:i* includes ! #dff orig9al illu/rations4 ,see #ehhaj-;h4htm or #ehhaj-;h4zip3 7https3_/_/www4gut5b]g4org_/ca*e_/epub_/ #ehhaj_/pg#ehhaj-;images4html7 or 7https3_/_/www4gut5b]g4org_/files_/#ehha j_/ehhaj-;h4zip7 ,images ( ! orig9al pages are available ?r\gh ,int]net ,ar*ive4 ,see https3_/_/ar*ive4org_/details_/heav5sabo vepopu#jj;gillri* ,transcrib]'s note3 ,text enclos$ by und]scores is 9 italics 7italics74 ,sup]scripts1 su* z ,p to ! second p[]1 are %[n by ! c>et "* be=e ! sup]script1 su* z ,p#b4 ,subscripts are simil>ly %[n by an und]score be=e ! subscript :i* is wrapp$ 9 curly braces1 su* z ,m#b4 ,illu/ration3 ,,spectra ,,( ,,v>i\s ,,s\rces ,,( ,,light4 ,! ,heav5s ,above3 ,a ,popul> ,h&book ( ,a/ronomy ,,! ,,heav5s ,,above3 ,a ,popul> ,h&book ( ,a/ronomy4 by ,j4 ,a4 ,,gillet1 ,pr(essor ( ,physics 9 ! ,normal ,college ( ! ,city ( ,new ,york1 & ,w4 ,j4 ,,rolfe1 ,=m]ly ,head ,ma/] ( ! ,high ,s*ool1 ,cambridge1 ,mass4 ,) ,six ,li?ographic ,plates & ,f\r ,hundr$ & ,sixty ,wood ,engrav+s4 ,pott]1 ,a9swor?1 ,co41 ,new ,york & ,*icago4 #ahhb4 ,copyright by ,j4 ,a4 ,gillet & ,w4 ,j4 ,rolfe1 #ahhb4 ,frankl9 ,press3 ,r&1 ,av]y1 & ,company1 ,bo/on4 ,,preface4 ,x has be5 ! aim ( ! au?ors to give 9 ?is little book a brief1 simple1 & accurate acc\nt ( ! heav5s z !y are kn[n to a/ronom]s ( ! pres5t day4 ,x is believ$ t !re is no?+ 9 ! book beyond ! compreh5sion ( read]s ( ord9>y intellig5ce1 & t x conta9s all ! in=mation on ! subject ( a/ronomy t is ne$ful to a p]son ( ord9>y culture4 ,! au?ors h c>efully avoid$ dry & ab/ruse ma!matical calculations1 yet !y h s\ght to make cle> ! me?ods by :i* a/ronom]s h ga9$ _! k ( ! heav5s4 ,! v>i\s k9ds ( telescopes & spectroscopes h be5 describ$1 & _! use 9 ! /udy ( ! heav5s has be5 fully expla9$4 ,! cuts ) :i* ! book is illu/rat$ h be5 drawn f all available s\rces2 & x is believ$ t !y excel 9 numb]1 fre%ness1 beauty1 & accuracy ^? to be f\nd 9 any simil> "w4 ,! li?ographic plates are1 ) a s+le exception1 r$uctions ( ! plates prep>$ at ! ,obs]vatory at ,cambridge1 ,mass4 ,! rema9+ li?ographic plate is a r$uc$ copy ( ,pr(essor ,langley's celebrat$ sun-spot engrav+4 ,_m ( ! views ( ! moon are f draw+s made f ! photographs 9 ,c>p5t] & ,nasmy?'s "w on ! moon4 ,! majority ( ! cuts illu/rat+ ! sol> sy/em are copi$ f ! ,fr5* edition ( ,guillem9's ,heav5s4 ,mo/ ( ! rema9d] are f ,locky]'s ,sol> ,physics1 ,"y's ,sun1 & o!r rec5t au?orities4 ,! cuts illu/rat+ comets1 meteors1 & nebul1 are ne>ly all tak5 f ! ,fr5* editions ( ,guillem9's ,comets & ,guillem9's ,heav5s4 ,,cont5ts4 ,i4 ,,! ,,cele/ial ,,sph]e #c ,,ii4 ,,! ,,sol> ,,sy/em #da ,i4 ,,!ory ,,( ,,! ,,sol> ,,sy/em #da ,! ,ptolemaic ,sy/em #da ,! ,cop]nican ,sy/em #dd ,ty*o ,brahe's ,sy/em #dd ,kepl]'s ,sy/em #dd ,! ,newtonian ,sy/em #dh ,,ii4 ,,! ,,sun ,,& ,,planets #ec ,i4 ,! ,e>? #ec ,=m & ,size #ec ,day & ,night #eg ,! ,seasons #fd ,tides #fh ,! ,day & ,"t #gd ,! ,ye> #gh ,weight ( ! ,e>? & ,precession #hc ,,ii4 ,! ,moon #hf ,di/ance1 ,size1 & ,motions #hf ,! ,atmosph]e ( ! ,moon #aji ,! ,surface ( ! ,moon #aad ,,iii4 ,inf]ior & ,sup]ior ,planets #acj ,inf]ior ,planets #acj ,sup]ior ,planets #acd ,,iv4 ,! ,sun #adj ,i4 ,magnitude & ,di/ance ( ! ,sun #adj ,,ii4 ,physical & ,*emical ,condition ( ! ,sun #adi ,physical ,condition ( ! ,sun #adi ,! ,spectroscope #aeb ,spectra #aeh ,*emical ,con/itution ( ! ,sun #afd ,motion at ! ,surface ( ! ,sun #afh ,,iii4 ,! ,photosph]e & ,sun-,spots #age ,! ,photosph]e #age ,sun-,spots #agi ,,iv4 ,! ,*romosph]e & ,prom95ces #aif ,v4 ,! ,corona #bjd ,v4 ,eclipses #baj ,,vi4 ,! ,?ree ,gr\ps ( ,planets #bba ,i4 ,g5]al ,*>act]i/ics ( ! ,gr\ps #bba ,,ii4 ,! ,inn] ,gr\p ( ,planets #bbe ,m]cury #bbe ,v5us #bcj ,m>s #bce ,,iii4 ,! ,a/]oids #bda ,,iv4 ,out] ,gr\p ( ,planets #bdd ,jupit] #bdd ,! ,satellites ( ,jupit] #bej ,saturn #bee ,! ,planet & 8 ,moons #bee ,! ,r+s ( ,saturn #bfa ,uranus #bfi ,neptune #bga ,,vii4 ,comets & ,meteors #bgd ,i4 ,comets #bgd ,g5]al ,ph5om5a ( ,comets #bgd ,motion & ,orig9 ( ,comets #bha ,rem>kable ,comets #bij ,connection betwe5 ,meteors & ,comets1 #cjj ,physical & ,*emical ,con/itution ( ,comets #cad ,,ii4 ,! ,zodiacal ,light #cah ,,iii4 ,,! ,,/ell> ,,univ]se #cbb ,i4 ,g5]al ,aspect ( ! ,heav5s #cbb ,,ii4 ,! ,/>s #ccj ,! ,con/ellations #ccj ,clu/]s #cej ,d\ble & ,multiple ,/>s #cee ,new & ,v>iable ,/>s #ceh ,di/ance ( ! ,/>s #cfd ,prop] ,motion ( ! ,/>s #cfe ,*emical & ,physical ,con/itution ( ! ,/>s #cga ,,iii4 ,nebul #cgc ,classification ( ,nebul #cgc ,irregul> ,nebul #cgf ,spiral ,nebul #chd ,! ,nebul> ,hypo!sis #cia ,,iv4 ,! ,/ructure ( ! ,/ell> ,univ]se #cif ,i4 ,,! ,,cele/ial ,,sph]e4 ,i4 ,! ,sph]e4--,a sph]e is a solid figure b\nd$ by a surface :i* curves equally 9 all directions at e po9t4 ,! rate at :i* ! surface curves is call$ ! curvature ( ! sph]e4 ,! small] ! sph]e1 ! great] is its curvature4 ,e po9t on ! surface ( a sph]e is equally di/ant f a po9t )91 call$ ! c5tre ( ! sph]e4 ,! circumf]5ce ( a sph]e is ! di/ance ar\nd its c5tre4 ,! diamet] ( a sph]e is ! di/ance ?r\gh its c5tre4 ,! radius ( a sph]e is ! di/ance f ! surface to ! c5tre4 ,! surfaces ( two sph]es are to ea* o!r z ! squ>es ( _! radii or diamet]s2 & ! volumes ( two sph]es are to ea* o!r z ! cubes ( _! radii or diamet]s4 ,di/ances on ! surface ( a sph]e are usually d5ot$ 9 degrees4 ,a degree is #a_/cfj ( ! circumf]5ce ( ! sph]e4 ,! l>g] a sph]e1 ! long] are ! degrees on x4 ,a curve describ$ ab\t any po9t on ! surface ( a sph]e1 ) a radius ( uni=m l5g?1 w be a circle4 ,z ! radius ( a circle describ$ on a sph]e is a curv$ l9e1 its l5g? is usually d5ot$ 9 degrees4 ,! circle describ$ on ! surface ( a sph]e increases ) ! l5g? ( ! radius1 until ! radius becomes #ij1 9 :i* case ! circle is ! l>ge/ t c possibly be describ$ on ! sph]e4 ,! l>ge/ circles t c be describ$ on ! surface ( a sph]e are call$ great circles1 & all o!r circles small circles4 ,any numb] ( great circles may be describ$ on ! surface ( a sph]e1 s9ce any po9t on ! sph]e may be us$ = ! c5tre ( ! circle4 ,! plane ( e great circle passes ?r\gh ! c5tre ( ! sph]e1 :ile ! planes ( all ! small circles pass ?r\gh ! sph]e away f ! c5tre4 ,all great circles on ! same sph]e are ( ! same size1 :ile ! small circles diff] 9 size accord+ to ! di/ance ( _! planes f ! c5tre ( ! sph]e4 ,! f>!r ! plane ( a circle is f ! c5tre ( ! sph]e1 ! small] is ! circle4 ,by a section ( a sph]e we usually mean ! figure ( ! surface =m$ by ! cutt+2 by a plane section we mean "o ^: surface is plane4 ,e plane section ( a sph]e is a circle4 ,:5 ! section passes ?r\gh ! c5tre ( ! sph]e1 x is a great circle2 9 e o!r case ! section is a small circle4 ,?us1 ,,an & ,,sb 7,fig4 #a7 are small circles1 & ,,mm' & ,,sn are l>ge circles4 ,illu/ration3 ,fig4 #a4 ,9 a diagram repres5t+ a sph]e 9 section1 all ! circles ^: planes cut ! section are repres5t$ by /raight l9es4 ,?us1 9 ,fig4 #b1 we h a diagram repres5t+ 9 section ! sph]e ( ,fig4 #a4 ,! /raight l9es ,,an1 ,,sb1 ,,mm'1 & ,,sn1 repres5t ! correspond+ circles ( ,fig4 #a4 ,! axis ( a sph]e is ! diamet] on :i* x rotates4 ,! poles ( a sph]e are ! ends ( its axis4 ,?us1 suppos+ ! sph]es ( ,figs4 #a & #b to rotate on ! diamet] ,,pp'1 ?is l9e w\ld be call$ ! axis ( ! sph]e1 & ! po9ts ,p & ,p' ! poles ( ! sph]e4 ,a great circle1 ,,mm'1 situat$ half way betwe5 ! poles ( a sph]e1 is call$ ! equator ( ! sph]e4 ,e great circle ( a sph]e has two poles4 ,^! are ! two po9ts on ! surface ( ! sph]e :i* lie #ij away f ! circle4 ,! poles ( a sph]e are ! poles ( its equator4 ,illu/ration3 ,fig4 #b4 #b4 ,! ,cele/ial ,sph]e4--,! heav5s appe> to h ! =m ( a sph]e1 ^: c5tre is at ! eye ( ! obs]v]2 & all ! />s seem to lie on ! surface ( ?is sph]e4 ,?is =m ( ! heav5s is a m]e matt] ( p]spective4 ,! />s are really at v unequal di/ances f u2 b !y are all se5 project$ ^u ! cele/ial sph]e 9 ! direction 9 :i* !y happ5 to lie4 ,?us1 suppose an obs]v] situat$ at ,c 7,fig4 #c71 />s situat$ at a1 b1 d1 e1 f1 & g1 w\ld be project$ ^u ! sph]e at ,a1 ,b1 ,d1 ,e1 ,f1 & ,g1 & w\ld appe> to lie on ! surface ( ! heav5s4 ,illu/ration3 ,fig4 #c4 #c4 ,! ,horizon4--,only half ( ! cele/ial sph]e is visible at a "t4 ,! plane t sep>ates ! visible f ! invisible portion is call$ ! horizon4 ,?is plane is tang5t to ! e>? at ! po9t ( obs]vation1 & ext5ds indef9itely into space 9 e direction4 ,9 ,fig4 #d1 ,e repres5ts ! e>?1 ,o ! po9t ( obs]vation1 & ,,sn ! horizon4 ,! po9ts on ! cele/ial sph]e directly above & bel[ ! obs]v] are ! poles ( ! horizon4 ,!y are call$ respectively ! z5i? & ! nadir4 ,no two obs]v]s 9 diff]5t p>ts ( ! e>? h ! same horizon2 & z a p]son moves ov] ! e>? he c>ries 8 horizon ) him4 ,illu/ration3 ,fig4 #d4 ,! dome ( ! heav5s appe>s to re/ on ! e>?1 z %[n 9 ,fig4 #e4 ,?is is because di/ant objects on ! e>? appe> project$ aga9/ ! heav5s 9 ! direction ( ! horizon4 ,illu/ration3 ,fig4 #e4 ,! s5sible horizon is a plane tang5t to ! e>? at ! po9t ( obs]vation4 ,! rational horizon is a plane p>allel ) ! s5sible horizon1 & pass+ ?r\gh ! c5tre ( ! e>?4 ,z x cuts ! cele/ial sph]e ?r\gh ! c5tre1 x =ms a great circle4 ,,sn 7,fig4 #f7 repres5ts ! s5sible horizon1 & ,s',n' ! rational horizon4 ,al?\gh ^! two horizons are really f\r ?\s& miles ap>t1 !y appe> to meet at ! di/ance ( ! cele/ial sph]e2 a l9e f\r ?\s& miles long at ! di/ance ( ! cele/ial sph]e becom+ a m]e po9t1 f> too small to be detect$ ) ! mo/ p[]ful telescope4 ,illu/ration3 ,fig4 #f4 ,illu/ration3 ,fig4 #g4 #d4 ,rotation ( ! ,cele/ial ,sph]e4--,x is well kn[n t ! sun & ! majority ( ! />s rise 9 ! ea/1 & set 9 ! we/4 ,9 our latitude !re are c]ta9 />s 9 ! nor? :i* nev] disappe> bel[ ! horizon4 ,^! />s are call$ ! circumpol> />s4 ,a close wat*1 h[ev]1 reveals ! fact t ^! all appe> to revolve ar\nd "o ( _! numb] call$ ! pole />1 9 ! direction indicat$ by ! arr[s 9 ,fig4 #g4 ,9 a ^w1 ! :ole heav5s appe> to rotate once a day1 f ea/ to we/1 ab\t an axis1 :i* is ! prolongation ( ! axis ( ! e>?4 ,! ends ( ?is axis are call$ ! poles ( ! heav5s2 & ! great circle ( ! heav5s1 midway betwe5 ^! poles1 is call$ ! cele/ial equator1 or ! equ9octial4 ,?is rotation ( ! heav5s is app>5t only1 be+ due to ! rotation ( ! e>? f we/ to ea/4 #e4 ,diurnal ,circles4--,9 ?is rotation ( ! heav5s1 ! />s appe> to describe circles :i* are p]p5dicul> to ! cele/ial axis1 & p>allel ) ! cele/ial equator4 ,^! circles are call$ diurnal circles4 ,! position ( ! poles 9 ! heav5s & ! direction ( ! diurnal circles ) ref]5ce to ! horizon1 *ange ) ! position ( ! obs]v] on ! e>?4 ,?is is ow+ to ! fact t ! horizon *anges ) ! position ( ! obs]v]4 ,illu/ration3 ,fig4 #h4 ,:5 ! obs]v] is nor? ( ! equator1 ! nor? pole ( ! heav5s is elevat$ above ! horizon1 & ! s\? pole is depress$ bel[ x1 & ! diurnal circles are oblique to ! horizon1 lean+ to ! s\?4 ,?is case is repres5t$ 9 ,fig4 #h1 9 :i* ,,pp' repres5ts ! cele/ial axis1 ,,eq ! cele/ial equator1 ,,sn ! horizon1 & ab1 c,n1 de1 fg1 ,%1 kl1 diurnal circles4 ,o is ! po9t ( obs]vation1 ,z ! z5i?1 & ,z' ! nadir4 ,illu/ration3 ,fig4 #i4 ,:5 ! obs]v] is s\? ( ! equator1 z at ,o 9 ,fig4 #i1 ! s\? pole is elevat$1 ! nor? pole depress$1 & ! diurnal circles are oblique to ! horizon1 lean+ to ! nor?4 ,:5 ! diurnal circles are oblique to ! horizon1 z 9 ,figs4 #h & #i1 ! cele/ial sph]e is call$ an oblique sph]e4 ,:5 ! obs]v] is at ! equator1 z 9 ,fig4 #aj1 ! poles ( ! heav5s are on ! horizon1 & ! diurnal circles are p]p5dicul> to ! horizon4 ,:5 ! obs]v] is at "o ( ! poles1 z 9 ,fig4 #aa1 ! poles ( ! heav5s are 9 ! z5i? & ! nadir1 & ! diurnal circles are p>allel ) ! horizon4 ,illu/ration3 ,fig4 #aj4 ,illu/ration3 ,fig4 #aa4 #f4 ,elevation ( ! ,pole & ( ! ,equ9octial4--,at ! equator ! poles ( ! heav5s lie on ! horizon1 & ! cele/ial equator passes ?r\gh ! z5i?4 ,z a p]son moves nor? f ! equator1 8 z5i? moves nor? f ! cele/ial equator1 & 8 horizon moves d[n f ! nor? pole1 & up f ! s\? pole4 ,! di/ance ( ! z5i? f ! equ9octial1 & ( ! horizon f ! cele/ial poles1 w always be equal to ! di/ance ( ! obs]v] f ! equator4 ,9 o!r words1 ! elevation ( ! pole is equal to ! latitude ( ! place4 ,9 ,fig4 #ab1 ,o is ! po9t ( obs]vation1 ,z ! z5i?1 & ,,sn ! horizon4 ,,np1 ! elevation ( ! pole1 is equal to ,,ze1 ! di/ance ( ! z5i? f ! equ9octial1 & to ! di/ance ( ,o f ! equator1 or ! latitude ( ! place4 ,two angles1 or two arcs1 :i* toge!r equal #ij1 are said to be complem5ts ( ea* o!r4 ,,ze & ,,es 9 ,fig4 #ab are toge!r equal to #ij3 h5ce !y are complem5ts ( ea* o!r4 ,,ze is equal to ! latitude ( ! place1 & ,,es is ! elevation ( ! equ9octial above ! horizon3 h5ce ! elevation ( ! equ9octial is equal to ! complem5t ( ! latitude ( ! place4 ,illu/ration3 ,fig4 #ab4 ,7 ! obs]v] s\? ( ! equator1 ! z5i? w\ld be s\? ( ! equ9octial1 & ! s\? pole ( ! heav5s w\ld be ! elevat$ pole4 ,illu/ration3 ,fig4 #ac4 #g4 ,f\r ,sets ( ,/>s4--,at mo/ po9ts ( obs]vation !re are f\r sets ( />s4 ,^! f\r sets are %[n 9 ,fig4 #ac4 7#a7 ,! />s 9 ! neighborhood ( ! elevat$ pole nev] set4 ,x w be se5 f ,fig4 #ac1 t if ! di/ance ( a /> f ! elevat$ pole does n exce$ ! elevation ( ! pole1 or ! latitude ( ! place1 its diurnal circle w be :olly above ! horizon4 ,z ! obs]v] approa*es ! equator1 ! elevation ( ! pole becomes less & less1 & ! belt ( circumpol> />s becomes n>r[] & n>r[]3 at ! equator x disappe>s entirely4 ,z ! obs]v] approa*es ! pole1 ! elevation ( ! pole increases1 & ! belt ( circumpol> />s becomes broad] & broad]1 until at ! pole x includes half ( ! heav5s4 ,at ! poles1 no />s rise or set1 & only half ( ! />s are ev] se5 at all4 7#b7 ,! />s 9 ! neighborhood ( ! depress$ pole nev] rise4 ,! bread? ( ?is belt also increases z ! obs]v] approa*es ! pole1 & decreases z he approa*es ! equator1 to vani% entirely :5 he rea*es ! equator4 ,! di/ance f ! depress$ pole to ! m>g9 ( ?is belt is always equal to ! latitude ( ! place4 7#c7 ,! />s 9 ! neighborhood ( ! equ9octial1 on ! side ( ! elevat$ pole1 set1 b are above ! horizon long] ?an !y are bel[ x4 ,?is belt ( />s ext5ds f ! equ9octial to a po9t ^: di/ance f ! elevat$ pole is equal to ! latitude ( ! place3 9 o!r words1 ! bread? ( ?is ?ird belt ( />s is equal to ! complem5t ( ! latitude ( ! place4 ,h5ce ?is belt ( />s becomes broad] & broad] z ! obs]v] approa*es ! equator1 & n>r[] & n>r[] z he approa*es ! pole4 ,h[ev]1 z ! obs]v] approa*es ! equator1 ! horizon comes ne>] & ne>] ! cele/ial axis1 & ! "t a /> is bel[ ! horizon becomes m ne>ly equal to ! "t x is above x4 ,z ! obs]v] approa*es ! pole1 ! horizon moves f>!r & f>!r f ! axis1 & ! "t any /> ( ?is belt is bel[ ! horizon becomes m & m unequal to ! "t x is above x4 ,! f>!r any /> ( ?is belt is f ! equ9octial1 ! long] ! "t x is above ! horizon1 & ! %ort] ! "t x is bel[ x4 7#d7 ,! />s :i* are 9 ! neighborhood ( ! equ9octial1 on ! side ( ! depress$ pole1 rise1 b are bel[ ! horizon long] ?an !y are above x4 ,! wid? ( ?is belt is also equal to ! complem5t ( ! latitude ( ! place4 ,! f>!r any /> ( ?is belt is f ! equ9octial1 ! long] "t x is bel[ ! horizon1 & ! %ort] "t x is above x2 &1 ! f>!r ! place f ! equator1 ! long] e /> ( ?is belt is bel[ ! horizon1 & ! %ort] ! "t x is above x4 ,at ! equator e /> is above ! horizon j half ( ! "t2 & any /> on ! equ9octial is above ! horizon j half ( ! "t 9 e "p ( ! e>?1 s9ce ! equ9octial & horizon1 be+ great circles1 bisect ea* o!r4 #h4 ,v]tical ,circles4--,great circles p]p5dicul> to ! horizon are call$ v]tical circles4 ,all v]tical circles pass ?r\gh ! z5i? & nadir4 ,a numb] ( ^! circles are %[n 9 ,fig4 #ad1 9 :i* ,,s5w repres5ts ! horizon1 & ,z ! z5i?4 ,illu/ration3 ,fig4 #ad4 ,! v]tical circle :i* passes ?r\gh ! nor? & s\? po9ts ( ! horizon is call$ ! m]idian2 & ! "o :i* passes ?r\gh ! ea/ & we/ po9ts1 ! prime v]tical4 ,^! two circles are %[n 9 ,fig4 #ae2 ,,szn be+ ! m]idian1 & ,,ezw ! prime v]tical4 ,^! two circles are at "r angles to ea* o!r1 or #ij ap>t2 & consequ5tly !y divide ! horizon into f\r quadrants4 ,illu/ration3 ,fig4 #ae4 #i4 ,altitude & ,z5i? ,di/ance4--,! altitude ( a heav5ly body is its di/ance above ! horizon1 & its z5i? di/ance is its di/ance f ! z5i?4 ,bo? ! altitude & ! z5i? di/ance ( a body are measur$ on ! v]tical circle :i* passes ?r\gh ! body4 ,! altitude & z5i? di/ance ( a heav5ly body are complem5ts ( ea* o!r4 #aj4 ,azimu? & ,amplitude4--,azimu? is di/ance measur$ ea/ or we/ f ! m]idian4 ,:5 a heav5ly body lies nor? ( ! prime v]tical1 its azimu? is measur$ f ! m]idian on ! nor?2 &1 :5 x lies s\? ( ! prime v]tical1 its azimu? is measur$ f ! m]idian on ! s\?4 ,! azimu? ( a body c1 !re=e1 nev] exce$ #ij4 ,! azimu? ( a body is ! angle :i* ! plane ( ! v]tical circle pass+ ?r\gh x makes ) t ( ! m]idian4 ,! amplitude ( a body is its di/ance measur$ nor? or s\? f ! prime v]tical4 ,! amplitude & azimu? ( a body are complem5ts ( ea* o!r4 #aa4 ,alt-azimu? ,in/rum5t4--,an in/rum5t = measur+ ! altitude & azimu? ( a heav5ly body is call$ an alt-azimu? in/rum5t4 ,"o =m ( ?is in/rum5t is %[n 9 ,fig4 #af4 ,x consi/s ess5tially ( a telescope m\nt$ on a v]tical circle1 & capable ( turn+ on a horizontal axis1 :i*1 9 turn1 is m\nt$ on ! v]tical axis ( a horizontal circle4 ,bo? ! horizontal & ! v]tical circles are graduat$1 & ! horizontal circle is plac$ exactly p>allel ) ! plane ( ! horizon4 ,:5 ! in/rum5t is prop]ly adju/$1 ! axis ( ! telescope w describe a v]tical circle :5 ! telescope is turn$ on ! horizontal axis1 no matt] to :at "p ( ! heav5s x has be5 po9t$4 ,! horizontal & v]tical axes c>ry ea* a po9t]4 ,^! po9t]s move ov] ! graduat$ circles1 & m>k h[ f> ea* axis turns4 ,to f9d ! azimu? ( a />1 ! in/rum5t is turn$ on its v]tical axis till its v]tical circle is br\ght into ! plane ( ! m]idian1 & ! read+ ( ! horizontal circle not$4 ,! telescope is !n direct$ to ! /> by turn+ x on bo? its v]tical & horizontal axes4 ,! read+ ( ! horizontal circle is aga9 not$4 ,! diff]5ce betwe5 ^! two read+s ( ! horizontal circle w be ! azimu? ( ! />4 ,illu/ration3 ,fig4 #af4 ,to f9d ! altitude ( a />1 ! read+ ( ! v]tical circle is fir/ asc]ta9$ :5 ! telescope is po9t$ horizontally1 & aga9 :5 ! telescope is po9t$ at ! />4 ,! diff]5ce betwe5 ^! two read+s ( ! v]tical circle w be ! altitude ( ! />4 #ab4 ,! ,v]ni]4--,to enable ! obs]v] to read ! fractions ( ! divisions on ! circles1 a device call$ a v]ni] is (t5 employ$4 ,x consi/s ( a %ort1 graduat$ arc1 atta*$ to ! end ( an arm c 7,fig4 #ag71 :i* is c>ri$ by ! axis1 & turns ) ! telescope4 ,?is arc is ( ! l5g? ( n9e divisions on ! circle1 & x is divid$ into t5 equal p>ts4 ,if #j ( ! v]ni] co9cides ) any division1 say #f1 ( ! circle1 #a ( ! v]ni] w be #a_/aj ( a division to ! left ( #g1 #b w be #b_/aj ( a division to ! left ( #h1 #c w be #c_/aj1 ( a division to ! left ( #i1 etc4 ,h5ce1 :5 #a co9cides ) #g1 #j w be at #f-a_/aj2 :5 #b co9cides ) #h1 #j w be at #f-b_/aj2 :5 #c co9cides ) #i1 #j w be at #f-c_/aj1 etc4 ,illu/ration3 ,fig4 #ag4 ,to asc]ta9 ! read+ ( ! circle by means ( ! v]ni]1 we fir/ notice ! z]o l9e4 ,if x exactly co9cides ) any division ( ! circle1 ! numb] ( t division w be ! read+ ( ! circle4 ,if !re is n an exact co9cid5ce ( ! z]o l9e ) any division ( ! circle1 we run ! eye along ! v]ni]1 & note :i* ( its divisions does co9cide ) a division ( ! circle4 ,! read+ ( ! circle w !n be ! numb] ( ! fir/ division on ! circle beh9d ! #j ( ! v]ni]1 & a numb] ( t5?s equal to ! numb] ( ! division ( ! v]ni]1 :i* co9cides ) a division ( ! circle4 ,= in/ance1 suppose #j ( ! v]ni] beyond #f ( ! circle1 & #g ( ! v]ni] to co9cide ) #ac ( ! circle4 ,! read+ ( ! circle w !n be #f-g_/aj4 #ac4 ,h\r ,circles4--,great circles p]p5dicul> to ! cele/ial equator are call$ h\r circles4 ,^! circles all pass ?r\gh ! poles ( ! heav5s1 z %[n 9 ,fig4 #ah4 ,,eq is ! cele/ial equator1 & ,p & ,p' are ! poles ( ! heav5s4 ,! po9t ,a on ! equ9octial 7,fig4 #ai7 is call$ ! v]nal equ9ox1 or ! fir/ po9t ( ,aries4 ,! h\r circle1 ,,app'1 :i* passes ?r\gh x1 is call$ ! equ9octial colure4 ,illu/ration3 ,fig4 #ah4 #ad4 ,decl9ation & ,"r ,asc5sion4--,! decl9ation ( a heav5ly body is its di/ance nor? or s\? ( ! cele/ial equator4 ,! pol> di/ance ( a heav5ly body is its di/ance f ! ne>] pole4 ,decl9ation & pol> di/ance are measur$ on h\r circles1 & = ! same heav5ly body !y are complem5ts ( ea* o!r4 ,illu/ration3 ,fig4 #ai4 ,! "r asc5sion ( a heav5ly body is its di/ance ea/w>d f ! fir/ po9t ( ,aries1 measur$ f ! equ9octial colure4 ,x is equal to ! arc ( ! cele/ial equator includ$ betwe5 ! fir/ po9t ( ,aries & ! h\r circle :i* passes ?r\gh ! heav5ly body4 ,z "r asc5sion is measur$ ea/w>d entirely ar\nd ! cele/ial sph]e1 x may h any value f #j up to #cfj4 ,"r asc5sion corresponds to longitude on ! e>?1 & decl9ation to latitude4 #ae4 ,! ,m]idian ,circle4--,! "r asc5sion & decl9ation ( a heav5ly body are asc]ta9$ by means ( an in/rum5t call$ ! m]idian circle1 or transit in/rum5t4 ,a side-view ( ?is in/rum5t is %[n 9 ,fig4 #bj4 ,illu/ration3 ,fig4 #bj4 ,x consi/s ess5tially ( a telescope m\nt$ betwe5 two pi]s1 s z to turn 9 ! plane ( ! m]idian1 & c>ry+ a graduat$ circle4 ,! read+s ( ?is circle are asc]ta9$ by means ( fix$ microscopes1 "u :i* x turns4 ,a heav5ly body c be obs]v$ ) ?is in/rum5t1 only :5 x is cross+ ! m]idian4 ,= ?is reason x is (t5 call$ ! transit circle4 ,to f9d ! decl9ation ( a /> ) ?is in/rum5t1 we fir/ asc]ta9 ! read+ ( ! circle :5 ! telescope is po9t$ to ! pole1 & !n ! read+ ( ! circle :5 po9t$ to ! /> on its passage across ! m]idian4 ,! diff]5ce betwe5 ^! two read+s w be ! pol> di/ance ( ! />1 & ! complem5t ( !m ! decl9ation ( ! />4 ,to asc]ta9 ! read+ ( ! circle :5 ! telescope is po9t$ to ! pole1 we mu/ select "o ( ! circumpol> />s ne> ! pole1 & !n po9t ! telescope to x :5 x crosses ! m]idian1 bo? above & bel[ ! pole1 & note ! read+ ( ! circle 9 ea* case4 ,! mean ( ^! two read+s w be ! read+ ( ! circle :5 ! telescope is po9t$ to ! pole4 #af4 ,a/ronomical ,clock4--,an a/ronomical clock1 or sid]eal clock z x is (t5 call$1 is a clock arrang$ s z to m>k h\rs f #a to #bd1 in/ead ( f #a to #ab1 z 9 ! case ( an ord9>y clock1 & s adju/$ z to m>k #j :5 ! v]nal equ9ox1 or fir/ po9t ( ,aries1 is on ! m]idian4 ,z ! fir/ po9t ( ,aries makes a complete circuit ( ! heav5s 9 tw5ty-f\r h\rs1 x mu/ move at ! rate ( #ae an h\r1 or ( #a 9 f\r m9utes3 h5ce1 :5 ! a/ronomical clock m>ks #a1 ! fir/ po9t ( ,aries mu/ be #ae we/ ( ! m]idian1 & :5 x m>ks #b1 #cj we/ ( ! m]idian1 etc4 ,t is to say1 by obs]v+ an accurate a/ronomical clock1 "o c always tell h[ f> ! m]idian at any "t is f ! fir/ po9t ( ,aries4 #ag4 ,h[ to f9d ,"r ,asc5sion ) ! ,m]idian ,circle4--,to f9d ! "r asc5sion ( a heav5ly body1 we h m]ely to asc]ta9 ! exact "t1 by ! a/ronomical clock1 at :i* ! body crosses ! m]idian4 ,if a /> crosses ! m]idian at #a h\r #bj m9utes by ! a/ronomical clock1 its "r asc5sion mu/ be #ai2 if at #bj h\rs1 its "r asc5sion mu/ be #cjj4 ,to enable ! obs]v] to asc]ta9 ) great exactness ! "t at :i* a /> crosses ! m]idian1 a numb] ( equidi/ant & p>allel spid]-l9es are /ret*$ across ! focus ( ! telescope1 z %[n 9 ,fig4 #ba4 ,! obs]v] notes ! "t :5 ! /> crosses ea* spid]-l9e2 & ! mean ( all ( ^! times w be ! "t :5 ! /> crosses ! m]idian4 ,! mean ( sev]al obs]vations is likely to be m ne>ly exact ?an any s+le obs]vation4 ,illu/ration3 ,fig4 #ba4 ,illu/ration3 ,fig4 #bb4 #ah4 ,! ,equatorial ,telescope4--,! equatorial telescope is m\nt$ on two axes1--"o p>allel ) ! axis ( ! e>?1 & ! o!r at "r angles to ?is1 & !re=e p>allel ) ! plane ( ! e>?'s equator4 ,! =m] is call$ ! pol> axis1 & ! latt] ! decl9ation axis4 ,ea* axis c>ries a graduat$ circle4 ,^! circles are call$ respectively ! h\r circle & ! decl9ation circle4 ,! telescope is atta*$ directly to ! decl9ation axis4 ,:5 ! telescope is fix$ 9 any decl9ation1 & !n turn$ on its pol> axis1 ! l9e ( sight w describe a diurnal circle2 s t1 :5 ! tube is once direct$ to a />1 x c be made to foll[ ! /> by simply turn+ ! telescope on its pol> axis4 ,9 ! case ( l>ge in/rum5ts ( ?is class1 ! pol> axis is usually turn$ by clock-"w at ! rate at :i* ! heav5s rotate2 s t1 :5 ! telescope has once be5 po9t$ to a planet or o!r heav5ly body1 x w cont9ue to foll[ ! body & keep x /eadily 9 ! field ( view )\t fur!r tr\ble on ! "p ( ! obs]v]4 ,! great ,wa%+ton ,equatorial is %[n 9 ,fig4 #bb4 ,its object-glass is #bf in*es 9 diamet]1 & its focal l5g? is #cb-a_/b feet4 ,x 0 con/ruct$ by ,alvan ,cl>k ,sons ( ,cambridge1 ,mass4 ,x is "o ( ! ?ree l>ge/ refract+ telescopes at pres5t 9 use4 ,! ,newall refractor at ,gate%ead1 ,eng41 has an objective #be in*es 9 diamet]1 & a focal l5g? ( #bi feet4 ,! great refractor at ,vi5na has an objective #bg in*es 9 diamet]4 ,!re are sev]al l>ge refractors n[ 9 process ( con/ruction4 ,illu/ration3 ,fig4 #bc4 #ai4 ,! ,wire ,micromet]4--,l>ge arcs 9 ! heav5s are measur$ by means ( ! graduat$ circles atta*$ to ! axes ( ! telescopes2 b small arcs )9 ! field ( view ( ! telescope are measur$ by means ( in/rum5ts call$ micromet]s1 m\nt$ 9 ! focus ( ! telescope4 ,"o ( ! mo/ conv5i5t ( ^! micromet]s is t kn[n z ! wire micromet]1 & %[n 9 ,fig4 #bc4 ,! frame ,,aa cov]s two slides1 ,c & ,d4 ,^! slides are mov$ by ! screws ,f & ,g4 ,! wires ,e & ,b are /ret*$ across ! ends ( ! slides s z to be p>allel to ea* o!r4 ,on turn+ ! screws ,f & ,g "o way1 ^! wires are c>ri$ ap>t2 & on turn+ !m ! o!r way !y are br\ght toge!r aga94 ,sometimes two p>allel wires1 x & y1 %[n 9 ! diagram at ! "r1 are /ret*$ across ! frame at "r angles to ! wires ,e1 ,b4 ,we may call ! wires x & y ! longitud9al wires ( ! micromet]1 & ,e & ,b ! transv]se wires4 ,_m in/rum5ts h only "o longitud9al wire1 :i* is /ret*$ across ! middle ( ! focus4 ,! longitud9al wires are j 9 front ( ! transv]se wires1 b d n t\* !m4 ,to f9d ! di/ance betwe5 any two po9ts 9 ! field ( view ) a micromet]1 ) a s+le longitud9al wire1 turn ! frame till ! longitud9al wire passes ?r\gh ! two po9ts2 !n set ! wires ,e & ,b "o on ea* po9t1 turn "o ( ! screws1 kn[n z ! micromet] screw1 till ! two wires are br\ght toge!r1 & note ! numb] ( times ! screw is turn$4 ,hav+ previ\sly asc]ta9$ ov] :at arc "o turn ( ! screw w move ! wire1 ! numb] ( turns w enable u to f9d ! l5g? ( ! arc betwe5 ! two po9ts4 ,! ?reads ( ! micromet] screw are cut ) great accuracy2 & ! screw is provid$ ) a l>ge head1 :i* is divid$ into a hundr$ or m equal p>ts4 ,^! divisions1 by means ( a fix$ po9t]1 enable u to asc]ta9 :at fraction ( a turn ! screw has made ov] & above its complete revolutions4 #bj4 ,reflect+ ,telescopes4--,x is possible to con/ruct mirrors ( mu* l>g] size ?an l5ses3 h5ce reflect+ telescopes h an advantage ov] refract+ telescopes z reg>ds size ( ap]ture & ( light-ga!r+ p[]4 ,!y are1 h[ev]1 inf]ior z reg>ds def9ition2 &1 9 ord] to prev5t flexure1 x is necess>y to give ! speculum1 or mirror1 a massiv5ess :i* makes ! telescope unwieldy4 ,x is also necess>y frequ5tly to repoli% ! speculum2 & ?is is an op]ation ( great delicacy1 z ! slighte/ *ange 9 ! =m ( ! surface impairs ! def9ition ( ! image4 ,^! defects h be5 rem$i$1 to a c]ta9 ext5t1 by ! introduction ( silv]-on-glass mirrors2 t is1 glass mirrors cov]$ 9 front ) a ?9 coat+ ( silv]4 ,glass is only "o-?ird z heavy z speculum-metal1 & silv] is mu* sup]ior to t metal 9 reflect+ p[]2 & :5 ! silv] becomes t>ni%$1 x c be remov$ & r5ew$ )\t dang] ( *ang+ ! =m ( ! glass4 ,! ,h]s*elian ,reflector4--,9 ?is =m ( telescope ! mirror is slightly tipp$1 s t ! image1 in/ead ( be+ =m$ 9 ! c5tre ( ! tube1 is =m$ ne> "o side ( x1 z 9 ,fig4 #bd4 ,! obs]v] c !n view x )\t putt+ 8 head inside ! tube1 & !re=e )\t cutt+ (f any mat]ial portion ( ! light4 ,9 obs]vation1 he mu/ /& at ! upp] or out] end ( ! tube1 & look into x1 8 back be+ turn$ t[>ds ! object4 ,f 8 look+ directly into ! mirror1 x is also sometimes call$ ! front-view telescope4 ,! great disadvantage ( ?is arrangem5t is1 t ! rays _c be br\ght to an exact focus :5 !y are ?r[n s f> to "o side ( ! axis1 & ! injury to ! def9ition is s great t ! front-view plan is n[ entirely ab&on$4 ,illu/ration3 ,fig4 #bd4 ,! ,newtonian ,reflector4--,! plan propos$ by ,sir ,isaac ,newton 0 to place a small plane mirror j inside ! focus1 incl9$ to ! telescope at an angle ( #de1 s z to ?r[ ! rays to ! side ( ! tube1 :]e !y come to a focus1 & =m ! image4 ,an op5+ is made 9 ! side ( ! tube1 j bel[ :]e ! image is =m$2 & 9 ?is op5+ ! eye-piece is ins]t$4 ,! small mirror cuts (f "s ( ! light1 b n en\gh to be a s]i\s defect4 ,an improvem5t :i* less5s ?is defect has be5 made by ,pr(essor ,h5ry ,drap]4 ,! incl9$ mirror is replac$ by a small rectangul> prism 7,fig4 #be71 by reflection f :i* ! image is =m$ v ne> ! prism4 ,a pair ( l5ses are !n ins]t$ 9 ! c\rse ( ! rays1 by :i* a second image is =m$ at ! op5+ 9 ! side ( ! tube2 & ?is second image is view$ by an ord9>y eye-piece4 ,illu/ration3 ,fig4 #be4 ,! ,gregorian ,reflector4--,?is is a =m propos$ by ,james ,gregory1 :o probably prec$$ ,newton z an inv5tor ( ! reflect+ telescope4 ,beh9d ! focus1 ,f 7,fig4 #bf71 a small concave mirror1 ,r1 is plac$1 by :i* ! light is reflect$ back aga9 d[n ! tube4 ,! l>g] mirror1 ,m1 has an op5+ ?r\gh its c5tre2 & ! small mirror1 ,r1 is s adju/$ z to =m a second image ( ! object 9 ?is op5+4 ,?is image is !n view$ by an eye-piece :i* is screw$ into ! op5+4 ,illu/ration3 ,fig4 #bf4 ,! ,cassegra9ian ,reflector4--,9 pr9ciple ?is is ! same ) ! ,gregorian2 b ! small mirror1 ,r1 is convex1 & is plac$ inside ! focus1 ,f1 s t ! rays are reflect$ f x be=e rea*+ ! focus1 & no image is =m$ until !y rea* ! op5+ 9 ! l>ge mirror4 ,?is =m has an advantage ov] ! ,gregorian1 9 t ! telescope may be made %ort]1 & ! small mirror c be m easily %ap$ to ! requir$ figure4 ,x has1 !re=e1 entirely sup]s$$ ! orig9al ,gregorian =m4 ,illu/ration3 ,fig4 #bg4 ,optically ^! =ms ( telescope are inf]ior to ! ,newtonian2 b ! latt] is subject to ! inconv5i5ce1 t ! obs]v] mu/ be /ation$ at ! upp] end ( ! telescope1 :]e he looks into an eye-piece screw$ into ! side ( ! tube4 ,on ! o!r h&1 ! ,cassegra9ian ,telescope is po9t$ directly at ! object to be view$1 l a refractor2 & ! obs]v] /&s at ! l[] end1 & looks 9 at ! op5+ ?r\gh ! l>ge mirror4 ,?is is1 !re=e1 ! mo/ conv5i5t =m ( all 9 managem5t4 ,illu/ration3 ,fig4 #bh4 ,! l>ge/ reflect+ telescope yet con/ruct$ is t ( ,"l ,rosse1 at ,p>son/[n1 ,irel&4 ,its speculum is #f feet 9 diamet]1 & its focal l5g? #ee feet4 ,x is commonly us$ z a ,newtonian4 ,?is telescope is %[n 9 ,fig4 #bg4 ,! great telescope ( ! ,melb\rne ,obs]vatory1 ,au/ralia1 is a ,cassegranian reflector4 ,its speculum is #d feet 9 diamet]1 & its focal l5g? is #cb feet4 ,x is %[n 9 ,fig4 #bh4 ,illu/ration3 ,fig4 #bi4 ,! great reflector ( ! ,p>is ,obs]vatory is a ,newtonian reflector4 ,its mirror ( silv]$ glass is #d feet 9 diamet]1 & its focal l5g? is #bc feet4 ,?is telescope is %[n 9 ,fig4 #bi4 #ba4 ,! ,sun's ,motion among ! ,/>s4--,if we notice ! />s at ! same h\r night aft] night1 we %all f9d t ! con/ellations are /eadily advanc+ t[>ds ! we/4 ,new con/ellations are cont9ually appe>+ 9 ! ea/1 & old ones disappe>+ 9 ! we/4 ,?is cont9ual advanc+ ( ! heav5s t[>ds ! we/ is due to ! fact t ! sun's place among ! />s is cont9ually mov+ t[>ds ! ea/4 ,! sun completes ! circuit ( ! heav5s 9 a ye>1 & is !re=e mov+ ea/w>d at ! rate ( ab\t a degree a day4 ,illu/ration3 ,fig4 #cj4 ,?is motion ( ! sun's place among ! />s is due to ! revolution ( ! e>? ar\nd ! sun1 & n to any real motion ( ! sun4 ,9 ,fig4 #cj suppose ! inn] circle to repres5t ! orbit ( ! e>? ar\nd ! sun1 & ! out] circle to repres5t ! cele/ial sph]e4 ,:5 ! e>? is at ,e1 ! sun's place on ! cele/ial sph]e is at ,s'4 ,z ! e>? moves 9 ! direction ,,ef1 ! sun's place on ! cele/ial sph]e mu/ move 9 ! direction ,s',t3 h5ce ! revolution ( ! e>? ar\nd ! sun w\ld cause ! sun's place among ! />s to move ar\nd ! heav5s 9 ! same direction t ! e>? is mov+ ar\nd ! sun4 #bb4 ,! ,ecliptic4--,! circle describ$ by ! sun 9 its app>5t motion ar\nd ! heav5s is call$ ! ecliptic4 ,! plane ( ?is circle passes ?r\gh ! c5tre ( ! e>?1 & !re=e ?r\gh ! c5tre ( ! cele/ial sph]e2 ! e>? be+ s small1 comp>$ ) ! cele/ial sph]e1 t x practically makes no diff]5ce :e!r we consid] a po9t on its surface1 or "o at its c5tre1 z ! c5tre ( ! cele/ial sph]e4 ,! ecliptic is1 !re=e1 a great circle4 ,! e>?'s orbit lies 9 ! plane ( ! ecliptic2 b x ext5ds only an inappreciable di/ance f ! sun t[>ds ! cele/ial sph]e4 ,illu/ration3 ,fig4 #ca4 #bc4 ,! ,obliquity ( ! ,ecliptic4--,! ecliptic is incl9$ to ! cele/ial equator by an angle ( ab\t #bc-a_/b4 ,?is incl9ation is call$ ! obliquity ( ! ecliptic4 ,! obliquity ( ! ecliptic is due to ! deviation ( ! e>?'s axis f a p]p5dicul> to ! plane ( its orbit4 ,! axis ( a rotat+ body t5ds to ma9ta9 ! same direction2 &1 z ! e>? revolves ar\nd ! sun1 its axis po9ts all ! "t 9 ne>ly ! same direction4 ,! e>?'s axis deviates ab\t #bc-a_/b f ! p]p5dicul> to its orbit2 &1 z ! e>?'s equator is at "r angles to its axis1 x w deviate ab\t #bc-a_/b f ! plane ( ! ecliptic4 ,! cele/ial equator has ! same direction z ! t]re/rial equator1 s9ce ! axis ( ! heav5s has ! same direction z ! axis ( ! e>?4 ,illu/ration3 ,fig4 #cb4 ,suppose ! globe at ! c5tre ( ! tub 7,fig4 #ca7 to repres5t ! sun1 & ! small] globes to repres5t ! e>? 9 v>i\s positions 9 its orbit4 ,! surface ( ! wat] w !n repres5t ! plane ( ! ecliptic1 & ! rod project+ f ! top ( ! e>? w repres5t ! e>?'s axis1 :i* is se5 to po9t all ! "t 9 ! same direction1 or to lean ! same way4 ,! lean+ ( ! axis f ! p]p5dicul> to ! surface ( ! wat] w\ld cause ! e>?'s equator to be incl9$ ! same am\nt to ! surface ( ! wat]1 half ( ! equator be+ above1 & half ( x bel[1 ! surface4 ,7 ! axis ( ! e>? p]p5dicul> to ! surface ( ! wat]1 ! e>?'s equator w\ld co9cide ) ! surface1 z is evid5t f ,fig4 #cb4 ,illu/ration3 ,fig4 #cc4 #bd4 ,! ,equ9oxes & ,sol/ices4--,! ecliptic & cele/ial equator1 be+ great circles1 bisect ea* o!r4 ,half ( ! ecliptic is nor?1 & half ( x is s\?1 ( ! equator4 ,! po9ts at :i* ! two circles cross are call$ ! equ9oxes4 ,! "o at :i* ! sun crosses ! equator f s\? to nor? is call$ ! v]nal equ9ox1 & ! "o at :i* x crosses f nor? to s\? ! autumnal equ9ox4 ,! po9ts on ! ecliptic midway betwe5 ! equ9oxes are call$ ! sol/ices4 ,! "o nor? ( ! equator is call$ ! summ] sol/ice1 & ! "o s\? ( ! equator ! w9t] sol/ice4 ,9 ,fig4 #cc1 ,,eq is ! cele/ial equator1 ,ec,e'c' ! ecliptic1 ,v ! v]nal equ9ox1 ,a ! autumnal equ9ox1 ,ec ! w9t] sol/ice1 & ,e'c' ! summ] sol/ice4 ,illu/ration3 ,fig4 #cd4 #be4 ,! ,incl9ation ( ! ,ecliptic to ! ,horizon4--,s9ce ! cele/ial equator is p]p5dicul> to ! axis ( ! heav5s1 x makes ! same angle ) x on e side3 h5ce1 at any place1 ! equator makes always ! same angle ) ! horizon1 :atev] "p ( x is above ! horizon4 ,b1 z ! ecliptic is oblique to ! equator1 x makes diff]5t angles ) ! cele/ial axis on diff]5t sides2 & h5ce1 at any place1 ! angle :i* ! ecliptic makes ) ! horizon v>ies accord+ to ! "p :i* is above ! horizon4 ,! two extreme angles = a place m ?an #bc-a_/b nor? ( ! equator are %[n 9 ,figs4 #cd & #ce4 ,! lea/ angle is =m$ :5 ! v]nal equ9ox is on ! ea/]n horizon1 ! autumnal on ! we/]n horizon1 & ! w9t] sol/ice on ! m]idian1 z 9 ,fig4 #cd4 ,! angle :i* ! ecliptic !n makes ) ! horizon is equal to ! elevation ( ! equ9octial m9us #bc-a_/b4 ,9 ! latitude ( ,new ,york ?is angle #di - #bc-a_/b #be-a_/b4 ,illu/ration3 ,fig4 #ce4 ,! greate/ angle is =m$ :5 ! autumnal equ9ox is on ! ea/]n horizon1 ! v]nal on ! we/]n horizon1 & ! summ] sol/ice is on ! m]idian 7,fig4 #ce74 ,! angle betwe5 ! ecliptic & ! horizon is !n equal to ! elevation ( ! equ9octial plus #bc-a_/b4 ,9 ! latitude ( ,new ,york ?is angle #di #bc-a_/b #gb-a_/b4 ,( c\rse ! equ9oxes1 ! sol/ices1 & all o!r po9ts on ! ecliptic1 describe diurnal circles1 l e o!r po9t 9 ! heav5s3 h5ce1 9 our latitude1 ^! po9ts rise & set e day4 #bf4 ,cele/ial ,latitude & ,longitude4--,cele/ial latitude is di/ance measur$ nor? or s\? f ! ecliptic2 & cele/ial longitude is di/ance measur$ on ! ecliptic ea/w>d f ! v]nal equ9ox1 or ! fir/ po9t ( ,aries4 ,great circles p]p5dicul> to ! ecliptic are call$ cele/ial m]idians4 ,^! circles all pass ?r\gh ! poles ( ! ecliptic1 :i* are "s #bc-a_/b f ! poles ( ! equ9octial4 ,! latitude ( a heav5ly body is measur$ by ! arc ( a cele/ial m]idian includ$ betwe5 ! body & ! ecliptic4 ,! longitude ( a heav5ly body is measur$ by ! arc ( ! ecliptic includ$ betwe5 ! fir/ po9t ( ,aries & ! m]idian :i* passes ?r\gh ! body4 ,!re are1 ( c\rse1 always two arcs includ$ betwe5 ! fir/ po9t ( ,aries & ! m]idian1--"o on ! ea/1 & ! o!r on ! we/1 ( ! fir/ po9t ( ,aries4 ,! "o on ! ea/ is always tak5 z ! measure ( ! longitude4 #bg4 ,! ,precession ( ! ,equ9oxes4--,! equ9octial po9ts h a sl[ we/w>d motion along ! ecliptic4 ,?is motion is at ! rate ( ab\t #ej'' a ye>1 & w\ld cause ! equ9oxes to make a complete circuit ( ! heav5s 9 a p]iod ( ab\t tw5ty-six ?