjugate foci4 ,illu/ration3 ,,fig4 #cb4--;,horizontal ,section ( ! ,eyeball4 ,scl1 ! scl]otic coat2 ,cn1 ! cornea2 ,r1 ! atta*m5ts ( ! t5dons ( ! recti muscles2 ,*1 ! *oroid2 ,cp1 ! cili>y processes2 ,cm1 ! cili>y muscle2 ,ir1 ! iris2 ,aq1 ! aque\s hum\r2 ,cry1 ! cry/all9e l5s2 ,vi1 ! vitre\s hum\r2 ,rt1 ! ret9a2 ,op1 ! optic n]ve2 ,ml1 ! yell[ spot4 ,if n[ rays be pass$ f ! lant]n or sun ?r\gh a concave l5s1 ,fig4 #ca1 !y are n br\ght to a focus1 b are disp]s$ & travel onw>ds1 z if !y came f a po9t1 ,f1 :i* is call$ its virtual focus2 & if rays are fir/ conv]g$ by a convex l5s1 & !n1 be=e !y rea* ! focus are all[$ to fall on a concave "o1 we c1 by plac+ ! l5ses a c]ta9 di/ance ap>t1 r5d] ! conv]g+ rays aga9 p>allel2 or we c make !m slightly div]g5t1 z if !y came1 n f an inf9ite di/ance1 b f a po9t a foot or two (f4 ,! application ( ?is arrangem5t w appe> h]eaft]4 ,:at has n[ be5 said on ! action ( ! convex l5s w enable u to consid] ! optical action ( ! eye1 )\t :i* we d little 9 a/ronomy4 ,z to ! way t ! bra9 receives impressions f ! eye we ne$ say no?+1 = t belongs to ! doma9 ( physiology1 except inde$ ?is1 t an image is =m$ on ! ret9a by a *emical decomposition1 br\ght ab\t by ! dissociat+ action ( c]ta9 rays ( light 9 exactly ! same way z on a photographic plate4 ,optically consid]$1 ! eye consi/s ( no?+ m ?an a convex l5s1 ,cry1 ,fig4 #cb1 & a surface1 ,rt1 ext5d+ ov] ! back ( ! eyeball1 call$ ! ret9a1 on :i* ! objects are focuss$1 b ! rays ( light fall+ on ! cornea ,cn1 are refract$ some:at1 s t x is n q true to say t ! cry/all9e l5s does all ! "w1 b = our pres5t purpose x is suffici5tly correct1 & we %all consid] _! comb9$ action z t ( a s+le l5s4 ,! out] coat ( ! eyeball1 %[n 9 section 9 ,fig4 #cb1 is call$ ! scl]otic1 ) ! exception ( t m convex "p 9 front ( ! eye1 call$ ! cornea2 beh9d ?is comes ! aque\s hum\r & !n ! iris1 t membrane ( :i* ! col\r v>ies 9 diff]5t p & races4 ,9 ! c5tre ( ?is is a circul> ap]ture call$ ! pupil1 :i* contracts or exp&s accord+ to ! brightness ( ! objects look$ at1 s t ! am\nt ( light pass+ into ! eye is kept z f> z possible con/ant4 ,close beh9d ! iris comes ! cry/all9e l5s1 ! ?ickness ( :i* c be alt]$ slightly by ! cili>y muscle4 ,9 ! space betwe5 ! l5s & ! back ( ! eye is a transp>5t jelly-l sub/ance call$ ! vitre\s hum\r4 ,f9ally comes ! ret9a1 a mo/ delicate surface *iefly compos$ ( n]ve fibres4 ,x is on ?is surface1 t ! image is =m$ by ! curv$ surfaces ( ! ant]ior membranes1 & ?r\gh ! back ( ! eyeball is ins]t$ ! mass ( filam5ts ( ! optic n]ve mak+ communication ) ! bra92 ^! filam5ts on rea*+ ! inside ( ! eye spread out to receive ! impressions ( light4 ,"h !n1 we h a complete photographic cam]a2 ! cry/all9e l5s & cornea1 sep>at$ by ! aque\s hum\r1 repres5t+ ! comp\nd-glass cam]a l5s1 & ! ret9a /&+ 9 ! place ( ! s5sitive plate4 ,illu/ration3 ,,fig4 #cc4--;,action ( ,eye 9 ,=mation ( ,images4 ,! pa? ( ! light =m+ an image on ! ret9a is %[n 9 ,fig4 #cc1 :]e ,a ,b is ! object1 & a b its image1 =m$ 9 exactly ! same way z ! image ( ! c&le-flame :i* we h j consid]$2 9 fact1 ! eye is exactly repres5t$ by a photographic cam]a1 ! iris act+ 9 ! same mann] z ! /ops 9 ! l5s1 limit+ its available area1 & by contract+1 decreas+ ! am\nt ( light f bright objects1 & at ! same "t increas+ ! %>pness ( def9ition1 = 9 ! case ( ! eye1 ! lum9\s rays obey ! kn[n laws ( propagation ( light 9 m$ia ( v>iable =m & d5sity1 & we h only simple refraction to deal )4 ,! next matt] to be consid]$ is t ! ne>] ! object ,a ,b is to ! eye1 ! l>g] is ! angle ,a1 o1 ,b1 & also a1 o1 b1 & !re=e ! image on ! ret9a is l>g]2 b !re is a limit to ! ne>ness to :i* ! object c be br\ght1 =1 z we f\nd ) ! c&le1 ! di/ance betwe5 ! l5s & ! image mu/ be increas$ z ! object approa*es1 or ! curvature ( ! l5s itself mu/ be alt]$1 = if n ! ray =m+ ! rays f ea* po9t ( ! object w be too div]g5t = ! l5s to be able to br+ !m to a focus4 ,n[ 9 ! eye !re is an adju/m5t ( ?is sort1 b x is limit$ s t objects beg9 to get indi/9ct :5 br\ght ne>] ! eye ?an p]haps six in*es1 because ! rays become too div]g5t = ! l5s to br+ !m to a focus on ! ret9a1 & !y t5d to come to a focus beh9d ! ret9a1 z 9 ,fig4 #cd2 b we may assi/ ! eye l5s by us+ a glass convex l5s 9 front ( x1 betwe5 x & ! object4 ,x is = ?is reason t spectacle glasses are us$ to enable long-sight$ p]sons to see cle>ly4 ,illu/ration3 ,,fig4 #cd4--;,action ( a ,long-sight$ ,eye4 ,we may also use a mu* /rong] l5s1 & s get ! object v ne> ! l5s & eye1 z 9 ,fig4 #ce1 :]e a b is ! object s ne> ! eye t1 if x 7 n = ! l5s ,l1 its image w\ld n come to a focus on ! ret9a at all4 ,! effect ( ! l5s is to make ! rays proce$+ 9 a cone f a & b less div]g5t1 s t aft] pass+ ?r\gh x1 !y proce$ to ! eye-l5s z if !y 7 com+ f ! po9ts ,a & ,b1 a foot or s away f ! eye1 & s ! object a b appe>s to be a mu* l>g] object at a great] di/ance f ! eye4 ,illu/ration3 ,,fig4 #ce4--a4 ,diagram %[+ pa? ( rays :5 view+ an object at an easy di/ance4 #b4 ,object br\ght close to eye :5 ! l5s ,l is requir$ to assi/ ! eye-l5s to obs]ve ! image :5 x is magnifi$4 ,a convex l5s !n has ! p[] ( magnify+ objects :5 br\ght ne> ! eye1 & its action is cle>ly se5 9 ,fig4 #ce1 :]e ! upp] figure %[s ! arr[ at z %ort a di/ance f ! eye z x c be se5 di/9ctly ) an ord9>y eye1 & ! l[] figure %[s ! same arr[ br\ght close to ! eye1 & r5d]$ di/9ctly visible by ! l5s :5 a magnifi$ image is ?r[n on ! ret9a1 z if !re 0 a real l>g] arr[ some:]e betwe5 ! dott$ l9es at ! ord9>y di/ance ( di/9ct vision4 ,x is also obvi\s t ! ne>] ! object c be br\ght to ! eye-l5s ! m magnifi$ x is1 j z an object appe>s l>g] ! ne>] x is br\ght to ! unaid$ eye4 ,we h be5 hi!rto deal+ ) ! effect ( a convex l5s on ! rays pass+ to ! eye4 ,we w n[ deal ) a concave "o4 ,we f\nd t ! p[] ( adju/m5t ( ! normal eye 0 suffici5t to br+ p>allel rays1 or ^? proce$+ f a v di/ant object1 & also slightly div]g+ rays1 to a focus on ! ret9a4 ,p>allel or slightly div]g5t rays are mo/ easily dealt )1 & slightly conv]g5t rays c also be focuss$ on ! ret9a2 b if ! eye-l5s is too convex1 z is ! case ) %ort-sight$ p1 ,fig4 #cf1 a concave l5s ( slight curvature is us$ to correct ! eye-l5s & br+ ! image to a focus on ! ret9a in/ead ( 9 front ( x4 ,illu/ration3 ,,fig4 #cf4--;,action ( ,%ort-sight$ ,eye4 ,if ! rays are v conv]g5t1 z ^? proce$+ f a convex l5s & com+ to a focus1 ! l5s ( a normal eye w br+ !m to a focus f> 9 front ( ! ret9a1 z if ! p]son 7 v %ort-sight$4 ,b by int]pos+ a suffici5tly p[]ful concave l5s ! rays are made less conv]g5t or p>allel1 & ! eye-l5s br+s !m to a focus on ! ret9a1 z if !y came f a ne> object1 s ! use ( convex & concave l5ses plac$ close to ! eye is to r5d] div]g5t or conv]g5t rays ne>ly p>allel1 s t ! eye-l5s c easily focus !m1 & !re=e "o ( ! conditions ( ! telescope is t ! rays :i* come into our eye %all be p>allel or ne>ly s4 ,,*apt] ,,vi4 ,,! ,,refractor4 ,9 ! telescope z fir/ con/ruct$ by ,galileo !re are two l5ses1 s arrang$ t ! fir/1 a convex "o1 ,a ,b ,fig4 #cg1 conv]ges ! rays1 :ile ! second1 ,c ,d1 a concave "o1 div]ges !m1 & r5d]s !m p>allel1 ready = ! eye2 ! rays !n1 aft] pass+ ?r\gh ,c ,d1 g to ! eye z if !y 7 proce$+ along ! dott$ l9es f an object ,m ,m1 clos] to ! eye in/ead ( f a di/ant object1 & s1 by means ( ! telescope1 ! object appe>s l>ge & close4 ,illu/ration3 ,,fig4 #cg4--;,galilean ,telescope4 ,a ,b1 convex l5s conv]g+ rays2 ,c ,d1 concave l5s s5d+ !m p>allel aga9 & fit = reception by ! eye4 ,x is ?is t con/itutes ! telescope4 ,b n[adays we h o!r =ms1 z we are n cont5t ) ! convex comb9$ ) ! concave l5s1 & mod]n a/ronomy requires ! eyepiece to be ( m elaborate con/ruction ?an ^? adopt$ by ,galileo & ! fir/ us]s ( telescopes1 al?\gh ?is =m is /ill us$ = op]a-glasses & 9 cases :]e small p[] only is requir$4 ,hav+ ! p[] ( conv]g+ ! light & =m+ an image by ! fir/ convex l5s or object glass1 z we saw ) ! c&le flame 7,fig4 #bi71 & an opportunity ( enl>g+ ?is image by means ( a magnify+ or convex eyepiece1 we c br+ an image ( ! moon1 or any o!r object1 close to ! eye1 & exam9e x by means ( a convex l5s1 or a comb9ation ( su* l5ses4 ,s we get ! mo/ simple =m ( refract+ telescopes repres5t$ 9 ,fig4 #ch1 9 :i* ! rays f all po9ts ( ! object--let u take = in/ance an arr[--are br\ght to a focus by ! object-glass ,a1 =m+ !re an exact repres5tation ( ! real arr[4 ,9 ! figure two cones ( rays only are del9eat$1 namely1 ^? =m+ ! po9t & fea!r ( ! arr[1 b e o!r po9t 9 ! arr[ is built up by an inf9ite numb] ( cones 9 ! same way1 ea* cone hav+ ! object-glass = its base4 ,by means ( ! l5s ,c we are able to exam9e ! image ( ! arr[ ,b1 s9ce ! rays f x are ?us r5d]$ p>allel1 or ne>ly s1 & to ! eye !y appe> to come f a mu* l>g] arr[ at a %ort di/ance away4 ,we c draw _! app>5t direction1 & ! app>5t arr[ 7z is done 9 ,fig4 #cg by ! dott$ l9es71 & s ! object appe>s z magnifi$1 or1 :at comes to ! same ?+1 z if x 7 ne>]4 ,! diff]5ce betwe5 ?is =m & t contriv$ by ,galileo is ?is3 9 ! latt] ! rays are receiv$ by ! eyepiece :ile conv]g+1 & r5d]$ p>allel by a concave l5s1 :ile 9 ! =m] case ! rays are receiv$ by ! eyepiece on ! o!r side ( ! focus1 :]e !y h cross$ ea* o!r & are div]g+1 & are r5d]$ p>allel by a convex l5s4 ,we may n[ sum up ! use ( ! eye-l5s4 ,! image is br\ght to a focus on ! ret9a1 because ! object is "s di/ance (f1 & ! rays f e po9t1 7z f ,a & ,b1 ,fig4 #ce71 on rea*+ ! eye1 are ne>ly p>allel2 b x is n necess>y t !y %\ld be absolutely p>allel1 z ! eye is capable ( a small adju/m5t1 b if "o wi%es to see an object mu* ne>] 7z 9 ! l[] figure71 x is impossible to d x unless "s optical aid is obta9$1 = ! rays are too div]g5t1 & _c be br\ght to a focus on ! ret9a4 ,:at does t optical aid effect8 ,x enables u to place ! object 9 ! focus ( ano!r l5s :i* %all make ! rays p>allel1 & fit = ! l5s ( ! eye to focus on ! ret9a1 & s9ce ! object c by ?is means be br\ght close to ! l5s & eye1 x =ms a l>g] image on ! ret9a4 ,dep5d5t on ?is is ! p[] ( ! telescope4 ,illu/ration3 ,,fig4 #ch4--,telescope4 ,a1 object-glass1 giv+ an image at ,b2 ,c1 l5s = magnify+ image ,b4 ,we %all ref] lat] on to ! me*anical con/ruction ( ! telescope4 ,"h x may be m]ely /at$ t ! small] ones consi/ ( a brass tube1 ! object-glass held 9 a brass r+ screw$ 9 at "o end ( ! tube & a small] tube c>ry+ ! eyepiece slid+ 9 & out ( ! l>ge tube & sometimes mov$ by a rack & p9ion motion1 at ! o!r4 ,! l>g] ones z m\nt$ = special uses w also be fully describ$ f>!r on4 ,illu/ration3 ,,fig4 #ci4--;,diagram ,expla9+ ! ,magnify+ ,p[] ( ,object-glass4 ,! p[] ( ! telescope dep5ds on ! object-glass z well z on ! eyepiece2 if we wi% to magnify ! moon1 = in/ance1 we mu/ h a l>ge image ( ! moon to look at1 & a p[]ful l5s to see t image4 ,by /udy+ ,fig4 #ci ! fundam5tal condition ( produc+ a l>ge image by a l5s w be se54 ,suppose we wi% to look at an object 9 ! heav5s1 ! diamet] ( :i* is "o degree2 if ! l5s ?r[s an image ( t body on to ! circumf]5ce ( a circle ( #cfj in*es1 !n1 z !re are #cfj degrees 9 a circle1 t image w cov] "o in*2 let ! circle be #cfj y>ds1 & ! image ( a body ( "o degree w cov] "o y>d2 & to take an extreme case & suppose ! circumf]5ce ( ! circle to be #cfj miles1 !n ! image w be "o mile 9 diamet]4 ,?is is "o ( ! pr9cipal conditions ( ! action ( ! object-glass 9 enabl+ u to obta9 images :i* c be magnifi$ by a l5s1 & by su* magnification made to appe> ne>] to u ?an !y are4 ,galileo us$ telescopes :i* magnifi$ f\r or five times1 & x 0 only ) great tr\ble & exp5se t he produc$ "o :i* magnifi$ tw5ty-?ree times4 ,n[1 aft] :at has be5 said ( focal l5g?1 "o w n be surpris$ to he> ( ^? long telescopes produc$ 9 ! v e>ly days1 a few ( :i* are /ill extant2 ^! %[ z well z any?+ ! enorm\s difficulty :i* ! e>ly employ]s ( telescopes _h to deal ) 9 ! mat]ial !y employ$4 ,"o c sc>cely tell "o end ( ! telescope f ! o!r2 all ! "w 0 done 9 "s cases by an object-glass n m ?an half an in* 9 effective diamet]4 ,x might be suppos$ t ^? :o /udi$ ! *anges ( places & ! positions ( ! heav5ly bodies w\ld h be5 ! fir/ to ga9 by ! inv5tion ( ! telescope1 & t telescopes w\ld h be5 add$ to ! in/rum5ts already describ$1 replac+ ! po9t]s4 ,= su* a use z ?is a telescope ( half an in* ap]ture w\ld h be5 a great assi/ance4 ,b ?+s did n happ5 s1 because ! inv5tion ( ! telescope gave su* an impetus to physical a/ronomy t ! :ole heav5s appe>$ novel to mank9d4 ,gr\ps ( />s appe>$ :i* _h nev] be5 se5 be=e2 ,jupit] & ,saturn 7 f\nd to be att5d$ by satellites2 ! sun1 ! immaculate sun1 0 det]m9$ aft] all to h spots1 & ! moon 0 at once set ^u & obs]v$ ) dilig5ce & c>e2 s t !re 0 a v good reason :y p %\ld n limit ! p[]s ( ! telescope to employ+ x to det]m9e positions only4 ,! numb] ( telescopes 0 small1 & !y c\ld n be bett] employ$ ?an 9 tak+ a survey ( all ! m>vell\s ?+s :i* !y reveal$4 ,x 0 at ?is "t t ! mod]n equatorial 0 =e%ad[$4 ,galileo1 & 8 contempor>ies ,s*e9] & o!rs1 7 obs]v+ sun-spots1 & ! telescope1 ,fig4 #dj1 :i* ,s*e9] arrang$1 a v r\gh in/rum5t1 ) its axis p>allel to ! e>?'s axis1 & all[$ to turn s t ,s*e9] might foll[ ! sun = _m h\rs a day1 0 "o ( ! fir/4 ,?is in/rum5t is "h reproduc$1 because x 0 "o ( ! mo/ important telescopes ( ! "t1 & ga!r$ 9 to ! h>ve/ _m ( ! e>lie/ obta9$ facts4 ,illu/ration3 ,,fig4 #dj4--,s*e9]'s ,telescope4 ,s9ce by means ( little in/rum5ts l ^!1 s mu* ( beauty & ( m>vel c\ld be discov]$ 9 ! skies1 x is no wond] t e "o :o _h any?+ to d ) telescopes /ra9$ 8 n]ves to make !m ( great] p[]1 by :i* m m>vels c\ld be reveal$4 ,x 0 n long be=e ^? little in/rum5ts ( ,s*e9] exp&$ into ! long telescopes to :i* ref]5ce has be5 made4 ,b !re 0 a difficulty introduc$ by ! l5g? ( ! in/rum5t4 ,! l5g? ( ! focus necess>y = magnification spread ! light ov] a l>ge area1 & !re=e x 0 necess>y to get an equival5t ( light by increas+ ! ap]ture ( ! object-glasses 9 ord] t ! object might be suffici5tly bright to be> consid]able magnification by ! eyepiece1--& n[ arose a trem5d\s difficulty4 ,"o "p ( refraction1 namely1 deviation1 enables u to obta91 b ! o!r half1 disp]sion1 prev5ts our obta9+1 except "u c]ta9 conditions1 an image we c make use (4 ,by disp]sion is meant ! prop]ty ( splitt+ up ord9>y light into its compon5t col\rs1 ( :i* we %all say m 9 deal+ ) spectrum analysis4 ,if we wi% to get m light by increas+ ! ap]ture ( ! telescope1 ! deviation ( ! light pass+ ?r\gh ! edge ( ! object-glass is increas$1 & ) x ! disp]sion1 ! result ( ?is increase ( deviation4 ,if ! light ( ! sun be all[$ to fall ?r\gh a hole into a d>k5$ *amb]1 & !n ?r\gh a prism1 ,fig4 #da1 x is refract$1 & in/ead ( hav+ an exact reproduction ( ! bright circle we h a col\r$ b& or spectrum4 ,! :ite light :5 refract$ is n only driv5 out ( its orig9al c\rse--deviat$--b x is also brok5 up--disp]s$--into _m col\rs4 ,we h a consid]able am\nt ( col\r2 & ?is ! e>ly obs]v]s f\nd :5 !y increas$ ! size ( _! telescopes1 = x mu/ be rememb]$ t a l5s is only a v complex prism4 ,illu/ration3 ,,fig4 #da4--;,disp]sion ( ,light by ,prism4 ,fir/1 !y increas$ ! size by enl>g+ ! object-glasses1 & n ! focal l5g?2 b :5 !y _h done t !y _h t extremely objectionable col\r :i* prev5t$ !m see+ any?+ well4 ,! col\r & indi/9ctness came f an ov]lapp+ ( a numb] ( images1 z ea* col\r _h its own focus1 ow+ to v>y+ refrangibilities4 ,!y f\nd1 !re=e1 t ! only effective way ( increas+ ! p[] ( ! telescope 0 by increas+ its focal l5g? s z to r$uce ! disp]s+ action z mu* z possible1 & s enl>g+ ! size ( ! actual image to be view$1 )\t at ! same "t increas+ ! angul> deviation ( ! rays transmitt$ ?r\gh ! edges ( ! l5s4 ,! size ( ! image correspond+ to a giv5 angul> diamet] ( ! object is 9 ! direct proportion ( ! focal l5g?1 :ile ! flexure ( ! rays :i* conv]ge to =m any po9t ( x is 9 ! same proportion inv]sely4 ,illu/ration3 ,,fig4 #db4--;,diagram ,%[+ ! ,am\nt ( ,col\r ,produc$ by a ,l5s4 ,to take an example4 ,9 ! case ( an object-glass ( cr[n-glass1 ! space ov] :i* ! rays are disp]s$ is "o-fiftie? ( ! di/ance ?r\gh :i* !y are deviat$1 & x w be se5 by ref]5ce to ,fig4 #db1 t if ! r$ rays are at ,r1 & ! blue at ,b1 ! di/ance ,a ,b is fifty times ,r ,b1 & z ^! di/ances dep5d on ! diamet] ( ! l5s only1 we c increase ! focal l5g?1 & s increase ! size ( ! image )\t alt]+ ! disp]sion ,r ,b1 & s ?r[ ! "w ( magnify+ on ! object-glass in/ead ( on ! eyepiece1 :i* w\ld magnify ,r ,b equally ) ! image itself4 ,s t 9 t "t1 & 9 ! "t ( ,huygh5s1 telescopes ( #ajj1 #bjj1 & #cjj feet focal l5g? 7 n only sugge/$ b made1 & "o en?usia/ic />gaz] f9i%$ an object-glass1 ! focal l5g? ( :i* 0 #fjj feet4 ,telescopes ( #ajj & #aej feet focal l5g? 7 m commonly us$4 ,! eyepiece 0 at ! end ( a /r+1 & ! object-glass 0 plac$ free to move on a tall pole1 s t an obs]v] on ! gr\nd1 by pull+ ! /r+1 might get ! two glasses 9 a l9e ) ! object :i* he wi%$ to obs]ve4 ,s x w5t on till ! "t ( ,sir ,isaac ,newton1 :o consid]$ ! problem v c>efully--b n 9 an absolutely complete way4 ,he came to ! conclusion1 z he /ates 9 8 ,optics1 t ! improvem5t ( ! refract+ telescope 0 8desp]ate20 & he gave 8 att5tion to reflect+ telescopes1 :i* are next to be notic$4 ,let u exam9e ! basis ( ,sir ,isaac ,newton's /atem5t1 t ! improvem5t ( ! refract+ telescope 0 desp]ate4 ,he came to ! conclusion t 9 refraction ?r\gh diff]5t sub/ances !re is always an un*ang$ relation betwe5 ! am\nt ( disp]sion & ! am\nt ( deviation1 s t if we attempt to correct ! action ( "o prism by ano!r act+ 9 an opposite direction 9 ord] to get :ite light1 we %all de/roy all deviation4 ,b ,sir ,isaac ,newton happ5$ to be wrong1 s9ce !re are sub/ances :i*1 = equival5t deviations1 disp]se ! light m or less4 ,s by means ( a l5s ( a c]ta9 sub/ance ( l[ disp]sive p[] we c =m an image slightly col\r$1 & we c add ano!r l5s ( a sub/ance hav+ a high disp]sive p[] & less curvature & j rev]se ! disp]sion ( ! fir/ l5s )\t rev]s+ all its deviat+ p[]4 ,! foll[+ exp]im5ts w %[ cle>ly ! application ( ?is pr9ciple4 ,we fir/ take two simil> prisms arrang$ z 9 ,fig4 #dc4 ,! la/ ?r\gh :i* ! light passes corrects ! deviation & disp]sion ( ! fir/4 ,we !n take two prisms1 "o ( cr[n glass & ! o!r ( fl9t glass1 & s9ce ! disp]sion ( ! fl9t is great] ?an t ( ! cr[n1 we imag9e ) ju/ice t ! fl9t-glass prism may be ( a less angle ?an ! o!r & /ill h ! same disp]sive p[]1 & at ! same "t1 see+ t ! angles ( ! prisms are diff]5t1 we may expect to f9d t we %all get a l>g] am\nt ( deviation f ! cr[n-glass prism ?an f ! o!r4 ,illu/ration3 ,,fig4 #dc4--;,decomposition & ,recomposition ( ,light by ,two ,prisms4 ,if !n a ray ( light be pass$ ?r\gh ! cr[n-glass prism1 we get ! disp]sion & deviation due to ! prism ,a ,fig4 #dd1 giv+ a spectrum at ,d4 ,& n[ we take away ! cr[n glass & place 9 its /ead a prism ( fl9t glass inv]t$2 ! ray 9 ?is in/ance is deviat$ less1 b !re is an equal am\nt ( col\r+ at ,d4 ,if n[ we use bo? prisms1 act+ 9 opposite directions1 we %all be able to get rid ( ! col\rs1 b n entirely comp5sate ! deviation4 ,we n[ place ! orig9al cr[n-glass prism 9 front ( ! lant]n & !n int]pose ! fl9t-glass prism1 s t ! light %all pass ?r\gh bo?4 ,! addition ( ?is prism ( fl9t1 ( great] disp]sive p[]1 comb9es1 or z x 7 %uts (f1 ! col\r1 leav+ ! deviation uncomp5sat$1 s t we get an uncol\r$ image ( ! hole 9 front ( ! lant]n at ,d4 ,?is is ! f\ndation ( ! mod]n a*romatic telescope4 ,illu/ration3 ,,fig4 #dd4--;,diagram ,expla9+ ! ,=mation ( an ,a*romatic ,l5s4 ,a1 cr[n-glass prism2 ,b1 fl9t-glass prism ( less angle1 b giv+ ! same am\nt ( col\r2 ,c1 ! two prisms comb9$1 giv+ a col\rless yet deviat$ b& ( light at ,d4 ,ano!r me?od ( %[+ ! same ?+ is to br+ a ,v-%ap$ wat]-tr\gh into ! pa? ( ! rays f ! lant]n2 !n1 :ile no wat] is 9 x1 ! beam ( light pass+ ?r\gh x is absolutely uncol\r$ & undeviat$4 ,9 ?is case we h no wat] inclos$ by ^! surfaces1 & x is n act+ z a prism at all4 ,if1 h[ev]1 a prism ( fl9t glass1 a sub/ance ( high disp]sive p[]1 is introduc$ into x1 ) its refract+ edge upw>ds1 x de/roys ! condition we _h be=e1 & we h a col\r$ b& on ! scre51 because ! glass t ! prism is made ( has ! faculty ( /rong disp]sion 9 addition to its deviation4 ,we c get rid ( t disp]sion by ?r[+ disp]sion 9 a contr>y direction by fill+ up ! tr\gh ) wat]1 & s mak+1 z x 71 a wat] prism on ei!r side ( ! glass "o1 wat] be+ a sub/ance ( l[ disp]sive p[]4 ,we h a col\rless beam ?r[n on ! scre51 :i* is deviat$ f ! orig9al level1 because ! wat] prisms are toge!r ( a great] angle ?an ! glass "o4 ,! exp]im5ts ( ,hall & ,doll& h result$ 9 our be+ able to comb9e l5ses 9 ! same way t we h "h comb9$ prisms1 be>+ 9 m9d :at has be5 said 9 ref]5ce to ! action ( l5ses be+ l t ( s _m prisms2 & we may consid] two l5ses1 "o ( cr[n & ! o!r ( fl9t glass1 ,fig #de4 ,! cr[n glass be+ ( a c]ta9 curvature w give a c]ta9 disp]sion2 ! fl9t glass1 9 consequ5ce ( its great disp]sive p[]1 w require less curvature to correct ! cr[n glass4 ,:at w happ5 w be ?is3 assum+ ! second l5s to be away1 ! rays w em]ge f ! fir/ 7convex7 l5s & =m a col\r$ image at ,a4 ,b if ! second fl9t-glass concave l5s be int]pos$ x w1 by means ( its action 9 a contr>y direction1 undo all ! disp]sion due to ?is fir/ l5s & a c]ta9 am\nt ( deviation1 s t we %all get ! comb9ation giv+ an almo/ col\rless image at ,b4 ,illu/ration3 ,,fig4 #de4--;,comb9ation ( ,fl9t- & ,cr[n-glass ,l5ses 9 an ,a*romatic ,l5s4 ,x w n be absolutely col\rless1 = ! reasons :i* w be n[ expla9$4 ,if light be pass$ ?r\gh diff]5t sub/ances plac$ 9 holl[ prisms1 or ?r\gh prisms ( fl9t & cr[n glass1 & ! spectra ?us produc$ be obs]v$1 we f9d !re are important diff]5ces4 ,:5 we exp& ! spectra consid]ably1 we see t ! action ( ^! diff]5t sub/ances is n absolutely uni=m1 "s col\rs ext5d+ ov] ! spectrum fur!r ?an o!rs4 ,9 ! case ( "o k9d ( glass ! r$ end ( ! spectrum is cru%$ up1 :ile 9 ! o!r we h ! r$ end exp&$4 ,?is is call$ ! irrationality ( ! spectrum produc$ by prisms ( diff]5t sub/ances4 ,! cr[n & ! fl9t-glass l5ses--& = telescopes we mu/ use su* glass--give irrational spectra1 s t ! a*romatic telescope is n absolutely a*romatic1 9 consequ5ce ( ?is peculi>ity2 = if ,r1 ,g1 ,b1 ,fig4 #df1 are ! c5tres ( ! r$1 gre51 & violet 9 ! spectrum giv5 by a prism compos$ ( ! glass ( :i* "o l5s is made1 & ,r1 ,g1 ,b1 are ^? ( ! o!r1 if ! l5ses are plac$ s z to c\nt]act ea* o!r1 & are ( su* curves t ! r$s & violets are comb9$1 ! gre5s w rema9 slightly out/&+4 ,suppose1 z 9 ! draw+1 ! second prism disp]ses ! violet z mu* z ! fir/ "o does1 !n1 :5 ^! are rev]s$ !y w exactly comp5sate r$ & violet4 ,b ! second "o acts m /rongly on ! gre5 ?an ! fir/1 :i* w be ov]-comp5sat$2 & if we weak5 ! second prism s t ! gre5 & r$ are correct1 !n ! violet w be slightly out/&+1 :i* 9 practice is n mu* notic$1 except ) a v bright object :5 !re is always out/&+ col\r4 ,illu/ration3 ,,fig4 #df4--;,diagram ,illu/rat+ ! ,irrationality ( ! ,spectrum4 ,?is is1 h[ev]1 n a matt] ( any v great importance = ord9>y "w1 s9ce ! visual rays all lie 9 ! neighb\rhood ( ! yell[1 s t opticians take c>e to correct _! l5ses = ! rays 9 ?is "p ( ! spectrum1 & at ! same "t1 z a matt] ( necessity1 ov]-correct = ! violet rays1 t is1 rev]se ! disp]sion ( ! ext]ior l5s1 s t ! violet rays h a long] in/ead ( a %ort] focus ?an ! r$1 &1 !re=e1 9 look+ at a bright object1 su* z a fir/ magnitude />1 x appe>s surr\nd$ by a violet halo2 ) fa9t] objects ! blue light is n ( suffici5t int5sity to be visible4 ,x is1 !re=e1 always pref]able to correct = ! mo/ visible rays & leave ! out/&+ violet to take c>e ( itself2 b nev]!less v>i\s proposals h be5 made to get rid ( x4 ,object-glasses conta9+ fluids ( diff]5t k9ds h be5 tri$1 b !y h nev] become ( any practical value1 & x does n seem probable t !y ev] w4 ,9 ord] to get rid ( ! out/&+ violet col\r :5 ! rema9d] ( ! spectrum 0 correct$1 ,dr4 ,blair con/ruct$ object-glasses ! space betwe5 ! l5ses ( :i* 7 fill$ ) c]ta9 liquids1 g5]ally a solution ( a salt ( m]cury or antimony1 ) ! addition ( hydro*loric acid2 = 9 ! spectrum giv5 by ! metallic solution ! gre5 is proportionally ne>] ! r$ ?an is ! case ) ! spectrum produc$ by hydro*loric acid1 s t by ! adju/m5t ( ! diff]5t solutions he exactly de/roy$ ! out/&+ col\r ( ! ord9>y comb9ation4 ,9 ?is way ,sir ,john ,h]s*el tells u he 0 able to con/ruct l5ses ( ?ree in*es ap]ture & only n9e in*es focal l5g?1 free f *romatic & sph]ical ab]ration4 ,x 0 propos$ by ,mr4 ,b>l[ to correct a convex cr[n-glass l5s = *romatic ab]ration by a holl[ concave l5s conta9+ bisulphide ( c>bon1 a highly disp]sive fluid1 hav+ d\ble ! p[] ( fl9t glass4 ,?is l5s 0 plac$ 9 ! cone ( rays betwe5 ! object-glass & ! eyepiece4 ,its surfaces 7 concavo-convex1 calculat$ to de/roy sph]ical ab]ration1 & its di/ance f ! object-glass 0 v>i$ until exact a*romatism 0 obta9$4 ,a telescope ( ?is pr9ciple ( eight in*es ap]ture 0 made by ,mr4 ,b>l[1 :i* prov$ highly satisfactory4 ,9 ! e>ly "p ( ! la/ c5tury x 0 propos$ by ,wolfius to int]pose betwe5 ! object-glass & eyepiece a concave l5s 9 ord] to give great] magnification ( ! image1 ) a slight increase ( focal l5g?2 if an ord9>y l5s be us$ ! a*romatism ( ! images giv5 by ! object-glass w be de/roy$4 ,messrs4 ,doll& & ,b>l[1 h[ev]1 propos$ to make ! concave l5s a*romatic1 s t ! image is z mu* )\t col\r :5 ! l5s is us$ z )\t x4 ,mr4 ,dawes f\nd su* a l5s to "w extremely well4 ,^! l5ses1 usually call$ 8,b>l[ l5ses10 are g5]ally made ab\t "o in* 9 diamet]1 & by v>y+ _! di/ance f ! eyepiece ! image is alt]$ 9 size at pleasure4 ,9 ! reflect+ telescope1 ) :i* we w n[ proce$ to deal1 !re is an abs5ce ( col\r2 b ! reflector is n )\t its drawbacks1 = !re are imp]fections 9 x z great z ^? we h be5 consid]+ 9 ! case ( ! refractor4 ,,*apt] ,,vii4 ,,! ,,reflection ,,( ,,light4 ,we h n[ dealt ) ! refraction ( light 9 g5]al1 includ+ deviation & disp]sion1 9 ord] to see h[ x c assi/ u 9 ! =mation ( ! telescope2 & we h %[n h[ ! *romatic effect ( a s+le l5s c be got rid ( by employ+ a comp\nd sy/em compos$ ( diff]5t mat]ials1 & s we h got a g5]al idea ( ! refract+ telescope4 ,we h n[ to deal ) ano!r prop]ty ( light1 call$ reflection2 & our object is to see h[ reflection c help u 9 telescopes4 ,9 ! case ( reflection we get ! orig9al direction ( ! ray *ang$ z 9 ! case ( refraction1 b ! deviation is due to a diff]5t cause4 ,take a bright light1 a c&le w d1 & a mirror fix$ s t ! light falls on its surface & is ?r[n back to ! eye1 ,fig4 #dg1 we see ! image ( ! c&le app>5tly beh9d ! mirror2 ! rays ( light fall+ on ! mirror are reflect$ f x at exactly ! same angle at :i* !y rea* x4 ,?is br+s u 9 ! pres5ce ( ! fir/ & mo/ important law ( reflection2 & x is ?is1 at :atev] angle ! light falls on a mirror1 at t angle w x be reflect$4 ,z x is usually express$1 ! angle ( incid5ce1 :i* is ! angle made by ! incid5t ray ) an imag9>y l9e drawn at "r angles to ! mirror1 call$ ! normal1 is equal to ! angle ( reflection1 t is1 ! angle conta9$ by ! reflect$ ray1 & ! normal to ! surface4 ,9 ord]1 !re=e1 to f9d 9 :at direction a ray ( light w travel aft] /rik+ a flat poli%$ surface1 we mu/ draw a l9e at "r angles to ! surface at ! po9t :]e ! ray imp+es on x1 !n ! reflect$ ray w make an angle ) ! normal equal to t :i* ! incid5t ray makes1 or ! angles ( incid5ce & reflection w be equal4 ,illu/ration3 ,,fig4 #dg4--;,diagram ,illu/rat+ ! ,action ( a ,reflect+ ,surface4 ,v simple exp]im5ts1 :i* e "o c make w %[ u ! laws :i* gov]n ! ph5om5a ( reflection4 ,let u employ a ba? ( m]cury = a reflect+ surface1 & = a lum9\s object a />1 ! rays ( :i*1 com+ f a di/ance :i* is practically inf9ite1 to ! surface ( ! e>?1 may be consid]$ exactly p>allel4 ,! direction ( ! beams ( light com+ f ! />1 & fall+ on ! mirror =m$ by ! m]cury1 is easily det]m9$ by means ( a !odolite1 ,fig4 #dh4 ,if we look directly at ! />1 ! l9e ,i ,s ( ! telescope indicates ! direction ( ! incid5t lum9\s rays1 & ! angle ,s ,i ,n1 equal to ! angle ,s1 ,i1 ,n1 is ! angle ( incid5ce1 t is to say1 t =m$ by ! lum9\s ray ) ! normal to ! surface at ! po9t ( incid5ce4 ,illu/ration3 ,,fig4 #dh4--;,exp]im5tal ,pro( t ! ,angle ( ,incid5ce ,angle ( ,reflection4 ,9 ord] to f9d ! direction ( ! reflect$ lum9\s rays1 we mu/ turn ! telescope on its axis1 until ! rays reflect$ by ! surface ( ! m]cury ba? ent] x & produce an image ( ! />4 ,:5 ! image is br\ght to ! c5tre ( ! telescope1 x is f\nd t ! angle ,r ,i ,n is equal to ! angle ( reflection ,n1 ,i1 ,r4 ,?us1 9 read+ ! measure on ! graduat$ circle ( ! !odolite ! angle ( reflection c be comp>$ ) ! angle ( incid5ce4 ,n[1 :atev] may be ! /> obs]v$1 & :atev] its height above ! horizon1 x is always f\nd t !re is p]fect equality betwe5 ^! angles4 ,moreov]1 ! position ( ! circle ( ! !odolite :i* enables ! /> & its image to be se5 evid5tly proves t ! ray :i* arrives directly f ! lum9\s po9t & t :i* is reflect$ at ! surface ( ! m]cury are bo? 9 ! same v]tical plane4 ,n[ ?is demon/rates "o ( ! mo/ important laws ( reflection4 ,! laws ( refraction d n deal directly ) ! angles !mselves1 b ) ! s9es ( ! angles2 9 reflection ! angles are equal2 9 refraction ! s9es h a con/ant relation to ea* o!r4 ,s f> we h dealt ) plane surfaces1 b 9 ! case ( telescopes we d n use plane surfaces1 b curv$ ones1 s we w proce$ at once to discuss ^!4 ,illu/ration3 ,,fig4 #di4--;,conv]g5ce ( ,light by ,concave ,mirror4 ,illu/ration3 ,,fig4 #ej4--;,conjugate ,foci ( ,convex ,mirror4 ,9 ,fig4 #di1 ,a repres5ts a curv$ surface1 su* z t ( a concave mirror1 ! c5tre ( curvature be+ ,c4 ,n[ we c consid] t ?is curv$ surface is made up ( an inf9ite numb] ( small plane surfaces1 & s9ce all l9es drawn f ! c5tre1 ,c1 to ! mirror1 w be at "r angles to ! surface at ! po9ts :]e !y meet x1 we f9d1 f our exp]im5t ) ! plane mirror1 t rays fall+ on ! mirror at ^! po9ts w be reflect$ s t ! angles on ei!r side ( ea* ( ^! l9es %all be equal2 s1 = in/ance1 9 ,fig4 #di1 we wi% to f9d to :at po9t ! upp] ray w be reflect$1 & we draw a l9e f ! c5tre1 ,c1 to ! po9t :]e x falls on ! mirror1 & !n draw ano!r l9e f t po9t mak+ ! angle ( reflection equal to t made by ! incid5t ray1 & we c consid] ! small surface conc]n$ 9 reflection flat1 s t ! ray w 9 ?is case be reflect$ to ,f4 ,if n[ we take any o!r ray1 & p]=m ! same op]ation we %all f9d t x is also reflect$ ne>ly to ,f1 & s on ) all o!r p>allel rays fall+ on ! mirror2 & ?is po9t1 ,f1 is !re=e said to be ! focus ( ! mirror4 ,if n[ ! rays1 in/ead ( fall+ p>allel on ! mirror1 z if !y came f ! sun or a v di/ant object1 are div]g5t1 z if !y came f a po9t ,s1 ,fig4 #ej1 ne> ! mirror1 ! rays approa* ne>] to ! l9es drawn f ! c5tre to ! mirror1 "o ( :i* is repres5t$ by ! dott$ l9e2 or1 9 o!r words1 ! angles ( incid5ce become r$uc$1 & s ! angles ( reflection w also be r$uc$1 & ! focus ( ! rays f ,s w approa* ! c5tre ( ! mirror1 & be at s2 j s x w be se5 t if an illum9at$ po9t be at s1 its focus w be at ,s1 & ^! two po9ts are !re=e call$ conjugate foci4 ,illu/ration3 ,,fig4 #ea4--;,=mation ( ,image ( ,c&le by ,reflection4 ,illu/ration3 ,,fig4 #eb4--;,diagram expla9+ ,fig4 #ea4 ,if a c&le is held at a %ort di/ance 9 front ( a concave mirror1 z repres5t$ 9 ,fig4 #ea1 its image appe>s on ! pap] betwe5 ! c&le & ! mirror1 s t ! rays f e po9t ( ! flame are br\ght to a focus1 & produce an image j z ! image is produc$ by a convex l5s4 ,if we /udy ,fig4 #eb ! =mation ( ?is image w be cle>ly und]/ood4 ,fir/ we mu/ note t ! rays ,a1 ,c1 a1 & ,b1 ,c1 b1 :i* pass ?r\gh ! c5tre ( curvature ( ! mirror ,c1 w fall p]p5dicul>ly on ! surface1 & be reflect$ back on !mselves1 s t ! focus ( ! "p a ( ! arr[ w be some:]e on ,a a1 & t ( ,b on ,b b1 & by draw+ ano!r ray we %all f9d x reflect$ to a1 :i* w be ! focus ( ! po9t ,a1 & s also by draw+ ano!r l9e f ,b1 we %all f9d x is reflect$ to b1 :i* is ! focus ( ! "p ,b2 & we might repeat ?is process = e "p ( ! arr[1 & = e ray f ^? p>ts4 ,we n[ see t s9ce ! rays ,a a & ,b b cross ea* o!r at ,c1 ! di/ance f a to b be>s ! same proportion to ! di/ance f ,a to ,b z _! respective di/ances f ! po9t ,c2 or1 9 o!r words1 ! image is small] ?an ! object 9 ! same proportion z ! di/ance f ! image to ,c is small] ?an ! di/ance f ! object to ,c4 ,n[1 9 deal+ ) ! />s1 :i* are at a practically inf9ite di/ance1 ! rays are p>allel1 & w be br\ght to a focus half-way betwe5 ! mirror & its c5tre ( curvature4 ,9 ?is case1 !re=e1 ! di/ance f ! image to ! mirror is equal to t f ! image to ! c5tre1 s t we c express ! size ( ! image by say+ t x is small] ?an ! object1 9 proportion z its di/ance f ! mirror is small] ?an ! di/ance ( ! object f ,c2 & z x makes little diff]5ce :e!r we measure ! di/ance ( ! />s f ,c or f ! mirror1 & z ,c is n always kn[n1 we c take ! relation ( ! di/ances ( ! object & image f ! mirror z repres5t+ ! proportionate sizes ( ! two4 ,we w n[ consid] ! case ( rays fall+ on a mirror curv$ ! o!r way1 t is1 a convex mirror4 ,let u consid] ! ray imp++ at ,d1 ,fig4 #ec1 :i* w\ld g on to ,c1 ! c5tre ( ! mirror4 ,n[1 z ,c ,d is drawn f ! c5tre1 x is at "r angles to ! mirror at ,d1 & ! ray ,l ,d1 be+ 9 ! same /raight l9e on ! opposite side1 w also be at "r angles1 & w be reflect$ back on itself4 ,n[ take ! ray ,i ,a1 draw ,c ,e ?r\gh ,a1 !n ,e ,a w be p]p5dicul> to ! surface at ,a1 & ,i ,a ,e w be ! angle ( incid5ce1 & ,e ,a ,g ! angle ( reflection1 s t ?is ray ,a ,g w be reflect$ away f ,l ,d1 & s w all ! o!r rays fall+ on ! mirror z ,k ,b3 & if we cont9ue ! l9es ,g ,a & ,h ,b backw>ds1 !y w meet at ,m1 & !re=e ! rays div]ge f ! mirror z if !y came f a po9t at ,m1 & ?is po9t is call$ ! virtual focus4 ,illu/ration3 ,,fig4 #ec4--,reflection ( ,rays by ,convex ,mirror4 ,s mu* = p>allel rays4 ,next let u consid] ano!r case :i* happ5s 9 ! telescope1 namely1 :]e conv]g+ rays fall on a convex mirror1 z 9 ,fig4 #ec1 :]e we consid] ! light proce$+ to ! mirror f a conv]g+ l5s along ! l9es ,h ,b & ,g ,a1 ^! w be made p>allel1 at ,b ,k & ,a ,f1 aft] reflection1 & x is manife/ t by mak+ ! mirror suffici5tly convex1 ^! rays1 t5d+ to come to a focus at ,m1 c\ld be r5d]$ div]g5t2 & if ! curvature is decreas$ by mak+ ! c5tre ( curvature at a c]ta9 di/ance beyond ,c1 x w be se5 at once by ! diagram t ^! rays w aft] reflection1 conv]ge t[>ds ,l & w come to a focus 9 front ( ! mirror at a po9t fur!r 9 front ?an ,c is beh9d x1 s t !y h be5 r5d]$ less conv]g5t only by ! mirror 9 ?is suppos$ case4 ,x w be se5 f :at has be5 /at$ "h & 9 ,*apt] ,v41 t we get ne>ly ! same results f reflection z we did f refraction :5 we 7 consid]+ ! functions ( glasses in/ead ( mirrors2 t a concave mirror acts exactly z a convex l5s1 & vice v]s1 s t !y c be sub/itut$ ! "o = ! o!r4 ,if we take a mirror1 & all[ ! light to fall on x f a lamp1 no "o w h any difficulty 9 see+ t ! mirror grasps ! beam1 & =ms an image :i* is se5 di/9ctly 9 front ( ! mirror1 j z "o gets an image f a convex l5s beh9d x4 ,,*apt] ,,viii4 ,,! ,,reflector4 ,! po9t we h next to det]m9e is h[ we c utilise ! prop]ties ( reflection = ! purposes ( a/ronomical obs]vation4 ,_m admirable plans h be5 sugge/$4 ,! fir/ t 0 put on pap] 0 made by ,gregory1 :o po9t$ out t if we _h a concave mirror1 we %\ld get f ?is mirror an image ( ! object view$ at ! focus 9 front ( x1 z 9 ,fig4 #ea4 ,( c\rse we _c at once utilise ?is focal image by us+ an eyepiece 9 ! same way z we d 9 a refractor1 because ! obs]v]'s head w\ld /op ! light1 & ! mirror w\ld be useless1 & all ! sugge/ions :i* h be5 made1 h ref]5ce to obta9+ ! image 9 su* a position t we are able to view x conv5i5tly4 ,gregory1 ! ,scotti% a/ronom] above ref]r$ to1 9 #affc sugge/$ a me?od1 & x has turn$ out to be a good "o1 ( utiliz+ reflection by plac+ a small mirror ,d ,c1 ,fig4 #ed1 on ! o!r side ( ! focus ,a ( ! l>ge "o1 at su* a di/ance t ! image at ,a is aga9 focuss$ at ,b by reflection f ! small mirror2 & at ,b we get ( c\rse an enl>g$ image ( ,a4 ,! rays ( light proce$+ to ,b w\ld1 h[ev]1 be int]cept$ by ! l>ge mirror1 unless an ap]ture 7 made 9 ! l>ge mirror ( ! size ( ! small "o ?r\gh :i* ! rays c\ld pass & be r5d]$ p>allel by means ( an eyepiece plac$ j beh9d ! l>ge mirror4 ,s t t[>ds ! object is ! small mirror ,c1 & !re is an eyepiece ,e1 :i* enables ! image ( ! object to be view$ aft] two reflections1 fir/ f ! l>ge mirror & !n f ! small "o4 ,mr4 ,%ort 7:o made ! be/ telescopes ( ?is con/ruction1 & did mu* = ! optical sci5ce ( ! la/ c5tury7 alt]$ ! position ( ! small mirror ) ref]5ce to ! focus ( ! l>ge "o1 by slid+ x along ! tube by a screw arrangem5t1 ,f1 & s 0 enabl$ to focus bo? ne> & di/ant objects )\t alt]+ ! eyepiece4 ,illu/ration3 ,,fig4 #ed4--,reflect+ ,telescope 7,gregorian74 ,b be=e ?is 0 put into practice1 ,sir ,isaac ,newton 79 #afff7 made telescopes on a totally diff]5t plan4 ,! eyepiece ( ! ,newtonian telescope is at ! side ( ! tube1 & n at ! end1 z 9 ,gregory's4 ,we h next to inquire h[ ?is arrangem5t is c>ri$ out1 &1 l mo/ ?+s1 x is p]fectly simple :5 "o kn[s h[ x is done4 ,!re is a l>ge mirror at ! bottom ( ! tube z 9 ! ,gregorian1 b n p]=at$1 & ! focus ( ! mirror w\ld be some:]e j 9 front ( ! end ( ! tube4 ,n[ 9 ?is case we d n all[ ! beam to get to ! focus at all 9 ! tube or 9 front ( x2 b be=e x comes to ! focus x is receiv$ on a small diagonal plane surface m1 & ?us x is at once ?r[n outw>ds at "r angles ?r\gh ! side ( ! tube1 & comes to a focus 9 front ( an eyepiece1 plac$ at ! side1 ready to be view$ ! same z an image f a refractor 7,fig4 #ee74 ,illu/ration3 ,,fig4 #ee4--,newton's ,telescope4 ,! next arrangem5t is "o :i* ,mr4 ,grubb has rec5tly rescu$ f obscurity1 & x is call$ ! ,cassegra9ian =m4 ,x w be se5 on ref]r+ to t1 ,fig4 #ef1 if ! small mirror1 ,c1 7 remov$1 ! rays f ! mirror ,a ,b w\ld come to a focus at ,f4 ,9 ! ,gregorian con/ruction a concave reflector 0 us$ outside t focus 7at ,c1 ,fig4 #ed71 b ,cassegra9 sugge/$ t if1 in/ead ( us+ a concave reflector outside ! focus1 a reflector ) a convex surface 7 plac$ inside x1 we %\ld arrive at v ne>ly ! same result1 provid$ we reta9 ! hole 9 ! l>ge mirror4 ,! conv]g+ rays f ,a ,b w fall on ! convex surface ( ! mirror ,c1 :i* is ( su* a curvature & at su* a di/ance f ,f1 ! focus ( ! l>ge mirror1 t ! rays are r5d]$ less conv]g+1 & d n come to a focus until !y rea* ,d1 :]e an image is =m$ ready to be view$ by ! eyepiece ,e4 ,x appe>s f ?is1 t ! convex mirror is 9 ?is case act+ some:at 9 ! same mann] z ! concave l5s does 9 ! ,galilean telescope4 ,illu/ration3 ,,fig4 #ef4--,reflect+ ,telescope 7,cassegra974 ,illu/ration3 ,,fig4 #eg4--;,front ,view ,telescope 7,h]s*el74 ,!n1 la/ly1 we h ! sugge/ion :i* ,sir ,william ,h]s*el soon turn$ into m ?an a sugge/ion4 ,! mirror ,m 9 ?is arrangem5t is plac$ at ! bottom ( ! tube z 9 ! o!r =ms1 b1 in/ead ( be+ plac$ flat on ! bottom x is slightly tipp$1 s t if ! eyepiece is plac$ at ! edge ( ! extremity ( ! tube all p>allel rays fall+ on ! mirror are reflect$ to ! side ( ! tube at ! top :]e ! eyepiece is1 in/ead ( be+ reflect$ to a convex or o!r mirror 9 ! middle4 ,?is is call$ ! front view telescope1 & x enabl$ ,sir ,william ,h]s*el to make 8 discov]ies ) ! =ty-feet reflector4 ,) small telescopes ?is =m c\ld n be adopt$1 z ! obs]v]'s head w\ld cov] "s "p ( ! tube & ob/ruct ! light1 b ) l>ge telescopes ! am\nt ( light /opp$ by ! head is small 9 proportion to :at w\ld be lo/ by us+ a small mirror4 ,^! are 9 ! ma9 ! f\r me?ods ( arrang+ reflect+ telescopes--! ,gregorian1 ! ,cassegra9ian1 ! ,newtonian1 & ! ,h]s*elian4 ,9 ord] to make l>ge reflectors p]fect--l>ge telescopes ( %ort focus1 because t is "o ( ! requirem5ts ( ! mod]n a/ronom]--we h to battle aga9/ sph]ical ab]ration4 ,we h already se5 t ! p[] ( sub/ances to refract light diff]s = diff]5t col\rs1 & we h se5 ! v>i$ refraction ( diff]5t p>ts ( ! spectrum1 & ! necessity ( mak+ l5ses a*romatic4 ,n[ !re is "o enorm\s advantage 9 fav\r ( ! reflector4 ,we d n take our light to bits & put x toge!r aga9 z ) an a*romatic l5s4 ,b curi\sly en\gh1 !re is a some?+ else :i* q l[]s ! position ( ! reflector ) reg>d to ! refractor4 ,al?\gh1 9 ! ma9 all ! light fall+ 9 p>allel l9es on a concave surface is reflect$ to a focus1 ?is is only true 9 a g5]al s5se1 because1 if we consid] x1 we f9d an error :i* increases v rapidly z ! diamet] ( ! mirror increases or z ! focal l5g? dim9i%es4 ,= in/ance1 ,d ,i1 ,fig4 #eh1 is ! segm5t ( a circle1 or ! section ( a sph]e--if we deal ) a solid figure4 ,d ,c1 ,e ,g & ,h ,i1 are ?ree l9es repres5t+ p>allel rays fall+ on diff]5t p>ts ( x4 ,accord+ to t law :i* we h consid]$1 we c f9d :]e ! ray ,e ,g w fall4 ,we draw a l9e ,l1 ,g1 f ! c5tre to ! po9t ( reflection1 & make ! angle ,f ,g ,l1 equal to ! angle ( incid5ce ,e ,g ,l2 !n ,f w be ! focus1 s f> z ?is "p ( ! mirror is conc]n$4 ,n[ let u repeat ! process = ! ray ,h ,i1 & we %all f9d t x w be reflect$ to ,k1 a po9t ne>] ! mirror ?an ,f1 & x w be se5 t ! fur!r ! rays are f ! axis ,d ,c1 ! fur!r f ! po9t ,f is ! light reflect$2 s t if we consid] rays fall+ f all p>ts ( ! reflect+ surface1 a n v l>ge b a di/9ctly visible surface is cov]$ ) light1 s t a sph]ical surface w n br+ all ! rays exactly to a po9t1 & ) a sph]ical mirror we %all get a blurr$ image4 ,we c comp>e ?is imp]fection ( ! reflector1 call$ sph]ical ab]ration1 ) ! *romatic ab]ration ( ! object-glass4 ,illu/ration3 ,,fig4 #eh4--;,diagram ,illu/rat+ ,sph]ical ,ab]ration4 ,illu/ration3 ,,fig4 #ei4--;,diagram ,%[+ ! ,prop] ,=m ( ,reflector to be an ,ellipse4 ,newton e>ly calculat$ ! ratio ( imp]fection dep5d+ ^u ^! prop]ties ( light1 fir/ ( disp]sion & !n ( sph]ical ab]ration1 & he f\nd t 9 ! refract+ telescope ! *romatic ab]ration 0 m difficult to correct & get rid ( ?an ! sph]ical ab]ration ( ! reflector1 s t 9 ,newton's "t1 be=e a*romatic l5ses 7 con/ruct$1 ! reflector ) its ab]ration _h ! advantage4 ,x mu/ n[ be expla9$ h[ ?is difficulty is got ov]4 ,:at is requir$ to produce a mirror capable ( be+ us$ = a/ronomical purposes1 is to ?r[ back ! edges ( ! mirror to ! dott$ l9e ,a ,c ,i1 ,fig4 #eh1 :i* w make ! m>g9 ( ! mirror a "p ( a less concave mirror1 & s its focus w be ?r[n fur!r f itself--to ,f1 in/ead ( to ,k4 ,n[ let u consid] :at curve ?is is1 t w ?r[ all ! rays to "o po9t4 ,x is an ellipse1 z w be se5 by ref]5ce to ,fig4 #ei1 9 :i*1 in/ead ( hav+ a sph]ical surface ! section ( :i* is a circle1 we deal ) a surface ^: section is an ellipse4 ,x w be se5 9 a mom5t1 t by ! con/ruction ( an ellipse any light com+ 9 any direction f ! po9t ,a1 :i* repres5ts "o ( ! foci ( ! curve1 mu/ necess>ily be reflect$ back to ! o!r focus1 ,b1 ( ! curve1 = x is a well-kn[n prop]ty ( ?is curve t ! angles made ) a tang5t ,c ,d1 by l9es f ! foci are equal2 & ! same holds good = ! angles made at all o!r tang5ts2 & x w be se5 at once t ?is is bett] ?an a circul> curve1 because by mak+ ! di/ance betwe5 ! foci almo/ inf9ite we %all h ! /> or object view$ at "o focus & its image at ! o!r2 if we use any portion ( ! reflect+ surface we %all /ill get ! rays reflect$ to "o po9t only4 ,x mu/ also be notic$1 t unless we h an ellipse s l>ge t "o focus %all repres5t ! sun or a p>ticul> /> we want to look at1 ?is curve w n help u 9 br++ ! light to "o po9t1 b if we use ! curve call$ ! p>abola1 :i* is practically an ellipse ) "o focus at an inf9ite di/ance1 we d get ! means ( br++ all ! rays f a di/ant object to a po9t4 ,h5ce ! reflector1 especially :5 ( l>ge diamet]1 is ( no use = a/ronomical purposes )\t ! p>abolic curve4 ,t x is extremely difficult to give ?is figure may be ga!r$ f ,sir ,john ,h]s*el's /atem5t1 t 9 ! case ( a reflect+ telescope1 ! mirror ( :i* is =ty-eight in*es 9 diamet] & ! focal di/ance ( :i* is =ty feet1 ! di/ance betwe5 ! p>abolic & ! sph]ical surface1 at ! edges ( ! mirror1 w be repres5t$ by some?+ less ?an a tw5ty-"o ?\s&? "p ( an in*1 or1 m accurately1 #a_/baccc in*4 ,9 ,fig4 #eh ! po9t ,a repres5ts ! extreme edge ( ! curve ( ! p>abolic mirror1 & ,d t ( ! circul> surface be=e alt]$ into a p>abola4 ,at ! "t ( ,sir ,william ,h]s*el ! practical difficulties 9 con/ruct+ l>ge a*romatic l5ses l$ to ! adoption by him ( reflectors beg9n+ ) small ap]tures ( six in*es to a foot1 & increas+ till he obta9$ "o ( f\r feet 9 diamet] & =ty-six feet focal l5g?4 ,?is has be5 surpass$ by ,"l ,rosse1 ^: well-kn[n telescope is six feet diamet]1 & fifty-?ree feet focal l5g?4 ,mr4 ,lassell1 ,mr4 ,de ,la ,rue1 ,m4 ,f\cault & ,mr4 ,grubb1 h also m rec5tly succe$$ 9 br++ reflectors to great p]fection4 ,h[ ! "w has be5 done w be fully /at$ 9 ! sequel4 ,,*apt] ,,ix4 ,,eyepieces4 ,we h consid]$ ! telescope z a comb9ation ( an object-glass & eyepiece 9 ! "o case1 & ( a speculum & eyepiece 9 ! o!r2 t is to say1 we h discuss$ ! optical pr9ciples :i* are appli$ 9 ! con/ruction ( refract+ & reflect+ telescopes1 ! telescope be+ tak5 z consi/+ ( an object-glass or speculum & an eyepiece ( ! mo/ simple =m1 viz41 a simple d\ble convex l5s4 ,we mu/ n[ g into detail some:at on ! subject ( eyepieces1 & expla9 ! diff]5t k9ds4 ,x w be recollect$ t :5 we spoke ( ! object-glass1 its ab]ration1 bo? *romatic & sph]ical1 0 m5tion$4 ,n[ e ord9>y l5s has ^! errors1 & eyepieces mu/ be correct$ = !m1 b ?is is n done 9 exactly ! same way z ) object-glasses4 ,9 ! case ( eyepieces ! error is correct$ by us+ two l5ses ( su* focal l5g?s or at su* a di/ance ap>t t ea* c\nt]acts ! defects ( ! o!r2 n by us+ two k9ds ( glass z 9 ! case ( ! object-glass1 b by s arrang+ ! l5ses t ! col\r$ rays produc$ by ! fir/ l5s %all fall at diff]5t angles ( incid5ce on ! second & become recomb9$4 ,illu/ration3 ,,fig4 #fj4--;,huygh5s' ,eyepiece4 ,let u take ! case ( a well-kn[n eyepiece1 call$ ! ,huygh5ian eyepiece1 aft] its inv5tor4 ,x consi/s ( two plano-convex l5ses1 ,a & ,b ,fig4 #fj1 ) _! convexities turn$ t[>ds ! object-glass1 & hav+ _! focal l5g?s 9 ! proportion ( ?ree to "o4 ,! /ronge/ l5s1 ,a1 be+ next ! eye1 ! l5s ,b is plac$ inside ! focus ( ! object-glass1 s t x assi/s 9 br++ ! image1 say ( a d\ble />1 to a focus at ,f1 half way betwe5 ! l5ses1 & ne>] to ! object-glass ?an x w\ld h be5 )\t ! l5s4 ,?is image is !n view$ by ! eye-l5s1 ,a1 & a magnifi$ image ( x se5 app>5tly at ,f1 z has be5 be=e expla9$4 ,n[ let u see h[ ! fieldl5s r5d]s ?is comb9ation a*romatic4 ,let u consid] ! pa? ( a ray fall+ on ! l5s ne> ,b1 %[n 9 section 9 ,fig4 #fa3 x is !re refract$1 b1 ! blue rays be+ refract$ m ?an ! r$1 !re w be two rays produc$1 r & v1 giv+ ( c\rse a col\r$ edge to ! image2 b :5 ?is image is view$ by ! eye-glass1 ,a1 x no long] appe>s col\r$1 = ! ray v1 fall+ ne>] ! axis ( ,a1 is less b5t ?an r1 & !y are r5d]$ ne>ly p>allel & appe> to proce$ f ! po9t ,f :]e ! :ole image appe>s )\t col\r4 ,9 ord] to get ! be/ result ) ?is =m ( eyepiece ! focal l5g? ( ! fieldl5s %\ld be ?ree times t ( ! eye-l5s & !y %\ld be plac$ at a di/ance ( half _! jo9t focal l5g?s ap>t4 ,illu/ration3 ,,fig4 #fa4--;,diagram ,expla9+ ! ,a*romaticity ( ! ,huygh5ian ,eyepiece4 ,! next eyepiece :i* comes "u consid]ation is t call$ ,ramsd5's1 ,fig4 #fb4 ,x consi/s ( two plano-convex l5ses ( ! same focus1 ,a & ,b1 plac$ at a di/ance ( two-?irds ( ! focal l5g? ( ei!r ap>t2 !y are bo? on ! eye side ( ! focus ( ! telescope1 & act toge!r1 to r5d] ! rays p>allel & give a magnifi$ virtual image ( ,f,f4 ,?is eyepiece is n /rictly a*romatic1 b x suff]s lea/ ( all l5ses f sph]ical ab]ration2 x also has ! advantage ( be+ plac$ beh9d ! focus ( ! object-glass1 :i* makes x sup]ior to o!rs 9 in/rum5ts ( precision1 z we %all pres5tly see4 ,illu/ration3 ,,fig4 #fb4--,ramsd5's ,eyepiece4 ,x mu/ be rememb]$ t ^! eyepieces give an inv]t$ image--or r ! object glass gives an inv]t$ image1 & ! eyepiece does n "r x aga92 b !re are eyepieces t w erect ! image1 & ,rheita's is "o ( ?is k9d4 ,x is1 z w be se5 f ,fig4 #fc1 m]ely a second application ( ! same means t fir/ inv]ts ! object1 namely1 a second small telescope4 ,a is ! object-glass1 a b ! image inv]t$ 9 ! usual way2 ,b is an ord9>y convex l5s s5d+ ! rays f a & b p>allel4 ,n[1 in/ead ( plac+ ! eye at ,c1 z 9 ! ord9>y mann]1 ano!r small l5s1 act+ z an object-glass1 is plac$ 9 ! pa? ( ! rays1 br++ !m to a focus at a1 b1 & =m+ !re an erect image :i* is view$ by ! eye-l5s ,d4 ,?is is ! erect+ eyepiece or 8day eyepiece10 ( ! common 8t]re/rial telescope40 ,dollond sub/itut$ an ,huygh5ian eyepiece = ! eye-l5s ,d1 & s made :at is call$ 8 f\r-glass eyepiece4 ,dr4 ,kit*5] devis$ & ,mr4 ,g4 ,dollond made an alt]ation 9 ?is eyepiece 9 ord] to v>y its p[] at pleasure4 ,x is done 9 ?is way3 ,! size ( ! image a b dep5ds ^u ! relation ( ! di/ances a ,b & ,e a1 :i* c be v>i$ by alt]+ ! di/ance ( ! comb9ation ( ! l5ses ,b & ,e1 f ! image a b1 & s mak+ a b l>g] & at a focus fur!r f ,e2 ! tube c>ry+ d slides 9 & out1 s t x c be focuss$ on a b at :atev] di/ance f ,e x may be4 ,?is arrangem5t is call$ ,dollond's ,pancratic eyepiece4 ,illu/ration3 ,,fig4 #fc4--;,erect+ or day eyepiece4 ,on ! slid+ tube c>ry+ ! l5s ,d1 or r ! ,huygh5ian eyepiece 9 place ( ! s+le l5s1 are m>k$ divisions1 %[+ ! p[] ( ! eyepiece :5 drawn out to c]ta9 l5g?s1 s t if we want ! eyepiece to magnify say #ajj times1 ! tube c>ry+ ! eye-l5s is drawn out to ! po9t m>k$ #ajj1 & ! :ole eyepiece mov$ 9 or out ( ! telescope tube by ! focuss+ screw1 until ! image ( ! object view$ is focuss$ 9 ! field ( ! eyepiece ,d4 ,to increase ! p[]1 we h only to draw out ! eyepiece ,d1 & move ! :ole comb9ation ne>] to ! object-glass s z to ?r[ ! image a b fur!r f ! l5s ,e4 ,?is eyepiece1 ?\gh s conv5i5t = *ang+ p[]s1 is little us$1 ow+ p]haps *iefly to f\r l5ses be+ requir$ in/ead ( two1 h5ce a loss ( light1 s a /ock ( eyepieces ( v>i\s p[]s is g5]ally f\nd 9 obs]vatories4 ,:5 v high p[]s are requir$1 a s+le plano-convex l5s is sometimes us$1 b al?\gh !re is less loss ( light 9 ?is case1 ! field ( view is s contract$ 9 comp>ison ) t giv5 ) o!r eyepieces t ! s+le l5s is seldom us$4 ,?is =m is1 h[ev]1 adopt$ 9 ,dawes' sol> eyepiece1 to be h]eaft] m5tion$1 & a numb] ( l5ses are 9 ?is case fix$ 9 holes ne> ! circumf]5ce ( a disc ( metal :i* turns on its c5tre1 s t by rotat+ ! disc ! l5ses come 9 succession 9 front ( ! focus ( ! object-glass1 & ! p[] c be *ang$ almo/ in/antane\sly4 ,9 ord] t objects ne> ! z5i? may be obs]v$ ) ease1 a diagonal reflector is sometimes us$1 s t ! eye looks sidewise into ! telescope tube in/ead ( directly upw>ds4 ,?is reflector may take ! =m ( two %ort pieces ( tube jo9$ toge!r at "r angles1 & hav+ a piece ( silv]$ glass or a "r-angl$ prism at ! angle1 s t :5 "o tube is screw$ into ! telescope1 ! rays ( light fall+ on ! reflector are s5t up ! o!r1 9 :i* ! ord9>y eyepiece is plac$4 ,! eyepieces j describ$ are suitable1 )\t fur!r addition1 = obs]v+ all ord9>y objects1 b :5 ! sun has to be exam9$ a difficulty pres5ts itself4 ,! heat rays are br\ght to a focus along ) ^? ( light1 & ) an object-glass ( m ?an "o or two in*es ap]ture !re is great dang] ( ! heat crack+ ! l5ses1 b ) su* telescopes ! int]position--& neglect ( ?is may co/ an eye--( smok$ or /rongly-col\r$ glass 9 front ( ! eye is g5]ally suffici5t to protect x f ! int5se gl>e4 ,) l>g] telescopes1 h[ev]1 d>k glasses are apt to split sudd5ly & all[ ! full blaze ( sunlight to ent] ! eye & d inf9ite mis*ief1 & "s o!r me?od ( r$uc+ ! heat & light is requir$4 ,p]haps ! mo/ simple me?od ( effect+ ?is object is to all[ ! light to fall on a diagonal plane glass reflector at an angle ( #de1 :i* lets ! great] "p ( ! light & heat pass ?r\gh1 reflect+ only a small portion onw>ds to ! eyepiece & !nce to ! eye2 a col\r$ glass is1 h[ev]1 requir$ z well1 & ! glass reflector mu/ =m "p ( a prism ( small angle1 o!rwise !re w be two images1 "o produc$ by ea* surface4 ,ano!r arrangem5t is to reflect ! rays f ! surfaces ( two plates ( glass incl9$ to !m at ! pol>iz+ angle1 s t by turn+ ! second plate1 or a ,nicols' prism1 9 its place r\nd ! ray z an axis1 ! am\nt ( light all[$ to pass to ! eye c be v>i$ at pleasure4 ,! late ,mr4 ,dawes con/ruct$ a v conv5i5t sol> eyepiece1 dep5d+ on ! pr9ciple ( view+ a v small portion ( ! sun's image at "o "t1 & !reby dim9i%+ ! total quantity ( heat pass+ ?r\gh ! eye-l5s4 ,! details ( ! eyepiece are z foll[s3 v m9ute holes ( v>y+ diamet]s are made 9 a brass disc ne> its circumf]5ce1 & z ?is is turn$ ea* successive hole is br\ght into ! c5tre ( ! field ( view & ! common focus ( ! eye-l5s & object-glass4 ,small areas on ! sun ( diff]5t sizes c ?us be exam9$ at pleasure4 ,a numb] ( eye-l5ses ( diff]5t p[]s arrang$ 9 a disc ( metal c be successively br\ght to be>1 giv+ a means ( quickly v>y+ ! p[]1 :ile col\r$ glasses ( diff]5t %ades c be pass$ 9 front ( ! eye 9 ! same mann]4 ,! surface ( ! disc ( brass conta9+ ! holes is cov]$ on "o side--t on :i* ! sun's image falls--) pla/] ( ,p>is1 :i*1 be+ a bad conductor1 prev5ts ! heat f affect+ ! :ole app>atus4 99 99 99 99 99 ,! true magnify+ p[] ( ! eyepiece is f\nd by divid+ ! focal l5g? ( ! object-glass by t ( ! eyepiece2 9 practice x is f\nd approximately by comp>+ ! diamet] ( ! object-glass ) t ( its image =m$ by ! eyepiece :5 ! telescope is 9 its usual adju/m5t2 ! =m] divid$ by ! latt] giv+ ! p[] requir$4 ,! diamet] ( ! image c be measur$ by a small comp\nd microscope c>ry+ a transp>5t scale 9 its focus1 :5 ! image ( ! object-glass is br\ght to a focus & enl>g$ on ! scale & !n view$1 toge!r ) ! divisions1 by ! microscope2 or ! image c be measur$ ) tol]able accuracy by ,mr4 ,b]?on's dynamet]1 consi/+ ( a plate ( metal trav]s$ longitud9ally by a w$ge-%ap$ op5+4 ,?is is plac$ close to ! eye-l5s 9 ! case ( ! ,huygh5ian eyepiece1 or at ! po9t :]e ! image ( ! object-glass is focuss$ ) o!r =ms ( eyepieces1 & ! plate mov$ until ! sides ( ! w$ge-%ap$ op5+ are exactly tang5tial to ! image2 ! po9t ( ! op5+ at :i* ?is occurs is read (f on a scale1 :i* gives ! wid? ( op5+ at ?is po9t & !re=e ! diamet] ( ! image4 ,,*apt] ,x4 ,,production ,,( ,,l5ses ,,& ,,specula4 ,be=e we g on to ! use & v>i\s m\nt+s ( telescopes1 ! optical pr9ciples ( :i* h be5 n[ consid]$1 a few words may be said ab\t ! mat]ials us$ & ! me?od ( obta9+ ! necess>y & prop] curves4 ,object-glasses1 ( c\rse1 h always be5 made ( glass1 & till a few ye>s ago specula 7 always made ( metal2 b s soon z ,liebig discov]$ a me?od ( coat+ glass ) a ?9 film ( metallic silv]1 ,/e9heil1 & aft] him ! illu/ri\s ,f\cault1 s well kn[n = 8 delicate exp]im5ts on ! velocity ( light & 8 inv5tion ( ! gyroscope1 sugge/$ ! con/ruction ( glass mirrors coat$ by ,liebig's process ) an exce$+ly ?9 film ( silv]1 *emically deposit$4 ,?is arrangem5t mu* r$uc$ ! price ( reflectors & r5d]$ _! poli%+ extremely easy1 & at ! pres5t "t discs ( glass up to f\r feet 9 diamet] are be+ ?us produc$ & =m$ into mirrors1 ?\gh 9 ! op9ion ( compet5t judges ?is size is likely to be ! limit = "s "t4 ,b !re is ?is important diff]5ce1 t al?\gh glass is n[ us$ bo? = reflectors & refractors1 almo/ any glass1 ev5 common glass1 w d1 if we wi% to use x = a speculum2 b if we wi% to gr9d x into l5ses x is impossible to ov]rate ! difficulty ( manufacture & ! skill & lab\r requir$ 9 ord] to prep>e x = use1 fir/ 9 ! simple mat]ial1 & !n 9 ! f9i%$ =m 9 :i* x is us$ by ! a/ronom]4 ,9 a =m] *apt] we consid]$ "s *efs-d'uvre ( ! e>ly opticians1 "s specim5s ( a qu>t] or half-an-in* 9 diamet]1 ) extremely long focus2 & z we w5t on we f\nd object-glasses gradually increas+ 9 diamet]1 b !y 7 limit$ to ! same mat]ial1 namely1 cr[n glass4 ,dollond1 ^: "n we h already m5tion$ 9 connection ) t ( ,hall1 gave u ! f\ndation ( ! manufacture ( ! preci\s fl9t glass1 ! connection ( :i* ) cr[n glass he _h insi/$ ^u z ( critical importance4 ,! exi/5ce ( a piece ( fl9t glass two in*es 9 diamet] 0 !n a ?+ to be dev\tly desir$1 t is to say1 fl9t glass ( suffici5t purity = ! purpose2 x c\ld n be made ( a size l>g] ?an t1 & n only 0 ! mat]ial want$1 b ! mat]ial 9 its pure /ate4 ,9 ! ye> #ahbj we he> ( a piece ( fl9t glass six in*es 9 diamet]1 & 9 #ahei ,mr4 ,simms report$ t a piece ( fl9t glass ( sev5 & ?ree-qu>t] in*es 0 produc$1 six in*es ( :i* 7 good = a/ronomical purposes4 ,b ev5 at ?is "t !y did ^! ?+s bett] 9 ,g]many & ,switz]l&1 :]e ,m4 ,gu9& made l>ge discs at ! beg9n+ ( ! pres5t c5tury4 ,he 0 engag$ by ,fraunh(] & ,utzs*neid] at _! e/abli%m5t 9 ,bav>ia 9 #ahje1 & by 8 process a*romatics ( f six to n9e in*es 9 diamet] 7 con/ruct$4 ,aft]w>ds ,m]z1 ! successor ( ,fraunh(]1 succe$$ 9 obta9+ fl9t glass ( ! !n unprec$5t$ diamet] ( fifte5 in*es4 ,n[ we h 9 "p turn$ ! tables1 & ,mr4 ,*ance1 ( ,birm+ham1 ow+ to ! introduction ( =eign tal5t1 has s9ce con/ruct$ discs ( glass ( a workable diamet] ( tw5ty-five in*es = ,mr4 ,newall's telescope1 & = ! ,am]ican ,gov]nm5t he has complet$ ! l>ge discs us$ 9 con/ruct+ ! refractor ( #bf in*es' diamet] = ! obs]vatory at ,wa%+ton 7! ,am]icans are nev] cont5t till !y g an in* beyond _! rivals71 :ile ,m4 ,feil ( ,p>is1 a desc5dant ( ! celebrat$ ,gu9&1 has also made "o ( ne>ly #bh in*es' diamet] = ! ,au/rian ,gov]nm5t4 ,messrs4 ,*ance & ,feil1 h[ev]1 h ! monopoly ( ?is manufacture1 & ! production ( ^! discs is a secret process4 ,:at we "k is t ! glass is prep>$ 9 pots 9 l>ge quantities1 x is !n all[$ to cool1 & is brok5 up 9 ord] t x may be det]m9$ :i* portions ( ! glass are wor? us+ = optical purposes4 ,^! are ga!r$ toge!r & fus$ at a r$ heat into a disc1 & x is ?is disc :i*1 aft] be+ anneal$ ) ! utmo/ c>e1 =ms ! basis ( ! optician's "w4 ,= ! glass us$ = reflectors1 purity is ( little mom5t1 z we only require a surface to take a poli%1 s9ce we look on to x1 & n ?r\gh x2 b 9 ! case ( ! glass t has to be %ap$ into a l5s ! purity is ( ! utmo/ importance4 ,! practical & sci5tific optician1 on 8 comm5cem5t to make an object-glass1 w gr9d ! two surfaces ( bo? fl9t & cr[n z ne>ly p>allel z possible1 & poli% !m4 ,9 ?is /ate he c ! bett] exam9e !m z to ve9s1 /ri1 & o!r defects1 :i* w\ld be fatal to any?+ made out ( x4 ,he has next to see t ! anneal+ is p]fectly done by exam9+ ! discs ) pol>iz$ light1 to see by ! abs5ce ( ! 8black cross0 t !re is no unequal t5sion4 ,x is s difficult to run ! gauntlet ?r\gh all ^! difficulties :5 ! ap]ture is consid]able t refractors ( =ty in*es' ap]ture may be p]haps despair$ ( = ye>s to come1 ?\gh ! glassmak] is will+ to try 8 "p4 ,next1 z to metallic specula4 ,z we are deal+ ) ! in/rum5ts t are n[ us$1 we w be cont5t ) consid]+ ! comp\nds t h be5 made successfully1 & omit ! v>iations :i* h nev] be5 br\ght into practice4 ,to put x r\ghly1 ! metal us$ = ,"l ,rosse's reflector consi/$ ( two p>ts ( copp] & "o "p ( t92 b "h we h an idea ( ! ,scylla & ! ,*>ybdis :i* are always pres5t 9 ^! inquiries4 ,if we use too mu* t91 :i* t5ds to give a surface ( brilliancy to ! speculum1 a few drops ( hot wat] p\r$ on x w be en\gh to %iv] x to atoms4 ,?is brittl5ess is objectionable1 & :at we h to d is to r$uce ! quantity ( t94 ,b !n comes ! ,*>ybdis4 ,if we d ?is1 ! col\r is no long] :ite1 b x is yell[1 & 9 addition we h introduc$ a surface t quickly t>ni%es in/ead ( a surface :i* rema9s bright4 ,! proportions :i* seem to answ] be/ are copp] sixty-f\r p>ts & t9 tw5ty-n9e4 ,"l ,rosse1 we believe1 uses #cagi p] c5t1 ( t92 or v ne>ly ! above proportions4 ,mr4 ,grubb 9 ! ,melb\rne mirrors us$ copp] & t9 9 ! proportion ( #cb to #adgg4 ,hav+ ! metal1 we h r\ghly to ca/ x 9 ! %ape ( a speculum1 b if an ord9>y ca/+ is made 9 a s& m\ld ! speculum metal is s spongy t we c d no?+ ) x4 ,if x is put 9 a close m\ld x w probably be ca/ v well1 b x w %iv] to atoms ) a v slight *ange ( temp]ature4 ,! difficulty 0 got ov] by ,"l ,rosse1 us+ an op5 m\ld call$ a 8b$ ( hoops20 ! bottom ( ! m\ld be+ compos$ ( /rips ( iron set edgeways1 held toge!r by an iron r+ & turn$ to ! prop] convexity2 s& is !n plac$ r\nd ! iron to =m ! edges1 ! metal is !n p\r$ 91 & ! bubbles & vap\rs run d[n ?r\gh ! small ap]tures at ! bottom ( ! m\ld1 s t ! speculum is fairly ca/4 ,mr4 ,lassell propos$ a diff]5t me?od1 :i* 0 introduc$ by ,mr4 ,grubb 9 8 arrangem5ts = ! ,melb\rne telescope4 ,in/ead ( hav+ ! bottom ( ! b$ ( hoops p]fectly horizontal x is slightly incl9$2 ! crucible1 :i* conta9s ! metal ( :i* ! speculum is to be ca/1 is !n br\ght up to x--! am\nt ( metal be+ some?+ "u two tons 9 ! case ( ! ,melb\rne telescope--& ! b$ ( ! m\ld is kept tipp$ up z ! metal is p\r$ into x1 & s arrang$ z to keep ! melt$ metal 9 contact ) "o side2 & z x gets full x is br\ght into a p]fectly horizontal position4 ,hav+ ca/ ! speculum1 ! next ?+ is to put x 9 an anneal+ ov51 rais$ to a temp]ature ( #a1jjj1 :]e x is all[$ to cool sl[ly = weeks till x has acquir$ ne>ly ! ord9>y temp]ature4 ,on be+ remov$ f ! ov5 ! speculum is plac$ on sev]al ?icknesses ( clo? & r\gh gr\nd on front1 back1 & edge4 ,hav+ got ! mat]ial r\ghly into =m we n[ pass on to see :at is done next4 ,9 ! case ( ! reflector1 :e!r ( metal or glass1 ! optician next attempts to get a p]fectly sph]ical surface ( ! prop] curvature = ! requir$ focus4 ,9 ! case ( ! refractor matt]s are some:at m complicat$2 we h !re f\r sph]ical surfaces to deal )1 & ! optician has "w to d ( q a diff]5t k9d be=e he ev5 comm5ces to gr9d4 ,presum+ ! refractive & disp]sive prop]ties ( ! glass n kn[n1 x w be necess>y to h a small bit ( glass ( ! same k9d to exp]im5t )4 ,t ! optician may make no mi/ake 9 ?is important matt]1 "s glass manufactur]s make ! discs ) project+ pieces to be cut (f2 ^! ! object-glass mak] works into prisms to det]m9e ! exact refraction & disp]sion1 includ+ ! position 9 ! spectrum ( ! ,fraunh(] l9es ,c & ,g1 = bo? ! cr[n & fl9t glass4 ,) ^! numb]s & ! desir$ focal l5g? he has all ! necess>y data = ! ma!matical op]ation ( calculat+ ! p[]s to be giv5 to ! two l5ses--fl9t & cr[n1 & ! radii ( curvature ( ! f\r surfaces 9 ord] t ! object-glass may be aplanatic or free f ab]ration bo? sph]ical & *romatic4 ,! problem is :at ma!maticians call an indet]m9ate "o1 z an inf9ite numb] ( diff]5t curvatures is possible4 ,assume1 h[ev]1 ! radius ( curvature ( "o surface1 & all ! re/ are limit$4 ,9 assum+ ! radius ( curvature on "o ( ! cr[n-glass surfaces1 x is well to avoid deep ones4 ,x is bett] to divide ! refraction ( ! f\r surfaces z equally z ! nature ( ! problem w admit1 z any little deviation f a true sph]ical figure 9 ! poli%+ w produce less effect 9 injur+ ! p]=mance ( ! object-glass f surfaces s arrang$ ?an if ! curves 7 deep4 ,b :atev] curves he *ooses he goes to "w s t ! sph]ical ab]ration ( ! comp\nd l5s %all be elim9at$ z f> z possible1 & ! *romatism 9 "o l5s %all be correct$ by ! o!r1 or 9 o!r words1 t :at is call$ ! second>y spectrum %all be z small z possible2 & x is to be fe>$ t ?is w nev] be aboli%$4#f ,illu/ration3 ,,fig4 #fd4--;,images ( planet produc$ by %ort & long focus l5ses ( ! same ap]ture giv+ images ( diff]5t size1 b ) ! same am\nt ( col\r r\nd ! edges4 ,?is matt] requires a some:at detail$ treatm5t 9 ord] t x may be se5 h[ ! f\r surfaces to :i* ref]5ce has be5 made are det]m9$4 ,! *romatic disp]sion1 9 ! case ( ! object-glass1 may be r\ghly /at$ to be measur$ by ab\t "o fiftie? ( ! ap]ture4 ,suppose = in/ance ! discs1 ,fig4 #fd1 to repres5t ! image ( any object1 say ! planet ,jupit]4 ,!n r\nd t planet we %\ld h a col\r$ fr+e1 & ! dim5sions ( t col\r$ fr+e1 t is1 ! jo9t ?ickness ( col\r at ,a & ,d1 w be f\nd by divid+ ! diamet] ( ! object-glass us$ by fifty4 ,n[ ?is is absolutely indep5d5t ( ! focal l5g? ( ! telescope2 !re=e "o way ( gett+ rid ( x is to increase ! focal l5g? ( telescopes2 & z ! size ( ! image dep5ds on focal l5g?1 & has no?+ :atev] to d ) ap]ture1 we may imag9e t ) ! same siz$ object-glass1 in/ead ( hav+ a little ,jupit] z on ! left ( ,fig4 #fd1 we may h a v l>ge ,jupit]1 due to ! increas$ focal l5g? ( ! telescope4 ,!n1 x may be ask$1 h[ ab\t ! *romatic ab]ration8 ,x w n be di/urb$4 ,! ap]ture ( ! object-glass rema9s unalt]$1 & !re is no m *romatic ab]ration "h ?an 9 ! fir/ case2 s t ! relation betwe5 ! visible planet ,jupit] & ! col\r r\nd x is *ang$ by alt]+ ! focal l5g?4 ,b z we h se51 we are able by means ( a comb9ation ( fl9t & cr[n glass to c\nt]act ?is disp]sion to a v great ext5t4 ,h[ !n ab\t sph]ical ab]ration8 ,up to ! pres5t we h assum$ t all rays fall+ on a convex l5s are br\ght to a po9t or focus1 b ?is is n /rictly true1 = ! edges ( a l5s turn ! rays r too mu* out ( _! c\rse1 s t !y w n come to a po9t2 j z ! rays reflect$ f a sph]ical mirror d n =m a s+le focus4 ,! m>g9al rays w be spread ov] a c]ta9 circul> surface1 j z ! col\r due to *romatic ab]ration cov]$ a surface surr\nd+ ! focus4 ,x 0 expla9$ t = ! same diamet] ( l5s ! circle ( col\r rema9$ ! same1 irrespective ( focal l5g?1 b 9 ! case ( sph]ical ab]ration ?is is n s2 x dim9i%es z ! squ>e ( ! focal l5g? increases2 t is to say1 if we d\ble ! focal l5g? we %all n only halve1 b half-halve1 or qu>t] ! ab]ration4 ,newton calculat$ ! size ( ! circle ( ab]ration 9 comp>ison ) t due to col\r1 & he f\nd t 9 ! case ( a l5s ( f\r in*es diamet] & t5 feet focus1 ! sph]ical ab]ration 0 eighty-"o & a half times less ?an t ( col\r4 ,x is f\nd t by alt]+ ! relative curvatures ( ! surfaces ( ! l5s1 ?is ab]ration c be correct$ )\t alt]+ ! focal l5g?2 = any numb] ( l5ses c be made ( diff]5t curvatures on ea* side b ( ! same ?ickness 9 ! middle1 s t !y h all ! same focal l5g?1 b ! "o1 hav+ "o surface ab\t ?ree times m convex ?an ! o!r1 w h lea/ ab]ration1 s t x is ! adaptation ( ! surfaces ( l5ses to ea* o!r t ex]cises ! art ( ! optician4 ,s f> we h got rid ( ?is ab]ration 9 a s+le l5s2 x c also be done 9 ! case ( a*romatic l5ses4 ,! foci ( ! two l5ses 9 an a*romatic comb9ation mu/ be> a c]ta9 relation to ea* o!r1 & ! curvatures ( ! surfaces mu/ also h a c]ta9 relation = sph]ical ab]ration4 ,9 ! a*romatic l5s !re are f\r surfaces1 two ( :i* c be alt]$ = "o ab]ration & two = ! o!r4 ,= in/ance1 9 ! case ( ! l5s1 ,fig4 #de1 :]e ! int]ior surfaces ( ! l5ses are cem5t$ toge!r1 al?\gh %[n sep>ate = cle>ness1 we f9d t if ! ext]ior surface ( ! cr[n d\ble convex l5s be ( a curvature /ruck by a radius #fgb units 9 l5g?1 & ! ext]ior surface ( ! fl9t glass l5s to a curvature due to a radius ( #a1dbj units1 ! l5s w be correct$ = sph]ical ab]ration1 & ^! conditions leave ! int]ior surfaces to be alt]$ s t ! relation betwe5 ! p[]s ( ! l5ses is su* z to give a*romatism4 ,! fl9t is z useful 9 correct+ ! sph]ical ab]ration z ! *romatic ab]ration2 = al?\gh ! relative ?icknesses ( ! fl9t & cr[n are fix$ 9 ord] to get a*romatism1 /ill we h by alt]+ bo? ! curvatures ( ea* l5s equally1 & keep+ ! same foci1 ! p[] ( alt]+ ! ext5t ( sph]ical ab]ration2 & x is 9 ! applications ( ^! two conditions t mu* ( ! high] art ( our opticians is ex]cis$4 ,we h n[ !re=e practically got rid ( bo? ab]rations 9 ! mod]n object-glass1 & h5ce x is t l5ses ( ! l>ge diamet] ( tw5ty-five & tw5ty-six in*es are possible4 ,! ne>e/ approa* to a*romatism is kn[n to be made :5 look+ at a /> ( ! fir/ or second magnitude1 ! eyepiece be+ pu%$ out ( focus t[>ds ! object-glass1 ! exp&$ disc has its m>g9 ( a cl>et col\r4 ,:5 ! eyepiece is pu%$ beyond ! focus outw>ds ! m>g9 ( ! exp&$ disc is ( a light gre5 col\r4 ,if ! object-glass is well correct$ = sph]ical ab]ration1 ! exp&$ discs bo? )9 & )\t ! focus w be con/itut$ ( a s]ies ( r+s equally d5se ) reg>d to light ?r\gh\t1 ) ! exception ( ! m>g9al r+1 :i* w be a little /rong] ?an ! re/4 99 99 99 99 99 ,hav+ det]m9$ ! radius ( curvature ( surface1 bo? he :o gr9ds ! speculum1 :e!r ( speculum metal or glass1 & he :o gr9ds ! object-glass1 />ts fair2 only "o has f\r times ! "w to d t ! o!r has4 ,! gr9d+ is manag$ 9 a simple way1 & ! process ( gr9d+ or poli%+ an object-glass or speculum1 ei!r ( glass or ( metal1 is ! same4 ,suppos+ we wi% to make a reflect+ telescope ( six feet focus1 or a surface ( an object-glass ( twelve feet radius1 all we h to d is to get a long rod1 a little m ?an twelve feet long1 & p9 x to a wall at its upp] end s t x c sw+1 p5dulum fa%ion2 !n at a di/ance ( twelve feet bel[ ! po9t ( susp5sion a p9 is /uck ?r\gh ! rod & its po9t made to scrat* a l9e on a %eet ( metal laid aga9/ ! wall2 !n ?is l9e w be "p ( a circle /ruck ) a radius ( twelve feet4 ,if !n ! plate be cut along ?is l9e we get a convex & a concave surface ( ! desir$ radius1 & !n we c take a block ( iron or brass & turn its surface1 convex or concave1 to fit ! %eet ( metal or template4 ,= a reflector we %\ld make a convex tool1 & = a refractor a concave "o4 ,g5]ally ?is gr9d+ tool is divid$ into squ>es or furr[s all ov] x1 9 ord] t ! em]y :i* is us$ 9 r\gh gr9d+ may fl[ freely ab\t ) ! wat]4 ,a disc ( glass is !n laid on ! tool1 or ! tool on ! glass1 ! two be+ press$ toge!r by a weight or spr+2 em]y p[d]1 ) wat]1 is /rewn betwe5 !m1 & "o is rubb$ ov] ! o!r by a ma*9e simil> to ^? us$ = poli%+1 :i* we %all expla9 pres5tly4 ,?is op]ation is cont9u$ until ! glass is gr\nd all ov]1 & 9 ?is process ( r\gh gr9d+ ! r\gh em]y is us$ betwe5 ! tool & ! glass1 s t :atev] irregul>ities ! glass or tool may h !y are got rid (1 & x is easy to obta9 a sph]ical surface1 & inde$1 x is ! only surface t c be obta9$4 ,!n f9] & f9] em]y is us$1 till x ceases to be a suffici5tly f9e sub/ance to use1 & a surface ( iron or lead is also too h>d a surface4 ,n[ ! poli%+ beg9s1 & ! optician & amateur avail !mselves ( a sugge/ion due to ,sir ,isaac ,newton1 :o always saw mu* fur!r ?r\gh ?+s ?an o!r p4 ,illu/ration3 ,,fig4 #fe4--,%[+ 9 an exagg]at$ =m h[ ! edge ( ! speculum is worn d[n by poli%+4 ,ev5 :5 he fir/ began to make ! fir/ reflector1 he us$ pit*1 a sub/ance n too h>d1 nor yet too s(t1 & "o t c be regulat$ by temp]ature2 !re=e = poli%+1 in/ead ( hav+ a tool made ( metal1 pit* laid on glass or wood & suppli$ ) r\ge & wat] is us$4 ,?is poli%] ( pit* is divid$ into squ>es by *annels to all[ free fl[ ( r\ge & wat]1 & is laid on ! mirror or object-glass1 or vice v]s1 & mov$ ab\t ov] x4 ,:5 ! maximum ( poli% is atta9$ ! "w is done1 & ! object-glass f9i%$1 z "h we h to d ) a sph]ical surface4 ,9 ! gr9d+ ( ! two discs = ,mr4 ,newall's telescope #a1efj h\rs 7 consum$1 ! ?ickness ( ! cr[n disc hav+ be5 r$uc$ "o in* 9 ! process4 ,9 ! case ( specula1 h[ev]1 !re is m to be done2 & x is 9 ?is poli%+ ( specula t ! curve is alt]$ f a circle to a p>abola by us+ a c]ta9 l5g? ( /roke1 size ( poli%]1 consi/5cy ( pit*1 & numb]s ( o!r small] matt]s1 ! prop] proportionm5t ( :i* con/itutes ! practical skill ( ! optician1 & x is 9 accompli%+ ?is t ! f9e/ niceties ( manipulation come into play1 & ! utmo/ pati5ce is requir$4 #a1agj h\rs 7 occupi$ 9 ! gr9d+ & poli%+ ( ! f\r-feet ,melb\rne speculum4 ,?is 0 equival5t to #b1jej1jjj /rokes ( ! ma*9e at #cc p] m9ute = r\gh & #bd = f9e gr9d+4 ,dr4 ,rob9son1 9 8 description ( ! gr9d+ op]ations1 /ates t at ! edge ( "o ( ! f\r-feet specula ! di/ance ( its p>abola f ! circle 0 only #jjjjajf4 ,9 ! e>ly times ( specula ! poli%+ 0 inv>iably done by h&1 a h&le be+ cem5t$ by pit* to ! back ( ! speculum to "w x )4 ,mudge tells u t at fir/1 :5 ! mirror 0 r\gh f ! em]y gr9d+1 x 0 work$ r\nd & r\nd on ! pit*1 :i* 0 suppli$ ) r\ge & wat] & cut by *annels into small squ>es1 c>ry+ ! edge b little ov] ! poli%]1 an occasional cross /roke be+ made4 ,! effect ( ?is 0 to press ! pit* t[>ds ! c5tre :]e ! poli% always comm5c$1 & gradually spread to ! circumf]5ce4 ,z soon z ! poli%+ 0 complete ! speculum 0 work$ by %ort /raight /rokes across ! c5tre1 t5d+ to br+ x back to a sph]e2 !n ! circul> /rokes 7 recomm5c$ to re/ore ! p>aboloid =m3 ^! 7 cont9u$ = a %ort "t only1 o!rwise x w\ld pass ! prop] curve & require rework+ ) /raight /rokes aga94 ,by ?is me?od "s small mirrors ( fir/-class def9ition 7 con/ruct$4 ,:5 ,sir ,w4 ,h]s*el began 8 lab\rs he con/ruct$ a ma*9e = work+ ! speculum ov] ! poli%]2 ! poli%] 0 a little l>g] ?an ! mirror1 ! proportion giv5 by him f a numb] ( trials be+ #ajf to #a4 ,! speculum 0 held 9 a circul> frame1 :i* 0 free to turn r\nd 9 ano!r r+ or frame2 ?is frame 0 mov$ backw>ds & =w>ds by a vibrat+ lev] to :i* x 0 atta*$ by rods1 c>ry+ ! speculum ov] ! poli%]4 ,?is motion he designates ! /roke4 ,besides ?is !re 0 ! side motion produc$ by a rod atta*$ to ! side ( ! frame opposite to t to :i* ! rods giv+ x ! /roke 7 atta*$ & at "r angles to ! direction ( /roke3 ?is rod 0 9 connection1 by means ( int]m$iate lev]s1 ) a p9 on a ra*et :eel1 :i* 0 turn$ a too? at a "t by a rod 9 connection ) ! lev] giv+ ! /roke motion1 s t ! rod giv+ ! side motion 0 pu%$ & pull$ back by ! p9 on ! ra*et :eel e "t x turn$ r\nd1 :i* x did e tw5ty or ?irty /rokes4 ,!re 7 also tee? on ! r+ fa/5$ r\nd ! edge at ! back ( ! speculum1 into :i* claws work$ :i* 7 atta*$ by rods to a po9t on ! lev] a little di/ance f ! atta*m5t ( ! rod giv+ ! /roke1 s t ! claws _h a less motion ?an ! speculum & its r+1 & consequ5tly pull$ ! r+1 & ) x ! speculum1 r\nd a too? or m at ea* /roke4 ,! poli%] 0 also turn$ r\nd 9 ! same mann] 9 a contr>y direction to ! motion ( ! speculum4 ,! speculum _h !re=e ?ree motions1 a revolv+ "o on its c5tre1 a /roke1 & a side motion1 mak+ its c5tre describe a numb] ( p>allel l9es ov] ! poli%] on ea* side ( its c5tre4 ,sir ,w4 ,h]s*el gives z a good work+ l5g? ( /roke1 #jbi1 & #jai side motion measur$ f side to side1 ! diamet] ( ! speculum be+ #a4 ,to produce a sev5-in* mirror ) ?is in/rum5t he w\ld "w cont9u\sly = sixte5 h\rs1 8 si/] 8putt+ ! victuals by bits into 8 m\?40 ,illu/ration3 ,,fig4 #fe994--,section ( ,"l ,rosse's poli%+ ma*9e4 ,"l ,rosse adopt$ a simil> arrangem5t2 ! poli%]1 ,k ,l1 ,fig4 #fe1 0 work$ ov] ! speculum 9 /raight /rokes ) side motion1 ! requisite /raight motion be+ giv5 by a crank-p9 & rod & ! side motion by ! cont9uation ( ?is latt] rod on ! o!r side ( ! poli%] work+ 9 a guide on ano!r crank-p91 :i* ?rew x f side to side z ! :eel c>ry+ ! p9 revolv$4 ,! tr\gh ,e ,f c>ry+ ! speculum also revolv$ sl[ly1 & ! requisite motions 7 giv5 by pulleys & /raps ( v>i\s sizes "u ! table on :i* ! ma*9e re/$2 ! weight ( ! poli%] 0 9 a great measure c\nt]pois$ by /r+s f its upp] surface to a weight$ lev] ,m above4 ,! poli%] 0 free to turn 9 its r+1 :i* x did once 9 ab\t tw5ty /rokes1 & = ! six feet speculum ! velocity ( work+ 0 ab\t eight /rokes a m9ute1 ! l5g? ( /roke be+ "o-?ird ( ! diamet] ( ! speculum1 & t ( ! side motion "o-fif?4 ,! speculum 0 poli%$ on ! same sy/em ( lev]s t 7 aft]w>ds to support x1 9 ord] t no *ange ( =m might be produc$ 9 mov+ x to a diff]5t m\nt+4 ,! consi/5cy ( ! pit* is a matt] ( importance1 ,mr4 ,lassell's te/ ( ! requisite h>dness be+ ! numb] ( impressions left by a sov]eign /&+ on edge on x2 ?is %\ld leave ?ree complete impressions ( ! mill$ edge 9 "o m9ute at ! ord9>y temp]ature ( ! atmosph]e4 ,illu/ration3 ,,fig4 #ff4--,mr4 ,lassell's poli%+ ma*9e4 ,fig4 #ff repres5ts ! ma*9e contriv$ by ,mr4 ,lassell = 8 me?od ( poli%+1 & %[s :at a complicat$ arrangem5t is ess5tial 9 ord] to arrive at any good result 9 ^! matt]s4 ,! speculum is plac$ on a b$1 & above x is a tra9 ( :eels t]m9at+ 9 a crank-p9 t gives motion to ! poli%]1 :i* is made to take a v devi\s pa? by ! motion ( ! :eels above4 ,! p9 giv+ motion to ! poli%] ,g at its c5tre c be set at a v>iable di/ance f ! axis ( ! l[e/ p9ion ,f to :i* x is atta*$1 by mov+ x 9 its slide1 s t :5 ! p9ion is turn$1 ! p9 & c5tre ( ! poli%] describe a circle4 ,! p9ion 9 "q is c>ri$ on a slide ,c above x1 atta*$ to ! ma9 v]tical driv+ %aft ,a1 s t z ! %aft revolves ! c5tre ( ! p9ion describes a circle ( a diamet] v>iable at pleasure by mov+ x 9 ! slide ,c1 ! result ( ! two motions be+ t ! c5tre ( ! poli%] describes circles ab\t a mov+ c5tre1 & consequ5tly 9 con/antly v>y+ positions on ! speculum4 ,motion is giv5 to ! v]tical %aft by ! cog-:eel & endless screw above1 work$ by "s prime mov]1 & z ! cog:eels on ! %aft ,e p>allel to ! ma9 %aft are c>ri$ r\nd ! latt] by ! arm ,d hold+ !m1 !y are caus$ to revolve by ge>+ into ! fix$ :eel ,b1 ?r\gh ! c5tre ( :i* ! ma9 %aft passes1 & !y 9 _! turn imp>t motion to ! p9ion c>ry+ ! p9 giv+ motion to ! poli%]4 ,! speculum is also ma9ta9$ 9 sl[ rotation by ! :eel & endless screw bel[ x4 ,! speculum & its supports are surr\nd$ by wat] conta9$ 9 a circul> tr\gh n %[n 9 ! engrav+1 s t ! consi/5cy ( ! pit* %all be con/ant4 ,?is arrangem5t1 pure & simple1 0 f\nd to br+ on ! poli% 9 r+s ov] ! speculum1 & z an improvem5t1 ! speculum1 or r ! sy/em ( lev]s support+ x1 0 c>ri$ on a plate :i* _h ! p[] ( slid+ backw>ds & =w>ds on ! :eel turn+ x r\nd2 ! edges ( ?is plate press$ aga9/ a fix$ roll]1 & x 0 made ( su* a %ape t z x revolv$ x 0 =c$ to take a side motion z its edges pass$ by ! fix$ roll]1 s t ! speculum _h a side motion 9 addition to ! rotatory "o4 ,mr4 ,de ,la ,rue improv$ on ?is by giv+ ! speculum a rotatory motion irrespective ( t ( ! slid+ plate1 s t ! side motion %\ld n always be along ! same diamet] ( ! speculum4 ,?is 0 done by all[+ ! speculum to turn freely on a pivot on ! slid+ plate1 & giv+ x a rotatory motion by means ( a cord go+ r\nd ! plate c>ry+ ! speculum supports4 ,z a fur!r improvem5t ,mr4 ,de ,la ,rue controls ! motion ( ! poli%] on ! c5tral p91 giv+ x motion by a crank c>ry+ a sy/em ( :eels 9 place ( ! l[e/ crank1 s t ! p9 gets a rotatory motion 9 addition to ^!4 ,mr4 ,grubb's arrangem5t = poli%+ is diff]5t4 ,! speculum is made to rotate1 ! poli%] is made to execute curves v>iable at pleasure by alt]+ ! ?r[ ( ! cranks :i* move rods atta*$ to ! c5tre ( ! poli%]1 giv+ x a motion simil> to t ( ,mr4 ,lassell's ma*9e4 ,! poli%] moves a little (f ! edge1 s t ! edge is worn d[n m ?an ! c5tre1 ?us giv+ ! p>abolic =m4 ,m4 ,f\cault1 ( :om we h already spok51 proce$s 9 a diff]5t mann] 9 p>abolis+ 8 glass mirrors4 ,he fir/ obta9s a sph]ical surface1 fairly reflective1 by gr9d+4 ,he !n alt]s ! surface to a p>aboloid =m by h&work1 only te/+ ! surface f "t to "t to asc]ta9 ! p>ts requir+ r$uction by ! poli%+ pad4 ,! me?od ( te/+ is z beautiful z x is simple4 ,! approximate e/imate ( ! curvature ( ! speculum is made by plac+ a small & well-def9$ object1 su* z ! po9t ( a p91 close to ! c5tre ( curvature & exam9+ its image =m$ close by its side ) a l5s4 ,z a nic] te/1 he places an object hav+ p>allel sides1 say a flat rul]1 ne> ! c5tre ( curvature1 & views its image ) ! nak$ eye at ! di/ance ( di/9ct vision1 !n ea* po9t ( ! edge is se5 by rays conv]g+ only f a small portion ( ! surface ( ! mirror1 ! rema9d] ( ! div]g+ cone f ea* po9t ( ! edge passes on beside ! eye1 & by mov+ ! eye ab\t1 any po9t ( ! edge c be se5 =m$ by rays proce$+ f any p>ticul> "p ( ! mirror1 viz41 t "p 9 l9e ) ! eye & po9t ( ! edge exam9$2 if ! curvature be n uni=m ! edge w appe> di/ort$1 & po9ts on x w appe> 9 diff]5t positions1 z rays f diff]5t p>ts ( ! mirror are receiv$ by ! eye z x is mov$1 mak+ ! edge appe> to move 9 waves4 ,f9ally1 he all[s light f a v small hole 9 a metal plate ne> ! c5tre ( curvature to fall on ! mirror1 & places ! eye j on ! side opposite to ! po9t :]e ! image is =m$1 s z to receive ! rays z !y div]ge aft] hav+ come to a focus4 ,! :ole ( ! light ?us passes into ! eye1 & ! mirror is se5 illum9at$ 9 e "p4 ,a %>p edge ( metal is !n gradually br\ght into ! focus1 :5 ! illum9ation ( ! mirror decreases1 & j be=e ! light disappe>s ! irregul>ities w pla9ly appe>1 %[+ !mselves by pat*es ( light1 :i* prove t ^? p>ts /ill bright are s incl9$ z to reflect ! rays by ! side ( ! true focus4 ,by mov+ ! metallic edge s z to advance ^u ! focus f all sides1 a v good idea ( ! irregul>ities may be obta9$4 ,if1 h[ev]1 ! surface be truly sph]ical1 ! light w disappe> regul>ly ov] ! :ole surface4 ,m4 ,f\cault comm5ces by mak+ ! surface truly sph]ical1 & !n by poli%+ (f 9 conc5tric circles1 increas+ ! poli%+ f ! c5tre1 an elliptic & at la/ a p>abolic curve is atta9$4 ,! ellipse is te/$ f "t to "t by remov+ ! p]=at$ plate fur!r & fur!r away f ! mirror until ! ellipse becomes practically a p>abola4 ,! great advantage ( ?is me?od is1 t ! effect ( ! poli%+ c be exam9$ z x proce$s1 & ! "w c always be appli$ :]ev] necess>y1 & ! te/ is entirely indep5d5t ( hot-air curr5ts :i* are se5 to fluctuate ov] ! mirror z waves ( light1 leav+ ! irregul>ities ( =m p]man5tly m>k$4 ,x fur!r appe>s t ! me?od may be v>i$ to =m a fir/-rate te/ ( a f9i%$ mirror already m\nt$2 = "o has no?+ to d b br+ a /> into ! field ( view1 & remove ! eyepiece1 & br+ ! eye into su* a position z to receive ! div]g+ rays f ! focus ( ! />4 ,a knife is !n gradually mov$ across 9 front ( ! eye1 say f ! "r2 !n if ! mirror comm5ces to get d>k5$ on ! "r side di/9ctly be=e ! left ! knife is on ! mirror side ( ! focus2 if1 h[ev]1 ! left side ( ! mirror becomes d>k5$ fir/ x is on ! eye side ( ! focus4 ,aft] a few trials x c be got to cut across ! focus & d>k5 ! mirror at all po9ts at once1 & %[ up all irregul>ities4 ,we h n[1 !n1 by "o sy/em or ano!r1 got our mirror1 ei!r ( speculum metal or ( glass1 & if ( ! latt] sub/ance we h to silv] x2 processes h be5 publi%$ by ,mr4 ,br[n+1 & ,m4 ,m>t91#g by :i*1 on ! plan propos$ 9 ! fir/ in/ance by ,liebig1 an extremely ?9 coat+ ( silv] is deposit$ on ! glass4 ,?is film is susceptible ( tak+ a high poli%1 :i*1 9 ! case ( small mirrors1 c be r5ew$ z (t5 z is wi%$ )\t repoli%+ ! mirror2 ! resilv]+ ( "o ( l>ge ap]ture h[ev] is a mo/ =midable affair4 ,to ^? :o wi% to silv] _! own mirrors1 let u say t x %\ld be done 9 summ]1 or 9 a room kept by a /ove at an equable summ] heat1 & ! silv]+ solution %\ld be kept = a day or m to settle1 & = probably "s *emical *ange to take place be=e ! r$uc+ solution is add$4 ,x w be f\nd easy en\gh to silv] ! small planes = ,newtonian reflectors1 b l>ge mirrors require mu* great] c>e & tr\ble4 ----- ,footnote #f3 ,pr(essor ,/okes & ,mr4 ,v]non ,h>c\rt "s "t ago made exp]im5ts ) phosphatic glass1 & "s ( ?is mat]ial 0 work$ into a l5s by ,mr4 ,grubb1 :o /ates t 8! result 0 successful s f> z ! obta9+ ( specim5s ( phosphatic glass ) rational spectra2 b phosphatic glass is almo/ unworkable1 & :5 ! exp]im5t 0 tri$ on a silice\s glass x fail$4 ,"s alleviation ( ?is second>y spectrum c be got by us+ a triple objective1 b )1 ( c\rse1 a correspond+ loss ( light40 ,footnote #g3 ,mr4 ,br[n+'s me?od ( silv]+ glass specula is z foll[s3-- ,prep>e ?ree /&>d solutions3 ,solution ,a ,cry/als ( nitrate ( silv] #ij gra9s ,dissolve4 ,di/ill$ wat] #d ounces ,solution ,b ,potassa1 pure by alcohol #a ounce ,dissolve4 ,di/ill$ wat] #be ounces ,solution ,c ,milk-sug> 79 p[d]7 ounce ,dissolve4 ,di/ill$ wat] #e ounces ,solutions ,a & ,b w keep1 9 /opp]$ bottles1 = any l5g? ( "t2 ,solution ,c mu/ be fre%4 ,to prep>e suffici5t = silv]+ an #h 94 speculum1 p\r two ounces ( ,solution ,a into a glass vessel capable ( hold+ ?irty-five fluid ounces4 ,add1 drop by drop1 /irr+ all ! "t 7) a glass rod71 z mu* liquid ammonia z is j necess>y to obta9 a cle> solution ( ! grey precipitate fir/ ?r[n d[n4 ,add f\r ounces ( ,solution ,b4 ,! br[n-black precipitate =m$ mu/ be j re-dissolv$ by ! addition ( m ammonia1 z be=e4 ,add di/ill$ wat] until ! bulk rea*es fifte5 ounces1 & add1 drop by drop1 "s ( ,solution ,a1 until a grey precipitate1 :i* does n re-dissolve aft] /irr+ = ?ree m9utes1 is obta9$2 !n add fifte5 ounces m ( di/ill$ wat]4 ,set ?is solution aside to settle2 d n filt]4 ,:5 all is ready = imm]s+ ! mirror1 add to ! silv]+ solution two ounces ( ,solution ,c1 & /ir g5tly & ?or\ghly4 ,solution ,c may be filt]$4 ,! mirror %\ld be susp5d$ face d[nw>ds ab\t -in* deep 9 ! liquid1 by /r+s atta*$ to pieces ( wood fa/5$ to ! back ( ! mirror ) pit*1 & be=e be+ imm]s$ %\ld be clean$ ) nitric acid & wa%$ ) di/ill$ wat]4 ,! silv]+ is complet$ 9 ab\t an h\r1 & :5 f9i%$ ! surface %\ld be wa%$ 9 di/ill$ wat] & dri$1 & !n poli%$ ) s(t lea!r1 f9i%+ ) a little r\ge4 ,! foll[+ me?od is us$ by ,m4 ,m>t93-- ,make solutions3 #a4 ,nitrate ( silv] #d p] c5t4 #b4 ,nitrate ( ammonia #f p] c5t4 p]fectly free #c4 ,cau/ic pota% #aj p] c5t4 f c>bonates4 #d4 ,dissolve tw5ty-five grammes ( sug> 9 #bej grammes ( wat]2 add ?ree grammes ( t>t>ic acid2 heat x to ebullition dur+ t5 m9utes to complete ! conv]sion ( sug>2 cool d[n1 & add fifty cubic c5timetres ( alcohol 9 summ] to prev5t f]m5tation1 add wat] to make ! volume to litre 9 w9t] & m 9 summ]4 ,clean well ! surface ( ! glass4 ,take equal quantities ( ! f\r solutions3 mix #a & #b toge!r1 & #c & #d also toge!r3 mix ! two1 p\r+ x at once into ! vessel :]e ! silv]+ is to be done4 ,! mirror is susp5d$ face d[nw>ds 9 ! liquid1 & ! deposit beg9s aft] ab\t ?ree m9utes1 & is f9i%$ aft] tw5ty m9utes4 ,take out ! mirror1 clean well ) wat]1 dry x 9 ! air1 & rub x !n g5tly ) a v f9e lea!r4 ,,*apt] ,,xi4 ,,! 8,,optick ,,tube40 ,hav+ n[ obta9$ ! l5ses & specula we come1 9 ord] to complete our consid]ation ( ! purely optical portion ( ! subject1 to ! "q ( m\nt+ ^! l5ses & specula 9 tubes & ?us connect+ !m ) ! eyepieces s z to become ( practical utility4 ,we w fir/ consid] ! adju/m5t ( l5ses 9 a tube1 ! comb9ation =m+ a simple telescope t c be support$1 9 any mann] desirable1 by m\nt+s we %all pres5tly consid]1 accord+ to ! purpose = :i* x is requir$4 ,! adju/m5t ( specula w be consid]$ z we advance fur!r4 ,! small] telescopes consi/ ( a brass tube1 ! object-glass1 held 9 a brass r+1 be+ screw$ 9 at "o end ( ! tube3 a small] tube slid+ 9 & out ( ! o!r end ( ! l>ge tube1 g5]ally mov$ by a rack & p9ion motion1 c>ries ! eyepiece4 ,9 l>g] telescopes ! m\nt+ is simil>1 only some:at m elaborate1 ! object-glass be+ c>ri$ 9 a brass cell1 or a /eel "o if ! dim5sions are v l>ge4 ,?is screws into ! r+ at ! end ( ! tube1 & ?is r+ c be slightly tipp$ on ei!r side by set screws1 s t ! object-glass c be br\ght exactly at "r angles to ! axis ( ! tube4 ,illu/ration3 ,,fig4 #fg4--,simple telescope tube1 %[+ arrangem5t ( object-glass & eyepiece4 ,x is important1 9 ord] t an object-glass %all p]=m its be/1 t ! l5ses =m+ x %all be prop]ly c5tr$3 ?is is g5]ally done by ! mak] once & = ev]4 ,wolla/on po9t$ out an +5i\s me?od ( c5tr+ !m2 x is z foll[s3--,! eyepiece is remov$1 & a light$ c&le put 9 its place3 ! object-glass is !n exam9$ f ! opposite side1 :51 if all ! l5ses are correctly plac$1 ! images ( ! c&le produc$ by ! successive reflections ( ! c&le f ! surfaces ( ! l5ses w be conc5tric1 & 9 a /raight l9e f ! c&le ?r\gh ! c5tre ( ! sy/em ( l5ses1 a fact easily judg$ (1 by mov+ ! eye slightly f side to side1 & if !y are n1 !y are easily correct$ by tipp+ ! l5s 9 fault slightly 9 ! cell4 ,9 case ! l5ses are cem5t$ toge!r1 ?is me?od ( c\rse is applicable 9 sett+ ! object-glass at "r angles to ! axis ( ! tube4 ,! adju/m5t ( an object-glass c also be judg$ ( by exam9+ a /> z x is ?r[n 9 & out ( focus by ! focus+ screw2 ! disc ( ! /> %\ld be p]fectly r\nd 9 & out ( focus1 & ! r+s produc$ by int]f]5ce %\ld also be circul> :5 9 focus1 & ! disc ( light1 :5 out ( focus1 mu/ be circul>4 ,any elongation ( ! disc or r+s1 or a 8fl>e0 appe>+1 %[s a want ( a slight alt]ation ( ! sett+ screw1 on ! same side ( ! object-glass z ! 8fl>e0 or elongation appe>s4 ,9 "s object-glasses ! curves ( ! two int]ior surfaces are su* t ?ree pieces ( t9 foil are plac$ at equal di/ances r\nd ! edge to prev5t ! c5tral portions f com+ 9 contact4 ,illu/ration3 ,,fig4 #fh4--;,appe>ance ( diffraction r+s r\nd a /> :5 ! object-glass is prop]ly adju/$4 ,illu/ration3 ,,fig4 #fi4--;,appe>ance ( same object :5 object-glass is out ( adju/m5t4 ,! flexure ( small object-glasses by _! own weight is ( little importance1 because e surface is affect$ alike2 b :5 ! ap]ture is l>ge special precautions h to be tak54 ,! late ,mr4 ,cooke :5 he _h complet$ ! #be-;in* object-glass = ,mr4 ,newall's telescope1 introduc$ a sy/em ( c\nt]poise lev]s j )9 ! edge :i* help$ to support ! object-glass 9 all positions4 ,mr4 ,grubb /ates t ) an ap]ture ( #ae in*es1 support$ on ?ree po9ts1 !re is decid$ evid5ce ( flexure1 & he proposes1 9 ! #bg-;in* ,vi5na refractor1 n only to introduce six int]m$iate supports1 !reby foll[+ 9 ! foot/eps ( ,mr4 ,cooke1 b ) l>g] ap]tures to introduce boldly a c5tral support1 or to h]metically seal ! tube & fill x ) compress$ air4 ,he has calculat$ t 9 ! case ( an object-glass #dj in*es ap]ture1 weigh+ #fjj lbs41 two-?irds ( its weight c\ld be support$ by an air pressure ( "o-?ird ( a p\nd to ! squ>e in*4 ,! tube ( ! telescope :5 ( l>ge size is usually made ( iron or wood1 & a tube ( ! latt] sub/ance may be made v light & yet suffici5tly /rong1 by wrapp+ lay]s ( v5e] r\nd a c5tral core & fa/5+ ! lay]s firmly ) glue4 ,!re are g5]ally two or m tubes slid+ inside ea* o!r at ! eye end ( ! telescope1 to c>ry ! eyepiece s z to give pl5ty ( p[] ( adju/m5t ( ! l5g? ( ! tube to suit ! diff]5t eyepieces1 or o!r in/rum5ts us$ 9 _! place4 ,! tube !n is ready to be adapt$ to any ( ! m\nt+s to be h]eaft] consid]$4 99 99 99 99 99 ,we n[ come to ! m\nt+ ( specula1 & :5 we recollect ! enorm\s weights ( "s ( ! specim5s to :i* we h ref]r$1 x w be obvi\s t "s additional precautions1 :i* are n at all necess>y 9 ! case ( a refractor1 mu/ be tak5 to insure success4 ,9 reflect+ telescopes1 ! speculum is c>ri$ at ! bottom ( a tube 9 a sort ( tray or cell1 :i* c be adju/$ by screws at ! back1 s z to set ! mirror at "r angles to ! tube1 & ! conditions ( support %\ld be su* t ! mirror %\ld be z free f /ra9 z if x 7 float+ 9 m]cury4 ,a sy/em ( lat]al supports 9 all positions is also necess>y4 ,! action ( ! telescope dep5ds greatly on ! back+ ( ! speculum1 & num]\s me?ods ( c>ry+ specula on s(t back+ & sy/ems ( lev]s h be5 sugge/$1 all aim+ at c>ry+ !m s t !y are free f all possible /ra9 & flexure occasion$ by _! own weight4 ,= small] mirrors a s(t back ( flannel or clo? c be us$1 & a lea!r /rap plac$ r\nd ! mirror & its back1 s z to =m ! side ( a sort ( circul> tray1 w give x suffici5t support :5 incl9$ to ! horizontal4 ,mr4 ,br[n+ adopts ! plan ( mak+ ! back ( ! mirror & its support p]fectly flat1 s z n to require lev]s or s(t back+2 ?is arrangem5t w\ld probably fail = mirrors l>g] ?an "o foot 9 diamet]1 al?\gh answ]+ admirably = ^? ( less size4 ,illu/ration3 ,,fig4 #gj4--,optical "p ( a ,newtonian reflector ( t5 in*es ap]ture1 %[+ eyepiece1 adju/+ screws = l>ge speculum1 f9d]1 door = uncov]+ speculum1 & c\nt]poise4 ,illu/ration3 ,,fig4 #ga4--,optical "p ( ,melb\rne reflector1 %[+ ! lattice arrangem5t = support+ ! convex mirror ,y1 ,t m solid "p ( tube fix$ to decl9ation axis1 ,w f9d]4 ,illu/ration3 ,,fig4 #gb4 ,mr4 ,br[n+'s me?od ( support+ small specula4 ,! bottom ( ! speculum ,a is a c>efully prep>$ plane surface1 & ! out] rim ( ! inn] iron cell ,b1 on :i* x re/s1 is also a plane4 ,! speculum is kept 9 ?is cell by ! r+ ,g ,g1 & x may be remov$ f1 & replac$ 91 ! telescope1 )\t alt]+ its adju/m5t4 ,we w n[ consid] ! me?ods ( m\nt+ specula ( l>g] size1 & w take z an in/ance ! m\nt+ ( "s ( ! l>ge/ specula 9 exi/5ce :i* mu/ act s z to prev5t flexure 9 any position ( ! speculum4 ,! speculum is1 9 ! case ( ! ,melb\rne telescope1 ( ! weight ( some?+ l two tons4 ,:5 x is incl9$ at any consid]able angle to ! horizon1 x is apt to b5d ov] at ! top1 & ?us de/roy its prop] curvature2 & :5 horizontal1 if n equally support$1 x w also b5d1 & unless "s measures are tak5 to prev5t ?is flexure x w s entirely alt] its figure by its own weight z to r5d] m9ute obs]vations ( any delicate />s absolutely impossible4 ,mr4 ,lassell 0 ! fir/ to sugge/ an arrangem5t = prev5t+ ?is flexure4 ,?r\gh ! back ( ! speculum case--! case :i* holds & supports ! speculum1 :i* we %all h to speak ab\t pres5tly--he ins]ts a l>ge numb] ( v small lev]s1 ! c5tres ( :i* are fix$ to ! ext]ior "p ( ?is case1 ! =w>d "p ( ea* re/+ aga9/ a small ap]ture made 9 ! back ( ! speculum4 ,! ends ( ! lev]s fur!/ f ! speculum are cr[n$ ) small weights1 ! weights v>y+ on diff]5t p>ts ( ! speculum4 ,n[ s long z ! speculum is p]fectly horizontal1 i4e4 s long z ! z5i? is be+ obs]v$1 ^! lev]s w h no action :atev]2 b ! mom5t ! reflector is br\ght into any o!r position1 z1 = in/ance1 :5 we wi% to obs]ve a /> ne> ! horizon1 ! m ! mirror is incl9$ to ! horizon ! great] w be ! p[] ( ^! small lev]s1 & at l5g? _! total effect comes into action :5 a /> close to ! horizon is be+ obs]v$4 ,!n ! :ole weight ( ! mirror is c>ri$ by ^! lev]s act+ at po9ts all ov] its back4 ,9 ! ,melb\rne reflector1 :i* has rec5tly be5 f9i%$1 ,mr4 ,grubb manages ?is some:at diff]5tly1 z w be se5 by ,figs4 #gc-gf4 ,9 ,fig4 #gc ! speculum is 9 a v]tical position4 ,x is support$ 9 a frame1 ,b ,b1 all r\nd x1 :i* consi/s ( a slightly flexible hoop ( metal a little l>g] ?an ! speculum4 ,?is 9 its turn is support$ by a l>ge fix$ hoop1 ,a ,a1 hav+ a hook-%ap$ section4 ,?is hoop is atta*$ to ! tube ( ! telescope ,c ,c4 ,! hoop1 ,b ,b1 is r l>g] ?an ! "p ( ,a on :i* x hangs1 s t x c adju/ itself to ! =m ( ! mirror2 & n only is ! mirror support$ 9 ! hoop ,b ,b1 l z 9 a /rap 9 ! position %[n1 b 9 e o!r position ( ! tube ! speculum /ill hangs ev5ly support$4 ,illu/ration3 ,,fig4 #gc4--,support ( ! mirror :5 v]tical4 ,z we h already se51 !re is ano!r po9t to consid]4 ,n only mu/ we be able to support ! mirror :5 incl9$ to ! horizon1 b we mu/ support x bodily at ! end ( ! tube :5 x is horizontal4 ,we w next exam9e an arrangem5t adopt$ by ,mr4 ,grubb1 simil> to t adopt$ by o!rs1 = support+ ! ,melb\rne speculum1 & we _c d bett] ?an quote ,mr4 ,grubb's own explanation ( x4 ,he says3-- 8,to und]/& x1 suppose ! speculum to be divid$ into =ty-eight portions1 z 9 ,fig4 #gd1 ea* ( !m be+ exactly equal 9 area1 & consequ5tly 9 weight4 ,n[1 if ! c5tre ( gravity ( ea* ( ^! pieces re/$ on po9ts :i* w\ld be> up ) a =ce ! weight ( ea* segm5tal piece1 x is evid5t t !re w\ld be no /ra9 9 ! mass f segm5t to segm5t4 ,illu/ration3 ,,fig4 #gd4--;,division ( ! speculum into equal areas4 8,?is is exactly :at is accompli%$ by ?is sy/em2 9 fact1 if :5 ! speculum is re/+ on ^! supports x c\ld be divid$ up into segm5ts correspond+ to ^? l9es1 !y w\ld h no incl9ation to leave _! places1 %[+ a p]fect abs5ce ( /ra9 across ^? l9es4 ,suppose n[ ! po9ts repres5t+ ! c5tres ( gravity ( ^! segm5ts 7 support$ on lev]s & triangles1 s z to c\ple !m toge!r1 z at ,a1 ,fig4 #ge1 & ea* ( ^! c\pl+s to be support$ f a po9t a1 repres5t+ ! c5tre ( gravity ( ! sum ( ! segm5ts support$ by t p>ticul> c\ple1 & x is evid5t t !re c be no /ra9 betwe5 ! compon5ts ( ^! c\ples4 ,aga91 let ^! po9ts1 a1 be c\pl$ toge!r by ! sy/em %[n at ,b1 ,fig4 #ge1 & _! c5tres ( gravity1 b1 c\pl$ z at ,c1 & x is evid5t t ! :ole weight ( ! speculum ultimately cond5s$ by ?is sy/em into ^! po9ts is support$ on =ty-eight po9ts ( equal support be+ ! c5tres ( gravity ( ! =ty-eight segm5ts at ,fig4 #ge4 ,9 ,fig4 #gf is se5 ! :ole sy/em complete4 ,x consi/s ( ?ree screws pass+ ?r\gh ! back ( ! speculum box 7:i* s]ve = levell+ ! mirror71 ! po9ts ( :i* c>ry lev]s 7prim>y sy/em7 support+ triangles on _! extremities 7second>y sy/em71 f ! v]tices ( :i* are hung two triangles & "o lev] 7t]ti>y sy/em74 ,all ! jo9ts ( ?is app>atus are capable ( a small rock+ motion1 to enable !m to take _! positions :5 ! speculum is laid ^u !m4 ,illu/ration3 ,,fig4 #ge4--,prim>y1 second>y1 & t]ti>y sy/ems ( lev]s %[n sep>ately4 ,illu/ration3 ,,fig4 #gf4--;,complete sy/em consolidat$ into ?ree screws4 8,9 ! sy/em ( lev]s made by ,"l ,rosse = 8 six-feet speculum1 ! prim>y1 second>y1 & t]ti>y sy/ems 7 pil$ up "o ov] ! o!r1 s t ! di/ance f ! support ( ! prim>y to ! back ( ! speculum 0 ab\t fifte5 in*es4 ,?is1 z w be readily se5 on consid]ation1 introduc$ a new /ra9 :5 ! telescope 0 turn$ (f ! z5i?1 & _h to be c\nt]pois$ by ano!r v complicat$ sy/em ( lev]s4 ,b 9 ! ,melb\rne telescope1 by ! sub/itution ( ca/-/eel = ca/-iron1 & by hang+ ! t]ti>y sy/em f ! second>y1 & all[+ x 7! t]ti>y7 to act 9 "s places ?r\gh ! second>y1 ! :ole sy/em is r$uc$ to ?ree & a half in*es 9 height1 & ! di/ance f ! support ( ! prim>y lev] to ! back ( ! speculum is only "o & ?ree-qu>t] in*1 by :i* means ?is cumb]some app>atus is entirely done away )4 8,! ultimate po9ts ( ! t]ti>y sy/em are gunmetal cups1 :i* hold truly gr\nd ca/-iron balls ) a little play1 & :5 ! speculum is laid on ^! x c be mov$ ab\t a little by a p]son's f+] ) su* ease z to seem to be float+ 9 "s liquid40 ,x may p]haps be ?\ght t x w\ld be bett] to support ^! great specula on a flat surface1 & x might be1 if we c\ld d s )\t extreme difficulty2 b ,"l ,rosse has /at$ t if we attempt to support a l>ge speculum on a surface extremely flat1 a ?read plac$ across t surface1 or ev5 a piece ( du/1 is q en\gh to b5d ! mirror & r5d] x absolutely useless4 ,t w %[ ! extreme importance ( ! support ( ! speculum4 ,let u !n assume t we h ! speculum & ! tube p]fectly adju/$4 ,! next ?+1 9 all con/ructions except ! ,h]s*elian1 is to apply ! second small reflector1 concave 9 ! case ( ! ,gregorian1 convex 9 ! case ( ! ,cassegra9ian1 & plane 9 ! case ( ! ,newtonian4 ,?is small mirror is g5]ally support$ by a ?9 /rip ( metal firmly fa/5$ to ! side ( ! tube1 ) p[] ( movem5t p>allel to ! axis ( ! telescope1 9 ! case ( ! ,gregorian & ,cassegra9ian1 = ! purpose ( focuss+4 ,9 ! ,newtonian1 ! reflect+ diagonal prism or plane mirror1 incl9$ at an angle ( #de to ! axis1 is pref]ably support$ 9 ! mann] sugge/$ by ,mr4 ,br[n+4 ,see ,figs4 #gg & #gh4 ,9 ^! ,b ,b ,b repres5t /rips ( /rong *ronomet] spr+ /eel1 plac$ edgewise t[>ds ! speculum2 by ^! ! prism or small mirror ,d is susp5d$4 ,! mirror ?us m\nt$1 does n produce su* co>se rays on bright />s z :5 x is fix$ to a s+le /\t arm2 x is also less liable to vibration1 :i* is v injuri\s to di/9ct vision1 or to flexure1 :i* int]f]es ) ! accuracy ( ! adju/m5ts4 ,illu/ration3 ,,fig4 #gg4--,support ( diagonal plane mirror 7,front view74 ,illu/ration3 ,,fig4 #gh4--,support ( diagonal plane mirror 7,side view74 ,! mo/ usual =m ( reflector is ! ,newtonian1 l>ge numb]s ( :i* k9d are n[ made2 & j z ! object-glasses ( refractors require adju/+1 s d n only ! l>ge mirror1 b also ! 8flat0 or diagonal mirror ( ?is =m4 ,9 ! ,newtonian ! flat mu/ be adju/$ fir/2 to d ?is1 fir/ place ! l>ge mirror 9 its cell 9 ! tube1 & secure x by turn+ x 9 ! bayonet jo9t1 ) ! cov] on ! mirror4 ,!n remove ! glasses f "o ( ! eyepieces1 ins]t x into ! eyetube1 & fix ! diagonal mirror loosely 9 its position4 ,!n1 look+ ?r\gh ! eyetube1 move ! diagonal mirror1 by means ( ! motions :i* are provid$1 until ! reflect$ image ( ! cov] ( ! speculum is se5 9 ! c5tre ( x4 ,?is is accompli%$ by fir/ loos5+ ! mill$-head$ screw beh9d ! mirror1 & turn+ ! mirror until ! image ( ! speculum cov] appe>s c5tral 9 "o direction4 ,! screw at ! back ( ! mirror enables ! reflect$ image to be br\ght c5tral 9 ! o!r direction4 ,next comes ! turn ( ! l>ge mirror4 ,take (f ! cov] by screw+ (f ! side op5+ & place ! eye at ! eyetube aft] hav+ remov$ ! eyepiece2 ! reflection ( ! diagonal mirror w be se5 9 ! reflect$ image ( ! speculum4 ,! adju/+ screws1 at ! back ( ! speculum1 mu/ !n be mov$ until ! diagonal mirror is se5 9 ! c5tre ( ! speculum4 ,! adju/m5t %\ld !n be complete4 ,?is may be judg$ ( by br++ a /> to ! c5tre ( ! field1 & slid+ ! focuss+-tube 9 or out1 :5 ! circle ( light %\ld exp& equally1 & its c5tre %\ld rema9 c5tral 9 ! field4 ,z ano!r te/ a bright /> %\ld be view$ ) a high p[]1 & ! image exam9$2 if x is r\nd & ! circles ( light r\nd x are conc5tric )\t rays 9 any "o direction1 !n all is correct2 b if a fl>e is se51 x is evid5ce t ! "p ( ! diagonal mirror t[>ds :i* ! fl>e ext5ds mu/ be mov$ f ! eye by ! sett+-screws at ! back4 ,,*apt] ,,xii4 ,,! ,,mod]n ,,telescope4 ,! ga9 to a/ronomy f ! discov]y ( ! telescope has be5 tw(old4 ,we h fir/1 ! ga9 to physical a/ronomy f ! magnification ( objects1 & secondly1 ! ga9 to a/ronomy ( position f ! magnification1 s to speak1 ( space1 :i* enables m9ute portions ( x to be mo/ accurately quantifi$4 ,look+ back1 no?+ is m curi\s 9 ! hi/ory ( a/ronomy ?an ! root$ objection :i* ,hevel & o!rs %[$ to apply ! telescope to ! po9t]s & p9nules ( ! in/rum5ts us$ 9 _! day2 b d\btless we mu/ look = ! explanation ( ?is n only 9 ! accuracy to :i* obs]v]s _h atta9$ by ! old me?od1 b 9 ! rude nature ( ! telescope itself 9 ! e>ly times1 be=e ! introduction ( ! micromet]4 ,we %all %[ 9 a future *apt] h[ ! mod]n accuracy has /ep by /ep be5 arriv$ at2 9 ! pres5t "o we h to see :at ! telescope does = u 9 ! doma9 ( t gr& physical a/ronomy :i* deals ) ! numb] & appe>ances ( ! v>i\s bodies :i* p space4 ,let u1 to beg9 )1 try to see h[ ! telescope helps u 9 ! matt] ( obs]vations ( ! sun4 ,! sun is ab\t n9ety millions ( miles away2 suppose1 !re=e1 by means ( a telescope reflect+ or refract+1 :i*ev] we l1 we use an eyepiece :i* w magnify say #ijj times1 we obvi\sly br+ ! sun )9 #ajj1jjj miles ( u2 t is to say1 by means ( ?is telescope we c obs]ve ! sun ) ! nak$ eye z if x 7 )9 #ajj1jjj miles ( u4 ,"o may say1 ?is is some?+1 b n mu*2 x is only ab\t half z f> z ! moon is f u4 ,b :5 we recollect ! enorm\s size ( ! sun1 & t if ! c5tre ( ! sun occupi$ ! c5tre ( our e>? ! circumf]5ce ( ! sun w\ld ext5d consid]ably beyond ! orbit ( ! moon1 !n "o mu/ ackn[l$ge we h done some?+ to br+ ! sun )9 half ! di/ance ( ! moon4 ,suppose = look+ at ! moon we use on a telescope a p[] ( #a1jjj1 t is a p[] :i* magnifies a ?\s& times1 we %all br+ ! moon )9 #bdj miles ( u1 & we %all be able to see ! moon ) a telescope ( t magnify+ p[] pretty mu* z if ! moon 7 situat$ some:]e 9 ,lanca%ire--,lanca/] be+ ab\t #bdj miles f ,london4 ,x might appe> at fir/ sight possible 9 ! case ( all bodies to magnify ! image =m$ by ! object-glass to an unlimit$ ext5t by us+ a suffici5tly p[]ful eyepiece4 ,?is1 h[ev]1 is n ! case1 = z an object is magnifi$ x is spread ov] a l>g] portion ( ! ret9a ?an be=e2 ! brightness1 !re=e1 becomes dim9i%$ z ! area increases1 & ?is takes place at a rate equal to ! squ>e ( ! increase 9 diamet]4 ,if1 !re=e1 we require an object to be l>gely magnifi$ we mu/ produce an image suffici5tly bright to be> su* magnification2 ?is means t we mu/ use an object-glass or speculum ( l>ge diamet]4 ,aga91 9 obs]v+ a v fa9t object1 su* z a nebula or comet1 we _c1 by decreas+ ! p[] ( ! eyepiece1 increase ! brightness to an unlimit$ ext5t1 = z ! p[] decreases1 ! focal l5g? ( ! eyepiece also increases1 & ! eyepiece has to be l>g]1 ! em]g5t p5cil is !n l>g] ?an ! pupil ( ! eye1 & consequ5tly a portion ( ! rays ( ! cone f ea* po9t ( ! object is wa/$4 ,illu/ration3 ,,fig4 #gi4--;,a portion ( ! con/ellation ,gem9i se5 ) ! nak$ eye4 ,we get an imm5se ga9 to physical a/ronomy by ! revelations ( ! fa9t] objects :i*1 )\t ! telescope1 w\ld h rema9$ invisible to u2 b1 z we "k1 z ea* l>ge telescope has exce$$ prec$+ ones 9 illum9at+ p[]1 ! =m] b\nds ( ! visible creation h be5 gradually ext5d$1 ?\gh ev5 n[ we _c be said to h got beyond c]ta9 small limits1 = !re are o!rs beyond ! region :i* ! mo/ p[]ful telescope reveals to u2 ?\gh we h got only into ! surface we h increas$ ! #c1jjj or #f1jjj />s visible to ! nak$ eye to some?+ l tw5ty millions4 ,?is space-p5etrat+ p[] ( ! telescope1 z x is call$1 dep5ds on ! pr9ciple t :5ev] ! image =m$ on ! ret9a is less ?an suffici5t to appe> ( an appreciable size ! light is app>5tly spread out by a purely physiological action until ! image1 say ( a />1 appe>s ( an appreciable diamet]1 & ! effect on ! ret9a ( su* small po9ts ( light is simply proportionate to ! am\nt ( light receiv$1 :e!r ! eye be assi/$ by ! telescope or n2 ! />s always1 except :5 suffici5tly bright to =m diffraction r+s1 appe>+ ( ! same size4 ,x1 !re=e1 happ5s t z ! ap]tures ( telescopes increase1 & ) !m ! am\nt ( light1 7! eyepieces be+ suffici5tly p[]ful to cause all ! light to ent] ! eye17 small] & small] />s become visible1 :ile ! l>g] />s appe> to get bright] & bright] )\t increas+ 9 size1 ! image ( ! brighte/ /> ) ! highe/ p[]1 if we neglect rays & diffraction r+s1 be+ really mu* small] ?an ! app>5t size due to physiological effects1 & ( ?is latt] size e /> mu/ appe>4 ,illu/ration3 ,,fig4 #hj4--,! same region1 z se5 ?r\gh a l>ge telescope4 ,! accompany+ woodcuts ( a region 9 ! con/ellation ( ,gem9i z se5 ) ! nak$ eye & ) a p[]ful telescope w give a bett] idea ?an m]e language c d ( ! effect ( ?is s-call$ space-p5etrat+ p[]4 ,illu/ration3 ,,fig4 #ha4--,orion & ! neighb\r+ con/ellations4 ,) nebul & comets matt]s are diff]5t1 = ^!1 ev5 ) small telescopes & l[ p[]s1 (t5 occupy an appreciable space on ! ret9a4 ,on increas+ ! ap]ture we mu/ also increase ! p[] ( ! eyepiece1 9 ord] t ! m div]g5t cones ( light f ea* po9t ( ! image %all ent] ! pupil1 & !re=e increase ! area on ! ret9a1 ov] :i* ! increas$ am\nt ( light1 due to great] ap]ture1 is spread2 ! brightness !re=e is n increas$1 unless inde$ we 7 at ! fir/ us+ an unnecess>y high p[]4 ,on ! o!r h&1 if we l5g!n ! focus ( ! object-glass1 & increase its ap]ture1 ! div]g5ce ( ! cones ( light is n increas$ & ! eyepiece ne$ n be alt]$1 b ! image at ! focus ( ! object-glass is increas$ 9 size by ! increase ( focal l5g?1 & ! image on ! ret9a also increases z 9 ! la/ case4 ,we may1 !re=e conclude t no comet or nebula ( appreciable diamet]1 z se5 ?r\gh a telescope hav+ an eyepiece ( j su* a focal l5g? z to admit all ! rays to ! eye1 c be made bright] by any increase ( p[]1 al?\gh x may easily be made to appe> l>g]4 ,illu/ration3 ,,fig4 #hb4--,nebula ( ,orion4 ,v beautiful draw+s ( ! nebula ( ,orion & ( o!r nebul1 z se5 by ,"l ,rosse 9 8 six-foot reflector1 & by ! ,am]ican a/ronom]s ) _! tw5ty-six in* refractor1 h be5 giv5 to ! _w4 ,! magnific5t nebula ( ,orion is sc>cely visible to ! nak$ eye2 "o c j see x glimm]+ on a f9e night2 b :5 a p[]ful telescope is us$1 x is by f> ! mo/ glori\s object ( its class 9 ! ,nor!rn hemisph]e1 & surpass$ only by t surr\nd+ ! v>iable /> ,args 9 ! ,s\!rn4 ,& al?\gh1 ( c\rse1 ! beauty & va/ness ( ?is /up5d\s & remote object increase ) ! increas$ p[] ( ! in/rum5t br\ght to be> ^u x1 a l>ge ap]ture is n ne$$ to r5d] x a mo/ impressive & awe-inspir+ object to ! behold]4 ,9 an ord9>y #e-;foot a*romatic1 _m ( its details are to be se5 "u fav\rable atmosph]ic conditions4 ,^? :o are desir\s ( /udy+ its appe>ance1 z se5 9 ! mo/ p[]ful telescopes1 are ref]r$ to ! plate 9 ,sir ,john ,h]s*el's 8,results ( ,a/ronomical ,obs]vations at ! ,cape ( ,good ,hope10 9 :i* all its features are admirably del9eat$1 & ! positions ( #aej />s :i* surr\nd 9 ! area occupi$ by ! ,nebula1 laid d[n4 ,9 ,fig4 #hb x is repres5t$ 9 great detail1 z se5 ) ! includ$ small />s1 all ( :i* h be5 mapp$ ) ref]5ce to _! positions & brightness4 ,?is !n comes f t p[] ( ! telescope :i* simply makes x a sort ( l>ge eye4 ,we may measure ! illum9at+ p[] ( ! telescope by a ref]5ce to ! size ( our own eye4 ,if "o takes ! pupil ( an ord9>y eye to be some?+ l ! fif? ( an in* 9 diamet]1 :i* 9 "s cases is an extreme e/imate1 we %all f9d t its area w\ld be r\ghly ab\t "o-?irtie? "p ( an in*4 ,if we take ,"l ,rosse's speculum ( six feet 9 diamet] ! area w be some?+ l #d1jjj in*es3 & if we multiply ! two toge!r we %all f9d1 if we lose no light1 we %\ld get #abj1jjj times m light f ,"l ,rosse's telescope ?an we d f our unaid$ eye1 ev]y?+ suppos$ p]fect4 ,let u consid] = a mom5t :at ?is means2 let u take a case 9 po9t4 ,suppose t ow+ to imp]fections 9 reflection & o!r matt]s two-?irds ( ! light is lo/ s t ! eye receives #dj1jjj times ! am\nt giv5 by ! unaid$ vision1 !n a six? magnitude />--a /> j visible to ! nak$ eye--w\ld h #dj1jjj times m light1 & x might be remov$ to a di/ance #bjj times z great z x at pres5t is & /ill be visible 9 ! field ( ! telescope1 j z x at pres5t is to ! unaid$ eye4 ,c we judge h[ f> (f ! />s are t are only j visible ) ,"l ,rosse's in/rum5t8 ,light travels at ! rate ( #ahe1jjj miles a second1 & f ! ne>e/ /> x takes "s #c ye>s = light to rea* u1 & we %all be )9 b\nds :5 we say t x w take light #cjj ye>s to rea* u f _m a six? magnitude />4 ,b we may remove ?is /> #bjj times fur!r away & yet see x ) ! telescope1 s t we c probably see />s s f> (f t light takes #fj1jjj ye>s to rea* u1 & :5 we gaze at ! heav5s at night we are view+ ! />s n z !y are at t mom5t1 b z !y 7 ye>s or ev5 hundr$s ( ye>s ago1 & :5 we call to our assi/ance ! telescope ! ye>s become ?\s&s & t5s ( ?\s&s--express$ 9 miles ^! di/ances become too great = ! imag9ation to grasp2 yet we actually look into ?is va/ abyss ( space & see ! laws ( gravitation hold+ good !re1 & calculate ! orbit ( "o /> ab\t ano!r4 ,:e!r ! telescope be ( ! fir/ or la/ ord] ( excell5ce1 its light-grasp+ p[]s w be practically ! same2 !re is !re=e a great di/9ction to be drawn betwe5 ! illum9at+ & def9+ p[]4 ,! =m]1 z we h se51 dep5ds ^u size 7& subsidi>ily ^u poli%71 ! latt] dep5ds ^u ! accuracy ( ! curvature ( ! surface4 ,illu/ration3 ,,fig4 #hc4--,saturn & 8 moons 7g5]al view ) a #c-;in* object-glass47 ,if ! def9+ p[] be n good1 ev5 if ! air be p]fect1 ea* increase ( ! magnify+ p[] s br+s out ! defects ( ! image1 t at la/ no details at all are visible1 all outl9es are blurr$1 or /ell> "* is lo/4 ,! te/+ ( a glass !re=e ref]s to two diff]5t qualities :i* x %\ld possess4 ,its quality z to mat]ial & ! f95ess ( its poli% %\ld be su* t ! maximum ( light %all be transmitt$4 ,its quality1 z to ! curves1 %\ld be su* t ! rays pass+ ?r\gh e "p ( its area %all conv]ge absolutely to ! same po9t1 ) a *romatic ab]ration n absolutely nil1 b suffici5t to surr\nd objects ) a fa9t violet light4 ,illu/ration3 ,,fig4 #hd4--;,details ( ! r+ ( ,saturn obs]v$ by ,tr\velot ) ! #bf-;in* ,wa%+ton ,refractor4 ,9 close d\ble />s !re=e1 or 9 ! m m9ute m>k+s ( ! sun1 moon1 or planets1 we h te/s ( its def9+ p[]2 & if ?is is equally good 9 ! in/rum5ts exam9$1 ! revelations ( telescopes z !y increase 9 p[] are ( ! mo/ amaz+ k9d4 ,a #c-;in* suffices to %[ ,saturn ) all ! detail %[n 9 ,fig4 #hc1 :ile ,fig4 #hd %[s u ! fur!r m9ute /ructure ( ! r+s :i* comes out :5 ! planet is obs]v$ ) an ap]ture ( #bf in*es4 ,9 ! matt] ( d\ble />s1 a telescope ( #b in*es ap]ture1 ) p[]s v>y+ f #fj to #ajj1 %\ld %[ ! foll[+ />s d\ble3-- ,pol>is4 ,piscium4 ,draconis4 ,arietis4 ,h]culis4 ,urs ,majoris4 ,gem9orum4 ,leonis4 ,cassiope4 ,a #d-;in* ap]ture1 p[]s #hj-abj1 reveals ! duplicity (-- ,orionis4 ,hydr4 ,botis4 ,leonis4 ,lyr4 ,urs ,majoris4 ,ceti4 ,gem9orum4 ,cassiope4 ,draconis4 ,a #f-;in*1 p[]s #bdj-cjj-- ,arietis4 #cb ,orionis4 ,ophiu*i4 #bj ,draconis4 ,gem9orum4 ,equulei4 ,h]culis4 ,botis4 ,an #h-;in*-- ,cygni4 #b ,&rom$4 ,sirius4 #ai ,draconis4 #b ,h]culis4 #b ,botis4 ,! 8spuri\s disk10 :i* a fix$ /> pres5ts1 z se5 9 ! telescope1 is an effect :i* results f ! passage ( ! light ?r\gh ! object-glass2 & x is ?is appe>ance :i* necessitates ! use ( ! l>ge/ ap]tures 9 ! obs]vation ( close d\ble />s1 z ! size ( ! />'s disk v>ies1 r\ghly speak+1 9 ! inv]se ratio ( ! ap]ture ( ! object-glass4 ,9 our climate1 :i* is n s bad z "s w\ld make x1 a #f- to an #h-;in* glass is d\btless ! size :i* w be f\nd ! mo/ con/antly useful2 a l>g] ap]ture be+ frequ5tly n only useless1 b hurtful4 ,/ill1 #d or #c in*es are ap]tures by all means to be enc\rag$2 & by object-glasses ( ^! sizes1 made ( c\rse by ! be/ mak]s1 views ( ! sun1 moon1 planets1 & d\ble />s may be obta9$1 suffici5tly /rik+ to set _m s]i\sly to "w z amateur obs]v]s1 & ) a prospect ( secur+ good1 useful results4 ,obs]vations %\ld always be comm5c$ ) ! l[e/ p[]1 gradually increas+ x until ! limit ( ! ap]ture1 or ( ! atmosph]ic condition at ! "t1 is rea*$4 ,! =m] may be tak5 z equal to ! numb] ( hundr$?s ( in*es :i* ! diamet] ( ! object-glass conta9s4 ,?us1 a #c-;in* object-glass1 if really good1 %\ld be> a p[] ( #cge on d\ble />s :]e light is no object2 ! planets1 ! ,moon1 c41 w be be/ obs]v$ ) a mu* l[] p[]4 7,see *apt] on eyepieces47 ,c>e %\ld be tak5 t ! object-glass is prop]ly adju/$4 ,& we may "h repeat t ?is may be done by obs]v+ ! image ( a l>ge /> out ( focus4 ,if ! light be n equally di/ribut$ ov] ! image1 or ! diffraction r+s are n circul>1 ! screws ( ! cell %\ld be c>efully loos5$1 & t "p ( ! cell t[>ds :i* ! r+s are ?r[n v g5tly tapp$ ) wood1 to =ce x t[>ds ! eyepiece1 or ! same purpose may be effect$ by means ( ! setscrews always pres5t on l>ge telescopes1 until p]fectly equal illum9ation is arriv$ at4 ,?is1 h[ev]1 %\ld only be done 9 extreme cases2 x is "h especially desirable t we %\ld let well alone4 ,! conv5i5t altitude at :i* ,orion culm9ates 9 ^! latitudes r5d]s x p>ticul>ly eligible = obs]vation2 & dur+ ! fir/ mon?s ( ! ye> our read]s :o w\ld te/ _! telescopes w d well n to lose ! opportunity ( try+ ! progressively difficult te/s1 bo? ( illum9at+ & sep>at+ p[]1 af=d$ by its v>i\s d\ble & multiple sy/ems1 :i* are collect$ toge!r 9 su* a circumscrib$ region ( ! heav5s t no ext5sive movem5t ( _! in/rum5ts--an important po9t 9 extreme cases--w be necess>y4 ,beg9n+ ) 1 ! upp] ( ! ?ree />s :i* =m ! belt1 ! two compon5ts w be visible 9 almo/ any in/rum5t :i* may be us$ = see+ !m1 be+ ( ! second & sev5? magnitudes1 & well sep>at$4 ,! companion to 1 ?\gh ( ! same magnitude z t to 1 is mu* m difficult to obs]ve1 9 consequ5ce ( its proximity to its bright prim>y1 a fir/-magnitude />4 ,qua9t old ,kit*5]1 9 8 "w on telescopes1 m5tions t ! companion to ,rigel has be5 se5 ) an object-glass ( #b-;in* ap]ture2 x %\ld be se51 at all ev5ts1 ) a #c-;in*4 1 ! bottom /> 9 ! belt1 is a capital te/ bo? ( ! divid+ & space-p5etrat+ p[]1 z ! two bright />s ( ! second & six? magnitudes1 ( :i* ! close d\ble is compos$1 are exactly #b ap>t1 :ile !re is a companion to "o ( ^! compon5ts ( ! twelf? magnitude ab\t di/ant4 ,! small /> bel[1 :i* ! late ,admiral ,smy?1 9 8 *>m+ book1 8,! ,cele/ial ,cycle10 m5tions z a te/ = 8 object-glass ( #ei in*es 9 diamet]1 is n[ pla9ly to be se5 9 a #c4 ,! col\rs ( ?is pair h be5 v>i\sly /at$2 ,/ruve dubb+ ! six? magnitude--:i*1 by ! way1 0 miss$ altoge!r by ,sir ,john ,h]s*el--8olivaceasubrubicunda40 ,t ei!r our mod]n opticians contrive to admit m light by means ( a sup]ior poli% imp>t$ to ! surfaces ( ! object-glass1 or t ! />s !mselves are becom+ bright]1 is aga9 evid5c$ by ! po9t ( light prec$+ "o ( ! brighte/ />s 9 ! sy/em compos+ 4 ,?is little tw9kl] is n[ always to be se5 9 a #c-;in*1 :ile ! same au?ority we h be=e quot$--,admiral ,smy?--speaks ( x z be+ ( v difficult vision 9 8 in/rum5t ( mu* l>g] dim5sions4 ,9 ?is v beautiful comp\nd sy/em !re are no less ?an sev5 pr9cipal />s2 & !re are sev]al o!r fa9t ones 9 ! field4 ,! upp] v fa9t companion ( is a delicate te/ = a #c-;in*1 :i* ap]ture1 h[ev]1 w readily divide ! clos] d\ble ( ! pr9cipal />s :i* are ab\t #e ap>t4 ,^! objects1 ) ! exception ( 1 h be5 giv5 m to te/ ! space-p5etrat+ ?an ! divid+ p[]2 ! telescope's action on #eb ,orionis w at once decide ?is latt] quality4 ,?is />1 j visible to ! nak$ eye on a f9e night1 to ! "r ( a l9e jo9+ & 1 is a v close d\ble4 ,! compon5ts1 ( ! six? magnitude1 are sep>at$ by less ?an two seconds ( arc1 & ! glass :i* %[s a good wide black division betwe5 !m1 free f all /ray light1 ! spuri\s disk be+ p]fectly r\nd1 & n too l>ge1 is by no means to be despis$4 ,!n1 aga91 we h a capital te/ object 9 ! great nebula to :i* ref]5ce has already be5 made4 ,! />1 to :i* we wi% to call especial att5tion1 is situate 7see ,fig4 #hb7 opposite ! bottom ( ! 8fauces10 ! "n giv5 to ! ind5tation :i* gives rise to ! appe>ance ( ! 8fi%'s m\?40 ,?is object1 :i* has be5 designat$ ! 8trapezium10 f ! figure =m$ by its pr9cipal compon5ts1 consi/s1 9 fact1 ( six />s1 ! fif? & six? 7 & 7 be+ excessively fa9t4 ,our previ\s rem>k1 relative to ! increas$ brightness ( ! />s1 applies "h ) great =ce2 = ! fif? escap$ ! gaze ( ! eld] ,h]s*el1 arm$ ) 8 p[]ful in/rum5ts1 & 0 n discov]$ till #ahbf1 by ,/ruve1 :o1 9 8 turn1 miss$ ! six? />1 :i*1 z well z ! fif?1 has be5 se5 9 mod]n a*romatics ( su* small size z to make all comp>ison ) ! giant telescopes us$ by ^! a/ronom]s ridicul\s4 ,sir ,john ,h]s*el has rat$ & ( ! twelf? & f\rte5? magnitudes--! latt] requires a high p[] to obs]ve x1 by reason ( its proximity to 4 ,bo? ^! />s h be5 se5 9 an ord9>y #e-;foot a*romatic1 by ,cooke1 ( #c-;in*es ap]ture1 a fact speak+ volumes = ! p]fection ( surface & poli% atta9$ by our mod]n opticians4 ,let u n[ try to =m "s idea ( ! p]fection ( ! mod]n object-glass4 ,we w take a telescope ( eight in*es ap]ture1 & t5 feet focal l5g?4 ,suppose we obs]ve a close d\ble />1 su* z ,urs1 !n ! images ( ^! two />s w be br\ght to a focus side by side1 z we h previ\sly expla9$1 & ! di/ance by :i* !y w be sep>at$ w be dep5d5t on ! focal l5g? ( ! object-glass4 ,if we ref] once aga9 to ,fig4 #ci we %all see t ?is di/ance dep5ds on ! focal l5g? & on ! angle subt5d$ by ! images ( ! />s at ! object-glass1 :i* is ( c\rse ! same z ! angle made by ! real />s at ! object-glass1 :i* is call$ _! angul> di/ance1 or simply _! di/ance1 & is express$ 9 seconds ( arc4 ,if we take a telescope t5 feet long & look at two />s #a ap>t1 ! angle w be #a2 & at t5 feet (f ! di/ance betwe5 ! two images w be some?+ l #b in*es1 & !re=e1 if ! angle be a second1 ! l9es w be ! #a_/cfjj? "p ( t1 or ab\t #a_/agjj? "p ( an in* ap>t1 s t 9 ord] to be able to see ! d\ble /> ,urs1 :i* is a #a />1 by means ( an eight-in* object-glass1 all ! surfaces1 ! #ej squ>e in*es ( surface1 ( bo? sides ( ! cr[n1 & bo? sides ( ! fl9t glass1 mu/ be s absolutely true & accurate1 t aft] ! light is seiz$ by ! object-glass1 we mu/ h ^? two />s absolutely p]fectly di/9ct at ! di/ance ( ! sev5te5 hundr$? "p ( an in*1 & 9 ord] to see />s ap>t1 _! images mu/ be di/9ct at "o-half ( ?is di/ance or at #a_/cdjj? "p ( an in* f ea* o!r4 ,we "k t bo? ) object-glasses & reflectors a c]ta9 am\nt ( light is lo/ by imp]fect reflection 9 ! "o case1 & by reflection f ! surfaces & absorption 9 ! o!r2 & 9 reflectors we h g5]ally two reflections in/ead ( "o4 ,?is loss is to ! di/9ct disadvantage ( ! reflector1 & x has be5 /at$ by au?orities on ! subject1 t1 light = light1 if we use a reflector1 we mu/ make ! ap]ture twice z l>ge z t ( a refractor 9 ord] to make up = ! loss ( light due to reflection4 ,b ,dr4 ,rob9son ?9ks t ?is is an extreme e/imate2 & ) ref]5ce to ! f\r-foot reflector :i* has rec5tly be5 con/ruct$1 & ( :i* m5tion has already be5 made1 he consid]s t a refractor ( #ccgc in*es ap]ture w\ld be probably some?