\s& ye>s4 ,x is call$ ! precession ( ! equ9oxes4 ,?is we/w>d motion ( ! equ9oxes is due to ! fact t ! axis ( ! e>? has a sl[ gyratory motion1 l ! h&le ( a sp9n+-top :i* has begun to wabble a little4 ,?is gyratory motion causes ! axis ( ! heav5s to describe a cone 9 ab\t tw5ty-six ?\s& ye>s1 & ! pole ( ! heav5s to describe a circle ab\t ! pole ( ! ecliptic 9 ! same "t4 ,! radius ( ?is circle is #bc-a_/b4 ,illu/ration3 ,fig4 #cf4 #bh4 ,illu/ration ( ,precession4--,! precession ( ! equ9oxes may be illu/rat$ by means ( ! app>atus %[n 9 ,fig4 #cf4 ,! horizontal & /ation>y r+ ,,ec repres5ts ! ecliptic2 ! oblique r+ ,e',q repres5ts ! equator2 ,v & ,a repres5t ! equ9octial po9t1 & ,e & ,c ! sol/itial po9ts2 ,b repres5ts ! pole ( ! ecliptic1 ,p ! pole ( ! equator1 & ,,po ! cele/ial axis4 ,! r+ ,e',q is support$ on a pivot at ,o2 & ! rod ,,bp1 :i* connects ,b & ,p1 is jo9t$ at ea* end s z to admit ( ! movem5t ( ,p & ,b4 ,on c>ry+ ,p ar\nd ,b1 we %all see t ,e',q w always pres]ve ! same obliquity to ,,ec1 & t ! po9ts ,v & ,a w move ar\nd ! circle ,,ec4 ,! same w also be true ( ! po9ts ,e & ,c4 #bi4 ,effects ( ,precession4--,"o effect ( precession1 z has already be5 /at$1 is ! revolution ( ! pole ( ! heav5s ar\nd ! pole ( ! ecliptic 9 a p]iod ( ab\t tw5ty-six ?\s& ye>s4 ,! circle describ$ by ! pole ( ! heav5s1 & ! position ( ! pole at v>i\s dates1 are %[n 9 ,fig4 #cg1 :]e o indicates ! position ( ! pole at ! bir? ( ,*ri/4 ,! numb]s r\nd ! circle to ! left ( o are dates ,a4,d41 & ^? to ! "r ( o are dates ,b4,c4 ,x w be se5 t ! /> at ! end ( ! ,little ,be>'s tail1 :i* is n[ ne> ! nor? pole1 w be exactly at ! pole ab\t ! ye> #bjjj4 ,x w !n rec$e f>!r & f>!r f ! pole till ! ye> #aejjj ,a4,d41 :5 x w be ab\t =ty-sev5 degrees away f ! pole4 ,x w be notic$ t "o ( ! />s ( ! ,dragon 0 ! pole /> ab\t #bhjj ye>s ,b4,c4 ,!re are reasons to suppose t ?is 0 ab\t ! "t ( ! build+ ( ! ,great ,pyramid4 ,a second effect ( precession is ! %ift+ ( ! signs along ! zodiac4 ,! zodiac is a belt ( ! heav5s along ! ecliptic1 ext5d+ eight degrees f x on ea* side4 ,?is belt is occupi$ by twelve con/ellations1 kn[n z ! zodiacal con/ellations4 ,!y are ,aries1 ,taurus1 ,gem9i1 ,canc]1 ,leo1 ,virgo1 ,libra1 ,scorpio1 ,sagitt>ius1 ,capricornus1 ,aqu>ius1 & ,pisces4 ,! zodiac is also divid$ into twelve equal p>ts ( ?irty degrees ea*1 call$ signs4 ,^! signs h ! same names z ! twelve zodiacal con/ellations1 & :5 !y 7 fir/ nam$1 ea* sign occupi$ ! same "p ( ! zodiac z ! correspond+ con/ellation2 t is to say1 ! sign ,aries 0 9 ! con/ellation ,aries1 & ! sign ,taurus 9 ! con/ellation ,taurus1 etc4 ,n[ ! signs are always reckon$ z beg9n+ at ! v]nal equ9ox1 :i* is cont9ually %ift+ along ! ecliptic2 s t ! signs are cont9ually mov+ along ! zodiac1 :ile ! con/ellations rema9 /ation>y3 h5ce x has come ab\t t ! fir/ po9t ( ,aries 7! sign7 is no long] 9 ! con/ellation ,aries1 b 9 ,pisces4 ,illu/ration3 ,fig4 #cg4 ,fig4 #ch %[s ! position ( ! v]nal equ9ox #bagj ,b4,c4 ,x 0 !n 9 ,taurus1 j s\? ( ! ,pleiades4 ,x has s9ce mov$ f ,taurus1 ?r\gh ,aries1 & into ,pisces1 z %[n 9 ,fig4 #ci4 ,illu/ration3 ,fig4 #ch4 ,illu/ration3 ,fig4 #ci4 ,s9ce cele/ial longitude & "r asc5sion are bo? measur$ f ! fir/ po9t ( ,aries1 ! longitude & "r asc5sion ( ! />s are sl[ly *ang+ f ye> to ye>4 ,x w be se51 f ,figs4 #ch & #ci1 t ! decl9ation is also sl[ly *ang+4 #cj4 ,nutation4--,! gyratory motion ( ! e>?'s axis is n p]fectly regul> & uni=m4 ,! e>?'s axis has a slight tremul\s motion1 oscillat+ to & fro ?r\gh a %ort di/ance once 9 ab\t n9ete5 ye>s4 ,?is tremul\s motion ( ! axis causes ! pole ( ! heav5s to describe an undulat+ curve1 z %[n 9 ,fig4 #dj1 & gives a slight unev5ness to ! motion ( ! equ9oxes along ! ecliptic4 ,?is nodd+ motion ( ! axis is call$ nutation4 ,illu/ration3 ,fig4 #dj4 #ca4 ,refraction4--,:5 a ray ( light f "o ( ! heav5ly bodies ent]s ! e>?'s atmosph]e obliquely1 x w be b5t t[>ds a p]p5dicul> to ! surface ( ! atmosph]e1 s9ce x w be ent]+ a d5s] m$ium4 ,z ! ray trav]ses ! atmosph]e1 x w be cont9ually pass+ into d5s] & d5s] lay]s1 & w !re=e be b5t m & m t[>ds ! p]p5dicul>4 ,?is b5d+ ( ! ray is %[n 9 ,fig4 #da4 ,a ray :i* />t$ f ,a w\ld ent] ! eye at ,c1 z if x came f ,i3 h5ce a /> at ,a w\ld appe> to be at ,i4 ,illu/ration3 ,fig4 #da4 ,atmosph]ic refraction displaces all ! heav5ly bodies f ! horizon t[>ds ! z5i?4 ,?is is evid5t f ,fig4 #db4 ,,od is ! horizon1 & ,z ! z5i?1 ( an obs]v] at ,o4 ,refraction w\ld make a /> at ,q appe> at ,p3 9 o!r words1 x w\ld displace x t[>ds ! z5i?4 ,a /> 9 ! z5i? is n displac$ by refraction1 s9ce ! rays :i* rea* ! eye f x trav]se ! atmosph]e v]tically4 ,! f>!r a /> is f ! z5i?1 ! m x is displac$ by refraction1 s9ce ! great] is ! obliquity ) :i* ! rays f x ent] ! atmosph]e4 ,illu/ration3 ,fig4 #db4 ,at ! horizon ! displacem5t by refraction is ab\t half a degree2 b x v>ies consid]ably ) ! /ate ( ! atmosph]e4 ,refraction causes a heav5ly body to appe> above ! horizon long] ?an x really is above x1 s9ce x makes x appe> to be on ! horizon :5 x is really half a degree bel[ x4 ,! increase ( refraction t[>ds ! horizon (t5 makes ! sun1 :5 ne> ! horizon1 appe> di/ort$1 ! l[] limb ( ! sun be+ rais$ m ?an ! upp] limb4 ,?is di/ortion is %[n 9 ,fig4 #dc4 ,! v]tical diamet] ( ! sun appe>s to be consid]ably less ?an ! horizontal diamet]4 ,illu/ration3 ,fig4 #dc4 #cb4 ,p>allax4--,p>allax is ! displacem5t ( an object caus$ by a *ange 9 ! po9t ( view f :i* x is se54 ,?us 9 ,fig4 #dd1 ! top ( ! t[] ,s w\ld be se5 project$ aga9/ ! sky at a by an obs]v] at ,a1 & at b by an obs]v] at ,b4 ,9 pass+ f ,a to ,b1 ! top ( ! t[] is displac$ f a to b1 or by ! angle a,sb4 ,?is angle is call$ ! p>allax ( ,s1 z se5 f ,b in/ead ( ,a4 ,illu/ration3 ,fig4 #dd4 ,! geoc5tric p>allax ( a heav5ly body is its displacem5t caus$ by its be+ se5 f ! surface ( ! e>?1 in/ead ( f ! c5tre ( ! e>?4 ,9 ,fig4 #de1 ,r is ! c5tre ( ! e>?1 & ,o ! po9t ( obs]vation on ! surface ( ! e>?4 ,/>s at ,s1 ,s'1 & ,s''1 w\ld1 f ! c5tre ( ! e>?1 appe> at ,q1 ,q'1 & ,q''2 :ile f ! po9t ,o on ! surface ( ! e>?1 ^! same />s w\ld appe> at ,p1 ,p' & ,p''1 be+ displac$ f _! position1 z se5 f ! c5tre ( ! e>?1 by ! angles ,,qsp1 ,q',s',p'1 & ,q'',s'',p''4 ,x w be se5 t p>allax displaces a body f ! z5i? t[>ds ! horizon1 & t ! p>allax ( a body is greate/ :5 x is on ! horizon4 ,! p>allax ( a heav5ly body :5 on ! horizon is call$ its horizontal p>allax4 ,a body 9 ! z5i? is n displac$ by p>allax1 s9ce x w\ld be se5 9 ! same direction f bo? ! c5tre & ! surface ( ! e>?4 ,illu/ration3 ,fig4 #de4 ,! p>allax ( a body at ,s''' is ,q''',s''',p1 :i* is se5 to be great] ?an ,,qsp2 t is to say1 ! p>allax ( a heav5ly body increases ) its ne>ness to ! e>?4 ,! di/ance & p>allax ( a body are s relat$1 t1 ei!r be+ kn[n1 ! o!r may be comput$4 #cc4 ,ab]ration4--,ab]ration is a slight displacem5t ( a />1 ow+ to an app>5t *ange 9 ! direction ( ! rays ( light :i* proce$ f x1 caus$ by ! motion ( ! e>? 9 its orbit4 ,if we walk rapidly 9 any direction 9 ! ra91 :5 ! drops are fall+ v]tically1 !y w appe> to come into our faces f ! direction 9 :i* we are walk+4 ,our own motion has app>5tly *ang$ ! direction 9 :i* ! drops are fall+4 ,illu/ration3 ,fig4 #df4 ,9 ,fig4 #df let ,a be a gun ( a batt]y1 f :i* a %ot is fir$ at a %ip1 ,,de1 t is pass+4 ,let ,,abc be ! c\rse ( ! %ot4 ,! %ot ent]s ! %ip's side at ,b1 & passes out at ! o!r side at ,c2 b 9 ! mean "t ! %ip has mov$ f ,e to e1 & ! "p ,b1 :]e ! %ot ent]$1 has be5 c>ri$ to b4 ,if a p]son on bo>d ! %ip c\ld see ! ball z x cross$ ! %ip1 he w\ld see x cross 9 ! diagonal l9e b,c2 & he w\ld at once say t ! cannon 0 9 ! direction ( ,cb4 ,if ! %ip 7 mov+ 9 ! opposite direction1 he w\ld say t ! cannon 0 j z f> ! o!r side ( its true position4 ,n[1 we see a /> 9 ! direction 9 :i* ! light com+ f ! /> appe>s to be mov+4 ,:5 we exam9e a /> ) a telescope1 we are 9 ! same condition z ! p]son :o on %ipbo>d saw ! cannon-ball cross ! %ip4 ,! telescope is c>ri$ along by ! e>? at ! rate ( eighte5 miles a second3 h5ce ! light w appe> to pass ?r\gh ! tube 9 a slightly diff]5t direction f t 9 :i* x is really mov+3 j z ! cannon-ball appe>s to pass ?r\gh ! %ip 9 a diff]5t direction f t 9 :i* x is really mov+4 ,?us 9 ,fig4 #dg1 a ray ( light com+ 9 ! direction ,,sot w\ld appe> to trav]se ! tube ,,ot ( a telescope1 mov+ 9 ! direction ( ! arr[1 z if x 7 com+ 9 ! direction ,s',o4 ,illu/ration3 ,fig4 #dg4 ,z light moves ) enorm\s velocity1 x passes ?r\gh ! tube s quickly1 t x is app>5tly *ang$ f its true direction only by a v slight angle3 b x is suffici5t to displace ! />4 ,?is app>5t *ange 9 ! direction ( light caus$ by ! motion ( ! e>? is call$ ab]ration ( light4 #cd4 ,! ,planets4--,on wat*+ ! />s att5tively night aft] night1 x w be f\nd1 t :ile ! majority ( !m appe> fix$ on ! surface ( ! cele/ial sph]e1 s z to ma9ta9 _! relative positions1 !re are a few t w&] ab\t among ! />s1 alt]nately advanc+ t[>ds ! ea/1 halt+1 & retrograd+ t[>ds ! we/4 ,^! w&]+ />s are call$ planets4 ,_! motions appe> q irregul>2 b1 on ! :ole1 _! ea/w>d motion is 9 excess ( _! we/w>d1 & 9 a long] or %ort] "t !y all complete ! circuit ( ! heav5s4 ,9 almo/ e in/ance1 _! pa?s are f\nd to lie :olly 9 ! belt ( ! zodiac4 ,illu/ration3 ,fig4 #dh4 ,fig4 #dh %[s a portion ( ! app>5t pa? ( "o ( ! planets4 ,,ii4 ,,! ,,sol> ,,sy/em4 ,i4 ,,!ory ,,( ,,! ,,sol> ,,sy/em4 #ce4 ,memb]s ( ! ,sol> ,sy/em4--,! sol> sy/em is compos$ ( ! sun1 planets1 moons1 comets1 & meteors4 ,five planets1 besides ! e>?1 are readily di/+ui%$ by ! nak$ eye1 & 7 kn[n to ! anci5ts3 ^! are ,m]cury1 ,v5us1 ,m>s1 ,jupit]1 & ,saturn4 ,^!1 ) ! sun & moon1 made up ! sev5 planets ( ! anci5ts1 f :i* ! sev5 days ( ! week 7 nam$4 ,! ,ptolemaic ,sy/em4 #cf4 ,! ,cry/all9e ,sph]es4--,we h se5 t all ! heav5ly bodies appe> to be situat$ on ! surface ( ! cele/ial sph]e4 ,! anci5ts assum$ t ! />s 7 really fix$ on ! surface ( a cry/all9e sph]e1 & t !y 7 c>ri$ ar\nd ! e>? daily by ! rotation ( ?is sph]e4 ,!y _h1 h[ev]1 le>n$ to di/+ui% ! planets f ! />s1 & !y _h come to ! conclusion t "s ( ! planets 7 ne>] ! e>? ?an o!rs1 & t all ( !m 7 ne>] ! e>? ?an ! />s are4 ,?is l$ !m to imag9e t ! heav5s 7 compos$ ( a numb] ( cry/all9e sph]es1 "o above ano!r1 ea* c>ry+ "o ( ! planets1 & all revolv+ ar\nd ! e>? f ea/ to we/1 b at diff]5t rates4 ,?is /ructure ( ! heav5s is %[n 9 section 9 ,fig4 #di4 ,illu/ration3 ,fig4 #di4 #cg4 ,cycles & ,epicycles4--,! anci5ts _h also notic$ t1 :ile all ! planets move ar\nd ! heav5s f we/ to ea/1 _! motion is n "o ( uni=m advancem5t4 ,m]cury & ,v5us appe> to oscillate to & fro across ! sun1 :ile ,jupit] & ,saturn appe> to oscillate to & fro across a c5tre :i* is mov+ ar\nd ! e>?1 s z to describe a s]ies ( loops1 z %[n 9 ,fig4 #ej4 ,illu/ration3 ,fig4 #ej4 ,! anci5ts assum$ t ! planets mov$ 9 exact circles1 &1 9 fact1 t all motion 9 ! heav5s 0 circul>1 ! circle be+ ! simple/ & mo/ p]fect curve4 ,to acc\nt = ! loops describ$ by ! planets1 !y imag9$ t ea* planet revolv$ 9 a circle ar\nd a c5tre1 :i*1 9 turn1 revolv$ 9 a circle ar\nd ! e>?4 ,! circle describ$ by ?is c5tre ar\nd ! e>? !y call$ ! cycle1 & ! circle describ$ by ! planet ar\nd ?is c5tre !y call$ ! epicycle4 #ch4 ,! ,ecc5tric4--,! anci5ts assum$ t ! planets mov$ at a uni=m rate 9 describ+ ! epicycle1 & also ! c5tre 9 describ+ ! cycle4 ,!y _h1 h[ev]1 discov]$ t ! planets advance ea/w>d m rapidly 9 "s p>ts ( _! orbits ?an 9 o!rs4 ,to acc\nt = ?is !y assum$ t ! cycles describ$ by ! c5tre1 ar\nd :i* ! planets revolv$1 7 ecc5tric2 t is to say1 t ! e>? 