+ l its equival5t if ! glass 7 p]fectly transp>5t1 :i* is n ! case1 & :5 ! ?ickness ( su* a l5s came to be consid]$1 x 0 calculat$ t in/ead ( its be+ equal to ! f\r-foot reflector1 x w\ld only be equal to "o ( #cg ( simil> con/ruction1 & t ev5 a refractor ( #dh in*es ap]ture1 if su* c\ld be made1 w\ld n come up to ! same siz$ reflector j ref]r$ to 9 illum9at+ p[]4 ,on ! assumption1 !re=e1 t no light is lo/ 9 transmission ?r\gh ! object-glass1 ,dr4 ,rob9son e/imates t ! ap]tures ( a refractor & a reflector ( ! ,newtonian con/ruction mu/ be> ! relation to ea* o!r ( #a to #adb4 ,9 small refractors ! light absorb$ by ! glass is small1 & !re=e ?is ratio holds approximately good1 b we see f ! example j quot$ h[ m ne>ly equal ! ratio becomes on an increase ( ap]ture1 until at a c]ta9 limit ! refractor1 ap]ture = ap]ture1 is surpass$ by its rival1 suppos+ ,dr4 ,rob]tson's e/imate to be correct4 ,b ) specula ( silv]$ glass ! reflective p[] is mu* high] ?an t ( speculum metal2 ! silv]$ glass1 be+ e/imat$ to reflect ab\t #ij p] c5t4#h ( ! incid5t light1 :ile speculum metal is e/imat$ to reflect ab\t #fc p] c5t42 b be ^! figures correct or n1 ! silv]$ surface has und\bt$ly ! great] reflective p[]2 &1 accord+ to ,sir ,j4 ,h]s*el1 a reflector ( ! ,newtonian con/ruction utilizes ab\t sev5-eigh?s ( ! light t a refractor w\ld d4 ,speak+ g5]ally1 refractors ( sizes usually obta9able are pref]able to reflectors ( equal & ev5 great] ap]ture = ord9>y "w2 z 9 addition to ! want ( illum9at+ p[] ( reflectors1 ! abs5ce ( rigidity ( ! m\nt+ ( ! speculum militates aga9/ its com=t ( manipulation4 ,9 treat+ ( ! "q ( ! future ( ! telescope1 we are liable to encroa* on ! doma9 ( op9ion & g beyond ! facts v\*$ = by evid5ce1 b !re are c]ta9 guid+ pr9ciples :i* are well wor?y ( discussion4 ,!re are ! two classes ( telescopes1 ! refractors & reflectors1 ea* possess+ advantages ov] ! o!r4 ,we may set out ) obs]v+ t ! light-grasp+ p[] ( ! reflector v>ies z ! squ>e ( ! ap]ture multipli$ by a c]ta9 fraction repres5t+ ! proportion ( ! am\nt ( reflect$ light to t ( ! total incid5t rays4 ,on ! o!r h&1 ! p[] ( ! refractor v>ies z ! squ>e ( ! ap]ture multipli$ by a c]ta9 fraction repres5t+ ! proportion ( transmitt$ light to t ( ! total incid5t rays4 ,n[ 9 ! case ( ! reflector ! reflect+ p[] ( ea* unit ( surface is con/ant :atev] be ! size ( ! mirror1 b 9 t ( ! refractor ! transmitt+ p[] decreases ) ! ?ickness ( ! glass1 r5d]$ requisite by increas$ size1 al?\gh = small ap]tures ! transmitt+ p[] ( ! refractor is great] ?an ! reflect+ p[] ( ! reflector2 /ill x is obvi\s t on increas+ ! size a /age mu/ be at la/ rea*$ :5 ! two rivals become equal to ea* o!r4 ,?is limit has be5 e/imat$ by ,dr4 ,rob9son to be #cedce in*es1 a size n yet rea*$ by our opticians by "s #aj in*es1 b object-glasses are increas+ in* by in*1 & x w\ld be ra% to say t ?is size _c be rea*$ )9 p]haps ! lifetime ( our pres5t work]s1 b up to ! pres5t limit ( size produc$1 refractors h ! advantage 9 light-grasp+ p[]4 ,! next po9t wor?y ( att5tion is ! "q ( p]man5ce ( optical qualities4 ,"h ! refractor und\bt$ly has ! advantage4 ,x is true t ! fl9t glass ( "s objectives gets attack$ by a sort ( t>ni%1 /ill1 t is n ! case g5]ally1 :ile1 on ! o!r h&1 metallic mirrors (t5 become consid]ably t>ni%$ aft] a few ye>s ( use1 & al?\gh repoli%+ is n a matt] ( any great difficulty 9 ! h&s ( ! mak]1 /ill x is a s]i\s drawback to be oblig$ to return mirrors e few ye>s to be repoli%$4 ,!re are1 h[ev]1 "s exceptions to ?is1 = !re are _m small mirrors 9 exi/5ce ^: poli% is good aft] _m ye>s ( cont9u\s use1 j z on ! o!r h& !re are _m object-glasses ^: poli% has suff]$ 9 a few ye>s1 b ^! are exceptions to ! rule4 ,! same rem>ks apply to ! silv]$ glass reflectors1 = al?\gh ! silv]+ ( small mirrors is n a difficult process1 ! matt] becomes exce$+ly difficult ) l>ge surfaces1 & inde$ at pres5t l>ge discs ( glass1 say ( f\r or six feet diamet]1 _c be produc$4 ,if1 h[ev]1 a process %\ld be discov]$ ( manufactur+ ^! discs satisfactorily & ( silv]+ !m1 !re are objections to !m on ! gr\nds ( ! bad conductivity ( glass1 :]eby *anges ( temp]ature alt] ! curvature to a fatal ext5t1 & !re is also a great t5d5cy = dew to be deposit$ on ! surface4 ,! next po9t to be consid]$ is ! g5]al suitability = obs]vatory "w1 & ?is dep5ds ^u ! quality ( ! "w requir$1 :e!r = measur+ positions1 z 9 ! case ( ! transit in/rum5t1 :]e p]man5cy ( m\nt+ is ( great importance1 or = physical a/ronomy1 :5 a /eady image = a "t is only requir$4 ,= ! fir/ purpose ! refractor has decid$ly ! advantage1 z ! object-glass c be fix$ v ne>ly immovably 9 its cell1 :]eas its rival mu/ ( necessity1 at lea/ ) pres5t appliances1 h a small1 yet 9 comp>ison consid]able1 motion4 ,aga91 ! refractor has ! advantage ov] ! o!r 9 n be+ ( s l>ge ap]ture :5 ( equal p[]1 s t ! di/urb+ effects ( air curr5ts is consid]ably less1 b ! me?od ( mak+ ! tubes ( op5 lattice-"w mat]ially r$uces ?is objection4 ,we h m5tion$ ! difficulty ( m\nt+ mirrors1 especially ( l>ge size1 b ?is has n[ be5 got ov] v p]fectly4 ,?is difficulty does n occur 9 ! m\nt+ ( object-glasses ( sizes at pres5t 9 use1 b :5 we come to deal ) l5ses ( "s #cj in*es diamet]1 ! pres5t simple me?od w 9 all probability be f\nd insuffici5t4 ,on ! o!r h& ! co/ ( mirrors is ( c\rse mu* less ?an t ( object-glasses1 a matt] ( consid]able importance4 ,! late ,m4 ,m]z1 on be+ ask$ z to price ( a #cj-;in* object-glass1 e/imat$ t1 if x 7 possible to make x1 its co/ w\ld be betwe5 #h1ejj & #i1jjj4 ,!re is "o great po9t ( advantage 9 ! use ( ! reflector 9 physical "w1--! abs5ce ( second>y spectrum2 b x is by no means c]ta9 t /ell> photography w n be m easy ) refractors4 ----- ,footnote #h3 ,sir ,john ,h]s*el1 9 8 "w on ! telescope1 gives ! foll[+ table ( reflective p[]s3-- ,aft] transmission ?r\gh "o surface ( glass n 9 contact #jieg ) any o!r surface ,aft] transmission ?r\gh "o common surface ( two glasses #ajjj cem5t$ toge!r ,aft] reflection on poli%$ speculum metal at a p]p5dicul> #jfcb incid5ce ,aft] reflection on poli%$ speculum metal at #de obliquity #jfij ,aft] reflection on pure poli%$ silv] at a p]p5dicul> #jije incid5ce ,aft] reflection on pure poli%$ silv] at #de obliquity #jiaj ,aft] reflection on glass 7ext]nal7 at a p]p5dicul> #jjdc incid5ce ,! effective light 9 reflectors 7irrespective ( ! eyepieces7 is z foll[s3-- ,h]s*elian 7,"l ,rosse's speculum metal7 ,a4 #jfcb ,newtonian 7bo? mirrors ditto7 ,b4 #jdcf ,newtonian 7small mirror or glass prism7 ,c4 #jfcb ,gregorian or ,cassegra9ian ,d4 #jcii ,a4 #jije ,! same telescopes1 all ! metallic ,b4 #jhbd reflections be+ f pure silv] ,c4 #jije ,d4 #jhai ,,book ,,iii4 ,,"t ,,& ,,space ,,measur]s4 ,,*apt] ,,xiii4 ,,! ,,clock ,,& ,,*ronomet]4 ,i4 ,,! ,,rise ,,& ,,progress ,,( ,,"t-,,keep+4 ,:5 we dealt ) ! a/ronomical in/rum5ts ( ,hipp>*us1 we saw t al?\gh ! a/rolabe :i* t great obs]v] us$ 0 ! g]m ( our mod]n in/rum5ts1 ! "t record$ by ,hipp>*us & ^? :o liv$ aft] him d[n to ! lat] times ( ! ,roman ,empire 01 z !y measur$ x1 a "t :i* w\ld be entirely useless = u4 ,! anci5ts cont5t$ !mselves ) divid+ ! int]val betwe5 sunrise & sunset1 reg>dless :e!r ?is 0 9 summ] or w9t]1 into twelve equal h\rs4 ,n[1 z 9 summ] ! sun is long] above ! horizon ?an 9 w9t] 9 ^! nor!rn latitudes1 we h m "t dur+ :i* ! sun is above ! horizon 9 summ] ?an 9 w9t]1 & if t p]iod ( "t is to be divid$ into twelve h\rs1 ! h\rs w\ld be mu* long] 9 summ] ?an 9 o!r seasons4 ,z we are in=m$ by ,h]odotus1 tables 7 made by :i* ^! v>y+ l5g?s ( h\rs might be indicat$ by ! %ad[s ( a pole1 :i* !y call$ a gnomon or /yle4 ,?is 0 plac$ 9 a giv5 locality1 & ! h\r ( ! day 0 det]m9$ by ! position ( ! %ad[ ( ! gnomon2 & we ne$ sc>cely say t z ,hipp>*us obs]v$ he 0 compell$ to f9d ! position ( ! sun 9 ord] to det]m9e ! absolute longitude ( a /> at night4 ,! anci5ts 7 limit$ to su* ideas ( "t z c\ld be got f slaves1 :o wat*$ ! ris+s & sett+s ( ! con/ellations1 & :o tri$ to br+ to _! own m9ds & ^? ( _! ma/]s "s idea ( ! lapse ( "t2 & ?is ev5 a few c5turies ago 0 ord9>ily dep5d$ ^u 9 sev]al c\ntries4 ,!n1 a little lat]1 we come to ! "t be+ measur$ by monks repeat+ psalms--a c]ta9 numb] p]haps 9 ! h\r2 & !re 7 ! wat] & s& clocks dat+ f ,ari/ophanes1 :i* 7 ! pr$ecessors ( our s&-glasses4 ,c&les 7 also at "o "t us$ ) divisions on !m to %[ h[ long !y _h be5 burn+4 ,b :5 we come to clocks prop]1 ! hi/ory ( :i* is v imp]fectly kn[n1 we f9d an enorm\s improvem5t ^u ?is /ate ( ?+s2 because ! clock1 be+ dep5d5t ^u a con/ant me*anical action produc$ by ! fall ( a weight1 c\ld n be got to imitate ^! v>y+ h\rs4 ,/ill ! clock _h to fight its own battle = all t2 & ! fir/ clocks 7 alt]$ f week to week1 or f mon? to mon?1 s t ! "t-keep]1 :i* did its be/ to be con/ant1 0 made incon/ant to repres5t ! ev]-v>y+ h\rs4 ,d\btless ! hi/ory ( ! fir/ clocks--by :i* we d n mean ! s& clocks or wat] clocks ( ! anci5ts1 b su* z ^? us$ by ,ar*im$es :5 he atta*$ :eels toge!r--is lo/ 9 obscurity2 & :e!r clocks1 z we h !m1 7 sugge/$ 9 ! six? 7,boe?ius1 ,a4,d4 #ebe7 or n9? c5tury matt]s little = our inquiry2 b beyond all d\bt ! fir/ clock ( consid]able importance t 0 put up 9 ,engl& 0 ! "o erect$ 9 ,old ,palace ,y>d 9 ! ye> #abhh1 z ! result ( a f9e impos$ ^u ! ,"l ,*ief ,ju/ice ( t "t4 ,illu/ration3 ,,fig4 #he4--;,anci5t ,clock ,escapem5t4 ,if we h a fall+ weight z a "t-measur] we mu/ also h "s oppos+ =ce--a regulator 9 fact1 s t ! weight becomes ! s\rce ( p[]1 & ! regulator ! "t-measur]2 !re=e1 9 addition to ! fall ( ! weight1 we f9d 9 ! e>lie/ clocks a regulat+ p[] to prev5t ! weight fall+ too fa/4 ,s we h ! two cont5d+ p[]s1 fir/ ! weight caus+ ! motion & !n ! regulator4 ,! fir/ ?+ :i* 0 introduc$ z a regulator 0 a fly-:eel4 ,!re 0 a fly-:eel ( a c]ta9 weight1 & ! =ce :i* 0 appli$ to ! clock _h to turn ! :eel aga9/ ! resi/ance ( ! air2 b t did n answ] well1 & ! fir/ tol]able arrangem5t 0 sugge/$ by ,h5ry de ,wyck1 :o con/ruct$ a bell & a clock 9 #acfd1 9 :i* ! fall ( ! weight 0 prev5t$ by an oscillat+ balance1 simil> to t %[n 9 ,fig4 #he4 ,illu/ration3 ,,fig4 #hf4--,! ,cr[n ,:eel4 ,"h we see :at is call$ ! cr[n :eel 7,s ,s1 %[n 9 plan1 ,fig4 #hf71 on :i* ! escapem5t dep5ds1 & into ! tee? ( :i* "w two pallets1 ,p#a ,p#b1 :i* are plac$ on a v]tical axis pivot$ above & bel[4 ,n[ if we suppose a weight atta*$ to ! cord pass+ ov] a drum1 s z to propel ! int]m$iate :eels & pull !m r\nd1 ! cr[n :eel t5ds to rotate1 b is prev5t$ f mov+ until ! pallets give way4 ,let u see h[ ! clock goes4 ,:5 ! bottom too?1 presses aga9/ ! pallet ,p#a1 9 ord] to make x get out ( ! way & enable ! :eel to g on1 x twi/s ! rod & moves ! horizontal b> ,m ,m1 on :i* are sev]al saw-l tee?1 on ! int]vals ( :i*1 z 9 ! mod]n /eely>d1 weights are plac$1 s t ! :eel pu%es away ! pallet & makes ! horizontal beam describe a "p ( a circle4 ,& :at happ5s is ?is3--! upp] pallet is turn$ out ( its position & driv5 into ! upp] tee? ( ! :eel1 & driv5 out by ! fur!r revolution ( ! :eel1 s t ! fall ( ! weight dep5ds on ! oscillations ( ! horizontal beam :i* c>ries ! weights4 ,! clock 0 regulat$ by ! di/ance ( ! weights f ! pivots on :i* ! balance swung4 ,su* 0 ! =m ( clock us$ by ,ty*o ,brahe1 b ) little success1 = x 0 extremely irregul> 9 its action1 & ,ty*o /ill _h to comp>e ! position ( "o /> ) ano!r in/ead ( tru/+ to 8 clock4 ,!re is no necessity to say mu* reg>d+ ! tra9 ( :eels betwe5 ! weight or spr+ & ! escapem5t4 ,_! (fice is simply to create a great diff]5ce 9 velocity ( rotation betwe5 ! :eel turn$ by ! weight or spr+ & ! escape :eel1 s t a sl[ motion ) great =ce may be trans=m$ into a quick motion ) small =ce4 ,! tra9 ( :eels is s arrang$1 by ! consid]ation ( ! numb] ( tee? 9 ! :eels1 t "o :eel %all g r\nd once an h\r1 & ano!r once a m9ute1 s t ! fir/ may c>ry ! m9ute-h& & ! o!r ! second-h&4 ,! h\r-h& :eel is also ge>$ to ! m9ute-:eel1 s t x %all turn once 9 twelve h\rs or tw5ty-f\r h\rs1 accord+ to ! purposes = :i* ! clock is requir$4 ,weights are usually us$ :5 space is no object1 be+ m regul> 9 _! action ?an spr+s2 b ! latt] are us$ = *ronomet]s & wat*es1 & o!r portable "t-keep]s4 ,! g5]al arrangem5t ( ! clock tra9 is %[n 9 ,fig4 #hg1 :]e ,w is ! weight1 hung by a cord pass+ ov] ! b>rel ,b1 on ! axis ( :eel ,g4 ,! tee? ( ! :eel ,g ge> into ! p9ion ,p#a1 :i* aga9 is c>ri$ on ! axis ( ! :eel ,c1 & s on up ! la/ :eel--! escape-:eel1 :i* g5]ally is cut to ?irty tee?1 s t x goes r\nd once a m9ute & c>ries a second-h&4 ,! p9ion ,p#a is s arrang$ by ! numb] ( tee? betwe5 x & ! escape-:eel t x goes r\nd once an h\r or to sixty turns ( ! escape-:eel4 ,illu/ration3 ,,fig4 #hg4--,! ,clock ,tra94 ,illu/ration3 ,,fig4 #hh4--,w9d+ ,arrangem5ts4 ,to w9d up ! clock ! b>rel ,b1 ,fig4 #hh1 is turn$ r\nd by ! key on ! squ>e2 ! pawl ,l fa/5$ to ! :eel ,g all[s ! b>rel to be turn$ 9 "o direction )\t turn+ ! :eel4 ,x is obvi\s1 h[ev] t directly we beg9 to w9d up1 ! pressure on ! pawl t5d+ to turn ! :eel ,g is remov$1 & ! clock /ops--a v objectionable ?+ 9 a/ronomical & o!r clocks suppos$ to keep good "t4 ,! foll[+ is "o ( ! devices = keep+ ! clock go+ dur+ w9d+1--9 ?is case ev]y?+ is ! same z be=e1 ) ! exception ( an additional ra*et-:eel ,r#b1 ,fig4 #hh1 c>ry+ ! pawl ,l2 ?is :eel is loose on ! axis b atta*$ to ! :eel ,g ?r\gh ! spr+ ,s4 ,! weight !re=e acts on ! pawl ,l1 & t5ds to drive ! :eel ,r#b1 :i* aga9 presses r\nd ! :eel ,g by means ( ! spr+ ,s1 &1 z ! :ole moves r\nd1 ! tee? ( ! :eel ,r#b pass ! pawl ,k ,k fix$ to "s "p ( ! clock-frame4 ,:5 n[ we comm5ce to w9d1 ! pressure on ! pawl ,l & :eel ,r#b is remov$1 & ! spr+ ,s ,s1 :i* is always kept b5t by ! action ( ! weight1 endeav\rs to op52 & s9ce ! :eel ,r#b is prev5t$ f go+ backw>ds by ! pawl ,k1 ! :eel ,g is cont9ually urg$ onw>ds by ! spr+1 & ! clock kept go+ = ! %ort p]iod ( w9d+4 ,,ii4 ,,! ,,p5dulum4 ,! clock1 z left by ,h5ry de ,wyck1 0 only an exce$+ly irregul> "t-keep]1 & "s me*anical contrivance t %\ld beat or m>k correct int]vals ( "t 0 urg5tly requir$4 ,! contrivance = beat+ correct int]vals ( "t--! p5dulum--0 ?\ght ( by ,galileo1 :o %[$ t its oscillations 7 iso*ron\s1 al?\gh _! l5g?s might v>y )9 small limits4 ,! p5dulum !n 0 j ! v ?+ requir$1 & ,huygh5s1 9 #afeh1 appli$ x to clocks4 ,9 ! next =m ( clock1 !re=e1 we f9d ! p5dulum introduc$ z a regulator4 ,!re 0 a cr[n :eel l ! "o 9 ! balance clock1 only in/ead ( be+ v]tical x 0 horizontal4 ,?is :eel 0 all[$ to g r\nd & ! weight 0 all[$ to fall by means ( alt]nat+ pallets2 x 0 9 fact l t %[n 9 ,fig4 #hf1 ) ! balance weights & ! rod c>ry+ !m remov$1 & in/ead !re( !re 0 a rod1 atta*$ at "r angles to ! end ( t c>ry+ ! pallets1 & hang+ d[nw>ds1 :i*1 by means ( a =k at its l[] end1 swung a p5dulum to an ext5t equal to ! g ( ! balance fir/ us$4 ,?us ! p5dulum 0 adapt$ by ,huygh5s4 ,we h "h some?+ extremely diff]5t f ! r\gh arrangem5t 9 :i* ! weight 0 controll$ by ! horizontal oscillat+ b> c>ry+ ! weights1 = ! balance w\ld g fa/] or sl[] z ! cr[n :eel press$ h>d] or s(t] aga9/ ! pallets1 & s1 if ! weight act$ at all irregul>ly ! clock w\ld g badly4 ,b ) ! p5dulum ! control ( ! weight ov] x is small1 = ! bob c be made ( consid]able weight1 because x sw+s f its susp5d+ spr+ )\t friction1 & su* a heavy weight at ! end ( a long rod is sc>cely alt]$ 9 its rate by v>iations ( pressure on ! pallets4 ,galileo & ,huygh5s :o foll[$ him f\nd t ! oscillations ( a simple p5dulum are iso*ron\s at all places :]e ! =ce ( gravity is equal1 & t ! "t ( oscillation dep5ds on ! l5g? ( ! p5dulum--! %ort] ! p5dulum ! %ort] "t ( oscillation1 & vice v]s4 ,! "t ( oscillation v>y+ z ! squ>e root ( ! l5g?4 ,9 #afeh1 !n1 ! p5dulum 0 appli$ to clocks1 z ! balance _h be5 be=e t "t4 ,b ,huygh5s 0 n sl[ to p]ceive t ! circul> arc ( a rigid p5dulum w\ld n be suffici5tly accurate = an a/ronomical "t-keep]1 :5 us$ ) a clock l t employ$ by ,ty*o ,brahe & ! ,l&grave ( ,hesse = _! a/ronomical obs]vations4 ,huygh5s next %[$ t ) a clock ( t k9d1 requir+ a l>ge sw+ ( p5dulum1 ! oscillations 7 n q iso*ron\s1 b v>i$ 9 "t accord+ z ! arc increas$ or dim9i%$4 ,x 0 cle> !re=e t ?is simple =m ( p5dulum w\ld n d well = ! l>ge & v>y+ arc requir$ to be describ$1 b t ! !oretical requirem5ts w\ld be satisfi$ if ! p5dulum1 in/ead ( be+ susp5d$ f a rigid rod1 7 susp5d$ by a cord or spr+ or "s ela/ic sub/ance :i* w\ld m\ld itself aga9/ two curv$ pieces ( metal1 ,c ,c1 ,fig4 #hi1 atta*$ "o on ei!r side ( ! susp5d+ spr+4 ,9 sw++1 ! spr+ w\ld wrap1 z x 71 gradually r\nd ei!r curv$ surface1 & s virtually alt] ! po9t ( susp5sion1 & ) x1 ( c\rse1 ! virtual l5g? ( ! p5dulum2 s t ! extreme po9t ( ! p5dulum ,u1 in/ead ( describ+ a circul> arc ,k ,b z be=e1 w\ld1 by means ( ! portions ( metal at ! top1 h a cycloidal motion ,d ,l1 ! p5dulum becom+ virtually %ort] z ! spr+ wrapp$ r\nd ! pieces ( metal1 s t x becomes iso*ron\s = any l5g? ( sw+4 ,b x 0 v soon f\nd t ! !oretically p]fect clock did n aft] all g z well z ! clock x 0 to replace4 ,& x w\ld n[ be difficult to say :at w\ld h happ5$ if a few ye>s aft]w>ds clocks _h n be5 made mu* m simple & p]fect by ! introduction ( an entirely new escapem5t :i* p]mitt$ a v small sw+4 ,illu/ration3 ,,fig4 #hi4--,! ,cycloidal ,p5dulum4 ,if we wi% a clock to g p]fectly well1 we h only to consid] a v few ?+s--,fir/1 ! weight %\ld be z small z possible2 secondly1 )9 reason1 ! p5dulum %\ld be z solidly susp5d$ & z heavy z possible2 &1 ?irdly1 ! less connection !re is betwe5 ! p5dulum :i* controls ! clock1 & ! weight :i* drives ! clock1 ! bett]4 ,! latt] po9t is provid$ = 9 ! dead beat arrangem5t ( ,graham1 & 9 ! 8gravity0 & o!r =ms ( escapem5t1 ab\t :i* m pres5tly4 ,at pres5t we h be5 deal+ ) p5dulums z if !y 7 simple p5dulums1 :i* are almo/ ma!matical ab/ractions4 ,ev]y?+ t we h said assumes t !re is a mass dep5d+ f su* a f9e l9e t ! mass ( ! l9e %all n be consid]$2 b if we exam9e ! p5dulum ( "s clocks we see t ! rod is ( /eel1 & t its weight or bob is elongat$1 & consi/s ( a long cyl9d] ( glass fill$ ) m]cury1 & c>ri$ 9 a sort ( /irrup ( /eel2 ?is is v diff]5t f our simple p5dulum--x is a comp\nd p5dulum4 ,9 a comp\nd p5dulum we h fir/ ( all ! axis ( susp5sion1 :i* is ! axis :]e ! p5dulum is support$ on ! top1 & bel[ t1 ne> ! c5tre ( gravity ( ! p5dulum1 we h :at is call$ ! c5tre ( oscillation4 ,x w at once be p]ceiv$ t z ! rate ( ! p5dulum dep5ds ^u its l5g?1 ! p>ticles 9 ! upp] "p ( ! p5dulum w be try+ to g m rapidly ?an !y c g1 see+ t !y are connect$ 9 "o s]ies ( p>ticles1 & t ! p>ticles at ! l[e/ portion are c>ri$ ) great] velocity ?an !y w\ld be if !y 7 left to !mselves1 because !y are connect$ rigidly ) ! upp] ones4 ,!re=e we h to f9d a po9t1 :i* oscillates at ! same rate z x w\ld if all ! o!r p>ticles 7 abs5t4 ,?is is call$ ! c5tre ( oscillation1 & x is on ! di/ance ( ?is f ! po9t ( susp5sion t ! rate dep5ds4 ,:at is ! use ( ! m]cury8 ,x is to comp5sate = ! expansion ( ! rod by temp]ature4 ,we %all at once see ! reason ( ?is f ! fact t ! p5dulum gets long] by be+ heat$1 & ! rate ( ! p5dulum dep5ds on ! squ>e root ( its l5g?2 t is1 if we multiply ! l5g? by f\r1 ! squ>e root ( :i* is two1 we %all only multiply ! rate by two1 or d\ble ! "t ( oscillation4 ,!re=e1 s9ce temp]ature causes all metals to v>y 9 l5g?1 & metals are ! mo/ useful ?+s we c employ = ! support ( ! weights1 we f9d t we h to consid] fur!r ! alt]ation ( ! l5g? ( ! p5dulum due to ! v>iation ( ! l5g? ( ! metal we employ4 ,h5ce1 9 addition to ! necessity ( an arrangem5t :i* gives ! %orte/ possible sw+1 we require also a me?od = comp5sat+ = *anges ( temp]ature4 ,illu/ration3 ,,fig4 #ij4--;,graham's1 ,h>rison's1 & ,gre5wi* ,p5dulums4 ,we h n space to g ?r\gh ! hi/ory ( comp5sat+ p5dulums1 b we may direct att5tion to "s ( ! be/ results :i* h be5 obta9$ 9 ?is matt]4 ,we w fir/ exam9e ! m]curial p5dulum1 ,fig4 #ij1 :i* we h ref]r$ to4 ,9 ?is case ! comp5sation is accompli%$ z foll[s3 ,m]cury is inclos$ 9 a glass cyl9d] ,m ,m2 %[n 9 ! left h& side ( ! figure2 & z ! m]cury exp&s m ?an ! glass1 x w rise to a high] level on be+ heat$2 & ! l5g!n+ ( ! /eel rod ,r ,r w be c\nt]act$ by a simil> l5g!n+ due to ! expansion ( m]cury1 s t ! c5tre ( oscillation is c>ri$ d[n by ! /eel rod1 & up by ! m]cury1 & x is !re=e n displac$ if ! prop] ratio is ma9ta9$ betwe5 ! l5g? ( ! /eel rod & ! column ( m]cury 9 ! glass vessel4 ,! m]cury 9 ! glass w l5g!n fifte5 times z mu* z ! /eel rod1 if we h equal l5g?s ( ea*1 s t 9 ord] t !y may exp& equally ! rod mu/ be fifte5 times z long z ! m]cury column4 ,?is w\ld keep ! top ( ! m]cury at ! same di/ance f ! po9t ( susp5sion1 b we want to keep ! c5tre ( oscillation1 :i* is ab\t half way d[n ! column1 at ! same di/ance1 s we d\ble ! height ( ! m]cury1 mak+ x two-fifte5?s ( ! l5g? ( ! /eel rod1 s t ! surface is ov]-comp5sat$1 b ! c5tre ( oscillation is exactly correct$4 ,an a/ronom] c alt] ! am\nt ( m]cury z he pleases1 mak+ x n[ m1 n[ less1 till ! />s tell him he has done ! "r ?+1 & ! p5dulum is comp5sat$1 & ! clock keeps correct "t at all temp]atures4 ,! little slid+ cup ,c is to c>ry small weights = f9al delicate adju/m5t1 ! addition ( a weight ?us obvi\sly t5d+ to increase ! rate ( ! p5dulum4 ,?is is ,graham's m]curial p5dulum1 inv5t$ by him 9 #agae4 ,!re is ano!r comp5sat+ p5dulum1 call$ ,h>rison's gridiron p5dulum1 f ! b>s ( metal su/a9+ ! p5dulum be+ arrang$ gridiron fa%ion1 ,fig4 #ij4 ,at ! top is a knife edge or spr+ = ! c5tre ( susp5sion1 & ! p5dulum bob is susp5d$ by a sy/em ( rods1 ! five black ones be+ made ( a less expansible metal ?an ! o!r f\r2 consequ5tly1 z ! five black ones exp& & t5d to l[] ! bob1 ! int]m$iate ones exp& also & t5d to raise x2 ! l5g? ( ! black rods exce$+ t ( ! o!rs1 ^! latt] mu/ be made ( a m expansible metal to make up = _! small] l5g?4 ,?us ! act+ l5g? ( ! %ad$ rods is two-?irds ( ! act+ l5g? ( ! black ones 7ea* pair is consid]$ z "o rod because !y act z su*71 s t a metal is us$ = ! =m] :i* exp&s m ?an t us$ = ! latt] 9 ! proportion ( ab\t ?ree to two1 & brass is f\nd to answ] = ! mo/ expansible metal1 & /eel = ! less4 ,^! rods are pack$ side by side1 & look v ornam5tal4 ,if l be ! l5g? ( ! brass rods1 & l t ( ! /eel rods1 & e ! coeffici5t ( expansion ( ! brass1 & e t ( ! /eel1 !n l3 l33 e3 e4 ,! p5dulum is !n comp5sat$1 & ! bob rema9s at ! same di/ance f ! c5tre ( susp5sion at all temp]atures4 ,= ! p5dulum ( ! clock at ! ,royal ,obs]vatory a modification ( ! gridiron =m has be5 adopt$2 = x 0 f\nd on trial ) a m]curial p5dulum t ! /eel rod ga9$ 9 temp]ature m rapidly ?an ! m]cury1 & lo/ heat quick]1 s t ! p5dulum did n comp5sate imm$iately on a *ange ( temp]ature4 ,! =m adopt$ is z foll[s 7,fig4 #ij73--;,a /eel rod is susp5d$ z usual1 & is encircl$ by a z9c tube re/+ on ! nut = rat+ ! p5dulum2 ! z9c tube is aga9 encircl$ by a /eel tube re/+ on ! top ( ! z9c tube & c>ry+ at its l[] end a cyl9drical lead5 bob atta*$ at its c5tre to ! /eel tube2 slots & holes are cut 9 ! tubes to expose ! inn] p>ts to ! air1 s t ea* w exp]i5ce ! *ange ( temp]ature at ! same "t4 ,x is ( c\rse possible t ! tubes =m+ ! p5dulum rod are n ( exactly ! "r l5g? to p]fectly comp5sate2 a f9al delicate adju/m5t is !re=e add$4 ,on ! crut* axis1 & held by a coll> to x1 are two comp\nd b>s ( brass & /eel1 h & i1 ,fig4 #if4 ,! coll> fits loosely on ! axis1 s t ! rods1 :i* c>ry small weights at _! extremities1 c be easily %ift$ to make any angle ) ! horizontal2 !n1 s9ce brass exp&s m ?an /eel = ! same degree ( heat1 ! b>s w b5d on be+ heat$ or cool$1 & if ! brass be upp]mo/ ! weights at ! ends ( ! rods w be l[]$ ) an increase ( temp]ature1 & w t5d to increase ! rate ( ! p5dulum1 & vice v]s4 ,s long z ! rods are horizontal & 9 ! same /raight l9e _! c5tre ( gravity is 9 ! crut* axis1 & !y are !re=e balanc$ 9 e position2 !y !re=e only ret>d ! p5dulum by _! in]tia2 b :5 ! ends are b5t d[n ! c5tre ( gravity is l[]$1 & !y h a t5d5cy to come to a horizontal position & to balance ea* o!r l a scale beam1 & s sw+ ) ! p5dulum & ov]come its ret>dation4 ,x is obvi\s t !y w\ld1 if alone1 sw+ 9 a %ort] "t ?an ! p5dulum & s1 be+ connect$1 !y increase its rate4 ,:5 ! rods are v]tical !y h no comp5sat+ action1 = ! c5tre ( gravity is simply ?r[n sidewise1 & acts z a cont9u\s =ce t5d+ to make ! p5dulum oscillate fur!r on "o side ?an on ! o!r2 & 9 ! int]m$iate positions ( ! rods _! action v>ies1 & a consid]ation ( ! position ( _! c5tre ( gravity w give ! int5sity ( ! comp5sat+ action4 ,9 ord] to make a small *ange 9 ! rate ( ! clock )\t /opp+ x to turn ! screw at ! bottom ( ! p5dulum1 ! foll[+ contrivance is adopt$4 ,a weight k slides freely on ! crut* rod1 b is tapp$ to receive ! screw cut on ! l[] portion ( ! sp9dle l1 ! upp] end ( :i* t]m9ates 9 a nut m at ! crut* axis4 ,by turn+ ?is nut ! position ( ! small weight on ! crut* rod is alt]$1 & ! clock rate correspond+ly *ang$4 ,to make ! clock lose1 ! weight mu/ be rais$4 ,!re is also ano!r me?od ( comp5sation1 dep5d+ on diff]5tial expansion4 ,atta*$ to an ord9>y p5dulum j above ! bob1 & at "r angles to x1 is a composite rod1 made ( copp] & iron1 ! l[] half be+ copp]2 !n1 z ! p5dulum rod l5g!ns & lets d[n ! bob1 ! copp] exp&s m ?an ! iron1 & causes ! rod to b5d1 l a piece ( wood wett$ on "o side1 & by ?is b5d+ or w>p+ ! weights at ei!r end are rais$ z ! bob is l[]$1 s ! c5tre ( oscillation keeps at ! same height at all temp]atures4 ,we h dealt ) clocks & p5dulums some:at 9 ! ord] ( _! inv5tion4 ,we may add t ! great majority ( clocks ( mod]n manufacture ( any pret5tion to "t-keep]s are con/ruct$ ) ! dead beat escapem5t ( ,graham or a modification ( x1 comb9$ ) a m]curial or gridiron p5dulum4 ,= ! be/ ,obs]vatory clocks ( ! m exp5sive k9d o!r m elaborate =ms ( escapem5t are sometimes us$1 z1 = example1 t 9 ! clock at ! ,royal ,obs]vatory1 ,gre5wi*1 :i* we %all ref] to 9 detail fur!r on1 on acc\nt ( o!r new po9ts 9 its con/ruction4 ,n[1 hav+ a clock good en\gh to use ) ! transit in/rum5t1 x is necess>y to take ! utmo/ precautions ) ref]5ce to x4 ,! ,russian a/ronom]s h inclos$ _! clock 9 a /one case1 & plac$ x _m y>ds bel[ ! gr\nd1 endeav\r+ ?us to get rid ( ! action ( temp]ature1 :i* *anges ! l5g? ( ! /eel p5dulum rod4 ,b t is n all2 aft] we h correct$ our clock z well z we c f ! po9t ( view ( temp]ature1 x is /ill f\nd t !re may be a v>iation1 am\nt+ to some?+ consid]able1 due to ano!r cause4 ,if ! b>omet] *anges an in* or an in* & a half by *ange ( pressure ( ! air1 ! rate ( ! p5dulum w alt]1 & ! cause ( ! v>iation x is impossible to prev5t )\t putt+ ! clock 9 a vacuum1 s t *anges ( ! b>omet] mu/ be all[$ =4 ,!re are1 h[ev]1 me?ods ( comp5sat+ ! p5dulum = *anges ( pressure if desirable3 "o way ( do+ ?is is to pass ! susp5d+ spr+ ( ! p5dulum ?r\gh a slit 9 a metal plate1 :i* !n becomes virtually ! po9t ( susp5sion2 ?is plate is !n rais$ or l[]$ by an an]oid b>omet]1 or by a float 9 an ord9>y ci/]n b>omet] s t ! l5g? ( ! p5dulum is virtually alt]$ ) ! pressure ( ! atmosph]e4 ,at ,gre5wi* ! ,a/ronom]-,royal has adopt$ ! foll[+ exp$i5t3 ,a magnet at ! l[] end ( ! p5dulum passes at ea* sw+ ne> a magnet :i* is rais$ or l[]$ by means ( a float 9 ! ci/]n ( a b>omet]4 ,! magnet !n has a great] or less influ5ce on ! p5dulum magnet accord+ z ! pressure ( ! air v>ies1 & s adds a v>iable am\nt to ! effect ( gravity & !re=e to ! rate ( oscillation4 ,illu/ration3 ,,fig4 #ia4--;,gre5wi* ,clock3 arrangem5t = ,comp5sation = ,b>ometric ,pressure4 ,?is pr9ciple is c>ri$ out z foll[s3--,two b> magnets1 ea* ab\t six in*es long1 are fix$ v]tically to ! bob ( ! clock p5dulum2 "o 9 front1 a1 ,fig4 #ia1 ! o!r at ! back4 ,! l[] pole ( ! front magnet is a nor? pole2 ! l[] pole ( ! back magnet is a s\? pole4 ,bel[ ^! a horse-%oe magnet1 b1 hav+ its poles precisely "u ^? ( ! p5dulum magnets1 is c>ri$ transv]sely at ! end ( ! lev] c1 ! extremity ( ! opposite arm ( ! lev] be+ atta*$ by ! rod d1 to ! float e 9 ! l[] leg ( a syphon b>omet]4 ,! lev] turns on knife edges4 ,a plan ( ! lev] 7on a small] scale7 is giv51 z well z a section ?r\gh ! po9t ,a4 ,weights c be add$ at f to c\nt]poise ! horse-%oe magnet4 ,! rise or fall ( ! m]curial b>omet] correspond+ly raises or depresses ! horse %oe magnet1 &1 increas+ or decreas+ ! magnetic action betwe5 its poles & ^? ( ! p5dulum magnets1 comp5sates1 by ! *ange ( rate produc$1 = t aris+ f v>iation 9 ! pressure ( ! atmosph]e4 ,! %ort] leg ( ! b>omet] 9 :i* ! float re/s has an area ( f\r times t ( ! b>omet] tube at ! upp] surface ( ! m]cury1 s t = a l>ge *ange ( b>ometric height ! magnet is only mov$ a small di/ance1 a *ange ( "o in* ( ! b>omet] l[]+ ! surface 9 ! %ort leg #b_/aj in*2 ! di/ance betwe5 ! p5dulum magnets & ! horse-%oe magnets is #c in*es4 ,,iii4 ,,escapem5ts4 ,! inv5tion ( ! p5dulum1 its application1 & ! improvem5ts !reon hav+ be5 describ$1 x rema9s to treat ( ! equally important improvem5ts on ! escapem5t4 ,! fir/ *ange = ! bett] appe>s to h be5 due to ,hooke1 :o 9 #afff br\ght be=e ! ,royal ,society ! crut*1 or an*or escapem5t1 :]eby ! arc ?r\gh :i* ! p5dulum vibrat$ 0 s mu* r$uc$ t ,huygh5s's cycloidal curves became unnecess>y1 & ! p[] requir$ to drive ! clock 0 mat]ially r$uc$4 ,?is escapem5t1 common 9 ord9>y eight-day clocks1 is diff]5t f t previ\sly describ$ 9 ! way 9 :i* ! cr[n :eel or escape :eel is regulat$4 ,we h come back to a v]tical escape :eel z x 0 9 ! clock us$ by ,ty*o2 b in/ead ( us+ two pallets on a rod :i* regulat$ ! :eel1 we h "h an an*or escapem5t 7,fig4 #ib7 9 connection ) ! p5dulum2 & :at happ5s is ?is--:5 ! p5dulum is made to oscillate1 ^! pallets ,p ,p gradually move 9 & out ( ! tee? ( ! :eel1 & let a too? pass at e sw+2 & x is obvi\s t :5 ! :eel & an*or are nicely adju/$1 an extremely small motion ( ! an*or1 & consequ5tly a small oscillation ( ! p5dulum1 all[s ! escape :eel to turn r\nd1 & ! clock to g4 ,! great] regul>ity ( ?is =m ( escapem5t is due to a small] oscillation ( ! p5dulum be+ requir$ ?an ) ! =m fir/ describ$2 = x is f\nd t ! motion ( a p5dulum :5 vibrat+ ?r\gh n m ?an six degrees is practically cycloidal1 & x is only ) l>g] arcs t ! circle mat]ially diff]s f ! !oretical curve requir$4 ,! p5dulum is kept 9 vibration by ! escape :eel1 or r by its tee? press+ aga9/ ! incl9$ surfaces ( ! pallets1 & =c+ !m outw>ds1 & s giv+ ! p5dulum an impulse prior to ea* tick4 ,illu/ration3 ,,fig4 #ib4--,! ,an*or ,escapem5t4 ,?is an*or escapem5t1 :i* 0 inv5t$ by 8,clem5t1 ( ,london1 clockmak]10 =ms1 z x 71 ! basis ( our mod]n clocks1 &1 ) ! exception ( ! dead beat1 :i* 0 due to ,graham "s ye>s aft]w>ds1 is 9 almo/ exclusive use at ! pres5t date4 ,we see t z soon z a too? has escap$ on "o side1 a too? on ! o!r beg9s imm$iately to ret>d ! action ( ! p5dulum by press+ aga9/ ! incl9$ surface ( ! o!r pallet1 & z ! p5dulum sw+s on1 ! too? gives way1 & ! motion ( ! :eel is rev]s$2 !n :5 ! p5dulum beg9s to return1 x is assi/$ aga9 by ! too?1 s t ! p5dulum is always "u ! influ5ce ( ! escape :eel1 "s times accel]at$1 & sometimes ret>d$4 ,! pr9ciple ( ,graham's dead beat is to get rid ( ! ret>d+ action ( ! escape :eel1 s t !re %\ld be no necessity = s mu* accel]at+ p[]1 & ! p5dulum %\ld be out ( ! influ5ce ( ! escape :eel dur+ a l>ge portion ( its vibration4 ,?is he accompli%$ by do+ away ) a l>ge portion ( ! incl9$ surface ( ! pallet 7,fig4 #ic71 s t ! tee? h no accel]at+ action on ! p5dulum until j z !y leave ! ends ( ! pallets :]e !y are incl9$2 ! great] portion ( bo? ! pallets on :i* ! escape :eel works be+ at "r angles to its direction ( motion1 ! tee? h no t5d5cy to =ce ! pallet outw>ds4 ,9 ,fig4 #ic ! too? ,v has fall5 on ! pallet ,d1 ! too? ,t hav+ j be5 releas$1 & z ! p5dulum /ill sw+s on 9 ! direction ( ! arr[1 ! pallet ,d w be pu%$ fur!r "u ! too? ,c b )\t press+ ! :eel backw>ds1 & )\t ret>dation o!r ?an t ( friction4 ,:5 ! p5dulum returns & ! pallet j gets pa/ ! position %[n1 x gets an impulse1 & ?is is giv5 z ne>ly z possible z mu* be=e ! p5dulum rea*es its v]tical position z aft] x passes x1 its action is !re=e nei!r to increase nor dim9i% ! rate4 ,9 ?is escapem5t n only is ! arc ( oscillation consid]ably less5$ & ! motion ( ! p5dulum br\ght ne> to ! cycloidal =m1 b 9 addition to ?is !re is ?is important po9t1 t ! weight is act+ ^u ! p5dulum = ! lea/ possible "t4 ,illu/ration3 ,,fig4 #ic4--;,graham's ,dead ,beat4 ,illu/ration3 ,,fig4 #id4--;,gravity ,escapem5t 7,mudge74 ,we w n[ describe ! m elaborate =ms ( escapem5t1 & we w take fir/ ! gravity escapem5t1 z x is call$4 ,! pr9ciple ( its action consi/s 9 !re be+ a small impulse giv5 to ! p5dulum at ea* oscillation1 by means ( two small rods hang+1 "o on ea* side ( x1 & t5d+ by _! own weight to =ce ! p5dulum into a v]tical position2 ^! rods are alt]nately pu%$ outw>ds by ! escapem5t be=e ! p5dulum 9 its sw+ arrives at !m1 & !n !y are all[$ to press aga9/ x on its return t[>ds ! v]tical1 s t ! p5dulum has a con/ant =ce act+ on x at ea* oscillation1 unconnect$ ) ! clock movem5t4 ,?is is c>ri$ out 9 ! escapem5t inv5t$ by ,mudge1 z %[n 9 ,fig4 #id4 ,! p5dulum rod is suppos$ to be hang+ j 9 front ( ! rods hang+ f ! pivots ,y#a ,y#b1 & on sw++ x presses aga9/ ! p9s at ! l[] ends ( ! rods & s lifts ! pallets ,s#a ,s#b out ( ! tee? ( ! escape :eel4 ,9 ! position %[n ! p5dulum is mov+ to ! "r1 hav+ be5 g5tly urg$ f ! left by ! weight ( ! pallet rod ,y#b ,s#b1 & ! pallet ,s#a has be5 lift$ outw>ds by ! too? act+ on its incl9$ surface4 ,on ! p5dulum rod rea*+ ! p9 ! rod is mov$ outw>ds & ! end ( ! pallet ,s#a pu%$ out ( ! too? :5 ! :eel moves on1 at ! same "t pu%+ outw>ds ! pallet ,s#b4 ,z ! p5dulum returns t[>ds ! left aga9 ! rod ,y#a foll[s x1 giv+ x a g5tle impulse by its own weight until x returns ne>ly to ! v]tical or to ! correspond+ position 9 :i* ,y#b ,s#b is %[n4 ,on ! p5dulum sw++ on & releas+ ,t#b ! pallet ,s#a is aga9 pu%$ outw>ds by ! incl9$ plane to ! position %[n 9 ! diagram4 ,9 ?is escapem5t !re 0 dang] ( ! pallets be+ ?r[n too viol5tly outw>ds s t ! tee? 7 n caught by ! flat surfaces at ! ends1 & ,mr4 ,bloxam improv$ on x by lett+ ! pallets be ?r[n outw>ds by a small :eel on ! axis ( ! escape :eel s t ! action 0 less rapid2 he accompli%$ ?is 9 ! foll[+ mann]4 ,on ! end ( ! axis ( ! la/ :eel are a numb] ( arms ,a ,a1 ,fig4 #ie1 say n9e1 ab\t #a in*es long1 :i* are prev5t$ f revolv+ by /uds ,l#a ,l#b on ! inside ( ea* hang+ rod ,p#a ,p#b2 !n1 z ea* rod is pu%$ outw>ds by ! p5dulum1 an arm escapes f a /ud & ! clock goes on "o second4 ,ea* rod is pu%$ outw>ds by ! clock almo/ suffici5tly f> = ! arm to escape1 b n q1 s t ! p5dulum j releases ! arm at ! end ( its sw+ 9 ! same mann] z 9 ,mudge's escapem5t1 ,fig4 #id2 b in/ead ( ! tee? ( ! escape :eel pu%+ ! rods outw>ds !re is ! small :eel ,t#a ,t#b1 hav+ ! same numb] ( tee? z !re are arms on ! axis & close to !m1 & ! project+ pieces ,h#a ,h#b at "r angles to ea* sw++ rod re/ aga9/ ! tee? ( ?is :eel1 "o re/+ aga9/ ! tee? at ! top & ! o!r at ! bottom1 s t !y cat* aga9/ ! tee? aft] ! mann] ( a rat*et1 & ! rods are pu%$ outw>ds by ?is :eel z x revolves4 ,! arms & rat*et :eel are s set t1 dur+ ! motion ( an arm ,a1 to a /ud1 a too? ( ! rat*et :eel is pu%+ outw>ds ! rod c>ry+ t /ud4 ,! action is z foll[s3--,! p5dulum hav+ j swung up to a rod & releas$ ! arm press+ aga9/ its /ud1 ! arms & rat*et :eel revolve1 & ! too? ( ! rat*et :eel1 :i* _h be5 press+ outw>ds ! sw++ rod1 passes on free ( ! project+ piece1 :i* c n[ move backw>ds to ! next too?2 s ! rod1 be+ no long] support$1 presses aga9/ ! p5dulum rod on its return oscillation4 ,! arms & rat*et :eel revolve until an arm on ! opposite side comes 9 contact ) ! /ud on ! o!r rod1 & 9 revolv+ ! rat*et :eel ?r[s outw>ds ?is rod j s f> t ! arm is n releas$4 ,! p5dulum is assi/$ by ! weight ( ! fir/ rod to ! v]tical position1 :5 ! project+ piece ( ! rod comes 9 contact ) ! next too? ( ! rat*et :eel :]e x re/s until ! oscillation is complet$1 & ! second arm is releas$4 ,x is !n =c$ outw>ds1 & ! next arm on t side presses aga9/ ! /ud1 :5 a repetition ( ! =ego+ takes place4 ,9 ?is way ! clock is kept go+ )\t any direct action ( ! clock tra9 on ! p5dulum4 ,illu/ration3 ,,fig4 #ie4--;,gravity ,escapem5t 7,bloxam74 ,ano!r v beautiful escapem5t is t devis$ by ! ,a/ronom]-,royal & c>ri$ out 9 ! clock erect$ 9 #ahga at ,gre5wi*4#i ,9 ?is case ! p5dulum is free except dur+ a portion ( e alt]nate second1 :5 x releases ! escapem5t & receives an impulse1 s t !re is a tick only at e o!r second4 ,illu/ration3 ,,fig4 #if4--;,gre5wi* ,clock ,escapem5t4 ,! details ( ! escapem5t may be se5 9 ,fig4 #if1 :i* gives a g5]al view ( a portion ( ! back plate ( ! clock movem5t1 suppos+ ! p5dulum remov$2 a & b are ! front & back plates respectively ( ! clock tra92 c is a cock support+ "o end ( ! crut* axis2 d is ! crut* rod c>ry+ ! pallets1 & e an arm c>ri$ by ! crut* axis & fix$ at f to ! left-h& pallet arm2 g is a cock support+ a det5t project+ t[>ds ! left & curv$ at its extreme end2 at a po9t ne> ! top ( ! escape :eel ?is det5t c>ries a p9 7jewel7 = lock+ ! :eel1 & at its extreme end !re is a v light 8pass+ spr+40 ,! action ( ! escapem5t is z foll[s3--,suppose ! p5dulum to be sw++ f ! "r h&4 ,x sw+s q freely until a p9 at ! end ( ! arm e lifts ! det5t2 ! :eel escapes f ! jewel be=e m5tion$1 & ! too? next above ! left-h& pallet drops on ! face ( ! pallet 7! /ate %[n 9 ! figure71 & gives impulse to ! p5dulum2 ! :eel is imm$iately lock$ aga9 by ! jewel1 & ! p5dulum1 n[ deta*$1 passes on to ! left2 9 return+ to ! "r1 ! light pass+ spr+1 be=e spok5 (1 all[s ! p5dulum to pass )\t di/urb+ ! det5t2 on go+ aga9 to ! left1 ! p5dulum aga9 receives impulse z already describ$4 ,! "r-h& pallet =ms no ess5tial "p ( ! escapem5t1 b is simply a safety pallet1 design$ to cat* ! :eel 9 case ( accid5t to ! lock+-/one dur+ ! "t t ! left-h& pallet is beyond ! range ( ! :eel4 ,! escape :eel c>ry+ ! seconds h& ?us moves once only 9 ea* complete or d\ble vibration ( ! p5dulum1 or e two seconds4 ,,iv4 ,,! ,,*ronomet]4 ,we h n[ giv5 a description ( ! a/ronomical clock--! mod]n a/ronomical in/rum5t :i* x 0 our duty to consid]4 ,!re is ano!r "t-keep]--! *ronomet]--:i* we h to dwell ^u4 ,9 ! *ronomet]1 in/ead ( us+ ! p5dulum1 we h a balance1 ! vibration ( :i* is gov]n$ by a spiral spr+1 in/ead ( by gravity1 z ! p5dulum is4 ,by su* means we keep almo/ z accurate "t z we d by employ+ a p5dulum1 ! balance be+ correct$ = temp]ature on pr9ciples1 "o ( :i* we %all describe4 ,we mu/ premise by say+ t fully f\r-fif?s ( ! comp5sation requir$ by a *ronomet] or wat*-balance is ow+ to ! *ange 9 ela/icity ( ! gov]n+ spiral spr+1 ! rema9d]1 comp>atively insignificant1 be+ due to ! balance's own expansion or contraction4 ,! segm5ts ,r#a1 ,r#b ( ! balance 7see ,fig4 #ig7 are compos$ ( two metals1 say copp] & /eel1 ! copp] be+ ext]ior2 !n z ! gov]n+ spiral spr+ loses its ela/icity by heat1 ! segm5ts ,r#a1 ,r#b curve r\nd & take up positions ne>] ! axis ( motion1 ! curvature be+ produc$ by ! great] expansion ( copp] ov] /eel2 & ?us ! loss ( "t due to ! loss ( ela/icity ( ! spiral spr+ is comp5sat$ =4 ,?is balance may be adju/able by plac+ on ! arms small weights1 ,w ,w1 :i* may be mov$ along ! arms1 & s increase or dim9i% ! effect ( temp]ature at pleasure4 ,illu/ration3 ,,fig4 #ig4--;,comp5sat+ ,balance4 ,( ! numb] ( wat* & *ronomet] escapem5ts we may m5tion ! deta*$ lev]--! "o mo/ g5]ally us$ = ! be/ wat*es1 ! =m is %[n 9 ,fig4 #ih4 ,p ,p are ! pallets work+ on a p9 at ,s z 9 ! dead-beat clock escapem5t2 ! pallets c>ry a lev] ,l :i* c vibrate betwe5 two p9s ,b ,b4 ,r is a disc c>ri$ on ! same axis ) ! balance1 & x c>ries a p9 ,i1 :i* z ! disc goes r\nd 9 ! direction ( ! arr[1 falls into ! =k ( ! lev]1 & moves x on & )draws ! pallet f ! too? ,d1 :i* at once moves onw>ds & gives ! lev] an impulse z x passes ! face ( ! pallet4 ,?is impulse is communicat$ to ! balance ?r\gh ! p9 ,i1 ! balance is kept vibrat+ 9 contr>y directions "u ! influ5ce ( ! hair-spr+1 ga9+ an impulse at ea* sw+4 ,on ! same axis z ,r is a second disc ,o ) a not* cut 9 x into :i* a tongue on ! lev] ent]s2 ?is acts z a safety lock1 z ! lev] c only move :ile ! p9 ,i is 9 ! =k ( ! lev]4 ,illu/ration3 ,,fig4 #ih4--;,deta*$ ,lev] ,escapem5t4 ,! escapem5t we next describe is t mo/ g5]ally us$ 9 *ronomet]s4 ,s ,s1 ,fig4 #ii1 is ! escape :eel :i* is kept f revolv+ by ! det5t ,d4 ,on ! axis ( ! balance are two discs1 ,r#a1 ,r#b1 plac$ "o "u ! o!r4 ,z ! balance revolves 9 ! direction ( ! arr[1 ! p9 ,p#b w come r\nd & cat* aga9/ ! po9t ( ! det5t1 lift+ x & releas+ ! escape-:eel1 :i* w revolve1 & ! too? ,t w hit aga9/ ! /ud ,p#a1 giv+ ! balance an impulse4 ,! balance !n sw+s on to ! end ( its c\rse & returns1 & ! /ud ,p#b passes ! det5t z foll[s3 a light spr+ ,y ,y is fa/5$ to ! det5t1 project+ a little beyond x1 & x is ?is spr+1 & n ! det5t itself1 t ! p9 ,p#b t\*es3 on ! return ( ,p#b x simply lifts ! spr+ away f ! det5t & passes x1 :]eas 9 advanc+ ! spr+ 0 support$ by ! po9t ( ! det5t1 & bo? 7 lift$ toge!r4 ,illu/ration3 ,,fig4 #ii4--;,*ronomet] ,escapem5t4 ,illu/ration3 ,,fig4 #ajj4--,! ,fusee4 ,9 wat*es & *ronomet]s & 9 small clocks a coil$ spr+ is us$ in/ead ( a weight1 b its action is irregul>1 s9ce :5 x is fully w\nd up x ex]cises great] =ce ?an :5 ne>ly d[n4 ,9 ord] to comp5sate = ?is ! cord or *a9 :i* is w\nd r\nd ! b>rel conta9+ ! spr+ passes r\nd a conical b>rel call$ a fusee 7,fig4 #ajj73 ,b is ! b>rel conta9+ ! spr+ & ,a ,a ! fusee4 ,"o end ( ! spr+ is fix$ to ! axis ( ! b>rel1 :i* is prev5t$ f turn+ r\nd1 & ! o!r end to ! b>rel1 s t on w9d+ up ! clock by turn+ ! fusee ! cord becomes coil$ on ! latt]1 & ! m ! spr+ is w\nd ! ne>] ! cord approa*es ! small end ( ! fusee1 & has !re=e less p[] ov] x2 :ile z ! clock goes & ! spr+ becomes unw\nd1 its p[] ov] ! axis becomes great]4 ,! p[]1 !re=e1 act+ to turn ! fusee rema9s pretty con/ant4 ----- ,footnote #i3 ,by ,messrs4 ,e4 ,d5t & ,co4 ( ! ,/r&4 ,,*apt] ,,xiv4 ,,circle ,,read+4 ,"o ( ! great advantages :i* a/ronomy has receiv$ f ! inv5tion ( ! telescope is ! improv$ me?od ( measur+ space & det]m9+ positions by ! use ( ! telescope 9 ! place ( po9t]s on ! old in/rum5ts4 ,! addition ( mod]n appliances to ! telescope to enable x to be us$ z an accurate po9t]1 has play$ a conspicu\s "p 9 ! accurate measurem5t ( space1 & ! results are ( su* importance1 & !y h increas$ s absolutely p>i passu ) ! telescope1 t we mu/ n[ say some?+ ( ! means by :i* !y h be5 br\ght ab\t4 ,= a/ronomy ( position1 9 o!r words = ! measurem5t ( space1 we want to po9t ! telescope accurately at an object4 ,t is to say1 9 ! fir/ in/ance we want circles1 & !n we want ! p[] ( n only mak+ p]fect circles1 b ( read+ !m ) p]fect accuracy2 & :]e ! arc is s small t ! circle1 h[ev] f9ely divid$1 w\ld help u b little1 we want "s means ( measur+ small arcs 9 ! eyepiece ( ! telescope itself1 :]e ! object appe>s to u1 z x is call$1 9 ! field ( view2 we want to measure & inspect t object 9 ! field ( view ( ! telescope1 indep5d5tly ( circles or any?+ extrane\s to ! field4 ,we %all !n h circles & micromet]s to deal ) divisions ( space1 & clocks & *ronographs to deal ) divisions ( "t4 ,we require to h 9 ! telescope some?+1 say two wires cross$1 plac$ 9 ! field ( view--9 ! r\nd disc ( light we see 9 a telescope ow+ to ! con/ruction ( ! diaphragm--s z to be se5 toge!r ) any object4 ,9 ! *apt] on eyepieces x 0 %[n t we get at ! focus ! image ( ! object2 & z t is also ! focus ( ! eyepiece1 x is obvi\s t n only ! image 9 ! air1 z x 71 b any?+ mat]ial we l to put 9 t focus1 is equally visible4 ,by ! simple contrivance ( ins]t+ 9 ?is common focus two or m wires cross$ & c>ri$ on a small circul> frame1 we c m>k any "p ( ! field1 & are enabl$ to direct ! telescope to any object4 ,9 ! ,huygh5ian eyepiece1 ,fig4 #fj1 ! cross %\ld be betwe5 ! two convex l5ses1 = if we h an eyepiece ( ?is k9d ! focus w be at ,f1 & s "h we mu/ h our cross wires2 b1 if in/ead ( ?is eyepiece we h "o ( ! k9d call$ ,ramsd5's eyepiece1 ,fig4 #fb1 ) ! two convex surfaces plac$ inw>ds1 !n ! focus w be outside1 at ,f1 & ne>] to ! object-glass3 !re=e we %all be able to *ange ^! eyepieces )\t int]f]+ ) ! sy/em ( wires 9 ! focus ( ! telescope4 ,we h5ce see at once t ! introduction ( ?is contrivance1 :i* is due to ,mr4 ,gascoigne1 at once enorm\sly increases ! possibility ( mak+ accurate obs]vations by means ( ! telescope4 ,illu/ration3 ,,fig4 #aja4--;,diggs' ,diagonal ,scale4 ,hipp>*us 0 cont5t to asc]ta9 ! position ( ! cele/ial bodies to )9 a ?ird ( a degree1 & we are in=m$ t ,ty*o ,brahe1 by a diagonal scale1 0 able to br+ x d[n to some?+ l t5 seconds4 ,fig4 #aja w %[ :at is meant by ?is4 ,suppose ?is to be "p ( ! arc ( ,ty*o's circle1 hav+ on x ! diff]5t divisions & degrees4 ,n[ x is cle> t :5 ! b> :i* c>ri$ ! po9t] swept ov] ?is arc1 divid$ simply into degrees1 x w\ld require a consid]able am\nt ( skill 9 e/imat+ to get v close to ! tru?1 unless "s o!r me?od 7 introduc$2 & ! me?od sugge/$ by ,diggs1 & adopt$ by ,ty*o1 0 to h a s]ies ( diagonal l9es = ! divisions ( degrees2 & x is cle> t ! height ( ! diagonal l9e measur$ f ! edge ( ! circle c\ld give1 z x 71 a long] base ?an ! direct di/ance betwe5 ea* division = det]m9+ ! subdivisions ( ! degree1 & a slight motion ( ! po9t] w\ld make a great diff]5ce 9 ! po9t :]e x cuts ! diagonal l9e4 ,= in/ance1 x w\ld n be easy to say exactly ! fraction ( division on ! inn] circle at :i* ! po9t] 9 ,fig4 #aja re/s1 b x is evid5t t ! lead+ edge ( ! po9t] cuts ! diagonal l9e at ?ree-f\r?s ( its l5g?1 z %[n by ! ?ird circle2 s ! read+ 9 ?is case is sev5 & ?ree-qu>t]s2 b t is1 aft] all1 a v r\gh me?od1 al?\gh x 0 all ! a/ronom] _h to dep5d ^u 9 "s important obs]vations4 ,illu/ration3 ,,fig4 #ajb4--,! ,v]ni]4 ,! next arrangem5t we get is "o :i* has held its own to ! pres5t day1 & :i* is beautifully simple4 ,x is due to a ,fr5*man nam$ ,v]ni]1 & 0 inv5t$ ab\t #afca4 ,we may illu/rate ! pr9ciple 9 ?is way4 ,suppose = in/ance we want to subdivide ! divisions m>k$ on ! arc ( a circle1 ,fig4 #ajb a b1 & say we wi% to divide !m into t5?s1 :at we h to d is ?is--,fir/1 take a l5g? equal to n9e ( ^! divisions on a piece ( metal1 c1 call$ ! v]ni]1 c>ri$ on an arm f ! c5tre ( ! circle1 & !n1 on a sep>ate scale altoge!r1 divide t di/ance n into n9e1 z x is divid$ on ! circle1 b into t5 portions4 ,n[ m>k :at happ5s z ! v]ni] sweeps along ! circle1 in/ead ( hav+ ,ty*o's po9t] sweep+ across ! diagonal scale4 ,let u suppose t ! v]ni] moves ) ! telescope & ! circle is fix$2 !n :5 division #j ( ! v]ni] is opposite division #f on ! circle we "k t ! telescope is po9t+ at #f f z]o measur$ by ! degrees on ?is scale2 b suppose1 = in/ance1 x moves along a little m1 we f9d t l9e #a ( ! v]ni] is 9 contact ) & opposite to ano!r on ! circle1 !n ! read+ is #f & 2 x moves a little fur!r1 & we f9d t ! next l9e #b1 is opposite to ano!r1 read+ #f & #b_/aj1 a little fur!r /ill1 & we f9d ! next opposite4 ,x is cle> t 9 ?is way we h a readi] means ( divid+ all ^? spaces into t5?s1 because if ! l5g? ( ! v]ni] is n9e circle divisions ! l5g? ( ea* division on ! v]ni] mu/ be z n9e is to t51 s t ea* division is "o-t5? less ?an t on ! circle4 ,we mu/ !re=e move ! v]ni] "o-t5? ( a circle division1 9 ord] to make ! next l9e correspond4 ,t is to say1 :5 ! division ( ! v]ni] m>k$ #j is opposite to any l9e1 z 9 ! diagram1 ! read+ is an exact numb] ( degrees2 & :5 ! division #a is opposite1 we h !n ! numb] ( degrees giv5 by ! division #j plus "o-t5?2 :5 #b is 9 contact1 plus two-t5?s2 :5 #c is 9 contact1 plus ?ree-t5?s2 :5 #d is 9 contact1 plus f\r-t5?s1 & s on1 till we get a p]fect contact all ?r\gh by ! #j ( ! v]ni] com+ to ! next division on ! circle1 & !n we get ! next degree4 ,x is obvi\s t we may take any o!r fraction ?an to = ! v]ni] to read to1 say #a_/fj1 !n we take a l5g? ( #ei circle divisions on ! v]ni] & divide x into #fj1 s t ea* v]ni] division is less ?an a circle division by #a_/fj4 ,?is is a me?od :i* holds its own on mo/ in/rum5ts1 & is a mo/ useful arrangem5t4 ,b mo/ ( u "k t ! division ( ! v]ni] has be5 object$ to z co>se & imp]fect2 & ,%>p1 ,graham1 ,bird1 ,ramsd51 ,tr\ghton1 & o!rs f\nd t x is easy to graduate a circle ( f\r or five feet 9 diamet]1 or m1 s accurately & m9utely t five m9utes ( arc %all be absolutely repres5t$ on e "p ( ! circle4 ,we c take a small microscope & place 9 its field ( view two cross wires1 some?+ l ^? we h already m5tion$1 s z to be se5 toge!r ) ! divisions on ! circle1 & !n1 by means ( a screw ) a divid$ head1 we c move ! cross wires f division to division1 & s1 by not+ ! numb] ( turns ( ! screw requir$ to br+ ! cross wires f a c]ta9 fix$ position1 correspond+ to ! po9t] 9 ! old] in/rum5ts1 to ! ne>e/ division1 we c measure ! di/ance ( t division f ! fix$ po9t or po9t]1 z x 71 j z well z if ! circle itself 7 mu* m closely divid$4 ,we c h matt]s s arrang$ t we may h to make1 if we l1 t5 turns ( ! screw 9 ord] to move ! cross wires f "o graduation to ! next1 & we may h ! mill$ head ( ! screw itself divid$ into #ajj divisions1 s t we %all be able to divide ea* ( ! t5 turns into #ajj1 or ! :ole division into #a1jjj p>ts4 ,x is !n simply a "q ( divid+ a portion ( arc equal to five m9utes into a ?\s&1 or1 if "o likes1 t5 ?\s& p>ts by a delicate screw motion4 ,we are n[ speak+ ( in/rum5ts ( precision1 9 :i* l>ge telescopes are n s necess>y z l>ge circles4 ,) ref]5ce to in/rum5ts = physical & o!r obs]vations1 l>ge circles are n s necess>y z l>ge telescopes1 z absolute positions c be det]m9$ by in/rum5ts ( precision1 & small arcs c1 z we %all see 9 ! next *apt]1 be det]m9$ by a micromet] 9 ! eyepiece ( ! telescope4 ,,*apt] ,,xv4 ,,! ,,micromet]4 ,x w h be5 ga!r$ f ! previ\s *apt] t ! p]fect circles n[adays turn$ out by our be/ opticians1 & arm$ 9 diff]5t p>ts by p[]ful read+ microscopes1 9 conjunction ) a cross wire 9 ! field ( view ( ! telescope to det]m9e ! exact axis ( collimation1 enable l>ge arcs to be measur$ ) an accuracy comp>able to t ) :i* an a/ronomical clock enables u to measure an int]val ( "t4 ,we h next to see by :at me?od small arcs are measur$ 9 ! field ( view ( ! telescope itself4 ,?is is accompli%$ by :at are t]m$ micromet]s1 :i* are ( v>i\s =ms4 ,?us we h ! wire micromet]1 ! heliomet]1 ! d\ble-image micromet]1 & s on4 ,^! we %all n[ consid] 9 succession1 ent]+ into fur!r details ( _! use1 & ! arrangem5ts !y necessitate :5 we come to consid] ! in/rum5t 9 conjunction ) :i* !y are g5]ally employ$4 ,! hi/ory ( ! micromet] is a v curi\s "o4 ,we h already spok5 ( a pair ( cross wires replac+ ! p9nules ( ! old a/ronom]s 9 ! field ( view ( ! telescope1 s t x might be po9t$ to any cele/ial object v mu* m accurately ?an x c\ld be )\t su* cross wires4 ,?is k9d ( micromet] 0 fir/ appli$ to a telescope by ,gascoigne 9 #afci4 ,9 a lett] to ,crabtree he writes3#aj 8,if "h 79 ! focus ( ! telescope7 y place ! scale t measures 444 or if "h a hair be set t x appe> p]fectly ?r\gh ! glass 444 y may use x 9 a quadrant = ! f9d+ ( ! altitude ( ! lea/ /> visible by ! p]spective :]e9 x is4 ,if ! night be s d>k t ! hair or ! po9t]s ( ! scale be n to be se51 ,i place a c&le 9 a lan?orn1 s z to ca/ light suffici5t into ! glass1 :i* ,i f9d v helpful :5 ! moon appe>e? n1 or x is n o!rwise light en\gh40 ,?is !n 0 ! fir/ 8telescopic sight10 z ^! arrangem5ts at ! common focus ( ! object-glass & eyepiece 7 at fir/ call$4 ,x is c]ta9 t we may date ! micromet] f ! middle ( ! sev5te5? c5tury2 b x is r difficult to say :o x 0 :o inv5t$ x4 ,x is frequ5tly attribut$ to a ,fr5*man nam$ ,auz\t1 :o is /at$ to h inv5t$ x 9 #afff2 b we h reason to "k t ,gascoigne _h inv5t$ an in/rum5t = measur+ small di/ances sev]al ye>s be=e4 ,?\gh fir/ employ$ by ,gascoigne1 h[ev]1 !y 7 c]ta9ly indep5d5tly introduc$ on ! ,cont95t1 & took v>i\s =ms1 "o ( !m be+ a reticule1 or network ( small silv] ?reads1 sugge/$ by ! ,m>quis ,malvasia1 ! arc int]val ( :i* 0 det]m9$ by ! aid ( a clock4 ,huygh5s _h be=e ?is propos$1 z specially applicable to ! measures ( ! diamet]s ( planets & ! l1 ! introduction ( a tap]+ slip ( metal4 ,! "p ( ! slip :i* exactly eclips$ ! planet 0 not$2 x 0 next measur$ by a pair ( compasses1 & hav+ ! focal l5g? ( ! telescope1 ! app>5t diamet] 0 asc]ta9$4 ,illu/ration3 ,,fig4 #ajc4--,sy/em ( ,wires 9 a ,transit ,eyepiece4 ,malvasia's sugge/ion 0 soon seiz$ ^u = det]m9ations ( position4 ,rm] introduc$ into ! fir/ transit in/rum5t a horizontal & a numb] ( v]tical wires4 ,! int]val betwe5 ! ?ree he g5]ally us$ 0 ?irty-f\r seconds 9 ! equator1 & ! "t 0 not$ to half seconds4 ,! field 0 illum9at$ by means ( a poli%$ r+ plac$ outside ( ! object-glass4 ,! simple sy/em ( cross wires1 !n1 ?\gh x has done its "w1 is n to be f\nd 9 ! telescope n[1 ei!r to m>k ! axis ( collimation1 or r\ghly to measure small di/ances4 ,= ! fir/ purpose a mu* m elaborate sy/em ?an t introduc$ by ,rm] is us$4 ,we h a l>ge numb] ( v]tical wires1 ! pr9cipal object ( :i* is1 9 su* telescopes z ! transit1 to det]m9e ! absolute "t ( ! passage ( ei!r a /> or planet1 or ! sun or moon1 ov] ! m]idian2 & "o or m horizontal ones4 ,^! con/itute ! mod]n transit eyepiece1 a v simple =m ( :i* is %[n 9 ! above woodcut4 ,,! ,,wire ,,micromet]4 ,! wire micromet] is due to sugge/ions made indep5d5tly by ,hooke & ,auz\t1 :o po9t$ out h[ valuable ! reticule ( ,malvasia w\ld be if "o ( ! wires 7 movable4 ,illu/ration3 ,,fig4 #ajd4--,wire ,micromet]4 x & y are ?ick] wires = measur+ positions on a sep>ate plate to be laid ov] ! f9e wires4 ,! fir/ micromet] 9 :i* motion 0 provid$ consi/$ ( two plates ( t9 plac$ 9 ! eyepiece1 be+ s arrang$ & connect$ by screws t ! di/ances betwe5 ! two edges ( ! t9 plates c\ld be det]m9$ ) consid]able accuracy4 ,a planet c\ld !n be1 z x 71 grasp$ betwe5 ! two plates1 & its diamet] measur$2 x is v obvi\s t :at w\ld d z well z ^! plates ( t9 w\ld be two wires or hairs repres5t+ ! edges ( ^! t9 plates2 & ?is soon aft] 0 c>ri$ out by ,hooke1 :o left 8 m>k 9 a v decid$ way on v _m a/ronomical arrangem5ts ( t "t4 ,he sugge/$ t all t 0 necess>y to det]m9e ! diamet] ( ,saturn's r+s 0 to h a fix$ wire 9 ! eyepiece1 & a second wire travell+ 9 ! field ( view1 s t ! planet or ! r+ c\ld be grasp$ betwe5 ^? two wires4 ,! wire-micromet]4 ,fig4 #ajd1 diff]s little f ! "o ,hooke & ,auz\t sugge/$1 ,a ,a is ! frame1 :i* c>ries two slides1 ,c & ,d1 across ! ends ( ea* ( :i* f9e wires1 ,e & ,b1 are /ret*$2 !n1 by means ( screws1 ,f & ,g1 ?read$ ?r\gh ^! movable slides & pass+ ?r\gh ! frame ,a ,a1 ! wires c be mov$ ne> to1 or away f1 ea* o!r4 ,c>e mu/ be tak5 t ! ?reads ( ! screw are accurate f "o end to ! o!r1 s t "o turn ( ! screw :5 9 "o position w\ld move ! wire ! same di/ance z a turn :5 9 ano!r position4 ,9 ?is micromet] bo? wires are movable1 s z to get a wide sep>ation if ne$ful1 b 9 practice only "o is s1 ! o!r rema9+ a fixture 9 ! middle ( ! field ( view4 ,!re is a l>ge head to ! screw1 :i* is call$ ! micromet] screw1 m>k$ into divisions1 s t ! motion ( ! wire due to ea* turn ( ! screw may be divid$1 say into #ajj p>ts1 by actual division aga9/ a fix$ po9t]1 & fur!r into #a1jjj p>ts by e/imation ( ! p>ts ( ea* division4 ,hooke sugge/$ t1 if we _h a screw ) #ajj turns to an in*1 & c\ld divide ^! into #a1jjj p>ts1 we %\ld obvi\sly get ! means ( divid+ an in* into #ajj1jjj p>ts2 & s1 if we _h a screw :i* w\ld give #ajj turns f "o side ( ! field ( view ( ! telescope to ! o!r1 we %\ld h an opportunity ( divid+ ! field ( view ( any telescope into some?+ l #ajj1jjj p>ts 9 any direction we *ose4 ,! ?ick wires1 x1 y1 are fix$ to ! plate 9 front (1 b almo/ t\*+1 ! f9e wires1 & 9 measur+1 = in/ance1 ! di/ance ( two />s ! :ole in/rum5t is turn$ r\nd until ^! wires are p>allel to ! direction ( ! imag9>y l9e jo9+ !m4 ,?is 0 ! way 9 :i* ,huygh5s made _m important measures ( ! diamet]s ( diff]5t objects & ! di/ances ( diff]5t />s4 ,?us f> we are enabl$ to f9d ! numb] ( divisions on ! micromet] screw t corresponds to ! di/ance f "o /> to ano!r1 or across a planet1 b we want to "k ! numb] ( seconds ( arc 9 ! di/ance measur$4 ,9 ord] to d ?is accurately we mu/ det]m9e h[ _m divisions ( ! screw correspond to ! di/ance ( ! wires :5 on two />s1 say1 "o second ap>t4 ,"h we mu/ take advantage ( ! rate at :i* a /> travels across ! field :5 ! telescope is fix$1 & we sep>ate ! wires by a numb] ( turns ( ! screw1 say tw5ty1 & f9d :at angle ?is corresponds to1 by lett+ a /> on or ne> ! equator#aa trav]se ! field1 & notic+ ! "t x requires to pass f "o wire to ! next4 ,suppose x takes #bf seconds1 !n1 z fifte5 seconds ( arc pass ov] 9 "o second ( "t1 we mu/ multiply #bf by #ae1 :i* gives #djj1 s t ! di/ance f wire to wire is #djj seconds ( arc2 b ?is is due to tw5ty revolutions ( ! screw1 s t ea* revolution corresponds to #djj_/bj1 or tw5ty seconds1 & z ea* revolution is divid$ into #ajj p>ts1 & #bj_/ajj !re=e ea* division corresponds to ( arc4 ,we %all return to ! use ( ?is mo/ important in/rum5t :5 we h describ$ ! equatorial1 ( :i* x is ! con/ant companion4 ,,! ,,heliomet]4 ,illu/ration3 ,,fig4 #aje4--;,a ,b ,c4 ,images ( ,jupit] suppos$ to be t\*+2 ,b be+ produc$ by duplication1 ,c duplicate image on ! o!r side ( ,a4 ,a ,b1 ,d\ble ,/>2 ,a1 ,a ,b1 ,b1 ! appe>ance :5 duplicate image is mov$ to ! "r2 ,a1 ,a ,b1 ,b1 ! same :5 mov$ to ! left4 ,illu/ration3 ,,fig4 #ajf4--,object-glass cut into two p>ts4 ,illu/ration3 ,,fig4 #ajg4--,! p>ts sep>at$1 & giv+ two images ( any object4 ,!re are o!r k9ds ( micromet]s :i* we mu/ also briefly consid]4 ,9 ! heliomet]#ab we get ! p[] ( measur+ di/ances by d\bl+ ! images ( ! objects we see1 by means ( divid+ ! object-glass4 ,! two circles1 ,a & ,b1 ,fig4 #aje1 repres5t ! two images ( ,jupit] =m$1 z we %all %[ pres5tly1 & t\*+ ea* o!r2 n[1 if by any means we c make ,b travel ov] ,a till x has ! position ,c1 also j t\*+ ,a1 x w manife/ly h travell$ ov] a di/ance equal to ! diamet]s ( ,a & ,b1 s t if we c measure ! di/ance trav]s$ & divide x by #b1 we %all get ! diamet] ( ! circle ,a1 or ! planet4 ,! same pr9ciple applies to d\ble />s1 = if we d\ble ! />s ,a & ,b1 ,fig4 #aje1 s t ! second>y images become ,a & ,b1 we c move ,a ov] ,b1 & !n only ?ree />s w be visible2 we c !n move ! second>y images back ov] ,a & ,b till ,b comes ov] ,a1 & ! second image ( ,a comes to ,a4 ,x is ?us manife/ t ! images ,a & ,b on be+ mov$ to ,a & ,b 9 ! second position h pass$ ov] d\ble _! di/ance ap>t4 ,n[ all d\ble-image micromet]s dep5d on ?is pr9ciple1 & fir/ we w expla9 h[ ?is duplication ( images is made 9 ! heliomet]4 ,x is cle> t we %all n alt] ! p[] ( an object-glass to br+ objects to focus if we cut ! object-glass 9 two1 = if we put any d>k l9e across ! object-glass1 :i* optically cuts x 9 two1 we %all get an image1 say ( ,jupit]1 unalt]$4 ,b suppose in/ead ( hav+ ! p>ts ( ! object-glass 9 _! orig9al position aft] we h cut ! object-glass 9 two1 we make "o half ( ! object-glass travel ov] ! o!r 9 ! mann] repres5t$ 9 ,fig4 #ajg4 ,ea* ( ^! halves ( ! object-glass w be compet5t to give u a diff]5t image1 & ! light =m+ ea* image w be half ! light we got f ! two halves ( ! object-glass comb9$2 b :5 "o half is mov$ we %all get two images 9 two diff]5t places 9 ! field ( view4 ,we c s alt] ! position ( ! images ( objects by slid+ "o half ( ! object-glass ov] ! o!r1 t we %all1 z 9 ! case ( ! planet ,jupit]1 get ! two images exactly to t\* ea* o!r1 z is repres5t$ 9 ,fig4 #aje2 & fur!r /ill1 we c cause "o image to travel ov] to ! o!r side4 ,if we are view+ a d\ble />1 !n ! two halves w give f\r />s1 & we c slide "o half1 until ! c5tral image =m$ by ! object-glasses w consi/ ( two images ( two diff]5t />s1 & on ei!r side !re w be an image ( ea* />1 s t !re w\ld appe> to be ?ree />s 9 ! field ( view in/ead ( two4 ,we h ?us ! means ( det]m9+ absolutely ! di/ance ( any two cele/ial objects f ea* o!r1 9 t]ms ( ! sep>ation ( ! c5tres ( ! two halves ( ! object-glass4 ,b z 9 ! case ( ! wire micromet] we mu/ "k ! value ( ! screw1 s 9 ! case ( ! heliomet] we mu/ "k h[ mu* arc is mov$ ov] by a c]ta9 motion ( "o half ( ! object-glass4 ,illu/ration3 ,,fig4 #ajh4--;,d\ble images se5 ?r\gh ,icel& sp>4 ,illu/ration3 ,,fig4 #aji4--;,diagram %[+ ! pa? ( ! ord9>y & extraord9>y rays 9 a cry/al ( ,icel& sp>1 produc+ two images app>5tly at ,e & ,o4 ,,! ,,d\ble-,,image ,,micromet]4 ,n[ !re is ano!r k9d ( d\ble-image micromet] :i* m]its att5tion4 ,9 ?is case ! d\ble image is d]iv$ f a diff]5t physical fact altoge!r1 namely1 d\ble refraction4 ,^? :o h look$ ?r\gh a cry/al ( ,icel& sp>1 ,fig4 #ajh1 h se5 two images ( ev]y?+ look$ at :5 ! cry/al is held 9 c]ta9 positions1 b ! surfaces ( ! cry/al c be cut 9 a c]ta9 plane su* t :5 look$ ?r\gh1 ! images are s+le4 ,= ! micromet] !re=e we h d\bly refract+ prisms1 cut 9 su* a way z to v>y ! di/ance ( ! images4 ,g5]ally speak+1 :5ev] a ray ( light falls on a cry/al ( ,icel& sp> or o!r d\ble refract+ sub/ance1 x is divid$ up into two portions1 "o ( :i* is refract$ m ?an ! o!r4 ,if we trace ! rays proce$+ f a po9t ,s1 ,fig4 #aji1 we f9d "o portion ( ! light rea*+ ! eye is m refract$ at ! surfaces ?an ! o!r1 & consequ5tly "o appe>s to come f ,e & ! o!r f ,o1 s t if we ins]t su* a cry/al 9 ! pa? ( rays f any object1 t object appe>s d\bl$4 ,!re is1 h[ev]1 a c]ta9 direction 9 ! cry/al1 along :i*1 if ! light travel1 x is n divid$ into two rays1 & ?is direction is t ( ! optic axis ( ! cry/al1 ,a ,a1 ,fig4 #aaj2 if !re=e two prisms ( ?is sp> are made s t 9 "o ! light %all travel p>allel to ! axis1 & 9 ! o!r at "r angles to x1 & if ^! be fa/5$ toge!r s t _! out] sides are p>allel1 z %[n 9 ,fig4 #aaa1 light w pass ?r\gh ! fir/ "o )\t be+ split up1 s9ce x passes p>allel to ! axis1 b on rea*+ ! second "o x is divid$ into two rays1 "o ( :i* proce$s on 9 ! orig9al c\rse1 s9ce ! two prisms c\nt]act ea* o!r = ?is ray1 :ile ! o!r ray div]ges f ! fir/ "o1 & gives a second image ( ! object 9 front ( ! telescope1 z %[n 9 ,fig4 b4 ,! sep>ation ( ! image dep5ds on ! di/ance ( ! prisms f ! eyepiece1 s t we c pass ! rays f a /> or planet ?r\gh "o ( ^! comp\nd cry/als & measure ! position ( ! cry/al & s ! sep>ation ( ! />s1 & !n we %all h ! means ( do+ ! same t we did by divid+ our object-glass1 & 9 a less exp5sive way1 = to take a l>ge object-glass ( eight or t5 in*es 9 diamet] & cut x 9 two is a brutal op]ation1 & has g5]ally be5 rep5t$ ( :5 x has be5 done4 ,illu/ration3 ,,fig4 #aaj4--;,cry/als ( ,icel& ,sp> %[+1 ,a ,a1 ! optic axis4 ,x is obvi\s t a ,b>l[ l5s1 cut 9 ! same mann] z ! object-glass ( ! heliomet]1 w answ] ! same purpose2 ! two halves are ( c\rse mov$ 9 j ! same mann] z ! halves ( ! divid$ object-glass4 ,mr4 ,br[n+ has con/ruct$ micromet]s on ?is pr9ciple4 ,illu/ration3 ,,fig4 #aaa4--;,d\ble ,image ,micromet]4 ,,fig4 a1 p q1 s+le image =m$ by object-glass4 ,,fig4 b1 p#a q#a1 p#b q#b1 images sep>at$ by ! d\ble refract+ prism4 ,,fig4 c1 same1 sep>at$ less1 by ! motion ( ! prism4 ,!re is yet ano!r d\ble-image micromet] dep5d+ on ! p[] ( a prism to alt] ! direction ( rays ( light4 ,x is con/ruct$ by mak+ two v weak prisms1 i4e41 hav+ _! sides v ne>ly p>allel1 & cutt+ !m to a circul> %ape2 ^! are m\nt$ 9 a frame "o ov] ! o!r ) p[] to turn "o r\nd1 s t 9 "o position !y bo? act 9 ! same direction1 & 9 ! opposite "o !y neutralise ea* o!r2 ^! are c>ri$ by radial arms1 & are plac$ ei!r 9 front ( ! object-glass or at su* a di/ance f x inside ! telescope t !y int]cept "o half ( ! light1 & ! rema9+ portion goes to =m ! usual image1 :ile ! o!r is alt]$ 9 its c\rse by ! prism & =ms ano!r image1 & ?is alt]ation dep5ds on ! position ( ! movable prism4 ----- ,footnote #aj3 ,grant's ,hi/ory ( ,physical ,a/ronomy1 p4 #ded4 ,footnote #aa3 ,m accurately ! "t ( transit is to be multipli$ by ! cos9e ( ! />'s decl9ation4 ,footnote #ab3 ,s call$ because ! contrivance 0 fir/ us$ to measure ! diamet] ( ! sun4 ,,book ,,iv4 ,,mod]n ,,m]idional ,,obs]vations4 ,,*apt] ,,xvi4 ,,! ,,transit ,,circle4 ,we are n[1 !n1 9 full possession ( ! /ock-9-trade ( ! mod]n a/ronom]--! telescope1 ! clock1 & ! circle1--& we h fir/ to deal ) :at is t]m$ a/ronomy ( position1 t bran* ( ! subject :i* enables u to det]m9e ! exact position ( ! heav5ly bodies 9 ! cele/ial sph]e at any in/ant ( "t4 ,be=e1 h[ev]1 we proce$ ) mod]n me?ods1 x w be well1 on ! pr9ciple ( recul] p\r mieux saut]1 to ref] back to ! old ones 9 ord] t we c ! bett] see h[ ! mod]n in/rum5ts are arrang$ = do+ ! "w :i* ,ty*o1 = in/ance1 _h to d1 & :i* he accompli%$ by means ( ! in/rum5ts ( :i* we h already spok54 ,fir/ ( all let u ref] to ! ,mural ,quadrant1 9 :i* we h ! g]m ( a great deal ( mod]n "w1 its direct desc5dant be+ ! ,transit ,circle ( ! pres5t "t4 ,we beg9 !n by ref]r+ to ! hole 9 ! wall at :i* ,ty*o is po9t+ 7see ,fig4 #aab71 & ! circle1 ( :i* ! hole 0 ! c5tre1 opposite to x1 on :i* ! position ( ! body 0 obs]v$1 & its decl9ation & "r asc5sion det]m9$4 ,?is !n 0 ,ty*o's arrangem5t = det]m9+ ! two co-ord9ates1 "r asc5sion & decl9ation1 measur$ f ! m]idian & equator4 ,x is to be hop$ t ! mean+ ( "r asc5sion & decl9ation is already cle> to our read]s1 because ^! t]ms ref] to ! fundam5tal planes1 & di/ances z measur$ f !m are ! v ,a ,b ,c ( any?+ t "o has to say ab\t a/ronomical in/rum5ts4 ,we "k t ,ty*o _h two ?+s to d4 ,9 ! fir/ place he _h to note :5 a /> 0 se5 ?r\gh ! slit 9 ! wall1 :i* 0 ,ty*o's arrangem5t = det]m9+ ! s\?+ ( a />1 ! sun1 or ! moon2 & !n to give ! in/ant :5 ! object cross$ ! sight to ! o!r obs]v]1 :o not$ ! "t by ! clocks4 ,secondly1 he _h to note at :i* p>ticul> portion ( ! arc ! sight _h to be plac$1 & s ! altitude or ! z5i? di/ance ( ! /> 0 det]m9$2 & !n1 kn[+ ! latitude ( ! place1 he got ! two co-ord9ates1 ! "r asc5sion & decl9ation4 ,h[ does ! mod]n a/ronom] d ?is8 ,"h is an in/rum5t :i*1 )\t ! circle to tell ! altitude at ! same "t1 w give "s idea ( ! way 9 :i* ! mod]n a/ronom] has to g to "w4 ,9 ?is we h :at is call$ ! ,transit ,in/rum5t1 ,fig4 #aac2 x is simply us$ = det]m9+ ! transit ( />s ov] ! m]idian4 ,x consi/s ess5tially ( a telescope m\nt$ on trunnions1 l a cannon1 hav+ 9 ! eyepiece1 n simple cross wires1 b a sy/em ( wires1 to :i* ref]5ce has already be5 made1 s t ! mean ( z _m obs]vations z !re are wires c be tak52 & 9 ?is way ,ty*o's hole 9 ! wall is completely sup]s$$4 ,! quadrant is repres5t$ by a circle on ! in/rum5t call$ ! transit circle1 ( :i* = ! pres5t we def] consid]ation4 ,illu/ration3 ,,fig4 #aab4--,ty*o ,brahe's ,mural ,quadrant4 ,illu/ration3 ,,fig4 #aac4--,transit ,in/rum5t 7,transit ( ,v5us ,exp$ition74 ,illu/ration3 ,,fig4 #aad4--,transit ,in/alm5t 9 a fix$ ,obs]vatory4 ,n[ !re are ?ree ?+s to be done 9 ord] to adju/ ?is in/rum5t = obs]vation4 ,9 ! fir/ place we mu/ see t ! l9e ( sight is exactly at "r angles to ! axis on :i* ! telescope turns1 & :5 we h satisfi$ ourselves ( t1 we mu/1 9 ! second place1 take c>e1 n only t ! pivots on :i* ! telescope re/s are p]fectly equal 9 size1 b t ! entire axis re/+ on ^! pivots is p]fectly horizontal4 ,hav+ made ^! two adju/m5ts1 we %all at all ev5ts be able1 by sw++ ! telescope1 to sweep ?r\gh ! z5i?4 ,!n1 ?irdly1 if we take c>e t "o end ( ?is axis po9ts to ! ea/1 & ! o!r to ! we/1 we %all "k1 n only t our transit in/rum5t sweeps ?r\gh ! z5i?1 b sweeps ?r\gh ! pole :i* happ5s to be above ! horizon--9 ,engl& ! nor? pole1 9 ,au/ralia ! s\? pole4 ,t is to say1 by ! fir/ adju/m5t we %all be able to describe a great circle2 by ! second1 ?is circle w pass ?r\gh ! z5i?2 & by ! ?ird1 f ! s\? ( ! horizon to ! nor?1 ?r\gh ! pole4 ,( c\rse1 if ! pole /> 7 at ! pole1 all we %\ld h to d w\ld be to adju/ ! in/rum5t 7hav+ det]m9$ ! in/rum5t to be o!rwise correct7 s z simply to po9t to ! pole />1 & !n we %\ld assure ourselves ( ! ea/ & we/ positions ( ! axis4 ,"s details may "h be ( int]e/4 ,! fir/ adju/m5t to be made is t ! l9e ( sight or collimation %all be at "r angles to ! axis on :i* ! in/rum5t moves3 to f9d ! error & correct x1 br+ ! telescope into a horizontal position & place a small object at a di/ance away1 9 su* a position t its image is bisect$ by ! c5tral wire ( ! transit1 !n lift ! in/rum5t f its be>+s or ,ys1 z !y are call$1 & rev]se ! pivots ea/ = we/1 & aga9 obs]ve ! object4 ,if x is /ill bisect$1 ! adju/m5t is correct1 b if n1 !n half ! angle betwe5 ! new direction 9 :i* ! telescope po9ts & ! fir/ "o z m>k$ by ! object is ! collimation error1 :i* may be asc]ta9$ by measur+ ! di/ance f ! object to ! c5tral wire1 by a micromet] 9 ! field ( view1 & conv]t+ ! di/ance into arc4 ,to correct x1 br+ ! c5tral wire half way up to ! object by motion ( ! wire1 & complete ! o!r half by mov+ ! object itself1 or by mov+ ! ,ys ( ! in/rum5t4 ,?is ( c\rse mu/ be aga9 repeat$ until ! adju/m5t is s5sibly correct4 ,! second adju/m5t is to make ! pivots horizontal4 ,place a /rid+ level on ! pivots & br+ ! bubble to z]o by ! set screws ( ! level1 or note ! position ( x2 !n rev]se ! level ea/ = we/1 & !n if ! bubble rema9s at ! same place ! axis ( motion is horizontal1 b1 if n1 raise or l[] ! movable ,y suffici5tly to br+ ! bubble half way to its orig9al position1 & complete ! motion ( ! bubble1 if necess>y1 by ! level screw until !re is no alt]ation 9 ! position ( ! bubble on rev]s+ ! level4 ,illu/ration3 ,,fig4 #aae4--;,diagram expla9+ ?ird adju/m5t1 ,h1 ,r1 plane ( ! horizon2 ,h1 ,z1 ,a1 ,p1 ,b1 ,r1 m]idian2 ,a & ,b places ( circumpol> /> at transit above & bel[ pole ,p4 ,! ?ird adju/m5t is to place ! pivots ea/ & we/4 ,note by ! clock ! "t ( transit ( a circumpol> />1 :5 above ! pole1 ov] ! c5tral wire1 & !n half a day lat] :5 bel[ x1 & aga9 :5 above x2 if ! times f upp] to l[] transit1 & f l[] to upp] are equal1 !n ! l9e ( collimation sw+s s z to bisect ! circle ( ! /> r\nd ! pole1 & !re=e x passes ?r\gh ! pole1 & fur!r x describes a m]idian :i* passes ?r\gh ! z5i? by reason ( ! second adju/m5t4 ,?is is !re=e ! m]idian ( ! place1 & !re=e ! pivots are ea/ & we/4 ,if ! p]iods betwe5 ! transits are n equal1 ! movable pivot mu/ be %ift$ horizontally1 until on repeat+ ! process ! p]iods are equal4 ,9 practice ^! adju/m5ts c nev] be made q p]fect1 & !re are always small errors out/&+1 :i* :5 kn[n are all[$ =1 & !y are e/imat$ by a long s]ies ( obs]vations made 9 diff]5t mann]s & positions4 ,! error ( ! fir/ adju/m5t is call$ ! collimation error1 t ( ! second ! level error1 & t ( ! ?ird ! deviation error4 ,:5 ! errors ( an in/rum5t are kn[n ! obs]vations c be easily correct$ to :at !y w\ld h be5 _h ! in/rum5t be5 9 p]fect adju/m5t4 99 99 99 99 99 ,n[ :at does ! mod]n a/ronom] d ) ?is in/rum5t :5 he has got x8 ,x is absolutely )\t circles1 b ! fai?ful companion ( ! ,transit ,in/rum5t is ! ,a/ronomical ,clock--& ! two toge!r s]ve ! purpose ( a circle ( ! mo/ p]fect accuracy1 s t by means ( ^! two in/rum5ts we %all be able to det]m9e ! "r asc5sions ( all ! />s m]ely by not+ ! "t at :i* ! e>?'s rotation br+s !m into ! field ( view4 ,! clock hav+ be5 regulat$ to sid]eal "t1 a t]m fully expla9$ 9 ! sequel1 x w %[ #j;h4 #jm4 #js4 :5 ! fir/ po9t ( ,aries passes ! m]idian1 & in/ead ( divid+ ! day into two p]iods ( twelve h\rs ea*1 ! clock goes up to tw5ty-f\r h\rs4 ,if n[ a /> is obs]v$ to pass ! c5tre ( ! field ( view 7t is ! m]idian7 at #a;h4 by ! clock1 or "o h\r aft] ! fir/ po9t ( ,aries1 x w be kn[n to be 9 #a;h4 ( "r asc5sion2 or if x passes at #ab;h4 x w be #ab;h4 "r asc5sion1 or opposite to ! fir/ po9t ( ,aries1 & s on up to ! tw5ty-f\r h\rs1 ! clock keep+ exact "t ) ! e>?4 ,! transit in/rum5t ?us gives u ! "r asc5sion ( a />1 or "o co-ord9ate3 & n[ we want ! o!r--! decl9ation4 ,,! ,,transit ,,circle4 ,?is is giv5 by ! ,transit ,circle1 :i* is a transit in/rum5t ) a circle atta*$1 to asc]ta9 ! angle betwe5 ! object & ! pole or equator4 ,illu/ration3 ,,fig4 #aaf4--,! ,mural ,circle4 ,! comb9ation ( ! circle ) ! transit1 =m+ ! transit- or m]idian-circle1 is ( comp>atively rec5t date1 & ! e>li] me?od 0 to use a circle ) a telescope atta*$1 fix$ to a pivot mov+ on be>+s 9 a wall1 & call$ !re=e ! ,mural ,circle1 ,fig4 #aaf4 ,s9ce x is support$ only on "o side x _c move s truly 9 ! m]idian z ! transit1 b1 hav+ a l>ge circle1 x gives accurate read+s4 ,illu/ration3 ,,fig4 #aag4--,transit ,circle1 %[+ ! addition ( circles to ! transit in/rum5t4 ,illu/ration3 ,,fig4 #aah4--,p]spective view ( ,gre5wi* ,transit ,circle4 ,fig4 #aag %[s 9 :at respect ! ,transit ,circle is an advance ^u ! transit in/rum5t & ! mural circle1 = 9 addition to ! transit in/rum5t we h ! circle4 ,?is is a p]spective view ( ! transit1 & ! telescope is repres5t$ sweep+ 9 ! v]tical plane or m]idian4 ,9 addition to ! in/rum5t re/+ ) its pivots on ! massive pi]s1 we h ! circle atta*$ to ! side ( ! telescope4 ,we see at once t by means ( ?is circle we are able to introduce ! o!r co-ord9ate ( decl9ation4 ,if ! clock goes true ) ! e>?--if !y bo? beat 9 unison & keep "t ) ea* o!r--& fur!r if ! clock %[s #j;h4 #jm4 #js4 :5 ! fir/ po9t ( ,aries passes ! c5tre ( ! field1 t is ?r\gh ! m]idian plane1 !n1 if we obs]ve a /> at ! mom5t x passes ov] ! m]idian1 ! clock w give its "r asc5sion & ! circle its decl9ation1 :5 ! latitude ( ! place is kn[n4 ,! con/ruction ( ! transit circle w repay a m detail$ exam9ation4 ,a sy/em ( weights susp5d$ ov] pulleys 7,fig4 #aah7 r$uces ! weight ( ! in/rum5t on ! pivots1 9 ord] t _! =m %all n be alt]$ by too mu* friction1 & on ! "r-h& side ( "o ( ! pi]s ! eyepieces ( ! microscopes = read+ ! circle are %[n4 ,?is is %[n bett] 9 section 9 ,fig4 #aai4 ,"o ( ! solid /one pi]s is pi]c$ ?r\gh diagonally1 z %[n at 7m7 7m71 s t light proce$+ f a gas-lamp 7q7 plac$ opposite ! pivot ( ! telescope is all[$ to fall ?r\gh ! op5+s1 & is cond5s$ by means ( ! l5s 7n7 on ! graduations ( ! circle ( five m9utes ea*1 already ref]r$ to4 ,by ! side ( ea* illum9at+ hole is ano!r hole 7o7 7o7 ?r\gh :i* ! read+ microscopes1 six 9 numb]1 two ( :i* are %[n at 7q7 7p71 hav+ _! eye-ends arrang$ 9 a circle at ! end ( ! pi]1 are focuss$ on to ! graduations ( ! circle4 ,!re is also ano!r read+ microscope1 besides ! six j m5tion$1 ( less p[] = read+ ! degrees1 or l>g] divisions ( ! circle4 ,h5ce f ! side ( ! pi] close to ! lamp ! obs]v] c read ! circle ) accuracy1 & measure ! angle1 to :i* we h allud$1 made by ! telescope :5 po9t$ to any p>ticul> />4 ,we h n[ se5 h[ ! circle is illum9at$1 & n[ we w inquire fur!r z to ! arrangem5ts t are necess>y 9 ord] to br+ ?is in/rum5t into use4 ,illu/ration3 ,,fig4 #aai4--,plan ( ! ,gre5wi* ,transit ,circle4 ,we mu/ def] giv+ m explanation ( ! practical work+ ( ! in/rum5t until we h consid]$ ! clock us$ 9 connection ) x1 & we %all !n %[ h[ ! obs]vations are made4 ,"o important po9t to :i* att5tion %\ld be giv5 is ! me?od ( illum9at+ ! wires 9 ! eyepiece4 ,?is is ! arrangem5t4 ,!re is a lamp at ! end ( "o ( ! pivots :i* is holl[1 ! light falls on a mirror1 plac$ 9 ! c5tre ( ! telescope1 ( su* a %ape & 9 su* a position t x w n int]cept ! light f ! object-glass fall+ ?r\gh ! diaphragms on to ! eyepiece4 ,! mirror is r+-%ap$1 some?+ l ! brim ( a hat1 & is c>ri$ on two pivots1 s t x c be plac$ diagonally 9 ! tube1 or at "r angles to x2 x is arrang$ j outside ! cone ( rays f ! object-glass1 s t :5 ! mirror is diagonally plac$ ! light w be grasp$ directly f ! lamp at ! end ( ! axis & reflect$ d[n & mix$ up ) ! light com+ f ! /> into ! eyepiece4 ,9 ?is way ( c\rse ! wires c be r5d]$ visible at night1 & )\t su* a me?od !y w\ld be invisible4 ,?is arrangem5t gives a bright field & d>k wires2 b !re is also a me?od ( rev]s+ matt]s2 = ne> ! edge ( ! r+-%ap$ reflector are fix$ prisms = reflect+ ! light1 & :5 ! reflector is plac$ squ>e ) ! axis ( ! telescope ! small prisms on ! reflector s5d ! light d[n ?r\gh ap]tures 9 ! diaphragms1 s t ! mirror 9 ?is position no long] s5ds ! light d[n ) ! rays f ! />1 b ?r\gh holes 9 ! diaphragms !mselves1 to two small reflect+ prisms1 "o on ea* side ( ! wires 9 ! eyepiece4 ,:at has t light to d8 ,x has simply to d ?is1 x has to fall sideways on ! wires !mselves 9 su* a mann] t x does n fall on ! eye except by reflection f ! wires4 ,9 ?is way we h ! means ( gett+ a bright sy/em ( wires on a d>k field1 9 :i* ! wires & objects to be measur$ are ! only ?+s to be se54 ,z ) ! pivots ( ! transit circle1 & 9 fact ( any a/ronomical in/rum5t1 s ) ! circles1 c]ta9 fundam5tal po9ts h to be borne 9 m9d2 &1 al?\gh x is absolutely impossible to ensure p]fection1 /ill1 to g z ne> to x z possible1 ! a/ronom] has to obs]ve a great _m times ov] 9 all sorts ( positions 9 ord] to br+ ! error d[n to its m9imum4 ,fir/1 ! circle mu/ be plac$ exactly at "r angles to ! axis ( ! telescope1 s t x is 9 ! plane ( ! m]idian4 ,secondly1 ! error ( c5t]+ mu/ be f\nd4 ,= in/ance1 if ! ,gre5wi* circle 7 to be read by only "o microscope1 an error 9 ! pivot or any "p ( ! axis r\nd :i* ! circle turns w\ld vitiate ! read+s2 b we c\ld get rid ( t error1 due to a fault ( ! axis1 or to a want ( c5t]+1 by means ( two read+s1 at ! extremities ( a diamet]2 b ev5 !n we %\ld n get rid ( ! possible error due to graduation1 = ev5 if ! divisions on ! circle 7 accurate at fir/1 !y w\ld n long rema9 s1 = ! metal ( :i* ^! circles are made is liable1 l o!r metals1 to c]ta9 *anges due to temp]ature2 & if a circle is v l>ge ! weight ( ! circle itself1 suppos+ its =m p]fect :5 horizontal1 w1 :5 v]tical1 sag x d[n & deflect x out ( %ape1 s t at ,gre5wi* ! me?od adopt$ is to use six read+ microscopes4 ,fig4 #abj1 :i* %[s ! ,cambridge ,transit ,circle1 indicates ! arrangem5t ( ! five microscopes 9 use !re1 set r\nd ! circumf]5ce ( ! circle1 mu* 9 ! same mann] z 9 ! case ( ! ,gre5wi* in/rum5t1 :]e !re are holes ?r\gh ! pi] 9 :i* ! microscopes are plac$ ) ! eye-ends arrang$ 9 a circle at ! side ( x4 ,illu/ration3 ,,fig4 #abj4--;,cambridge 7,u4,s47 m]idian circle4 ,:51 !re=e1 ! transit is po9t$ to any p>ticul> />1 n only is ! "t not$ 9 ord] to det]m9e ! "r asc5sion ( ! />1 9 a c>eful & elaborate way1 b ! read+s ( ! circle are made by e "o ( ^! microscopes--read+ f ! next five m9utes division ( ! circle :i* happ5s to be visible1--& !re is an additional microscope giv+ ! r\gh read+ ( ! l>g] divisions ( ! circle f a c]ta9 z]o4 ,& :at1 !n1 is ?is z]o8 ,!re is no d\bt ab\t ! read+ ( ! z]o ( "r asc5sion1 x is ! int]section ( ! two fundam5tal planes at ! fir/ po9t ( ,aries2 b :at z]o %all be us$ 9 ! case ( ! v]tical circle8 ,illu/ration3 ,,fig4 #aba4--;,diagram illu/rat+ h[ ! pole is f\nd4 ,let ! circle1 ,h1 ,z1 ,r1 ,fig4 #aba1 repres5t a great circle ( ! heav5s1 ! m]idian 9 fact1 & let ! c5tre ( ?is circle repres5t ! c5tre ( ! transit in/rum5t4 ,n[ :at we want is1 n only to be able to measure degrees ( arc along ?is circle1 b to det]m9e "s />t+-po9t = ^? degrees4 ,"o arrangem5t is to obs]ve ! reflection ( ! wires 9 ! eyepiece ( ! transit circle1 f ! surface ( m]cury 9 a vessel :i* is plac$ bel[ ! telescope1 turn$ ) its object-glass d[nw>ds2 ! vessel conta9+ ! m]cury is out ( sight1 betwe5 ! two pi]s1 b 9 ,fig4 #aah are se5 ! two p>allel b>s1 ) weights at ! ends1 c>ry+ x1 by :i* x may be br\ght into any position = ! purpose ref]r$ to1 s t ! light f ! wires 9 ! eyepiece may pass ?r\gh ! tube & be reflect$ back by ! m]cury 7! surface ( :i* is ( c\rse p]fectly horizontal71 up ?r\gh ! tube aga9 to ! eyepiece4 ,:5 ! telescope is absolutely 9 ! v]tical position ! images ( ! cross wires w be sup]pos$ ov] ! cross wires !mselves2 & !n an obs]vation w give ! actual read+ ( ! circle :5 ! in/rum5t is po9t+ at #ahj f ! z5i?2 d$uct #ahj f ?is read+1 & we get ! read+ :5 ! in/rum5t is po9t+ at ! z5i?--! z]o requir$4 ,?is %\ld be #j1 & ! quantity by :i* x diff]s f #j mu/ be appli$ to ! obs]v$ position ( />s1 s t ! di/ance ( a /> f ! z5i? c be at once det]m9$4 ,b ?is is n all4 ,if we assume = ! mom5t t ! obs]v] is at ! nor? pole1 ! pole /> w be exactly ov] head1 & !re=e1 suppos+ ! pole /> to absolutely repres5t ! pole ( ! heav5s1 all ! obs]v] has to d is simply to take a read+ ( ! pole /> on ! arc ( 8 circle--call x #j ,o #j--;& !n use x z ano!r z]o to reckon pol> di/ance f1 see+ t e p>ticul> /> or body we obs]ve has s _m degrees1 m9utes1 seconds1 or t5?s ( seconds1 f ! pole />4 ,b we are n at ! nor? pole4 ,/ill we are 9 a position :]e ! pole is well above ! horizon1 & f t fact we c det]m9e ! pol> di/ance1 al?\gh ! absolute place ( ! pole is n po9t$ out by ! pole />4 ,?us1 if we suppose any />1 ,a1 ,fig4 #aba1 to be a c]ta9 di/ance f ! pole1 & ! e>? c>ry+ ! in/rum5t to be 9 ! c5tre ( ! circle ,h1 ,z1 ,r1 we c obs]ve ! z5i? di/ance ( t />1 ,z1 ,a1 :5 x transits our m]idian above ! pole1 ,p2 & we c !n obs]ve its di/ance1 ,z1 ,b1 :5 x transits bel[ ! pole2 & x is cle> t ! diff]5ce betwe5 ^? two measures w give ! di/ance ,a1 ,b1 or d\ble ! pol> di/ance ( t />1 & ! mean ( ! read+s w give ! di/ance1 ,z1 ,p1 ! z5i? di/ance ( ! pole1 s t x is p]fectly easy to det]m9e ! di/ance betwe5 ! pole & ! z5i?1 :i*1 subtract$ f n9ety degrees1 gives u ! latitude ( ! place4 ,x is !re=e p]fectly easy by means ( ?is in/rum5t to det]m9e ei!r ! z5i? or pol> di/ance1 &1 kn[+ ! pol> di/ance1 we get ! decl9ation1 or di/ance f ! equator1 by subtract+ x f n9ety degrees4 ,9 our case x is ! nor? pol> di/ance or decl9ation ( any object 9 ! heav5s t we record2 & if we take ! precaution to d s ) ?is in/rum5t at ! "t giv5 by ! clock1 :5 ! object passes ! m]idian1 we h ! actual app>5t place ( t body 9 ! sky2 & 9 ?is way all ! positions ( ! />s & o!r bodies1 & _! v>i\s *anges1 & ! c\rses ( ! planets1 h be5 det]m9$4 ,! transit circle is ! mo/ important in/rum5t ( a/ronomy1 & su* is ! p]fection ( ! ,gre5wi* in/rum5t t no?+ c\ld be m un=tunate = a/ronomy ?an t t in/rum5t %\ld be 9 any way damag$4 ,& ?\gh _m ( u are admir]s ( physical a/ronomy1 we h yet to f9d ! in/rum5t t is z important to physical a/ronomy z ! transit circle at ,gre5wi* is to a/ronomy ( position4 ,! room 9 :i* ^! transit circles are work$--! transit room--is requir$ to be ( special con/ruction4 ,a cle> space f ! s\!rn horizon ?r\gh ! z5i? to ! nor? mu/ at any "t be available2 ?is entails ! cutt+ ( a n>r[ slit 9 ! ro( & bo? walls1 )\t ! int]v5tion ( any beams across ! room4 ,?is slit is clos$ by %utt]s or w9d[s :i* are made to op5 9 sections1 s t any "p ( ! m]idian c be obs]v$ at pleasure4 ,,*apt] ,,xvii4 ,,! ,,transit ,,clock ,,& ,,*ronograph4 ,we h n[ to consid] ! way 9 :i* ! transit in/rum5t is us$ & ! functions :i* bo? x & ! transit circle fulfil4 ,! connection betwe5 ! transit in/rum5t & ! transit clock is s intimate t ei!r is useless )\t ! o!r4 ,9 ! "o case we %\ld note ! passage ( a /> across ! m]idian )\t kn[+ at :at "t x took place2 :ile1 on ! o!r h&1 we %\ld n le>n :e!r ! clock %[$ true "t or n1 unless we c\ld *eck its indications 9 ! mann] r5d]$ possible by transit obs]vations4 ,9 :at has be5 already said ( "t we ref]r$ to x z measur$ by our ord9>y clocks1 i4e4 reckon+ x f noon to midnight & midnight to noon1 & regulat$ entirely by ! l5g? ( ! sol> day4 ,x w\ld at fir/ sight seem t x %\ld be twelve o'clock by a clock s regulat$ :5 ! sun passes ! m]idian2 b ! e>?'s orbit is n circul>1 & ! sun's c\rse is incl9$ to ! equator1 s t1 z det]m9$ by su* a clock1 sometimes he w\ld get to ! m]idian a little too late1 & sometimes too e>ly1 s t we %\ld be cont9ually alt]+ our clocks if we attempt$ to keep "t ) ! sun4 ,"o ( ! greate/ boons conf]r$ by a/ronomy ^u our daily life is an imag9>y sun t keeps exact "t1 call$ ! ,mean ,sun1 s t ! mean sun is on ! m]idian at twelve o'clock ea* day by our clocks1 regulat$ by ! me?ods we h n[ to discuss4 ,su* clocks regulat$1 z x is call$1 to mean "t are sometimes a few m9utes be=e1 & at o!rs a few m9utes beh9d ! true sun1 by an am\nt call$ ! ,equation ( ,"t1 :i* is giv5 9 ! almanacs4 ,x w\ld !re=e be difficult to regulate our /&>d clock by ! sun1 s we d x ?r\gh ! m$ium ( ! />s1 :i* g pa/ our m]idian ) ! greate/ regul>ity1 s9ce _! app>5t motion dep5ds almo/ :olly ^u ! equable rotation ( ! e>? on its axis1 :ile ! app>5t motion ( ! sun is complicat$ by ! e>?'s revolution r\nd x4 ,?is me?od at fir/ sight is complex1 & 9 fact we _c obta9 mean "t directly by su* transits ( />s4 ,x is accompli%$ indirectly by means ( a clock set to />- or sid]eal-"t1 & su* a clock is ! a/ronom]'s companion1 to :i* he always ref]s 8 obs]vations1 & ! indications ( :i* alone are always 9 8 m9d4 ,?is he calls ! ,sid]eal ,clock4 ,illu/ration3 ,,fig4 #abb4--;,diagram illu/rat+ ! diff]5t l5g?s ( sol> & sid]eal day4 ,we h1 !n1 next to consid] ! diff]5ce betwe5 ! clock us$ = ! transit1 or ! sid]eal clock1 & an ord9>y sol> clock1 or betwe5 a sol> & a sid]eal day4 ,let ,s1 ,fig4 #abb1 repres5t ! sun1 & ! arc a "p ( ! orbit ( ! e>?1 ! e>? go+ 9 ! direction ( ! arr[4 ,let #b repres5t ! position ( ! e>? "o day1 & let #a repres5t ! position ( ! e>? on ! day be=e4 ,a l9e drawn f ! sun ?r\gh ! e>?'s c5tre w give u ! places a1 b1 on ! e>? at :i* x is midday on ! side turn$ t[>ds ! sun1 & midnight on ! side turn$ f ! sun4 ,n[ :5 a revolution ( ! e>? ) ref]5ce to ! />s has be5 accompli%$ ! e>? comes to ! second position1 #b2 & c is ! po9t ( midday2 & !re is a c]ta9 angle "h betwe5 a & c1 ?r\gh :i* ! e>? mu/ turn be=e x is noon at a1 due to ! *ange ( position ( ! e>?1 or to ! app>5t motion ( ! sun among ! />s1 by :i* ! sun comes to ! m]idian r lat] ?an ! />s ea* day4 ,n[ let u suppose t1 :ile "o obs]v] 9 ,engl& is obs]v+ ! sun at midday1 ano!r is obs]v+ ! />s at ! antipodes at midnight1 ! /> is se5 9 ! direction 4 ,we are aw>e t ! />s are s f> away1 t f any po9t ( ! e>?'s orbit !y seem to be 9 absolutely ! same place--!y d n *ange _! positions 9 ! same way z ! sun appe>s to d among/ !m--an obs]v] at b !re=e sees on 8 m]idian ! /> :ile ! obs]v] at a sees ! sun on 8 m]idian2 suppos+ b to repres5t ! same obs]v]1 on ! second day1 he w see ! /> due s\? be=e ! o!r obs]v] at a sees ! sun due s\?4 ,! result ( t is1 t ! sid]eal day is %ort] ?an ! sol> day1 & ! sun appe>s to lose on ! />s4 ,if we wi% to h a clock to %[ #ab o'clock :5 ! sun is s\?+1 we %all want x to g sl[] by ne>ly f\r m9utes a day ?an "o :i* is regulat$ by ! />s & is at #ab o'clock :5 our />t+-po9t ( "r asc5sion--:i* is ! int]section ( ^? two fundam5tal planes1 ! equator & ! ecliptic--passes ov] ! m]idian4 ,"o ( ! uses ( ! clock %[+ sid]eal "t 9 connection ) ! conv5i5t fiction ( ! 8,mean ,sun10 is to give to ! outside _w a con/ant fl[ ( mean "t regulat$ to ! av]age s\?+ ( ! sun 9 ! middle ( ! p]iod = :i* ! sun is above ! horizon ea* day 9 ! ye>4 ,! /ell> day1 t is ! "t f "o transit ( a /> to ! next1 is %ort] ?an a sol> day by #cm4 #efs41 s :at is call$ sid]eal "t1 regulat$ by ! transits ( well-kn[n />s1 9 ! mann] we %all pres5tly expla91 by no means runs p>allel ) mean "t s f> z ! clock indications g4 ,inde$ :5 we look at a sid]eal clock1 we see some?+ diff]5t to ! clock we are g5]ally accu/om$ to see4 ,9 ! fir/ place1 we h tw5ty-f\r h\rs in/ead ( twelve1 & !n g5]ally !re is "o dial = h\rs1 ano!r = m9utes1 & ano!r = seconds4 ,t ( c\rse might happ5 9 ! case ( ! mean-"t clock2 b ! mean-"t clock is n (t5 divid$ into tw5ty-f\r h\rs1 al?\gh x =m]ly us$ to be1 z ! dials 9 ,v5ice /ill te/ify4 ,we n[ see ! importance ( an absolutely correct det]m9ation ( ! "r asc5sion ( />s2 = ?is "r asc5sion1 express$ 9 h\rs1 m9utes1 & seconds1 is no?+ m nor less ?an ! "t indicat$ by ! sid]eal clock1 by ! side ( ! transit in/rum5t1 :5 a /> passes ov]1 or transits1 ! c5tral wire ( t in/rum5t4 ,h5ce x is ! sid]eal clock :i* keeps "t ) ! />s1 & :i* we keep correct by means ( ! transit in/rum5t4 ,illu/ration3 ,,fig4 #abc4--,sy/em ( wires 9 transit eyepiece4 ,let u %[ h[ ?is 0 always done "s tw5ty or ?irty ye>s ago1 & h[ x is sometimes done n[4 ,! transit room is kept s quiet t "o c he> no?+ b ! tick+ ( ! sid]eal clock2 ! /> to be obs]v$ is !n c>efully wat*$ z x trav]ses ! field ( view ov] ! wires1 & ! "t ( transit ov] ea* wire is e/imat$ to ! t5? ( ! "t betwe5 ea* beat by ! obs]v]4 ,we reproduce 9 ,fig4 #abc a r\gh repres5tation ( :at is se5 9 ! field ( view ( a transit in/rum5t4 ,n[ if we c\ld be p]fectly sure ( mak+ an accurate obs]vation by means ( ! c5tral wire1 x is n to be suppos$ t a/ronom]s w\ld ev] h c>$ to use ?is complicat$ sy/em ( wires 9 _! eyepieces2 b s great is ! difficulty ( det]m9+ accurately ! "t at :i* a /> passes a wire1 t we h 9 eyepieces introduc$ a sy/em ( sev]al wires1 s t we may take ! transit ( ! /> fir/ at "o wire1 !n at ano!r1 until e wire has be5 pass$ ov]4 ,we want "o wire exactly 9 ! middle to repres5t ! real physical middle ( ! eyepiece s f> z skill c d x1 & !n !re is a simil> numb] ( wires on ei!r side at exactly equal di/ances2 s t ! av]age ( all ! obs]vations made at ea* ( ! wires w be mu* m likely to be accurate ?an a s+le obs]vation at "o wire4 ,9 ?is way ! a/ronom] gives himself a good _m *ances aga9/ "o to be "r4 ,if he lo/ 8 *ance f any reason :5 us+ only "o wire1 he w\ld h to wait tw5ty-f\r m sid]eal h\rs be=e he c\ld make 8 measure aga91 b by hav+ five1 or sev51 or tw5ty-five or m wires 9 ! eyepiece ( ! telescope1 he increases 8 *ances ( correctness3 & ! way 9 :i* he works is ?is3 ,:ile ! heav5s !mselves are tak+ ! />s across ! wires he li/5s to ! beat+ ( ! clock4 ,if a /> crosses "o ( ! wires exactly z ! clock is beat+1 he kn[s t x has pass$ ! wire at "s second1 & he takes c>e to "k :at second t is2 b if1 in/ead ( be+ absolutely co9cid5t ) "o ( ! beats ( ! clock1 x is half-way betwe5 "o beat & ano!r1 or ne>] to "o beat ?an ano!r1 he e/imates ! fraction ( a second1 & by practice he has no difficulty at all 9 e/imat+ divisions ( "t equal to t5?s ( a second1 & at ea* p>ticul> wire 9 ! eyepiece ! transit ( ! /> is ?us m9utely obs]v$4 ,!n if ! obs]vations are complete & ! mean ( !m is tak51 x %\ld1 aft] ! necess>y corrections = in/rum5tal errors h be5 appli$1 give ! actual obs]vation made at ! c5tral wire2 if ! a/ronom] _c make obs]vations at e wire1 he introduces a correction 9 8 mean to make up = ! lo/ obs]vations4 ,?is is :at is call$ ! 8eye & e>0 me?od1 because ! obs]v] is plac$ ) 8 eye to ! telescope1 & he dep5ds ^u 8 e> to give him ! exact int]val at :i* ea* beat ( ! clock takes place1 & he requires an exact p[] ( m5tally divid+ ! di/ance betwe5 ea* beat into t5 equal p>ts1 :i* are t5?s ( seconds4 ,9 ?is me?od ( obs]vation e obs]v] diff]s slightly 9 8 judgm5t ( ! in/ant t ! /> crosses ! wire1 & 8 e/imation diff]s f ! tru? by a c]ta9 con/ant quantity :i* he mu/ always all[ =2 ?is error is call$ 8 p]sonal equation4 ,9 ?is way !n ! transit in/rum5t enables u1 hav+ true "t1 to det]m9e ! "r asc5sion ( a heav5ly body z x transits ! m]idian1 &1 kn[+ ! "r asc5sion ( a heav5ly body1 we h only to wat* its transit 9 ord] to "k ! true "t2 s if ! obs]v] kn[s at :at "t a kn[n /> ought to transit1 he has an opportunity ( correct+ 8 clock4 ,s mu* = ! eye & e> me?od ( transit obs]vation4 ,!re is ano!r :i* has n[ to a v l>ge ext5t sup]s$$ x4 ,?is is call$ ! 8*ronographic me?od02 we owe x to ,sir ,*>les ,:eat/one1 :o made x possible ab\t #ahdj4 ,figs4 #abd-g are f draw+s ( ! *ronograph 9 use at ,gre5wi*1 & by _! means we hope to make ! pr9ciple ( ! in/rum5t cle>4 ,9 ?is *ronograph1 g is a long conical p5dulum :i* regulates ! driv+ clock 9 ! case bel[ x1 ?r\gh ! ge>+ ( :eel-"w1 z x turns ! cyl9d]1 ,e1 g5tly & regul>ly r\nd4 ,on ! cyl9d] is plac$ pap] to receive ! m>k regi/]+ ! obs]vations2 along ! side ( ! cyl9d] or roll] run two long screws1 ,k & ,n1 ,fig4 #abe1 :i* are also turn$ by ! clock1 & on !m are c>ri$ electro-magnets1 ,a1 ,b1 ,fig4 #abe1 & prick]s1 #ce1 ,fig4 #abf2 z ! screws turn1 ! magnets & prick]s are mov$ along ! roll]1 &1 z ! roll] turns1 ! po9t]1 #cf1 ,fig4 #abg1 traces a f9e l9e on ! pap] l ! worm ( a screw on ! surface2 & x is close to ?is l9e1 :i* s]ves z a guide to ! eye1 t ! prick]s make a m>k ea* "t a curr5t is s5t ?r\gh ! electro-magnets2 ?is turns ea* ( !m into a magnet1 & !y !n attract a piece ( iron :i*1 9 mov+ upw>ds1 presses d[n its prick] by means ( a lev]1 & regi/]s ! in/ant ! curr5t is s5t4 ,! diff]5t wires are br\ght1 fir/ f ! transit circle to "w "o prick]1 & !n f ! clock to "w ! o!r1 ! clock s5d+ a curr5t & produc+ a prick on ! roll] e second4 ,illu/ration3 ,,fig4 #abd4--,! ,gre5wi* *ronograph4 ,g5]al view4 ,! obs]v]1 in/ead ( dep5d+ ^u ! eye & e> z he _h to d be=e1 has !n ! means ( impress+ a m>k at any in/ant ^u ! same cyl9d]1 9 exactly ! same way t ! p5dulum ( ! clock impresses ! m>k ( any second1 s t z ea* wire 9 ! eyepiece ( ! transit in/rum5t is pass$ by ! />1 he is able1 by ! same me?od z ! clock1 to record on ?is same revolv+ surface ea* obs]vation1 :i* c aft]w>ds be comp>$ ) ! m>ks repres5t+ ! seconds1 & s ! exact "t ( ea* obs]vation is read (f m accurately & ) less tr\ble ?an by ! old me?od4 ,let u suppose we are mak+ a transit obs]vation3 ! clock w be dilig5tly prick+ sid]eal seconds1 :ile we1 by a contact-mak] held 9 ! h&1 are z dilig5tly record+ ! mom5ts at :i* ! /> passes ea* wire4 ,illu/ration3 ,,fig4 #abe4--;,details ( ! travell+ c>riage :i* c>ries ! magnets & prick]s4 ,side view & view f above4 ,illu/ration3 ,,fig4 #abf4--,%[+ h[ on ! passage ( a curr5t r\nd ! s(t iron ! prick] is made to make a m>k on ! spiral l9e on ! cyl9d]4 ,illu/ration3 ,,fig4 #abg4--,side view ( ! c>riage c>ry+ ! magnets & ! po9t] t draws ! spiral4 ,?is is done by press+ a /ud1 & s5d+ a curr5t at ea* transit2 s t we %all h a dot 9 e o!r space betwe5 ! clock dots1 suppos+ ! wires to be two seconds 9 "t ap>t2 suppos+ !m to be ?ree seconds ap>t1 our dots w be 9 e ?ird space2 suppos+ !m to be f\r seconds ap>t1 our dots w be 9 e f\r? space1 & s on2 & t5?s & hundr$?s ( seconds are e/imat$1 by ! position ( ea* transit dot betwe5 ^? :i* record ! seconds4 ,9 ?is way "o sees t we h on ! b>rel an absolute record1 by "o ( ! po9t]s1 ( ! seconds record$ by ! clock1 &1 by ! o!r1 ( ! exact times at :i* a /> has be5 se5 at ea* wire ( ! transit in/rum5t4 ,n[ ( c\rse :at is ess5tial 9 ?is me?od is t !re %all be a p[] ( det]m9+ n only ! precise second or t5? ( a second ( "t1 b also ! m9ute at :i* contact takes place1 o!rwise !re w\ld be a numb] ( seconds dots )\t kn[+ to :at m9ute !y correspond$2 x w\ld be l hav+ a clock ) only a second-h& & no m9ute-h&4 ,! brass v]tical slid+ piece %[n at ! l[] left-h& side 9 ,fig4 #if1 c>ries at its upp] end two brass b>s1 ea* ( :i* has1 at its "r-h& extremity1 betwe5 ! jaws1 a sl5d] /eel spr+ = galvanic contact2 ! l[] spr+ c>ries a semicircul> piece project+ d[nw>ds1 :i* a p9 on ! crut* rod lifts 9 pass+1 br++ ! spr+s 9 contact at ea* vibration3 ! contact takes place :5 ! p5dulum is v]tical1 & ! act+ surfaces ( ! spr+s are1 "o plat9um1 ! o!r gold2 an arrangem5t t has be5 suppos$ to be pref]able to mak+ bo? surfaces ( plat9um4 ,by means ( ! screws n & o1 :i* bo? act on slid]s1 ! contact spr+s c be adju/$ 9 ! v]tical & horizontal directions respectively4 ,o!r contact spr+s 9 connection ) ! brass b>s p & q1 on ! o!r side ( ! back plate1 are ord9>ily 9 contact1 b ! contact is brok5 at "o second 9 ea* m9ute by an arm on ! escape-:eel sp9dle4 ,! comb9ation ( ^! contacts p]mits ! clock to complete a galvanic circuit at fifty-n9e ( ! seconds 9 ea* m9ute1 & omit ! sixtie?4#ac ,9 ?is way we may suppress ! sixtie? second1 ?us leav+ a blank t m>ks ! m9ute2 & all t ! obs]v] has to d aft] he has made a record ( ! transit1 is to g quietly to ! b>rel1 & m>k ! h\r & m9ute 9 ! vacant space4 ,a b>rel ( ?is size w conta9 ! obs]vations :i* w\ld be made 9 "s h\rs2 s t at ! end ( t "t x may be tak5 (f1 & x w give1 ) ! lea/ possible *ance ( error1 a p]man5t record ( ! "w ( ! a/ronom]4 ,x is at once app>5t t by ! introduction ( ?is application ( electricity1 a/ronomy has be5 an enorm\s ga9]2 b s f> we h simply giv5 a description ( "o in/rum5t :i* has be5 sugge/$ = t purpose4 ,a few words may be said on o!r =ms4 ,9 ! in/rum5t us$ 9 ! ,royal ,obs]vatory at ,gre5wi* ! rotation ( ! roll] is kept uni=m1 z we h se51 by a conical p5dulum2 b !re are o!r me?ods ( atta9+ ?is end--!re is ! fly-:eel & fan1 simil> to ! arrangem5t = regulat+ ! /rik+ "p ( a clock2 !re is ! gov]nor us$ = ! /eam-eng9e1 & o!rs :i* give a fairly regul> motion--= ! motion ne$ n be absolutely uni=m1 because ! dots1 :i* =m ! po9ts f :i* to measure1 are made by ! /&>d clock4 ,! p>ticul> in/ant at :i* ea* m9ute occurs may be record$ 9 ano!r way4 ,! two /eel spr+s above describ$ may be press$ toge!r1 n by a p9 9 ! crut*1 b by cogs on a :eel atta*$ to ! sp9dle ( ! escape-:eel ( ! clock 7see ,fig4 #abh72 & !n all we h to d to /op ! transmission ( a curr5t at ! sixtie? second is to remove "o ( ! cogs4 ,illu/ration3 ,,fig4 #abh4--,:eel ( ! sid]eal clock1 & arrangem5t = mak+ contact at ea* second4 ,ano!r simple me?od = transmitt+ seconds' curr5ts has also be5 occasionally tri$4 ,a wire runs d[n ! :ole l5g? ( ! p5dulum1 & ends 9 a projection ( su* a l5g? t x sw+s ?r\gh a small globule ( m]cury 9 a cup bel[ x1 ! p5dulum be+ connect$ ) "o wire f ! *ronograph & ! m]cury ) ! o!r2 ?us !re w be a mak+ & break+ ( contact ea* "t ! po9t ( ! p5dulum sw+s ?r\gh ! m]cury4 ,x is unc]ta9 :i* me?od is ! bett]2 "o w\ld pref] t :i*1 "u any circum/ances1 c\ld di/urb ! p5dulum lea/3 b z to :i* ?is is op9ions diff]4 ,we h n[ describ$ ! modus op]&i ( mak+ "t obs]vations ) ! transit in/rum5t1 ! f9al result ( :i* is t ! "t %[n by ! sid]eal clock corresponds ) ! "r asc5sion ( ! 8clock />s0 z !y transit ! c5tral wire4 ,! great use1 z we h already /at$1 made ( ! sid]eal clock ?us kept "r by ! />s is to correct ! mean-"t clock ) a view ( supply+ mean sol> "t to ! outside _w4 ,z ! sid]eal clock is regulat$ by ! />s1 x c be correct$ by !m at any "t by ! clock />s giv5 9 ! 8,nautical ,almanac10 ^: "t ( pass+ ! m]idian is calculat$ be=eh& mu* m accurately ?an a mean-"t clock c\ld be correct$ by ! sun2 we !re=e correct our mean clock by ! sid]eal1 ! two agree+ at ! v]nal equ9ox1 :5 ! sun is 9 ! fir/ po9t ( ,aries1 & ! sid]eal clock ga9+ ab\t #cm4 #efs4 ea* day until x has ga9$ a :ole day1 & agrees aga9 at ! next v]nal equ9ox4 ,illu/ration3 ,,fig4 #abi4--;,arrangem5t = correct+ mean sol> "t clock at ,gre5wi*4 ,at ,gre5wi* !re is1 z we h already se51 a /&>d1 sid]eal clock1 t is1 a clock keep+ sid]eal "t2 & regulat$ f ?is is ! /&>d sol> "t clock1 giv+ ! "t by :i* all our clocks & wat*es are gov]n$4 ,9 practice at ,gre5wi* ! sol> clock is regulat$ z foll[s3 9 ! comput+ room are two *ronomet]s1 c & b1 ,fig4 #abi1 ! "o1 c1 regulat$ electrically by ! mean-"t clock1 & ! o!r1 b1 regulat$ by ! sid]eal clock--! error ( ! latt] be+ kn[n by transit obs]vations ( />s on ! ,nautical ,almanac li/1 ! diff]5ce betwe5 ! obs]v$ "t ( transit & ! "r asc5sion ( ! /> be+ ! error requir$4 ,! prop] diff]5ce betwe5 ! two clocks is !n calculat$ & ! error all[$ =1 :i* %[s :e!r ! sol> clock is fa/ or sl[2 to correct x ! foll[+ me?od is adopt$3 ,c>ri$ on ! p5dulum ( ! sol> clock is a sl5d] b> magnet1 ab\t five in*es long1 & bel[ x1 fa/5$ to ! clock-case1 is a galvanic coil2 ! magnet passes at ea* sw+ ov] ! upp] end ( ! coil2 if n[ a curr5t is s5t ?r\gh ?is coil 9 "o direction repulsion takes place betwe5 ! magnet & coil1 & ! clock is sl[$2 if1 on ! o!r h&1 ! curr5t is rev]s$1 ! clock is made to ga94 ,n[ betwe5 ! two *ronomet]s is a commutator1 d1 :i*1 by mov+ ! h&le to "o side or ! o!r1 s5ds ! curr5t ?r\gh ! coil 9 su* a mann] t ! clock is accel]at$ or ret>d$ suffici5tly to set x "r2 :5 ! h&le ( ! commutator is 9 ! position %[n 9 ! draw+ no action takes place4 ,z an in/ance ( ano!r me?od ( regulat+ "o clock f ano!r1 we w quote :at ,pr(essor ,piazzi ,smy? says ( ! clock arrangem5ts at ,ed9burgh4 ,correction ( ,mean-"t ,clock4--8,fir/ get its error on ! obs]v+1 i4e4 sid]eal clock4 ,?is is always done by co9cid5ce ( beats1 safe & c]ta9 to )9 "o-t5? ( a second1 & ) great ease & com=t by means ( ! l\d-beat+ hamm] :i* /rikes ! seconds ( ! sid]eal clock on ! outside ( ! case2 "o c !n wat* ! neck-&-neck race :i* takes place e six m9utes betwe5 ! second ( a sid]eal clock & ! second ( a mean-"t clock1 ! =m] always w9n+ :ile y look at ! motion ( ! mean-"t seconds h&1 & he> ! seconds ( ! sid]eal "t4 ,hav+ got ! error1 say ?ree 7#jc7-t5?s ( a second sl[1 ?is is ! arrangem5t = correct+ x4 ,! p5dulum is susp5d$ by a spr+ extra long1 & a long arm goes across ! clock pi]1 & ! p5dulum spr+ passes ?r\gh a f9e slit 9 ! middle ( x1 & ! left end 7( said arm7 turns on a pivot1 :ile ! "r end re/s on a cam1 :i* c be turn$ by a h&le outside ! clock-case4 ,turn+ ! h&le "o way raises ! arm1 & ) t l5g!ns ! act+ l5g? ( ! p5dulum spr+1 & turn+ ! o!r way1 l[]s x & %ort5s ! p5dulum1 b s slightly t x takes fifte5 m9utes ( ! quick5$ rate ( ! p5dulum1 :5 %ort5$1 to add ! requir$ #jc seconds to ! indications ( ! clock40#ad ,! sid]eal clock is us$ 9 _m ways besides ! purpose ( giv+ a basis f :i* we c at any "t get sol> "t1 ! di/ribution ( :i* =ms ! subject ( our next *apt]4 ----- ,footnote #ac3 ,nature1 ,april #a1 #ahge4 ,footnote #ad3 ,?is plan 0 devis$ & execut$ by ,mr4 ,sang1 ,c4,e41 ,ed9burgh4 ,,*apt] ,,xviii4 8,,gre5wi* ,,"t0 ,,& ,,! ,,use ,,made ,,( ,,x4 ,we h n[ describ$ ! me?od ( obta9+ & keep+ true ,gre5wi* "t by means ( transit obs]vations1 & ! next ?+ is to di/ribute x ei!r by controll+ or driv+ o!r clocks electrically1 or by s5d+ electric signals at kn[n times = p]sons to set _! clocks "r4 ,ne>ly all1 if n q ! :ole1 ( ! mean-"t clocks 9 ! ,obs]vatory are driv5 by a curr5t controll$ by ! /&>d clock1 z also is a seconds relay1 a ,fig4 #abi4 ,! clock controls1 by curr5ts s5t e second by ! relay1 "o or two clocks 9 ,london1 by special wires4 ,s long ago z ! ye> #ahdj ,sir ,*>les ,:eat/one read a pap] be=e ! ,royal ,society 9 :i* he describ$ an app>atus = controll+ any numb] ( clocks by "o /&>d clock at a di/ance away4 ,! pr9ciple 01 t at ea* beat ( ! /&>d clock an electric curr5t 0 s5t f x ?r\gh a wire to ! clocks to be work$ by x or gov]n$2 & ?is curr5t made an electro-magnet attract a piece ( iron ea* "t x 0 s5t2 & ?is piece ( iron mov$ backw>ds & =w>ds two pallets1 some?+ l ^? ( an ord9>y clock1 :i* turn$ a :eel1 & s work$ ! clock4 ,in/ead ( a spr+ or weight be+ us$ to "w x regulat$ by ! pallets1 ! pallets mov$ ! clock !mselves1 & ( c\rse keep "t ) ! /&>d clock4 ,sir ,*>les ,:eat/one 9 ?is mo/ valuable pione] pap]1 indicates sev]al modifications ( ?is plan4 ,he propos$ to ! ,a/ronom]-,royal to te/ 8 me?od by us+ ! !n new telegraph l9e to ,sl\gh1 b ! idea 0 n c>ri$ out4 ,?is me?od ( driv+ clocks by electricity naturally requir$ consid]able batt]y p[]1 & 9 ! m mod]n sy/ems ! clocks are simply controll$1 & n driv51 by electric curr5ts4 ,a v pretty me?od ( regulat+ clocks by a /&>d clock is t 9 use at ,ed9burgh4 ,on ! p5dulum rod ( ! clock to be regulat$1 & l[ d[n on ! same1 is a coil ( f9e cov]$ wire w\nd r\nd a %ort tube4 ,two p]man5t magnets are plac$ 9 l9e ) ea* o!r1 ) _! ,n or ,s ends close toge!r & ! o!r ends atta*$ to ! clock-case1 9 su* a mann] t ! coil1 on sw++ ) ! p5dulum1 c slide ov] ! magnets )\t t\*+4 ,! t]m9al wires ( ! coil are l$ up to ne> ! po9t ( susp5sion ( ! p5dulum1 s z n to affect its sw+1 & ! regulat+ curr5t is s5t ?r\gh a wire l a telegraph wire f ! /&>d clock1 & f ?is wire r\nd ! coil & !n to ! e>?1 or back by ano!r wire4 ,curr5ts are s5t ?r\gh ! wires 9 contr>y directions dur+ ea* successive second1 s t ! curr5t 9 ! coil fl[s 9 "o direction dur+ its sw+ f1 say1 "r to left1 & 9 ! contr>y direction :5 sw++ f left to "r2 ! effect ( ! curr5t fl[+ 9 "o direction is to cause "o magnet to repel ! coil (f x1 & ! o!r to attract x ov] x1 s t !re is a t5d5cy to ?r[ ! coil f "o side ( its sw+ to ! o!r1 & back aga9 :5 ! curr5t is rev]s$4 ,a little consid]ation w make x cle> t if ! p5dulum tries to g too fa/ ! coil w t5d to comm5ce its return sw+ be=e ! curr5t assi/+ ! previ\s sw+ has /opp$1 & x w !re=e meet ) resi/ance1 & be br\ght back to correct "t4 ,! alt]nate curr5ts dur+ ea* second may be s5t by hav+ a :eel ( ?irty long tee? on ! axis ( ! seconds h&4 ,above ! :eel1 & insulat$ f ea* o!r1 are fix$ two light spr+s :i* desc5d side by side on ei!r side ( ! tee? ( ! :eel1 & at "r angles to ea* spr+ !re projects sideways a little b> ( agate ) slop+ sides1 :i* is lift$ up by ! tee? z !y pass2 "o agate is fa/5$ a little l[] d[n its spr+ ?an ! o!r1 s t !y are held "o above ! o!r1 & half ! di/ance betwe5 two tee? ap>t3 ! :eel is s arrang$ t :ile at re/ "o ( ! tee? presses aga9/ "o ( ! agates & pu%es ! spr+ outw>ds1 :ile ! o!r agate drops betwe5 two tee?4 ,at ! next tick ( ! clock ! :eel w move "o-half a too?'s di/ance & ! o!r agate w be rais$ & ! fir/ dropp$4 ,at ! bottom ( ea* spr+ is a little plat9um knob t is br\ght aga9/ a plat9um plate z ea* spr+ is rais$1 s z to make electric contact4 ,two batt]ies 7s+le cells ( 8sawdu/-,daniell's0 answ] admirably = %ort di/ances7 are us$1 ! pole ( "o be+ put 9 contact ) ! upp] atta*m5t ( "o spr+ & ! - pole ( ! o!r batt]y 9 contact ) ! o!r spr+4 ,! o!r poles are put to e>?1 or connect$ to ! return wire f ! gov]n$ clock4 ,! plate aga9/ :i* ! spr+s are lift$ is put 9 connection ) ! l9e wire go+ to ! regulat$ clock4 ,!n1 z ei!r spr+ is lift$ up dur+ ! sw+ ( ! p5dulum f side to side1 a or - curr5t is s5t ?r\gh ! l9e wire f "o ( ! batt]ies4 ,x is n absolutely necess>y to use two batt]ies1 "o be+ sometimes suffici5t1 & 9 ?is case "o spr+ is ?r[n out ( action1 & a curr5t s5t only dur+ e o!r second 9 ! same direction4 ,! batt]y may 9 ?is case be plac$ close to ! regulat$ clock1 or any:]e 9 ! circuit1 s long z a curr5t fl[s :5ev] ! /&>d clock completes ! circuit at ! o!r end4 ,?is me?od has ! advantage t ! am\nt ( curr5t s5t c be regulat$ at w by a p]son at ! regulat$ clock1 s t x is possible by putt+ on m batt]y p[] to get suffici5t curr5t ?r\gh ! wire to "w a bell r++ at e o!r second1 or a galvanomet]1 %[+ :5 ! seconds h& ( ! /&>d clock is at ! ,os1 = !re is "o too? cut f ! :eel 9 su* a position t :5 ! seconds h& is at ,os no curr5t is s5t = two or m foll[+ seconds accord+ z "o or bo? spr+s are act+2 kn[+ ?is1 ! obs]v] wat*es = ! fir/ miss+ curr5t or 8dropp$ second10 & s f9ds if 8 clock is be+ correctly regulat$4 ,we see n[ ! necessity = correct+ ! /&>d clock by gradually increas+ or decreas+ ! rate1 = if x 7 done rapidly1 ! controll$ clocks w\ld break away f ! control1 & n be sl[$ & accel]at$ ) ! /&>d4 ,at ,gre5wi* ! correction1 usually only a fraction ( a second1 is made a little be=e ! h\rs ( #aj ,a4,m4 & #a ,p4,m41 s9ce at ^? in/ants a di/ribution ( "t is made ?r\gh\t ! c\ntry4 ,?is di/ribution is made z foll[s3-- ,an electric circuit is brok5 9 two places at ! /&>d clock1 "o place ( :i* is connect$ = "s seconds on ei!r side ( ea* h\r1 :ile ! o!r is connect$ at ea* sixtie? second2 bo? breaks c !re=e be only connect$ at ! comm5cem5t ( ea* h\r1 & !n only c ! curr5t pass4 ,we w call ?is1 !re=e1 ! h\rly curr5t3 x acts on ! magnet dis*>g+ ! ,gre5wi* "t ball at "o o'clock daily1 & on ! magnet ( ! h\rly relay %[n 9 ,fig4 #abi1 :i* completes v>i\s circuits4 ,"o goes to ! ,london ,bridge /ation ( ! ,s\?-,ea/]n ,railway ,co41 & ! o!r to ! ,g5]al ,po/ ,(fice = fur!r di/ribution4 ,! bell & galvanomet] 9 ! figure m>k$ 8,s4 ,e4 ,r4 h\rly signal & ,deal ball10 & 8,po/ ,(fice ,telegraphs0 %[ ! passage ( ^! signals4 ,we h n[ got ! h\rly signal at ! ,po/ ,(fice1 & ?is is di/ribut$ by means ( ! ,*ronoph]1 or r ,*ronoph]s1 = !re are two1 ! old "o orig9ally con/ruct$ by ,mr4 ,y>ley1 & br\ght f ,telegraph ,/reet on ! removal to ,/4 ,m>t9's-le-,gr&1 & a new "o1 mu* l>g]1 %[n 9 ! accompany+ ,fig4 #acj4 ,x is to ?is t ! ,gre5wi* wire is l$1 & ! curr5t transmitt$ to ! diff]5t l9es4 ,! l9es are divid$ into f\r gr\ps1 7#a7 ! metropolitan1 7#b7 %ort prov9cial1 7#c7 m$ium prov9cial1 7#d7 long prov9cial2 ! fir/ be+ wires pass+ to po9ts 9 ,london only1 ! second to places )9 ab\t #ej miles ( ,london1 ! ?ird to m di/ant places1 & ! f\r? to ! m di/ant places /ill1 requir+ signals4 ,! ends ( ea* ( ! f\r gr\ps are br\ght toge!r1 & ea* gr\p has its sep>ate relay4 ,^! f\r relays--! left-h& f\r %[n 9 ,fig4 #acj--;are all act$ ^u by ! ,gre5wi* signal & !re=e act simultane\sly1 ea* relay s5d+ a portion ( ! curr5t ( its batt]y ?r\gh ea* wire ( its gr\p4 ,illu/ration3 ,,fig4 #acj4--,! ,*ronoph]4 ,! metropolitan gr\p1 be+ us$ only = "t purposes1 is always connect$ ) ! relay1 b to ! c\ntry1 signals are s5t only twice a day1 namely1 at #aj ,a4,m4 & at #a ,p4,m41 & z ! ord9>y wires are us$ = ?is purpose1 !y mu/ be swit*$ into communication ) ,nos4 #b1 #c1 & #d relays4 ,! action at ea* h\r is z foll[s3--,! wires lead+ to ! respective t[ns are connect$ ) _! speak+ in/rum5ts ?r\gh a contact spr+2 ^! contact spr+s are %[n 9 ! figure 9 a r[1 l ! keys ( a piano2 along ! keys runs a flat b> :i* at a %ort "t be=e #aj ,a4,m4 & #a ,p4,m4 is turn$ on its axis by ! clockwork above1 by s do+ x presses back all ! keys f _! respective /uds1 & s cuts (f communication ) ! speak+ in/rum5ts1 & puts ! wires into communication ) ! b>1 :i* is divid$ into ?ree insulat$ portions1 ea* 9 communication ) a relay & batt]y2 ! batt]ies & relays become connect$ ) _! respective gr\ps1 & a con/ant curr5t fl[s ?r\gh all ! wires to ! di/ant /ations s]v+ z a w>n+4 ,:5 ! ,gre5wi* curr5t arrives ! relays rev]se ! curr5ts1 & ?is gives ! exact "t4 ,%ortly aft]w>ds ! clock turns back ! rod & ! spr+s g into contact ) _! respective in/rum5ts1 & all goes on z be=e4 ,"o ( ! rema9+ relays ( ! app>atus s5ds a curr5t to ,we/m9/] clock t[] = ! rat+ ( ! clock !re1 b x is 9 no way me*anically gov]n$ by ! curr5t4 ,! app>atus is entirely automatic1 & to judge ( ! degree ( accuracy obta9$ an exp]im5t 0 made4 ,"o ( ! di/ribut+ wires 0 connect$ ) a return wire to ,gre5wi*1 & ! outgo+ curr5t to ! ,po/ ,(fice & ! incom+ "o 7 pass$ r\nd galvanomet]s1 :5 no s5sible diff]5ce c\ld be se5 9 ! indications4 ,at #aj ,a4,m4 a consid]able di/ribution goes on by h&4 ,at ?is in/ant a s\nd signal is he>d f ! *ronoph]1 & ! cl]ks imm$iately transmit signals ?r\gh ! ord9>y in/rum5ts to "s #fjj places2 ^! aga9 act z c5tres di/ribut+ ! "t to railway /ations & small] places4 ,! me?ods ( signall+ ! "t are v>i\s2 at "s places1 z at ,ed9burgh1 ,newca/le1 ,sund]l&1 ,dundee1 ,middlesbor\gh1 & ,k5dal1 a gun is fir$ at #a ,p4,m4 ,! hi/ory ( ! introduction ( "t-guns is a some:at curi\s "o4 ,9 ,augu/ #ahfc1 dur+ ! meet+ ( ! ,briti% ,association at ,newca/le1 ,mr4 ,n4 ,j4 ,holmes contriv$ ! fir/ electric "t-gun4 ,?is gun 0 fir$ by ! electric curr5t direct f ! ,royal ,obs]vatory at ,ed9burgh1 #abj miles di/ant4 ,"t-guns 7 aft]w>ds exp]im5tally fir$ at ,nor? ,%ields & ,sund]l&2 ! ,sund]l& gun 0 aft] a "t )drawn2 ! ,newca/le & ,nor? ,%ields "t-guns are regul>ly fir$ e day at #a ,p4,m4 ,f\r "t-guns 7 m\nt$ 9 ,glasg[1 also to be fir$ by ! electric curr5t f ,ed9burgh2 a l>ge #cb-p\nd] 0 plac$ at ,port ,dundas1 on ! banks ( ! ,=? & ,clyde ,canal2 a second small gun 0 plac$ ne> ! ,royal ,ex*ange2 a ?ird #ah-p\nd] at ! ,bromielaw1 = ! b5efit ( ,clyde %ips 9 h>b\r2 & a f\r? tw5ty-five miles fur!r d[n ! ,clyde1 at ! ,alb]t ,quay1 ,gre5ock1 = ! vessels an*or$ (f ! tail ( ! bank4 ,^! f\r guns1 & ! two at ,newca/le1 7 regul>ly fir$ f ! ,royal ,obs]vatory1 ,ed9burgh1 = "s weeks4 ,a local jeal\sy spr++ up among/ a few ( ! ,glasg[ ,college ,pr(essors & ! ,ed9burgh ,obs]vatory1 aga9/ ! introduction ( mean-"t into ,glasg[ f ! ,royal ,obs]vatory ,ed9burgh1 in/ead ( d]iv+ x f ! ,glasg[ ,obs]vatory clock 7! longitude ( :i* 0 undet]m9$ at t "t71 ! orig9ator ( ! guns1 ,mr4 ,holmes1 0 cit$ be=e ! police-c\rt1 *>g$ "u ! ,act ) dis*>g+ fire>ms 9 ! public /reets4 ,! jeal\sy end$ 9 ! )drawal ( ! guns1 & ,glasg[1 f !n until n[1 has be5 )\t any practical regi/] ( true "t4#ae ,ano!r sy/em ( "t signall+ is to expose a ball to view on ! top ( a build+1 & drop x1 z 9 ! case ( ! ball automatically dropp$ at ,gre5wi* e day4 ,we h already m5tion$ t "o ( ! wires f ! ,gre5wi* ,obs]vatory connects x ) ! ,london ,bridge ,/ation1 & ?is is us$ = dropp+ ! "t-ball at ,deal4 ,9 return = ! h\rly signals ! ,company give up ! use ( ! wires to ,deal = two or ?ree m9utes ab\t #a ,p4,m41 :5 ! ,deal wire is swit*$ into communication ) ! ,gre5wi* wire by a clock1 j 9 ! same mann] z at ! ,po/ ,(fice1 & communication is also made at ,a%=d & ,deal1 9 ord] t ! curr5t %all g to ! "t-ball4 ,9 ord] t !y %all "k at ,gre5wi* t ! ball has fall5 correctly1 arrangem5ts are made s t ! ball on fall+ s5ds a return curr5t back to ,gre5wi*4 ,x appe>s t errone\s drops are r>e1 b1 if su* is ! case1 a black flag is imm$iately hoi/$ & ! ball dropp$ at #b ,p4,m4 ,h\rly signals are di/ribut$ on ! metropolitan l9es & to ! 8,briti% ,horological ,in/itute0 = ,cl]k5well2 ! lead+ ,london *ronomet] mak]s also receive !m privately4 ,we n[ come to deal ) "o ( ! practical uses ( ! clock & transit in/rum5t ) ref]5ce to det]m9+ longitudes4 ,! e>? rotates once e tw5ty-f\r h\rs1 & if at any "t a /> is directly s\? ( ,gre5wi* x is also due s\? ( all places on ! m]idian ( ,gre5wi* nor? ( ! equator1 & nor? ( all places on ! same m]idian s\? ( ! equator2 !n1 z ! e>? rotates1 ! m]idian ( ,gre5wi* w pass f "u ! />1 & o!rs to ! we/ w take its place1 & 9 an h\rs "t1 at #a ,p4,m41 a c]ta9 m]idian to ! we/ ( ,gre5wi* w be "u ! />1 & 9 t case all places on ?is m]idian w be an h\r we/ ( ,gre5wi*1 & s on ?r\gh all ! tw5ty-f\r h\rs1 ! m]idian be+ call$ s _m h\rs1 m9utes1 or seconds1 we/1 z x passes "u any /> t l5g? ( "t aft] ! m]idian ( ,gre5wi*4 ,x is immat]ial :e!r we reckon longitude 9 degrees or 9 "t1 = s9ce !re are #cfj degrees or tw5ty-f\r h\rs into :i* ! equator is divid$1 ea* h\r corresponds to #ae4 ,we also express ! longitude ( a place by its di/ance ea/ ( ,gre5wi* 9 h\rs1 s in/ead ( call+ a place tw5ty-?ree h\rs we/1 x is call$ "o h\r ea/4 ,suppose we wi% to f9d ! longitude ( any place1 all t is requir$ to be kn[n to an obs]v] !re is ! exact "t t a c]ta9 /> is on ! m]idian ( ,gre5wi*2 he !n obs]ves ! "t t elapses be=e ! /> comes to 8 m]idian1 & ?is "t is ! longitude requir$4 ,?is1 ( c\rse1 only %[s ! pr9ciple1 = 9 practice x is n absolutely necess>y = ! /> to be on ei!r m]idian1 provid$ its di/ance on ei!r side is kn[n1 :51 ( c\rse1 ! diff]5ce betwe5 ! times :5 x actually crosses ! m]idian c be reckon$4 ,9 practice a difficulty arises 9 f9d+ out at a di/ance f ,gre5wi* :at "t x is !re4 ,x is ( c\rse twelve o'clock at ,gre5wi* :5 ! sun crosses ! m]idian1 & x is also twelve o'clock at all ! o!r places :5 ! sun crosses _! m]idian3 b if a place is two h\rs we/ ( ,gre5wi*1 ! sun crosses ! m]idian two h\rs lat] ?an x does at ,gre5wi*1 & consequ5tly _! clock is two h\rs sl[] ?an ,gre5wi* "t1 h5ce ! t]m 8local "t10 :i* is diff]5t = diff]5t places ea/ or we/ ( ,gre5wi*4 ,we h tak5 above a /> = our fix$ po9t1 b obvi\sly ! sun answ]s ! same purpose4 ,x w appe> f ?is1 t if we "k ! diff]5ce betwe5 ! local times ( two places1 we also "k ! longitude ( "o place f ! o!r1 :i* is ! same4 ,a great numb] ( ways h be5 tri$ 9 ord] to make x kn[n at "o obs]v+ /ation :at "t x is at ! o!r4 ,rockets are s5t up1 gunp[d] fir$1 & all k9ds ( signals made at fix$ times = ?is purpose2 b ^!1 ( c\rse1 only answ] = %ort di/ances1 s = long ones c>efully adju/$ *ronomet]s h to be c>ri$ f "o /ation to ! o!r to convey ! correct "t2 unless telegraph wires are laid f "o place to ano!r1 z f ,engl& to ,am]ica2 !n x is easy to let ei!r /ation "k :at "t x is at ! o!r4 ,= %ips at sea *ronomet]s answ] well = a %ort "t1 b !y are liable to v>iation4 ,!re are c]ta9 a/ronomical ph5om5a ! in/ant ( occurr5ce ( :i* c be =etold--& publi%$ 9 ! nautical almanacs--su* z ! eclipses ( ,jupit]'s moons1 & ! position ( our own moon among/ ! />s4 ,suppose !n an eclipse ( "o ( ,jupit]'s moons is to take place at #a ,p4,m4 ,gre5wi* "t1 & x is obs]v$ at a place at #b ,p4,m4 ( ! obs]v]'s local "t1 i4e41 two h\rs aft] ! sun has pass$ 8 m]idian1 !n manife/ly ! clock at ,gre5wi* is at #a ,p4,m4 :ile 8 is at #b ,p4,m41 & ! diff]5ce ( local "t is "o h\r1 & ! place is "o h\r1 or #ae1 ea/ ( ,gre5wi*4 ,if1 h[ev]1 ! eclipse 0 obs]v$ at #ab noon1 !n ! place mu/ be "o h\r we/ ( ,gre5wi*4 ,! local "t be+ "o h\r sl[] ?an ,gre5wi* %[s t ! sun does n s\? till an h\r aft] x does at ,gre5wi*1 or1 9 reality1 ! place does n come "u ! sun till aft] ! m]idian at ,gre5wi* has pass$ an h\r be=e1 cle>ly %[+ x to be we/ ( ,gre5wi*4 ,we %all n[ see h[ easy x is to f9d ! longitude :5 ! two /ations are electrically connect$4 ,suppose we wi% to det]m9e ! diff]5ce ( longitude ( two places 9 ,engl&1--?is c be det]m9$ ) ! utmo/ accuracy 9 a %ort "t if ! obs]v]s h a *ronograph1 ( ! k9d j describ$1 to record ! transit ( a /> at ^! two places4 ,! obs]v]s at ea* /ation arrange t ! obs]v] at ,/ation ,a %all obs]ve ! transit ( a c]ta9 /> on 8 *ronograph1 & ! obs]v] at ,/ation ,b %all obs]ve ! transit ( ! same /> on 81 & !n ) ! fai?ful clock1 beat+ seconds & m>k+ !m on ! surface ( bo? *ronographs simultane\sly1 ! diff]5ce ( sid]eal "t betwe5 ! transit ( ! same /> ov] ,/ation ,a & ,/ation ,b w be an absolute di/ance to be measur$ (f 9 z delicate a way z possible by comp>ison ( ! roll] ( ea* *ronograph1 & w give exactly h[ mu* "t elapses betwe5 ! two transits4 ,?is is ! longitude requir$4 ,!re are v>i\s me?ods ( utiliz+ ! same pr9ciple1 z1 = in/ance1 "o *ronograph only may be us$1 & bo? obs]v]s !n regi/] _! transits on ! same cyl9d]4 ,b :5 we h to deal ) consid]able di/ances1 su* z betwe5 ,engl& & ! ,unit$ ,/ates1 !n we no long] employ ?is me?od4 ,f ,val5tia we telegraph to ,newf\ndl& 9 effect 8,our "t is s-&-s10 & !n ! obs]v] at ,newf\ndl& telegraphs to ,val5tia 8,our "t is s-&-s40 ,9 ?is way ! absolute longitude ( ! ,we/ ( ,irel& & ,am]ica & ! diff]5t obs]vatories ( ,europe has be5 det]m9$ ) ! greate/ accuracy4 ,s x appe>s !re are two me?ods1 ! fir/ %[+ "o "t1 say ,gre5wi* "t1 at bo? places1 & %[+ ! diff]5ce 9 times ( transit ( />s2 or secondly1 hav+ ! clock at ea* place go+ to its own local "t1 s t a c]ta9 /> transits at ! same local "t at ea* place1 & f9d+ ! diff]5ce betwe5 ! two clocks4 ----- ,footnote #ae3 ,x 0 f\nd1 t betwe5 ! pass+ ( ! sp>k into ! gun1 & ! ignition ( ! p[d] & dis*>ge ( ! piece1 "o t5? ( a second elaps$4 ,,*apt] ,,xix4 ,,o!r ,,in/rum5ts ,,us$ ,,9 ,,a/ronomy ,,( ,,precision4 ,9 =m] *apt]s we h describ$ ! transit circle z x n[ exi/s z ! result ( ! ?