0 n at ! c5tre ( ! cycle1 b "s di/ance away f x1 z %[n 9 ,fig4 #ea4 ,e is ! position ( ! e>?1 & ,c is ! c5tre ( ! cycle4 ,! l9es f ,e are drawn s z to int]cept equal arcs ( ! cycle4 ,x w be se5 at once t ! angle betwe5 any pair ( l9es is greate/ at ,p1 & lea/ at ,a2 s t1 7 a planet mov+ at ! same rate at ,p & ,a1 x w\ld seem to be mov+ mu* fa/] at ,p4 ,! po9t ,p ( ! planet's cycle 0 call$ its p]igee1 & ! po9t ,a its apogee4 ,illu/ration3 ,fig4 #ea4 ,z ! app>5t motion ( ! planets became m accurately kn[n1 x 0 f\nd necess>y to make ! sy/em ( cycles1 epicycles1 & ecc5trics exce$+ly complicat$ to repres5t t motion4 ,! ,cop]nican ,sy/em4 #ci4 ,cop]nicus4--,cop]nicus simplifi$ ! ,ptolemaic sy/em greatly by assum+ t ! e>? & all ! planets revolv$ ab\t ! sun z a c5tre4 ,he1 h[ev]1 /ill ma9ta9$ t all motion 9 ! heav5s 0 circul>1 & h5ce he c\ld n rid 8 sy/em entirely ( cycles & epicycles4 ,ty*o ,brahe's ,sy/em4 #dj4 ,ty*o ,brahe4--,ty*o ,brahe 0 ! greate/ ( ! e>ly a/ronomical obs]v]s4 ,he1 h[ev]1 reject$ ! sy/em ( ,cop]nicus1 & adopt$ "o ( 8 own1 :i* 0 mu* m complicat$4 ,he held t all ! planets b ! e>? revolv$ ar\nd ! sun1 :ile ! sun & moon revolv$ ar\nd ! e>?4 ,?is sy/em is %[n 9 ,fig4 #eb4 ,illu/ration3 ,fig4 #eb4 ,kepl]'s ,sy/em4 #da4 ,kepl]4--,:ile ,ty*o ,brahe devot$ 8 life to ! obs]vation ( ! planets4 ,kepl] gave 8 to ! /udy ( ,ty*o's obs]vations1 = ! purpose ( discov]+ ! true laws ( planet>y motion4 ,he bani%$ ! complicat$ sy/em ( cycles1 epicycles1 & ecc5trics =ev] f ! heav5s1 & discov]$ ! ?ree laws ( planet>y motion :i* h r5d]$ 8 "n immortal4 #db4 ,! ,ellipse4--,an ellipse is a clos$ curve :i* has two po9ts )9 x1 ! sum ( ^: di/ances f e po9t on ! curve is ! same4 ,^! two po9ts are call$ ! foci ( ! ellipse4 ,illu/ration3 ,fig4 #ec4 ,"o me?od ( describ+ an ellipse is %[n 9 ,fig4 #ec4 ,two tacks1 ,f & ,f'1 are /uck into a piece ( pap]1 & to ^! are fa/5$ ! two ends ( a /r+ :i* is long] ?an ! di/ance betwe5 ! tacks4 ,a p5cil is !n plac$ aga9/ ! /r+1 & c>ri$ ar\nd1 z %[n 9 ! figure4 ,! curve describ$ by ! p5cil is an ellipse4 ,! two po9ts ,f & ,f' are ! foci ( ! ellipse3 ! sum ( ! di/ances ( ^! two po9ts f e po9t on ! curve is equal to ! l5g? ( ! /r+4 ,:5 half ( ! ellipse has be5 describ$1 ! p5cil mu/ be held aga9/ ! o!r side ( ! /r+ 9 ! same way1 & c>ri$ ar\nd z be=e4 ,! po9t ,o1 half way betwe5 ,f & ,f'1 is call$ ! c5tre ( ! ellipse2 ,,aa' is ! major axis ( ! ellipse1 & ,,cd is ! m9or axis4 #dc4 ,! ,ecc5tricity ( ! ,ellipse4--,! ratio ( ! di/ance betwe5 ! two foci to ! major axis ( ! ellipse is call$ ! ecc5tricity ( ! ellipse4 ,! great] ! di/ance betwe5 ! two foci1 comp>$ ) ! major axis ( ! ellipse1 ! great] is ! ecc5tricity ( ! ellipse2 & ! less ! di/ance betwe5 ! foci1 comp>$ ) ! l5g? ( ! major axis1 ! less ! ecc5tricity ( ! ellipse4 ,! ellipse ( ,fig4 #ed has an ecc5tricity ( #a_/h4 ,?is ellipse sc>cely diff]s 9 appe>ance f a circle4 ,! ellipse ( ,fig4 #ee has an ecc5tricity ( #a_/b1 & t ( ,fig4 #ef an ecc5tricity ( #g_/h4 ,illu/ration3 ,fig4 #ed4 ,illu/ration3 ,fig4 #ee4 ,illu/ration3 ,fig4 #ef4 #dd4 ,kepl]'s ,fir/ ,law4--,kepl] fir/ discov]$ t all ! planets move f we/ to ea/ 9 ellipses :i* h ! sun z a common focus4 ,?is law ( planet>y motion is kn[n z ,kepl]'s ,fir/ ,law4 ,! planets appe> to describe loops1 because we view !m f a mov+ po9t4 ,! ellipses describ$ by ! planets diff] 9 ecc5tricity2 &1 ?\gh !y all h "o focus at ! sun1 _! major axes h diff]5t directions4 ,! ecc5tricity ( ! planet>y orbits is comp>atively small4 ,! ellipse ( ,fig4 #ed has sev5 times ! ecc5tricity ( ! e>?'s orbit1 & twice t ( ! orbit ( any ( ! l>g] planets except ,m]cury2 & its ecc5tricity is m ?an half ( t ( ! orbit ( ,m]cury4 ,ow+ to _! small ecc5tricity1 ! orbits ( ! planets are usually repres5t$ by circles 9 a/ronomical diagrams4 ,illu/ration3 ,fig4 #eg4 #de4 ,kepl]'s ,second ,law4--,kepl] next discov]$ t a planet's rate ( motion 9 ! v>i\s p>ts ( its orbit is su* t a l9e drawn f ! planet to ! sun w\ld always sweep ov] equal areas 9 equal times4 ,?us1 9 ,fig4 #eg1 suppose ! planet w\ld move f ,p to ,p#a 9 ! same "t t x w\ld move f ,p#b to ,p#c1 or f ,p#d to ,p#e2 !n ! d>k spaces1 :i* w\ld be swept ov] by a l9e jo9+ ! sun & ! planet1 9 ^! equal times1 w\ld all be equal4 ,a l9e drawn f ! sun to a planet is call$ ! radius vector ( ! planet4 ,! radius vector ( a planet is %orte/ :5 ! planet is ne>e/ ! sun1 or at p]ihelion1 & longe/ :5 ! planet is f>!/ f ! sun1 or at aphelion3 h5ce1 9 ord] to h ! areas equal1 x foll[s t a planet mu/ move fa/e/ :5 at p]ihelion1 & sl[e/ at aphelion4 ,kepl]'s ,second ,law ( planet>y motion is usually /at$ z foll[s3 ,! radius vector ( a planet describes equal areas 9 equal times 9 e "p ( ! planet's orbit4 #df4 ,kepl]'s ,?ird ,law4--,kepl] f9ally discov]$ t ! p]iodic times ( ! planets be> ! foll[+ relation to ! di/ances ( ! planets f ! sun3 ,! squ>es ( ! p]iodic times ( ! planets are to ea* o!r z ! cubes ( _! mean di/ances f ! sun4 ,?is is kn[n z ,kepl]'s ,?ird ,law ( planet>y motion4 ,by p]iodic "t is meant ! "t x takes a planet to revolve ar\nd ! sun4 ,^! ?ree laws ( ,kepl]'s are ! f\ndation ( mod]n physical a/ronomy4 ,! ,newtonian ,sy/em4 #dg4 ,newton's ,discov]y4--,newton foll[$ ,kepl]1 & by means ( 8 ?ree laws ( planet>y motion made 8 own immortal discov]y ( ! law ( gravitation4 ,?is law is z foll[s3 ,e portion ( matt] 9 ! univ]se attracts e o!r portion ) a =ce v>y+ directly z ! product ( ! masses act$ ^u1 & inv]sely z ! squ>e ( ! di/ances betwe5 !m4 #dh4 ,! ,conic ,sections4--,! conic sections are ! figures =m$ by ! v>i\s plane sections ( a "r cone4 ,!re are f\r classes ( figures =m$ by ^! sections1 accord+ to ! angle :i* ! plane ( ! section makes ) ! axis ( ! cone4 ,,opq1 ,fig4 #eh1 is a "r cone1 & ,,on is its axis4 ,any section1 ,,ab1 ( ?is cone1 ^: plane is p]p5dicul> to ! axis ( ! cone1 is a circle4 ,illu/ration3 ,fig4 #eh4 ,any section1 ,,cd1 ( ?is cone1 ^: plane is oblique to ! axis1 b =ms ) x an angle great] ?an ,,nop1 is an ellipse4 ,! less ! angle :i* ! plane ( ! section makes ) ! axis1 ! m elongat$ is ! ellipse4 ,any section1 ,,ef1 ( ?is cone1 ^: plane makes ) ! axis an angle equal to ,,nop1 is a p>abola4 ,x w be se51 t1 by *ang+ ! obliquity ( ! plane ,,cd to ! axis ,,no1 we may pass un9t]rupt$ly f ! circle ?r\gh ellipses ( great] & great] elongation to ! p>abola4 ,any section1 ,,gh1 ( ?is cone1 ^: plane makes ) ! axis ,,on an angle less ?an ,,nop1 is a hyp]bola4 ,illu/ration3 ,fig4 #ei4 ,x w be se5 f ,fig4 #ei1 9 :i* comp>ative views ( ! f\r conic sections are giv51 t ! circle & ! ellipse are clos$ curves1 or curves :i* return into !mselves4 ,! p>abola & ! hyp]bola are1 on ! contr>y1 op5 curves1 or curves :i* d n return into !mselves4 #di4 ,a ,revolv+ ,body is cont9ually ,fall+ t[>ds its ,c5tre ( ,revolution4--,9 ,fig4 #fj let ,m repres5t ! moon1 & ,e ! e>? ar\nd :i* ! moon is revolv+ 9 ! direction ,,mn4 ,x w be se5 t ! moon1 9 mov+ f ,m to ,n1 falls t[>ds ! e>? a di/ance equal to m,n4 ,x is kept f fall+ into ! e>? by its orbital motion4 ,illu/ration3 ,fig4 #fj4 ,! fact t a body might be project$ =w>d fa/ en\gh to keep x f fall+ into ! e>? is evid5t f ,fig4 #fa4 ,,ab repres5ts ! level surface ( ! ocean1 ,c a m\nta9 f ! summit ( :i* a cannon-ball is suppos$ to be fir$ 9 ! direction ,,ce4 ,,ad is a l9e p>allel ) ,,ce2 ,,db is a l9e equal to ! di/ance betwe5 ! two p>allel l9es ,,ad & ,,ce4 ,?is di/ance is equal to t ov] :i* gravity w\ld pull a ball t[>ds ! c5tre ( ! e>? 9 a m9ute4 ,no matt]1 !n1 ) :at velocity ! ball ,c is fir$1 at ! end ( a m9ute x w be some:]e on ! l9e ,,ad4 ,suppose x 7 fir$ fa/ en\gh to rea* ! po9t ,d 9 a m9ute3 x w\ld be on ! l9e ,,ad at ! end ( ! m9ute1 b /ill j z f> f ! surface ( ! wat] z :5 x />t$4 ,x w be se51 t1 al?\gh x has all ! :ile be5 fall+ t[>ds ! e>?1 x has all ! :ile kept at exactly ! same di/ance f ! surface4 ,! same ?+ w\ld ( c\rse be true dur+ ea* succe$+ m9ute1 till ! ball came r\nd to ,c aga91 & ! ball w\ld cont9ue to revolve 9 a circle ar\nd ! e>?4 ,illu/ration3 ,fig4 #fa4 #ej4 ,! ,=m ( a ,body's ,orbit dep5ds ^u ! ,rate ( its ,=w>d ,motion4--,if ! ball ,c 7 fir$ fa/ en\gh to rea* ! l9e ,,ad beyond ! po9t ,d1 x w\ld be f>!r f ! surface at ! end ( ! second ?an :5 x />t$4 ,its orbit w\ld no long] be circul>1 b elliptical4 ,if ! spe$ ( projection 7 gradually augm5t$1 ! orbit w\ld become a m & m elongat$ ellipse4 ,at a c]ta9 rate ( projection1 ! orbit w\ld become a p>abola2 at a /ill great] rate1 a hyp]bola4 #ea4 ,! ,moon held 9 h] ,orbit by ,gravity4--,newton comp>$ ! di/ance m,n t ! moon is drawn to ! e>? 9 a giv5 "t1 ) ! di/ance a body ne> ! surface ( ! e>? w\ld be pull$ t[>d ! e>? 9 ! same "t2 & he f\nd t ^! di/ances are to ea* o!r inv]sely z ! squ>es ( ! di/ances ( ! two bodies f ! c5tre ( ! e>?4 ,he !re=e conclud$ t ! moon is drawn to ! e>? by gravity1 & t ! int5sity ( gravity decreases z ! squ>e ( ! di/ance increases4 ,illu/ration3 ,fig4 #fb4 #eb4 ,any ,body ^: ,orbit is a ,conic ,section1 & :i* moves accord+ to ,kepl]'s ,second ,law1 is act$ ^u by a ,=ce v>y+ inv]sely z ! ,squ>e ( ! ,di/ance4--,newton comp>$ ! di/ance :i* any body1 mov+ 9 an ellipse1 accord+ to ,kepl]'s ,second ,law1 is drawn t[>ds ! sun 9 ! same "t 9 diff]5t p>ts ( its orbit4 ,he f\nd ^! di/ances 9 all cases to v>y inv]sely z ! squ>e ( ! di/ance ( ! planet f ! sun4 ,?us1 9 ,fig4 #fb1 suppose a planet w\ld move f ,k to ,b 9 ! same "t t x w\ld move f k to b 9 ano!r "p ( its orbit4 ,9 ! fir/ in/ance ! planet w\ld be drawn t[>ds ! sun ! di/ance ,,ab1 & 9 ! second in/ance ! di/ance ab4 ,newton f\nd t ,,ab 3 ab 7,,sk7#b 3 7,sk7#b4 ,he also f\nd t ! same w\ld be true :5 ! body mov$ 9 a p>abola or a hyp]bola3 h5ce he conclud$ t e body t moves ar\nd ! sun 9 an ellipse1 a p>abola1 or a hyp]bola1 is mov+ "u ! influ5ce ( gravity4 ,transcrib]'s ,note3 ,9 ,newton's equation above1 7,,sk7#b means to gr\p ,s & ,k toge!r & squ>e _! product4 ,9 ! orig9al book1 in/ead ( us+ p>5!ses1 !re 0 a v9culum1 a horizontal b>1 drawn ov] ! ,s & ! ,k to express ! same gr\p+4 ,illu/ration3 ,fig4 #fc4 #ec4 ,! ,=ce t draws ! ,diff]5t ,planets to ! ,sun ,v>ies inv]sely z ! ,squ>es ( ! ,di/ances ( ! ,planets f ! ,sun4--,newton comp>$ ! di/ances j,k & e,f1 ov] :i* two planets are drawn t[>ds ! sun 9 ! same "t1 & f\nd ^! di/ances to v>y inv]sely z ! squ>es ( ! di/ances ( ! planets f ! sun3 h5ce he conclud$ t all ! planets are held 9 _! orbits by gravity4 ,he also %[$ t ?is w\ld be true ( any two bodies t 7 revolv+ ar\nd ! sun's c5tre1 accord+ to ,kepl]'s ,?ird ,law4 #ed4 ,! ,cop]nican ,sy/em4--,! !ory ( ! sol> sy/em :i* orig9at$ ) ,cop]nicus1 & :i* 0 develop$ & complet$ by ,kepl] & ,newton1 is commonly kn[n z ! ,cop]nican ,sy/em4 ,?is sy/em is %[n 9 ,fig4 #fd4 ,illu/ration3 ,fig4 #fd4 ,,ii4 ,,! ,,sun ,,& ,,planets4 ,i4 ,,! ,,e>?4 ,=m & ,size4 #ee4 ,=m ( ! ,e>?4--,9 ord9>y language ! t]m horizon d5otes ! l9e t b\nds ! portion ( ! e>?'s surface t is visible at any po9t4 7#a7 ,x is well kn[n t ! horizon ( a pla9 pres5ts ! =m ( a circle surr\nd+ ! obs]v]4 ,if ! latt] moves1 ! circle moves also2 b its =m rema9s ! same1 & is modifi$ only :5 m\nta9s or o!r ob/acles limit ! view4 ,out at sea1 ! circul> =m ( ! horizon is /ill m decid$1 & *anges only ne> ! coa/s1 ! outl9e ( :i* breaks ! regul>ity4 ,"h1 !n1 we obta9 a fir/ notion ( ! rotundity ( ! e>?1 s9ce a sph]e is ! only body :i* is pres5t$ always to u "u ! =m ( a circle1 f :atev] po9t on its surface x is view$4 7#b7 ,moreov]1 x _c be ma9ta9$ t ! horizon is ! vani%+ po9t ( di/9ct vision1 & t x is ?is :i* causes ! appe>ance ( a circul> b\nd>y1 because ! horizon is enl>g$ :5 we m\nt above ! surface ( ! pla94 ,?is w be evid5t f ,fig4 #fe1 9 :i* a m\nta9 is depict$ 9 ! middle ( a pla91 ^: uni=m curvature is t ( a sph]e4 ,f ! foot ( ! m\nta9 ! spectator w h b a v limit$ horizon4 ,let him asc5d half way1 8 visual radius ext5ds1 is incl9$ bel[ ! fir/ horizon1 & reveals a m ext5d$ circul> area4 ,at ! summit ( ! m\nta9 ! horizon /ill increases2 &1 if ! atmosph]e is pure1 ! spectator w see num]\s objects :]e f ! l[] /ations ! sky alone 0 visible4 ,illu/ration3 ,fig4 #fe4 ,?is ext5sion ( ! horizon w\ld be inexplicable if ! e>? _h ! =m ( an ext5d$ plane4 7#c7 ,! curvature ( ! surface ( ! sea manife/s itself 9 a /ill m /rik+ mann]4 ,if we are on ! coa/ at ! summit ( a hill1 & a vessel appe>s on ! horizon 7,fig4 #ff71 we see only ! tops ( ! ma/s & ! highe/ sails2 ! l[] sails & ! hull are invisible4 ,z ! vessel approa*es1 its l[] "p comes into view above ! horizon1 & soon x appe>s entire4 ,illu/ration3 ,fig4 #ff4 ,9 ! same mann] ! sailors f ! %ip see ! diff]5t p>ts ( objects on ! l& appe> successively1 beg9n+ ) ! highe/4 ,! reason ( ?is w be evid5t f ,fig4 #fg1 :]e ! c\rse ( a vessel1 se5 9 pr(ile1 is figur$ on ! convex surface ( ! sea4 ,illu/ration3 ,fig4 #fg4 ,z ! curvature ( ! ocean is ! same 9 e direction1 x foll[s t ! surface ( ! ocean is sph]ical4 ,! same is true ( ! surface ( ! l&1 all[ance be+ made = ! v>i\s inequalities ( ! surface4 ,f ^! & v>i\s o!r indications1 we conclude t ! e>? is a sph]e4 #ef4 ,size ( ! ,e>?4--,! size ( ! e>? is asc]ta9$ by measur+ ! l5g? ( a degree ( a m]idian1 & multiply+ ?is by ?ree hundr$ & sixty4 ,?is gives ! circumf]5ce ( ! e>? z ab\t tw5ty-five ?\s& miles1 & its diamet] z ab\t eight ?\s& miles4 ,we "k t ! two /ations betwe5 :i* we measure are "o degree ap>t :5 ! elevation ( ! pole at "o /ation is "o degree great] ?an at ! o!r4 #eg4 ,! ,e>? ,flatt5$ at ! ,poles4--,degrees on ! m]idian h be5 measur$ 9 v>i\s p>ts ( ! e>?1 & x has be5 f\nd t !y inv>iably increase 9 l5g? z we proce$ f ! equator t[>ds ! pole3 h5ce ! e>? mu/ curve less & less rapidly z we approa* ! poles2 = ! less ! curvature ( a circle1 ! l>g] ! degrees on x4 ,illu/ration3 ,fig4 #fh4 #eh4 ,! ,e>? 9 ,space4--,9 ,fig4 #fh we h a view ( ! e>? susp5d$ 9 space4 ,! side ( ! e>? turn$ t[>ds ! sun is illum9$1 & ! o!r side is 9 d>kness4 ,z ! planet rotates on its axis1 successive portions ( x w be turn$ t[>ds ! sun4 ,z view$ f a po9t 9 space betwe5 x & ! sun1 x w pres5t light & d>k portions1 :i* w assume diff]5t =ms accord+ to ! portion :i* is illum9$4 ,^! diff]5t appe>ances are %[n 9 ,fig4 #fi4 ,illu/ration3 ,fig4 #fi4 ,day & ,night4 #ei4 ,day & ,night4--,! succession ( day & night is due to ! rotation ( ! e>? on its axis1 by :i* a place on ! surface ( ! e>? is c>ri$ alt]nately into ! sun%9e & out ( x4 ,z ! sun moves ar\nd ! heav5s on ! ecliptic1 x w be on ! cele/ial equator :5 at ! equ9oxes1 & #bc-a_/b nor? ( ! equator :5 at ! summ] sol/ice1 & #bc-a_/b s\? ( ! equator :5 at ! w9t] sol/ice4 #fj4 ,day & ,night :5 ! ,sun is at ! ,equ9oxes4--,:5 ! sun is at ei!r equ9ox1 ! diurnal circle describ$ by ! sun w co9cide ) ! cele/ial equator2 & !re=e half ( ?is diurnal circle w be above ! horizon at e po9t on ! surface ( ! globe4 ,at ^! times day & night w be equal 9 e "p ( ! e>?4 ,illu/ration3 ,fig4 #gj4 ,illu/ration3 ,fig4 #ga4 ,! equality ( days & nights :5 ! sun is on ! cele/ial equator is also evid5t f ! foll[+ consid]ations3 "o-half ( ! e>? is 9 sun%9e all ( ! "t2 :5 ! sun is on ! cele/ial equator1 x is directly ov] ! equator ( ! e>?1 & ! illum9ation ext5ds f pole to pole1 z is evid5t f ,figs4 #gj & #ga1 9 ! =m] ( :i* ! sun is repres5t$ z on ! ea/]n horizon at a place along ! c5tral l9e ( ! figure1 & 9 ! latt] z on ! m]idian along ! same l9e4 ,9 ea* diagram x is se5 t ! illum9ation ext5ds f pole to pole3 h5ce1 z ! e>? rotates on its axis1 e place on ! surface w be 9 ! sun%9e & out ( x j half ( ! "t4 #fa4 ,day & ,night :5 ! ,sun is at ! ,summ] ,sol/ice4--,:5 ! sun is at ! summ] sol/ice1 x w be #bc-a_/b nor? ( ! cele/ial equator4 ,! diurnal circle describ$ by ! sun w !n be #bc-a_/b nor? ( ! cele/ial equator2 & m ?an half ( ?is diurnal circle w be above ! horizon at all places nor? ( ! equator1 & less ?an half ( x at places s\? ( ! equator3 h5ce ! days w be long] ?an ! nights at places nor? ( ! equator1 & %ort] ?an ! nights at places s\? ( ! equator4 ,at places )9 #bc-a_/b ( ! nor? pole1 ! entire diurnal circle describ$ by ! sun w be above ! horizon1 s t ! sun w n set4 ,at places )9 #bc-a_/b ( ! s\? pole ( ! e>?1 ! entire diurnal circle w be bel[ ! horizon1 s t ! sun w n rise4 ,illu/ration3 ,fig4 #gb4 ,illu/ration3 ,fig4 #gc4 ,! illum9ation ( ! e>? at ?is "t is %[n 9 ,figs4 #gb & #gc4 ,9 ,fig4 #gb ! sun is repres5t$ z on ! we/]n horizon along ! middle l9e ( ! figure1 & 9 ,fig4 #gc z on ! m]idian4 ,x is se5 at once t ! illum9ation ext5ds #bc-a_/b beyond ! nor? pole1 & falls #bc-a_/b %ort ( ! s\? pole4 ,z ! e>? rotates on its axis1 places ne> ! nor? pole w be 9 ! sun%9e all ! "t1 :ile places ne> ! s\? pole w be out ( ! sun%9e all ! "t4 ,all places nor? ( ! equator w be 9 ! sun%9e long] ?an !y are out ( x1 :ile all places s\? ( ! equator w be out ( ! sun%9e long] ?an !y are 9 x4 #fb4 ,day & ,night :5 ! ,sun is at ! ,w9t] ,sol/ice4--,:5 ! sun is at ! w9t] sol/ice1 x is #bc-a_/b s\? ( ! cele/ial equator4 ,! diurnal circle describ$ by ! sun is !n #bc-a_/b s\? ( ! cele/ial equator4 ,m ?an half ( ?is diurnal circle w !re=e be above ! horizon at all places s\? ( ! equator1 & less ?an half ( x at all places nor? ( ! equator3 h5ce ! days w be long] ?an ! nights s\? ( ! equator1 & %ort] ?an ! nights at places nor? ( ! equator4 ,at places )9 #bc-a_/b ( ! s\? pole1 ! diurnal circle describ$ by ! sun w be entirely above ! horizon1 & ! sun w !re=e n set4 ,at places )9 #bc-a_/b ( ! nor? pole1 ! diurnal circle describ$ by ! sun w be :olly bel[ ! horizon1 & !re=e ! sun w n rise4 ,! illum9ation ( ! e>? at ?is "t is %[n 9 ,figs4 #gd & #ge1 & is se5 to be ! rev]se ( t %[n 9 ,figs4 #gb & #gc4 ,illu/ration3 ,fig4 #gd4 ,illu/ration3 ,fig4 #ge4 #fc4 ,v>iation 9 ! ,l5g? ( ,day & ,night4--,z long z ! sun is nor? ( ! equ9octial1 ! nights w be long] ?an ! days s\? ( ! equator1 & %ort] ?an ! days nor? ( ! equator4 ,x is j ! rev]se :5 ! sun is s\? ( ! equator4 ,! f>!r ! sun is f ! equator1 ! great] is ! inequality ( ! days & nights4 ,! f>!r ! place is f ! equator1 ! great] ! inequality ( its days & nights4 ,:5 ! di/ance ( a place f ! nor? pole is less ?an ! di/ance ( ! sun nor? ( ! equ9octial1 x w h cont9u\s day )\t night1 s9ce ! :ole ( ! sun's diurnal circle w be above ! horizon4 ,a place )9 ! same di/ance ( ! s\? pole w h cont9u\s night4 ,:5 ! di/ance ( a place f ! nor? pole is less ?an ! di/ance ( ! sun s\? ( ! equ9octial1 x w h cont9u\s night1 s9ce ! :ole ( ! sun's diurnal circle w !n be bel[ ! horizon4 ,a place )9 ! same di/ance ( ! s\? pole w !n h cont9u\s day4 ,at ! equator ! days & nights are always equal2 s9ce1 no matt] :]e ! sun is 9 ! heav5s1 half ( all ! diurnal circles describ$ by x w be above ! horizon1 & half ( !m bel[ x4 #fd4 ,! ,zones4--,x w be se51 f :at has be5 /at$ above1 t ! sun w at "s "t dur+ ! ye> be directly ov]head at e place )9 #bc-a_/b ( ! equator on ei!r side4 ,?is belt ( ! e>? is call$ ! torrid zone4 ,! torrid zone is b\nd$ by circles call$ ! tropics2 t ( ,canc] on ! nor?1 & t ( ,capricorn on ! s\?4 ,x w also be se51 t1 at e place )9 #bc-a_/b ( ei!r pole1 !re w be1 "s "t dur+ ! ye>1 a day dur+ :i* ! sun w n rise1 or on :i* x w n set4 ,^! two belts ( ! e>?'s surface are call$ ! frigid zones4 ,^! zones are b\nd$ by ! arctic circles4 ,! ne>] a place is to ! poles1 ! great] ! numb] ( days on :i* ! sun does n rise or set4 ,betwe5 ! frigid zones & ! torrid zones1 !re are two belts on ! e>? :i* are call$ ! temp]ate zones4 ,! sun is nev] ov]head at any place 9 ^! two zones1 b x rises & sets e day at e place )9 _! limits4 #fe4 ,! ,wid? ( ! ,zones4--,! di/ance ! frigid zones ext5d f ! poles1 & ! torrid zones f ! equator1 is exactly equal to ! obliquity ( ! ecliptic1 or ! deviation ( ! axis ( ! e>? f ! p]p5dicul> to ! plane ( its orbit4 ,7 ?is deviation =ty-five degrees1 ! obliquity ( ! ecliptic w\ld be =ty-five degrees1 ! torrid zone w\ld ext5d =ty-five degrees f ! equator1 & ! frigid zones =ty-five degrees f ! poles4 ,9 ?is case !re w\ld be no temp]ate zones4 ,7 ?is deviation fifty degrees1 ! torrid & frigid zones w\ld ov]lap t5 degrees1 & !re w\ld be two belts ( t5 degrees on ! e>?1 :i* w\ld exp]i5ce alt]nately dur+ ! ye> a torrid & a frigid climate4 ,7 ! axis ( ! e>? p]p5dicul> to ! plane ( ! e>?'s orbit1 !re w\ld be no zones on ! e>?1 & no v>iation 9 ! l5g? ( day & night4 #ff4 ,twilight4--,7 x n = ! atmosph]e1 ! d>kness ( midnight w\ld beg9 ! mom5t ! sun sank bel[ ! horizon1 & w\ld cont9ue till he rose aga9 above ! horizon 9 ! ea/1 :5 ! d>kness ( ! night w\ld be sudd5ly succe$$ by ! full light ( day4 ,! gradual transition f ! light ( day to ! d>kness ( ! night1 & f ! d>kness ( ! night to ! light ( day1 is call$ twilight1 & is due to ! diffusion ( light f ! upp] lay]s ( ! atmosph]e aft] ! sun has ceas$ to %9e on ! l[] lay]s at night1 or be=e x has begun to %9e on !m 9 ! morn+4 ,illu/ration3 ,fig4 #gf4 ,let ,,abcd 7,fig4 #gf7 repres5t a portion ( ! e>?1 ,a a po9t on its surface :]e ! sun ,s is sett+2 & let ,,sah be a ray ( light j graz+ ! e>? at ,a1 & leav+ ! atmosph]e at ! po9t ,h4 ,! po9t ,a is illum9at$ by ! :ole reflective atmosph]e ,,hgfe4 ,! po9t ,b1 to :i* ! sun has set1 receives no direct sol> light1 nor any reflect$ f t "p ( ! atmosph]e :i* is bel[ ,,alh2 b x receives a twilight f ! portion ,,hlf1 :i* lies above ! visible horizon ,,bf4 ,! po9t ,c receives a twilight only f ! small portion ( ! atmosph]e2 :ile at ,d ! twilight has ceas$ altoge!r4 #fg4 ,duration ( ,twilight4--,! a/ronomical limit ( twilight is g5]ally und]/ood to be ! in/ant :5 />s ( ! six? magnitude beg9 to be visible 9 ! z5i? at ev5+1 or disappe> 9 ! morn+4 ,twilight is usually reckon$ to la/ until ! sun's depression bel[ ! horizon am\nts to eighte5 degrees3 ?is1 h[ev]1 v>ies2 9 ! tropics a depression ( sixte5 or sev5te5 degrees be+ suffici5t to put an end to ! ph5om5on1 :ile 9 ,engl& a depression ( sev5te5 to tw5ty-"o degrees is requir$4 ,! duration ( twilight diff]s 9 diff]5t latitudes2 x v>ies also 9 ! same latitude at diff]5t seasons ( ! ye>1 & dep5ds1 9 "s measure1 on ! meteorological condition ( ! atmosph]e4 ,:5 ! sky is ( a pale color1 indicat+ ! pres5ce ( an unusual am\nt ( cond5s$ vapor1 twilight is ( long] duration4 ,?is happ5s habitually 9 ! pol> regions4 ,on ! contr>y1 )9 ! tropics1 :]e ! air is pure & dry1 twilight sometimes la/s only fifte5 m9utes4 ,/rictly speak+1 9 ! latitude ( ,gre5wi* !re is no true night f ,may #bb to ,july #ba1 b con/ant twilight f sunset to sunrise4 ,twilight rea*es its m9imum ?ree weeks be=e ! v]nal equ9ox1 & ?ree weeks aft] ! autumnal equ9ox1 :5 its duration is an h\r & fifty m9utes4 ,at midw9t] x is long] by ab\t sev5te5 m9utes2 b ! augm5tation is frequ5tly n p]ceptible1 ow+ to ! great] preval5ce ( cl\ds & haze at t season ( ! ye>1 :i* int]cept ! light1 & h9d] x f rea*+ ! e>?4 ,! duration is lea/ at ! equator 7an h\r & twelve m9utes71 & increases z we approa* ! poles2 = at ! =m] !re are two twilights e tw5ty-f\r h\rs1 b at ! latt] only two 9 a ye>1 ea* la/+ ab\t fifty days4 ,at ! nor? pole ! sun is bel[ ! horizon = six mon?s1 b f ,jan4 #bi to ! v]nal equ9ox1 & f ! autumnal equ9ox to ,nov4 #ab1 ! sun is less ?an eighte5 degrees bel[ ! horizon2 s t !re is twilight dur+ ! :ole ( ^! int]vals1 & ?us ! l5g? ( ! actual night is r$uc$ to two mon?s & a half4 ,! l5g? ( ! day 9 ^! regions is ab\t six mon?s1 dur+ ! :ole ( :i* "t ! sun is con/antly above ! horizon4 ,! g5]al rule is1 t to ! inhabitants ( an oblique sph]e ! twilight is long] 9 proportion z ! place is ne>] ! elevat$ pole1 & ! sun is f>!r f ! equator on ! side ( ! elevat$ pole4 ,! ,seasons4 #fh4 ,! ,seasons4--,:ile ! sun is nor? ( ! cele/ial equator1 places nor? ( ! equator are receiv+ heat f ! sun by day long] ?an !y are los+ x by radiation at night1 :ile places s\? ( ! equator are los+ heat by radiation at night long] ?an !y are receiv+ x f ! sun by day4 ,:51 !re=e1 ! sun passes nor? ( ! equator1 ! temp]ature beg9s to rise at places nor? ( ! equator1 & to fall at places s\? ( x4 ,! rise ( temp]ature is mo/ rapid nor? ( ! equator :5 ! sun is at ! summ] sol/ice2 b1 = "s "t aft] ?is1 ! e>? cont9ues to receive m heat by day ?an x loses by night1 & !re=e ! temp]ature cont9ues to rise4 ,= ?is reason1 ! heat is m excessive aft] ! sun passes ! summ] sol/ice ?an be=e x rea*es x4 #fi4 ,! ,duration ( ! ,seasons4--,summ] is c\nt$ z beg9n+ 9 ,june1 :5 ! sun is at ! summ] sol/ice1 & z cont9u+ until ! sun rea*es ! autumnal equ9ox1 9 ,septemb]4 ,autumn !n beg9s1 & cont9ues until ! sun is at ! w9t] sol/ice1 9 ,decemb]4 ,w9t] foll[s1 cont9u+ until ! sun comes to ! v]nal equ9ox1 9 ,m>*1 :5 spr+ beg9s1 & cont9ues to ! summ] sol/ice4 ,9 popul> reckon+ ! seasons beg9 ) ! fir/ day ( ,june1 ,septemb]1 ,decemb]1 & ,m>*4 ,! reason :y w9t] is c\nt$ z occurr+ aft] ! w9t] sol/ice is simil> to ! reason :y ! summ] is plac$ aft] ! summ] sol/ice4 ,! e>? nor? ( ! equator is los+ heat mo/ rapidly at ! "t ( ! w9t] sol/ice2 b = "s "t aft] ?is x loses m heat