\ght ( ,ty*o1 ,pic>d1 ,rm]1 & ,airy4 ,?is1 ?\gh ! fundam5tal in/rum5t 9 a m]idional obs]vatory1 is by no means ! only "o1 & we mu/ take a glance at ! o!rs4 ,9 ,rm]'s 8,obs]vatorium ,tusculaneum10 ne> ,cop5hag51 built 9 #agjd1 !re 0 n only a transit circle 9 ! m]idian ( c\rse1 b a transit in/rum5t 9 ! prime v]tical1 i4e4 sw++ 9 a v]tical plane at "r angles to ! =m] "o1 s t :ile ! optical axis ( "o always lies 9 a ,n4,s4 plane1 t ( ! o!r lies 9 an ,e4,w4 "o4 ,rm] did n use ?is in/rum5t mu*2 x rema9$ = ! great ,bessel to po9t out its value 9 det]m9ations ( latitude4 ,?is in/rum5t is1 s to speak1 self-correct+1 because betwe5 ! transit ( a /> ov] its wires :ile po9t+ to ! ea/ ( ! m]idian1 & t :ile po9t+ to ! we/ its telescope c be rev]s$ 9 its ,ys1 or "o position may be tak5 = "o night's obs]vations1 & ! o!r = ! next1 & s on4 ,9 ,/ruve's =m ( ?is in/rum5t ! transit ( />s c be obs]v$ at an int]val ( "o m9ute & tw5ty seconds1 ?is "t only be+ requir$ to raise x f ! ,ys1 to rotate x ?r\gh #ahj1 & l[] x aga94 ,?is rapid rev]sal1 & consequ5t elim9ation ( in/rum5tal imp]fections1 enable obs]vations ( ! mo/ extreme precision to be made 9 su* delicate matt]s z ! slight diff]5ces ( decl9ation ( />s due to ab]ration1 nutation1 & ! l4 ,! int]section ( ! m]idian ) ! prime v]tical m>ks ! z5i?4 ,to det]m9e ?is3--fir/1 !re is ! z5i? sector1 inv5t$ by ,hooke2 x consi/s ( a telescope1 c>ri$ by an axis on "o side ( ! tube1 & at "r angles to x1 s t ! telescope sw+s exactly z a transit does1 & x is provid$ ) cross wires 9 ! same mann]2 in/ead1 h[ev]1 ( hav+ a :ole circle1 x has only two segm5ts ( a circle2 & z x is nev] requir$ to sw+ ! telescope f> f its v]tical position1 !re is a diagonal reflector at ! eyepiece1 s t ! obs]v] c look sideways1 in/ead ( upw>ds1 9 an awkw>d position4 ,its use is to det]m9e ! z5i? di/ance ( />s z !y pass ne> t po9t4 ,^! di/ances are read (f on ! p>ts ( ! circle by v]ni]s or microscopes1 z 9 ! transit circle4 ,! z5i? telescope1 *iefly design$ by ,talcott1 is ! mod]n equival5t ( ! sector1 & bo? in/rum5ts are m us$ 9 geodetical op]ations ?an 9 fix$ obs]vatories4 ,at ,gre5wi*1 h[ev]1 !re is an in/rum5t = det]m9+ z5i? di/ances ( v special con/ruction4 ,?is is call$ ! reflex z5i? tube1 %[n 9 ,fig4 #aca4 ,x is a sectional draw+ ( "o ( ^? in/rum5ts %[+ ! pa? ( ! rays ( light4 ,a1 ,b1 is an object-glass1 fix$ horizontally1 & bel[ x is a tr\gh ( m]cury1 ,c1 ! surface ( :i* is always ( c\rse horizontal4 ,! light f a /> ne> ! z5i? is all[$ to fall ?r\gh ! object-glass1 :i* conv]ges ! rays j s mu* t !y come to a focus at ,f1 aft] hav+ be5 reflect$ f ! surface ( ! m]cury1 & also by ! diagonal mirror or prism1 ,g2 at ,f1 !re=e1 we h an image ( ! />1 :i* c be exam9$ toge!r ) ! cross-wires at ! eyepiece1 ,m4 ,!re is 9 ?is in/rum5t no necessity = ! accurate adju/m5ts t !re is 9 ! case ( ! transit1 ! surface ( ! m]cury be+ always horizontal1 & s giv+ an unalt]+ datum plane4 ,illu/ration3 ,,fig4 #aca4--,reflex ,z5i? ,tube4 ,:5 ! /> is p]fectly v]tical1 its image w fall on a c]ta9 kn[n "p 9 ! eyepiece2 b1 z x leaves ! v]tical1 ! angle ( incid5ce ( its light on ! m]cury alt]s1 & likewise t ( reflection1 s t ! position ( ! image *anges1 & ?is *ange ( position 9 ! eyepiece is measur$ by movable cross-wires & a micromet] screw1 simil> to t employ$ = read+ ! circle 9 ! transit circle4 ,at ! pres5t "t ,draconis is ! /> :i* passes v ne>ly ?r\gh ! z5i? ( ,gre5wi*1 & obs]vations ( ?is /> are accord+ly made at e available opportunity4 ,we n[ pass to an enl>gem5t ( ! sph]e ( obs]vation ( ! transit circle 9 ord] t any object c be view$ at all times :5 above ! horizon2 9 ?is case ! transit circle passes into ! alt-azimu?1 or altitude & azimu? in/rum5t1 a/ronomical !odolite1 or univ]sal in/rum5t4 ,a ref]5ce to ,fig4 #acb--;a woodcut ( an ord9>y !odolite--w %[ ! new po9t introduc$ by ?is con/ruction4 ,imag9e ! upp] "p ( ! !odolite fix$ ) its telescope & circle 9 ! plane ( ! m]idian--we h ! transit circle2 sw+ ! !odolite r\nd ?r\gh #ij--we h ! prime v]tical in/rum5t4 ,n[ in/ead ( hav+ ! upp] "p fix$ let x be free to rotate on ! c5tre ( ! horizontal circle--we h ! alt-azimu?4 ,9 ! description ( ! in/rum5ts us$ 9 ,ty*o's obs]vatory 7,*apt] ,,iv471 we describ$ ano!r in/rum5t by :i* ,ty*o & ! ,l&grave ( ,hesse-,cassel endeav\r$ to make obs]vations out ( ! m]idian2 & we may rememb] t !y almo/ _h to give ! matt] up 9 despair1 because !y c\ld n f9d any clocks suffici5tly good to enable !m to fix ! position ( ! />4 ,illu/ration3 ,,fig4 #acb4--,!odolite4 ,illu/ration3 ,,fig4 #acc4--,portable ,alt-azimu?4 ,if we ref] aga9 to ,fig4 #ah1 we see ! me?od by :i* ,ty*o tri$ to get ! two co-ord9ates4 ,on ! horizontal circle !re are ! graduations = azimu?1 or ! measurem5t f ! s\? along ! horizon1 & on ! v]tical quadrant are ! graduations = altitude4 ,n[ let u turn to ! mod]n equival5t ( t in/rum5t4 ,fig4 #acc %[s ?is 9 a portable =m4 ,! upp] "p ( ! in/rum5t is1 z "o sees1 no?+ m ?an a transit circle exactly equival5t to ! "o describ$4 ,we h a telescope c>ri$ on a horizontal axis1 support$ by a pill>2 we h ! read+ microscopes1 & ! l2 b ! support ( ! horizontal axis1 in/ead ( be+ on ! solid gr\nd1 z x is 9 ! transit circle1 re/s on a movable horizontal circle1 :i* is also read by microscopes arrang$ r\nd x1 s t all errors may be elim9at$4 ,) ?is in/rum5t we c get ! altitude ( an object at any di/ance f ! m]idian1 & at ! same "t measure its di/ance ea/ & we/ ( x4 ,! arrangem5ts design$ by ! ,a/ronom] ,royal = obs]vations ( ! moon at ,gre5wi* are m elaborate4 ,9 ! ,gre5wi* alt-azimu?1 ! telescope is swung on pivots betwe5 two pi]s1 j z 9 ! case ( ! transit1 ^! pi]s be+ fix$ to ! horizontal circle4 ,! great advantage ( ?is in/rum5t is t ! true place ( a heav5ly body c be det]m9$ :5ev] x is above ! horizon2 we h nei!r to wait = a transit ov] ! m]idian nor ov] ! prime v]tical4 ,nev]!less its use is n g5]al 9 fix$ obs]vatories4 ,r$uce ! dim5sions ( ! horizontal circle & increase ^? ( ! v]tical "o1 & we h ! v]tical circle design$ by ,ertel1 & l>gely us$ 9 =eign obs]vatories4 ,,book ,v4 ,,! ,,equatorial4 ,,*apt] ,,xx4 ,,v>i\s ,,me?ods ,,( ,,m\nt+ ,,l>ge ,,telescopes4 ,we h already gone some:at 9 detail into ! con/ruction ( ! transit circle1 :i* is almo/ ! mo/ important ( mod]n a/ronomical in/rum5ts4 ,we !n ref]r$ to ! alt-azimu?1 9 :i*1 in/ead ( deal+ ) ^? m]idional measurem5ts :i* we _h t\*$ ^u 9 ! case ( ! transit circle1 we left1 z x 71 ! m]idian = o!r p>ts ( ! sph]e & work$ ) o!r great circles1 pass+ n ?r\gh ! pole ( ! heav5s1 b ?r\gh ! z5i?4 ,we n[ pass to ! 8optick tube10 z us$ 9 ! physical bran* ( a/ronomy1 & we h fir/ to trace ! passage f ! alt-azimu? to ! ,equatorial1 z ! mo/ conv5i5t m\nt+ is call$4 ,?is equatorial gives ! obs]v] ! p[] ( f9d+ any object at once1 ev5 9 ! day-"t1 if x be above ! horizon2 &1 :5 ! object is f\nd1 ( keep+ x /ation>y 9 ! field ( view4 ,b al?\gh ?is =m is ! mo/ conv5i5t1 x is n ! "o univ]sally adopt$1 because x is exp5sive1 & because1 aga91 till )9 ! la/ few ye>s our opticians 7 n able to grapple ) all its difficulties4 ,h5ce x is t "s ( ! in/rum5ts :i* h be5 mo/ nobly occupi$ 9 inve/igations 9 physical a/ronomy h be5 m\nt$ 9 a mo/ simple mann]1 "s ( !m be+ on an alt-azimu? m\nt+4 ,( ^! ! mo/ notewor?y example is suppli$ by ! =ty-feet in/rum5t erect$ by ,sir ,william ,h]s*el at ,sl\gh4 ,illu/ration3 ,,fig4 #acd4--,! #dj-;feet at ,sl\gh4 ,"l ,rosse's six-feet reflector aga9 is m\nt$ 9 a diff]5t mann]4 ,x is n equatorially m\nt$2 ! tube1 support$ at ! bottom on a pivot1 is mov$ by manual p[] z desir$ betwe5 two high side walls1 c>ry+ ! /ag+ = obs]v]s1 & s all[+ ! telescope a small motion 9 "r asc5sion ( ab\t two h\rs4 ,our amateurs !n may be =giv5 = /ill adh]+ to ! alt-azimu? m\nt+ = m]e />-gaz+ purposes4 ,illu/ration3 ,,fig4 #ace4--,"l ,rosse's #f-;feet4 ,illu/ration3 ,,fig4 #acf4--,refractor m\nt$ on ,alt-azimu? ,tripod = ord9>y ,/>gaz+4 ,we mu/ recollect t1 ) ! alt-azimu?1 we are able to measure ! position ( an object ) ref]5ce to ! horizon & m]idian2 b suppose we tip up ! :ole in/rum5t f ! base1 s t1 in/ead ( hav+ ! axis ( ! in/rum5t v]tical1 we incl9e x s z to make ! axis1 r\nd :i* ! in/rum5t turns 9 azimu?1 absolutely p>allel to ! e>?'s axis4 ,( c\rse1 if we 7 us+ x at ! nor? pole or ! s\? pole1 ! axis w\ld be absolutely v]tical1 z :5 x is us$ z an alt-azimu?1 or o!rwise x w\ld n be absolutely p>allel to ! axis ( ! e>?4 ,on ! o!r h&1 if we 7 us+ x at ! equator1 x w\ld be ess5tial t ! axis %\ld be horizontal1 s9ce to an obs]v] at ! equator ! e>?'s axis is p]fectly horizontal2 b1 = a middle latitude l our own1 we h to tip ?is axis ab\t #ea f ! horizontal1 s z to be 9 prop] relation%ip )1 i4e4 p>allel to1 ! e>?'s axis4 ,hav+ done ?is1 we c1 by turn+ ! in/rum5t r\nd ?is axis1 call$ ! pol> axis1 keep a /> visible 9 ! field ( view = any l5g? ( "t we *oose by exactly c\nt]act+ ! rotation ( ! e>?1 )\t mov+ ! telescope ab\t its upp]1 or :at 0 its horizontal1 axis4 ,! l[] circle ( ! in/rum5t w !n be 9 ! plane ( ! cele/ial equator1 & ! upp] "o1 at "r angles to x1 w enable u to measure ! di/ance f t plane1 or ! decl9ation ( an object1 :ile ! l[] circle w tell u ! di/ance ( ! object f ! m]idian 9 h\rs or degrees4 ,) ! aid ( good circles & good clocks1 we c ?us det]m9e a />'s position4 ,fig4 #acg %[s an ,equatorial ,/&1 "o ( ! fir/ k9d ( equatorials us$ by a/ronom]s4 ,we see at once ! g5]al arrangem5ts ( ! in/rum5t4 ,9 ! fir/ place1 we h a horizontal base1 ,d1 & on x1 & incl9$ to x1 is a disc ( metal1 ,c2 aga9 on ?is disc lies ano!r disc1 ,a1 ,b1 :i* c revolve r\nd on ,c1 be+ held to x by a c5tral /ud1 s t :5 ,a ,b is 9 ! plane ( ! e>?'s equator its axis po9ts to ! pole & is p>allel to ! axis ( ! e>?4 ,on ! upp] disc !re are two supports = ! axis ( ! telescope1 ,e1 :i* is at "r angles to ! pol> axis & is call$ ! decl9ation axis ( ! telescope2 r\nd x ! telescope has a motion 9 a direction f ! pole to ! equator4 ,illu/ration3 ,,fig4 #acg4--,simple ,equatorial ,m\nt+4 ,9 ! equatorial m\nt+1 clockwork is introduc$1 & aft] ! in/rum5t has be5 po9t$ to any p>ticul> /> or cele/ial body1 ! clock is clamp$ to ! circle mov+ r\nd ! pol> axis1 & s made to drive x r\nd 9 exactly ! "t ! e>? takes to make a rotation4 ,by a clock is meant an in/rum5t = giv+ motion1 n ) ref]5ce to "t1 b s arrang$ t1 if x 7 possible to use x cont9u\sly1 ! motion w\ld exactly br+ ! telescope r\nd once 9 ! tw5ty-f\r sid]eal h\rs :i* are necess>y = ! successive transits ( />s ov] ! m]idian4 ,!re is an objection to ! =m ( in/rum5t giv5 above1--! telescope _c be po9t$ to any position ne> ! pole1 s9ce ! /& comes 9 ! way4 ,?is is obviat$ 9 ! v>i\s me?ods ( m\nt+1 :i* we %all n[ pass "u review4 ,! ,g]man ,m\nt+4 ,?is is ! =m n[ almo/ univ]sally adopt$ = refractors & reflectors "u #bj in*es ap]ture4 ,! pol> axis has atta*$ to x at "r angles a socket ?r\gh :i* ! decl9ation axis passes1 & ?is axis c>ries ! telescope at "o end & a c\nt]weight at ! o!r4 ,! pol> axis lies :olly bel[ ! decl9ation axis1 & bo? are support$ by a c5tral pill> entirely ( iron1 or p>tly ( /one & p>tly ( iron4 ,by ! c\rtesy ( ,messrs4 ,cooke & ,sons1 ,mr4 ,h[>d ,grubb1 & ,mr4 ,br[n+1 we are enabl$ to give examples ( ! v>i\s =ms ( ?is m\nt+ n[ 9 use 9 ?is c\ntry = in/rum5ts ( less ?an #bj in*es ap]ture4 ,9 ,fig4 #ach1 we h ! type =m ( ,equatorial ,refractor introduc$ "s #cj ye>s ago by ! late ,mr4 ,?omas ,cooke4 ,! telescope is repres5t$ p>allel to ! pol> axis1 :i* is inclos$ 9 ! cas+ support$ by ! c5tral pill>1 & c>ries "o l>ge "r asc5sion circle above & ano!r small] "o bel[1 ! =m] be+ read by microscopes atta*$ to ! cas+4 ,! socket or tube c>ry+ ! decl9ation axis is connect$ ) ! top ( ! pol> axis4 ,to ?is ! decl9ation circle is fix$1 :ile an inn] axis fix$ to ! telescope c>ries ! v]ni]s4 ,illu/ration3 ,,fig4 #ach4--;,cooke's =m = ,refractors4 ,illu/ration3 ,,fig4 #aci4--,mr4 ,grubb's =m appli$ to a ,cassegra9 ,reflector4 ,! clock is se5 to ! nor? ( ! pill>4 ,:ile ?is is driv+ ! telescope1 rods com+ d[n to ! eyepiece enable ! obs]v] to make any small alt]ations 9 "r asc5sion or decl9ation2 inde$ 9 all mod]n in/rum5ts ev]y?+ except w9d+ ! clock is done at ! eyepiece1 s t ! obs]v] :5 fairly at "w is n di/urb$4 ,! lamp to illum9ate ! micromet] wires is %[n ne> ! f9d]4 ,! friction roll]s1 :i* take ne>ly all ! weight (f ! surfaces ( ! pol> axis1 are connect$ ) ! comp\nd lev]s %[n above ! cas+ ( ! pol> axis4 ,9 ,fig4 #aci we h ,mr4 ,grubb's revision ( ! ,g]man =m4 ,! pill> is composite1 & ! support ( ! upp] "p ( ! pol> axis is n s direct z 9 ! m\nt+ :i* has j be5 ref]r$ to4 ,!re are1 h[ev]1 sev]al int]e/+ modifications to :i* att5tion may be drawn4 ,! lamp is plac$ at ! end ( ! holl[ pol> axis1 & supplies light n only = ! micromet] wires1 b = read+ ! circles2 ! c5tral cavity ( ! l[] support is utilis$ = ! clock1 :i* works on "p ( a circle1 in/ead ( a complete "o1 z 9 ! in/rum5t already describ$4 ,9 ! case ( ,newtonian reflectors ! obs]v] requires to d 8 "w at ! upp] end ( ! tube2 ?is !re=e %\ld be z ne> ! gr\nd z possible4 ,?is is accompli%$ by r$uc+ ! support to a m9imum4 ,figs4 #adj & #ada %[ two =ms ( ?is m\nt+1 design$ by ,mr4 ,grubb & ,mr4 ,br[n+4 ,! two l>ge/ & mo/ p]fectly m\nt$ refractors on ! ,g]man =m at pres5t 9 exi/5ce are ^? at ,gate%ead & ,wa%+ton1 ,u4,s4 ,! =m] belongs to ,mr4 ,newall1 a g5tleman :o1 connect$ ) ^? :o 7 among ! fir/ to recognise ! g5ius ( our great ,engli% optician1 ,cooke1 did n hesitate to risk ?\s&s ( p\nds 9 "o great exp]im5t1 ! success ( :i* w h a mo/ important be>+ ^u ! a/ronomy ( ! future4 ,illu/ration3 ,,fig4 #adj4--;,grubb's =m = ,newtonians4 ,illu/ration3 ,,fig4 #ada4--;,br[n+'s m\nt+ = ,newtonians4 ,9 ! ye> #ahfj ! l>ge/ refractors :i* _h be5 turn$ out ( ! ,optical ,in/itute at ,muni* "u ! control1 fir/1 ( ! great ,fraunh(]1 & aft]w>ds ( ,m]z1 7 ^? ( #agg squ>e in*es area at ,p\lk[a & ,cambridge 7,u4,s474 ,our own ,cooke1 :o 0 rapidly br++ back "s ( ! old pre/ige ( ,dollond & ,tulley's "t to ,engl&--a pre/ige :i* 0 lo/ to u by ! unwise m$dl+ ( our excise laws & ! duty on glass1#af :i* prev5t$ exp]im5ts 9 glass-mak+--_h complet$ a #i in* = ,mr4 ,flet*] & a #aj in* = ,mr4 ,b>clay2 :ile 9 ,am]ica ,alvan ,cl>ke _h gone f /r5g? to /r5g? till he _h complet$ a refractor ( #ah in*es = ,*icago4 ,! areas ( ^! objectives are #fg1 #ghe1 & #bfh in*es respectively4 ,^? :o saw ! great ,exhibition ( #ahfb may h obs]v$ ne> ! ,arm/rong ,gun trophy two circul> blocks ( glass "s #bf in*es 9 diamet] & ab\t two in*es ?ick /&+ on _! edges4 ,^! 7 two ( ! mu*-priz$ 8discs0 ( optical glass manufactur$ by ,messrs4 ,*ance ( ,birm+ham4 ,at ! close ( ! ,exhibition !y 7 pur*as$ by ,mr4 ,newall1 & transf]r$ to ! work%ops ( ,messrs4 ,cooke & ,sons at ,york4 ,! glass 0 exam9$ & f\nd p]fect4 ,9 "t ! object-glass 0 poli%$ & te/$1 & ! _w 0 9 possession ( an a/ronomical in/rum5t ( ne>ly twice ! p[] ( ! #ah in* ,*icago in/rum5t--#dhe in*es area to #bfh4 ,su* an a*ievem5t m>ks an epo* 9 telescopic a/ronomy1 & ! skill ( ,mr4 ,cooke & ! munific5ce ( ,mr4 ,newall w long be rememb]$4 ,! g5]al design & appe>ance ( ?is mon/] among telescopes w be ga!r$ f ! g5]al view giv5 9 ! frontispiece1 = :i* we are indebt$ to ,mr4 ,newall4 ,x is ! same z t ( ! well-kn[n ,cooke equatorials2 b ! extraord9>y size ( all ! p>ts has necessitat$ ! special arrangem5t ( mo/ ( !m4 ,! l5g? ( ! tube1 includ+ dew-cap & eye-end1 is #cb feet1 & x is ( a cig> %ape1 ! diamet] at ! object-end be+ #bi in*es1 at ! c5tre ( ! tube #cd in*es1 & at ! eye-end #bb in*es4 ,! ca/-iron pill> support+ ! :ole is #ai feet 9 height f ! gr\nd to ! c5tre ( ! decl9ation axis1 :5 horizontal2 & ! base ( x is #e feet #i in*es 9 diamet]4 ,! tr\gh = ! pol> axis alone weighs #ad cwt41 ! weight ( ! :ole in/rum5t be+ ne>ly #f tons4 ,! tube is con/ruct$ ( /eel plates rivet$ toge!r1 & is made 9 five l5g?s screw$ toge!r ) bolts4 ,! flanges 7 turn$ 9 a la!1 s z to be p>allel to ea* o!r4 ,x weighs only #ac cwt41 & is rem>kably rigid4 ,inside ! out] tube are five o!r tubes ( z9c1 increas+ 9 diamet] f ! eye to ! object-end2 ! wide end ( ea* z9c tube ov]lapp+ ! n>r[ end ( ! foll[+ tube1 & leav+ an annul> space ( ab\t an in* 9 wid? r\nd ! end ( ea* = ! purpose ( v5tilat+ ! tube1 & prev5t+1 z mu* z possible1 all int]f]5ce by curr5ts ( w>m air ) ! cone ( rays4 ,! z9c tubes are also made to act z diaphragms4 ,! two glasses =m+ ! object-glass weigh #add lb41 & ! brass cell weighs #hj lb4 ,! object-glass has an ap]ture ( ne>ly #be in*es1 or #dhe in*es area1 & 9 ord] z mu* z possible to avoid flexure f unequal pressure on ! cell1 x is made to re/ ^u ?ree fix$ po9ts 9 its cell1 & betwe5 ea* ( ^! are arrang$ ?ree lev]s & c\nt]poises r\nd a c\nt]-cell1 :i* act ?r\gh ! cell direct on to ! glass1 s t its weight 9 all positions is equally di/ribut$ among ! twelve po9ts ( support1 ) a slight excess ^u ! ?ree fix$ ones4 ,! focal l5g? ( ! l5s is #bi feet4 ,atta*$ to ! eye-end ( ! tube are two f9d]s1 ea* ( #abe in*es area2 !y are fix$ above & bel[ ! eye-end ( ! ma9 tube1 s t "o may be readily accessible 9 all positions ( ! in/rum5t4 ,x is also suppli$ ) a telescope hav+ an object-glass ( #cc in*es area4 ,?is is fix$ betwe5 ! two f9d]s1 & is = ! purpose ( assi/+ 9 ! obs]vations ( comets & o!r objects = :i* ! l>ge in/rum5t is n s suitable4 ,?is assi/ant telescope is provid$ ) a r\gh position circle & micromet] eyepieces4 ,two read+ microscopes = ! decl9ation circle are br\ght d[n to ! eye-end ( ! ma9 tube2 ! circle--#ch in*es 9 diamet]--is divid$ on its face & edge1 & read by means ( ! microscopes & prisms4 ,! sl[ motions 9 decl9ation & ,r4 ,a4 are giv5 by means ( tang5t screws1 c>ry+ groov$ pulleys1 ov] :i* pass endless cords br\ght to ! eye-end4 ,! decl9ation clamp+ h&le is also at ! eye-end4 ,! clock = driv+ ?is mon/] telescope is fix$ to ! l[] "p ( ! pill>1 & is ( comp>atively small proportions1 ! in/rum5t be+ s nicely c\nt]pois$ t a v slight p[] is requir$ to be ex]t$ by ! clock1 ?r\gh ! tang5t screw1 on ! driv+-:eel 7sev5 feet 9 diamet]71 9 ord] to give ! necess>y equatorial motion4 ,! decl9ation axis is ( peculi> con/ruction1 necessitat$ by ! weight ( ! tubes & _! fitt+s1 & correspond+ c\nt]poises on ! o!r end1 t5d+ to cause flexure ( ! axis4 ,?is difficulty is entirely ov]come by mak+ ! axis holl[1 & pass+ a /rong iron lev] ?r\gh x hav+ its fulcrum imm$iately ov] ! be>+ ( ! axis ne> ! ma9 tube1 & act+ ^u a /rong iron plate rigidly fix$ z ne> ! c5tre ( ! tube z possible1 cle> ( ! cone ( rays4 ,?is lev]1 tak+ ne>ly ! :ole weight ( ! tubes1 c41 (f ! axis1 frees x f all liability to b5d4 ,! weight ( ! pol> axis on its upp] be>+ is reliev$ by anti-friction roll]s & weight$ lev]s2 ! l[] end ( ! axis is conical1 & !re is a correspond+ conical surface on ! l[] end ( ! tr\gh2 betwe5 ^! two surfaces are ?ree conical roll]s c>ri$ by a loose or 8live0 r+1 :i* adju/ !mselves to equalize ! pressure4 ,! h\r-circle on ! bottom ( ! pol> axis is #bf in*es 9 diamet]1 & is divid$ on ! edge1 & read r\ghly f ! floor by means ( a small diagonal telescope atta*$ to ! pill>2 a r\gh motion 9 ,r4 ,a4 by h& is also arrang$ =1 by a sy/em ( cog:eels1 mov$ by a groov$ :eel & endless cord at ! l[] end ( ! pol> axis1 s z to enable ! obs]v] to set ! in/rum5t r\ghly 9 ,r4 ,a4 by ! aid ( ! diagonal telescope4 ,x is also divid$ on its face1 & read by means ( microscopes4 ,! decl9ation & h\r-circle w probably be illum9at$ by means ( ,geissl] tubes1 & ! d>k & bright field illum9ations = ! micromet]s w be effect$ by ! same means4 ,illu/ration3 ,,fig4 #adb4--,! ,wa%+ton ,great ,equatorial4 ,s soon z ! success ( ! ,newall exp]im5t 0 put beyond all "q by ,cooke1 ,commodore ,b4 ,f4 ,s&s1 ! sup]9t5d5t ( ! ,u4,s4 ,naval ,obs]vatory1 s5t a deputation1 consi/+ ( ,pr(essors ,s4 ,newcomb1 ,asaph ,hall1 & ,mr4 ,h>kness1 accompani$ by ,mr4 ,alvan ,cl>ke1 to exam9e & report ^u ! ,newall telescope1 & ! result 0 t !y commission$ ,alvan ,cl>ke to con/ruct a l>ge telescope = t c\ntry4 ,9 ! ,wa%+ton telescope ! ap]ture ( ! object-glass is #bf in*es--t is1 "o in* l>g] ?an ! ,engli% type-in/rum5t4 ,! g5]al arrangem5ts are %[n 9 ! accompany+ woodcut4 ,x w be se5 t ! m\nt+ is mu* light] ?an 9 ! ,engli% in/rum5t1 & a composite pill> gives place = ! clock 9 ! c5tral cavity4 ,! ,engli% ,m\nt+4 ,9 ! ,engli% m\nt+ ! telescope1 l a transit in/rum5t1 has on ea* side a pivot1 & ^! pivots re/ on a frame some:at l>g] ?an ! telescope1 po9t+ to ! pole & support$ by two pivots1 "o at ! bottom re/+ on be>+s ne> ! gr\nd1 & ! o!r c>ri$ by a high] pill> cle> ( ! obs]v]'s *air4 ,! motions ( ! telescope are simil> to ^? giv5 by ! ,g]man m\nt+ 9 all ess5tials2 ! ,gre5wi* equatorial is m\nt$ 9 ?is mann]4 ,x is c>ri$ 9 a l>ge cyl9drical frame1 support$ at bo? ends by two pill>s--above by a /rong iron pill>1 :ile ! o!r end re/s on a firm /one pill>1 go+ "r to ! e>?1 indep5d5tly ( ! floor+4 ,?is m\nt+1 ?\gh pref]r$ = ! l>ge in/rum5t at ,gre5wi*1 has be5 disc>d$ g5]ally1 z ! long pol> axis is necess>ily a s]i\s elem5t ( weakness2 ! telescope is support$ on its weake/ "p1 & x is liable to great *anges f contraction & expansion ( ! frame4 ,! ,=k$ ,m\nt+4 ,x is n[ gett+ m usual to m\nt ,newtonians ( l>ge dim5sions equatorially1 9 spite ( ! imm5se weight to be c>ri$4 ,"o ( ! fir/ me?ods 0 to use a pol> axis 9 ! same mann] z = a refractor1 only t x bifurcat$ at ! top1 =m+ !re a =k1 & betwe5 ?is =k ! telescope is swung1 aft] ! same mann] z a transit4 ,?is me?od ( m\nt+ 0 adopt$ by ,m4 ,f\cault 9 ! case ( 8 fir/ l>ge silv]$-glass reflector4 ,! height ( ! bifurcation is dep5d5t on ! di/ance betwe5 ! c5tre ( gravity ( ! tube & ! speculum1 & if we use an extremely light tube1 or if1--z x is ! fa%ion to aboli% !m n[ altoge!r = reflectors1--we use a skeleton tube ( iron lattice "w1 ?is bifurcation ( ! pol> axis ne$ n be ( any great l5g?4 ,! pol> axis be+ entirely bel[ ! telescope & be+ driv5 by ! clock1 we h a p]fect me?od ( m\nt+ a speculum ( any weight we please4 ,?is arrangem5t 0 fir/ sugge/$ & c>ri$ into effect by ,mr4 ,lassell = 8 f\r-foot ,newtonian1 :i* 0 m\nt$ at ,malta4 ,! pol> axis 0 a heavy cone-%ap$ ca/+ re/+ on its po9t bel[1 & mov+ on its l>ge/ diamet] j bel[ ! base ( ! =k4 ,"l ,rosse has rec5tly mu* improv$ ^u ! orig9al idea4 ,z ! obs]v] mu/ be at ! m\? ( ! tube1 he is 9 a v bad position z f> z com=t goes1 especially z ! eye-end *anges its position rapidly 9 consequ5ce ( ! great l5g? ( ! tube f its c5tre ( gravity outw>ds4 ,! plat=m on :i* he /&s is rais$ on supports1 ext5d+ f ! floor & go+ up to ! op5+ ?r\gh :i* ! telescope po9ts to ! heav5s1 & ! :ole plat=m is sometimes fix$ to ! dome ( ! obs]vatory1 s t x travels r\nd ) x4 ,) ,mr4 ,lassell's f\r-foot ! obs]v] /ood 9 a gigantic read+ box1 ab\t ?irty feet high1 ) op5+s 9 x at diff]5t elevations4 ,?is /ructure 0 support$ on a circul> plat=m movable on rails r\nd ! base ( ! m\nt+4 ,almo/ cont9ual v>iations1 bo? ( ! obs]v+ height & ( ! circul> plat=m1 7 necess>y1 z ! di/ance f ! c5tre ( motion ( ! tube & ! eyepiece 0 no less ?an #cd feet4 ,9 ,"l ,rosse's rec5t adaptation ( ?is =m ! obs]v] is plac$ 9 a sw++ basket1 at ! end ( an arm almo/ z long z ! telescope tube4 ,he is "h c\nt]pois$1 & moves r\nd a railway :i* surr\nds ! m\nt+ at ! height ( ! tip ( ! =k4 ,! ,composite ,m\nt+4 ,illu/ration3 ,,fig4 #adc4--;,g5]al view ( ! ,melb\rne ,reflector4 ,!re is /ill ano!r =m ( m\nt+ :i* promises to be l>gely us$ = reflectors 9 ! future1 :e!r ! tube be light5$ by its be+ con/ruct$ ( only a framework ( iron or n4 ,?is m\nt+ is nei!r ,g]man nor ,engli%1 b 9 "p imitates bo? ( ^! me?ods3 h5ce ,i give x ! "n ( ,composite4 ,!re is a %ort pol> axis support$ at bo? ends4 ,illu/ration3 ,,fig4 #add4--,! m\nt+ ( ! ,melb\rne ,telescope4 ,c1 pol> axis 7cube #a y>d squ>e1 cone #h feet long72 ,d1 ,clock sector2 ,u1 ,c\nt]poise weights 7#b tons74 ,)9 ! la/ few ye>s two l>ge reflectors h be5 erect$1 equatorially m\nt$ 9 ?is composite mann]--! great ,melb\rne ,equatorial1 con/ruct$ by ,mr4 ,grubb1 & ! new ,p>is ,equatorial1 con/ruct$ by ,mr4 ,ei*5s4 ,( ! =m]1 ,fig4 #adc gives a g5]al view1 %[+ h[ ! con/ruction ( ?is in/rum5t diff]s f o!r equatorials :i* we h se54 ,fig4 #add %[s ! m\nt+ 9 m detail4 ,c is ! pol> axis1 ,t ,p is ! decl9ation axis1 & ,t ! small portion ( ! tube ( ! telescope1 ! rema9d] ( ! tube be+ repres5t$ by delicate lattice "w1 :i* is z light z possible1 & us$ m]ely = support+ ! reflector1 by means ( :i* ! light is ?r[n back aga91 accord+ to ! sugge/ion ( ,cassegra91 & comes ?r\gh ! hole 9 ! c5tre ( ! speculum into ! eyepiece1 :i* is se5 at y1 s t ! obs]v] /&s at ! bottom ( ! telescope 9 exactly ! same way z if he 7 us+ a refractor4 ,9 ?is enorm\s in/rum5t1 ! tube & speculum ( :i* alone weigh ne>ly ?ree tons1 ! sy/em ( c\nt]poises is s p]fect t we describe ! me?od adopt$ 9 ord] to give an idea ( ! g5]al arrangem5t ( ! be>+ & anti-frictional app>atus4 ,! s]ies ( weights hang+ beh9d ! support ( ! upp] end ( ! pol> axis are int5d$ to take a great "p ( ! weight ( t axis (f ! l[] support2 beside :i* !re are friction-roll]s press$ upw>ds aga9/ ! axis by ! weights inside ! support4 ,all ! be>+s are con/ruct$ on ! same pr9ciple z ! ,y be>+s ( a !odolite--t is1 ! pivots re/ on two small portions ( _! arc1 #ij or #ajj ap>t4 ,if all[$ to re/ on ^! be>+s )\t "s anti-frictional app>atus1 ! =ce requir$ to move su* an in/rum5t w\ld r5d] x simply unmanageable & de/roy ! be>+s4 ,! plan adopt$ by ,mr4 ,grubb is to all[ ! axis to re/ 9 its be>+s ) j a suffici5t portion ( its weight to insure p]fect contact1 & to support ! rema9d] by "s anti-frictional app>atus4 ,g5]ally #a_/ej to #a_/ajj ( ! weight is q suffici5t to all[ ! axis to take its be>+1 & ! rema9d] #di_/ej to #ii_/ajj c ?us be support$ on friction roll]s1 & r$uc$ to any desir$ ext5t1 )\t injur+ 9 ! slighte/ degree ! p]fection ( /ead9ess obta9$ by ! use ( ! ,y's4 ,?is is ! plan us$ 9 ! be>+s ( ! pol> axis1 & ! result is t ! in/rum5t c be turn$ r\nd ?is axis by a =ce ( #e p\nds at a lev]age ( #bj feet4 ,! be>+s ( ! decl9ation axis are support$ on virtually ! same pr9ciple2 b ! details ( t con/ruction are necess>ily mu* m complicat$1 on acc\nt ( ! v>iability ( direction ( ! resolv$ =ces ) respect to ! axis4 ,we may n[ turn to ! f\r-foot silv]-on-glass ,newtonian n[ 9 c\rse ( completion at ! ,p>is ,obs]vatory4 ,! illu/ration :i* we give repres5ts ! telescope 9 a position = obs]vation4 ,! :eel$ hut "u :i* x usually /&s1 a sort ( waggon sev5 metres high by n9e long & five broad1 is pu%$ back t[>ds ! nor? along d\ble rails4 ,! obs]v+ /aircase has be5 fitt$ to a second sy/em ( rails1 :i* p]mits x to circulate all r\nd ! foot ( ! telescope1 at ! same "t t x c turn ^u itself1 = ! purpose ( plac+ ! obs]v]1 /&+ ei!r on ! /eps or on ! upp] balcony1 )9 rea* ( ! eyepiece4 ,?is eyepiece itself may be turn$ r\nd ! end ( ! telescope into :atev] position is mo/ easily accessible to ! obs]v]4 ,illu/ration3 ,,fig4 #ade4--;,great ,silv]-on-,glass ,reflector at ! ,p>is ,obs]vatory4 ,! tube ( ! telescope1 #gcj metres 9 l5g?1 consi/s ( a c5tral cyl9d]1 to ! extremities ( :i* are fa/5$ two tubes ?ree metres long1 consi/+ ( f\r r+s ( wr\ght-iron hold+ toge!r twelve longitud9al b>s also ( iron4 ,! :ole is l9$ ) small %eets ( /eel plate4 ,! total weight is ab\t #b1djj kilogrammes4 ,at ! l[] extremity is fix$ ! cell :i* holds ! mirror2 at ! o!r end a circle1 movable on ! op5 m\? ( ! telescope1 c>ries at its c5tre a plane mirror1 :i* ?r[s to ! side ! cone ( rays reflect$ by ! great mirror4 ,! weight ( ! mirror 9 its b>rel is ab\t #hjj kilogrammes2 ! eyepiece & its accessories h ! same weight4#ag ,x w be q cle> f :at has be5 said t ! manipulation ( ^! l>ge telescopes at pres5t entails mu* manual & ev5 bodily lab\r1 & :5 we come 9 future to consid] ! w9d+ ( ! clock1 ! turn+ ( ! dome1 & ! adju/m5t ( ! obs]v+ *air1 x w be se5 t ! lab\r is enorm\s4 ,to save ?is1 9 all ! be/ in/rum5ts ev]y?+ is br\ght to ! eye-end ( ! telescope1 movem5ts bo? 9 "r asc5sion & decl9ation1 read+ ( circles1 & adju/m5t ( illum9ation4 ,mr4 ,grubb has sugge/$ t ev]y?+ %\ld be br\ght to ?is po9t1 & t1 by ! employm5t ( hydraulic p[]1 8! obs]v]1 )\t mov+ f 8 *air1 might1 by simply press+ "o or o!r ( a few electrical buttons1 cause ! telescope to move r\nd 9 "r asc5sion1 or decl9ation1 ! dome to revolve1 ! %utt]s to op51 & ! clock to be w\nd40 ,he v prop]ly adds1 8,?is is no m]e ,utopian idea4 ,su* ?+s are done1 & 9 common use 9 _m ( our great eng9e]+ e/abli%m5ts1 & x is only 9 ! application t !re w\ld be any difficulty enc\nt]$40 ,! ,driv+ ,clock4 ,9 a previ\s *apt] x 0 /at$ t 9 all l>ge telescopes us$ = ! a/ronomy ( position1 :e!r a transit circle or ! alt-azimu?1 :at we want$ to d 0 to note ! transit ( ! /> across ! field--! transit due to ! motion ( ! e>?2 b t :5 we deal ) o!r ph5om5a1 su*1 = in/ance1 z ^? a l>ge equatorial is capable ( br++ be=e u1 we no long] want ^! objects to trav]se ! field1 we want to keep !m1 if possible1 absolutely immovable 9 ! field ( view ( ! eyepiece1 s t we may exam9e !m & measure !m1 & d :at we please ) !m4 ,h5ce x 0 t we f\nd driv+ clocks appli$ to equatorials2 & our description w\ld n be complete did we fail to expla9 ! g5]al pr9ciples ( _! con/ruction4 ,!y are in/rum5ts = c\nt]act+ ! motion ( ! e>? by supply+ an exactly equal motion to ! tube ( ! telescope 9 an opposite direction4 ,)\t su* a clock we may get an image ( ! object we wi% to exam9e2 b be=e we %\ld be able to d any?+ ) x1 ei!r 9 ! way ( measurem5t or obs]vation1 x w\ld h gone f u4 ,a glimpse ( a planet or /> ) a l>ge telescope w give a g5]al notion ( ! extreme difficulty :i* any obs]v] w\ld h to deal ) if he want$ to obs]ve any heav5ly body )\t a driv+ clock4 ,we c easily see at once t x w\ld n d to h an ord9>y clock regulat$ by a p5dulum = driv+ ! telescope1 x w\ld be driv5 by fits & />ts1 :i* w\ld make ! object view$ jump 9 ! field at ea* tick ( ! p5dulum4 ,! mo/ simple clock is !re=e "o 9 :i* ! conical p5dulum is us$ 9 ! =m ( ! gov]nor ( a /eam-eng9e1 s t :5 ! balls ,a ,a1 ,fig4 #adf1 fly up by reason ( ! clock driv+ too fa/1 !y rub aga9/ a r+1 ,b1 or some?+ else t r$uces _! velocity4 ,illu/ration3 ,,fig4 #adf4--;,clock ,gov]nor4 ,illu/ration3 ,,fig4 #adg4--;,bond's ,spr+ ,gov]nor4 ,!re is ano!r =m made by ,alvan ,cl>ke1 9 :i* a p5dulum regulates ! clock1 b n q 9 ! ord9>y way4 ,! draw+ w p]haps make x cle>3 ,a ,a1 ,fig4 #adg1 is "o ( ! :eels ( ! clock-tra9 driv+ a small weight$ fan1 ,b1 :i* is regulat$ s z to all[ ! clock to drive a little too fa/4 ,n[ let u see h[ ! p5dulum regulates x4 ,on ! axis ( ,a ,a is plac$ an arm1 ,c1 :i* is ( su* a l5g? t x cat*es aga9/ ! /uds ,s ,s1 & is /opp$ until ! p5dulum1 ,p1 sw+s up aga9/ "o ( ! /uds1 ,r1 :i* moves ! piece ,d1 l a p5dulum ab\t its spr+ at ,e1 until ! /ud1 ,s1 is suffici5tly remov$ to let ! arm1 ,c1 pass1 s t ! clock is "u p]fect control4 ,if1 h[ev]1 ! arm ,c 7 fix$ rigidly to ! axis ( ! :eel ,a ,a1 !re w\ld be a j]k e "t ,c t\*$ "o ( ! /uds4 ,! :eel is !re=e atta*$ to ! axis ?r\gh ! m$ium ( a spr+1 ,f1 s t :5 ! arm is /opp$ ! :eel goes on1 b has its velocity ret>d$ by ! pressure ( ! spr+4 ,! p5dulum is kept go+ 9 ! foll[+ mann]3--,!re is a p9 fix$ to ! axis on ! same side ( ! c5tre z ,c1 :i*1 z ! arm approa*es ei!r /ud ,s1 raises ! piece ,d1 b n suffici5tly to lib]ate ! arm2 ! p5dulum has !n only a v little "w to d to raise ,d & dis5gage ! arm1 ,c2 b z soon z x is free x />ts (f ) a j]k1 due to ! t5sion ( ! spr+ on ! axis1 & leaves ,d by means ( its /ud1 ,r1 to ex]t its full =ce on ! p5dulum & accel]ate its return /roke1 s t ! p5dulum is kept 9 motion by ! regulat+ arrangem5t itself4 ,! late ,mr4 ,cooke ( ,york con/ruct$ a v accurately-go+ driv+ clock4 ,?is diff]s 9 important p>ticul>s f ,bond's =m1 ?\gh ! control ( ! p5dulum is reta9$4 ,! foll[+ extracts f a description ( x w %[ ! pr9cipal po9ts 9 its con/ruction3-- ,! regulator adopt$ is ! vibrat+ p5dulum1 because among/ ! means at ! me*anician's comm& = obta9+ p]fect "t-keep+ !re is none o!r by :i* ! same degree ( accuracy c be obta9$4 ,! difficulty 9 ?is con/ruction is ! conv]sion ( ! j]k+ or int]mitt5t motion produc$ by su* p5dulums into a uni=m rotatory motion :i* c be available ) little or no di/urb+ influ5ce on ! p5dulum itself1 :5 ! ma*9e is subject to v>y+ frictions & =ces to be ov]come 9 driv+ l>ge equatorials4 ,! p5dulum is a half-second "o1 ) a heavy bob1 adju/$ by slid+ ! susp5sion ?r\gh a fix$ slit4 ,x is drawn up & let d[n by a lev] & screw1 ! act+ l5g? ( ! p5dulum be+ ?us regulat$4 ,! arrangem5t ( ! :eels repres5ts some?+ l ! lett] ,u4 ,at ! upp] end ( "o bran* is ! scape-:eel4 ,at ! upp] end ( ! o!r bran* is an air-fan4 ,! l>ge driv+-:eel & b>rel are situat$ at ! bottom or b5d4 ,all ! :eels are ge>$ toge!r 9 "o cont9u\s tra91 :i* consi/s ( eight :eels & z _m p9ions4 ,! scape-:eel & ! two foll[+ :eels h an int]mitt5t motion2 all ! o!rs h a cont9u\s & uni=m "o4 ,! *ange f "o motion to ! o!r is made at ! ?ird :eel1 :i*1 in/ead ( hav+ its pivot at ! end ( ! arbor :]e ! :eel is fix$--fix$ to ! frame l ! o!rs--is susp5d$ f above by a long arm hav+ a small motion on a p9 fix$ to ! frame2 ! pivot at ! o!r end ( ! arbor is fix$ to ! frame z ! o!rs are1 b its bole & its pivot are arrang$ s z to p]mit a v small horizontal angul> motion r\nd !m1 z a c5tre1 )\t int]f]+ ) ! action ( ! ge>+ ( ! :eel itself4 ,if ! weight is appli$ to ! clock1 & ! p5dulum is made to vibrate1 ! mom5t x beg9s to move1 ! scape-:eel moves its quantity = a beat2 ! remontoire :eel1 by ! v small =ce outw>dly caus$ by ! reaction ( ! break-spr+1 relaxes its pressure aga9/ a friction-:eel1 & sets at lib]ty ! tra9 ( ! clock4 ,! spr+ is n[ driv5 back to ! break-:eel1 b be=e x c produce m ?an ! necess>y friction to keep ! tra9 9 uni=m motion1 ano!r beat ( ! clock aga9 releases x4 ,! repetition ( ^! actions produces a s]ies ( impulses on ! break-:eel ( su* a =ce & nature z to keep ! tra9 freely gov]n$ by ! p5dulum4 ,! uni=m rotatory motion obta9$ by ?is clock z f> z exp]im5ts c be made by apply+ widely diff]5t weights1 & comp>+ ! times ) a *ronomet]1 is p]fectly satisfactory4 ,a clock con/ruct$ on ! same pr9ciple1 connect$1 & giv+ motion to a cyl9d]1 w1 x is presum$1 make an excell5t *ronograph4 ,illu/ration3 ,,fig4 #adh4--;,f\cault's gov]nor4 ,! =m ( gov]nor mo/ usually employ$ w be se5 9 figures previ\sly giv54 ,! gov]nor raises a plate & ?us becomes a frictional gov]nor1 by :i* all ov]plus ( p[] is us$ up 9 frictions1 or by t d\bl+ ! driv+ p[] no1 or only a small1 diff]5ce %\ld be br\ght ab\t 9 ! rate4 ,o!r =ms ( driv+ clocks or gov]nors inv5t$ by ,f\cault & ,yvon ,vill>ceau are n[ be+ l>gely employ$4 ,9 !m ! rapid motion ( a fan & o!r devices are introduc$4 ,a driv+ clock adju/$ to sid]eal "t requires adju/m5ts = obs]vations ( ! sun & moon4 ,?is 7z at z 9 ,fig4 #add7 is sometimes done once = all by diff]5tial ge>+ ?r[n into action by lev]s :5 requir$4 ,mr4 ,grubb has lately made a notable improvem5t ^u ! usual =m by controll+ ! motion ( ! gov]nor by a sid]eal clock & an electric curr5t4 ,!re are v>i\s me?ods ( atta*+ ! clock to ! pol> axis4 ,"o is to make ! clock turn a tang5t screw1 ge>+ into a screw-:eel on ! axis ( ! telescope1 :i* c be ?r[n 9 & out ( ge> = mov+ ! telescope rapidly 9 "r asc5sion4 ,ano!r me?od is to h a segm5t ( a circle on ! pol> axis :i* c be clamp$ or unclamp$ at pleasure by means ( a screw atta*$ to x4 ,a /rip ( metal is atta*$ to ea* end ( ! segm5t & is w\nd r\nd a drum turn$ by ! clock1 s t ! two are ge>$ toge!r j z :eels are ge>$ by an endless /rap pass+ r\nd !m4 ,?is arrangem5t gives a rem>kably ev5 motion to ! telescope4 ,:5 ! /rap is w\nd up to ! end ( ! segm5t1 :i* is done 9 ab\t two or ?ree h\rs' "w1 ! drum is ?r[n out ( ge> & ! arc pu%$ back to its />t+-place aga94 ,,! ,,lamp4 ,illu/ration3 ,,fig4 #adi4--;,illum9at+ lamp = equatorial4 ,9 ! description ( ! transit circle we saw h[ ! ,a/ronom]-,royal _h contriv$ to ?r[ light into ! axis ( ! telescope1 s t ! wires 7 ei!r r5d]$ visible 9 a bright field1 or1 ! field be+ kept d>k1 ! wires 7 visible z bright l9es 9 a d>k field4 ,t is ! diff]5ce betwe5 a bright field1 & a d>k field ( illum9ation4 ,n[ a bright field ( illum9ation 9 ! case ( equatorials is manag$ by an arrangem5t z foll[s4--,a ,a1 ,fig4 #adi1 is a section ( ! tube ( ! telescope4 ,ne> ! eyepiece is a small lamp1 ,d1 swung on p9s on ei!r side :i* re/ on a circul> piece ( brass sw++ on a p9 at ,c1 & a %ort piece ( tube at ,e1 ?r\gh :i* ! light passes into ! telescope & falls on a small diagonal reflector1 ,f4 ,?is reflects ! rays d[nw>ds into ! eyepiece4 ,:5 ! telescope is mov$ into any position ! lamp sw+s l a m>9]'s compass on its gimbals1 & /ill ?r[s its light into ! tube1 & ! light mixes up ) t com+ f ! />1 b spreads all ov] ! field ( view in/ead ( com+ to a po9t1 s t ! /> is se5 on a bright field1 & ! wires z black l9es4 ,n[ if ! /> :i* is obs]v$ is a v fa9t "o1 we defeat our own object1 = ! light com+ f ! lamp puts out ! fa9t />4 ,illu/ration3 ,,fig4 #aej4--;,cooke's illum9at+ lamp4 ,we h se5 h[ ! illum9ation ( ! wires1 in/ead ( ! field1 is c>ri$ out 9 ! ,gre5wi* transit4 ,! same me?od c be adopt$ 9 ! case ( equatorials1 ! light f ! diagonal reflector be+ ?r[n on o!r diagonal reflectors or prisms on ei!r side ! wires 9 ! micromet] s z to illum9ate !m4 ,messrs4 ,cooke & ,sons h devis$ a lamp ( v great +5uity1 ,fig4 #aej4 ,x is a lamp :i* does = ! equatorial1 9 any position1 exactly :at ! fix$ lamp does = ! transit circle4 ,x is impossible to put x out ( ord] by mov+ ! telescope4 ,!re is a prism at ,p reflect+ ! light into ! telescope tube1 & at :atev] diff]5t angle ( incl9ation1 or :atev] may be ! size ( ! telescope on :i* ?is lamp is plac$1 x is obvi\s t ! lamp nev] ceases to ?r[ its light into ! reflector inside ! telescope2 & any am\nt ( light1 or any col\r ( light requir$ c be obta9$ by turn+ ! disc conta9+ glass ( diff]5t col\rs or ! o!r hav+ diff]5tly siz$ ap]tures1 9 ord] to admit m or less light1 or give ! light any col\r4 ,9 bo? ^! arrangem5ts ! lamp is hung on ! side ( ! telescope1 :ile ,mr4 ,grubb pref]s to hang x at ! end ( ! decl9ation axis1 z %[n 9 ,figs4 #aci & #adj4 ,! function ( ! lamp !n is to illum9ate ! wires ( ! micromet] eyepiece1 ( :i* m pres5tly2 b ,mr4 ,george ,bidd] places ! micromet] itself outside ! tube ( ! telescope1 ! light ( a lamp be+ ?r[n on ! wires4 ,?is is done z foll[s3--,on ! same side ( ! wires z ! lamp is a convex l5s & reflector s arrang$ t ! rays f ! wires are reflect$ ?r\gh a hole 9 ! tube1 & aga9 d[n ! tube to ! eyepiece1 :]e ! images ( ! wires are br\ght to a focus at ! same place z ! />s to be measur$1 s t any eyepiece c be us$4 ,! wires %[ z bright l9es 9 ! field1 & !y are work$ ab\t 9 ! field j z real wires might be by mov+ ! wires outside ! tube4 ,a %eet ( metal c be mov$ 9 front ( ! di/ance-wires s z to ob/ruct ! light f !m at any "p ( _! l5g?1 & _! bright images appe> !n abruptly to t]m9ate 9 ! field ( view1 s t fa9t />s c be br\ght up to ! t]m9ations ( ! wires & be measur$ )\t be+ ov]come by bright l9es4 ----- ,footnote #af3 ,x is n too mu* to say t ! duty on glass entirely /ifl$1 if inde$ x did n kill1 ! optical art 9 ,engl&4 ,we 7 s dep5d5t = _m ye>s ^u ,france & ,g]many = our telescopes1 t ! l>ge/ object-glasses at ,gre5wi*1 ,ox=d1 & ,cambridge are all ( =eign make4 ,footnote #ag3 ,^! details are giv5 f ! ,=ces ( ,nature 7,macmillan74 ,,*apt] ,,xxi4 ,,! ,,adju/m5ts ,,( ,,! ,,equatorial4 ,z ! equatorial is p> excell5ce ! amateur's in/rum5t1 & z 9 sett+ up an equatorial x is important t ! sev]al adju/m5ts %\ld be correctly made1 !y are "h dwelt ^u z briefly z possible4 ,!y are six 9 numb]4 #a4 ,! incl9ation ( ! pol> axis mu/ be ! same z t ( ! pole ( ! heav5s4 #b4 ,! decl9ation circle mu/ read #j :5 ! telescope is at "r angles to ! pol> axis4 #c4 ,! pol> axis mu/ be plac$ 9 ! m]idian4 #d4 ,! optic axis ( ! telescope1 or l9e ( collimation mu/ be at "r angles to ! decl9ation axis1 s t x describes a great circle on mov+ ab\t t axis4 #e4 ,! decl9ation axis mu/ be at "r angles to ! pol> axis1 9 ord] t ! telescope %all describe true m]idians ab\t t axis4 #f4 ,! h\r circle mu/ read #j;h4 #jm4 #jsec4 :5 ! telescope is 9 ! m]idian4 ,:5 ^! are correctly made ! l9e ( collimation w1 on be+ turn$ ab\t ! decl9ation axis1 describe great circles ?r\gh ! pole1 or m]idians1 & :5 mov$ ab\t ! pol> axis1 true p>allels ( decl9ation2 & ! circles w give ! true read+s ( ! app>5t decl9ation1 & h\r angles f ! m]idian4 ,to make ^! adju/m5ts1 ! telescope is set up by means ( a compass & protractor1 or o!rwise 9 an approximately correct position1 ! decl9ation circle put s z to read ne>ly #ij :5 ! telescope po9ts to ! pole1 & ! h\r circle read+ #j;h4 #jm4 #jsec4 :5 ! telescope is po9t+ s\?4 ,fir/1 !n1 to f9d ! error 9 altitude ( ! pol> axis4 ,take any /> f ! ,nautical ,almanac ( kn[n decl9ation on or ne> ! m]idian1 & put an eyepiece ) cross wires 9 x 9 ! telescope1 & br+ ! /> to ! c5tre ( ! field z %[n by ! wires4 ,!n read ! decl9ation circle1 note ! read+ d[n & correct x = atmosph]ic refraction1 accord+ to ! altitude#ah ( ! /> by ! table giv5 9 ! ,nautical ,almanac1 turn ! telescope on ! pol> axis r\nd half a circle s t ! telescope comes on ! o!r side ( ! pi]4 ,! telescope is !n mov$ on its decl9ation axis until ! same /> is br\ght to ! c5tre ( ! field1 & ! circle read z be=e & correct$4 ,! mean ( ! two read+s is !n f\nd1 & ?is is ! decl9ation ( ! /> z measur$ f ! equator ( ! in/rum5t1 & its diff]5ce f ! true decl9ation giv5 by ! almanac is ! error ( ! in/rum5tal equator & ( c\rse1 also ( ! pole at "r angles to x4 ,x is obvi\s t if ! decl9ation circle 7 already adju/$ to z]o1 :5 ! telescope 0 po9t+ to ! equator ( ! in/rum5t1 "o obs]vation ( decl9ation w\ld det]m9e ! error 9 "q2 & x is to elim9ate ! index error ( ! circle1 z x is call$1 t ! two obs]vations are tak5 9 su* a mann] t ! index error increases "o read+ j z mu* z x decreases ! o!r1 s t ! mean is ! true in/rum5tal decl9ation4 ,index ,error4--,f :at has j be5 /at$ x foll[s t half ! diff]5ce ( ! two read+s is ! index error1 :i* c be at once correct$ by ! screws mov+ ! v]ni]1 giv+ correction ,no4 #b4 ,to correct ! error 9 altitude ( ! pole1 ! circle is !n set to ! decl9ation ( ! /> giv5 by ! almanac1 correct$ = refraction1 & ! telescope br\ght above or bel[ ! /> z ! error may be1 & ! pol> axis c>ry+ ! telescope is mov$ by ! sett+ screws1 until ! /> is 9 ! c5tre ( ! field4 #crd ,adju/m5t4--,a s+le obs]vation ( any kn[n />1 ab\t #f h\rs to ! ea/ or we/ w give ! error ( ! pol> axis ea/ & we/1 ! diff]5ce betwe5 ! obs]v$ & true decl9ation be+ ?is error1 & x c be correct$ 9 ! same mann] z ! la/4 ,^! obs]vations %\ld be repeat$1 & />s 9 diff]5t p>ts ( ! heav5s obs]v$1 9 ord] to elim9ate errors ( division ( ! circle until ! necess>y accuracy is obta9$4 ,= example3 ,obs]v$ dec4 ( ,capella #dc #ej #cj ,telescope we/4 #dg #j #j ,telescope ea/4 ------ ------ ------ #b7 #ij #ej #cj ------ ------ ------ #de #be #ae #dg #j #j ,error due to refraction #j #j #g #dc #ej #cj ------ ------ ------ ------ ------ ------ ,in/rum5tal decl9ation #de #be #h #b7 #c #i #cj ,true decl9ation #de #eb #j ------ ------ ------ ------ ------ ------ ,index error #a #cd #de #bf #eb ,?is indicates t ! pole ( ! in/rum5t is po9t+ bel[ ! true pole1 & index error #a #cd #de4 ,obs]v$ decl9ation ( ,pollux #f;h4 we/ #bh #ai #ah ,refraction #j #j #df ------ ------ ------ #bh #ah #c ,true decl9ation #bh #bj #aj ------ ------ ------ #j #a #ch ,?is %[s ! pole to be #a #ch ea/ ( true pole4 #d? ,adju/m5t4--,= ! e/imation & correction ( ! ?ird error1 t ( collimation1 an equatorial /> is br\ght to ! c5tre ( ! field ( ! telescope1 ! "t by a clock not$1 & ! h\r circle read4 ,! pol> axis is !n turn$ ?r\gh half a circle1 & ! /> obs]v$ ) ! telescope on ! opposite side 7say ! we/7 ( ! pi]1 ! "t not$1 & ! h\r circle read4 ,subtract ! fir/ read+ f ! second 7plus tw5ty-f\r h\rs if necess>y7 & subtract ! "t elaps$ betwe5 !m1 & ! result %\ld be exactly twelve h\rs1 & half ! diff]5ce betwe5 x & twelve h\rs is ! error 9 "q4 ,if x is m ?an twelve h\rs ! angle betwe5 ! object end ( ! telescope & ! decl9ation axis is acute1 & if less !n x is obtuse4 ,?is error c !n be correct$ by ! prop] screws4 ,a little consid]ation w %[1 t if ! angle betwe5 ! object end ( ! telescope & ! decl9ation axis be acute1 & ! telescope is on ! ea/ side ( ! pi]1 & po9t+ to a />1 say on ! m]idian1 ! h\r circle w n read s mu* z x w\ld d if ! l9e p]p5dicul> to ! decl9ation axis 7 po9t+ to ! m]idian4 ,:5 ! telescope is on ! wre/ side ( ! pi]1 ! circle w read high] = ! same reason1 & !re=e ! diff]5ce betwe5 ! angle ?r\gh :i* ! h\r circle is mov$ & #ahj is equal to d\ble ! angle betwe5 ! l9e p]p5dicul> to ! decl9ation axis & ! collimation axis ( ! telescope2 all[ance be+ made = ! />'s motion4 ,= example ,virg9is1 ,dec4 #j #dfe4 ,"t by clock4 ,h\r circle read+4 #aa;h4 #bcm4 #ebs4 #aa;h4 #eem4 #cjs4 ,telescope ea/4 #aa;h4 #cam4 #ees4 #bd;h4 #hm4 #bds4 ,telescope we/4 -------- -------- -------- -------- -------- ------------ #hm4 #cs4 #ab;h4 #abm4 #eds4 #hm4 #cs4 -------- ------------ #b7 #dm4 #eas4 -------- ------------ ,collimation error at #bm4 #bees4 dec4 #dfe angle betwe5 object glass & decl9ation axis acute4 ,if ?is error is n correct$1 x mu/ be add$ :5 ! telescope is on ! ea/ side ( ! pi]1 & subtract$ :5 on ! we/4#ai #e? ,adju/m5t4--,place a /rid+ level on ! pivots ( ! decl9ation axis & br+ ! bubble to z]o by turn+ ! pol> axis2 read (f ! h\r circle & note x2 !n rev]se ! decl9ation axis ea/ & we/ & replace ! level2 br+ ! bubble to z]o & aga9 read ! circle4 ,! read+s %\ld %[ ! axis to be turn$ ?r\gh half a circle1 & ! diff]5ce %[s ! error4 ,if ! second read+ m9us ! fir/ be m ?an half a circle or #ab h\rs1 x %[s t ! pivot at ! ea/ at ! fir/ obs]vation is too high1 & !re=e 9 br++ ! decl9ation axis level1 ! fir/ read+ ( ! h\r circle is dim9i%$ f its prop] am\nt & increas$ on ! axis be+ rev]s$4 ,to adju/ ! error1 f9d half ! diff]5ce ( circle read+s & apply x1 ) ! prop] sign1 to ea* ( ! two circle read+s1 :i* w !n diff] by exactly twelve h\rs2 br+ ! circles to read "o ( ! correct$ read+s & alt] ! decl9ation axis until ! bubble ( ! level comes to z]o4 ,if ! pivots ( ! decl9ation axis are n expos$1 s t ! level c be appli$1 ! foll[+ me?od mu/ be adopt$3--,fa/5 a small level on any "p ( ! decl9ation axis or its belong+s1 say on ! top ( ! c\nt]poise weight2 br+ ! axis app>5tly horizontal & ! bubble to z]o2 turn ! telescope on ! decl9ation axis1 s t by ! turn+ ( ! c\nt]poise ! level comes bel[ x2 if !n ! bubble is at z]o1 ! axis ( ! level is p>allel to ! decl9ation axis1 & bo? are horizontal1 & if n x is cle> t nei!r ( ^! conditions holds2 !re=e br+ ! bubble to z]o by ! two motions ( ! level ) ref]5ce to ! c\nt]poise & ! motion ( ! decl9ation axis on ! pol> axis1 s t ! error is equally correct$ betwe5 !m2 repeat ! proce$+ until ! level is p>allel ) ! axis1 :5 x w %[ :5 ! axis is horizontal z well z ! /rid+ level4 ,= example3-- ,h\r circle read+ :5 #aa;h4 #egm4 #egs4 ,telescope ea/4 decl9ation axis is horizontal4 #bc;h4 #eim4 #dgs4 ,telescope we/4 -------- -------- -------- #ab;h4 #am4 #ejs4 ,error #j;h4 #am4 #ejs4 ,or ?is error c be f\nd & correct$ )\t a level by tak+ two obs]vations ( a /> ( l>ge decl9ation 9 ! same mann] z 9 e/imat+ ! collimation error1 = example3-- ,,urs ,,majoris4 ,"t by clock4 ,h\r circle read+4 #ab;h4 #hm4 #egs4 #j;h4 #bhm4 #dds4 ,telescope ea/4 #ab;h4 #ahm4 #ecs4 #ab;h4 #dfm4 #dbs4 ,telescope we/4 -------- -------- -------- -------- -------- -------- #im4 #efs4 #ab;h4 #agm4 #ehs4 #im4 #efs4 -------- -------- #b7 #hm4 #bs4 -------- -------- ,error ( h\r circle due to error ( #dm4 #as4 incl9ation ( axes#bj #f? ,adju/m5t4--,br+ ! decl9ation axis to a horizontal position ) a level & set ! h\r circle to z]o1 or obta9 ! sid]eal "t f ! ne>e/ obs]vatory1 or aga9 f9d x f ! sol> "t by ! tables1 & correct x = ! longitude ( ! place 7subtract+ ! longitude r$uc$ to "t :5 ! place is we/ & add+ :5 ea/ ( ! "t-giv+ obs]vatory7 & set a clock or wat* to x4 ,take ! "t ( transit ( a kn[n /> ne> ! m]idian & !n ! sid]eal "t by ! clock at transit m9us ! "r asc5sion ( ! /> w give ! h\r angle pa/ ! m]idian1 & its diff]5ce f ! circle read+ is ! index error1 :i* is easily correct$ by ! v]ni]4 ,if ! /> is ea/ ( ! m]idian ! "t mu/ be subtract$ f ! "r asc5sion to give ! circle read+4 ,9 ! above examples we h assum$1 = ! sake ( bett] illu/ration1 t ! h\r circle is divid$ into tw5ty-f\r h\rs1 b m usually !y are divid$ into two halves ( twelve h\rs ea*4 ,a movem5t ?r\gh half a circle1 !re=e1 br+s ! h\r circle to ! same read+ aga9 in/ead ( produc+ a diff]5ce ( twelve h\rs1 z 9 ! above example4 ,:5 ! equatorial is once prop]ly 9 adju/m5t1 n only c ! co-ord9ates ( a cele/ial body be obs]v$ ) accuracy :5 ! "t is kn[n1 b a planet or o!r body c easily be f\nd 9 ! day-"t4 ,! object is f\nd by ! two circles--! decl9ation circle & ! h\r or "r-asc5sion circle4 ,! decl9ation ( ! requir$ object be+ giv51 ! telescope is set by ! circle to ! prop] angle ) ! equator4 ,! ,r4,a4 ( ! object is !n subtract$ f ! sid]eal "t1 or t "t plus tw5ty-f\r h\rs1 :i* w give ! di/ance ( ! object f ! m]idian1 & to ?is di/ance ! h\r-circle is set4 ,! object %\ld !n be 9 ! field ( ! telescope1 or at lea/ 9 t ( ! f9d]4 ,we subtract ! />'s ,r4,a4 f ! sid]eal "t because ! clock %[s ! "t s9ce ! fir/ po9t ( ,aries pass$ ! m]idian1 & ! /> passes ! m]idian lat] by j its ,r4,a41 s t if ! "t is #b;h41 or ! fir/ po9t ( ,aries has pass$ #b;h4 ago1 a /> ( #a;h4 ,r4,a41 or transit+ #a;h4 aft] t po9t1 w h pass$ ! m]idian #b;h4 - #a;h4 #a;h4 ago2 s if we set ! telescope #a;h4 we/ ( ! m]idian we %all f9d ! />4 ,! mom5t ! object is f\nd ! telescope is clamp$ 9 decl9ation1 & ! clock ?r[n into ge>1 s t ! /> may be foll[$ & obs]v$ = any l5g? ( "t4 ----- ,footnote #ah3 ,! altitude ( ! /> 9 ?is case is its decl9ation plus ! co-latitude ( ! place1 b ?is only applies :5 ! /> is on ! m]idian4 ,:5 ! altitude ( a /> 9 ano!r situation is requir$1 x is f\nd suffici5tly accurately by means ( a globe4 ,a sextant1 if at h&1 w ( c\rse give x at once4 ,footnote #ai3 ,s9ce ! velocity ( ! /> v>ies z ! cos9e ( ! decl9ation1 ! error ( collimation at ! equator #bm4 #bees4 cos4 #j #dee #bm4 #bejhs42 & = non-equatorial />s1 #bm4 #bejhs4 sec4 dec4 ,footnote #bj3 ,?is error v>ies z ! tang5t ( ! decl9ation1 & !re=e to f9d ! con/ant = ! in/rum5t1 9 case ! p>ts d n admit ( easy adju/m5t1 we divide #dm4 #as4 by #aah ! tan4 ( ,dec4 ( ,urs ,majoris1 giv+ #c m94 #bh sec4 ,,*apt] ,,xxii4 ,,! ,,equatorial ,,obs]vatory4 ,we h n[ consid]$ ! m\nt+ & adju/m5t ( ! equatorial1 be x reflector or refractor4 ,if ( l>ge dim5sions x w require a special build+ to conta9 x1 & ?is build+ mu/ be s con/ruct$ t1 z 9 ! case ( ! ,melb\rne & ,p>is in/rum5ts1 x c be :eel$ away bodily to ! nor?1 leav+ ! in/rum5t out 9 ! op52 or ! ro( mu/ be s arrang$ t ! telescope c po9t ?r\gh an ap]ture 9 x :5 mov$ to any position4 ,?is requirem5t entails 7#a7 ! removal ( ! ro( altoge!r1 by hav+ x made ne>ly flat1 & slid+ x bodily (f ! ,obs]vatory1 or 7#b7 ! m usual =m ( a revolv+ dome1 ) a slit d[n "o side1 or 7#c7 ! ,obs]vatory maybe drum-%ap$1 & may run on roll]s ne> ! gr\nd4 ,! la/ =m is adopt$ = reflectors ^: axis ( motion is l[2 b ) refractors hav+ _! decl9ation axis ov] six or sev5 feet f ! gr\nd1 ! walls ( ! ,obs]vatory c be fix$1 z ! telescope1 :5 horizontal1 po9ts ov] ! top4 ,! ro(1 :i* may be made ( %eet-iron or ( wood well brac$ toge!r to prev5t x alt]+ 9 %ape1 is built up on a /rong r+ :i* runs on :eels plac$ a few feet ap>t r\nd ! circul> wall1 or1 in/ead ( :eels1 cannon balls may be us$1 roll+ 9 a groove ) a correspond+ groove re/+ on !m4 ,a small ro(1 if c>efully made1 may be pull$ r\nd by a rope atta*$ to any "p ( x1 b l>ge ones g5]ally h a too!d circle inside ! "o on :i* ! ro( is built1 or ?is circle itself is too!d1 s t a p9ion & h&-w9* c ge> into x & w9d x r\nd4 ,if ! ro( is conical 9 %ape ! ap]ture on "o side c be cov]$ by two glaz$ doors1 op5+ back l fold+-doors2 b if x is dome-%ap$1 ! %utt] is made l a ,v5etian bl9d or revolv+ %op-w9d[ %utt]1 & slides 9 grooves on ei!r side ( ! op5+4 ,illu/ration3 ,,fig4 #aea4--;,dome4 ,illu/ration3 ,,fig4 #aeb4--;,drum4 ,illu/ration3 ,,fig4 #aec4--,new ,c9c9nati ,obs]vatory--,front elevation1 %[+ ext]ior ( ,drum4 ,illu/ration3 ,,fig4 #aed4--;,cambridge 7,u4,s47 ,equatorial1 %[+ ,obs]v+ ,*air & rails4 ,! equatorial & ! build+ to conta9 x h n[ be5 describ$1 b !re is ano!r piece ( app>atus :i* is requir$ z mu* z any adjunct to ! equatorial1 & t is ! *air or re/ = ! obs]v]4 ,s9ce ! telescope may be sometimes horizontal1 & at o!r times v]tical1 ! obs]v] mu/ be at "o "t 9 an upright position1 & at ano!r ly+ d[n & look+ /raight up4 ,a re/ is requir$ :i* w c>ry ! obs]v] 9 ^! or 9 int]m$iate positions4 ,a conv5i5t =m ( re/ = small telescopes consi/s ( a seat l t ( a *air1 ) a support mov+ on h+es at ! back ( ! seat2 a rack motion fixes ?is at any incl9ation1 s t ! obs]v]'s back c be su/a9$ 9 any position1 betwe5 upright & ne>ly horizontal4 ,! seat ) its back slides on two /raight b>s ( wood1 slop+ upw>ds f ne> ! gr\nd at an angle ( ab\t #cj1 & ab\t #h;ft4 long2 ^! are support$ at _! upp] ends by uprights ( wood1 & at _! l[] ends 9 ! same mann] by %ort] pieces4 ,^! f\r uprights are firmly brac$ toge!r1 & h ca/ors at ! bottom4 ,a rack is cut on "o ( ! incl9$ slides1 & a cat* falls into x1 s z to fix ! seat at any height to :i* x is plac$4 ,9 l>g] obs]vatories a m elaborate arrangem5t is adopt$1 ! rails1 on :i* ! seat moves1 are curv$ to =m "p ( a circle1 hav+ ! c5tre ( motion ( ! telescope = its c5tre2 z ! seat ) its back is mov$ up or d[n on ! curv$ slides1 its incl9ation is *ang$1 s t ! obs]v] is always 9 a fav\rable position = obs]v+4 ,! seat on its frame runs on circul> rails r\nd ! pi] ( ! telescope1 s t ! eyepiece c be foll[$ r\nd z ! telescope moves 9 foll[+ a />4 ,a w9* by ! side ( ! obs]v]1 act+ on tee? on "o ( ! rails1 enables him to move ! *air along1 & a simil> arrangem5t enables him to raise or l[] ! seat on ! slides )\t remov+ f 8 place4 ,a /eady m\nt+ = ! telescope1 & a com=table seat = ! obs]v]1 are ! two ?+s )\t :i* a telescope is almo/ useless4 ,! obs]v+ *air is well se5 9 ! engrav+s ( ,mr4 ,newall's & ! ,cambridge telescopes4 ,! eyepieces & micromet] c be c>ri$ on ! re/1 close to ! obs]v]1 :5 mu* tr\ble is sav$ 9 mov+ ab\t = ?+s 9 ! d>k2 & = ! same reason !re %\ld be a place = ev]y?+ 9 ! obs]vatory1 & ev]y?+ 9 its place4 ,illu/ration3 ,,fig4 #aee4--,section ( ,ma9 ,build+--,unit$ ,/ates ,naval ,obs]vatory1 %[+ support ( ,equatorial4 ,! v high magnify+ p[] employ$ ^u equatorials 9 ! f9e/ /ates ( ! air necessitates a v firm f\ndation = ! c5tral pill>4 ,! be/ position = su* an in/rum5t is on ! gr\nd1 b x is almo/ always necess>y to make !m high 9 ord] to be able to sweep ! :ole horizon4 ,! accompany+ woodcut w give an idea ( ! precautions t h to be tak5 "u ^! circum/ances4 ,a solid pill> mu/ be c>ri$ up f a concrete f\ndation1 & !re mu/ be no contact betwe5 ?is & ! walls or floors ( ! build+1 :5 ! dome ?us occupies ! c5tre ( ! obs]vatory4 ,! o!r rooms1 g5]ally built adjo9+ ! equatorial room1 radiate f ! dome1 ea/ & we/1 n suffici5tly high to int]f]e ) ! outlook ( ! equatorial4 ,9 "o ( ^! ! transit is plac$2 an op5+ is made 9 ! walls & ro(1 s t x has an unimp$$ view :5 swung f nor? ?r\gh ! z5i? to s\?1 & ?is is clos$ :5 ! in/rum5t is n 9 use by %utt]s simil> to ^? ( ! dome4 ,,*apt] ,,xxiii4 ,,! ,,sid]o/at4 ,at "o ( ! v e>lie/ meet+s ( ! ,royal ,society1 ! difficulties ( m\nt+ ! long focus l5ses ( ,huygh5s be+ "u discussion1 ,hooke po9t$ out t all difficulties w\ld be done away ) if in/ead ( giv+ movem5t to ! huge telescope itself1 a plane mirror 7 made to move 9 front ( x4 ,?is idea has tak5 two c5turies to be> fruit1 & n[ all ackn[l$ge its excell5ce4 ,"o ( ! mo/ rec5t additions to a/ronomical tools is ! ,sid]o/at1 ! "n giv5 to ! in/rum5t sugge/$ by ,hooke4 ,by its means we c make ! sun or />s rema9 virtually fix$ 9 a horizontal telescope fix$ 9 ! plane ( ! m]idian to ! s\? ( ! in/rum5t1 in/ead ( requir+ ! usual pond]\s m\nt+ = keep+ a /> 9 ! field ( view4 ,x consi/s ( a mirror driv5 by clockwork s z to cont9ually reflect ! beam ( light com+ f a />1 or o!r cele/ial object1 9 ! same direction2 ! pr9ciple consi/+ 9 s mov+ ! mirror t its normal %all always bisect ! angle subt5d$ at ! mirror by ! object & ! telescope or o!r app>atus on :i* ! object is reflect$4 ,illu/ration3 ,,fig4 #aef4--;,f\cault's ,sid]o/at4 ,x 0 ,f\cault :o1 t[>ds ! end ( 8 life1 ?