by night ?an x receives by day3 h5ce = "s "t ! temp]ature cont9ues to fall1 & ! cold is m int5se aft] ! w9t] sol/ice ?an be=e x4 ,illu/ration3 ,fig4 #gg4 ,( c\rse1 :5 x is summ] 9 ! nor!rn hemisph]e1 x is w9t] 9 ! s\!rn hemisph]e1 & ! rev]se4 ,fig4 #gg %[s ! portion ( ! e>?'s orbit includ$ 9 ea* season4 ,x w be se5 t ! e>? is at p]ihelion 9 ! w9t] season = places nor? ( ! equator1 & at aphelion 9 ! summ] season4 ,?is t5ds to mitigate some:at ! extreme temp]atures ( our w9t]s & summ]s4 ,illu/ration3 ,fig4 #gh4 #gj4 ,! ,illum9ation ( ! ,e>? at ! diff]5t ,seasons4--,fig4 #gh %[s ! e>? z x w\ld appe> to an obs]v] at ! sun dur+ ea* ( ! f\r seasons2 t is to say1 ! portion ( ! e>? t is receiv+ ! sun's rays4 ,figs4 #gi1 #hj1 #ha1 & #hb are enl>g$ views ( ! e>?1 z se5 f ! sun at ! "t ( ! summ] sol/ice1 ( ! autumnal equ9ox1 ( ! w9t] sol/ice1 & ( ! v]nal equ9ox4 ,illu/ration3 ,fig4 #gi4 ,illu/ration3 ,fig4 #hj4 ,illu/ration3 ,fig4 #ha4 ,illu/ration3 ,fig4 #hb4 ,illu/ration3 ,fig4 #hc4 ,fig4 #hc is1 s to speak1 a side view ( ! e>?1 %[+ ! limit ( sun%9e on ! e>? :5 ! sun is at ! summ] sol/ice2 & ,fig4 #hd1 %[+ ! limit ( sun%9e :5 ! sun is at ! autumnal equ9ox4 ,illu/ration3 ,fig4 #hd4 #ga4 ,cause ( ! ,*ange ( ,seasons4--,v>iety 9 ! l5g? ( day & night1 & div]sity 9 ! seasons1 dep5d ^u ! obliquity ( ! ecliptic4 ,7 !re no obliquity ( ! ecliptic1 !re w\ld be no inequality 9 ! l5g? ( day & night1 & b slight div]sity ( seasons4 ,! great] ! obliquity ( ! ecliptic1 ! great] w\ld be ! v>iation 9 ! l5g? ( ! days & nights1 & ! m extreme ! *anges ( ! seasons4 ,tides4 #gb4 ,tides4--,! alt]nate rise & fall ( ! surface ( ! sea twice 9 ! c\rse ( a lun> day1 or ( tw5ty-f\r h\rs & fifty-"o m9utes1 is kn[n z ! tides4 ,:5 ! wat] is ris+1 x is said to be flood tide2 & :5 x is fall+1 ebb tide4 ,:5 ! wat] is at its greate/ height1 x is said to be high wat]2 & :5 at its lea/ height1 l[ wat]4 #gc4 ,cause ( ! ,tides4--,x has be5 kn[n to seaf>+ nations f a remote antiquity t !re is a s+ul> connection betwe5 ! ebb & fl[ ( ! tides & ! diurnal motion ( ! moon4 ,illu/ration3 ,fig4 #he4 ,?is tidal movem5t 9 seem+ ob$i5ce to ! moon 0 a my/]y until ! /udy ( ! law ( gravitation %[$ x to be due to ! attraction ( ! moon on ! wat]s ( ! ocean4 ,! reason :y !re are two tides a day w appe> f ,fig4 #he4 ,let ,m be ! moon1 ,e ! e>?1 & ,,em ! l9e jo9+ _! c5tres4 ,n[1 /rictly speak+1 ! moon does n revolve ar\nd ! e>? any m ?an ! e>? ar\nd ! moon2 b ! c5tre ( ea* body moves ar\nd ! common c5tre ( gravity ( ! two bodies4 ,! e>? be+ eighty times z heavy z ! moon1 ?is c5tre is situat$ )9 ! =m]1 ab\t ?ree-qu>t]s ( ! way f its c5tre to its surface1 at ! po9t ,g4 ,! body ( ! e>? itself be+ solid1 e "p ( x1 9 consequ5ce ( ! moon's attraction1 may be consid]$ z describ+ a circle once 9 a mon?1 ) a radius equal to ,,eg4 ,! c5trifugal =ce caus$ by ?is rotation is j balanc$ by ! mean attraction ( ! moon ^u ! e>?4 ,if ?is attraction 7 ! same on e "p ( ! e>?1 !re w\ld be ev]y:]e an exact balance betwe5 x & ! c5trifugal =ce4 ,b z we pass f ,e to ,d ! attraction ( ! moon dim9i%es1 ow+ to ! increas$ di/ance3 h5ce at ,d ! c5trifugal =ce pr$om9ates1 & ! wat] !re=e t5ds to move away f ! c5tre ,e4 ,z we pass f ,e t[>ds ,c1 ! attraction ( ! moon increases1 & !re=e exce$s ! c5trifugal =ce3 consequ5tly at ,c !re is a t5d5cy to draw ! wat] t[>ds ! moon1 b /ill away f ! c5tre ,e4 ,at ,a & ,b ! attraction ( ! moon increases ! gravity ( ! wat]1 ow+ to ! conv]g5ce ( ! l9es ,,bm & ,,am1 along :i* x acts3 h5ce ! action ( ! moon t5ds to make ! wat]s rise at ,d & ,c1 & to fall at ,a & ,b1 caus+ two tides to ea* app>5t diurnal revolution ( ! moon4 #gd4 ,! ,lagg+ ( ! ,tides4--,if ! wat]s ev]y:]e yield$ imm$iately to ! attractive =ce ( ! moon1 x w\ld always be high wat] :5 ! moon 0 on ! m]idian1 l[ wat] :5 %e 0 ris+ or sett+1 & high wat] aga9 :5 %e 0 on ! m]idian bel[ ! horizon4 ,b1 ow+ to ! in]tia ( ! wat]1 "s "t is necess>y = s slight a =ce to set x 9 motion2 &1 once 9 motion1 x cont9ues s aft] ! =ce has ceas$1 & until x has act$ "s "t 9 ! opposite direction4 ,!re=e1 if ! motion ( ! wat] 7 unimp$$1 x w\ld n be high wat] until "s h\rs aft] ! moon _h pass$ ! m]idian4 ,! free motion ( ! wat] is also imp$$ by ! isl&s & cont95ts4 ,^! deflect ! tidal wave f its c\rse 9 su* a way t x may1 9 "s cases1 be _m h\rs1 or ev5 a :ole day1 beh9d its "t4 ,sometimes two waves meet ea* o!r1 & raise a v high tide4 ,9 "s places ! tides run up a long bay1 :]e ! motion ( a l>ge mass ( wat] w cause an enorm\s tide to be rais$4 ,9 ! ,bay ( ,fundy bo? ( ^! causes are comb9$4 ,a tidal wave com+ up ! ,atlantic coa/ meets ! ocean wave f ! ea/1 &1 ent]+ ! bay ) _! comb9$ =ce1 !y raise ! wat] at ! head ( x to ! height ( sixty or sev5ty feet4 #ge4 ,spr+-,tides & ,neap-,tides4--,! sun produces a tide z well z ! moon2 b ! tide-produc+ =ce ( ! sun is only ab\t f\r-t5?s ( t ( ! moon4 ,at new & full moon ! two bodies unite _! =ces1 ! ebb & fl[ become great] ?an ! av]age1 & we h ! spr+-tides4 ,:5 ! moon is 9 h] fir/ or ?ird qu>t]1 ! two =ces act aga9/ ea* o!r2 ! tide-produc+ =ce is ! diff]5ce ( ! two2 ! ebb & fl[ are less ?an ! av]age2 & we h ! neap-tides4 ,illu/ration3 ,fig4 #hf4 ,illu/ration3 ,fig4 #hg4 ,illu/ration3 ,fig4 #hh4 ,fig4 #hf %[s ! tide t w\ld be produc$ by ! moon alone2 ,fig4 #hg1 ! tide produc$ by ! comb9$ action ( ! sun & moon2 & ,fig4 #hh1 by ! sun & moon act+ at "r angles to ea* o!r4 ,! tide is affect$ by ! di/ance ( ! moon f ! e>?1 be+ highe/ ne> ! "t :5 ! moon is 9 p]igee1 & l[e/ ne> ! "t :5 %e is 9 apogee4 ,:5 ! moon is 9 p]igee1 at or ne> ! "t ( a new or full moon1 unusually high tides occur4 #gf4 ,diurnal ,inequality ( ,tides4--,! height ( ! tide at a giv5 place is influ5c$ by ! decl9ation ( ! moon4 ,:5 ! moon has no decl9ation1 ! highe/ tides %\ld occur along ! equator1 & ! heights %\ld dim9i% f !nce t[>d ! nor? & s\?2 b ! two daily tides at any place %\ld h ! same height4 ,:5 ! moon has nor? decl9ation1 z %[n 9 ,fig4 #hi1 ! highe/ tides on ! side ( ! e>? next ! moon w be at places hav+ a correspond+ nor? latitude1 z at ,b1 & on ! opposite side at ^? :i* h an equal s\? latitude4 ,( ! two daily tides at any place1 t :i* occurs :5 ! moon is ne>e/ ! z5i? %\ld be ! greate/3 h5ce1 :5 ! moon's decl9ation is nor?1 ! height ( ! tide at a place 9 nor? latitude %\ld be great] :5 ! moon is above ! horizon ?an :5 %e is bel[ x4 ,at ! same "t1 places s\? ( ! equator h ! highe/ tides :5 ! moon is bel[ ! horizon1 & ! lea/ :5 %e is above x4 ,?is is call$ ! diurnal inequality1 because its cycle is "o day2 b x v>ies greatly 9 am\nt at diff]5t places4 ,illu/ration3 ,fig4 #hi4 #gg4 ,height ( ,tides4--,at small isl&s 9 mid-ocean ! tides nev] rise to a great height1 sometimes ev5 less ?an "o foot2 & ! av]age height ( ! tides = ! isl&s ( ! ,atlantic & ,pacific ,oceans is only ?ree feet & a half4 ,^u approa*+ an ext5sive coa/ :]e ! wat] is %all[1 ! height ( ! tide is increas$2 s t1 :ile 9 mid-ocean ! av]age height does n exce$ ?ree feet & a half1 ! av]age 9 ! neighborhood ( cont95ts is n less ?an f\r or five feet4 ,! ,day & ,"t4 #gh4 ,! ,day4--,by ! t]m day we sometimes d5ote ! p]iod ( sun%9e z contra/$ ) t ( ! abs5ce ( sun%9e1 :i* we call night1 & sometimes ! p]iod ( ! e>?'s rotation on its axis4 ,x is ) ! latt] signification t ! t]m is us$ 9 ?is section4 ,z ! e>? rotates on its axis1 x c>ries ! m]idian ( a place ) x2 s t1 dur+ ea* complete rotation ( ! e>?1 ! portion ( ! m]idian :i* passes ov]head f pole to pole sweeps pa/ e /> 9 ! heav5s f we/ to ea/4 ,! int]val betwe5 two successive passages ( ?is portion ( ! m]idian across ! same /> is ! exact p]iod ( ! complete rotation ( ! e>?4 ,?is p]iod is call$ a sid]eal day4 ,! sid]eal day may also be def9$ z ! int]val betwe5 two successive passages ( ! same /> across ! m]idian2 ! passage ( ! m]idian across ! />1 & ! passage or transit ( ! /> across ! m]idian1 be+ ! same ?+ look$ at f a diff]5t po9t ( view4 ,! int]val betwe5 two successive passages ( ! m]idian across ! sun1 or ( ! sun across ! m]idian1 is call$ a sol> day4 #gi4 ,l5g? ( ! ,sol> ,day4--,! sol> day is a little long] ?an ! sid]eal day4 ,?is is ow+ to ! sun's ea/w>d motion among ! />s4 ,we h already se5 t ! sun's app>5t position among ! />s is cont9ually %ift+ t[>ds ! ea/ at a rate :i* causes x to make a complete circuit ( ! heav5s 9 a ye>1 or ?ree hundr$ & sixty-five days4 ,?is is at ! rate ( ab\t "o degree a day3 h5ce1 7 ! sun & a /> on ! m]idian toge!r to-day1 :5 ! m]idian aga9 came ar\nd to ! />1 ! sun w\ld appe> ab\t "o degree to ! ea/w>d3 h5ce ! m]idian mu/ be c>ri$ ab\t "o degree f>!r 9 ord] to come up to ! sun4 ,! sol> day mu/ !re=e be ab\t f\r m9utes long] ?an ! sid]eal day4 ,illu/ration3 ,fig4 #ij4 ,illu/ration3 ,fig4 #ia4 ,! fact t ! e>? mu/ make m ?an a complete rotation is also evid5t f ,figs4 #ij & #ia4 ,9 ,fig4 #ij1 ba repres5ts ! plane ( ! m]idian1 & ! small arr[s indicate ! direction ! e>? is rotat+ on its axis1 & revolv+ 9 its orbit4 ,:5 ! e>? is at #a1 ! sun is on ! m]idian at a4 ,:5 ! e>? has mov$ to #b1 x has made a complete rotation1 z is %[n by ! fact t ! plane ( ! m]idian is p>allel ) its position at #a2 b x is evid5t t ! m]idian has n yet come up ) ! sun4 ,9 ,fig4 #ia1 ,,oa repres5ts ! plane ( ! m]idian1 & ,,os ! direction ( ! sun4 ,! small arr[s indicate ! direction ( ! rotation & revolution ( ! e>?4 ,9 pass+ f ! fir/ position to ! second ! e>? makes a complete rotation1 b ! m]idian is n br\ght up to ! sun4 #hj4 ,inequality 9 ! ,l5g? ( ,sol> ,days4--,! sid]eal days are all ( ! same l5g?2 b ! sol> days diff] some:at 9 l5g?4 ,?is diff]5ce is due to ! fact t ! sun's app>5t position moves ea/w>d1 or away f ! m]idian1 at a v>iable rate4 ,!re are ?ree reasons :y ?is rate is v>iable3-- 7#a7 ,! sun's ea/w>d motion is due to ! revolution ( ! e>? 9 its orbit4 ,n[1 ! e>?'s orbital motion is n uni=m1 be+ fa/e/ :5 ! e>? is at p]ihelion1 & sl[e/ :5 ! e>? is at aphelion3 h5ce1 o!r ?+s be+ equal1 sol> days w be longe/ :5 ! e>? is at p]ihelion1 & %orte/ :5 ! e>? is at aphelion4 ,illu/ration3 ,fig4 #ib4 ,illu/ration3 ,fig4 #ic4 7#b7 ,! sun's ea/w>d motion is along ! ecliptic4 ,n[1 f ,figs4 #ib & #ic1 x w be se51 t1 :5 ! sun is at "o ( ! equ9oxes1 x w be mov+ away f ! m]idian obliquely2 &1 f ,figs4 #id & #ie1 t1 :5 ! sun is at "o ( ! sol/ices1 x w be mov+ away f ! m]idian p]p5dicul>ly3 h5ce1 o!r ?+s be+ equal1 ! sun w\ld move away f ! m]idian fa/e/1 & ! days be longe/1 :5 ! sun is at ! sol/ices2 :ile x w\ld move away f ! m]idian sl[e/1 & ! days be %orte/1 :5 ! sun is at ! equ9oxes4 ,t a body mov+ along ! ecliptic mu/ be mov+ at a v>iable angle to ! m]idian becomes v evid5t on turn+ a cele/ial globe s z to br+ ea* portion ( ! ecliptic "u ! m]idian 9 turn4 ,illu/ration3 ,fig4 #id4 ,illu/ration3 ,fig4 #ie4 7#c7 ,! sun1 mov+ along ! ecliptic1 always moves 9 a great circle1 :ile ! po9t ( ! m]idian :i* is to ov]take ! sun moves 9 a diurnal circle1 :i* is sometimes a great circle & sometimes a small circle4 ,:5 ! sun is at ! equ9oxes1 ! po9t ( ! m]idian :i* is to ov]take x moves 9 a great circle4 ,z ! sun passes f ! equ9oxes to ! sol/ices1 ! po9t ( ! m]idian :i* is to ov]take x moves on a small] & small] circle3 h5ce1 z we pass away f ! cele/ial equator1 ! po9ts ( ! m]idian move sl[] & sl[]4 ,!re=e1 o!r ?+s be+ equal1 ! m]idian w ga9 ^u ! sun mo/ rapidly1 & ! days be %orte/1 :5 ! sun is at ! equ9oxes2 :ile x w ga9 on ! sun lea/ rapidly1 & ! days w be longe/1 :5 ! sun is at ! sol/ices4 ,! ord9>y or civil day is ! mean ( all ! sol> days 9 a ye>4 #ha4 ,sun ,"t & ,clock ,"t4--,x is noon by ! sun :5 ! sun is on ! m]idian1 & by ! clock at ! middle ( ! civil day4 ,n[1 z ! civil days are all ( ! same l5g?1 :ile sol> days are ( v>iable l5g?1 x seldom happ5s t ! middles ( ^! two days co9cide1 or t sun "t & clock "t agree4 ,! diff]5ce betwe5 sun "t & clock "t1 or :at is (t5 call$ app>5t sol> "t & mean sol> "t1 is call$ ! equation ( "t4 ,! sun is said to be sl[ :5 x crosses ! m]idian aft] noon by ! clock1 & fa/ :5 x crosses ! m]idian be=e noon by ! clock4 ,sun "t & clock "t co9cide f\r times a ye>2 dur+ two int]m$iate seasons ! clock "t is ahead1 & dur+ two x is beh9d4 99 99 99 99 99 ,! foll[+ are ! dates ( co9cid5ce & ( maximum deviation1 :i* v>y b slightly f ye> to ye>3-- ,febru>y #aj ,true sun fifte5 m9utes sl[4 ,april #ae ,true sun correct4 ,may #ad ,true sun f\r m9utes fa/4 ,june #ad ,true sun correct4 ,july #be ,true sun six m9utes sl[4 ,augu/ #ca ,true sun correct4 ,novemb] #b ,true sun sixte5 m9utes fa/4 ,decemb] #bd ,true sun correct4 ,"o ( ! effects ( ! equation ( "t :i* is frequ5tly misund]/ood is1 t ! int]val f sunrise until noon1 z giv5 9 ! almanacs1 is n ! same z t betwe5 noon & sunset4 ,! =5oon c\ld n be long] or %ort] ?an ! aft]noon1 if by noon we meant ! passage ( ! sun across ! m]idian2 b ! noon ( our clocks be+ sometimes fifte5 m9utes be=e or aft] noon by ! sun1 ! =m] may be half an h\r ne>] to sunrise ?an to sunset1 or vice v]sa4 ,! ,ye>4 #hb4 ,! ,ye>4--,! ye> is ! "t x takes ! e>? to revolve ar\nd ! sun1 or1 :at am\nts to ! same ?