\ght ( ! imm5se use ( an in/rum5t ( ?is k9d z a sub/itute = ! motion ( equatorials2 he1 h[ev]1 un=tunately did n live to see 8 ideas realiz$1 b ! ,commission = ! purpose ( c>ry+ out ! publication ( ! works ( ,f\cault direct$ ,mr4 ,ei*5s to con/ruct a sid]o/at1 & ?is "o 0 pres5t$ to ! ,academy ( ,sci5ce on ,decemb] #ac?1 #ahfi1 & is n[ at ! ,p>is ,obs]vatory4 ,s9ce t date o!rs h be5 produc$1 & !y h e *ance ( com+ l>gely into use1 especially 9 physical a/ronomy4 ,fig4 #aef %[s ! elevation ( ! in/rum5t1 ! mirror ( :i*1 9 ! case ( ! in/rum5t at ,p>is1 is ?irty c5timetres 9 diamet]1 & is support$ by a horizontal axis ^u two uprights1 :i* are capable ( revolv+ freely ^u _! base4 ,! back ( ! m\nt+ ( ! mirror has an ext5sion 9 ! =m ( a rod at "r angles to x1 by :i* x is connect$ ) ! clock1 :i* moves ! mirror ?r\gh ! m$ium ( a =k jo9t$ at ! bottom ( ! pol> axis4 ,! l5g? ( ! =k is exactly equal to ! di/ance f ! horizontal axis ( ! mirror to ! axis ( ! jo9t ( ! =k to ! pol> axis1 & ! direction ( ! l9e jo9+ ^! two po9ts is ! direction 9 :i* ! reflect$ ray is requir$ to proce$4 ,! =k is mov$ on its jo9t to su* a position t its axis po9ts to ! object to be view$1 &1 be+ c>ri$ by a pol> axis1 x rema9s po9t+ to t object z long z ! clock drives x1 9 ! same mann] z a telescope w\ld d on ! same m\nt+4 ,!n1 s9ce ! di/ance f ! axis ( ! mirror to ! jo9t ( ! =k is equal to ! di/ance f ! latt] po9t to ! axis ( its jo9t to ! slid+ tube on ! direct+ rod1 an isosceles triangle is =m$ hav+ ! direct+ rod at its base2 ! angles at ! base are !re=e equal to ea* o!r4 ,fur!r1 if we imag9e a l9e drawn 9 cont9uation ( ! axis ( ! =k t[>ds ! object1 !n ! angle made by ?is l9e & t f ! axis ( ! mirror to ! elb[ jo9t ( ! =k 7! direction ( ! reflect$ ray7 w be equal to ! two angles at ! base ( ! isosceles triangle2 &1 s9ce !y are equal to ea* o!r1 ! angle made by ! direct+ rod & ! axis ( ! =k 7or ! incid5t ray7 f ! object1 is equal to half ! angle made by ! latt] ray & ! direction ( ! reflect$ ray2 & if l9es are drawn ?r\gh ! surface ( ! mirror 9 cont9uation ( ! direct+ rod & ! l9e f ! elb[ jo9t to ! axis ( ! mirror2 & a l9e to ! po9t ( int]section be drawn f ! object1 ?is la/ l9e w be p>allel to ! axis ( ! =k1 & ! angle x makes ) ! cont9uation ( ! direct+ rod1 or normal to ! surface ( ! mirror1 w be half ! angle made by x & ! l9e repres5t+ ! reflect$ ray4 ,!re=e ! angle made by ! incid5t ray & ! requir$ direction ( ! reflect$ ray is always bisect$ by ! normal1 s t ! reflect$ ray is con/ant 9 ! requir$ direction4 ,! clock is driv5 9 ! usual mann] by a weight4 ,a rod c>ries ! motion up to ! sy/em ( :eels by :i* ! pol> axis is rotat$4 ,z ?is axis rotates x c>ries ) x ! =k1 :i* transmits ! requir$ motion to ! mirror4 ,& z ! =k alt]s its direction ! tube slides ^u ! direct+ rod1 ?us alt]+ ! incl9ation ( ! mirror4 ,9 ord] to v>y ! position ( ! mirror )\t /opp+ ! in/rum5t !re are sl[ motion rods or cords proce$+ f ! in/rum5t :i* may be c>ri$ to any di/ance desirable4 ,illu/ration3 ,,fig4 #aeg4--,! ,sid]o/at at ,"l ,l9dsay's ,obs]vatory4 ,! pol> axis is set 9 ! m]idian simil>ly to an equatorial telescope1 ! :ole app>atus be+ firmly m\nt$ ^u a massive /one pill> :i* is set sev]al feet 9 ! gr\nd1 & re/s ^u a b$ ( concrete1 if ! soil is light4 ,a h\se ^u :eels1 runn+ ^u a tramway1 is us$ to protect ! in/rum5t f ! wea!r1 & :5 9 use ?is hut is run back to ! nor?1 leav+ ! sid]o/at expos$4 ,9 ! nor? wall ( ! obs]vatory is a w9d[1 & ! telescope is m\nt$ horizontally opposite to x3 s ! obs]v] c seat himself com=tably at 8 "w1 & by 8 guide rods direct ! mirror ( ! sid]o/at to almo/ any "p ( ! sky1 view+ any object 9 ! eyepiece ( 8 telescope )\t alt]+ 8 position4 ,9 spectroscopy & cele/ial photography its use is ( imm5se importance1 = 9 ^! rese>*es ! image ( an object is requir$ to be kept /eadily on ! slit ( ! spectroscope or on ! photographic plate1 & = ?is purpose a v /rongly-made & accurate clock is requir$ to drive ! telescope & m\nt+1 :i* are necess>ily made heavy & massive to prev5t flexure & vibration4 ,! sid]o/at1 on ! o!r h&1 is extremely light1 )\t tube or accessories1 & a light1 delicate clock is able to drive x ) accuracy1 :ile ! heavy telescope & its adjuncts are at re/ 9 "o position4 ,! sun & />s c1 !re=e1 z x 71 be 8laid on0 to ! obs]v]'s /udy to be view$ )\t ! %ift+ ( ! obs]vatory ro( & equatorial1 or ( ! obs]v+ *air1 :i* br+s its occupant sometimes into mo/ uneasy positions4 ,we figure to ourselves ! future ( ! physical obs]vatory 9 ! %ape ( an ord9>y room ) sid]o/at outside ?r[+ sunlight or rays f :atev] object we wa% into any fix$ in/rum5t at ! pleasure ( ! obs]v]4 ,!re are1 h[ev]1 inconv5i5ces att5d+ its use 9 "s cases2 = in/ance1 9 measur+ ! position ( d\ble />s1 ! diurnal motion gradually *anges _! position 9 ! field ( ! telescope1 s t a new z]o mu/ be con/antly tak5 or else ! "t ( obs]vation not$ & ! necess>y corrections made4 ,,*apt] ,,xxiv4 ,,! ,,ord9>y ,,"w ,,( ,,! ,,equatorial4 ,! equatorial enables u to make n only physical obs]vations1 b diff]5tial obs]vations ( ! mo/ absolute accuracy4 ,fir/ we may t\* ^u ! physical obs]vations made ) ! eyepiece alone--/>-gaz+1 9 fact4 ,! ,sun fir/ claims our att5tion3 our dep5d5ce on him = ! light ( day1 = heat1 & = 9 fact almo/ ev]y?+ we enjoy1 urges u to inquire into ! physics ( ?is magnific5t object4 ,precautions mu/ h[ev] be tak52 m ?an "o obs]v] has already be5 bl9d$ by ! int5se light & heat1 & "s sol> eyepiece mu/ be us$4 ,= small telescopes up to two in*es1 a d>k glass plac$ betwe5 ! eye & ! eyepiece is suffici5tly safe2 = l>g] ap]tures1 ! diagonal reflector1 or ,dawes' sol> eyepiece1 already describ$1 comes into requisition4 ,ano!r me?od ( view+ ! sun is to focus ! sun's image ) ! ord9>y eyepiece on a %eet ( pap] or c>d1 or1 bett] /ill1 on a surface ( pla/] ( ,p>is c>efully smoo!d4 ,! bright ridges or /reaks1 usually se5 9 spott$ regions ne> ! edge1 call$ ! facul1 & ! mottl$ surface1 appe>+1 accord+ to ,nasmy?1 l a numb] ( int]lac+ will[-leaves--! m9ute 8granules0 ( ,dawes1 are be/ se5 ) a blue glass2 b = obs]v+ ! delicately-t9t$ veils 9 ! umbr ( ! spots a glass ( neutral t9t %\ld be us$4 ,! ,moon is a f9e object ev5 9 small telescopes4 ,! be/ obs]v+ "t is ne> ! qu>t]s1 z ne> full moon ! sun %9es on ! surface s ne>ly 9 ! same direction z t 9 :i* we look1 t !re is no light & %ade to ?r[ objects into view4 ,h\rs may be sp5t 9 exam9+ ! crat]s1 rilles1 & valleys on ! surface1 accompani$ ) a good descriptive map or su* a book z t :i* ,mr4 ,neison has rec5tly publi%$4 ,! planets also come 9 = _! %>e ( exam9ation4 ,m]cury is s ne> ! sun z seldom to be se54 ,v5us 9 small telescopes is only int]e/+ ) ref]5ce to h] *anges1 l ! moon1 b 9 l>g] ones ) great c>e ! spots are visible4 ,m>s is int]e/+ z be+ s ne> a c\nt]p>t ( our own planet4 ,on x we see ! pol> sn[s1 cont95ts & seas1 p>tially obscur$ by cl\ds1 & ^! appe>ances are br\ght "u our view 9 succession by ! rotation ( ! planet4 ,) a good six-in* glass & a p[] ( #bjj :5 ! air is pure & ! opposition is fav\rable1 !re is no difficulty 9 mak+ out ! coa/-l9es1 & ! v>i\s tones ( %ade on ! wat] surface may be obs]v$1 %[+ t "h ! sea is tranquil1 & !re x is driv5 by /orms4 ,up to v lately x 0 ! only planet ( consid]able size fur!r (f ! sun ?an ,v5us t 0 suppos$ to h no satellite2 two ( ^! bodies h h[ev] be5 lately discov]$ by ,hall ) ! l>ge ,wa%+ton refractor ( tw5ty-six in*es diamet]1 & !y appe> to be ! t9ie/ cele/ial bodies kn[n1 "o ( !m 9 all probability n exce$+ #aj miles 9 diamet]4 ,jupit] & ,saturn are v conspicu\s objects1 & ! eclipses1 transits1 & occultations ( ! moons1 & ! belts ( ! =m] & r+s ( ! latt]1 are among ! mo/ int]e/+ ph5om5a reveal$ to u by our telescopes1 :ile ! delicate m>k+s on ! ?ird satellite ( ,jupit] furni% u ) "o ( ! mo/ difficult te/s ( def9ition4 ,uranus & ,neptune are only j se5 9 small telescopes1 & ev5 9 spite ( ! use ( l>g] ones1 we are 9 ignorance ( mu* relat+ to ^! planets4 ,! amateur w d well to attack all ^! ) t *>m+ book1 ! ,rev4 ,t4 ,w4 ,webb's ,cele/ial ,objects = ,common ,telescopes1 9 8 h&4 ,to obs]ve ! fa9t] satellites ( ! bright] planets1 or1 inde$1 fa9t objects g5]ally1 ne> v bright ones1 ! bright object may be scre5$ by a metallic b>1 or r$ or blue glass plac$ 9 ! common focus4 ,s mu* ) reg>d to our own sy/em4 ,:5 we leave x we are conf\nd$ ) ! weal? ( nebul1 />-clu/]s1 & s+le or multiple sy/ems ( />s1 :i* await our scrut9y4 ,) ! />s1 n mu* c be done )\t fur!r assi/ance ?an ! eyepiece alone4 ,! col\rs ( />s may h[ev] be obs]v$1 & = ?is purpose a *romatic scale has be5 propos$1 & a memoir !reon writt51 by ,admiral ,smy?1 = comp>ison ) ! />s4 ,! col\r ( a /> mu/ n be confus$ ) ! col\rs--(t5 v vivid--produc$ by sc9tillations1 ^! rapid *anges ( brightness & col\r dep5d+ on atmosph]ic causes4 ,( ! l>ge />s1 ,sirius1 ,vega & ,regulus are :ite1 :ile ,aldeb>an & ,betelgueux are r$4 ,9 _m d\ble & multiple />s h[ev] ! contra/ ( col\rs %[s up beautifully2 9 ,cygni = in/ance we h a yell[ & blue />1 9 ,leonis1 a yell[ & a gre5 />2 & ( su* !re are num]\s examples4 ,int]e/+ z all ^! obs]vations are1 a new life & utility are ?r[n into !m :5 in/ead ( us+ a simple eyepiece ! wire micromet] is introduc$4 ,?is1 z we h be=e /at$1 g5]ally consi/s ( "o wire1 or two p>allel wires1 fix$1 & "o or two o!r wires at "r angles to ^!1 movable across ! field4 ,?is micromet] is us$ 9 connection ) a "p ( ! eyepiece end ( ! telescope1 :i* has n[ to be describ$4 ,?is is a circle1 ! f95ess ( ! graduation ( :i* increases ) ! size ( ! telescope1 read by two or f\r v]ni]s4 ,! circle is fix$ to ! telescope1 :ile ! v]ni]s are atta*$ to ! eyepiece1 c>ry+ ! micromet]1 :i* is rotat$ by a rack & p9ion4 ,! :ole sy/em ( position circle 7z x is call$7 & wire micromet]1 is 9 adju/m5t :5 7#a7 ! s+le or d\ble fix$ wires & ! movable ones cross 9 ! c5tre ( ! field1 & 7#b7 :5 ) a /> travell+ along ! s+le fix$ or betwe5 ! two fix$ wires1 ! upp] v]ni] reads #ahj & ! l[] "o reads z]o4 ,?is motion across ! field gives ! direction ( a p>allel ( decl9ation2 t is to say1 x gives a l9e p>allel to ! cele/ial equator1 &1 kn[+ t1 "o w be able at once1 by all[+ ! object to pass ?r\gh ! field ( view1 to get ?is datum l9e4 ,= in/ance1 suppos+ ! :ole in/rum5t is turn$ r\nd on ! end ( ! telescope1 s t "o ( ! two wires x & y1 ,fig4 #ajd1 at "r angles to ! ?9 wires = measur+ di/ance1 %all lie on a /> dur+ all its motion across ! field ( view2 !n ^? two wires1 be+ p>allel to ! />'s motion1 w repres5t two p>allels ( decl9ation2 & we use ! direction ( ! p>allels ( decl9ation to det]m9e ! datum po9t at "r angles to !m1 t is1 ! nor? po9t ( ! field4 ,we h !n a position micromet]1 t is1 "o 9 :i* ! field ( view is divid$ into f\r quadrants1 call$ nor? prec$+1 nor? foll[+1 s\? prec$+1 & s\? foll[+1 because if !re be an object at ! c5tral po9t x w be prec$$ & foll[$ by ^? 9 ! v>i\s quadrants4 ,! movable wires lie on m]idians & ! fix$ ones on p>allels :5 adju/$ z above4 ,illu/ration3 ,,fig4 #aeh4--,position ,circle4 ,! position circle is (t5 atta*$ to1 & =ms "p (1 ! micromet] in/ead ( be+ fix$ to ! telescope1 & 9 screw+ x on f "t to "t1 ! adju/m5t ( ! z]o *anges1 & ! index error mu/ be f\nd ea* "t ! micromet] is put on ! telescope4 ,9 practice x is usual to take ! nor? & s\? l9e z ! datum l9e1 & positions are always express$ 9 degrees f ! nor? r\nd by ea/ #ij1 s\? #ahj1 & we/ #bgj1 to nor? aga9 9 ! direction contr>y to t ( ! h&s ( a clock4 ,! angle f ! ea/ & we/ l9e be+ f\nd by ! micromet]1 #ij is ei!r add$ or subtract$1 to give ! angul> measurem5t f nor?4 ,b to make ^! measurem5ts we want a clock2 a clock :i*1 :5 we h got "o ( ^! objects 9 ! middle ( ! field ( view1 %all keep x !re1 & enable ! telescope to keep any object t we may wi% to obs]ve fix$ absolutely 9 ! field ( view4 ,b 9 ! case ( fa9t objects ?is is n en\gh4 ,we want n only to see ! object1 b also ! wires we h ref]r$ to4 ,n[ !n ! illum9at+-lamp & bright wires1 if necess>y1 come into use4 ,! foll[+1 ,fig4 #aei1 w %[ h[ we proce$ if we m]ely wi% to measure a di/ance1 ! value ( ! divisions ( ! micromet] screw hav+ be5 previ\sly det]m9$ by all[+ an equatorial /> to transit4 ,x repres5ts ! position ( ! c5tral & ! movable wire :5 ! %ad[ ?r[n by ! c5tral hill ( ! ! lun> crat] ,cop]nicus is be+ measur$ to det]m9e ! height ( ! hill above ! floor ( ! crat]4 ,x has be5 necess>y to let ! fix$ wire lie along ! %ad[2 ?is has be5 done by turn+ ! micromet]2 b !re is no occasion to read ! v]ni]4 ,illu/ration3 ,,fig4 #aei4--;,h[ ! ,l5g? ( a ,%ad[ ?r[n by a ,lun> ,hill is measur$4 ,except on ! f9e/ ( nights ! />s %ake 9 ! field ( view or appe> woolly1 & ev5 on good nights ! read+s made by a practis$ eye (t5 diff]1 int] se1 m ?an w\ld be ?\ght possible4 ,9 measur+ di/ances we h suppos$ = simplicity t we f9d ! di/ance t "o wire has to be mov$ f co9cid5ce ) ! fix$ wire f "o po9t to ano!r1 & !oretically speak+ ! po9t] %\ld po9t to ,o on ! screw head :5 ! wires are ov] ea* o!r1 & !n :5 ! wires are on ! po9ts1 ! read+ ( ! screw head divid$ by ! numb] ( divisions correspond+ to #a w give ! di/ance ( ! po9ts 9 seconds ( arc4 ,b 9 practice x is unnecess>y to adju/ ! head to ,o :5 ! wires co9cide1 & ! unequal expansion ( ! metals ( ! in/rum5t1 due to *anges ( temp]ature1 w\ld soon dis>range x4 ,x is also some:at difficult to say :5 ! wires exactly co9cide1 & an error 9 ?is w affect ! di/ance betwe5 ! po9ts4 ,x is !re=e f\nd be/ to only r\ghly adju/ ! screw head to ,o1 & !n op5 out ! wires until !y are on ! po9ts & take a read+1 say tw5ty-two2 ! screw is !n turn$1 9 ! opposite direction & ! movable wire pass$ ov] to ! o!r side ( ! fix$ "o1 & ano!r read+ tak51 say eighty-two2 n[ ! screw has to be mov$ 9 ! direction :i* decreases ! read+s on its head f "o hundr$ d[nw>ds1 z ! di/ance ( ! wires increases1 s t we mu/ subtract ! read+ eighty-two f a hundr$ to give ! numb] ( divisions f ! ,o ?r\gh :i* ! screw is turn$1 & ! read+ 9 ?is direction we w call ! indirect read+1 9 contradi/9ction to ! direct read+ tak5 at fir/4 ,s f> we h got a read+ ( tw5ty-two direct & eighte5 indirect1 :i* means t we h mov$ ! screw f tw5ty-two on "o side ( ,o to eighte5 on ! o!r side1 or ?r\gh =ty divisions1 & 9 do+ s ! movable wire has be5 mov$ f ! di/ance ( ! two po9ts on "o side ( ! fix$ wire to ! same di/ance on ! o!r1 or ?r\gh d\ble ! di/ance requir$4 ,!re=e =ty divisions is ! measure ( twice ! di/ance1 & ! half ( =ty1 or tw5ty divisions1 is ! measure ( ! di/ance itself betwe5 ! two po9ts to :i* our att5tion has be5 direct$1 :e!r />s1 crat]s 9 ! moon1 spots on ! sun1 & ! l4 ,let u consid] :at is ga9$ by ?is me?od ov] a measure tak5 by co9cid5ce ( ! wires z a />t+-po9t1 & op5+ out ! wires until !y cut ! po9ts4 ,9 ! me?od we h j describ$ !re are two *ances ( error 9 tak+ ! measurem5ts--! direct & indirect2 b ! result obta9$ is divid$ by two1 s t ! error is also halv$ 9 ! f9al result4 ,n[ by tak+ ! co9cid5ce ( ! wires z ! z]o1 or />t+-po9t1 ! measure is op5 to two errors1 z 9 ! la/ case--! error ( measurem5t ( ! po9ts1 plus ! error ( co9cid5ce ( wires1 an error (t5 ( consid]able am\nt1 especially z ! w>m? ( ! face & brea? causes consid]able alt]ation 9 ! p>ts ( ! in/rum5t1 mak+ a new read+ ( co9cid5ce necess>y at ea* read+ ( di/ance4 ,z ! result is n divid$ by two1 z 9 ! fir/ case1 ! two errors rema9 undivid$1 s we may say t !re is ! half ( two errors 9 "o case & two :ole errors 9 ! o!r4 ,"h !n we use ! micromet] to measure di/ances2 b f a v %ort acqua9tance ) ! "w ( an equatorial x w at once be se5 t "o wants to d some?+ else besides measure di/ances4 ,= in/ance1 if we take ! case ( ! planet ,saturn1 x w\ld be an object ( int]e/ to u to det]m9e h[ _m turns1 or p>ts ( a turn1 ( ! screw w give ! exact diamet] ( ! diff]5t r+s2 b we might want to "k ! exact angle made by ! axis ) ! direction ( ! planet's motion1 across ! field1 or )1 ! nor? & s\? l9e4 ,if we h fir/ got ! read+ :5 ! wires are 9 a p>allel ( decl9ation1 & !n br+ ,saturn back aga9 to ! middle ( ! field & alt] ! direction ( ! wires until !y are p>allel to ! major axis ( ! r+1 we c read (f ! position on ! circle1 & on subtract+ ! fir/ read+ f ?is1 we get ! angle ?r\gh :i* we h mov$ ! wires1 made by ! direction ( ! r+ ) ! p>allel ( decl9ation1 :i* is ! angle requir$4 ,we are ?us n only able to det]m9e ! v>i\s measurem5ts ( ! diamet] ( ! out] r+ by "o edge ( ! r+ fall+ on "o ( ! f9e wires1 & ! o!r edge on ! o!r wire1 b1 by ! position circle outside ! micromet] we c det]m9e exactly h[ f> we h mov$ t sy/em1 & ?us ! angle =m$ by ! axis ( ! r+ ( ! planet at t p>ticul> "t4 ,illu/ration3 ,,fig4 #afj4--,! ,det]m9ation ( ! ,angle ( ,position ( ! axis ( ,saturn's ,r+4 ,! uses ( ! position micromet] z x is call$ are v v>i\s4 ,9 exam9ation ( ! sun x is us$ to asc]ta9 ! position ( spots on ! surface1 & ! rate ( _! motion & *ange4 ,! lun> crat]s require mapp+1 & _! di/ances & be>+ f c]ta9 fix$ po9ts measur+1 = ?is !n ! position micromet] comes into use4 ,! v>y+ diamet]s & ! incl9ations ( ! axes ( ! planets & ! p]iods ( revolution ( ! satellites are det]m9$1 & ! position ( _! orbits fix$1 9 l mann]4 ,:5 a comet appe>s x is ( importance to det]m9e n only ! direction ( its motion among ! />s1 b ! position ( its axis ( figure1 & ! angles ( position & dim5sions ( its jets4 ,! foll[+ diagram gives an example ( ! mann] 9 :i* ! position ( its axis ( figure is det]m9$4 ,fir/ ! nucleus is made to run along ! fix$ wire1 s t x may be se5 t ! nor? v]ni] truly reads z]o "u ?is condition2 if x does n its index error is not$4 ,! sy/em ( wires is !n rotat$ till "o ( ! wires passes ?r\gh ! nucleus & fairly bisects ! d>k "p beh9d ! nucleus4 ,illu/ration3 ,,fig4 #afa4--,measurem5t ( ! ,angle ( ,position ( ! ,axis ( ,figure ( a ,comet1 a a1 positions ( fix$ wire :5 ! nor? v]ni] is at z]o2 d d position ( movable wire "u l conditions2 a a1 d d1 positions ( ^! wires :i* enable ! angle ( position ( ! comet's axis to be measur$4 ,! angle a a or d d is ! angle requir$4 ,x ne$ sc>cely be said t ^! obs]vations are also ( importance ) ref]5ce to ! motion ( ! b9>y />s1 ^? comp\nd bodies1 ^? suns revolv+ r\nd ea* o!r1 ! discov]y ( :i* we owe to ! eld] ,h]s*el4 ,we may ?us h two />s a small di/ance ap>t2 at ano!r "t we may h !m clos] /ill2 & at ano!r we may h !m gradually sep>at+1 ) _! relative position completely *ang$4 ,by means ( ! wire micromet] & ! arrangem5t = turn+ ! sy/em ( wires into diff]5t positions ) reg>d to ! p>allel ( decl9ation1 we h a means ( det]m9+ ! positions occupi$ by ! b9>y />s 9 all p>ts ( _! app>5t orbit1 z well z _! di/ances 9 seconds ( arc4 ,x is f\nd1 h[ev]1 by exp]i5ce t ! errors ( obs]vation made 9 e/imat+ di/ances are s l>ge1 relatively to ! v small quantities measur$1 t x is absolutely necess>y to make ! det]m9ation ( ! orbit dep5d *iefly on ! positions4 ,& ?is is done 9 ! foll[+ way4 ,illu/ration3 ,,fig4 #afb4--;,d\ble ,/> ,measurem5t1 a a1 b b1 fir/ position ( fix$1 d\ble wire :5 ! v]ni] reads #j1 & ! /> runs betwe5 ! wires2 c c1 d d1 fir/ position ( movable wires4 a a1 b b1 new position ( fix$ d\ble wire :i* det]m9es ! angle ( position2 c c1 d d1 new positions ( ! movable wires :i* measure ! di/ance4 ,x is possible1 by kn[+ ! position angles at diff]5t dates1 to f9d ! angul> velocity1 & s9ce ! areas describ$ by ! radius vector are equal 9 equal times1 ! l5g? ( ! radius vector mu/ v>y inv]sely z ! squ>e root ( ! angul> velocity1 & by tak+ a numb] ( positions on ! orbit ( kn[n angul> velocity1 we c set (f radii vectores1 & con/ruct an ellipse1 or "p ( "o1 by draw+ a curve ?r\gh ! ends ( ! radii vectores2 & f ! "p ( ! ellipse s con/ruct$ x is possible to make a good guess at ! rema9d]4 ,! angul> size ( ?is ellipse is obta9$ f ! av]age ( all ! measures ( di/ance ( ! />s4 ,?is ellipse is !n ! app>5t ellipse describ$ by ! />1 & ! =m & position ( ! true ellipse c be con/ruct$ f x f ! consid]ation ( ! position ( ! l>g] /> 7:i* mu/ really be ! focus71 ) ref]5ce to ! focus ( ! app>5t ellipse2 = if an ellipse be se5 or project$ on a plane o!r ?an its own1 its real foci w no long] co9cide ) ! foci ( ! project$ ellipse4 ,! me?ods adopt$ 9 practice1 = :i* we mu/ ref] ! read] to o!r works on ! subject1 are1 h[ev]1 mu* m labori\s & l5g?y ?an ! above outl9e1 :i* is int5d$ m]ely to %[ ! possibility1 or ! fa9t outl9e ( a me?od ( con/ruct+ ! real ellipse4 ,:5 ! real ellipse or orbit is kn[n1 x is !n ( c\rse possible to pr$ict ! relative positions ( ! two compon5ts4 ,let u consid] 9 "s little detail ! actual "w ( measur+ a d\ble />4 ,a useful =m = ent]+ obs]vations ^u1 z tak51 is ! foll[+1 :i* is copi$ f "o actually us$4 ,,temple ,,obs]vatory4 ,no4 #a4 ,april #ab1 #ahgebgf4 ,,d\ble ,,/>s4 ,,/ruve #acch4 ,r4,a4--#i;h4 #acm4 #bhs4 ,,decl4 #ch #da #bj4 ,magnitudes--#fg1 #gb4 ,,position4 ,z]o1 #ajih4 ,illu/ration ,,di/ance4 ,direct4 ,indirect4 ,diff4 #ag #ig #aj #af #ig #ie -------------- #ige mean4 ,read+s4 #agja #agj #afie #afih ---------- #d7 #fgid ---------- #afih #ajih #ijj ---------- #aih #afih ,position #aej #aih ---------- ,di/ance #ahbh4 #aej 99 99 99 99 99 ,no4 #b4 ,feb4 #e?1 #ahgeji4 ,,d\ble ,,/>s4 ,,/ruve #egg4 ,r4 ,a4--#d;h4 #cdm4 #is4 ,,decl4 #cg #ag ,magnitudes--#g1 #h4 ,,position4 ,z]o1 #hhi4 ,illu/ration ,,di/ance4 ,direct4 ,indirect4 ,diff4 #abe #iie #fe #abf #iib #fg -------------- #ff mean4 ,read+s4 #gie #hae #hab ---------- #c7 #bdbb ---------- #haa mean4 #hhi #ijj ---------- -#aa #haa -#aa ---------- #hbb ,position #bfbb4 #ahjj ---------- ,di/ance #abcg4 #bfbb ,! /> hav+ be5 f\nd1 ! date & decimal ( ! ye> are ent]$ at ! top1 & a position tak5 by br++ ! ?ick wires p>allel to ! />s4 ,a di/ance--say direct--is !n tak51 & ! degrees ( position #agja1 & divisions ( ! micromet] screw sev5te51 read (f ) ! assi/ance ( a lamp & ent]$ 9 _! prop] columns4 ,! micromet] is !n dis>rang$ & a new measure ( position & an indirect di/ance tak51 & s on4 ,at ! end ( ! read+s1 or at any conv5i5t "t1 ! z]o = position is f\nd by turn+ ! micromet] until ! wires are approximately horizontal1 & !n all[+ a /> to trav]se ! field by its own motion1 or r t ( ! e>?1 & br++ ! ?ick wires p>allel to its direction ( motion2 ?is may be m conv5i5tly done by means ( ! sl[-motion h&le ( ! telescope 9 ,r4 ,a41 :i* gives "o ! p[] ( app>5tly mak+ ! /> trav]se backw>ds & =w>ds 9 ! field4 ,! position ( ! wires is alt]$ until ! /> runs along "o ( !m4 ,! position is !n read (f & ent]$ z ! z]o4 ,9 describ+ ! adju/m5ts ( ! position circle we made ! v]ni] read #j :5 ! /> runs along ! wire1 = t is practically ! only datum l9e atta9able2 s9ce1 h[ev]1 ! angles are reckon$ f ! nor?1 x is conv5i5t to set ! circle to read #ij :5 ! /> runs along ! wire1 s t x reads #j :5 ! wires are nor? & s\?4 ,n[ z positions are measur$ f nor? #j 9 a direction contr>y to t ( ! h&s ( a wat*1 & an a/ronomical telescope inv]ts1 we repeat ! bottom ( ! field is #j1 ! "r #ij1 & s on2 n[ ! read+ j tak5 = z]o is ! read+ :5 ! wires are ,e4 & ,w41 s t we mu/ d$uct #ij f ?is read+1 giv+ #aih z ! read+ ( ! circle :5 ! wires 7 nor? & s\?1 or 9 ! position ( ! real z]o ( ! field4 ,( c\rse !oretically ! micromet] ought to read #j :5 ! wires are nor? & s\?1 b 9 screw+ on ! in/rum5t f night to night x nev] comes exactly to ! same place1 s t x is f\nd easi] to make ! requisite correction = index error r ?an alt] ! eye end ( ! telescope to adju/m5t e night4 ,! read+s ( position mu/ !re=e be correct$ by ! numb] ( degrees not$ :5 ! wires are at ! real z]o1 :i* 9 ! case 9 po9t is #aih1 :i* may be call$ ! index error4 ,x is also obvi\s t ! micromet] may be turn$ ?r\gh #ahj & /ill h its wires p>allel to any p>ticul> l9e4 ,! position ( ! />s also dep5ds ^u ! /> fix$ on = ! c5tre r\nd :i* our degrees are c\nt$2 = 9 ! case ( two />s j "o ov] ! o!r 9 ! field ( view1 if we take ! upp] "o z c5tre1 !n ! position ( ! sy/em is #j1 b if ! l[] "o1 !n x is #ahj2 9 ! case ( two equal or ne>ly equal />s1 x is difficult to say :i* %all be consid]$ z c5tre1 & s ! position giv5 by two diff]5t p]sons might diff] by #ahj4 ,!re are also g5]ally two v]ni]s on ! position circle1 "o on ea* side1 & ^! ( c\rse give read+s #ahj diff]5t f ea* o!r1 s t #ahj has (t5 to be add$ or subtract$ f ! calculat$ result to give ! true position4 ,all t is really measur$ by ! position micromet] is ! relative position ( ! l9e jo9+ ! />s ) ! ,n4 & ,s4 l9e4 ,9 ord]1 !re=e1 to f9d1 :e!r #ahj %\ld be add$ or n1 a circle is pr9t$ on ! =m1 ) two b>s across = a guide to ! eye1 & ! />s z se5 are r\ghly dott$ d[n 9 _! app>5t position--9 ! case 9 po9t ab\t #aej4 ,our read+s be+ n[ made1 we fir/ take a mean ( ^? ( position1 :i* is #afih1 ne>ly1 & ! z]o is #ajih2 d$uct #ij f ?is to give ! read+ ( ! ,n4 & ,s4 l9e #aih1 !n we d$uct ?is f ! mean ( position1 #afih1 giv+ u #aej z ! position angle ( ! />s4 ,x (t5 happ5s t ! obs]v$ z]o is less ?an #ij1 & !n we mu/ add #cfj to x be=e subtract+ ! #ij1 or :at is p]haps be/1 subtract ! obs]v$ z]o f #ij1 & treat ! result z a m9us quantity1 & !re=e add x to ! mean ( position read+s in/ead ( subtract+ z usual4 ,! obs]vations ( ! second /> give a case 9 po9t3 ! z]o is #hhi1 & subtract+ ?is f #ij1 we get #aa2 we put ?is d[n z -#aa to di/+ui% x f a result :5 #ij is subtract$ f ! z]o2 x is !n add$ to ! mean ( position read+s #haa1 giv+ #hbb1 b on ref]5ce to ! dots %[+ ! approximate position ( ! />s1 x is se5 t #ahj mu/ be add$ to _! result1 giv+ #bfbb z ! position ( ! />s4 ,n[ z to di/ance1 take ! case ( ! second />4 ,subtract ! fir/ indirect read+ f #ajj1 giv+ #je1 & add ?is to ! direct read+1 #abe1 mak+ #acj1 :i* is ! diff]5ce betwe5 ! two read+s tak5 on ei!r side ( ! fix$ wire2 ! half ( ?is1 #fe1 is plac$ 9 ! next column1 & ! same process is repeat$ ) ! next two read+s3 a mean ( ^! is !n tak51 :i* is #ff = ! numb] ( divisions correspond+ to ! di/ance ( ! />s4 ,9 ! micromet] us$ 9 ?is case1 #ec divisions g to #a1 s t #ff is divid$ by #ec1 giv+ #abcg z ! di/ance4 ,a table %[+ ! value 9 seconds ( ! divisions f "o to tw5ty or m1 saves mu* "t 9 mak+ di/ance calculations2 ! foll[+ is ! comm5cem5t ( a table ( ?is k9d :]e #ec divisions correspond to #a4 ,divi- #j #a #b #c #d #e #f #g #h #i sions ( micro- met]4 #j #jjjjjahjcgjefjgejicaabacaaejafh #a #jahgbjebbdbdcbfbbhjbiicahccgcef #b #jcgecicdabdcadejdfhdhgejfebeedc ,9 ! fir/ column are ! divisions1 & 9 ! top horizontal l9e ! p>ts ( a division1 & ! numb] indicat$ by any two figures consult$ is ! correspond+ numb] ( seconds ( arc4 ,9 ! case ( a half diff]5ce ( #bc we look along ! l9e comm5c+ at #b until we get "u #c1 :5 we get #jdca z ! seconds correspond+ to #bc divisions4 ,x is necess>y to adju/ ! quantity ( light f ! lamp 9 ! field1 s t ! wires are suffici5tly visible :ile ! />s are n put out by too mu* illum9ation2 = ! majority ( />s a r$ glass be=e ! lamp is be/4 ,?is gives a field ( view :i* r5d]s ! wires visible )\t mask+ ! />s1 b a gre5 or blue light is sometimes v s]viceable4 ,a %ad$ lamp %\ld be us$ = read+ ! circles on ! micromet]1 s z n to injure ! s5sitiv5ess ( ! eye by diffus$ light 9 ! obs]vatory4 ,a lamp fix$ to ! telescope1 hav+ its light reflect$ on ! circles1 b o!rwise cov]$ up1 is a great advantage ov] ! h&-lamp4 ,9 v fa9t />s1 :i* are mask$ by a light 9 ! field suffici5t to see ! wires1 ! wires c be illum9at$ 9 ! same mann] z 9 ! transit1 b !re is ?is disadvantage--! f9e wires appe> mu* ?ick5$ by irradiation1 s t di/ances1 especially ( close />s1 become difficult to take4 99 99 99 99 99 ,we come n[ to ! diff]5tial obs]vations made ) ! equatorial4 ,let u expla9 :at is meant4 ,suppose x is desir$ to det]m9e ) ! utmo/ accuracy ! position ( a new comet 9 ! sky4 ,if we take an ord9>y equatorial1 or an extraord9>y equatorial 7except+ probably ! f9e equatorial at ,gre5wi*71 & try to det]m9e its place by means ( ! circles1 its di/ance f ! m]idian giv+ its "r asc5sion & its di/ance f ! equator giv+ its decl9ation1 we %all be sev]al seconds out1 on acc\nt ( want ( rigidity ( its p>ts2 b if we d x by means ( su* an in/rum5t z ! transit circle at ,gre5wi*1 we wait till ! comet is exactly on ! m]idian1 & det]m9e its position 9 ! way already describ$4 ,z a matt] ( fact1 h[ev]1 ! transit circle is n ! in/rum5t usually us$ = ?is purpose1 b ! equatorial4 ,we d n h[ev] j br+ ! comet or o!r object into ! middle ( ! field & !n read (f ! circles1 b we diff]5tiate f ! positions ( kn[n />s2 s t all t has to be done 9 ord] to get z p]fect a place = ! comet z c be got = x by wait+ till x comes to ! m]idian--:i* p]haps x w d 9 ! day-"t1 :5 x w n be visible at all--is to det]m9e its di/ance 9 "r asc5sion & decl9ation f a kn[n />1 by means ( a micromet]4 ,( c\rse "o w *oose ! brighte/ "p ( ! comet & a well-kn[n />1 ! place ( :i* has be5 det]m9$ ei!r by its appe>ance 9 "o ( ! catalogues1 or by special transit obs]vations made 9 t behalf4 ,we !n by ! position micromet] det]m9e its angle ( position & di/ance f ! kn[n /> at a "t c>efully not$1 or we measure ! diff]5ce 9 "r asc5sion & ! diff]5ce 9 decl9ation4 ,illu/ration3 ,,fig4 #afc4--,r+ ,micromet]4 ,cont95tal a/ronom]s h ano!r way ( do+ ?is :i* we w attempt to expla94 ,suppose we wi% to f9d ! diff]5ce 9 decl9ation ( a /> & ,jupit]1 we place ! r+1 ,a ,d1 ,fig4 #afc1 9 ! eyepiece ( ! telescope & wat* ! passage ( ,jupit] & ! /> ov] ?is r+ micromet]4 ,x w be cle> t1 z ! motion ( ! heav5s is p]fectly uni=m1 x w take v mu* less "t = ! /> to travel ov] ! r+ f ,b to ,c ?an x w = ,jupit] to travel ov] ! r+ f b to c1 because ! /> is fur!r f ! c5tre2 & by tak+ ! "t ( ext]nal & int]nal contact at ea* side ( ! r+1 ! details ( :i* we ne$ n ent] ^u "h1 ! ,cont95tal a/ronom]s are 9 ! habit ( mak+ diff]5tial obs]vations ( ! m9ute/ accuracy by means ( ?is r+ micromet]1 :il/ we pref] to make !m by ! wire micromet]4 ,,book ,,vi4 ,,a/ronomical ,,physics4 ,,*apt] ,,xxv4 ,,! ,,g5]al ,,field ,,( ,,physical ,,inquiry4 ,we h n[ gone d[n ! /ream ( "t1 f ,hipp>*us to our own days4 ,we f9d n[ enorm\s telescopes :i* enable u to see & exam9e cele/ial bodies ly+ at di/ances s great t ! m5tion ( !m conveys little to ! m9d4 ,we f9d also p]fect sy/ems ( det]m9+ _! places4 ,! foll[+ *apt]s w %[1 h[ev]1 t mod]n a/ronomy has n be5 cont5t$ ) annex+ ^? two bran*es ( physics :i* h enabl$ u to make ! object-glass & ! clock1 & ano!r /ill :i* enables u to make t clock record its own "t ) accuracy4 ,^! applications ( ,sci5ce h be5 effect$ = ! purpose ei!r ( det]m9+ ) accuracy ! motion & positions ( ! heav5ly bodies or ( enabl+ u to inve/igate _! appe>ances "u ! be/ possible conditions4 ,! o!r class ( obs]vations to :i* we h n[ to ref]1 h to d ) ! quantity & ! quality ( ! vibrations :i* ^! bodies imp>t to ! e!r1 by virtue ( :i* vibrations !y are visible to u4 ,we began by measurem5t ( angles1 we end ) a wide range ( in/rum5ts illu/rat+ ! application ( almo/ e bran* ( physical z well z ( ma!matical sci5ce4 ,9 mod]n obs]vatories applications ( ! laws ( ,optics1 ,heat1 ,*emi/ry & ,electricity1 are met ) at e turn4 ,ea* introduction ( a new in/rum5t1 or ( a new me?od ( attack1 has by no means aboli%$ ! preexi/+ "o2 accretion r ?an sub/itution has be5 ! rule4 ,on ! "o h&1 measurem5t ( angles goes on n[ m dilig5tly ?an x did 9 ! days ( ,hipp>*us1 b ! angles are bett] measur$1 because ! telescope has be5 add$ to ! divid$ arc4 ,"t is z necess>y n[ z x 0 9 ! days ( ! clepsydra1 b n[ we make a p5dulum divide its fl[ into equal int]vals & electricity record x4 ,on ! o!r h&1 ! col\rs ( ! />s are not$ z c>efully n[ z !y 7 be=e ! spectroscope 0 appli$ to ! telescope1 b n[ we /udy ! spectrum & inquire into ! cause ( ! col\r4 ,! gr[? ( ! p[] ( ! telescope z an in/rum5t = eye obs]vations has gone on1 al?\gh n[ almo/ all ph5om5a c be photographically record$4 ,! uses to :i* all a/ronomical in/rum5ts may be put may be r\ghly sep>at$ into two l>ge gr\ps3-- ,i4 ,!y may be us$ to /udy ! positions1 motions1 & sizes ( ! v>i\s masses ( matt] 9 ! univ]se4 ,"h we are /udy+ cele/ial me*anics or me*anical a/ronomy1 & ) ^! we h already dealt4 ,,ii4 ,!y maybe us$ to /udy ! motions ( ! molecules ( :i* ^! v>i\s masses are built up1 to le>n _! quality1 arrangem5t1 & motions4 ,"h we are /udy+ cele/ial physics1 or physical a/ronomy4 ,x is ) ?is latt] bran* t we n[ h to d4 ,fir/ we h to deal ) ! quantity & int5sity ( ! e!real vibrations set up by ! con/itu5t molecules ( ^! di/ant bodies4 ,we wi% to comp>e ! quantity ( light giv5 out by "o /> ) t giv5 out by ano!r4 ,we wi%1 say1 to comp>e ! light ( ,m>s ) ! light ( ,saturn2 we are l&$ 9 ! sci5ce ( photometry1 :i* = t]re/rial light-s\rces has be5 s admirably inve/igat$ by ,rum=d1 ,b\gu]1 & o!rs4 ,"h we deal ) t radiation f ea* body :i* affects ! eye--b by no means ! total radiation4 ,?is is a po9t ( v consid]able importance4 ,mod]n sci5ce recognises t 9 ! radiation f all bodies :i* give u :ite light !re is s great a diff]5ce ( l5g? ( wave 9 ! vibrations t diff]5t effects are produc$ on diff]5t bodies4 ,?us :ite light is a comp\nd ?+ conta9+ long waves ) :i* heat ph5om5a are associat$1 waves ( m$ium l5g? to :i* alone ! eye is tun$1 & %ort waves :i* h a decid$ action on "s metallic salts :i* are unaffect$ by ! o!rs4 ,to ?us exam9e ! con/itu5ts ( a beam ( light a lant]n1 ) a lime-light or electric light1 may be us$ = ?r[+ a con/ant beam2 we may !n produce an image ( ! cyl9d]s ( lime or ! c>bon po9ts 9 ! lant]n on a piece ( pap] or a scre51 & our eyes w tell u t ?is is an in/ance ( h[ ! radiations f any inc&esc5t sub/ance are compet5t to give u light4 ,we receive all ! rays to :i* our eyes are tun$ & we see a :ite image on ! scre54 ,we %all see also t ! light is m int5se ?an t ( a c&le1 9 o!r words t ! radiation f ! light-s\rces we h nam$ is v great4 ,illu/ration3 ,,fig4 #afd4--,!rmopile & ,galvanomet]4 ,n[ let u ins]t 9 front ( ! lant]n a piece ( deep r$ glass1 t is1 glass :i* all[s only ! r$ con/itu5ts ( ! :ite light to pass4 ,n[ if a !rmo-electric pile1 ,fig4 #afd1 be introduc$ into ! beam we %all see t ! ne$le ( ! galvanomet] w alt] its position4 ,n[1 :y does ! ne$le turn8 ,?is is n ! place = giv+ all ! details ( ?is in/rum5t1 b x is suffici5t to say 7#a7 t ! ne$le moves :5ev] a curr5t ( electricity fl[s ?r\gh ! coil ( wire surr\nd+ ! ne$les1 & 7#b7 t ! pile consi/s ( a numb] ( b>s ( antimony & bismu? jo9$ at ! alt]nate ends1 & :5ev] "o end ( ! pile is heat$ m ?an ! o!r1 a curr5t ( electricity is caus$ to fl[4 ,su* is ! delicacy ( ! in/rum5t1 t ! heat radiat$ f ! h&1 held "s y>ds away f x1 is suffici5t to set ! ne$le sw++ viol5tly2 ?is !n acts z a mo/ delicate !rmomet]4 ,9 ?is case x %[s t heat effects are produc$ by ! r$ con/itu5ts ( ! light f ! lamp4 ,n[ replace ! !rmopile by a glass plate coat$ ) a salt ( silv] 9 ! ord9>y way adopt$ by photograph]s4 ,no effect w be produc$4 ,replace ! r$ glass by a blue "o4 ,if ! light is n[ all[$ to fall on ! photographic plate1 its effect is to decompose1 or alt] ! arrangem5t (1 ! atoms ( silv]1 s t on apply+ ! develop+ solution1 ! silv] comp\nd is r$uc$ to its metallic /ate on ! places :]e ! light has act$2 & ?us1 if ! image ( ! light-s\rce has be5 focuss$ on ! plate1 a photograph ( x is ! result4 ,if ! !rmopile is br\ght into ! beam x w be n[ z ins5sitive to ! blue light z ! photographic plate 0 to ! r$ light 9 ! =m] case4 ,we h !re=e ?ree k9ds ( effects produc$1 viz41 light1 heat1 & *emical or act9ic action1 & :5 light is pass$ ?r\gh a prism1 ^! ?ree diff]5t radiations1 or en]gies1 are mo/ develop$ 9 ?ree diff]5t portions ( ! spectrum4 ,if inde$ a small spectrum be ?r[n on ! scre5 & ! diff]5t col\rs are exam9$ ) ! !rmopile1 x w be f\nd t z long z we all[ x to rema9 at ! blue end ( ! spectrum1 !re w be no effect on ! galvanomet]1 b if in/ead ( hold+ x at ! blue end we br+ x t[>ds ! r$1 ! galvanomet] ne$le is deflect$ f its normal position1 to t x _h :5 ! r$ rays fell on x1 %[+ t x is beyond all d\bt ! r$ rays & n ! blue to :i* x is s5sitive4 ,:]e !n 9 ! spectrum are ! rays :i* affect ! photographic plate8 ,we c at once settle ?is po9t4 ,if "o be plac$ 9 ! spectrum = a %ort "t1 & !n develop$1 x w be f\nd to be affect$ only 9 ! "p on :i* ! blue rays h fall54 ,inde$ to demon/rate ?is no lamp is necess>y4 ,if = half-an-h\r or s two pieces ( s5sitive pap] are plac$ 9 ! daylight1 "o cov]$ ) r$ glass1 & ! o!r ) violet1 s t ! sunlight is made to travel1 9 ! "o case1 ?r\gh r$ glass1 & 9 ! o!r ?r\gh violet1 x w be f\nd t ! violet light w act1 & produce a d>k5+ ( ! pap]1 :ile ! r$ glass w pres]ve ! pap] bel[ x f all action4 ,?is is a pro( t ! blue end ( ! spectrum has ano!r k9d ( en]gy1 a *emical en]gy1 by means ( :i* c]ta9 *emicals are decompos$1 ?is is ! basis ( photography4 ,^! diff]5t qualities ( light h be5 utiliz$ by ! a/ronom]4 ,he atta*es a !rmopile to 8 telescope & e/abli%es a cele/ial !rmometry4 ,! radiations repay a /ill m m9ute exam9ation1 & aid$ by ! spectroscope1 he is able to /udy ) ! utmo/ c]titude ! *emical condition ( ! heav5ly ho/1 :ile ! pol>iscope enables him to acquire in=mation 9 /ill ano!r direction4 ,nor does he end "h4 ,he replaces 8 eye by a s5sitive plate1 :i* n only enables him to inquire into ! ri*ness ( ! v>i\s bodies 9 ^! %ort waves1 b actually to obta9 images ( !m ( mo/ m>vell\s beauty & exactness4 ,^! v>i\s l9es ( "w we h to consid] 9 ! rema9+ *apt]s4 ,,*apt] ,,xxvi4 ,,det]m9ation ,,( ,,! ,,light ,,& ,,heat ,,( ,,! ,,/>s4 ,"o bran* ( obs]vatory "w is t ( det]m9+ ! relative magnitude ( />s1 ! ^w magnitude be+ ( c\rse us$ 9 a conv5tional s5se = brightness4 ,!re are1 moreov]1 />s :i* v>y 9 brightness or magnitude f "t to "t2 ^! are call$ v>iable />s1 & ! inve/igation ( ! am\nt & p]iod ( v>iation op5s up ano!r use = ! equatorial1 & an in/rum5t is requir$ = f9d+ ! value ( ! am\nt ( light giv5 by a /> at any in/ant2 9 fact1 a photomet] is necess>y4 ,! me?ods ( det]m9+ ! brilliancy ( />s are s simil> 9 pr9ciple to ^? employ$ = ord9>y light-s\rces t ! ord9>y me?ods ( photometry may be ref]r$ to 9 ! fir/ in/ance4 ,we may det]m9e ! relative brilliancy ( two or m lights1 or we may employ a /&>d light & ref] all o!r lights to t4 ,rum=d's photomet]1 ,fig4 #afe1 is bas$ ^u ! fact t if ! int5sity ( ! %ad[s ( an opaque body be equal1 ! lights ?r[+ ! %ad[s are equal4 ,h5ce ! lights are mov$ t[>ds or f a scre5 until ! %ad[s are equal2 !n if ! di/ances f ! scre5 are unequal ! lights are unequal1 & ! int5sities v>y 9 ! inv]se ratio ( ! squ>es ( ! di/ances4 ,?is me?od is practically c>ri$ out 9 ! telescope by r$uc+ ! ap]ture till ! />s become invisible1 & not+ ! ap]tures at :i* ea* vani%es 9 turn4 ,! mo/ simple me?od ( do+ ?is is t us$ by ,dawes1 :i* is simply an adju/able diaphragm limit+ ! available area ( ! object-glass2 we c ?us view a />1 & gradually r$uce ! ap]ture until ! /> is j visible1 or until x j disappe>s1 ! latt] limit be+ p]haps ! mo/ accurate & mo/ usually us$2 ! ap]ture is read (f on ! scale atta*$4 ,illu/ration3 ,,fig4 #afe4--,rum=d's ,photomet]4 ,! photomet] ( ,mr4 ,knobel is1 h[ev]1 a v h&y "o2 x consi/s ( a plate ( metal hav+ a l>ge ,v-%ap$ piece ) an angle ( #fj cut out ( x2 ano!r plate slides ov] ! fir/ 9 su* a mann] t its edge =ms a base = ! ,v-%ap$ op5+1 ?us =m+ an equilat]al triangul> hole1 :i* is adju/able at pleasure by mov+ ! second plate4 ,! edge ( ! moveable plate is divid$ s t ! size ( ! base ( op5+ is kn[n at once1 & its area easily calculat$4 ,! annex$ woodcut w give an idea ( ! second me?od :i* is possible4 ,illu/ration3 ,,fig4 #aff4--;,b\gu]'s ,photomet]4 ,let ! gas flame be suppos$ to repres5t a con/ant light at con/ant di/ance2 !n ! int5sity ( ! light to be exp]im5t$ ^u 7repres5t$ by ! c&le7 is det]m9$ by mov+ x t[>ds or f ! mirror till ! illum9ation ( bo? ! halves ( ! porcela9 scre5 is equal4 ,! in/rum5t by :i* ?is k9d ( inve/igation is c>ri$ out by a/ronom]s has be5 introduc$ by ,zlln]1 & is call$ ! ,a/rophotomet]4 ,9 ?is ! /> is comp>$ ) a small image ( a portion ( ! flame ( a lamp atta*$ to ! telescope4 ,x be+ f\nd t1 ?\gh ! total light emitt$ by ! flame v>ies ) its size1 ! int5sity ( ! brighte/ "p does n1 appreciably4 ,two artificial />s are =m$ by means ( a p9-hole1 a d\ble concave l5s1 & a d\ble convex l5s4 ,^! appe> 9 ! field by reflexion f ! front & back faces ( a plate ( glass alongside ! image ( ! real />1 ! light ( :i* passes ?r\gh ! plate4 ,! int5sity ( ! artificial /> is v>i$1 fir/ by *ang+ ! p9-hole1 & f9ally by two ,nicol's prisms1 ! col\r be+ fir/ mat*$ ) t ( ! /> by means ( a ?ird ,nicol1 ) a qu>tz plate betwe5 x & ! fir/ ( ! o!r two ,nicols4 ,! in/rum5t is provid$ ) object-glasses ( v>i\s sizes 7& diaphragms7 up to #b in*es1 &1 if fa9t] />s are to be exam9$1 x c be screw$ on to ! eyepiece ( an equatorial in/rum5t4 ,a second arrangem5t1 l ! fir/1 b )\t ! qu>tz plate arrangem5t1 =ms an artificial /> f moonlight1 = comp>ison ( ! light ( t body ) ! artificial />4 ,s f> !re is no difficulty1 b ?is measure mu/ be int]pret$ into magnitude1 & we mu/ "k :at magnitude a /> is :i* j disappe>s ) a giv5 ap]ture (1 say1 "o in*1 & secondly1 ! ratio ( light betwe5 ! magnitudes1 or h[ mu* less light is receiv$ f a /> ( ! next magnitude 9 proportion to ! giv5 "o4 ,if n[ we 7 able to />t a new scale ( magnitude1 x w\ld be easy to say t a /> j visible ) an in* ap]ture on a f9e night %all be call$ a n9? magnitude />1 & fix a c]ta9 numb] ( n9? magnitude />s = ref]5ce1 s t ! errors induc$ by hazy nights & v>iable eyes might be elim9at$4 ,an obs]v] on a bad night c\ld limit 8 ap]ture on a kn[n />1 :5 he might f9d t d\ble ! area giv5 by an ap]ture ( "o in* 0 requir$ z a limit = "o ( ! />s ( ref]5ce1 & 9 t case he w\ld "k t half ! usual am\nt ( light f e /> 0 /opp$ by atmosph]ic causes1 & he w\ld make ! requisite corrections ?r\gh\t 8 obs]vations4 ,we might also say t a /> ( a :ole magnitude1 great] or less ?an ano!r1 %all give u half or d\ble ! am\nt ( light--9 fact1 t ?is %all be ! ratio betwe5 magnitudes4 ,we are n1 h[ev]1 able to make ^! rules1 = an arbitr>y scale has be5 adopt$ = ye>s1 & we c only r$uce ?is scale to a law1 9 su* a mann] z n to int]f]e greatly ) ! g5]ally receiv$ magnitudes4 ,among/ ! bright] />s !re is a close agreem5t 9 ! e/imate ( magnitude by diff]5t obs]v]s1 b among/ ! high] magnitudes a diff]5ce appe>s4 ,sir ,j4 ,h]s*el & ,admiral ,smy?1 = in/ance1 g into mu* high] numb]s ( magnitudes ?an ,/ruve2 ! limit ( ,admiral ,smy?'s vision ) 8 #f-;in* telescope 0 a #af? magnitude1 :ile ! limit ( ,/ruve's vision ) a #i-;in* telescope he calls a #ab? magnitude2 ! e/imates ( ! latt] obs]v] are1 h[ev]1 ga9+ great] adoption4 ,9 ord] to r$uce ! relative magnitude to a law1 ,mr4 ,pogson#ba took />s diff]+ l>gely 9 magnitude1 & comp>$ ! am\nt ( light f ea*1 & s r$uc$ ! ratio betwe5 ! magnitudes giv5 by ,knott & all ! be/ obs]v]s4 ,f ?is he f\nd t a mean ( #bd repres5t$ ! ratio1 & = reasons giv5 he adopt$ ! quantity #beab z a conv5i5t ratio2 z he /ates1 8! reciprocal ( log4 ,r 79 8 pap] ,r ! ratio #beab71 a con/ant cont9ually occurr+ 9 photometric =mul1 is 9 ?is case exactly #e40 ,s f> ! ratio is e/abli%$4 ,! next ?+ is ! basis f :i* to comm5ce reckon+2 ?is ,mr4 ,pogson fix$ by ref]5ce to ,argel&]'s catalogu$ />s1 e/imat$ by him at ab\t ! #i? magnitude1 & ) ^!1 comp>ison is made ) ! /> ^: light is measur$1 & ! above con/ant ( ratio appli$1 :i* at once gives ! magnitude ( ! measur$ />4 ,to d ?is1 9 ,mr4 ,pogson's words3 8,if !n any obs]v] w det]m9e = himself ! smalle/ ( ,argel&]'s magnitudes1 j visible by fits1 on a f9e moonless night1 ) an ap]ture ( "o in*1 & call ?is quantity ,l1 or ! limit ( vision = "o in*1 ! limit l1 = any o!r ap]ture1 w be giv5 by ! simple =mula1 l ,l #e log4 ap]ture40 ,! value ( ,l f\nd$ by ,mr4 ,pogson is #ib2 t is1 a /> ( #ib magnitude1 accord+ to ,argel&]1 is limit$ by #a-;in* ap]ture1 ) ,mr4 ,pogson's eye4 ,on diff]5t nights & ) diff]5t eyes1 ?is numb]1 or ! magnitude limit$1 mu/ v>y1 & x v>ies f exactly ! same causes t produce v>iation 9 ! light ( ! />s to be measur$1 s t we are indep5d5t ( transp>5cy ( ! air1 at lea/ )9 consid]able limits4 ,hav+ f\nd ! value ( ,l = any night1 we turn ! telescope on a /> to be measur$1 !n alt] ! ap]ture if we employ ! fir/ me?od1 until ! limit is f\nd1 & ins]t ! value 9 ! equation1 ! value ( l1 or ! />'s magnitude1 !n at once appe>s4 ,by ?is means a numb] ( well-kn[n />s ( all magnitudes may be settl$ = future ref]5ce & comp>ison ) v>iable />s4 ,! comp>ison />s !n be+ fix$ ^u1 & _! magnitude accurately kn[n1 !re is n mu* difficulty 9 comp>+ any v>iable /> ) "o or m ( ^? ( approximately ! same magnitude4 ,by ?is means a numb] ( indep5d5t e/imates ( ! magnitude ( ! v>iable is obta9$ free f errors f ! di/urb+ effects ( mi/ or moonlight1 :i* affects bo? ! />s ( comp>ison & v>iable alike4 ,if we call ! />s ( comp>ison ,a ,b ,c ,d1 we ent] ! comp>isons some:at z foll[s2 7v>iable7 #b ,a1 #d ,b1 #a ,c1 #g ,d1 ! numb] %[+ h[ _m t5?s ( a magnitude ! v>iable is m or less bright ?an ea* comp>ison />1 & ! magnitude ( ! latt] be+ kn[n1 we get sev]al values ( ! magnitude ( ! v>iable1 a mean ( :i* is tak5 = ! night4 ,9 ord] to %[ cle>ly to ! eye ! v>iations ( a />1 & to compute ! p]iods ( maximum & m9imum1 a graphical me?od is adopt$3 a %eet ( cross-rul$ pap] is prep>$1 on :i* ! dates ( obs]vation are repres5t$ by ! absciss1 & ! correspond+ obs]v$ magnitudes by ! ord9ates4 ,dots are !n made repres5t+ ! sev]al obs]vations1 & a free-h& curve drawn among/ ! dots1 :i* at once gives ! probable magnitude at any epo* 9 ! p]iod ( obs]vation1 ! *ange ( ! curve f a b5d upw>ds to d[nw>ds1 or vice v]s1 indicat+ a maximum or m9imum ( magnitude4 ,s mu* !n = ! me?od ( det]m9+ ! int5sity ( ! visible radiation4 ,! next po9t to consid] is ! int5sity ( ! !rmal radiations--we pass f photometry to !rmometry4 ,! !rmopile w 9 ! future be an a/ronomical in/rum5t ( great importance4 ,we ne$ n g into its uses 9 o!r bran*es ( physics1 we %all "h limit ourselves to ! a/ronomical results :i* h be5 already obta9$4 ,"l ,rosse us$ a pile ( ?is k9d1 made ( alt]nate b>s ( bismu? & antimony4 ,he attack$ ! moon1 & by obs]v+ x f new to full1 & f full to new1 he got a di/9ct v>iation ( ! am\nt ( heat1 accord+ z ! moon 0 ne>e/ to ! epo* ( full moon1 or fur!r f t epo*4 ,z ! moon 0 gett+ full1 he f\nd ! ne$le mov$1 %[+ heat1 &1 aft] ! full1 x w5t d[n aga9 & f\nd its z]o aga9 at new4 ,by diff]5tial obs]vations ,"l ,rosse %[$ t ?is little in/rum5t1 at ! focus ( 8 trem5d\s reflector1 0 able to give "s e/imate ( ! heat ( ! moon1 :i* may be #ejj degrees ,fahr4 at ! surface4 ,x may be said t ! moon is v ne> u1 & we ought to get a consid]able am\nt ( heat f x2 b ! am\nt is sc>cely p]ceptible )\t delicate in/rum5ts4 ,/ill ! in/rum5t is s delicate1 t ! heat ( ! />s has be5 e/imat$4 ,a pile ( v simil> con/ruction to ! "o j m5tion$ has be5 atta*$ by ,mr4 ,/one to ! l>ge equatorial at ,gre5wi*4 ,! in/rum5t consi/s ( two small piles ab\t "o-t5? ( an in* across ! face2 ! wires f ea* are w\nd 9 contr>y directions r\nd a galvanomet]1 s t :5 equal curr5ts ( electricity are pass+ !y c\nt]act ea* o!r1 & ! ne$le rema9s /ation>y4 ,x only moves :5 ! two curr5ts are unequal2 we h !n a diff]5tial galvanomet]1 %[+ ! diff]5ce ( temp]ature ( ! faces ( ! two piles2 ! image ( a /> is all[$ to fall half-way betwe5 ! two piles--!n on "o pile & !n on ano!r2 !n matt]s are rev]s$1 & a mean ( ! galvanomet] read+s tak51 beg9n+ ) z]o :5 ! image ( a /> 0 exactly betwe5 ! two piles4 ,! result 0 ?is1 t ! heat receiv$ f ,arcturus1 :5 at an altitude ( #be1 0 f\nd to be j equal to t receiv$ f a cube ( boil+ wat]1 ?ree in*es across ea* side1 at ! di/ance ( #djj y>ds4 ,arcturus is n ! only /> :i* has be5 obs]v$ 9 ?is way2 9 ano!r />1 ,vega1 :i* is bright] ?an ,arcturus1 x has be5 demon/rat$ t ! am\nt ( heat :i* x gives out1 :5 at an altitude ( #fj1 is equal to t f ! same cube at #fjj y>ds1 s t ,mr4 ,/one %[s beyond all "q1 t ,arcturus gives u m heat ?an ,vega4 ,?is op5s a new field1 = if we get heat effects diff]5t f ! effects on ! eye1 ! />s ought to be catalogu$ ) ref]5ce to _! !rmal relations z well z _! visual brightness4 ,ano!r valuable application ( ?is me?od is due to ,pr(essor ,h5ry1 ( ,wa%+ton4 ,pr(essor ,h5ry imag9$ t1 by means ( a !rmo-electric pile plac$ at ! eyepiece ( ! telescope1 s t a sun-spot1 or a "p ( ! ord9>y surface1 c\ld be br\ght on ! face ( ! pile1 he c\ld tell :e!r !re 0 a great]1 or less radiation ( heat f a spot1 ?an f any o!r "p2 & he 0 able ) ! !rmopile to %[ t !re 0 a small] radiation ( heat f ! spots ?an f ! o!r p>ts ( ! sun's surface4 ----- ,footnote #ba3 ,mon?ly ,notices1 ,r4,a4,s41 vol4 xvii41 p4 #ag4 ,,*apt] ,,xxvii4 ,,! ,,*emi/ry ,,( ,,! ,,/>s3 ,,con/ruction ,,( ,,! ,,spectroscope4 ,9 ! addition ( *emical ideas to a/ronomical inquiries1 we h "o ( ! mo/ fruitful & int]e/+ among ! _m advances ( mod]n sci5ce1 & "o also :i* has made ! connection betwe5 physics & a/ronomy "o ( ! close/4 ,to deal prop]ly ) ?is "p ( our book1 z ! con/itution ( "o ( ! heav5ly bodies c be /udi$ 9 ! laboratory z well z 9 ! obs]vatory1 we h to describe physical in/rum5ts & me?ods1 z well z ! m purely a/ronomical ones4 ,9 a n[ r>e book publi%$ 9 ,london 9 ! ye> #afec1 t is to say1 "s ye>s be=e ,sir ,isaac ,newton made 8 important obs]vations on ! action ( a prism on ! rays ( light--obs]vations :i* h be5 s v ri* 9 results--is giv5 ,kepl]'s treatise on ,dioptrics4 ,f ?is "o f9ds t ! great ,kepl] _h done all he c\ld to try to inve/igate ! action ( a ?ree-corn]$ piece ( glass4 ,x has be5 consid]$1 t1 because ,newton 0 ! fir/ to tea* u mu* ( its use1 he 0 ! fir/ to inve/igate ! prop]ties ( ! prism4 ,?is is n s4 ,fig4 #afg is an illu/ration tak5 f ?is book1 by :i* ,kepl] %[s t if we h a prism & pass light ?r\gh x1 we get ?ree di/9ct results :5 a ray 7,f7 falls on ! prism4 ,he %[s t ! fir/ surface reflects a c]ta9 am\nt ( light1 7,d ,i71 & t ?is is uncol\r$1 because x does n pass ?r\gh ! glass1 & t ! rema9d] is refract$ by ! glass & "p em]ges at ,e1 col\r$ l ! ra9b[4 ,!n he goes on to %[ t ! second surface ( ! prism also reflects "s light int]nally1 & t !re is a c]ta9 am\nt ( light leav+ ! prism at ,m1 & go+ to ,k4 ,illu/ration3 ,,fig4 #afg4--,kepl]'s ,diagram4 ,by means ( a v few exp]im5ts ,newton 0 able to %[ h[ mu* k c\ld be got by exam9ation ( ! prism4 ,! fir/ proposition 9 ,newton's ,optics is an attempt to prove t light1 :i* diff]s 9 col\r1 diff]s also 9 degree ( refrangibility4 ,we %all recollect f ! fif? *apt] :at ?is t]m means1 = x 0 !re %[n t :5ev] a ray ( light ent]s obliquely a m$ium d5s] ?an t 9 :i* x _h be5 travell+1 x is b5t t[>ds ! p]p5dicul> to ! surface1 9 fact x is refract$1 & ^? rays :i* are mo/ refract$ by ! same sub/ance ) ! same angle are said to be m refrangible ?an o!rs4 ,newton's exp]im5t 0 v simple4 ,he took a piece ( pap]1 "o half ( :i* 0 col\r$ r$ & ! o!r half blue2 & ?is 0 plac$ on a /& horizontally1 9 ! light f a w9d[1 ) a prism betwe5 x & ! eye4 ,illu/ration3 ,,fig4 #afh4--,newton's ,exp]im5t %[+ ! diff]5t ,refrangibilities ( ,col\rs4 ,he w5t on to %[1 t :5 he all[$ ! beam ( sunlight to fall ^u ! pap]1 /rongly illum9at+ ! r$ & blue portions1 mak+ at ! same "t all ! re/ ( ! room z d>k z possible 7s t ! op]ation 0 n imp$$ by extrane\s light71 :5 he held a prism 9 a p>ticul> way1 he f\nd t ! r$ & ! blue occupi$ diff]5t positions :5 look$ at ?r\gh ! prism4 ,:5 ! prism is held z %[n1 ! r$ is se5 bel[ & ! blue above4 ,if ! prism be turn$ ) ! refract+ edge d[nw>ds1 ! r$ is se5 above & ! blue bel[4 ,:5 ! refract+ edge is upw>ds1 x is v cle> t if ! violet is se5 upp]mo/ x mu/ be because ! violet ray is m refract$1 & :5 ! r$ ray is upp]mo/1 ) ! refract+ edge ( ! prism d[nw>ds1 x is because ! r$ ray is ! lea/ refract$4 ,!re are o!r exp]im5ts to :i* he alludes1 & by :i* ,sir ,isaac ,newton consid]$ he _h prov$ t lights :i* diff] 9 col\r diff] also 9 degrees ( refrangibility4 ,newton at "o /ep w5t to ! sun1 & 8 second !orem is 8,! light ( ! sun consi/s ( rays ( diff]5t refrangibility10 & !n he ent]s into ! pro( by exp]im5t4 ,! light f ! sun passes ?r\gh a hole 9 ! w9d[-%utt] & ?r\gh ! prism :i* ?r[s a spectrum on a scre54 ,we n[ see ! full mean+ ( ! diff]5t degrees ( refrangibility4 ,!re he _h a long b& ( light ( all col\rs1 ! r$ at "o end & ! blue at ! o!r1 %[+ t ! diff]5t col\rs are unequally refract$1 or turn$ f _! c\rse4 ,9 ?is way ,sir ,isaac ,newton det]m9$ :e!r ! law1 t light :i* diff]$ 9 col\r diff]$ also 9 refrangibility1 held true ) reg>d to ! sun2 & he cle>ly %[$ t 9 ?is case also ! light diff]s 9 refrangibility1 9 exactly ! same way z ! r$ light & ! blue light _h done 9 8 exp]im5t ) ! pieces ( pap]4 ,he 0 soon able to prove to himself t ! circul> ap]ture 0 n ! be/ ?+ he c\ld use1 because 9 ! spectrum he _h a circle ( col\r repres5t+ e ray into :i* ! light c\ld be brok5 up4 ,if we put a bit ( r$ glass 9 ! pa? ( ! rays we get an image ( ! hole 9 r$2 if we use o!r col\r$ glasses1 we h a circle = ea* p>ticul> col\r2 all ^! images ov]lap1 & ! sum total gives u an extremely mix$ spectrum1 some?+ q diff]5t f :at is se5 :5 we introduce a slight alt]ation1 :i* curi\sly en\gh 0 delay$ = a great _m ye>s4 ,sir ,isaac ,newton recognis$ ! difficulties !re 7 9 gett+ a pure spectrum by means ( a circul> ap]ture1 b al?\gh he us$ aft]w>ds an oblong op5+ in/ead ( a circul> ap]ture1 9 :i* we _h some?+ m or less l :at we n[ use1 namely1 a 8slit0--a n>r[ l9e ( light2 he does n seem to h grasp$ ! po9t ( ! ?+1 because 9 "o ( 8 !orems he says he also tri$ triangul> op5+s4 ,we %all %[ h[ important x is t we %\ld n only h an oblong op5+ z propos$ by ,newton1 b t t oblong op5+ %\ld be ( small bread?4 ,! mom5t we ex*ange ! circul> ap]ture = ! oblong op5+ ( ,newton1 we get a spectrum ( great] purity1 &1 z 9 ! case ( ! circul> op5+ ! purity dep5d$ on ! size ( ! circle1 s also 9 ! case ( ! oblong op5+ ! purity ( ! spectrum dep5ds v mu* on ! bread? ( ! oblong op5+4 ,we ?us sort out ! r$1 orange1 yell[1 gre51 blue1 & violet2 !y are no long] mix$ z !y are :5 we employ a circul> op5+4 ,if we attempt ! same exp]im5t ) r$ glass int]pos$ we get some?+ m decid$ ?an be=e2 we h no long] a circul> pat* ( light1 b an oblong "o 9 ! r$2 9 fact1 ! exact =m ( ! ap]ture1 or slit1 ?r\gh :i* we h all[$ ! light to pass ?r\gh ! prism & l5s to =m an image4 ,illu/ration3 ,,fig4 #afi4--,wolla/on's fir/ ,obs]vation ( ! ,l9es 9 ! ,sol> ,spectrum4 ,n[ al?\gh ,newton made ^! important obs]vations on sunlight1 he miss$ "o ( ! ?+s1 9 fact we may say ! ?+1 :i* has made sunlight & />light ( s mu* importance to ,a/ronomy4 ,! oblong op5+ :i* ,newton us$ v>i$ f "o-t5? to "o-tw5tie? ( an in* 9 wid?2 b ,dr4 ,wolla/on 9 #ahab--we _h to wait f #afgb till #ahab to get ?is app>5tly ridicul\sly small ext5sion--us$ su* a n>r[ slit z we h m5tion$1 & he f\nd t :5 he exam9$ ! light ( ! sun ) a prism be=e ! eye1 he got results ( :i* ,newton _h nev] dreamt4 ,dr4 ,wolla/on n only f\nd ! light ( ! sun diff]+ 9 refrangibility2 b 9 ! diff]5t col\rs ( ! sol> light he f\nd a numb] ( d>k l9es1 :i* are repres5t$ by ! black l9es across ! spectrum 9 ,fig4 #afi4 ,illu/ration3 ,,fig4 #agj4--;,copy ( ,fraunh(]'s fir/ ,map ( ! ,l9es 9 ! ,sol> ,spectrum4 ,illu/ration3 ,,fig4 #aga4--,/ud5t's ,spectroscope4 ,9 ! ye> #ahad ,fraunh(] exam9$ ! spectrum by means ( ! telescope ( a !odolite1 direct+ x t[>ds a di/ant slit1 ) a prism int]pos$4 ,9 ?is mann] he obs]v$ & mapp$ #egf l9es1 ! appe>ance ( ! spectrum to him be+ repres5t$ 9 ,fig4 #agj4 ,f ?is "t !y 7 call$ ! 8,fraunh(] l9es40 ,x ne$ sc>cely be said t f ! "t ( ,wolla/on until a few ye>s ago ^! /range my/]i\s l9es 7 a s\rce ( wond] to all obs]v]s :o attempt$ to attack ! problem4 ,! diff]5ce betwe5 ! simple prism & slit :i* ,newton1 ,wolla/on1 & ,fraunh(] us$ to map ^! l9es1 & ! mod]n spectroscope1 z us$ ) or )\t ! telescope1 is due to a sugge/ion ( ,mr4 ,simms 9 #ahcj4 ,let u ref] to a mod]n spectroscope4 ,fig4 #aga repres5ts a =m usually us$ = *emical analysis4 ,! only diff]5ce betwe5 ! spectroscope & ! simple prism 9 ,newton's exp]im5t is ?is1 t 9 ! "o case ! light falls directly f ! slit ?r\gh ! prism on a scre5 & is view$ !re2 & 9 ! o!r ! eye is plac$ :]e ! scre5 is1 & looks ?r\gh ! prism & c]ta9 l5ses at ! slit4 ,! great improvem5t :i* ,mr4 ,simms sugge/$ 0 ?is simple "o4 ,he said1 8,x w\ld surely be bett] t ! light :i* passes ?r\gh ! prism or prisms indep5d5tly ( ! numb] ,i use1 %\ld1 if possible1 pass ?r\gh !m z a p>allel beam ( light2 & !re=e1 in/ead ( putt+ ! slit m]ely on "o side ( a prism & ! eye on ! o!r1 ,i w1 betwe5 ! slit & ! prism1 ins]t an object-glass10 z %[n 9 ,fig4 #agb2 s t ! slit ( ! spectroscope is ! repres5tative ( ! hole 9 ! %utt]4 ,illu/ration3 ,,fig4 #agb4--,section ( a ,spectroscope1 %[+ ! ,pa? ( ! ,ray f ! ,slit4 ,! slit is exactly 9 ! focus ( ! little object-glass1 ,c1 or collimat+ l5s1 z x is call$2 s t naturally ! light is grasp$ by ?is l5s1 & comes out 9 a p>allel beam1 & travels among ! prism or prisms1 q irrespective ( c\rse ( _! numb]4 ,?is p>allel beam1 9 ord] to be utiliz$ by ! eye aft] x has pass$ ?r\gh ! sy/em ( prisms1 is aga9 tak5 up by ano!r object-glass & r$uc$ f its p>allel /ate into a /ate ( conv]g5ce1 & br\ght to a focus :i* c be exam9$ by means ( an eyepiece4 ,! r$ rays f ! slit come to a focus at ,r1 & ! blue at ,b1 =m+ !re _! respective images ( ! slit1 & betwe5 ,b & ,r are a numb] ( o!r images ( ! slit1 pa9t$ 9 e col\r t is illum9at+ x1 ?us =m+ a spectrum :i* is view$ by ! eyepiece4 ,9 fact1 ! object-glass & eyepiece con/itute a telescope1 ?r\gh :i* ! slit is view$1 & ! collimat+ l5s makes ! light p>allel1 j z if x _h come f a di/ant object1 & fit to be utiliz$ 9 ! telescope4 ,?is is ! pr9ciple to be obs]v$ 9 ! con/ruction ( e spectroscope4 ,we h n[ giv5 an idea ( ! g5]al nature ( ! in/rum5t dep5d+ on ?is important addition made by ,mr4 ,simms1 :i* is ! basis ( ! mod]n spectroscope1 & x is obvi\s t if we want consid]able disp]sion1 we c ei!r increase ! numb] ( prisms1 or increase _! disp]sive p[]4 ,we h already %[n 9 a previ\s *apt] t ! disp]sion dep5ds on ! angle ( ! prisms1 & t ! calculations necess>y = mak+ ! object-glass ( a telescope 7 bas$ ^u an obs]vation made by pass+ light ?r\gh a prism ( a p>ticul> angle made ( ! same glass z t ( :i* ! propos$ object-glass 0 to be con/ruct$4 ,!n1 aga91 we took ! opportunity ( %[+ t ) v d5se sub/ances great] disp]sion c\ld be obta9$4 ,we %[$ h[ ! prism ( d5se fl9t glass ov]p[]$ ! disp]sion ( ! prism ( ! cr[n glass1 & h[ ! comb9ation gave u refraction )\t disp]sion4 ,illu/ration3 ,,fig4 #agc4--,spectroscope ) ,f\r ,prisms4 ,fig4 #agc is a draw+ ( a spectroscope conta9+ f\r prisms4 ,x is a repres5tation ( t us$ by ,buns5 & ,kir*h(f :5 !y made _! maps ( ! sol> spectrum3 x is s arrang$ t ! light aft] pass+ ?r\gh ! slit goes ?r\gh ! collimat+ l5s1 & !n ?r\gh ! prisms2 x is aft]w>ds caught by ! telescope l5s & br\ght to a focus 9 front ( ! eyepiece4 ,x is v important1 :5 we h _m prisms1 to be able to arrange !m s t :e!r we use "o "p ( ! spectrum or ! o!r1 ea* prism %all be 9 ! be/ condition = all[+ ! light to trav]se x2 t is to say1 t x %all be 9 ! position ( m9imum deviation1 :5 ! angles ( incid5ce & em]g5ce are equal1 & ea* surface refracts ! ray equally4 ,!y c be arrang$ s1 t z ! telescope is mov$ to obs]ve a new "p ( ! spectrum1 e prism w be automatically adju/$4 ,to insure ?is ! prisms are unit$ to =m a *a9 s t !y all move toge!r1 & ea* has a radial b> to a c5tral p9 :i* keeps !m at ! prop] angle4 ,illu/ration3 ,,fig4 #agd4--;,automatic ,spectroscope 7,grubb's =m74 ,!re is ano!r arrangem5t :i* is v simple1 9 :i* we get ! condition ( m9imum deviation by m]ely m\nt+ ! prisms on a spr+1 & !n mov+ ! spr+ ) ! telescope1 9 ! same way z ! telescope moves ! o!r automatic arrangem5t4 ,illu/ration3 ,,fig4 #age4--;,automatic ,spectroscope 7,br[n+'s =m74 ,= "s obs]vations1 especially sol> obs]vations1 9 :i* ! light is v int5se1 x is extremely important1 9 fact ess5tial1 to r$uce ! brilliancy ( ! spectrum2 & ( c\rse ?is enables u1 9 ! case ( ! sun especially1 to increase ! disp]sion almo/ )\t limit1 by hav+ a great numb] ( prisms1 or ev5 us+ ! same twice ov]1 9 ! foll[+ mann]3 ,on ! spectroscope !re is a numb] ( prisms s arrang$ t ! light comes f ! slit1 & travels ?r\gh ! l[] portion ( ! prisms2 x !n /rikes aga9/ ! int]nal reflect+ surface ( a "r-angl$ prism at ! back ( ! la/ prism1 ,fig4 #agf1 & is s5t1 up to ano!r reflect+ surface1 & !n comes back aga9 ?r\gh ! same prisms along an upp] /orey1 & !n is caught by means ( a telescope above ! collimator1 on ! slit ( :i* ! sun's image is all[$ to fall4 ,illu/ration3 ,,fig4 #agf4--,la/ ,prism ( ,tra9 = return+ ! ,rays4 ,?is contrivance1 sugge/$ by ! au?or & ,pr(4 ,"y indep5d5tly1 is n[ l>gely us$4 ,fig4 #agg %[s an ord9>y spectroscope s arm$4 ,! light f ! slit trav]ses ! upp] portions ( ! prisms2 x is !n ?r[n d[n by ! reflect+ prism se5 beh9d ! collimator1 !n1 return+ along ! l[] "p1 x is receiv$ by a "r-angl$ prism 9 front ( ! object-glass ( ! obs]v+ telescope4 ,in/ead ( ! rays ( light be+ reflect$ back ?r\gh ! upp] /orey ( ! prisms1 ano!r me?od has be5 adopt$2 ! la/ prism is 9 ?is case a half prism1 & ! la/ surface on :i* ! rays ( light fall is silv]$2 ! rays !n are return$ on !mselves1 &1 :5 ! in/rum5t is adju/$1 come to a focus on ! inside ( ! slit plate1 =m+ !re a spectrum1 any "p ( :i* c1 by mov+ ! prisms1 be made to fall on a small diagonal reflect+ prism on "o side ( ! slit1 by :i* x is reflect$ to ! eyepiece4 ,9 ?is arrangem5t ! collimat+ l5s becomes its own telescope l5s on ! return ( ! ray4 ,illu/ration3 ,,fig4 #agg4--,spectroscope ) return+ ,beam4 ,!re is ano!r =m ( spectroscope1 call$ ! direct vision1 :i* is l>gely us$ = pocket in/rum5ts4 ,! pr9ciple ( x is t ! light pass+ ?r\gh x is disp]s$ b n turn$ f its c\rse1 j ! rev]se ( ! a*romatic comb9ation ( ! object-glass2 a cr[n-glass prism is cem5t$ on a fl9t "o ( suffici5t angle t _! deviative p[]s rev]se ea* o!r b leave a c]ta9 portion ( ! fl9t-glass disp]sion uncorrect$2 s9ce1 h[ev]1 ! disp]sive p[] ( ! fl9t-glass is to a great ext5t neutraliz$1 !re=e1 9 ord] to make ! in/rum5t z p[]ful z "o ( ! ord9>y con/ruction1 a numb] ( fl9t-glass prisms are comb9$ ) cr[n-glass ones1 z %[n 9 ,fig4 #agh4 ,illu/ration3 ,,fig4 #agh4--;,direct ,vision ,prism4 ,!re is ano!r =m ( direct-vision prism1 call$ ! ,h]s*el-,br[n+1 9 :i* ! ray is caus$ to take its orig9al c\rse on em]g+ by means ( two int]nal reflections4 ,,*apt] ,,xxviii4 ,,! ,,*emi/ry ,,( ,,! ,,/>s 7,,cont9u$73 ,,pr9ciples ,,( ,,spectrum ,,analysis4 ,we h next to say some?+ ab\t ! pr9ciples on :i* ! use ( ! spectroscope dep5ds2 if we look ?r\gh "o we c readily obs]ve h[ ea* p>ticul> ray ( light pa9ts an image ( ! slit4 ,?us1 if we are deal+ ) a r$ ray ( light1 t ray1 aft] pass+ ?r\gh ! prisms1 w pa9t a r$ image ( ! slit2 if ! light be violet1 ! ray w pa9t a violet image ( ! slit1 & ^! images w be sep>at$1 because "o col\r is refract$ m ?an ! o!r4 ,n[ x foll[s f ?is t :5 ! slit is illum9at$ by :ite light1 :ite light be+ :ite because x conta9s all col\rs1 we get an inf9ite numb] ( images ( slits t\*+ or ov]lapp+ ea* o!r1 & =m+ :at is call$ a cont9u\s spectrum4 ,h5ce x is t if we exam9e ! light ( a mat* or c&le1 or ev5 ! electric light1 we get su* a cont9u\s spectrum1 because ^! light s\rces emit rays ( e refrangibility4 ,mod]n sci5ce tea*es u t !y d s because ! molecules--! vibrations ( :i* produce1 ?r\gh ! int]m$i>y ( ! e!r1 ! s5sation ( light on our optic n]ve--are ( a c]ta9 complexity4 ,9 ! prec$+ li/ ( light s\rces ! sun 0 n m5tion$1 because its light :5 exam9$ by ,wolla/on & ,fraunh(]1 0 f\nd to be discont9u\s4 ,n[ x is cle> t if 9 a beam ( light !re be no light ( c]ta9 p>ticul> col\rs1 ( c\rse we %all n f9d ! image ( ! slit pa9t$ at all 9 ! correspond+ regions ( ! spectrum4 ,?is is ! :ole /ory ( ! black l9es 9 ! spectrum ( ! sun & 9 ! spectra ( ! />s4 ,"h & !re 9 ! spectrum ( ^! !re are col\rs1 or refrangibilities1 ( light :i* are n repres5t$ 9 light :i* comes f ^? bodies1 & !re=e !re is no?+ to pa9t ! image ( ! slit 9 t p>ticul> "p ( ! spectrum2 we get :at we call a d>k l9e1 :i* is ! abs5ce ( ! p[] ( pa9t+ an image4 ,b !n x may be ask$1 ,h[ comes x t ! prism & ! spectroscope are s useful to a/ronom]s8 ,9 answ] we may say1 t if we knew no m ab\t ! black l9es 9 ! spectra ( ! sun & />s ?an we knew =ty ye>s ago1 ! spectroscope ought /ill to be an a/ronomical in/rum5t1 because x is our duty to obs]ve e fact 9 nature1 ev5 if we _c expla9 x4 ,b ^! d>k l9es h be5 expla9$1 & x is ! v explanation ( !m1 & ! flood ( k :i* has be5 acquir$ 9 ! se>* aft] ! explanation1 :i* makes ! spectroscope "o ( ! mo/ valuable ( a/ronomical in/rum5ts4 ,_m ( u are aw>e ( ! magnific5t g5]alizations by :i* our c\ntrym51 ,pr(essors ,/okes & ,balf\r ,/ew>t1 & ng/rm1 ,kir*h(f & ,buns51 7 enabl$ to expla9 ^? wond]ful l9es 9 ! sol> spectrum4 ,^! l9es 9 ! sol> spectrum are !re because some?+ is at "w cutt+ out ^? rays ( light :i* are want+1 & !y expla9$ ?is want by %[+ to u t ar\nd ! sun & all ! />s !re are absorb+ atmosph]es conta9+ ! vap\rs ( c]ta9 sub/ances cool] ?an ! int]ior ( ! sun or ( ! />s4 ,^! philosoph]s also %[$ u1 t we c divide radiation & absorption into f\r classes1 & t we c h g5]al radiation & selective radiation1 & g5]al absorption & selective absorption1 s t ! ph5om5a t we see 9 our *emical & physical laboratories & our obs]vatories may all be class$ z g5]al & selective radiation1 or g5]al & selective absorption4 ,let u expla9 ^! t]ms m fully4 ,kir*h(f %[$ u t f inc&esc5t solid & liquid bodies we get a cont9u\s spectrum2 ?us f ! c>bon poles ( an electric lamp we get a complete spectrum4 ,t is call$ a cont9u\s spectrum1 & x is an in/ance ( cont9u\s radiation1 :i* we get f ! molecul> complexity ( solids or liquids1 & likewise1 f d5se gases or vap\rs4 ,:5 we exam9e vap\rs or gases :i* are n v d5se we get an indication ( selective radiation--t is to say1 ! light "o gets f ^! sub/ances1 in/ead ( be+ spread broadca/ f ! r$ to ! violet1 w simply fall "h & !re on ! spectrum2 9 ! case ( "o vap\r we may get a yell[ l9e--a yell[ image ( ! slit--& 9 ! case ( ano!r vap\r1 we may get a gre5 "o2 ! light selects its po9t ( appe>ance1 & does n appe> all along ! spectrum4 ,illu/ration3 ,,fig4 #agi4--;,electric ,lamp4 y1 z1 wires connect+ batt]y ( #ej ,grove or ,buns5 elem5ts2 ,g1 ,h1 c>bon hold]s2 ,k1 rod1 :i* /ops a clockwork movem5t1 :i* :5 go+ makes ! poles approa* until ! curr5t passes2 ,a1 armature ( a magnet :i* by means ( ,k frees ! clockwork :5 n 9 contact2 ,e1 electro-magnet r\nd :i* ! curr5t passes :5 ! poles are at ! prop] di/ance ap>t1 caus+ x to attract ! armature ,a4 ,?is selective radiation is due to a simplification ( ! molecul> /ructure ( ! vap\rs1 ! simpl] /ates are less ri* 9 vibrations1 & !re=e in/ead ( gett+ rays ( all refrangibilities we only get rays ( "s4 ,illu/ration3 ,,fig4 #ahj4--;,electric ,lamp arrang$ = ?r[+ a spectrum on a scre54 ,d1 l5s2 ,e ,e1 bisulphide ( c>bon prisms4 ,v /rik+ exp]im5ts %[+ ! spectra ( bodies may be made ) an electric lamp arm$ ) a cond5s] & a n>r[ slit2 by means ( a l5s ?is slit is magnifi$ on a scre54 ,!n "o or two prisms ( glass conta9+ bisulphide ( c>bon are plac$ 9 ! beam aft] x has trav]s$ ! l5s1 :i* draw out ! image ( ! slit into a spectrum4 ,we c !n place a piece ( sodium on ! l[] c>bon pole1 & :5 ! poles are br\ght toge!r x w be volatiliz$1 & its vap\r r5d]$ lum9\s4 ,its spectrum on ! scre5 w be se5 to consi/ ( f\r l9es only1 ! yell[ l9e be+ = m brilliant ?an ! re/4 ,sodium 0 select$ on acc\nt ( ! simplicity ( its spectrum4 ,illu/ration3 ,,fig4 #aha4--;,comp>ison ( ! l9e spectra ( ,iron1 ,calcium1 & ,alum9ium1 ) ,common ,impurities4 ,copy ( a photograph1 9 :i* by divid+ ! slit ( ! spectroscope into sections1 & admitt+ light f ! v>i\s light s\rces ?r\gh !m 9 succession1 spectra ( diff]5t elem5ts are record$ on ! same photographic plate4 ,if we put ano!r metal1 say calcium1 9 ! place ( ! sodium1 !re w appe> on ! scre5 ! *>act]i/ic l9es ( t metal4 ,a numb] ( di/9ct images ( ! slit 9 diff]5t col\rs is se52 if we are well acqua9t$ ) ! spectrum ( any metal1 & see x ) ! spectroscope1 x is easy to at once recognise x4 ,fig4 #aha %[s at "o glance ! spectra 7#a7 ( iron1 7#b7 ( calcium1 & 7#c7 ( alum9ium2 & w cle>ly indicate ! great diff]5ce !re is betwe5 ! radiation spectra ( ! r>e vap\rs ( ea* ( ! metallic elem5ts4 ,illu/ration3 ,,fig4 #ahb4--;,col\r$ ,flame ( ,salts 9 ! flame ( a ,buns5's ,burn]4 ,! electric light is only requir$ :]e great brilliancy is ess5tial1 z = %[+ spectra on a scre54 ,a ,buns5's burn] is ! be/ in/rum5t = /udy+ ! spectra ( metallic salts4 ,by its means ! nature ( a salt c be easily /udi$ ) a h& spectroscope1 & 9 ?is way an almo/ inf9itesimal quantity c be detect$4 ,^! are in/ances ( selective radiation4 ,we w n[ turn to absorption4 ,if we fir/ get a cont9u\s spectrum f our lant]n & !n int]pose sub/ances 9 ! pa? ( ! beam1 we c exam9e _! effects on ! light4 ,if we fir/ use a piece ( neutral-t9t$ glass1 :i* is a repres5tative ( a great _m sub/ances :i* d1 = /opp+ light1 :at solids & liquids d = giv+ light--namely1 x cuts (f a portion ( e col\r2 ! spectrum on ! scre5 w be dimm$2 "h we h a case ( g5]al absorption4 ,if1 in/ead ( ?is1 we hold 9 ! beam a vessel conta9+ mag5ta1 a d>k b& 9 ! spectrum is se51 & if we put a te/-tube 9 its place conta9+ iod9e vap\r1 a numb] ( well-def9$ l9es p]vad+ ! spectrum is obs]v$4 ,9 ^! cases cle>ly1 ! mag5ta 9 "o case1 & ! iod9e vap\r 9 ! o!r1 h cut (f c]ta9 col\rs1 & s ! slit is n pa9t$ 9 ^! col\rs1 & d>k l9es or b&s appe>4 ,^! are in/ances ( selective absorption1 c]ta9 rays are select$ & absorb$1 :ile o!rs pass on unhe$$4 ,! easie/ me?od ( p]=m+ ^! absorption exp]im5ts 9 ! case ( liquids is to place ! sub/ance 9 a te/-tube 9 front ( ! slit ( ! spectroscope1 z %[n 9 ,fig4 #ahc1 & po9t ! collimator to a /rong light4 ,besides ! absorption by liquids1 ! vap\rs ( ! metals also absorb selectively1 & if a tube conta9+ a piece ( sodium & fill$ ) hydrog5 7s t ! metal w n get oxidiz$7 is plac$ 9 ! pa? ( ! rays1 & ! sodium heat$1 ! spectrum is at fir/ unaffect$1 b z ! sodium gets hot & its vap\r comes (f1 we c m>k its effect on ! spectrum4 ,we see a d>k l9e beg9n+ to appe> 9 ! yell[1 f9ally ! :ole light ( t p>ticul> col\r is absorb$1 & we h a d>k l9e 9 its place4 ,to sum up !n3-- ,we get f solids1 :5 heat$1 g5]al radiation1 & :5 !y act z absorb]s1 we get g5]al absorption2 f gases & vap\rs we get selective radiation & selective absorption4 ,illu/ration3 ,,fig4 #ahc4--,spectroscope arrang$ = %[+ ,absorption4 ,n[ x at once /rikes any "o p]=m+ ^! exp]im5ts t ! d>k l9e ( yell[ sodium appe>s 9 ! same place 9 ! spectrum z ! bright "o1 & ?is is s4 ,:5 ! absorption by sodium vap\r is exam9$ by ! spectroscope1 x is !n se5 to consi/ ( two well-def9$ l9es close toge!r1 & :5 ! radiation is exam9$1 x is f\nd to consi/ ( two bright ones1 & ! absorption & radiation l9es1 ! d>k & bright ones1 are f\nd to exactly agree 9 position 9 ! spectrum1 %[+ t ! sub/ance t emits a c]ta9 light is able to absorb t same light1 s t x matt]s n :e!r a body is act+ z an absorb] or radiator1 = /ill we recognize its *>act]i/ic l9es4 ,9 #ahad ,fraunh(] /rongly suspect$ ! co9cid5ce ( ! two bright sodium l9es ) ! d>k l9es 9 ! sun2 aft]w>ds ,brew/]1 ,f\cault1 & ,mill] %[$ cle>ly ! absolute co9cid5ce2 & ,pr(essor ,/okes 9 #aheb came to ! conclusion t ! d\ble l9e ,d1 :e!r bright or d>k1 belong$ to ! metal sodium1 & t x absorb$ f light pass+ ?r\gh x ! v same rays :i* x is able1 :5 inc&esc5t1 to emit4 ,! ph5om5a r5d]$ visible to u by ! spectroscope h _! orig91 z we h said1 9 molecul> vibration1 & ! reason ( ! id5tical position ( ! light & d>k l9es1 & inde$ ! :ole !ory ( spectrum analysis1 may be %ortly /at$ z foll[s3-- ,! spectroscope tells u t :5 we break a mass ( matt] d[n to its f9e/ p>ticles1 or1 z "s p pref] to call !m1 ultimate molecules1 ! vibrations ( ^! ultimate p>ts ( ea* diff]5t k9d ( matt] are absolutely di/9ct2 s t if we get ! ultimate p>ticle1 say ( calcium1 & obs]ve its vibrations we f9d t ! k9d ( vibration or unre/ ( "o sub/ance--( ! calcium1 = in/ance--is diff]5t f ! k9d ( unre/ or mode ( vibration--:i* is ! same ?+--( ano!r sub/ance1 let u say sodium4 ,m>k well ! expression1 ultimate molecule1 because ! vibrations ( ! l>g] molecul> aggregations are absolutely p[]less to tell u any?+ ab\t _! *emical nature4 ,:5 we br+ d[n a sub/ance to its f9e/ /ate1 & obs]ve1 by means ( ! prism1 ! vibrations x communicates to ! e!r1 we f9d t1 us+ a slit 9 ! spectroscope & mak+ ^! vibrations pa9t diff]5t images ( ! slit1 we get at once j z di/9ct a s]ies ( images ( ! slit = ea* sub/ance z we %\ld get a di/9ct sequ5ce ( notes if we 7 play+ diff]5t tunes on a piano4 ,next1 ?is important consid]ation comes into play--:5ev] any elem5t f9ds itself 9 ?is /ate ( f95ess1 & !re=e compet5t to give rise to ^! ph5om5a1 x w give rise to !m 9 diff]5t degrees accord+ to c]ta9 conditions4 ,! int5se/ =m is obs]v$ :5 we employ electricity4 ,9 a great _m cases ! vibrations may be r5d]$ v int5se by heat4 ,! heat ( a furnace or ( gas w1 = in/ance1 9 a great _m cases1 suffice to give u ^! ph5om5a2 b to see !m 9 all _! magnific5ce--_! mo/ extreme cases--we want ! highe/ possible temp]atures1 or bett] /ill1 ! mo/ extreme electric en]gy4 ,:at we get is ! vibration ( ^! p>ticles r5d]$ visible to our eye by ! bright images ( ! slit or by _! bright 8l9es40 ,b t is n ! only means we h ( /udy+ ^! /ates ( unre/4 ,we c /udy !m almo/ equally well if1 in/ead ( deal+ ) ! radiation ( light f ! p>ticles !mselves1 we int]pose !m betwe5 u & a light s\rce ( m complicat$ molecul> /ructure1 & hott] or m viol5tly excit$ ?an ! p>ticles !mselves4 ,f su* a s\rce ! light w\ld come to u absolutely complete2 t is to say1 a p]fectly complete gamut ( waves ( light1 f extreme r$ to extreme violet4 ,:5 we deal ) ^! p>ticles betwe5 u & a light-s\rce compet5t to give u a cont9u\s spectrum1 !n we f9d t ! functions ( ^! molecules are /ill ! same1 b t _! effect ^u our ret9as is diff]5t4 ,!y are n vibrat+ /rongly en\gh to give u effectively light ( _! own1 b !y are eag] to vibrate1 &1 be+ s1 !y are employ$1 s to speak1 9 absorb+ ! light :i* o!rwise w\ld come to our eyes4 ,s t :e!r we obs]ve ! bright spectrum ( calcium or any o!r metal1 or ! absorption spectrum "u ! conditions above /at$1 we get l9es exactly 9 ! same "p ( ! *romatic gamut1 ) ! diff]5ce t :5 we are deal+ ) radiation we get bright l9es1 & :5 deal+ ) absorption we get d>k ones4 ,x 0 su* consid]ations z ^! by :i* ! pres5ce ( sodium 0 det]m9$ 9 ! sun4 ,soon foll[$ ! discov]y ( co9cid5ce ( o!r d>k l9es ) ! bright l9es ( numb]s ( our elem5ts1 & we _h maps made by ,kir*h(f1 & ,buns51 & ng/rm1 9 :i* almo/ e d>k l9e is mapp$ ) ! greate/ accuracy4 ,! d>k l9es 9 ! spectra ( ! />s1 & ! light ones 9 nebul1 comets1 & meteorites h also yield$ to u a k m or less accurate ( ! elem5ts ( :i* ^! cele/ial bodies are built up4 ,^! radiations & absorptions are ! ,a ,b ,c ( spectrum analysis1 & !y h _! application 9 e "p ( ! heav5s :i* ! a/ronom] /udies ) ! spectroscope4 ,b al?\gh x is ! ,a ,b ,c x is n q ! :ole alphabet4 ,aft] ,kir*h(f & ,buns5 _h made _! exp]im5ts %[+ t we might diff]5tiate betwe5 solids1 liquids1 gases1 & vap\rs1 by means ( _! spectra1 & say1 "h we h su* a sub/ance1 & !re ano!r1 ei!r by its spectrum :5 x is inc&esc5t or f ! absorption l9es produc$ by x on a cont9u\s spectrum :5 x is absorb+1 ,plck] & ,hittorf %[$ t n only 7 ! spectra v diff]5t among !mselves1 b !re 7 c]ta9 conditions "u :i* ! spectrum ( ! same sub/ance 0 n always ! same2 & al?\gh !y did n make out cle>ly :at x 01 !y %[$ t x dep5d$ ei!r on ! pressure ( ! gas or vap\r1 or ! d5sity1 or ! temp]ature4 ,& o!r obs]vations s9ce !n indicate t we get *anges 9 spectra :i* are due to pressure1 & n to temp]ature p] se2 s t we h ano!r l9e ( rese>* op5$ to u by ! fact1 t n only are ! spectra ( diff]5t sub/ances diff]5t1 b t ! spectra ( ! same sub/ances are diff]5t "u diff]5t conditions4 ,illu/ration3 ,,fig4 #ahd4--;,geissl]'s ,tube4 ,fig4 #ahd repres5ts a hydrog5 tube1 call$ a ,geissl]'s tube--a glass tube ) hydrog5 9 x & two plat9um wires1 "o pass+ into ea* bulb1 by :i* a curr5t ( electricity c be pass$ ?r\gh ! gas4 ,9 ?is case we use hydrog5 gas 9 a /ate ( extreme t5uity4 ,if n[ "o ( ^! tubes be connect$ ) a ,spr5gel pump1 we c alt] ! condition ( t5uity at pleasure1 ei!r r$uc+ ! cont5ts ( ! tube or increas+ !m by admitt+ hydrog5 f a receiv]1 by a tap connect$ to ! tub+ ( ! air-pump2 we c ?us consid]ably increase ! am\nt ( gas 9 ! tube & br+ x to some?+ l atmosph]ic pressure4 ,we %all f9d ! col\r ( ! gas ?r\gh :i* ! sp>k passes v>ies consid]ably z we increase ! pressure ( ! hydrog5 9 ! tube4 ,! hydrog5 at />t+ is ne>ly z r>e z x c be1 & if m hydrog5 be let 9 we %all see a *ange ( col\r f gre5i% :ite to r$2 ! hydrog5 admitt$ has increas$ ! pressure & ! col\r ( ! sp>k is entirely *ang$4 ,x is a v brilliant r$ col\r1 ! col\r ( ! prom95ces r\nd ! sun4 ,x may be ask$1 probably1 :e!r !re are any applications ( ?is exp]im5t to a/ronomical obs]vation4 ,x is ( importance to ! a/ronom] to get ! diff]5ces ( ! spectra ( ! same sub/ance "u diff]5t conditions1 & x is f\nd z important to get ^! diff]5ces betwe5 ! spectra ( ! same sub/ance1 z ^? betwe5 ! spectra ( diff]5t sub/ances4 ,!re is ano!r exp]im5t :i* w %[ ano!r outcome ( ?is k9d ( rese>*4 ,*ange ( col\r 9 ! sp>k is accompani$ by a consid]able diff]5ce 9 ! spectrum--t is to say1 x is cle>1 to ref] back to ! col\r ( ! hydrog5 :5 ! light 0 gre51 t we %\ld get "s gre5 9 ! spectrum1 & :5 ! light became r$1 !re w\ld be "s *ange or increase ( light t[>ds ! r$ end ( ! spectrum4 ,we see t t is p]fectly true2 b !re is n only a *ange produc$ by ! diff]5t pressures1 z %[n by ! diff]5t col\rs2 b if we c>ry ! analysis /ill fur!r--if1 in/ead ( deal+ ) ! :ole ( ! spectrum1 we exam9e p>ticul> l9es1 we f9d 9 "s cases t !re are v great *anges 9 !m4 ,if1 = in/ance1 we exam9e ! blui%-gre5 l9e giv5 by hydrog51 we %all f9d x increase 9 wid? z ! pressure increases4 ,?is k9d ( effect c be %[n on ! scre5 by means ( ! electric lamp4 ,we place "s sodium on ! c>bon poles 9 ! lamp1 & h an arrangem5t by :i* we c use ei!r tw5ty or fifty cells at pleasure4 ,! action ( a numb] ( cells ^u ! vap\r ( sodium 9 ! lamp is ?is3 ! m cells we "w )1 ! great] is ! quantity ( ! sodium vap\r ?r[n out1 & associat$ ) ! great] quantity ( vap\r is a di/9ct v>iation ( ! light--9 fact1 an increase 9 ! wid? & brightness ( ! yell[ l9es on ! scre54 ,illu/ration3 ,,fig4 #ahe4--,spectrum ( ,sun-,spot4 ,n[ j to give an illu/ration ( ! pr(itable application ( ?is3 we "k1 = in/ance1 f o!r s\rces1 /r5g!n$ by ?is1 t 9 c]ta9 regions ( ! sun1 call$ sun-spots1 !re are great] quantities ( sodium vap\r pres5t ?an 9 o!rs1 or x exi/s !re at great] pressure4 ,if t be s1 we ought to get ! same sort ( result f ! sun z we get on ! scre5 by v>y+ ! d5sity ( ! sodium vap\r4 ,t is s4 ,we d get *anges exactly simil> to ! *anges on ! scre51 only ( c\rse x is ! d>k l9es we see1 & n ! bright ones3 ! d>k l9es ( sodium are wid5$ out ov] a sun-spot1 ,fig4 #ahe1 %[+ its pres5ce 9 great] quantity1 or at great] pressure4 ,illu/ration3 ,,fig4 #ahf4--;,diagram expla9+ ,long & ,%ort ,l9es4 ,besides ! wid5+ ( ! l9es due to pressure1 !re is some?+ else :i* mu/ be m5tion$4 ,:ile exp]im5t+ ) ! sp>k tak5 betwe5 two magnesium wires focuss$ on ! slit ( ! spectroscope by a l5s1 ! l9es due to ! metal 7 f\nd to be ( unequal l5g?s4 ,n[1 z ! l9es are simply images ( ! slit1 ! l5g?s ( ! l9es dep5d on ! l5g? ( ! slit illum9at$1 s t 9 ?is case x appe>$ t ! slit 0 n illum9at$ to an equal ext5t by all ! col\rs giv5 out by magnesium vap\r1 b t ! vap\r exi/$ 9 lay]s r\nd ! wires1 ! l[] ones giv+ m col\rs1 & s also m l9es1 ?an ! upp] ones fur!r f ! wire1 z is repres5t$ 9 ,fig4 #ahf2 ?is is only meant to give an idea ( ! ?+1 & is n1 ( c\rse1 exactly :at is se54 ,s is ! slit ( ! spectroscope1 ,p ! image ( "o ( ! magnesium poles2 ! o!r1 be+ at "s little di/ance away1 does n ?r[ its image on ! slit1 & !re=e does n int]f]e4 ,! circles %[n are int5d$ to repres5t ! lay]s ( vap\r giv+ out ! spectrum2 on ! "r ! l[] lay]s give ,a1 ,b1 & ,c1 ! next ,a & ,b1 & ! upp] ones only ,b4 ,n[ we may reason f ?is t ! lay]s next ! poles are d5s] ?an ^? fur!r (f1 & give a m complicat$ spectrum ?an ! o!rs2 & also1 if ! quantity ( vap\r ( any metal is small1 we may only get j ^! longe/ l9es4 ,( late1 exp]im5ts h be5 made 9 ,engl& on o!r metals--= in/ance1 alum9ium & z9c1 & _! comp\nds2 & x is f\nd t1 :5 ! vap\r is dilut$1 z x 71 "o gets only ! longe/ l9e or l9es2 & 9 ! comp\nds1 :]e ! b&s due to ! comp\nd compose ! *ief "p ( ! spectrum1 ! longe/ l9e or l9es ( ! metal only appe>4 ,n[ :at is ! application ( ?is8 ,9 ! sun are f\nd "s ( ! d>k l9es ( c]ta9 metals1 b n all2 = in/ance1 !re are two l9es 9 ! sol> spectrum correspond+ to z9c1 b !re are tw5ty-sev5 bright l9es f ! metal :5 volatiliz$ by ! electric sp>k4 ,:y %\ld n ^! also h _! correspond+ d>k l9es 9 ! sun8 ,! answ] is1 t ! non-correspond+ l9es ( ! metal are ! %ort ones1 & only exi/ close to ! metal :]e ! vap\r is d5se2 & 9 ! sun ! d5sity is n suffici5t to give ^! l9es4 ,"h1 !n1 we h at once a means ( measur+ ! quantity ( vap\r ( c]ta9 metals compos+ ! sun4 ,x 0 ?\ght t alum9ium 0 n 9 ! sun1 z only two l9es ( ! metal out ( f\rte5 correspond$ to black l9es 9 ! sol> spectrum4 ,x is n[ kn[n t ^! two are ! longe/ l9es1 & t alum9ium probably exi/s 9 ! sun1 & z9c1 /rontium1 & b>ium mu/ also be add$4 ,^! probably exi/ 9 small quantities1 insuffici5tly d5se to give all ! l9es se5 f a sp>k 9 ! air4 ,illu/ration3 ,,fig4 #ahg4--;,comp>ison ( ! ,absorption ,spectrum ( ! ,sun ) ! ,radiation ,spectra ( ,iron & ,calcium1 ) ,common ,impurities4 ,!re is also ano!r q di/9ct l9e ( inquiry 9 :i* ! spectroscope helps u4 ,imag9e y\rself 9 a %ip at an*or1 & ! waves pass+ y1 y c c\nt ! numb] p] m9ute2 n[ let ! vessel move 9 ! direction :5ce ! waves come1 y w\ld !n meet m waves p] m9ute ?an be=e2 & if ! vessel goes ! o!r way1 less w pass y1 & by c\nt+ ! increase or decrease 9 ! numb] pass+1 y might e/imate ! rates at :i* y 7 mov+4 ,aga91 suppose "s mov+ object causes ripples on "s smoo? wat]1 & y c\nt ! numb] p] m9ute rea*+ y1 !n if t object approa* y1 /ill mov+1 & s produc+ waves at ! same rate1 ! numb] ( ripples a m9ute w increase1 & !y w be ( c\rse clos] toge!r2 = z ! object is approa*+ y1 e subsequ5t ripple is />t$1 n f ! same place z ! prec$+ "o1 b a little ne>] to y1 & also ne>] to ! "o prec$+1 on ^: heels x w foll[ clos]4 ,by ! increase 9 ! numb] ( ripples1 & also ! decrease 9 ! di/ance betwe5 !m1 "o c e/imate ! rate ( motion ( ! object produc+ !m1 = ! decrease 9 di/ance betwe5 ! ripples is j ! di/ance ! object travels 9 ! "t occupi$ betwe5 ! production ( two waves1 :i* 0 asc]ta9$ :5 ! object 0 /ation>y4 ,n[ let u apply ?is reason+ to light4 ,light1 we n[ hold1 is due to a /ate ( vibration ( ! p>ticles ( an invisible e!r1 or extremely r>e fluid1 p]vad+ all space2 & ! waves ( light1 al?\gh inf9itesimally small1 move among ^! p>ticles4 ,n[ we "k t x is ! l5g? ( ! waves ( light :i* det]m9es _! refrangibility or col\r1 & !re=e any?+ t increases or dim9i%es _! l5g? alt]s _! place 9 ! spectrum2 & z waves ( wat] are alt]$ by ! body produc+ !m mov+ to or f ! obs]v]1 s ! waves ( light are *ang$ by ! motion ( ! lum9\s body2 & ?is *ange ( refrangibility is detect$ ) ! spectroscope4 ,by measur+ ! wave-l5g? ( let u say ! ,f l9e1 & ! new wave-l5g? z %[n by ! *ang$ position1 we c e/imate ! velocity at :i* ! light s\rce is approa*+ or rec$+ f u4 ,?is application1 z we %all see 9 ! next *apt]1 enables u to det]m9e ! rate at :i* movem5ts take place 9 ! sol> atmosph]e4 ,x also gives u ! p[] ( measur+ ! ?ird co-ord9ate ( ! motion ( />s4 ,we c1 by ! exam9ation ( _! positions1 measure ! motion at "r angles to our l9e ( sight1 & s det]m9e _! motion ) ref]5ce to ! two co-ord9ates1 ,r4,a4 & ,dec41 or ,lat4 & ,long41 & j 9 ! same way z we c measure ! velocity ( ! sol> gases to or f u1 s we c measure ! motion ( ! />s to or f u1 !reby giv+ u ! ?ird co-ord9ate ( motion4 ,x ne$ sc>cely be said t by ! introduction ( ! spectroscope a new me?od ( obs]vation1 & a new p[] ( ga9+ facts1 has dawn$1 & ! soon] x is us$ all ov] ! _w ) ! enorm\s in/rum5ts :i* are requir$1 ! bett] x w be = sci5ce4 99 99 99 99 99 ,^! !n are "s ( ! *ief po9ts ( spectroscopic !ory :i* makes ! spectroscope "o ( ! mo/ p[]ful in/rum5ts ( rese>* 9 ! h&s ( ! mod]n a/ronom]4 ,,*apt] ,,xxix4 ,,! ,,*emi/ry ,,( ,,! ,,/>s 7,,cont9u$73 ,,! ,,telespectroscope4 ,we h n[ to speak ( ! me?ods ( us+ ^! spectroscopes = ! purpose ( a/ronomical obs]vations4 ,= a c]ta9 class ( obs]vations ( ! sun no telescope is necess>y1 b "s special arrangem5ts h to be made4 ,?us :ile ,dr4 ,wolla/on & ,fraunh(] 7 cont5t$ ) simple prisms1 :5 ,kir*h(f obs]v$ ! sol> spectrum1 & made 8 c>eful maps ( ! l9es1 he us$ an in/rum5t l ,fig4 #agc1 & = ! purpose ( comp>+ ! spectrum ( ! sun ) t ( ea* ( ! *emical elem5ts 9 turn1 he us$ a small reflect+ prism1 cov]+ "o-half ( ! slit1 ,fig4 #ahh1 s t any light ?r[n sideways on to ! slit w\ld be caught by ?is prism1 & reflect$ on to ! slit z if x came f an object ne> ! s\rce ( light at :i* ! spectroscope is po9t+1 s t "o-half ( ! slit c be illum9at$ by ! sun1 :ile ! o!r is illum9at$ by ano!r light2 & on look+ ?r\gh ! eyepiece "o sees ! two spectra1 "o above ! o!r2 s t we are able to comp>e ! l9es 9 ! two spectra4 ,! sunlight1 :e!r com+ f ! sun itself or a bright cl\d1 is reflect$1 into ! comp>ison prism1 ,fig4 #ahi1 ( ! spectroscope4 ,an in/rum5t call$ a helio/at c be us$ = ?is1 reflect+ ! light ei!r directly into ! prism or ?r\gh ! m$ium ( o!r reflectors4 ,illu/ration3 ,,fig4 #ahh4--;,comp>ison ,prism1 %[+ ! pa? ( ! ,ray4 ,! helio/at is a mirror1 m\nt$ on an axis1 :i* moves at ! same rate z ! sun appe>s to travel1 s t :]ev] ! sun is1 ! reflector1 once adju/$1 automatically ?r[s ! beam into ! in/rum5t1 s t ! light ( ! mov+ sun c be obs]v$ )\t mov+ ! spectroscope4 ,illu/ration3 ,,fig4 #ahi4--;,comp>ison ,prism fix$ 9 ! ,slit4 ,an av]age sol> spectrum is ?us obta9$1 &1 by means ( a prism ov] "o-half ( ! slit1 x 0 q possible = ,kir*h(f & ,buns5 to ?r[ 9 a spectrum f any o!r s\rce = comp>ison1 & s !y comp>$ ! spectra ( ! metals & o!r elem5ts ) ! sol> spectrum1 & te/$ e l9e !y c\ld f9d 9 ! spectra4 ,!y fir/ f\nd t ! two l9es ( sodium correspond$ ) ! two l9es call$ ,d 9 ! spectrum1 !n t ! #dfj l9es ( iron correspond$ 9 ! ma9 ) d>k l9es 9 ! sol> spectrum2 & s !y w5t on4 ,illu/ration3 ,,fig4 #aij4--;,f\cault's ,helio/at4 ,!re is1 h[ev]1 a me?od ( v>y+ ! attack on ?is body altoge!r1 by means ( ! spectroscope & telescope4 ,we saw t ,kir*h(f & ,buns5 cont5t$ !mselves ) an av]age spectrum ( ! sun--t is to say1 !y dealt ) ! g5]al spectrum :i* !y got f ! g5]al surface ( ! sun1 or reflect$ f a cl\d or any o!r portion ( ! sky to :i* !y might direct ! reflector2 b by means ( "s su* an arrangem5t z is %[n 9 ,fig4 #aib1 we c arrange our spectroscope s t we %all be able to =m an image ( ! sun by ! object-glass ( a telescope1 on ! slit1 & all[ x to be imm]s$ 9 any portion ( ! sun's image we may *oose4 ,we !n h a delicate means ( te/+ :at are ! spectroscopic conditions ( ! spots & ( ^? bright] portions ( ! sun :i* are call$ facul1 & ! l4 ,& x is kn[n t1 by an arrangem5t ( ?is k9d1 x is ev5 possible to pick up1 )\t an eclipse1 ^? /range ?+s :i* are call$ ! r$ prom95ces1 or ! r$ flames1 :i* h be5 se5 f "t to "t dur+ eclipses4 ,if we wi% to obs]ve any ( ! o!r cele/ial bodies1 we mu/ employ a telescope & =m an image on ! slit1 or else use ! heav5ly body itself z a slit4 ,9 ! =m] case spectroscopes mu/ be atta*$ to telescopes1 & h5ce aga9 !y mu/ be light & small1 unless a sid]o/at is employ$4 ,9 ! latt] case ! prism is plac$ outside ! object-glass1 & ! true telescope becomes ! obs]v+ telescope4 ,fraunh(]1 at ! beg9n+ ( ! pres5t c5tury1 0 ! fir/ to obs]ve ! spectra ( ! />s by plac+ a l>ge prism outside ! object-glass1 ?ree or f\r in*es 9 diamet]1 ( 8 telescope1 & s virtually mak+ ! /> itself ! slit ( ! spectroscope2 & 9 fact he almo/ anticipat$ ! arrangem5t ( ,mr4 ,simms1 & satisfi$ ! conditions ( ! problem4 ,! p>allel light f ! /> pass$ ?r\gh ! prism1 & by means ( ! object-glass 0 br\ght to a focus 9 front ( ! eyepiece1 s t ! spectrum ( ! /> 0 se5 9 ! place ( ! /> itself4 ,?is sy/em has rec5tly be5 re-inv5t$1 & ! accompany+ woodcut1 ,fig4 #aia1 %[s a prism arrang$ to be plac$ 9 front ( an object-glass ( f\r in*es ap]ture4 ,x is se5 t ! angle ( ! prism is v small4 ,! objection to ?is me?od ( proc$ure is t ! telescope has to be po9t$ away f ! object at an angle dep5d+ ^u ! angle ( ! prism4 ,illu/ration3 ,,fig4 #aia4--,object-glass ,prism4 ,9 ! o!r arrangem5t we h ! ?+ manag$ 9 a diff]5t way3 we h ! object-glass collect+ ! light f ! /> & br++ x to a focus on ! slit1 & x !n passes on to ! prisms1 ?r\gh :i* ! light has to pass be=e x comes to ! eye4 ,9 ?is comb9ation ( telescope & spectroscope we h :at has be5 call$ ! telespectroscope2 "o me?od ( comb9ation is se5 9 ! accompany+ draw+ ( ! spectroscope atta*$ to ,mr4 ,newall's great refractor2 b any me?od w d :i* unites rigidity ) lightness & all[s ! :ole in/rum5t to be rotat$ ) smoo?ness4 ,illu/ration3 ,,fig4 #aib4--,! ,eyepiece ,end ( ! ,newall ,refractor 7( #be in*es ap]ture71 ) ,spectroscope atta*$4 ,= sol> obs]vation1 z !re is light en\gh to admit ( great disp]sion1 _m prisms are employ$1 z %[n 9 ,fig4 #aib2 or ! prisms may be made s tall t ! light may be s5t backw>ds & =w>ds _m times by means ( return prisms1 to :i* ref]5ce has be5 already made4 ,= ! obs]vation ( ^? bodies :i* give a small am\nt ( light1 few] prisms mu/ be us$1 & arrangem5ts are made = ! employm5t ( ref]5ce spectra1 i4e41 to ?r[ ! light com+ f diff]5t *emical elem5ts into ! spectroscope1 9 ord] t we may te/ ! l9es2 :e!r any l9e ( ,sirius1 = in/ance1 is due to ! vap\r ( magnesium1 z ,kir*h(f te/$ :e!r any l9e 9 ! sunlight 0 ref]able to iron or ! o!r vap\rs :i* he subsequ5tly /udi$4 ,illu/ration3 ,,fig4 #aic4--,sol> ,spectroscope 7,br[n+'s =m74 ,illu/ration3 ,,fig4 #aid4--,sol> ,spectroscope 7,grubb's =m74 ,illu/ration3 ,,fig4 #aie4--,side view ( ,spectroscope1 %[+ ! arrangem5t by :i* ! light f a sp>k is ?r[n into ! in/rum5t by means ( ! reflect+ prism1 e1 by a mirror ,f4 7,hugg9s47 ,illu/ration3 ,,fig4 #aif4--,plan ( ,spectroscope4 ,t1 eyepiece end ( telescope1 ,b int]ior tube1 c>ry+ ,a1 cyl9drical l5s2 ,d1 slit ( spectroscope2 ,g1 collimat+ l5s2 h h1 prisms2 ,q1 micromet]4 7,hugg9s47 ,illu/ration3 ,,fig4 #aig4--;,cambridge ,/> ,spectroscope ,elevation4 ,illu/ration3 ,,fig4 #aih4--;,cambridge ,spectroscope ,plan4 ,^! are %[n 9 ,fig4 #aie4 e is a reflect+ prism1 & ,f is ano!r movable reflector to reflect ! light f a sp>k pass$ betwe5 two wires ( ! metal to be comp>$1 & to ?r[ x on ! prism1 :i* reflects ! light ?r\gh ! slit ( ! spectroscope to ! prisms & eye2 if ! in/rum5t 7 9 p]fect adju/m5t & turn$ on a />1 & a p]son 7 to place 8 eye to ! spectroscope1 he w\ld see 9 "o-half ( ! field ( view ! spectrum ( ! /> ) d>k l9es1 & 9 ! o!r half ! spectrum ( ! vap\r ) its bright l9es2 & if he f\nd ! bright l9es ( ! vap\r to correspond ) any p>ticul> d>k l9e ( ! spectrum ( ! />1 he w\ld "k :e!r ! metal exi/s at t /> or n2 s ?is little me*anical arrangem5t at once tells him :at !re is at ! />1 :e!r x be iron or any?+ else4 ,9 ,figs4 #aig & #aih is %[n ano!r =m ( /ell> spectroscope1 t ( ! ,cambridge 7,u4,s47 obs]vatory2 x is ! same 9 pr9ciple z t j describ$4 ,a direct vision /> spectroscope is %[n 9 ,fig4 #aii4 ,illu/ration3 ,,fig4 #aii4--;,direct-vision ,/> ,spectroscope4 7,sec*i47 ,a new optical contrivance altoge!r has to be us$ :5 /> spectra are obs]v$4 ,! image ( a /> is a po9t1 & if focuss$ on ! slit w ( c\rse give only an extremely n>r[ spectrum2 to obviate ?is a cyl9drical l5s is employ$1 :i* may be plac$ ei!r be=e ! slit or betwe5 ! eyepiece & ! eye4 ,if plac$ be=e ! slit1 x draws out ! image ( ! /> to a f9e l9e :i* j fits ! slit1 s t a suffici5t portion ( ! slit is illum9at$ to give a spectrum wide en\gh to %[ ! l9es1 or ! slit may be disp5s$ ) altoge!r4 ,9 /ell> obs]vations1 :5 ! cyl9drical l5s is us$ 9 front ( ! slit1 special precautions %\ld be tak5 s z to secure t ! position ( ! cyl9drical l5s & slit 9 :i* ! spectrum appe>s brighte/ %\ld be us$4 ,9 any b ! l>ge/ telescopes ! spectra ( ! />s are s dim t unless great c>e is us$ ! f9] l9es w be miss$4 ,a slit is n at all necess>y = m]ely see+ ! spectra2 inde$ !y are be/ se5 )\t "o4 ,if a slit be us$1 x %\ld lie 9 a p>allel & n 9 a m]idian2 "u ^! circum/ances slight v>iations 9 ! rate ( ! clock are ( no mom5t4 ,9 ?is & 9 o!r obs]vational matt]s x is good to "k :at to look =1 & !re are great g5]ic diff]5ces betwe5 ! spectra ( ! v>i\s />s4 ,9 ,fig4 #bjj are repres5t$ spectra f ! obs]vations ( ,fa!r ,sec*i4 ,9 ! spectrum ( ,sirius1 a repres5tative ( ,type ,i41 v few l9es are repres5t$1 b ! l9es are v ?ick2 & />s ( ?is class are ! easie/ to obs]ve4 ,next we h ! sol> spectrum1 :i* is a repres5tative ( ,type ,,ii41 "o 9 :i* m l9es are repres5t$4 ,9 ,type ,,iii4 flut$ spaces beg9 to appe>2 & 9 ,type ,,iv41 :i* is t ( ! r$ />s1 no?+ b flut$ spaces is visible1 & ?is spectrum %[s t !re is some?+ diff]5t at "w 9 ! atmosph]e ( ^? r$ />s to :at !re is 9 ! simpl] atmosph]e ( ! fir/--( ,type ,i4 ,^! obs]vations 7 fir/ attempt$1 & c>ri$ on ) "s success1 by ,fraunh(]1 & we "k ) :at skill & p]sev]ance ,mr4 ,hugg9s has cont9u$ ! "w 9 lat] ye>s1 ev5 employ+ ref]5ce spectra & det]m9+ _! *emical con/itution z well z _! class4 ,illu/ration3 ,,fig4 #bjj4--,types ( ,/ell> ,spectra 7,sec*i74 ,we ne$ sc>cely say t ! same arrangem5t1 m9us ! cyl9drical l5s1 is good = obs]v+ ! nebul & su* o!r cele/ial objects z comets & planets4 ,= all spectrum "w1 x has to be borne 9 m9d t ! be/ def9ition is to be _h :5 ! actual col\r "u exam9ation is focuss$ on ! slit4 ,) reflectors1 ( c\rse1 !re is no diff]5ce ( focus = ! diff]5t col\rs4 ,z ! be/ object-glasses are ov]-correct$ = *romatic ab]ration1 ! r$ focus is g5]ally inside & ! blue "o outside ! visual "o4 ,x is n necess>y to move ! :ole spectroscope to secure ?is2 all collimators %\ld be provid$ ) a rack & p9ion giv+ !m a bodily movem5t backw>ds & =w>ds4 ,?is precaution is ( especial importance 9 ! case ( sol> obs]vations1 to :i* we h next to ref]4 ,if 9 any portion ( ! sun's image on ! plate c>ry+ ! slit we see a spot1 all we h to d is to move ! telescope1 & ) x ( c\rse ! sun's image1 s t ! slit is imm]s$ 9 ! image ( ! spot2 if1 h[ev]1 we wi% to obs]ve a bright portion ( ! sun1 we c imm]se ?is slit 9 ! bright portion4 ,aga91 if we wi% to exam9e ! *romosph]e ( ! sun1 we simply h to cov] half ! slit ) ! sun1 & all[ ! o!r "p ( ! slit to be cov]$ by any surr\nd+s ( ! sun1 &1 s to speak1 to fi% r\nd ! edge2 ! l[] half ( ! slit1 say1 is cov]$ by ! sun itself1 & !re=e we %all get f t half ! ord9>y sol> spectrum2 ! upp] half is1 h[ev]1 imm]s$ 9 ! light reflect$ f our atmosph]e1 giv+ a weak sol> spectrum1 s t we get a bright & feeble spectrum side by side4 ,b besides ! atmosph]ic light fall+ on ! upp] "p ( ! slit1 ! image ( any?+ surr\nd+ ! sun falls !re also1 & its spectrum is se5 ) ! fa9t sol> spectrum1 & we f9d !re a spectrum ( sev]al bright l9es4 ,n[1 z an increase ( disp]sive p[] w spread out a cont9u\s spectrum & weak5 x1 we may almo/ indef9itely weak5 ! atmosph]ic spectrum1 & s practically get rid ( x1 /ill leav+ ! bright-l9e spectrum ) ! l9es /ill fur!r sep>at$2 s t if x 7 n = our atmosph]e1 we %\ld get only ! spectrum ( ! sun & t ( its surr\nd+s2 "o a cont9u\s spectrum ) black l9es1 & ! o!r consi/+ ( bright l9es only4 ,n[ if we suppose ^! obs]vations made--if ! precaution to :i* we h allud$ be n tak51 ! spectrum ( ! sun-spot w diff] b little f t ( ! g5]al surface1 & ! *romosph]ic l9es w sc>cely be visible4 ,if ! precaution be tak51 9 ! case ( ! spot x w be f\nd t e "o ( ! surr\nd+ pores is also a spot2 & if ! air be pure ! spectrum w be full ( h>d l9es runn+ along ! spectrum1 j l du/ l9es1 b emphatically n du/ l9es1 because !y *ange ) e movem5t ( ! sun4 ,! figure ( ! spot spectrum on p4 #dae w %[ :at is meant4 ,fig4 #bja w %[ ! appe>ance ( ! *romosph]ic l9e :5 ! blue-gre5 light is exactly focuss$2 ! b\nd>y ( ! spectrum ( ! photosph]e approa*es 9 h>dness t at ! end ( ! slit4 ,by measur+ ! l5g?s ( ! l9es we c e/imate ! height ( ! vap\rs produc+ !m2 we f9d f ?is t magnesium is usually pres5t to a height ( a few hundr$ miles1 & t hydrog5 ext5ds to betwe5 #c1jjj & #d1jjj miles2 9 "s positions ( ! slit ! hydrog5 l9es are se5 to />t up to great heights1 %[+ ! pres5ce ( flames or prom95ces ext5d+ 9 height to sometimes #ajj1jjj miles4 ,illu/ration3 ,,fig4 #bja4--,"p ( ,sol> ,spectrum ne> ,f4 ,if1 )\t *ang+ ! focus1 we op5 ! slit wid]1 & ?r[ ! sun's image j (f ! slit1 s t ! v bright cont9u\s spectrum no long] dazzles ! eye1 we %all be able to see ^! flames :5ev] !y cross ! op5+1 = ! image ( ! slit is focuss$ on ! eye1 & ! sun & its flames are focuss$ on ! slit1 s if we virtually remove ! slit by op5+ x wide1 we see ! flames2 /ill ! limit ( op5+ is soon approa*$1 & ! flood ( atmosph]ic light soon masks !m4 ,! r$ hydrog5 l9e ( ! spectrum is ! be/ = view+ !m1 al?\gh ! yell[ or blue w answ]4 ,we may also place ! sun's image s t ! slit is tang5tial to x1 9 :i* case a great] l5g? ( ! hydrog5 lay]1 or *romosph]e1 z x is call$1 is visible1 al?\gh its height is limit$ by ! op5+ ( ! slit4 ,by ^! means we are able to view a small "p ( ! *romosph]e at a "t1 & to g all r\nd ! sun 9 ord] to obta9 a daily record ( :at is go+ on4 ,if1 h[ev]1 we ?r[ ! image ( ! sun on a disc ( metal ( exactly ! same size1 we eclipse ! sun1 b all[ ! light ( ! *romosph]e to pass ! edge ( ! disc2 ?is ( c\rse is mask$ by ! atmosph]ic light1 b if ! annulus1 or r+ ( *romosph]e1 be r$uc$ suffici5tly small1 x c be view$ ) a spectroscope 9 ! place ( a slit1 9 fact x is virtually a circul> slit on :i* ! *romosph]e re/s4 ,by ?is means ne>ly ! :ole ( ! *romosph]e c be se5 at once4 ,?is is accompli%$ z foll[s3-- ,! image ( ! sun is br\ght to focus on a diaphragm hav+ a circul> disk ( brass 9 ! c5tre1 ( ! same size z ! sun's image1 s t ! sun's light is ob/ruct$ & ! *romosph]ic light is all[$ to pass4 ,! *romosph]e is aft]w>ds br\ght to a focus aga9 at ! position usually occupi$ by ! slit ( ! spectroscope2 & 9 ! eyepiece is se5 ! *romosph]e 9 circles correspond+ to ! 8,c0 or o!r l9es4 ,a l5s is us$ to r$uce ! size ( ! sun's image1 & keep x ( ! same size z ! diaphragm at diff]5t times ( ! ye>2 & o!r l5ses are us$ 9 ord] to r$uce ! size ( ! annulus ( light to ab\t in*1 s t ! p5cils ( light f ei!r side ( x may n be too div]g5t to pass ?r\gh ! prisms at ! same "t1 9 ord] t ! image ( ! :ole annulus may be se5 at once4 ,!re are me*anical difficulties 9 produc+ a p]fect annulus ( ! requir$ size1 s "o in* 9 diamet] is us$1 & c be r$uc$ virtually to any size at pleasure4 ,f :at has be5 said x is easy to see t we really n[ get a new language ( light altoge!r1 & a language :i* requires a good deal ( int]pretation4 ,illu/ration3 ,,fig4 #bjb4--;,di/ortions ( ,f l9e on ,sun4 ,we h /ill1 inde$1 to consid] "s curi\s obs]vations :i* are n[ capable ( be+ made e day :5 any?+ l a sun-/orm is go+ on1 by means ( ! arrangem5t 9 :i* ! spectroscope simply deals ) ! light t comes f a small portion ( ! sun in/ead ( f all ! sun4 ,if we make ! slit travel ov] diff]5t portions ( ! sun on :i* any up-ru%es ( heat$ mat]ial1 or d[n-ru%es ( cold mat]ial1 or o!r *anges1 are go+ on f *ange ( surface temp]ature1 ! ,fraunh(] l9es1 :i* we h be=e %[n to be /raight1 in/ead ( be+ s1 appe> contort$ & twi/$ 9 all directions4 ,on ! o!r h&1 if we exam9e ! *romosph]e "u ! same conditions1 we f9d ! bright l9es contort$ 9 ! same mann]4 ,! usually d>k l9es1 moreov]1 sometimes appe> bright1 ev5 on ! sun itself2 sometimes !y are mu* *ang$ 9 _! relative positions ) ref]5ce to ! sol> spectrum4 ,! mean+ ( ^! contortions has already be5 h9t$ at 7p4 #dbj74 ,x 0 !re %[n t e col\r1 or light ( e refrangibility1 is plac$ by ! prisms 9 its own p>ticul> position1 s if a ray ( light alt]s its position 9 ! spectrum x mu/ *ange its col\r or refrangibility1 s ! light produc+ ! ,f l9e 9 ! "o case1 & ! abs5t light produc+ ! d>k l9e 9 ! o!r1 diff] slightly 9 col\r1 or are r m or less refrangible ?an ! normal light f hydrog54 ,9 ! case :5 ! ,f l9e is waft$ t[>ds ! blue end ( ! spectrum1 ! light fall+ on ! slit is r m refrangible ?an usual2 & 9 ! middle draw+1 ,fig4 #bjc1 :]e ! ,f l9e bifurcates1 ! slit is suppli$ ) two k9ds ( light diff]+ slightly 9 refrangibility4 ,n only does ! light radiat$ by a sub/ance *ange 9 ?is way1 b ! light absorb$ by t sub/ance also *anges1 h5ce ! contortions ( ! black l9es are due to a simil> cause4 ,illu/ration3 ,,fig4 #bjc4--;,displacem5t ( ,f l9e on edge ( ,sun4 ,"h1 !re=e1 we h evid5ce ( a *ange ( refrangibility1 or col\r1 ( ! light com+ f ! hydrog5 surr\nd+ ! sun4 ,?is *ange ( refrangibility is due to ! motion ( ! sol> gases1 z expla9$ 9 ! la/ *apt]4 ,s we f9d t ! hydrog5 produc+ ! light giv+ u "o ( ! =ms ( ! ,f l9e1 %[n 9 ,fig4 #bjc1 is mov+ t[>ds u at ! rate ( #abj miles a second1 :ile t giv+ ! o!r =m is mov+ away f u4 ,let u see h[ ^! imm5se velocities are e/imat$4 ,by means ( c>eful measurem5ts1 ng/rm has %[n on 8 map ( ! sol> spectrum ! absolute l5g? ( ! waves ( light correspond+ to ! l9es2 ?us ! l5g? ( ! wave ( light ( hydrog5 giv+ ! ,f l9e is #dhfj_/ajjjjjjj ( a millimet]4 ,9 ,fig4 #bjc ! dots on ei!r side ( ! ,f l9e %[ ! positions1 :]e light w\ld fall1 if x diff]$ f ! ,f light by #a1 #b1 #c1 or #d t5-million?s ( a millimet]1 s t 9 ! figure ! light ( t "p ( ! l9e waft$ ov] ! f\r? dot is ( a wave-l5g? ( #d t5-million?s ( a millimet] less ?an t ( ! normal ,f light1 :i* has a wave-l5g? #dhfj_/ajjjjjjj ( a millimet]4 ,! ,f light !re=e has _h its wave-l5g? r$uc$ by #d_/dhfj #a_/abae "p2 & 9 ord] t ea* wave may be decreas$ by ?is am\nt1 ! s\rce ( ! light mu/ move t[>ds u ) a velocity ( #a_/abae ( ! velocity ( light1 :i* is #ahf1jjj miles p] second1 & #a_/abae ( #ahf1jjj is ab\t #aej2 ?is !n is ! velocity1 9 miles p] second1 at :i* ! hydrog5 gas mu/ h be5 mov+ t[>ds u 9 ord] to displace ! light to ! f\r? dot1 z %[n 9 ! figure4 ,,*apt] ,,xxx4 ,,! ,,telepol>iscope4 ,9 previ\s *apt]s we h consid]$ ! lessons t we c le>n f light--f ! vibrations ( ! s-call$ e!r--:5 we put que/ions to x ?r\gh v>i\s in/rum5ts z int]pret]s4 ,!re is /ill ano!r me?od ( putt+ que/ions to ^! same vibrations1 & ! in/rum5t we h n[ to consid] is ! ,pol>iscope4 ,! spectroscope help$ u to inquire into ! l5g?s ( ! lum9if]\s waves2 f ! pol>iscope we le>n :e!r !re is any special plane 9 :i* ^! waves h _! motion4 ,! pol>iscope is an in/rum5t :i* ( late ye>s has become a useful adjunct to ! telescope 9 exam9+ ! light f a body 9 ord] to decide :e!r x is reflect$ or n1 & to asc]ta9 indirectly ! plane 9 :i* ! rays reflect$ to ! eye lie4 ,! action ( ! in/rum5t dep5ds ^u ! fact t light :i* consi/s solely ( vibrations p]p5dicul> to a giv5 plane is said to be completely pol>iz$ 9 t plane4 ,light t conta9s an excess ( vibrations p]p5dicul> to a giv5 plane is said to be p>tially pol>iz$ 9 t plane4 ,x 0 ,huygh5s t discov]$ ! action ( ,icel& sp> 9 d\bly refract+ light2 & ! light :i* pass$ ! cry/al 0 call$ pol>iz$ light at ! sugge/ion ( ,newton1 :o1 x mu/ be rememb]$1 look$ ^u light z some?+ actually emitt$ f lum9\s bodies2 ^! project$ p>ticles 7 suppos$1 aft] passage ?r\gh ,icel& sp>1 to be furni%$ ) poles analog\s to ! poles ( a magnet1 & to be unable to pass ?r\gh c]ta9 bodies :5 ! poles 7 n po9t+ 9 a c]ta9 direction4 ,x 0 n until ! ye> #ahjh t ,malus discov]$ ! ph5om5on ( pol>ization by reflection4 ,he 0 look+ ?r\gh a d\ble-refract+ prism at ! w9d[s ( ! ,luxemb\rg ,palace1 on :i* 7 fall+ ! rays ( ! sett+ sun4 ,on turn+ ! prism he notic$ ! ord9>y & extraord9>y images alt]nately become bright & d>k4 ,?is ph5om5on he at once saw 0 9 close analogy to t :i* is obs]v$ :5 light is pass$ ?r\gh ,icel& sp>4 ,at fir/ he ?\ght x 0 ! air t pol>iz$ ! light1 b subsequ5t exp]im5ts %[$ him t x 0 due to reflection f ! glass4 ,let u exam9e "s ( ! ph5om5a be=e we proce$ to %[ ! use a/ronom]s make ( !m4 ,x is ! prop]ty ( "s cry/als1 su* z t\rmal9e1 :5 cut p>allel to a giv5 direction1 call$ ! optic axis ( ! cry/al1 to absorb all vibrations or resolv$ p>ts ( vibrations p]p5dicul> to ?is l9e1 transmitt+ only vibrations p>allel to x4 ,a simil> absorption ( vibrations p]p5dicul> to a giv5 direction may be effect$ by v>i\s o!r comb9ations1 ( :i* "o1 ,nicol's prism1 is 9 mo/ common use4 ,any ( ^! arrangem5ts may be us$ z an analyz] ) ! telescope1 = det]m9+ :e!r ! light is completely or p>tially pol>iz$1 & 9 ei!r ( ^! cases :i* is ! plane ( pol>ization4 ,! plane conta9+ ! direction ( ! rays & ! l9e 9 ! analyz] to :i* ! transmitt$ vibrations are p>allel1 is call$ ! plane ( analyzation3 all ! light :i* rea*es ! eye consi/s ( vibrations 9 ! plane ( analyzation4 ,z we rotate ! analyz]1 we rotate equally ! plane ( analyzation4 ,if we f9d a position ( ! plane ( analyzation = :i* ! light receiv$ by ! eye is a maximum1 we "k t ! light f ! object is p>tially or completely pol>iz$ 9 a plane p]p5dicul> to ! plane ( analyzation :5 9 ?is position4 ,to det]m9e :e!r ! pol>ization is p>tial or complete1 we mu/ turn ! analyz] ?r\gh an angle ( #ij f ?is position3 if we n[ obta9 complete d>kness1 we "k t !re are no vibrations hav+ a resolv$ "p p>allel to ! plane ( analyzation 9 ?is position1 or t ! light is completely pol>iz$ 9 ?is plane3 if !re be /ill "s light visible1 ! pol>ization is only p>tial4 ,to expla9 ?is a little m fully1 we may comp>e ! vibrations or waves ( light to waves ( m mat]ial ?+s3 we may h ! vibrat+ p>ticles ( ! e!r mov+ up & d[n z ! p>ticles d 9 ! case ( a wave ( wat]1 or ! p>ticles may move horizontally z a snake does 9 mov+ along ! gr\nd4 ,we may consid] t ord9>y light consi/s ( vibrations tak+ place 9 all planes1 b if x passes ?r\gh or is reflect$ by c]ta9 sub/ances at c]ta9 angles1 ! vibrations 9 c]ta9 planes are1 z x 71 filt]$ out1 leav+ only vibrations 9 a c]ta9 plane4 ,?is light is !n said to be pol>iz$1 & its plane ( pol>ization is f\nd by its p[] ( pass+ ?r\gh pol>iz+ bodies only :5 !y are 9 c]ta9 positions4 ,if1 = in/ance1 a ray ( ord9>y light is pass$ ?r\gh a cry/al ( t\rmal9e1 ! vibrations ( ! filt]$ ray w only lie 9 "o plane2 if !n a second cry/al ( t\rmal9e be held 9 a simil> position to ! fir/1 ! ray w pass ?r\gh x unaffect$2 b if x be turn$ ?r\gh a qu>t] ( a circle ab\t ! ray z an axis1 ! ray w no long] be able to pass1 = be+ 9 a position at "r angles to ! fir/1 x w filt] out j ! rays t ! fir/ all[s to pass4 ,= illu/ration1 take a gridiron3 if we attempt to pass a numb] ( %eets ( pap] held 9 all positions ?r\gh x1 only ^? 9 a c]ta9 plane1 viz41 t ( ! rods =m+ ! gridiron1 c\ld be pass$ ?r\gh1 & ^? t w\ld g ?r\gh w\ld also g ?r\gh any numb] ( gridirons held 9 a simil> position4 ,b if ano!r gridiron be plac$ s t its b>s cross ^? ( ! fir/1 ! %eets ( pap] c\ld no long] pass1 & x is evid5t t if we c\ld n see or feel ! pap]1 we c\ld tell 9 :at plane x 0 by ! position 9 :i* ! gridiron mu/ be held to let x pass1 & hav+ f\nd ! pap] to be1 say horizontal1 we "k t ! b>s ( ! fir/ gridiron are also horizontal4 ,s ) light1 we c analyze a ray ( pol>iz$ light & say 9 :at plane x is pol>iz$4 ,! example ( ! gridiron1 h[ev]1 does n q repres5t ! action ( ! second cry/al2 = if ! b>s ( ! second gridiron are turn$ a v small di/ance out ( co9cid5ce ) ^? ( ! fir/1 ! %eets ( pap] w\ld be /opp$2 b ) light1 ! int5sity ( ! ray is only gradually dim9i%$1 until x is f9ally qu5*$ :5 ! axes ( ! cry/als are at "r angles to ea* o!r4 ,illu/ration3 ,,fig4 #bjd4--;,diagram %[+ ! ,pa? ( ! ,ord9>y & ,extraord9>y ,ray 9 ,cry/als ( ,icel& ,sp>4 ,light is pol>iz$ by transmission & by reflection4 ,we h already1 :5 we 7 discuss+ ! pr9ciple involv$ 9 ! d\ble-image micromet]1 se5 h[ a cry/al ( ,icel& sp> divides a ray into two p>ts at ! po9t ( incid5ce4 ,n[ ^! two rays are oppositely pol>iz$1 t is to say1 ! vibrations take place 9 planes p]p5dicul> to ea* o!r2 ! vibrations ( ! incid5t light 9 "o plane are refract$ m ?an ! vibrations 9 ! opposite plane1 & we h !re=e two rays1 "o call$ ! ord9>y ray1 & ! o!r ! extraord9>y ray4 ,fig4 #bjd %[s a ray ( light1 ,s ,i1 incid5t on ! fir/ cry/al at ,i2 x is !n divid$ up into ! ord9>y ray ,i ,r & ! extraord9>y "o ,i ,r2 a scre5 is !n int]pos$1 /opp+ ! extraord9>y ray & all[+ ! ord9>y "o to fall on ! second cry/al at ,i4 ,if !n ?is cry/al be 9 a simil> position to ! fir/1 ?is ray1 vibrat+ only 9 "o plane1 w pass onw>ds z an ord9>y ray1 ,i ,r2 !re be+ no vibrations 9 ! p]p5dicul> plane to =m an extraord9>y ray1 !re w be only "o circle ( light ?r[n on ! scre5 at ,o by ! l5s4 ,b1 if ! second cry/al be turn$ r\nd ! l9e ,s ,s z an axis1 ! plane ( vibration ( ! ray fall+ on its surface w no long] co9cide ) ! plane 9 :i* an ord9>y ray vibrates 9 ! cry/al1 & x !re=e becomes split up into two1 "o vibrat+ 9 ! plane z an ord9>y ray1 & ! o!r 9 t ( an extraord9>y ray2 we h !re=e ! ray ,i ,r 9 addition to ! fir/1 & consequ5tly a second circle on ! scre5 at ,e4 ,z ! cry/al rotates1 ! plane ( extraord9>y refraction becomes m & m co9cid5t ) ! plane ( vibration ( ! incid5t ray1 until1 :5 x has revolv$ ?r\gh #ij1 x co9cides ) x exactly2 x !n passes ?r\gh totally z an extraord9>y ray1 & z ! refractive p[] ( ! cry/al is great] = vibrations 9 ?is plane1 we get all ! light trav]s+ ! direction ,i ,r & fall+ on ! scre5 at ,e1 & !re be+ !n no light ord9>ily refract$1 ! circle ,o disappe>s4 ,fig4 #bje %[s ! relative brightness ( ! circles ,e & ,o z !y revolve r\nd ! c5tre ,s ( ! scre51 ! images produc$ by ! ord9>y & ! extraord9>y ray becom+ alt]nately bright & d>k z ! cry/al is rotat$4 ,fig4 #bjf %[s ! images on ! scre5 :5 ! ord9>y ray is /opp$ by ! fir/ scre5 in/ead ( ! extraord9>y "o4 ,illu/ration3 ,,fig4 #bje4--;,appe>ance ( ! ,spots ( ,light on ! ,scre5 %[n 9 ! prec$+ ,figure1 all[+ ! ord9>y ray to pass & rotat+ ! second ,cry/al4 ,illu/ration3 ,,fig4 #bjf4--;,appe>ance ( ,spots ( ,light on ,scre5 on rotat+ ! second ,cry/al1 :5 ! extraord9>y ray is all[$ to pass ?r\gh ! fir/ ,scre54 ,a cry/al ( t\rmal9e acts 9 a l mann] to ,icel& sp>1 b ! ord9>y ray is rapidly absorb$ by ! cry/al1 s t ! extraord9>y ray only passes4 ,!re is an objection to ! use ( x1 z x is n v transp>5t1 & a ,nicol's prism is n[ g5]ally us$ = pol>iz+ light4 ,x is con/ruct$ out ( a rhombo-h$ron ( ,icel& sp> cut into two p>ts 9 a plane pass+ ?r\gh ! obtuse angles1 & ! two halves are !n jo9$ by ,canada balsam4 ,! pr9ciple ( con/ruction is ?is3 ! p[] ( refract+ light possess$ by ,canada balsam is less ?an t possess$ by ,icel& sp> = ! ord9>y ray1 & great] 9 ! case ( ! extraord9>y ray2 9 consequ5ce1 ! ord9>y ray is reflect$ at ! surface ( junction1 :ile ! extraord9>y ray passes onw>ds ?r\gh ! cry/al4 ,illu/ration3 ,,fig4 #bjg4--;,in/rum5t = %[+ ,pol>ization by ,reflection4 ,x is manife/ !n t if two ,nicols are us$ in/ead ( two simple cry/als1 repres5t$ 9 ,fig4 #bjd1 !re w be only "o spot ( light on ! scre51 :i* is due to ! extraord9>y ray1 & z 9 c]ta9 positions ?is no long] passes 7= ! ord9>y ray1 :i* appe>s 9 ! place ( ! extraord9>y :5 ! cry/al is us$1 _c pass ?r\gh ! ,nicol71 no light at all passes 9 su* positions1 s t we c use ! second ,nicol z an analyz] to asc]ta9 9 :at plane ! light is pol>iz$4 ,light is also pol>iz$ by reflection f ! surface ( a transp>5t m$ium4 ,:5 a ray ( ord9>y light falls on a plate ( glass at an angle ( #ed #ee ) ! normal1 ! reflect$ ray is p]fectly pol>iz$1 & at o!r incl9ations ! pol>ization is incomplete4 ,"h !n is pol>ization by reflection4 ,fig4 #bjg %[s an app>atus = produc+ ?is ph5om5on4 ,! light foil+ on ! fir/ mirror f ,e is reflect$ ?r\gh ! tube z a pol>iz$ beam1 & ?is is analyz$ by ! o!r mirror 7,i71 ^: plane c be rotat$ r\nd ! axis ( ! tube4 ,! angle ( pol>ization diff]s ) diff]5t sub/ances accord+ to _! refractive p[]1 = pol>ization ( ! reflect$ ray is p]fect only :5 ! angle ( incid5ce is su* t ! reflect$ ray is at "r angles to ! refract$ "o4 ,z a result ( :at we h said1 ! light ( ! sun reflect$ f ! surface ( wat] or f ! glass ( a w9d[ is pol>iz$1 & al?\gh x may be dazzl+ to ! eye1 x is r$uc$1 or ev5 entirely cut (f1 :5 fall+ at ! pol>iz+ angle1 by look+ ?r\gh ! transp>5t ,nicol's prism or plate ( glass held 9 c]ta9 positions & act+ z an analyz]4 ,on rotat+ ! analyz] !re is an alt]nation ( int5sity1 & by look+ at ! w9d[ ?r\gh a cry/al ( ,icel& sp> z an analyz]1 two images w\ld be se5 :i* w\ld alt]nate 9 brightness z ! cry/al is rotat$4 ,s also !re is a diff]5ce 9 ! int5sity ( ! light f ! sky :5 ! analyz] is rotat$1 %[+ t ! light reflect$ f ! wat]y & du/ p>ticles 9 ! air is pol>iz$1 & by ! position ( ! analyz] we f9d t x is pol>iz$ 9 ! plane we %\ld expect if x be1 z x is1 reflect$ f ! sun4 99 99 99 99 99 ,x w be ask$1 h[ev]1 :at is ! a/ronomical use ( det]m9+ :e!r light has an excess ( vibrations 9 any giv5 direction8 ,to ?is we may reply t light t is reflect$ f any body is g5]ally p>tially pol>iz$ 9 ! plane ( reflection1 & t if we f9d t ! light receiv$ f any body is p>tially pol>iz$ 9 a giv5 plane1 we may conclude t x has v likely be5 reflect$ 9 t plane4 ,h5ce !n 9 ! case ( any cele/ial body ! orig9 ( ! light ( :i* is d\btful1 ! pol>iscope tells u :e!r ! light is intr9sic or reflect$4 ,x tells u m ?an ?is1 x tells u ! plane 9 :i* ! reflection has tak5 place4 ,z ! pol>ization takes place1 :5 x does take place1 at ! cele/ial body1 all we h to d is to atta* an analyz] to ! telescope4 ,a c>eful application ( ! above pr9ciples has %[n t ! light f ! sun's corona is p>tially pol>iz$1 & 9 ! same plane z x w\ld be if reflect$ f small p>ticles 9 ! neighb\rhood ( ! sun3 s also a portion ( ! light ( ,coggia's ,comet 0 f\nd to be pol>iz$1 & !re=e we say t x reflect$ sunlight 9 addition to its own prop] light4 ,9 :at has be5 hi!rto said we h only consid]$ ! use ( a ,nicol1 or glass plates1 or cry/al ( ,icel& sp> z an analyz]1 & by ! v>iation ( brightness ! pres5ce & plane ( pol>ization h be5 det]m9$2 b unless ! pol>ization is some:at decid$1 x c\ld n be detect$ by ?is me?od4 ,advantage is !re=e tak5 ( ! fact t a plate ( qu>tz rotates ! plane ( pol>ization ( a ray pass+ ?r\gh x1 & x rotates ! m refrangible col\rs m ?an ! o!rs1 & "s cry/als rotate ! plane "o way1 & o!rs 9 ! opposite direction3 ! cry/als are !re=e call$ respectively "r- & left-h&$ qu>tz2 ! ?ick] ! qu>tz ! great] ! angle ?r\gh :i* ! plane ( pol>ization is twi/$4 ,?is supplies u ) a mo/ delicate app>atus1 :i* we next describe4 ,a cry/al ( "r- & a cry/al ( left-h&$ qu>tz are tak5 & cut to su* ?ickness t a ray ( any col\r1 say gre51 has its plane turn$ ?r\gh #ij on pass+ ?r\gh ea* ( !m4 ,!y are !n cut into ! =m ( a semicircle & plac$ side by side4 ,any *ange ( ! angle ( pol>ization w n[ affect ea* plate diff]5tly4 ,9 "o plate ! col\rs w *ange f r$ to violet1 9 ! o!r f violet to r$4 ,if n[ a ray ( pol>iz$ light1 say vibrat+ 9 a v]tical plane1 falls on !m1 ! gre5 rays w h _! plane ( vibration turn$ ?r\gh #ij by ea* cry/al1 & ! vibration ( ! gre5 f bo? cry/als w !n be 9 ! horizontal plane4 ,nicol's prism int]pos$ betwe5 ! qu>tz plates & ! eye1 s z to all[ horizontal vibrations to pass1 w %[ ! gre5 f bo? cry/als ( equal int5sity2 ! rays ( o!r col\rs1 be+ turn$ ?r\gh a great] or less angle ?an #ij1 w n be vibrat+ horizontally1 & w !re=e only p>tially pass ?r\gh1 s gre5 w be ! prevail+ col\r4 ,if n[ ! plane ( vibration ( ! orig9al ray be turn$ a little out ( ! v]tical1 ! ray1 on ! r$ side ( ! gre51 w appe> 9 "o half1 & t on ! violet side ( ! gre5 9 ! o!r3 s t imm$iately ! plane ( pol>ization *anges1 ! plates transmit a diff]5t col\r1 & ! app>atus mu/ be twi/$ r\nd ?r\gh j ! same angle z ! pol>iz$ ray 9 ord] to get ! cry/als ( ! same col\r4 ,x is !re=e obvi\s t ! angle made by a pol>iz$ ray ) a fix$ plane is easily asc]ta9$ 9 ?is mann]4 ,!re is also ano!r in/rum5t = detect+ pol>ization :i* is p]haps m commonly us$ ?an ! biqu>tz3 x is g5]ally call$ ,sav>t's analys]1 & is extremely s5sitive 9 its action4 ,on look+ ?r\gh x at any object emitt+ ord9>y light1 ! :ite circle ( light limit$ by ! ap]ture ( ! in/rum5t only is se52 b if any pol>iz$ light %\ld happ5 to be pres5t1 a numb] ( p>allel b&s1 ea* %ad$ f r$ to violet1 make _! appe>ance2 on rotat+ ! in/rum5t a po9t is f\nd :5 a v slight motion causes ! b&s to vani% & o!rs to appe> 9 ! int]m$iate spaces1 & kn[+ ! position requir$ = ! *ange ( b&s ) light pol>iz$ 9 a kn[n plane1 say ! v]tical plane1 x is easy to f9d h[ f> ! plane ( pol>ization ( any ray is f ! v]tical1 by ! numb] ( degrees ?r\gh :i* ! in/rum5t mu/ be turn$ to *ange ! b&s4 ,! con/ruction ( ! in/rum5t1 & especially its action1 is n easy to und]/& )\t a consid]able k ( optics1 b x may be /at$ t a plate ( qu>tz is cut1 9 a direction incl9$ at #de to its axis1 into two p>ts ( ! same ?ickness2 "o "p is !n turn$ ?r\gh a "r angle & plac$ ) ! same surfaces 9 contact z be=e2 ^! are fix$ 9 ! in/rum5t s t ! light %all trav]se !m p]p5dicul>ly to ! plane ( section2 ! light !n passes ?r\gh a ,nicol's prism z an analys] to ! eye4 ,! l9es obs]v$1 8black c5tr$0 9 "o position1 & 8:ite c5tr$0 9 ! position at "r angles to ?is1 are always 9 ! direction be=e ref]r$ to4 ,! delicacy ( ! te/ suppli$ by ?is arrangem5t increases z ?is direction is m ne>ly p>allel or p]p5dicul> to ! plane ( pol>ization ( ! ray "u exam9ation4 ,,*apt] ,,xxxi4 ,,cele/ial ,,photography4--,,! ,,ways ,,& ,,means4 ,we come n[ la/ ( all to t bran* ( ! "w ( ! physical a/ronom] :i* bids fair 9 ! future to replace all exi/+ me?ods ( obs]vation4 ,9 ! introductory *apt] we ref]r$ to ! introduction ( photographic records ( a/ronomical ph5om5a z m>k+ an epo* 9 ! developm5t ( ! sci5ce4 ,9 ! la/ ones we h to dwell briefly on ! modus op]&i ( ! v>i\s me?ods by :i* ! eye is ?us be+ gradually replac$4 ,! po9t ( cele/ial photography is t x n only enables u to det]m9e =m & place1 absolutely irrespective ( p]sonal equation s f> z ! eye is conc]n$1 b t1 prop]ly done1 x gives u a fai?ful & la/+ record ( ! op]ation1 s t x is n =gott52 ,mr4 ,de ,la ,rue has call$ ! photographic plate ! ret9a :i* does n =get1 & an excell5t "n x is4 ,we may pass ov] altoge!r ! ord9>y photographic processes1 :i* h be5 c>ri$ on ) a degree ( skill & pati5ce :i* is beyond all praise1 & conf9e our att5tion exclusively to ! in/rum5tal processes4 ,be x rememb]$1 we h no long] to consid] ! visual rays1 b ! s-call$ *emical rays1 :i* lie at ! violet end ( ! spectrum4 ,we mu/ also recollect t1 9 a =m] *apt]1 we h se5 t ! optician's bus9ess 0 to ?r[ aside ! violet rays altoge!r--to disc>d !m1 c>+ no?+ = !m1 because1 s f> z ! visible =m ( ! objects is conc]n$1 !y help v little4 ,b we %all see 9 a mom5t t1 if we wi% to use refractors = photograph+1 we mu/ aboli% ?is idea1 & undo ev]y?+ we did to get a p]fect telescope to see ! body1 because 9 ! case ( ! photographic processes employ$ at pres5t1 ! visible rays h z little to d ) build+ up ! image on ! photographic plate z ! blue rays h to d ) build+ up ! image on ! ret9a ( ! eye4 ,we %all see pres5tly h[ admirably ?is has be5 done by ,mr4 ,ru!rfurd4 ,if1 h[ev]1 we use reflectors in/ead ( refractors1 we are able to utilize all ! rays by means ( ! same mirror )\t alt]ation1 z ! focus is ! same = all rays1 s t a reflector is equally good = all classes ( obs]vation4 ,let u fir/ consid] ! cases 9 :i* ! plate is made to replace ! ret9a ) ! ord9>y telescope4 ,we %all see 9 ! sequel t :e!r ! spectroscope1 pol>iscope1 or o!r physical in/rum5t be add$ to ! telescope--:5 we pass1 t is to say1 f me*anical to physical a/ronomy--! plate c /ill replace ! eye ) advantage4 ,! body ( ! telescope1 ) ! object-glass or mirror at "o end & ! plate at its focus 9 place ( ! eyepiece1 =ms ! cam]a1 correspond+ to ^? we f9d 9 photographic /udies4 ,! plate-hold] %[n 9 section 9 ! accompany+ figure is !re=e ! only addition requir$ to make a telescope into a cam]a = ord9>y "w4 ,fig4 #bjh4 ,illu/ration3 ,,fig4 #bjh4--,section ( ,plate-hold]4 ,a is a screw ( su* a size t x c be ins]t$ into ! eyepiece end ( ! telescope2 ! s5sitive plate is held betwe5 a lid at ! back1 :i* op5s = ! plate to be ins]t$1 & a slide 9 front1 :i* is drawn out s z to expose ! face ( ! plate to ! object4 ,a piece ( gr\nd glass ( extreme f95ess is ins]t$ 9 ! slide1 on :i* ! object is focuss$ be=e ! s5sitive plate is put 94 ,x is easy !n by ! eyepiece focuss+-screw to put ?is ne>] or fur!r away f ! object-glass1 s t ! image is ?r[n %>ply on ! gr\nd glass4 ,:5 t is done ! gr\nd glass is tak5 away1 & ! s5sitive plate put !re 9 its place1 & !n expos$ z requir$1 s t ! me?ods are simil> to ! ord9>y photographic process4 ,we h "h an arrangem5t t enables u to photograph ! moon1 />s1 & planets4 ,m4 ,faye has propos$ t = ! transit circle also ! photographic me?od %\ld be appli$1 ! *ronograph regi/]+ ! "t ( ! in/antane\s op5+ ( ! slide1 in/ead ( ! "t ! /> is se5 to transit1 s t ! position ( ! /> ) respect to ! wires is regi/]$ at a c]ta9 kn[n "t2 !re=e1 n only = physical a/ronomy h we ! means ( mak+ obs]vations )\t an obs]v] at all1 b also = position obs]vations4 ,e "o kn[s suffici5t ( photography to be aw>e t1 if we wi% to secure ! image ( a fa9t object1 su* z a fa9t /> or a fa9t "p ( ! moon1 we mu/ expose ! plate = "s little "t1 z we h to d 9 ord9>y photography if ! day is dull1 & !re=e ! l>g] ! ap]ture ( ! telescope ! m light passes2 & ! %ort] ! focus is1 & ! m rapid ! process1 ! %ort] w be ! exposure2 if ! focus is %ort1 ! image w be small2 b z we c magnify ! image aft]w>ds1 rapidity becomes ( great] mom5t1 z ! %ort] ! "t ( exposure is ! less atmosph]ic & o!r di/urbances & errors 9 driv+ ! telescope come into play4 ,/ill1 if we photograph ! moon or o!r object1 we d n wi% to limit ourselves to ! size ( ! orig9al negative obta9$ at ! focus4 ,if ! negative is well def9$--t is1 if x possesses ! quality ( enl>geabl5ess--!re is no difficulty 9 gett+ enl>g$ pr9ts4 ,! me?od ( enl>g+ photographs is v simple2 all t is requir$ is a l>ge cam]a1 ! negative to be copi$ be+ plac$ ne>] ! l5s ?an ! prep>$ pap]1 s t ! image is l>g] ?an ! orig9al4 ,fig4 #bji %[s an enl>g+ cam]a3 ! body1 ,a1 c be made ( wood1 or bett] /ill1 ( a s(t mat]ial1 bell[s-fa%ion1 s t ! l5g? c be alt]$ at pleasure4 ,9 ! end1 at ,b1 is fix$ a l5s--an ord9>y portrait l5s w d1 b a prop] copy+ l5s is pref]able2 & ,e is a piece ( wood ) a hole 9 its c5tre1 ov] :i* ! negative is plac$1 ! di/ance ( ,e to ,b be+ also adju/ible2 !n1 by alt]+ ! l5g?s ( ,b ,e & ,b ,c1 ! image ( ! negative c be made to appe> ( suitable size4 ,at ! end1 ,c1 a piece ( s5sitive pap] is plac$1 & ! light ( ! sun be+ all[$ to fall ?r\gh ! negative & l5s1 ! pap] soon becomes pr9t$1 & c be ton$ & fix$ z an ord9>y pap] positive4 ,! cam]a may be c>ri$ on a r\gh equatorial m\nt+1 consi/+ ( an axis po9t+ to ! pole1 & pull$ r\nd ) ! sun by atta*+ a /r+ to an equatorial telescope1 mov$ by clockwork2 or a helio/at c be us$ ) m advantage1 !reby all[+ ! cam]a to be /ation>y2 a good enl>g+ l5s is a v desirable ?+1 = mo/ l5ses seem to di/ort ! image consid]ably4 ,illu/ration3 ,,fig4 #bji4--;,enl>g+ ,cam]a4 ,f1 helio/at = ?r[+ beam ( sunlight on ! reflector1 :i* ?r[s x into ! cam]a2 ,e1 negative2 ,b1 focuss+-l5s2 ,c1 plate- or pap]-hold]2 ,d1 focuss+-screw4 ,if we wi% to obta9 a l>ge direct image ( ! moon1 we mu/1 z said be=e1 employ a telescope ( z long a focal l5g? z possible2 = reasons j m5tion$1 ?is is n always desirable4 ,if1 h[ev]1 l>ge images c be obta9$ z good z small ones1 !y c ( c\rse be enl>g$ to a mu* great] size4 ,! prim>y image ( ! moon tak5 by ,mr4 ,de ,la ,rue's exquisite reflector is n q an in* 9 diamet]4 ,9 "o ( ,mr4 ,ru!rfurd's telescopes ( fifte5 feet focus1 ! image ( ! moon is some:at l>g]--ab\t "o & a half in* 9 diamet]4 ,9 ,mr4 ,newall's magnific5t refractor1 ! focal l5g? ( :i* is ?irty feet1 ! diamet] is ov] ?ree in*es4 ,9 ! ,melb\rne reflector ! image obta9$ is l>g] /ill4 ,9 cele/ial photography we h n only to deal ) fa9t objects4 ,) ! sun ! difficulty is ( no ord9>y "* 9 ! opposite direction1 because ! light is s p[]ful t we h to get rid ( x4 ,n[ !re are two me?ods ( do+ ?is1 & z 9 a fa9t object we get m light by increas+ ! ap]ture1 s ) a bright light l t ( ! sun we c get rid ( a l>ge am\nt ( x by r$uc+ ! ap]ture ( our telescope2 b x is f\nd bett] to r$uce inf9itesimally ! "t ( exposure1 & me?ods h be5 adopt$ by :i* t has be5 br\ght d[n to ! "o-hundr$? "p ( a second4 ,let u %[ ! simple way 9 :i* ?is c be done by ! means ( an addition to an ord9>y plate-hold]4 ,fig4 #bjh %[s ! ord9>y plate-hold]1 l ^? us$ g5]ally = photography4 ,:at is t]m$ ! in/antane\s slide1 ,b1 ,fig4 #baj1 consi/s ( a plate ) an adju/ible slit 9 x ins]t$ betwe5 ! object itself & ! focus4 ,?is c be drawn rapidly across ! pa? ( ! rays by means ( a spr+1 ,d2 we c br+ x to "o side1 & fix x by a piece ( cotton1 ,e1 & !n we c release x by burn+ ! cotton1 :5 ! spr+ draws x rapidly across4 ,! velocity ( ! ru% ( ! ap]ture across ! plate1 & ! "t ( exposure1 c be det]m9$ by ! /r5g? ( ! spr+ & ! ap]ture ( ! slit4 ,if ! velocity is too great1 we c alt] ! size ( ! slit1 ,c4 ,if we absorb "s ( ! sup]abundant light by means ( yell[ glass1 or "s simil> mat]ial1 we c keep ! op5+ wide en\gh to prev5t any bad effects ( diffraction com+ into play4 ,illu/ration3 ,,fig4 #baj4--;,in/antane\s ,%utt]4 ,! light ( ! sun is s int5se t ano!r me?od may be employ$4 ,in/ead ( hav+ ! plate at ! focus ( ! object-glass we may introduce a second>y magnifi] 9 ! telescope itself1 & ?us obta9 an enl>g$ image1 ! "t necess>y = its production be+ /ill s %ort 7#a_/ej? ( a second7 t no?+ is lo/ f ! di/urbances ( ! air4 ,a telescope ) ?is addition is call$ a photoheliograph4 ,! fir/ in/rum5t ( ?is k9d 0 devis$ by ,mr4 ,de ,la ,rue1 & = _m ye>s 0 regul>ly employ$ 9 tak+ photographs ( ! sun at ,kew4 ,illu/ration3 ,,fig4 #baa4--,photoheliograph z erect$ 9 a ,tempor>y ,obs]vatory = ,photograph+ ! ,transit ( ,v5us 9 #ahgd4 ,"s a/ronom]s object to ?is second>y magnifi]1 & to obta9 l>ge images use v long focal l5g?s1 & ( c\rse a sid]o/at is employ$4 ,9 ?is way ,pr(essor ,w9lock obta9$ photographs ( ! sun :i* h surpass$ ! limits ( ,mr4 ,newall's refractor2 ! negatives h a good def9ition1 & %[ a consid]able am\nt ( detail ab\t ! spots2 !y 7 tak5 by a l5s1 ins]t$ at ! end ( a gas-pipe =ty feet long4 ,! pipe 0 fix$ 9 a horizontal position1 fac+ ! nor?1 & at ! extreme nor? "p ( x 0 ! l5s1 a s+le "o ( cr[n glass1 ) no attempt to correct x4 ,9 front ( x 0 a sid]o/at1 mov$ by a clock1 reflect+ ! light d[n ! tube1 s t ! image ( ! sun c\ld be focuss$ on ! gr\nd glass at ! opposite end4 ,"o w see ! importance ( %ort5+ ! "t = ev5 ! brighte/ object4 ,^? :o are fav\r$ ) _m opportunities ( look+ ?r\gh l>ge telescopes "k t ! great difficulty we h to deal ) is ! atmosph]e2 because we h to wait = def9ition1 & ! sum total ( ! photograph ( any "o p>ticul> ?+ dep5ds ^u ^! atmosph]ic fits4 ,if we require to photograph an object1 x w be obvi\s t ! m fits we h1 ! worse x w be1 because we get a numb] ( images p>tially sup]pos$ :i* w\ld o!rwise give z good an effect z we c\ld get by an ord9>y eye obs]vation4 ,x is !re=e mo/ important to r$uce ! int]val z mu* z possible4 ,,*apt] ,,xxxii4 ,,cele/ial ,,photography 7,,cont9u$74--,,"s ,,results4 ,! process us$ %\ld !re=e be ! mo/ rapid atta9able2 any "w on photography w give a numb] ( processes ( diff]5t degrees ( rapidity1 b a process t suits "o p]son's manipulation may prove a failure 9 ano!r's1 & ! g5]al pr9ciples are ! only rules suitable = all4 ,fir/1 ! glass plate %\ld be c>efully clean$1 ! collodion lightly col\r$1 ! ba? /rong & neutral1 c]ta9ly n acid1 & ! develop] fairly /rong4 ,pyrogallic acid & silv] %\ld n be us$ = int5sify+2 a good int5sifi] is made by add+ to a solution ( iodide ( potassium1 /r5g? "o gra9 to ! ounce ( wat]1 a saturat$ solution ( bi*loride ( m]cury1 drop by drop1 until ! precipitate at fir/ =m$ ceases to be re-dissolv$2 use ?is aft] fix+4 ,n[ let u inquire :at has be5 done by ?is important adjunct to ord9>y means ( obs]v+4 ,we may say t cele/ial photography 0 f\nd$ 9 ! ye> #ahej by ,pr(essor ,bond1 :o obta9$ a dagu]reotype ( ! moon ab\t t date4 ,an imm5se advance has be5 made1 b n s great z !re might h be5 if ! true importance ( ! me?od _h be5 recogniz$ z x ought to h be52 & if we /udy ! hi/ory ( ! subject we f9d t till )9 ! la/ few ye>s we h to limit ourselves to ! works ( two m5 :o1 aft] ,bond1 set ! "w roll+4 ,sev]al obs]v]s took x up = a "t2 b ! "w requires mu* bo? ( "t & money1 & diff]5t m5 dropp$ (f f "t to "t4 ,!re rema9$ always /eadfa/ "o ,engli%man & "o ,am]ican--,mr4 ,de ,la ,rue & ,mr4 ,ru!rfurd4 ,! magnific5t "w ,mr4 ,de ,la ,rue has done 0 begun 9 #aheb4 ,he 0 s anxi\s to see :e!r ,engl& c\ld n d some?+ simil> to :at _h be5 done 9 ,am]ica1 t1 )\t wait+ = a driv+ clock1 he ?\ght he w\ld see :e!r photographs ( ! moon c\ld be tak5 by mov+ ! telescope by h&4 ,he soon f\nd t he 0 work+ aga9/ nature--t nature refus$ to be woo$ 9 ?is way2 ! moon 9 q a decid$ mann] decl9$ to be photograph$1 & we wait$ five ye>s till ,mr4 ,de ,la ,rue 0 arm$ ) a p]fect driv+ clock4 ,mr4 ,ru!rfurd 0 wait+ = ! same ?+ 9 ,am]ica4 ,at la/1 9 #aheg1 ,mr4 ,de ,la ,rue got a driv+ clock to 8 reflector ( ?irte5 in*es ap]ture1 & began ^? admirable photographs ( ! moon :i* are n[ s well kn[n4 ,s9ce ! above date ! moon has be5 photograph$ times )\t numb]1 & ,mr4 ,de ,la ,rue has made a s]ies :i* %[s ! moon 9 all h] diff]5t phases4 ,!y are rem>kable = ! beautiful way 9 :i* ! details come out 9 all p>ts ( ! surface4 ,we mu/ recollect t ^! pictures ( :i* we h spok51 "s ( !m a y>d 9 diamet]1 7 fir/ tak5 on glass ab\t ?ree in*es across1 ! image cov]+ ! c5tral in*4 ,at ! same "t ! ,briti% ,association grant$ funds = ! photographic regi/ration ( sun-spots at ! ,kew ,obs]vatory1 :]e ! sun 0 photograph$ e day = _m ye>s4 ,enc\rag$ by success1 ,mr4 ,de ,la ,rue1 9 #aheh1 attack$ ! planets ,jupit] & ,saturn1 & "s ( ! />s4 ,he discov]$ t photographs ( ! moon c be comb9$ 9 ! /]eoscope s t ! moon %[s itself p]fectly globul>4 ,to accompli% ?is result x 0 necess>y to photograph h] at diff]5t epo*s1 s t ! libration1 :i* gives x ! appe>ance ( be+ turn$ r\nd slightly & look+ z x w\ld d to a p]son sev]al ?\s& miles to ! "r or left ( ! telescope1 %\ld be utiliz$4 ,^! two views :5 comb9$ give ! appe>ance ( solidity j z ! image ( a ne> object comb9$ by ! two eyes gives t appe>ance4 ,! reason ( ?is appe>ance ( solidity is easily se5 by look+ at an orange or ball fir/ ) "o eye & !n ) ! o!r1 :5 x is notic$ t ea* eye sees a little m ( "o side ?an ! o!r2 & x is ! comb9ation ( ^! slightly dissimil> images t gives ! solid appe>ance4 ,if we exam9e two ( ^! photographs comb9$ = ! /]eoscope1 we see t !y h ! appe>ance ( be+ tak5 f two /ations a long di/ance ap>t4 ,"o %[s a little m ( ! surface on "o side ?an ! o!r4 ,!y are obta9$ 9 diff]5t lunations1 :5 ! moon1 9 ! same phase1 has turn$ h]self slightly r\nd1 %[+ m ( "o side4 ,9 ?is way we h a di/9ct effect due to libration4 ,9 ! ye> #ahei ,mr4 ,de ,la ,rue f\nd t sun-pictures c\ld be comb9$ /]eoscopically 9 ! same mann]4 ,:5 we turn to ! lab\rs ( ,mr4 ,ru!rfurd1 we f9d him 9 #aheg arm$ ) a refractor ( #aa in*es ap]ture2 ! act9ic focus1 or r ! ne>e/ approa* to a focus1 0 #g_/aj?s ( an in* f ! visual focus4 ,) ?is telescope1 )\t any correction :atev]1 he1 9 #aheg & #aheh1 obta9$ photographs ( ! moon :i*1 :5 enl>g$ to five in*es 9 diamet]1 7 well def9$4 ,he also obta9$ impressions ( />s d[n to z f> z ! fif? magnitude1 & also ( d\ble />s "s #c ap>t--= in/ance1 ,virg9is 0 photograph$ d\ble4 ,! r+ ( ,saturn & belts ( ,jupit] 7 also pla9ly visible1 b ill-def9$4 ,! satellites ( ,jupit] fail$ to give an image ) any exposure1 :ile _! prim>y did s 9 five or t5 seconds4 ,! act9ic rays1 in/ead ( com+ to a po9t & produc+ an image ( a satellite1 7 spread ov] a c]ta9 area & !reby r5d]$ too weak to impress ! plate4 ,9 ! summ] ( #aheh ,mr4 ,ru!rfurd comb9$ 8 fir/ /]eograph ( ! moon indep5d5tly ( ,mr4 ,de ,la ,rue's success 9 ,engl&4 ,mr4 ,ru!rfurd !n comm5c$ an inquiry ( ! greate/ importance1 :i* w 9 "t br+ ab\t a revolution 9 ! processes employ$4 ,9 #ahei he attempt$1 by plac+ l5ses ( diff]5t curvatures betwe5 ! object-glass & ! focus1 to br+ ! *emical rays toge!r1 leav+ ! visual rays out ( ! "q2 ?is _h ! effect ( %ort5+ ! focus consid]ably & improv+ ! photographs2 b he f\nd t1 except = ! middle ( ! field1 ?is me?od w\ld n answ]4 ,he !re=e 9 #ahfj attempt$ ano!r arrangem5t1 & "o :i* he f\nd answ]$ extremely well = %ort telescopes4 ,betwe5 ! l5ses ( ! object-glass ( a #d-;in* refractor he put a r+ :i* sep>at$ ! l5ses by ?ree-qu>t]s ( an in*1 & r$uc$ ! p[] ( ! fl9t-glass l5s1 :i* corrects ! cr[n-glass = col\r1 s t ! comb9ation became a*romatic = ! violet rays in/ead ( = ! yell[4 ,) ?is l5s he 0 successful to a c]ta9 ext5t3 he obta9$ ev5 bett] results ?an ) ! #aa in*2 b ev5tually he reject$ ?is me?od1 :i* we may add has rec5tly be5 te/$ by ,m4 ,cornu1 :o ?9ks v highly ( x4 ,he next attempt$ a silv]-on-glass mirror 9 #ahfa2 9 ! atmosph]e ( ,new ,york x only la/$ t5 days2 he gave x up2 & he !n v bravely1 9 #ahfd1 attack$ ! project de novo1 & began an object-glass ( a telescope :i* %\ld be con/ruct$ s z to give be/ def9ition ) ! act9ic rays1 j z ord9>y object-glasses are made to act be/ ) ! visual rays4 ,he f\nd t 9 ord] to br+ ! act9ic portion ( ! rays to a p]fect focus1 x 0 necess>y t a giv5 cr[n-glass l5s %\ld be comb9$ ) a fl9t1 :i* w produce a comb9$ focal l5g? ( ab\t %ort] ?an w\ld be requir$ to satisfy ! conditions ( a*romatism = ! eye4 ,?is comb9ation 0 ( c\rse absolutely wor?less = ord9>y visual obs]vation2 8 new l5s :5 f9i%$ 0 #aa in*es ap]ture & a little less ?an #ad feet focal l5g?4 ,) ?is he obta9$ impressions ( n9? magnitude />s1 & )9 ! area ( a squ>e degree 9 ! ,prsepe 9 ,canc] tw5ty-?ree />s 7 photograph$ 9 ?ree m9utes' exposure4 ,ca/or gave a /rong impression 9 "o second1 & />s ( #b di/ance %[$ z d\ble4 ,b ev5 ) ?is me?od ,mr4 ,ru!rfurd 0 n satisfi$4 ,com+ back to ! #aa-;in* object-glass :i* he _h us$ at fir/1 he det]m9$ to see :e!r or n ! addition ( a m5iscus l5s outside ! front l5s w\ld n give him ! requisite %ortness ( ! focus & br+ ! act9ic rays absolutely toge!r4 ,by ?is arrangem5t he got a telescope :i* c be us$ = all purposes ( a/ronomical rese>*1 & he has also eclips$ all 8 =m] photographic ef=ts4 ,,*apt] ,,xxxiii4 ,,cele/ial ,,photography 7,,cont9u$7--,,rec5t ,,results4 ,hav+ 9 ! previ\s *apt] dealt ) "s ( ! pione] "w1 we come f9ally to consid] "s ( ! applications :i* 9 ! la/ ye>s h occupi$ mo/ att5tion4 ,) reg>d to ! sun1 we ne$ sc>cely say t ,messrs4 ,de ,la ,rue & ,/ew>t h be5 enabl$1 by ! photographic me?od1 to give u data ( a mo/ rem>kable "*1 %[+ ! p]iodicity ( ! *anges on ! sun's surface1 & s e/abli%+ _! correlation ) magnetic & o!r physical ph5om5a4 ,^! photographic rese>*es1 foll[+ ^u ! eye obs]vations ( ,s*wabe1 ,spr]1 ,c>r+ton & o!rs1 h op5$ up to u a new field ( inquiry 9 connection ) ! meteorology ( ! globe2 & x is satisfactory to le>n t photoheliographs are n[ daily at "w at ,gre5wi*1 ,p>is1 ,potsdam1 & ! ,mauritius1 & t %ortly ,india w be includ$ 9 ! li/4 ,q rec5tly1 ! importance ( ^! p]man5t records ( ! sol> surface has be5 demon/rat$ by ,dr4 ,janss51 ! di/+ui%$ director ( ! ,physical ,obs]vatory at ,meudon1 9 a v rem>kable mann]4 ,x seems a p>adox t discov]ies c be made dep5d+ on ! appe>ance ( ! sun's surface by obs]vations 9 :i* ! eye appli$ to ! telescope is p[]less2 b ?is is ! /atem5t made by ,dr4 ,janss5 himself1 & !re is little d\bt t he has prov$ 8 po9t4 ,be=e we come to ! discov]y itself let u say a little conc]n+ ,dr4 ,janss5's rec5t endeav\rs4 ,among ! six l>ge telescopes :i* n[ =m a "p ( ! equipm5t ( ! new ,physical ,obs]vatory rec5tly e/abli%$ by ! ,fr5* gov]nm5t at ,meudon1 9 ! gr\nds ( ! pr9cely ,*ateau !re1 is "o to :i* ,dr4 ,janss5 has rec5tly almo/ exclusively conf9$ 8 att5tion4 ,x is a photoheliograph giv+ images ( ! sun on an enorm\s scale--comp>$ ) :i* ! pictures obta9$ by ! ,kew photoheliograph are1 s to speak1 pigmies1 :ile ! p]fection ( ! image & ! photographic processes employ$ are s exquisite1 t ! f9e/ mottl+ on ! sun's surface _c be ov]look$ by ^? ev5 :o are pr(\ndly ignorant ( ! int]e/ :i* atta*es to x4 ,?is p]fection ( size & image h be5 obta9$ by ,dr4 ,janss5 by comb9+ all t is be/ 9 ! pr9ciples utilis$ 9 "o direction by ,mr4 ,de ,la ,rue1 & 9 ! o!r by ,mr4 ,ru!rfurd1 to :i* we h be=e ref]r$4 ,9 ! ,kew photoheliograph1 :i* has done su* noble "w 9 its day t x w be reg>d$ ) ! utmo/ v5]ation 9 ! future1 we h fir/ a small object-glass correct$ aft] ! mann] ( photographic l5ses1 s z to make ! s-call$ act9ic & ! visual rays co9cide1 & !n ! image =m$ by ?is l5s is enl>g$ by a second>y magnifi] con/ruct$1 ?\gh p]haps n too accurately1 s z to make ! act9ic & visual rays unite 9 a second image on a prep>$ plate4 ,mr4 ,ru!rfurd's beautiful photographs ( ! sun 7 obta9$ 9 a some:at diff]5t mann]4 ,9 8 object-glass1 z we h se51 he disc>d$ ! visual rays altoge!r & br\ght only ! blue rays to a focus1 b :5 enl>gem5ts 7 made1 an ord9>y photographic l5s--t is1 "o 9 :i* ! blue & yell[ rays are made to co9cide--0 us$4 ,dr4 ,janss5 uses a second>y magnifi]1 b ) ! assi/ance ( ,m4 ,pragm[ski he has tak5 c>e t bo? x & ! object-glass are effective only = ^? rays :i* are mo/ /rongly photographic4 ,nor is ?is all2 he has n fe>$ l>gely to increase ! ap]ture & focal l5g?1 s t ! total l5g? ( ! ,kew in/rum5t is less ?an "o-?ird ( t 9 op]ation 9 ,p>is4 ,! l>gely-increas$ ap]ture :i* ,dr4 ,janss5 has giv5 to 8 in/rum5t is a po9t ( great importance4 ,9 ! e>ly days ( sol> photography ! ap]ture us$ 0 small1 9 ord] to prev5t ov]-exposure4 ,x 0 soon f\nd t ?is small ap]ture1 z 0 to be expect$1 produc$ poor images 9 consequ5ce ( ! diffraction effects br\ght ab\t by x4 ,x !n became a "q ( increas+ ! ap]ture :ile ! exposure 0 r$uc$1 & _m =ms ( in/antane\s %utt]s h be5 sugge/$ ) ?is end 9 view4 ,) ^!1 if a spr+ be us$1 ! n>r[ slit :i* fla%es across ! beam to pay ! light out into ! plate *anges its velocity dur+ its passage z ! t5sion ( ! spr+ *anges4 ,( ?is aga9 ,dr4 ,janss5 has n be5 unm9dful1 & he has inv5t$ a contrivance 9 :i* ! velocity is con/ant dur+ ! :ole l5g? ( run ( ! %utt]4 ,by ^! v>i\s arrangem5ts ! plates h n[ be5 produc$ at ,meudon ( fifte5 in*es diamet]1 %[+ details on ! sun's surface subt5d+ an angle ( less ?an "o second ( arc4 ,s mu* = ! modus op]&i4 ,n[ = ! bran* ( sol> "w :i* has be5 advanc$4 ,x is m ?an fifte5 ye>s ago s9ce ! "q ( ! m9ute /ructure ( ! sol> photosph]e 0 "o ( ! que/ions ( ! day4 ,! s-call$ 8mottl+0 _h long be5 obs]v$4 ,! ke5-ey$ ,dawes _h po9t$ out ! ?at*-l =mation ( ! p5umbra ( spots1 :5 "o day ,mr4 ,nasmy? ann\nc$ ! discov]y t ! :ole sun 0 cov]$ ) objects resembl+ will[-leaves1 mo/ /rangely & effectively int]lac$4 ,we may sum up ! "w ( _m c>eful obs]v]s s9ce t "t by /at+ t ! mottl+ on ! sun's surface is due to dome-l masses1 & t ! 8?at*0 ( ! p5umbra is due to ^! dome-l masses be+ drawn1 ei!r directly or 9 ! mann] ( a cyclone1 t[>ds ! c5tre ( ! spot4 ,9 fact ! 8pores0 9 ! int]val betwe5 ! domes are s _m small spots1 :ile ! facul are ! high] levels ( ! cl\dy surface4 ,! fact t facul are s mu* bett] se5 ne> ! limb proves t ! absorption ( ! sol> atmosph]e rapidly *anges betwe5 ! levels rea*$ by ! upp] facul & ! pores4 ,?us mu* premis$1 we n[ come to ,dr4 ,janss5's discov]y4 ,an att5tive exam9ation ( 8 photographs %[s t ! surface ( ! photosph]e has n a con/itution uni=m 9 all its p>ts1 b t x is divid$ into a s]ies ( figures m or less di/ant f ea* o!r1 & pres5t+ a peculi> con/itution4 ,^! figures h cont\rs m or less r\nd$1 (t5 v rectil9e>1 & g5]ally resembl+ polygons4 ,! dim5sions ( ^! figures are v v>iable2 !y atta9 sometimes a m9ute & m 9 diamet]4 ,:ile 9 ! int]ior ( ! figures ( :i* we speak ! gra9s are cle>1 di/9ctly t]m9at$1 al?\gh ( v v>iable size1 9 ! b\nd>y ! gra9s are z if half effac$1 /ret*$1 /a9$2 = ! mo/ "p1 inde$1 !y h disappe>$ to make way = tra9s ( matt] :i* h replac$ ! granulation4 ,ev]y?+ indicates t 9 ^! spaces1 z 9 ! p5umbr ( spots1 ! photosph]ic matt] is submitt$ to viol5t movem5ts :i* h confus$ ! granul> elem5ts4 ,we h already ref]r$ to ! p>adox t ! sun's appe>ance c n[ be be/ /udi$ )\t ! eye appli$ to ! telescope4 ,?is is :at ,dr4 ,janss5 says on t po9t4 8,! photosph]ic network _c be discov]$ by optical me?ods appli$ directly to ! sun4 ,9 fact1 to asc]ta9 x f ! plate1 x is necess>y to employ glasses :i* enabl$ u to embrace a c]ta9 ext5t ( ! photographic image4 ,!n if ! magnify+ p[] is q suitable1 if ! pro( is q pure1 & especially if x has receiv$ rigor\sly ! prop] exposure1 x w be se5 t ! granulation has n ev]y:]e ! same di/9ctness2 t ! p>ts consi/+ ( well-=m$ gra9s appe> z curr5ts :i* circulate s z to circumscribe spaces :]e ! ph5om5a pres5t ! aspect we h describ$4 ,b to e/abli% ?is fact1 x is necess>y to embrace a consid]able portion ( ! sol> disc1 & x is ?is :i* x is impossible to realise :5 we look at ! sun 9 a v p[]ful in/rum5t1 ! field ( :i* is1 by ! v fact ( its p[]1 v small4 ,9 ^! conditions we may v easily conclude t !re exi/ portions :]e ! granulation ceases to be di/9ct or ev5 visible2 b x is impossible to suppose t ?is fact is connect$ ) a g5]al sy/em40 ,b x is n alone ) ! uneclips$ sun t ! new me?od enables u to make discov]ies4 ,! extreme importance ( photography 9 ref]5ce to eclipse obs]vations _c be ov] e/imat$4 ,mo/ ( our be/ obs]vations ( eclipses h be5 wr\ght by means ( photography4 ,! "t ( an eclipse is an excit+ "t to a/ronom]s2 & x is important t we %\ld h "s me*anical op]ation :i* %\ld n fail to record x4 ,illu/ration3 ,,fig4 #bab4--;,copy ( ,photograph tak5 dur+ ! ,eclipse ( #ahfi4 ,! fir/ eclipse photograph 0 tak5 9 #ahea4 ,9 #ahfj1 *iefly ow+ to ! lab\rs ( ,mr4 ,de ,la ,rue1 our k 0 enorm\sly increas$4 ,! ,kew photoheliograph 0 ! in/rum5t us$1 & ! s]ies ( pictures obta9$ %[$ conclusively t ! prom95ces belong$ to ! sun4 ,9 #ahfh ! prom95ces 7 aga9 photograph$4 ,9 #ahfi ! ,am]icans attack$ ! corona1 & _! sugge/ion t ! base ( x 0 truly sol> has be5 confirm$ by o!r photographs tak5 9 #ahgj1 #ahga1 & #ahge4 ,al?\gh to ! eye ! ph5om5a *ang$ f place to place1 to ! cam]a x 0 ev]y:]e ! same ) ! same duration ( exposure4 99 99 99 99 99 ,x is n to be wond]$ at1 !n1 t on ! occasion ( ! la/ transit ( ,v5us1 :i* may be reg>d$ z a p>tial eclipse ( ! sun1 photography 0 sugge/$ z a means ( record+ ! ph5om5a4 ,sci5ce is l>gely indebt$ to ,dr4 ,janss51 ,mr4 ,de ,la ,rue1 & o!rs = br++ cele/ial photography to aid u 9 ?is bran* ( "w also4 ,:ile on ! "o h& a/ronom]s h to deal ) preci\s mom5ts1 to d v mu* 9 v little "t1 9 circum/ances ( great excitem5t2 ! photograph] on ! o!r goes on quietly prep>+ & expos+ 8 plates1 & not+ ! "t ( ! exposure1 & ?us c make ! :ole "t tak5 by ! planet 9 its transit ov] ! sun's disc "o enorm\s base l9e4 ,8 micrometrical measures ( ! position ( ! planet on ! sun's disc c be made aft] all is ov]4 ,x 0 sugge/$ by ,dr4 ,janss5 t a circul> plate ( suffici5t size to conta9 sixty photographs ( ! limb ( ! sun1 at ! po9ts at :i* ,v5us ent]$ & left x c\ld be mov$ on /ep by /ep r\nd its c5tre1 & s expose a fre% surface to ! sun's image focuss$ on x1 say e second4 ,9 ?is way ! ph5om5a ( ! transit 7 actually record$ at sev]al /ations4 99 99 99 99 99 ,illu/ration3 ,,fig4 #bac4--,"p ( ,be] & ,mdl]'s ,map ( ! ,moon4 ,) ref]5ce to ! moon1 we h said en\gh to %[ t if we wi% to map h] correctly1 x is n[ no long] necess>y to dep5d on ord9>y eye obs]vations alone2 x is p]fectly cle> t by means ( an image ( ! moon1 tak5 by photography1 we are able to fix _m po9ts on ! lun> surface4 ,/ill1 al?\gh we c ?us fix ^! & use !m z s _m po9ts ( ! fir/ ord]1 z "o might say1 9 a triangulation1 !re is mu* t photography _c d2 ! "w ( ! eye obs]v] w\ld be ess5tial 9 fill+ 9 ! details & giv+ ! cont\r l9es requir$ to make a map ( ! moon4 ,! accompany+ draw+s on ! same scale %[ t up to ! pres5t1 = m9ute "w1 ! eye beats ! cam]a4 ,illu/ration3 ,,fig4 #bad4--,! same ,region copi$ f a ,photograph by ,de ,la ,rue4 ,! light ( ! moon is s feeble 9 blue rays t a long exposure is necess>y = a l>ge image1 & dur+ ! exposure all ! errors 9 ! rate ( ! clock are magnifi$4 ,we ne$ n enl>ge on ! extreme importance ( :at ,mr4 ,ru!rfurd has be5 do+ 9 photograph+ /> clu/]s & /> gr\ps4 ,x is d\bly important to a/ronomy1 & />ts a new mode ( us+ ! equatorial & ! clock2 9 fact1 x gives u a me?od by :i* obs]vations may be photographically made ( ! prop] motion ( />s1 & ev5 ! p>allax ( />s may be ?us det]m9$ indep5d5tly ( any errors ( obs]v]s4 ,mr4 ,ru!rfurd %[s t ! places ( />s c be measur$ by a micromet] on a plate 9 ! same way z by ord9>y obs]vation2 h5ce photography c be made use ( 9 ! measurem5t ( position & di/ance ( d\ble />s4 ,z an in/ance ( ! extreme beauty ( ! photographs ( />s produc$ by a prop] in/rum5t1 x may be /at$ t ) ! full ap]ture ( ! #aa-;in* object-glass correct$ only = ! ord9>y rays1 ,mr4 ,ru!rfurd f\nd t he requir$ an exposure ( m ?an t5 seconds to get an image ( ! bright /> ,ca/or2 b n[1 in/ead ( requir+ t5 seconds1 he c get a bett] image 9 "o4 ,! reason ( ?is is1 t1 ) ! object-glass correct$ only = ! visual rays1 ! *emical ones are spread ov] a c]ta9 small area in/ead ( com+ to a po9t1 & s1 ( c\rse1 ! int5sity is r$uc$2 b :5 ! *emical rays all come to "o po9t ! int5sity is great]1 s9ce ! image ( ! /> is small] & ! action m int5se4 ,let u foll[ ,mr4 ,ru!rfurd a little 9 8 actual "w4 ,fir/1 a wet plate is expos$ = f\r m9utes4 ,?is gives />s d[n to ! t5? magnitude4 ,b !re may be po9ts on ! plate :i* are n />s1 h5ce a second impression is tak5 on ! same plate aft] x has be5 slightly mov$4 ,all po9ts n[ d\bl$ are true />s4 ,n[ = measures ( arc4 ,ano!r photograph is tak51 & ! driv+ clock is /opp$2 ! n[ mov+ />s d[n to ! f\r? magnitude are bright en\gh to leave a cont9u\s l9e1 ! l5g? ( ?is 9 a v accurately kn[n int]val1 say two m9utes1 enables ! arc to be calculat$4 ,next comes ! mapp+4 ,! negative is fix$ on a horizontal divid$ circle on glass illum9at$ f bel[4 ,above x is a sy/em ( two rails1 along :i* travels a c>ri] ) two microscopes1 magnify+ fifty diamet]s4 ,by ! "o 9 ! c5tre1 ) two cross wires 9 ! field ( view1 ! photograph is obs]v$2 by ! o!r1 arm$ ) a wire micromet]1 a divid$ scale on glass :i* is fix$ alongside ! rail is read4 ,suppose we wi% to measure ! di/ance betwe5 two />s on ! plate4 ,! plate is rotat$1 s t ! l9e :i* jo9s !m co9cides ) t :i* is describ$ by ! optical axis ( ! c5tral microscope m>k$ by ! cross wires :5 ! c>ri] runs along ! rails4 ,?is microscope is !n br\ght successively ov] ! two />s1 & ! o!r microscope ov] ! scale reads ! ne>e/ division1 :ile ! fractions are measur$ by ! micromet]4 ,h5ce1 !n1 ! fix$ scale1 & n a micromet] screw1 is dep5d$ ^u = ! complete di/ance4 ,9 ?is way ! di/ance betwe5 ! />s on ! plate c be measur$ to ! #a_/ejj "p ( a millimetre4 99 99 99 99 99 ,s f> !n we h %[n h[ photography has be5 call$ 9 to ! aid ( ! a/ronom]1 & h[1 by means ( photography1 pictures ( ! diff]5t cele/ial bodies h be5 obta9$ ( surpass+ excell5ce4 ,n[1 photography is also ! h&maid5 to ! spectroscope 9 ! same way z x is ! h&maid5 to ! telescope4 ,n only are we able to det]m9e & regi/] ! appe>ance ( ! moon & planets1 b1 day by day1 or h\r by h\r1 we c photograph a l>ge portion ( ! sol> spectrum2 & n only s1 b ! spectrum ( diff]5t portions ( ! sun3 nay1 ev5 ! prom95ces h be5 photograph$ 9 ! same mann]2 :ile m rec5tly /ill1 ,drs4 ,hugg9s & ,drap] h succe$$ 9 photograph+ ! spectrum ( "s ( ! />s4 ,we owe ! fir/ spectrum ( ! sun1 %[+ ! v>i\s l9es1 to ,becqu]el & ,drap]2 ! f9e/ hi!rto publi%$ we owe to ,mr4 ,ru!rfurd4 ,illu/ration3 ,,fig4 #bae4--;,comp>ison betwe5 ,kir*h(f's ,map & ,ru!rfurd's ,photograph4 ,?is magnific5t spectrum ext5ds f ! gre5 "p ( ! spectrum "r into t "p ( ! spectrum call$ ! ultra-violet4 ,( c\rse x _h to be put toge!r f diff]5t pictures1 because !re is a diff]5t l5g? ( exposure requir$ = ! diff]5t p>ts2 ! exposure ( any p>ticul> "p ( ! spectrum mu/ be v>i$ accord+ to ! am\nt ( *emical int5sity 9 t "p4 ,if ! l9e ,g 0 expos$1 say = fifte5 seconds1 ! spectrum ne> ! l9e ,f w\ld require to be expos$ = eight m9utes1 & at ! l9e ,h1 :i* is fur!r away f ! lum9\s "p ( ! spectrum ?an ,g1 !re ! exposure requisite w\ld be two or ?ree m9utes4 ,illu/ration3 ,,fig4 #baf4--;,arrangem5t = ,photographically ,det]m9+ ! ,co9cid5ce ( ,sol> & ,metallic ,l9es4 ,illu/ration3 ,,fig4 #bag4--,telespectroscope ) ,cam]a = obta9+ ,photographs ( ! ,sol> ,prom95ces4 ,9 ord] to obta9 a photograph ( ! av]age sol> spectrum1 ! cam]a replaces ! obs]v+ telescope1 & a helio/at is us$1 z 9 ! ord9>y way4 ,! beam1 h[ev]1 %\ld be s5t ?r\gh an op]a-glass 9 ord] to cond5se x1 & !reby to r5d] ! exposure z %ort z possible4 ,fur!r1 if an electric lamp be m\nt$ z %[n 9 ,fig4 #baf1 obs]vations1 simil> to ^? orig9ally made by ,kir*h(f1 ( ! co9cid5ce on ! v>i\s metallic l9es ) ! ,fraunh(] ones1 c be p]man5tly record$ on ! photographic plate4 ,! l5s betwe5 ! lamp & ! helio/at is = ! purpose ( ?r[+ an image ( ! sun betwe5 ! c>bon poles4 ,! l5s betwe5 ! lamp & spectroscope !n focuses bo? ! poles & ! image ( ! sun on to ! slit4 ,! spectrum ( ! sun is fir/ obta9$ by uncov]+ a small "p ( ! slit & all[+ ! image ( ! sun to fall on ?is uncov]$ portion1 ! lamp n be+ 9 action4 ,:5 ?is has be5 done ! light ( ! sun is %ut (f4 ,! metal to be /udi$ is plac$ 9 ! l[] pole2 ! adjac5t portion ( ! slit is uncov]$1 t at fir/ us$ be+ clos$ 9 ! process4 ,! curr5t is !n pass$ to r5d] ! metal inc&esc5t4 ,aft] ! prop] exposure ! plate is develop$ & ! spectra are se5 side by side4 ,fig4 #ahg is a woodcut ( a plate s obta9$4 ,if ! spectrum ( any special "p ( ! sun1 or ! prom95ces1 has to be photograph$1 !n ei!r a sid]o/at mu/ be employ$1 or a cam]a is adju/$ to ! telespectroscope1 z %[n 9 ,fig4 #bag4 ,= ! />s1 ( c\rse1 mu* small] disp]sion mu/ be us$1 b ! me?od is ! same2 & :at has already be5 said by way ( precaution ab\t ! obs]vation ( /ell> spectra applies equally to ! attempt to obta9 spectrum photographs ( ^! di/ant suns4 ,,index4 ,a4 ,ab]ration 7see ,*romatic ,ab]ration1 ,sph]ical ,ab]ration7 ,absorption1 g5]al & selective1 #djc1 #djh2 spectroscope arrang$ = %[+1 #dji ,adju/m5t ( ! transit in/rum5t1 #bch ,,adju/m5ts ,,( ,,! ,,equatorial 7,*ap4 ,,xxi471 #cbh ,a*romaticity ( ,huygh5's eyepiece1 #aaj ,a*romatic l5ses1 #hd1 #hf ,a*romatism1 #abf ,airy's transit circle1 #bhd ,alex&rian ,museum1 a/ronomical obs]vations1 #ai ,alt-azimu?1 #bhg1 #bhi ,altitudes1 in/rum5t us$ by ,ptolemy = measur+1 #ce ,alum9ium1 l9e spectrum (1 #djf2 ! sun1 #dag ,analys] = pol>ization ( light1 #ddc1 #dej ,anaxim&]1 8 !ory ( ! =m ( ! e>?1 #f2 inv5tion ( ! gnomon ascrib$ to him1 #af1 #ag2 m]idian obs]vations by1 #be ,an*or escapem5t1 #aig ,angles ( position1 measurem5t (1 #ceh-cff1 #cgb ng/rm1 spectrum analysis1 #djb1 #dab2 wave-l5g?s1 #djf ,anneal+ ( l5ses & specula1 #aba ,ar*im$es1 clocks us$ by1 #agf ,arcturus1 heat (1 #che ,argel&]1 magnitudes ( />s1 #chb ,aries1 its position 9 ! zodiac1 #cd ,ari/illus1 8 obs]vations 9 ! ,alex&rian ,museum1 #ai ,armill quatori ( ,ty*o ,brahe1 #bf1 #da1 #de2 8 ,armill ,zodiacales1 #bh ,asc5sion1 ,"r 7see ,"r ,asc5sion7 ,arctic circle1 ,euclid's obs]vations ( />s 9 !1 #aj ,a/rolabe1 inv5t$ by ,hipp>*us1 #be2 engrav+ ( ,ty*o ,brahe's1 #bf1 #da2 8 ecliptic a/rolabe1 #bh ,a/ronomical clock1 #bdj 7see ,clock7 ,,a/ronomical ,,physics 7,book ,,vi471 #cga ,,a/ronomy ,,( ,,precision1 ,,in/rum5ts ,,us$ ,,9 7,*ap4 ,,xix471 #bhd-bij ,a/rophotomet]1 ,zlln]'s1 #cgi ,autolycus1 fir/ map ( ! />s by1 #h1 #i ,automatic spectroscope1 #cig ,auz\t1 inv5tion ( micromet] ascrib$ to1 #bai1 #bba ,axis ( collimation1 #bah1 #bbj ,b4 ,b>ium1 9 ! sun1 #dai ,b>l[1 correction ( ab]ration 9 l5ses1 #hh2 8,b>l[ l5ses10 #hi1 #bbi ,b>ometrical pressure1 its effect on ! p5dulum1 #aic ,b]?on's dynamet]1 #aaf ,bessel's transit in/rum5t1 #bhd ,b9>y />s1 #cea1 #cei1 #cfj ,blair 7,dr471 object-glasses1 #hh ,bloxam's improv$ gravity escapem5t1 #bja ,bond 7,pr(471 spr+ gov]nor1 #cbj1 #cba2 cele/ial photography1 #dfc ,b\gu]'s photomet]1 #cgi ,brahe1 ,ty*o 7see ,ty*o ,brahe7 ,brew/] 7,sir ,david71 8 li/ ( ,ty*o ,brahe's in/rum5ts1 #ch2 spectrum analysis1 #daj ,briti% ,horological ,in/itute1 "t signals1 #bhj ,br[n+'s me?od ( silv]+ glass specula1 #acg2 ( m\nt+ specula1 #add2 automatic spectroscope1 #cig2 sol> spectroscope1 #dbh ,buns5 7,erne/ de71 on anci5t a/ronomical obs]vations1 #f ,buns5 7,pr(47 spectroscope1 #cif2 8 burn]1 flame (1 #djg2 8 "w 9 spectrum analysis1 #djb1 #dab1 #dbc ,c4 ,calcium1 l9e spectra (1 #djf1 #dah ,cambridge ,obs]vatory 7,u4,s471 equatorial at1 #cci2 /> spectroscope1 #dcj2 transit circle1 #bdg1 #bdh1 #bea ,cam]a1 enl>g+1 = cele/ial photography1 #deh ,canada balsam1 its p[] ( refract+ light1 #ddg ,c&les us$ to measure "t1 #agf ,canopus1 obs]vations (1 by ,posidonius1 #h ,cassegra9's reflect+ telescope1 #ajc1 #adi1 #afi2 ) ,mr4 ,grubb's m\nt+1 #cja ,ca/+ l5ses & specula1 #aba ,ca/or1 photograph (1 #dgh ,catalogues ( />s 7see ,/>s7 ,cele/ial globe1 #bc ,,cele/ial ,,photography 7,*ap4 ,,xxxi41 ,,xxxii471 #ded ,*air1 obs]v+1 = equatorial telescopes1 #cci ,*aldeans1 _! obs]vations ( ! motions ( ! moon1 #d2 e>ly use ( ! gnomon1 #af ,*ance & ,feil1 manufacture ( glass discs1 #aai1 #cje ,,*emi/ry ,,( ,,! ,,/>s 7,*ap4 ,,xxvii4-,,xxx471 #chf-dec ,*9ese1 obs]vations ( conjunctions ( planets1 #d1 #e2 e>ly use ( ! gnomon1 #af1 #ag ,*romatic ab]ration ( object-glasses & eyepieces1 #hg1 #aji1 #abc ,,*ronograph1 ,,! 7,*ap4 ,,xvii471 #bec-bgj 8,*ronographic me?od0 ( transit obs]vation1 #bei ,*ronograph at ,gre5wi* ,obs]vatory1 #bfj-bfd ,,*ronomet]1 ,,! 7,*ap4 ,,xiii471 rise & progress ( "t-keep+1 #bjf-baj2 comp5sat+ balance1 #bjg2 deta*$ lev] escapem5t1 #bjh2 *ronomet] escapem5t fusee1 #bji ,*ronomet]s us$ = det]m9+ 8local "t10 #bha ,*ronoph]s1 = di/ribut+ 8,gre5wi* "t10 #bge1 #bgf ,c9c9nati ,obs]vatory1 #cch ,circle1 !2 its fir/ application z an a/ronomical in/rum5t1 #f1 #g1 #h1 #aj2 division into degrees1 #h1 #ag1 #ba ,circles1 great1 def9$ by ,euclid1 #ab ,,circle ,,read+ 7,*ap4 ,,xiv471 #baa-bag2 ,digges' diagonal scale1 #bac2 ! v]ni]1 #bad ,,circle1 ,,transit 7see ,transit ,circle7 ,circle1 m]idian1 at ,cambridge 7,u4,s471 #bdh2 mural1 #bda1 #bdb ,circumpol> />s1 #bci ,cl>ke 7,alvan71 improvem5t 9 telescope l5ses1 #cje2 great equatorial at ,wa%+ton1 #cji1 #cai ,clem5t1 inv5tor ( ! an*or escapem5t1 #aig ,clepsydras1 #cf ,,clock1 ,,! 7,*ap4 ,,xiii471 #age-bje2 anci5t escapem5t1 #agg2 cr[n :eel1 #agh2 clock tra91 #ahj2 w9d+ arrangem5ts1 #aha2 p5dulum1 #ahc2 cycloidal p5dulum1 #ahe2 comp5sat+ p5dulums1 #ahg2 ,graham's1 ,h>rison's1 & ,gre5wi* p5dulums1 #ahh2 clock at ,royal ,obs]vatory1 ,gre5wi*1 #aid2 escapem5ts1 #aif2 an*or escapem5t1 #aig2 ,graham's dead-beat1 #aii2 ,mudge's gravity escapem5t1 #bjj2 escapem5t ( clock at ,gre5wi*1 #bjc2 arrangem5ts at ,ed9burgh ,obs]vatory1 #bfi2 a/ronomical1 #bdj1 #bdd1 #bde1 #cdf2 sid]eal1 #bed1 #bef1 #bff2 sol>1 #bed2 /&>d1 at ,gre5wi*1 #aid1 #bjc1 #bjd1 #bga1 #bgd ,clock1 driv+1 = l>ge telescopes1 #cah ,clocks driv5 & controll$ by electricity1 #bgb ,clock />s1 #bfg ,clock t[] at ,we/m9/]1 #bgg ,coggia's comet1 its light pol>iz$1 #dej ,collimation & collimation-error 9 ! transit in/rum5t & equatorial1 #bch1 #bdg1 #cbh ,col\r1 am\nt produc$ by a l5s1 #ha1 #hd1 #hf2 spectrum analysis1 #djg1 #djh1 #dad1 #daf2 ( />s1 #afe1 #cea1 #dcc2 ( waves ( light1 #dbj2 refrangibility (1 #chg ,comet ( #afgg1 discov]$ by ,ty*o ,brahe1 #dg ,comet1 measurem5t ( ! angle ( position ( its axis1 #cei ,comp>ison prism ( ! spectroscope1 #dbc ,comp5sat+ balance1 #bjg ,comp5sat+ p5dulums1 #ahg-aic ,composite m\nt+ ( l>ge telescopes1 #caj ,concave l5ses 7see ,l5ses7 ,concave mirrors 7see ,mirrors7 ,conjugate images1 #fd ,conjunctions ( planets1 fir/ obs]vations1 #d ,con/ellations1 fir/ obs]vations1 #e1 #i2 ,orion & its neighb\rhood1 #aef ,convex l5ses 7see ,l5ses7 ,convex mirrors 7see ,mirrors7 ,cooke1 adju/m5t ( object-glasses1 #ada2 improvem5t 9 telescope l5ses1 #cje2 equatorial refractor1 #cjj2 driv+ clock = l>ge telescopes1 #cba2 illum9at+ lamp = equatorial telescopes1 #cbf ,cop]nicus1 p>allactic rules (1 #da ,cop]nicus 7lun> crat]71 #ced ,cross wires = circle read+1 #bab1 #baf1 #bah2 9 transit eyepiece1 #bcd1 #beg ,cr[n-glass prisms1 #hc1 #hd2 l5ses1 #hf1 #hh ,cry/als ( ,icel& sp>1 d\ble refraction by 7see ,icel& ,sp>7 ,culm9ation ( />s1 fir/ obs]vations (1 #e ,cycloidal p5dulum1 #ahe ,d4 ,dawes1 sol> eyepiece1 #aad1 #aae1 #cdi2 photometry1 #cgh ,day1 sol> & sid]eal1 #bec1 #bed1 #bef ,day eyepiece1 #aac ,days1 fir/ reckon+ (1 #ai2 measurem5t (1 #agf ,dead-beat escapem5t1 #aih ,deal "t-ball1 #bge1 #bgi ,decl9ation1 #bd1 #bcd1 #bda1 #bdc1 #bea2 measur$ by ,ty*o ,brahe1 #de ,decl9ation axis ( ! equatorial1 #bii1 #cjh1 #cbg1 #cbh ,def9+ p[] ( ! mod]n telescope1 #afj1 #afd2 />s 9 ,orion a te/ (1 #afe ,degrees1 division ( ! circle into1 #h1 #ag1 #ba ,de ,la ,rue 7,w>r51 ,f4,r4,s471 8 reflect+ telescope1 #ajh2 improvem5ts 9 poli%+ specula1 #acd2 cele/ial photography1 #ded1 #dei1 #dfj1 #dfd1 #dfe1 #dge ,d5d]ah1 ! zodiac (1 #g ,d5t 7,e4 ,co471 clock at ,royal ,obs]vatory1 ,gre5wi*1 #aid1 #bjc1 #bjd1 #bga1 #bgd ,deta*$ lev] escapem5t1 #bjh ,deviation ( light1 #gi1 #hb ,deviation error 9 ! transit in/rum5t1 #bdj1 #bdh ,dials ( anci5t clocks1 #beg ,diagonal scale1 ,digges'1 #bac ,diff]5tial obs]vations made ) ! equatorial1 #cfg ,digges' diagonal scale1 #bac ,diog5es ,la]tes1 on ! inv5tion ( ! gnomon1 #af ,dioptrics1 ,kepl]'s treatise on1 #chf ,direct vision spectroscope1 #dca ,disp]sion ( light by prism1 #gi1 #hj1 #hb ,divid+ p[] ( telescopes1 #afe ,dollond1 exp]im5ts ) l5ses1 #he2 correction ( *romatic ab]ration1 #hi2 on manufacture ( fl9t-glass discs1 #aah2 pancratic eyepiece1 #aac ,dome =m ( obs]vatory1 #cch1 #cci ,d\ble />s1 #cea1 #cei2 measurem5t (1 #cfj ,d\ble-image micromet]1 #bbe1 #bbi ,d\ble refraction by cry/als ( ,icel& sp> 7see ,icel& ,sp>7 ,driv+ clock1 = l>ge telescopes1 #cah1 #cdf ,drum =m ( obs]vatory1 #cch ,dundee "t signal1 #bgh ,e4 ,e>?1 ,!1 its position 9 ,ptolemy's sy/em1 #c2 e>ly !ories ( its =m1 #f2 circumf]5ce measur$ by ,posidonius1 #h2 ,euclid's !ory ( its position1 #ab2 incl9ation ( its axis1 #ad1 #ag2 size measur$ by ,erato/h5es1 #ai2 position 9 ,ty*o ,brahe's sy/em1 #df ,eclipses1 fir/ obs]vations (1 #d2 eclipses ( ,jupit]'s moons2 eclipses1 sol>1 photograph (1 #dgd ,ecliptic1 plane ( !1 #ac1 #ad2 discov]y ( its incl9ation1 #ag2 incl9ation measur$ by ,erato/h5es1 #ai ,ecliptic a/rolabe ( ,ty*o ,brahe1 #bh ,ed9burgh ,obs]vatory1 clock arrangem5ts at1 #bfi2 /&>d clock1 #bgb2 "t signals1 #bgh ,egyptians1 _! record ( eclipses1 #d2 zodiac ( ,d5d]ah1 #g ,ei*5s1 8 equatorial telescope at ,p>is1 #cad1 #cae2 sid]o/at con/ruct$ by him1 #cdd ,electricity1 its application to ! *ronograph1 #bfe2 to driv+ & controll+ clocks1 #bgb ,electric lamp1 #djd2 arrang$ = spectrum analysis1 #dje ,em]y us$ 9 gr9d+ l5ses & specula1 #abg ,engli% m\nt+ ( l>ge telescopes1 #caj ,equation ( "t1 #bed ,,equatorial1 ,,! 7,book ,v471 #bic-cfh 7see ,telescopes7 ,,equatorial ,,obs]vatory1 ,,! 7,*ap4 ,,xxii471 #ccg-cdb 7see ,obs]vatories7 ,,equatorial1 ,,!2 its ord9>y "w1 7,*ap4 ,,xxiv471 #cdi-cfh ,equ9octial circle1 obs]vations (1 by ,euclid1 #aa ,equ9oxes1 fir/ obs]vations (1 #ae1 #af1 #ag1 #bb2 precession ( !1 #cc ,erato/h5es1 obs]vations (1 #ag2 8 measurem5t ( ! e>?1 & incl9ation ( ! ecliptic1 #ai2 m]idian circle inv5t$ by1 #bj ,erect+ eyepiece1 #aac ,errors1 collimation & deviation1 9 ! transit in/rum5t1 #bch1 #bdj1 #bdg1 #cbh ,errors2 p]sonal equation1 #bei2 adju/m5ts ( ! equatorial1 #cbi ,ertel1 v]tical circle design$ by1 #bij ,escapem5ts ( clocks1 #aif-bje2 anci5t1 #agg2 an*or1 #aig2 ,graham's1 #aii2 ,mudge's1 #bjj2 ,gre5wi* clock1 #bjc2 deta*$ lev]1 #bjh2 *ronomet] escapem5t1 #bji ,e!real vibrations1 #cgc1 #dja1 #daj1 #dbj1 #ddi1 #dej ,euclid1 8 obs]vations ( ! />s1 #h1 #i1 #aj2 ( great circles1 horizon1 m]idian & tropics1 #aa1 #ab2 !ory ( ! e>?'s position1 #ab2 pole />1 #ad ,extra-m]idional obs]vations1 fir/ employm5t (1 #bc1 #be 8,eye & e>0 me?od 9 transit obs]vations1 #bei ,eyeball1 section ( !1 #ff ,eyepieces1 ,huygh5's1 #aaj2 ,ramsd5's1 ,dollond's1 #aab2 erect+ or 8day eyepiece10 #aab2 ,dawes's sol> eyepiece1 #aad2 magnify+ p[] (1 #aaf ,eyepiece ( ,gre5wi* transit circle1 #bdf2 ( transit in/rum5t1 #beg ,f4 ,faye1 ,m41 cele/ial photography1 #def ,feil & ,*ance1 manufacture ( fl9t glass discs1 #aai1 #cje ,fix$ />s 7see ,/>s7 ,flame ( salts 9 a ,buns5's burn]1 #djg ,fl9t-glass prisms1 #hc1 #hd2 l5ses1 #hf1 #agj ,fl9t-glass1 improvem5ts 9 ! manufacture ( discs (1 #aah1 #aai1 #cje ,focal l5g? ( telescopes1 #hb1 #deh2 ( l5ses1 #fb1 #fc2 ( convex mirrors1 #id ,f\cault2 8 reflect+ telescope1 #ajh2 improvem5t ( specula1 #aag2 mode ( poli%+ specula1 #acd1 #acf2 m\nt+ ( 8 telescope1 #caa2 gov]nor ( driv+ clock = l>ge telescopes1 #cbc2 sid]o/at1 #cdc2 spectrum analysis1 #daj2 helio/at1 #dbd ,fraunh(]2 manufacture ( fl9t-glass discs1 #aah2 l>ge telescopes1 #cjc2 l9es 9 ! sol> spectrum1 #cib2 spectrum analysis1 #djb1 #daj1 #dbb1 #dbe1 #dcb1 #dch ,fr$]ick ,,ii4 ( ,d5m>k1 8 patronage ( ,ty*o ,brahe1 #ch ,fusee = *ronomet]s1 #bji ,g4 ,galileo2 8 telescopes1 #gc1 #gh2 _! magnify+ p[]1 #gg2 ! p5dulum1 #ahc1 #ahd ,gascoigne1 eyepieces & circle read+1 #bab2 cross wires = 8telescopic sight10 #bai ,gate%ead1 ,mr4 ,newall's refractor1 #cjb ,geissl]'s tubes1 #dac ,g]man m\nt+ ( l>ge telescopes1 #bii ,gizeh1 great pyramid (1 an a/ronomical in/rum5t1 #f ,glasg[1 electric "t-gun1 #bgh ,glass1 injuri\s effects ( ! duty on1 #cje ,glass specula1 me?ods ( silv]+1 #acg ,globe1 cele/ial1 #bc2 t]re/rial1 #bc ,gnomon2 its inv5tion & e>ly use1 #af2 improvem5ts 91 #ah1 #age ,graham2 dead-beat escapem5t1 #aib1 #aii2 m]curial p5dulum1 #ahh ,gravity escapem5t1 #bjj1 #bjb ,greeks1 _! e>ly use ( ! gnomon1 #af ,gre5wi*1 ,royal ,obs]vatory2 p]spective view & plan ( transit circle1 #bdc1 #bde1 #bea2 transit room1 #bea1 #beg2 m]idian (1 #beb2 *ronograph1 #bfj-bfd2 comput+ room1 #bfg2 /&>d sid]eal clock1 #bfg2 mean sol> "t clock1 #bfh2 /&>d clock1 #bgd2 p5dulum1 #ahh2 reflex z5i? tube1 #bhf2 alt-azimu?1 #bij2 equatorial1 #caj2 !rmopile1 #chd2 photoheliograph1 #dfi 8,,gre5wi* ,,"t0 ,,& ,,! ,,use ,,made ,,( ,,x 7,*ap4 ,,xviii471 #bga-bhc ,gregorian telescope1 #adi ,gridiron p5dulum1 #ahh1 #ahi1 #aib ,gr9d+ ( l5ses & specula1 #abg ,grubb2 production & poli%+ ( metallic specula1 #aba1 #acd2 adju/m5t ( object-glasses1 #ada2 ,cassegra9ian & ,newtonian reflectors1 #ajb1 #ajh1 #cja1 #cjc2 great ,melb\rne equatorial telescope1 #ajh1 #cad1 #cae1 #cag1 #cbd1 #cbg2 mode ( m\nt+ its speculum1 #ade-adi2 automatic spectroscope1 #cig2 sol> spectroscope1 #dbh ,gu9&1 manufacture ( fl9t-glass discs1 #aah ,guns fir$ z "t-signals1 #bgh ,h4 ,haliburton1 on anci5t a/ronomical obs]vations1 #f ,hall2 exp]im5ts ) l5ses1 #he2 manufacture ( fl9t-glass discs1 #aah ,h>c\rt1 ,v]non1 exp]im5ts ) phosphatic glass1 #abc ,h>rison's gridiron p5dulum1 #ahh ,,heat ,,( ,,/>s1 ,,det]m9ation ,,( 7,*ap4 ,,xxvi471 #cgg-che ,heliomet]1 #bbd ,helio/at1 #dbc1 #deh ,h5ry 7,pr(471 radiation ( heat f sun-spots1 #che ,h]s*el 7,sir ,john71 l5ses correct$ = ab]ration1 #hh2 table ( reflective p[]s1 #afi2 /> magnitudes1 #cha ,h]s*el1 ,sir ,william1 8 reflect+ telescopes1 #ajc1 #ajh2 8 mode ( poli%+ specula1 #abi2 great telescope at ,sl\gh1 #afi1 #bid ,h]s*el-,br[n+ direct-vision prism1 #djj ,hipp>*us1 trigonometrical tables con/ruct$ by1 #ag2 discov]ies (1 #be-ce2 8 measurem5t ( space1 #bac ,hittorf1 spectrum analysis1 #dac ,holmes 7,n4 ,j471 8 proposal ( ! electric "t-gun1 #bgh ,hooke1 improvem5t 9 clock escapem5ts1 #aif2 micromet]1 #bba1 #bbb2 z5i? sector inv5t$ by1 #bhe2 sid]o/at sugge/$ by1 #cdc ,horizon1 ! fir/ a/ronomical in/rum5t1 #d1 #g1 #h2 def9$ by ,euclid1 #ab ,horological ,in/itute1 "t-signals1 #bhj ,h\rs1 fir/ reckon+ (1 #ai2 measurem5t (1 #agf ,h\r circle ( ! equatorial telescope1 #cbh1 #cce ,hu51 isl& (1 grant$ to ,ty*o ,brahe1 #ch ,hugg9s 7,dr471 telespectroscope1 #dbi1 #dcb ,huygh5s2 telescopes us$ by1 #ha2 eyepiece1 #aaj1 #aaf1 #bab2 application ( ! p5dulum to clocks1 #ahc2 8 measurem5ts ( space1 #bai1 #bbc1 #cdc2 pol>iz$ light1 #ddb ,hydrog5 9 ! sun1 #dce ,i4 ,icel& sp> cry/als2 d\ble refraction by1 #bbf1 #bbh2 pol>ization ( light1 #ddb1 #dde1 #ddg1 #ddi1 #dej ,illum9at+ p[] ( ! telescope1 #aeh1 #aff1 #afh1 #afi2 />s 9 ,orion1 a te/ (1 #afd ,images1 d\ble1 se5 ?r\gh ,icel& sp>1 #bbg ,incl9ation ( ! e>?'s axis1 #ad1 #ag ,incl9ation ( ! ecliptic1 #ag2 measur$ by ,erato/h5es1 #ai ,index error1 adju/m5ts ( ! equatorial1 #ccj ,iron1 l9e spectrum (1 #djf1 #dah ,irrationality ( ! spectrum1 #hg ,j4 ,janss5 7,dr471 sol> photography1 #dga2 discov]ies 9 sol> physics1 #dgb ,jupit]1 9 ,ptolemy's sy/em1 #c2 9 ,ty*o ,brahe's1 #df2 z a telescopic object1 #cea2 photographs (1 #dfe1 #dff ,jupit]'s moons1 obs]vation ( _! eclipses to det]m9e 8local "t10 #bhb ,k4 ,kepl]'s treatise on dioptrics1 #chf ,kew ,obs]vatory1 photographs ( ! sun & sun-spots1 #dfj1 #dfe1 #dgj1 #dge ,kir*h(f2 spectroscope1 #cif2 spectrum analysis1 #djb1 #djc1 #dab1 #dbb1 #dbh ,kit*5] 7,dr471 improv$ eyepiece1 #aac2 />s 9 ,orion1 #afd ,knobel's photomet]1 #cgh ,knott1 /> magnitudes1 #cha ,l4 ,lamp = equatorial telescope1 #cbe ,lamp1 electric 7see ,electric ,lamp7 ,lassell2 8 ,newtonian telescope1 #ajh1 #caa2 production1 poli%+1 & m\nt+ metallic specula1 #aba1 #acb1 #add ,latitude2 obs]vations ( ,posidonius1 #h2 p>allels (1 #bc ,lattice-"w = tubes ( telescopes1 #agb ,l5ses2 action (1 #ee1 #eh1 #he2 concave & convex1 #fa1 #ga1 #ge2 am\nt ( col\r produc$ by1 #ha2 a*romatic1 #hd2 ,hall & ,dollond's exp]im5ts1 #he2 correction = col\r1 #hg2 correction = ab]ration 9 eyepieces1 #aji1 #aaf2 production (1 #aag ,l5s1 cry/all9e1 ( ! eye1 #fg ,lewis 7,sir ,g4 ,c471 8 8,a/ronomy ( ! ,anci5ts10 #i ,liebig1 improvem5t 9 specula1 #aag ,light2 refraction1 #ee-gb2 deviation & disp]sion1 #gi1 #hj1 #hb1 #hc2 decomposition & recomposition1 #hc2 reflection1 #ij-ii2 action ( a reflect+ surface1 #ia2 angles ( incid5ce & reflection1 #ib2 concave & convex mirrors1 #id-ih2 velocity (1 #aei2 loss due to reflection1 #afh2 effective1 9 reflectors1 #afi2 vibration ( p>ticles1 #cgc1 #dja2 pol>ization1 #dda-dec ,,light ,,( ,,/>s1 ,,det]m9ation ,,( 7,*ap4 ,,xxvi471 #cgg-che ,l9dsay 7,"l71 sid]o/at at 8 obs]vatory1 #cdg ,local "t1 #bha ,longitude1 m]idians (1 #bc2 z det]m9$ by ,hipp>*us & ,ty*o ,brahe1 #dd2 det]m9$ by clock & transit in/rum5t1 #bhj2 express$ 9 degrees & "t1 #bhj ,m4 ,magnesium vap\r2 col\r (1 #daf2 9 ! sun1 #dce ,magnify+ p[] ( l>ge telescopes1 #aed1 #aee2 />s 9 ,orion1 a te/ (1 #afc ,magnitude ( />s1 #cgg ,malus1 discov]y ( pol>ization by reflection1 #ddb1 #ddh ,malvasia 7,m>quis71 8 micromet]1 #bai1 #bba ,manlius1 gnomon erect$ by him at ,rome1 #ah ,maps ( ! />s 7see ,/>s7 ,m>s1 9 ,ptolemy's sy/em1 #c2 9 ,ty*o ,brahe's1 #df2 z a telescopic object1 #cej ,m>t9's me?od ( silv]+ glass specula1 #ach ,mauritius1 photoheliograph at1 #dfi ,mean "t1 #bed ,mean sol> "t clock at ,gre5wi*1 #bfh ,melb\rne ,obs]vatory1 great reflect+ telescope1 #cab1 #cac1 #ccg2 composition & production ( specula1 #abj1 #aba1 #abi2 view ( optical "p1 #adc2 mode ( m\nt+ speculum1 #add-adi2 photographs ( ! moon1 #dei ,m]curial p5dulum1 #ahg1 #ahh1 #aib ,m]cury1 9 ,ptolemy's sy/em1 #c2 9 ,ty*o ,brahe's1 #df2 z a telescopic object1 #cej ,m]idian1 def9$ by ,euclid1 #ab ,m]idional obs]vations1 fir/ employm5t (1 #bj ,m]idian ( ,gre5wi*1 #beb ,m]idian circle1 ! fir/1 #bj2 at ,cambridge 7,u4,s471 #bdh ,m]idians ( longitude 7see ,longitude7 ,,m]idional ,,obs]vations1 ,,mod]n 7,book ,,iv471 #bcc-bij ,m]z 7,m471 manufacture ( fl9t-glass discs1 #aai2 co/ ( l>ge object-glasses1 #agb2 l>ge telescopes1 #cjc ,metallic specula1 #abj1 #aga ,meton1 m]idian obs]vations by1 #be ,meudon ,obs]vatory1 sol> photography at1 #dgj ,,micromet]1 ,,! 7,*ap4 ,,xv471 #bah-bcb2 wire micromet]1 #bba1 #ceb2 heliomet]1 #bbd2 d\ble image1 #bbi2 position1 #cec2 measurem5ts made by1 #cee1 #cei-cff1 #cfh ,microscopes1 = read+ transit circles1 #bdg2 = ,newall's telescope1 #cjg ,middlesbor\gh1 "t signal1 #bgh ,milky ,way1 obs]vations ( ,euclid1 #aa ,mill]1 spectrum analysis1 #daj ,mirrors1 concave & convex1 #id-ih ,mirrors = reflect+ telescopes 7see ,specula7 ,,mod]n ,,m]idional ,,obs]vations 7,book ,,iv471 #bcc-bij ,molecul> vibration1 #cgc1 #dja1 #daj1 #dbi1 #ddi1 #dej ,mon?s1 fir/ obs]vations (1 #e ,moon1 ,!1 9 ,ptolemy's sy/em1 #c2 motions obs]v$ by ! ,*aldeans1 #d2 p>allax obs]v$ by ,ptolemy1 #ce2 us$ by ,hipp>*us to det]m9e longitude1 #dd2 z a telescopic object1 #cej2 ! lun> crat]1 ,cop]nicus1 #ced2 measurem5t ( %ad[ ?r[n by a lun> hill1 #cee2 photographs & /]eographs1 #dei1 #dfd1 #dfe1 #dff2 "p ( ,be] & ,mdl]'s map1 #dgf2 ( ,de ,la ,rue's photograph1 #dgg ,,m\nt+ ,,( ,,l>ge ,,telescopes 7,*ap4 ,,xx471 #bic-cbg ,m\nt+ ( specula = reflect+ telescopes1 #add1 #adi1 #afi ,mudge1 gr9d+ & poli%+ specula1 #abi2 gravity escapem5t1 #bjj ,mural circle1 #bda1 #bdb ,mural quadrant1 ,ty*o ,brahe's1 #bcc1 #bce ,multiple />s1 #cea ,n4 ,nebul1 #cea ,nebula ( ,orion1 #aeg1 #aeh ,neptune1 z a telescopic object1 #cea ,newall's equatorial refractor1 #cjb2 ) spectroscope1 #dbg2 fl9t-glass discs =1 #aai2 production ( discs = object-glass1 #abh2 photographs ( ! moon1 #dei ,newca/le1 "t signals1 #bgh ,newton 7,sir ,isaac71 on refract+ telescopes1 #hb2 8 reflect+ telescope1 #aja1 #ajb2 use ( pit* 9 poli%+ specula1 #abh2 refrangibility ( light1 #chg2 pol>iz$ light1 #ddb ,newtonian reflector1 #adi2 view ( optical "p1 #adc2 effective light1 #afi2 ,grubb's =m1 #cjc2 ,br[n+'s =m1 #cjd2 m\nt+ (1 #caj ,nicols' prism1 #aae2 measurem5t ( ! light ( />s1 #chj2 pol>ization ( light1 #ddc1 #ddg1 #ddh1 #ddi1 #dej ,nor? pole1 diagram illu/rat+ h[ x is f\nd1 #bdi1 #bea ,o4 ,object-glasses1 production (1 #aah1 #aai2 correction ( col\r1 #hh2 correction = sph]ical ab]ration1 #abf2 mode ( poli%+1 #abh2 mode ( c5tr+1 #adj2 illu/rations ( defective adju/m5t1 #ada2 adju/m5t (1 #afc2 its p]fection 9 mod]n telescopes1 #aff1 #cje2 co/ ( production1 #agb2 divid$1 = duplication ( image1 #bbe ,object-glass prism1 #dbf ,obs]vatories see ,alex&rian ,museum1 ,cambridge 7,u4,s471 ,c9c9nati1 ,ed9burgh1 ,gre5wi*1 ,hu5 7,ty*o ,brahe's71 ,kew1 ,"l ,l9dsay's1 ,mauritius1 ,melb\rne1 ,meudon1 ,p>is1 ,potsdam1 ,vi5na1 ,wa%+ton ,obs]v+ *air = equatorial telescopes1 #cci ,optical action ( ! eye1 #fg2 long & %ort sight1 #fi1 #ga ,optical qualities ( telescopes1 p]man5ce (1 #agj ,optic axis 9 cry/als ( ,icel& sp>1 #bbh 8,optick tube10 telescope s fir/ call$1 #ee1 #aci-aea ,orion1 fir/ obs]vations (1 #e2 ,orion & ! neighb\r+ con/ellations1 #aef2 nebula (1 #aeg1 #aeh2 />s 91 a te/ = p[] ( telescopes1 #afd-aff2 facilities = obs]v+1 #afd ,p4 ,p>allactic rules1 #ea2 us$ by ,ptolemy1 #ce2 by ,ty*o ,brahe1 #ch1 #da ,p>allax ( ! moon1 obs]v$ by ,ptolemy1 #ce ,p>is ,obs]vatory1 reflect+ equatorial telescope1 #cad1 #cae1 #ccg2 sid]o/at1 #cdd2 photoheliograph1 #dfi ,p5dulum1 #ahc1 #ahe1 #ahg1 #ahh ,p]sonal equation1 #bei ,phosphatic glass = l5ses1 #abc ,,photography1 ,,cele/ial 7,*ap4 ,,xxxi41 ,,xxxii471 #ded-dhc ,photography1 /ell>1 #agb ,photoheliograph1 = photographs ( ! sun1 #dfj1 #dgj2 = transit ( ,v5us 7#ahgd71 #dfa ,photometry1 #cgc1 #cgg ,,physics1 ,,a/ronomical 7,book ,,vi471 #cga ,,physical ,,inquiry1 ,,g5]al ,,field ,,( 7,*ap4 ,,xxv471 #cga-cgf ,pic>d1 transit circle1 #bhd ,pisces1 its position 9 ! zodiac1 #cd ,pit* employ$ 9 poli%+ l5ses & specula1 #abh1 #acb ,plane ( ! ecliptic1 #ac1 #ad ,planets1 9 ,ptolemy's sy/em1 #c2 fir/ obs]vations ( conjunction1 #d1 #e2 motions obs]v$ by ,autolycus1 #i2 9 ,ty*o ,brahe's sy/em1 #df2 ,saturn se5 ) object-glasses ( #c & #bf in*es1 #afj1 #afa2 z telescopic objects1 #cej2 photographs (1 #dfe ,pleiades1 ! fir/ obs]vations (1 #e ,plck]1 spectrum analysis1 #dac ,pogson1 /> magnitudes1 #cha1 #chb ,po9t]s ( pre-telescopic in/rum5ts1 #ce1 #di1 #bad1 #baf ,pol> axis ( ! equatorial1 #bii1 #cjb1 #cjh1 #caa1 #cab1 #cbd1 #cbh1 #cbi1 #cdf ,pol>iscope1 #dda-dec ,pol>ization ( light1 #dda-dec ,pole1 ,nor?1 #bch2 diagram illu/rat+ h[ x is f\nd1 #bdi ,pole />1 fir/ obs]vations (1 #f2 obs]vations ( ,euclid1 #aj1 #ad2 its position1 #bch ,poli%+ l5ses & specula1 #abh1 #aga2 ,"l ,rosse's poli%+ ma*9e1 #aca2 ,mr4 ,lassell's1 #acb ,posidonius1 measurem5t ( ! e>?'s circumf]5ce1 #h ,position circle1 #cec ,position micromet]1 #cec1 #ceh ,po/ ,(fice ,telegraphs1 = di/ribution ( ,gre5wi* "t1 #bge ,potsdam1 photoheliograph at1 #dfi ,precession ( ! equ9oxes1 #cc ,prime-v]tical1 #bhe ,prime-v]tical in/rum5t1 #bhg ,primum mobile ( ,ptolemy1 #c ,prisms1 action (1 #ee2 cr[n & fl9t-glass1 #hc1 #hd2 wat]1 #he2 d\bly refract+1 = ! micromet]1 #bbf2 direct vision1 #djj2 9 ! spectroscope1 #cic-djj2 object-glass prism1 #dbf ,ptolemy1 ! ,heav5s accord+ to1 #c2 trigonometrical tables1 #ag2 sun's altitude1 #ba2 8 discov]ies1 #ce2 p>allax ( ! moon1 #ce2 8 measurem5t ( "t1 #cf2 p>allactic rules1 #ch1 #ea ,purba*1 obs]vation ( altitudes by1 #cf ,pyramids1 ! fir/ con/ruct$ a/ronomical in/rum5ts1 #e1 #f ,q4 ,quadrants us$ by ,ty*o ,brahe1 #ch2 8 quadrans maximus1 #dh ,quadrant1 mural1 #bcc1 #bce ,qu>tz cry/als = pol>iz+ light1 #dej1 #deb ,r4 ,radiation ( />s1 visual1 #chc2 !rmal1 #che ,radiation1 g5]al & selective1 #djc1 #djh ,ramsd5's eyepiece1 #aab1 #bab ,read+ microscopes1 = ,gre5wi* & ,cambridge 7,u4,s47 transit circles1 #bdg2 = ,newall's telescope1 #cjg ,r$ />s 7see ,col\r ( ,/>s7 ,reflection ( light 7see ,light7 ,reflect+ telescopes 7see ,telescope7 ,reflective p[]s1 ,sir ,john ,h]s*el's table (1 #afh ,reflector1 diagonal1 = sol> obs]vations1 #aad ,reflect+ & refract+ telescopes comp>$1 #agj ,reflex z5i?-tube at ,gre5wi*1 #bhf ,refract+ telescopes 7see ,telescopes7 ,refract+ & reflect+ telescopes comp>$1 #agj ,refraction ( light 7see ,light7 ,refraction1 d\ble1 by cry/als ( ,icel& sp> 7see ,icel& ,sp>7 ,refrangibility ( col\rs1 #chg2 ( light1 #dbj ,regiomontanus1 altitudes measur$ by1 #cf ,regulation ( clocks by electricity1 #bgb ,ris+ ( />s 7see ,/>s7 ,"r asc5sion1 #bd1 #bcd1 #bda1 #bdi1 #beg2 measur$ by ,hipp>*us1 #dd2 by ,ty*o ,brahe1 #de ,r+ micromet]1 #cfh ,rob9son 7,dr471 specula ( ,melb\rne telescope1 #abi2 ap]tures ( object-glasses1 #afh ,rockets fir$ z "t signals1 #bha ,rm]1 wires 9 a transit eyepiece1 #bbj2 transit circle & transit in/rum5t1 #bhd ,rosse 7,"l71 8 reflect+ telescope1 #ajh1 #bid1 #caa1 #cab2 composition ( reflector1 #abj2 production ( metallic specula1 #aba1 #aca2 nebula ( ,orion z se5 by 8 reflector1 #aeg1 #aeh2 illum9at+ p[] ( 8 telescope1 #aei2 effective light1 #afi2 !rmopile obs]vations1 #chd ,royal ,obs]vatory1 ,gre5wi* 7see ,gre5wi*7 ,rudolph ,,ii4 7,emp]or71 8 patronage ( ,ty*o ,brahe1 #db ,rum=d's photomet]1 #cgg ,ru!rfurd1 8 "w 9 cele/ial photography1 #dee1 #dfd1 #dff1 #dga1 #dgg1 #dhj ,s4 ,salts1 flame (1 9 a ,buns5's burn]1 #djg ,s& clocks & s& glasses1 #agf ,saturn1 9 ,ptolemy's sy/em1 #c2 9 ,ty*o ,brahe's1 #df2 z se5 ) a #c in* & #bf in* object-glass1 #afj1 #afa2 z a telescopic object1 #cea2 mode ( measur+ its r+s1 #ceg2 photographs (1 #dfe1 #dff ,sav>t's analys] = pol>ization ( light1 #deb ,sc>phie1 employ$ by ,erato/h5es1 #ai ,s*e9]'s telescope1 #gh ,seasons1 ,!1 #ae1 #af ,sec*i 7,fa!r71 direct-vision /> spectroscope1 #dca2 /ell> spectra1 #dcc ,sett+ ( />s 7see ,/>s7 ,sextants us$ by ,ty*o ,brahe1 #ch1 #ej ,sid]eal clock1 #bed1 #bff 7see ,clock7 ,sid]eal day1 #bef ,sid]eal "t1 #bdj1 #bed1 #cbd ,,sid]o/at1 ,,! 7,*ap4 ,,xxiii471 #cdc-cdh1 #dfa2 at ,"l ,l9dsay's ,obs]vatory1 #cdg ,signals = di/ribut+ 8,gre5wi* "t10 #bgh ,signals1 "t1 #bha1 #bhc ,signs ( ! zodiac 7see ,zodiac7 ,silv]-on-glass reflector at ! ,p>is ,obs]vatory1 #caf ,silv]+ glass specula1 modes (1 #acg2 silv]$ glass reflectors1 #aga ,simms1 8 introduction ( ! collimator 9 ! spectroscope1 #cic1 #dbe ,sirius1 fir/ obs]vations (1 #e2 spectrum (1 #dcb ,sl\gh1 ,sir ,wm4 ,h]s*el's telescope at1 #bid ,smy? 7,admiral71 />s 9 ,orion1 #afe2 col\rs ( />s1 #cea2 /> magnitudes1 #cha ,smy? 7,pr(4 ,piazzi71 on ! pyramids z a/ronomical in/rum5ts1 #f2 position ( ! v]nal equ9ox1 #cd2 clock arrangem5ts at ,ed9burgh ,obs]vatory1 #bfi ,sodium1 discov]y ( its pres5ce 9 ! sun1 #dab ,sol> photography1 #dei1 #dfe ,sol> spectroscope1 #dce2 ,br[n+'s & ,grubb's =ms1 #dbh ,sol> spectrum1 #cij1 #cia1 #cib1 #dbc1 #dcc1 #dcf1 #dch1 #dci2 photographs (1 #dgi1 #dhj ,sol> "t1 #bec1 #bee ,sol/ices1 fir/ obs]vations ( !1 #ae1 #af1 #ag1 #bb ,s\?+ ( />s1 #bcd ,,space ,,measur]s 7,book ,,iii471 #ace-bcb2 circle read+1 #baa2 ,digges' diagonal scale1 #bac2 ! v]ni]1 #bad2 micromet]s1 #bah ,space-p5etrat+ p[] ( ! telescope1 #aed2 />s 9 ,orion1 a te/ (1 #afe ,spectroscope1 con/ruction ( !1 #cic-djj2 automatic1 #cig2 arrang$ = %[+ absorption1 #dji2 atta*$ to ,newall's refractor1 #dbg2 sol>1 ,br[n+'s & ,grubb's =ms1 #dbh ,spectrum produc$ by prisms1 irrationality ( !1 #hf1 #hg ,spectrum1 sol>1 #cij1 #cia1 #cib ,spectrum analysis1 pr9ciples (1 #dja-dba ,specula1 production (1 #aag1 #abj2 ca/+1 anneal+1 #aba2 curvature1 #abb2 gr9d+1 #abg2 poli%+1 #abh2 silv]+1 #acg2 m\nt+1 #adb1 #afi1 #agb2 effective light1 #afi2 repoli%+1 #aga2 co/ z comp>$ ) object-glasses1 #agb ,sph]ical ab]ration1 #hg2 diagram illu/rat+1 #ajd1 #aje2 its correction 9 eyepieces1 #aji1 #aaa2 ( specula1 #abc1 #abd ,spr5gel pump1 #dac ,spr+ gov]nor ( driv+-clock = l>ge telescopes1 #cai1 #cbj 8,spuri\s disc0 ( fix$ />s1 #afc ,/&>d clock at ,ed9burgh ,obs]vatory1 #bgb ,/&>d sid]eal clock ( ,gre5wi* ,obs]vatory1 #bfg ,/&>d sol> "t clock ( ,gre5wi* ,obs]vatory1 #bfg ,,/>s1 ,,*emi/ry ,,( ,,! 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