+1 ! "t x takes ! sun to pass ar\nd ! ecliptic4 7#a7 ,! "t x takes ! sun to pass f a /> ar\nd to ! same /> aga9 is call$ a sid]eal ye>4 ,?is is1 ( c\rse1 ! exact "t x takes ! e>? to make a complete revolution ar\nd ! sun4 ,illu/ration3 ,fig4 #if4 7#b7 ,! "t x takes ! sun to pass ar\nd f ! v]nal equ9ox1 or ! fir/ po9t ( ,aries1 to ! v]nal equ9ox aga91 is call$ ! tropical ye>4 ,?is is a little %ort] ?an ! sid]eal ye>1 ow+ to ! precession ( ! equ9oxes4 ,?is w be evid5t f ,fig4 #if4 ,! circle repres5ts ! ecliptic1 ,s ! sun1 & ,e ! v]nal equ9ox4 ,! sun moves ar\nd ! ecliptic ea/w>d1 z indicat$ by ! long arr[1 :ile ! equ9ox moves sl[ly we/w>d1 z indicat$ by ! %ort arr[4 ,! sun w !re=e meet ! equ9ox be=e x has q complet$ ! circuit ( ! heav5s4 ,! exact l5g?s ( ^! respective ye>s are3-- ,sid]eal ye> #cfe4befcfcfe days #f h\rs #i m9 #i sec ,tropical ye> #cfe4bdbbjcfe days #e h\rs #dh m9 #df sec ,s9ce ! recurr5ce ( ! seasons dep5ds on ! tropical ye>1 ! latt] is ! "o to be us$ 9 =m+ ! cal5d> & = ! purposes ( civil life g5]ally4 ,its true l5g? is elev5 m9utes & f\rte5 seconds less ?an ?ree hundr$ & sixty-five days & a f\r?4 ,x w be se5 t ! tropical ye> is ab\t tw5ty m9utes %ort] ?an ! sid]eal ye>4 7#c7 ,! "t x takes ! e>? to pass f its p]ihelion po9t ar\nd to ! p]ihelion po9t aga9 is call$ ! anomali/ic ye>4 ,?is ye> is ab\t f\r m9utes long] ?an ! sid]eal ye>4 ,?is is ow+ to ! fact t ! major axis ( ! e>?'s orbit is sl[ly mov+ ar\nd to ! ea/ at ! rate ( ab\t t5 seconds a ye>4 ,?is causes ! p]ihelion po9t ,p 7,fig4 #ig7 to move ea/w>d at t rate1 z indicat$ by ! %ort arr[4 ,! e>? ,e is also mov+ ea/w>d1 z indicat$ by ! long arr[4 ,h5ce ! e>?1 on />t+ at ! p]ihelion1 has to make a little m ?an a complete circuit to rea* ! p]ihelion po9t aga94 ,illu/ration3 ,fig4 #ig4 #hc4 ,! ,cal5d>4--,! sol> ye>1 or ! int]val betwe5 two successive passages ( ! same equ9ox by ! sun1 is #cfe days1 #e h\rs1 #dh m9utes1 #df seconds4 ,if1 !n1 we reckon only #cfe days to a common or civil ye>1 ! sun w come to ! equ9ox #e h\rs1 #dh m9utes1 #df seconds1 or ne>ly a qu>t] ( a day1 lat] ea* ye>2 s t1 if ! sun ent]$ ,aries on ! #bj? ( ,m>* "o ye>1 he w\ld ent] x on ! #ba/ f\r ye>s aft]1 on ! #bb;d eight ye>s aft]1 & s on4 ,?us 9 a comp>atively %ort "t ! spr+ mon?s w\ld come 9 ! w9t]1 & ! summ] mon?s 9 ! spr+4 ,among diff]5t anci5t nations diff]5t me?ods ( comput+ ! ye> 7 9 use4 ,"s reckon$ x by ! revolution ( ! moon1 "s by t ( ! sun2 b none1 s f> z we "k1 made prop] all[ances = defici5cies & excesses4 ,twelve moons fell %ort ( ! true ye>1 ?irte5 exce$$ x2 #cfe days 7 n en\gh1 #cff 7 too _m4 ,to prev5t ! confusion result+ f ^! errors1 ,julius ,cs> re=m$ ! cal5d> by mak+ ! ye> consi/ ( #cfe days1 #f h\rs 7:i* is h5ce call$ a ,julian ye>71 & made e f\r? ye> consi/ ( #cff days4 ,?is me?od ( reckon+ is call$ ,old ,/yle4 ,b z ?is made ! ye> some:at too long1 & ! error 9 #aehb am\nt$ to t5 days1 ,pope ,gregory ,,xiii41 9 ord] to br+ ! v]nal equ9ox back to ! #ba/ ( ,m>* aga91 ord]$ t5 days to be /ruck out ( t ye>1 call+ ! next day aft] ! #d? ( ,octob] ! #ae?2 &1 to prev5t simil> confusion 9 ! future1 he decre$ t ?ree leap-ye>s %\ld be omitt$ 9 ! c\rse ( e f\r hundr$ ye>s4 ,?is way ( reckon+ "t is call$ ,new ,/yle4 ,x 0 imm$iately adopt$ by mo/ ( ! ,european nations1 b 0 n accept$ by ! ,engli% until ! ye> #ageb4 ,! error !n am\nt$ to elev5 days1 :i* 7 tak5 f ! mon? ( ,septemb] by call+ ! #c;d ( t mon? ! #ad?4 ,! ,old ,/yle is /ill reta9$ by ,russia4 ,accord+ to ! ,gregorian cal5d>1 e ye> ^: numb] is divisible by f\r is a leap-ye>1 except1 t1 9 ! case ( ! ye>s ^: numb]s are exact hundr$s1 ^? only are leap-ye>s :i* are divisible by f\r aft] cutt+ (f ! la/ two figures4 ,?us ! ye>s #afjj1 #bjjj1 #bdjj1 etc41 are leap-ye>s2 #agjj1 #ahjj1 #aijj1 #bajj1 #bbjj1 etc41 are n4 ,! error w n am\nt to a day 9 ov] ?ree ?\s& ye>s4 #hd4 ,! ,dom9ical ,lett]4--,! dom9ical lett] = any ye> is t :i* we (t5 see plac$ aga9/ ,sunday 9 ! almanacs1 & is always "o ( ! fir/ sev5 9 ! alphabet4 ,s9ce a common ye> consi/s ( #cfe days1 if ?is numb] is divid$ by sev5 7! numb] ( days 9 a week71 !re w be a rema9d] ( "o3 h5ce a ye> commonly beg9s "o day lat] 9 ! week ?an ! prec$+ "o did4 ,if a ye> ( #cfe days beg9s on ,sunday1 ! next w beg9 on ,monday2 if x beg9s on ,?ursday1 ! next w beg9 on ,friday2 & s on4 ,if ,sunday falls on ! #a/ ( ,janu>y1 ! fir/ lett] ( ! alphabet1 or ,a1 is ! dom9ical lett]4 ,if ,sunday falls on ! #g? ( ,janu>y 7z x w ! next ye>1 unless ! fir/ is leap-ye>71 ! sev5? lett]1 ,g1 is ! dom9ical lett]4 ,if ,sunday falls on ! #f? ( ,janu>y 7z x w ! ?ird ye>1 unless ! fir/ or second is leap-ye>71 ! six? lett]1 ,f1 w be ! dom9ical lett]4 ,?us1 if !re 7 no leap-ye>s1 ! dom9ical lett]s w\ld regul>ly foll[ a retrograde ord]1 ,g1 ,f1 ,e1 ,d1 ,c1 ,b1 ,a4 ,b leap-ye>s h #cff days1 :i*1 divid$ by sev51 leaves two rema9d]3 h5ce ! ye>s foll[+ leap-ye>s w beg9 two days lat] 9 ! week ?an ! leap-ye>s did4 ,to prev5t ! int]ruption :i* w\ld h5ce occur 9 ! ord] ( ! dom9ical lett]s1 leap-ye>s h two dom9ical lett]s1 "o indicat+ ,sunday till ! #bi? ( ,febru>y1 & ! o!r = ! re/ ( ! ye>4 ,by ,table ,i4 bel[1 ! dom9ical lett] = any ye> 7,new ,/yle7 = f\r ?\s& ye>s f ! beg9n+ ( ! ,*ri/ian ,era may be f\nd2 & x w be readily se5 h[ ! ,table c\ld be ext5d$ indef9itely by cont9u+ ! c5turies at ! top 9 ! same ord]4 ,to f9d ! dom9ical lett] by ?is table1 look = ! hundr$s ( ye>s at ! top1 & = ! ye>s bel[ a hundr$1 at ! left h&4 ,?us ! lett] = #ahhb w be opposite ! numb] #hb1 & 9 ! column hav+ #ahjj at ! top2 t is1 x w be ,a4 ,9 ! same way1 ! lett]s = #ahhd1 :i* is a leap-ye>1 w be f\nd to be ,,fe4 ,hav+ ! dom9ical lett] ( any ye>1 ,table ,,ii4 %[s :at days ( e mon? ( ! ye> w be ,sundays4 ,to f9d ! ,sundays ( any mon? 9 ! ye> by ?is table1 look 9 ! column1 "u ! dom9ical lett]1 opposite ! "n ( ! mon? giv5 at ! left4 ,f ! ,sundays ! date ( any o!r day ( ! week c be readily f\nd4 ,?us1 if we wi% to "k on :at day ( ! week ,*ri/mas falls 9 #ahhi1 we look opposite ,decemb]1 "u ! lett] ,f 7:i* we h f\nd to be ! dom9ical lett] = ! ye>71 & f9d t ! #bb;d ( ! mon? is a ,sunday2 ! #be?1 or ,*ri/mas1 w !n be ,w$nesday4 ,9 ! same way we may f9d ! day ( ! week correspond+ to any date 7,new ,/yle7 9 hi/ory4 ,= in/ance1 ! #ag? ( ,june1 #agge1 ! day ( ! fight at ,bunk] ,hill1 is f\nd to h be5 a ,saturday4 ,^! two tables !n s]ve z a p]petual almanac4 ,,table ,i4 #ajj #bjj #cjj #djj #ejj #fjj #gjj #hjj #ijj #ajjj #aajj #abjj #acjj #adjj #aejj #afjj #agjj #ahjj #aijj #bjjj #bajj #bbjj #bcjj #bdjj --- --- --- ---- ,c ,e ,g ,,ba #a #bi #eg #he ,b ,d ,f ,g #b #cj #eh #hf ,a ,c ,e ,f #c #ca #ei #hg ,g ,b ,d ,e #d #cb #fj #hh ,,fe ,,ag ,,cb ,,dc #e #cc #fa #hi ,d ,f ,a ,b #f #cd #fb #ij ,c ,e ,g ,a #g #ce #fc #ia ,b ,d ,f ,g #h #cf #fd #ib ,,ag ,,cb ,,ed ,,fe #i #cg #fe #ic ,f ,a ,c ,d #aj #ch #ff #id ,e ,g ,b ,c #aa #ci #fg #ie ,d ,f ,a ,b #ab #dj #fh #if ,,cb ,,ed ,,gf ,,ag #ac #da #fi #ig ,a ,c ,e ,f #ad #db #gj #ih ,g ,b ,d ,e #ae #dc #ga #ii ,f ,a ,c ,d #af #dd #gb 44 ,,ed ,,gf ,,ba ,,cb #ag #de #gc 44 ,c ,e ,g ,a #ah #df #gd 44 ,b ,d ,f ,g #ai #dg #ge 44 ,a ,c ,e ,f #bj #dh #gf 44 ,,gf ,,ba ,,dc ,,ed #ba #di #gg 44 ,e ,g ,b ,c #bb #ej #gh 44 ,d ,f ,a ,b #bc #ea #gi 44 ,c ,e ,g ,a #bd #eb #hj 44 ,,ba ,,dc ,,fe ,,gf #be #ec #ha 44 ,g ,b ,d ,e #bf #ed #hb 44 ,f ,a ,c ,d #bg #ee #hc 44 ,e ,g ,b ,c #bh #ef #hd 44 ,,dc ,,fe ,,ag ,,ba ,,table ,,ii4 ,a ,b ,c ,d ,e ,f ,g #a #b #c #d #e #f #g ,jan4 #ca4 #h #i #aj #aa #ab #ac #ad #ae #af #ag #ah #ai #bj #ba ,oct4 #ca4 #bb #bc #bd #be #bf #bg #bh #bi #cj #ca 44 44 44 44 ,feb4 #bh-bi4 44 44 44 #a #b #c #d #e #f #g #h #i #aj #aa ,m>* #ca4 #ab #ac #ad #ae #af #ag #ah #ai #bj #ba #bb #bc #bd #be ,nov4 #cj4 #bf #bg #bh #bi #cj #ca 44 44 44 44 44 44 44 #a ,april #cj4 #b #c #d #e #f #g #h #i #aj #aa #ab #ac #ad #ae ,july #ca #af #ag #ah #ai #bj #ba #bb #bc #bd #be #bf #bg #bh #bi #cj #ca 44 44 44 44 44 44 44 #a #b #c #d #e #f #g #h #i #aj #aa #ab ,aug4 #ca4 #ac #ad #ae #af #ag #ah #ai #bj #ba #bb #bc #bd #be #bf #bg #bh #bi #cj #ca 44 44 44 44 44 44 44 #a #b ,sept4 #cj4 #c #d #e #f #g #h #i #aj #aa #ab #ac #ad #ae #af #ag #ah #ai #bj #ba #bb #bc ,dec4 #ca4 #bd #be #bf #bg #bh #bi #cj #ca 44 44 44 44 44 44 44 #a #b #c #d #e #f #g #h #i #aj #aa #ab #ac ,may4 #ca4 #ad #ae #af #ag #ah #ai #bj #ba #bb #bc #bd #be #bf #bg #bh #bi #cj #ca 44 44 44 44 44 44 44 #a #b #c #d #e #f #g #h #i #aj ,june #cj4 #aa #ab #ac #ad #ae #af #ag #ah #ai #bj #ba #bb #bc #bd #be #bf #bg #bh #bi #cj 44 ,weight ( ! ,e>? & ,precession4 #he4 ,! ,weight ( ! ,e>?4--,!re are sev]al me?ods ( asc]ta9+ ! weight & mass ( ! e>?4 ,! simple/1 & p]haps ! mo/ tru/wor?y me?od is to comp>e ! pull ( ! e>? ^u a ball ( lead ) t ( a kn[n mass ( lead ^u x4 ,! pull ( a kn[n mass ( lead ^u ! ball may be measur$ by means ( a torsion balance4 ,"o =m ( ! balance employ$ = ?is purpose is %[n 9 ,figs4 #ih & #ii4 ,two small balls ( lead1 b & b1 are fa/5$ to ! ends ( a light rod e1 :i* is susp5d$ f ! po9t ,f by means ( ! ?read ,,fe4 ,two l>ge balls ( lead1 ,w & ,w1 are plac$ on a turn-table1 s t "o ( !m %all be j 9 front ( "o ( ! small balls1 & ! o!r j beh9d ! o!r small ball4 ,! pull ( ! l>ge balls turns ! rod ar\nd a little s z to br+ ! small balls ne>] ! l>ge ones4 ,! small balls move t[>ds ! l>ge ones till !y are /opp$ by ! torsion ( ! ?read1 :i* is !n equal to ! pull ( ! l>ge balls4 ,! deflection ( ! rod is c>efully measur$4 ,! table is !n turn$ into ! position indicat$ by ! dott$ l9es 9 ,fig4 #ii1 s z to rev]se ! position ( ! l>ge balls ) ref]5ce to ! small ones4 ,! rod is n[ deflect$ 9 ! opposite direction1 & ! am\nt ( deflection is aga9 c>efully measur$4 ,! second measurem5t is made z a *eck ^u ! accuracy ( ! fir/4 ,! =ce requir$ to twi/ ! ?read z mu* z x 0 twi/$ by ! deflection ( ! rod is asc]ta9$ by measurem5t4 ,?is gives ! pull ( ! two l>ge balls ^u ! two small ones4 ,we next calculate :at ?is pull w\ld be 7 ! balls z f> ap>t z ! small balls are f ! c5tre ( ! e>?4 ,we c !n =m ! foll[+ proportion3 ! pull ( ! l>ge balls ^u ! small ones is to ! pull ( ! e>? ^u ! small ones z ! mass ( ! l>ge balls is to ! mass ( ! e>?1 or z ! weight ( ! l>ge balls is to ! weight ( ! e>?4 ,( c\rse1 ! pull ( ! e>? ^u ! small balls is ! weight ( ! small balls4 ,9 ?is way x has be5 asc]ta9$ t ! mass ( ! e>? is ab\t #e4f times t ( a globe ( wat] ( ! same size4 ,9 o!r words1 ! mean d5sity ( ! e>? is ab\t #e4f4 ,illu/ration3 ,fig4 #ih4 ,illu/ration3 ,fig4 #ii4 ,! weight ( ! e>? 9 p\nds may be f\nd by multiply+ ! numb] ( cubic feet 9 x by #fb-a_/b 7! weight1 9 p\nds1 ( "o cubic foot ( wat]71 & ?is product by #e4f4 ,illu/ration3 ,fig4 #ajj4 #hf4 ,cause ( ,precession4--,we h se5 t ! e>? is flatt5$ at ! poles3 9 o!r words1 ! e>? has ! =m ( a sph]e1 ) a protub]ant r+ ar\nd its equator4 ,?is equatorial r+ is incl9$ to ! plane ( ! ecliptic at an angle ( ab\t #bc-a_/b4 ,9 ,fig4 #ajj ?is r+ is repres5t$ z deta*$ f ! enclos$ sph]e4 ,s repres5ts ! sun1 & ,sc ! ecliptic4 ,z ! po9t ,a ( ! r+ is ne>] ! sun ?an ! po9t ,b is1 ! sun's pull ^u ,a is great] ?an ^u ,b3 h5ce ! sun t5ds to pull ! r+ ov] into ! plane ( ! ecliptic2 b ! rotation ( ! e>? t5ds to keep ! r+ 9 ! same plane4 ,! /ruggle betwe5 ^! two t5d5cies causes ! e>?1 to :i* ! r+ is atta*$1 to wabble l a sp9n+-top1 ^: rotation t5ds to keep x erect1 :ile gravity t5ds to pull x ov]4 ,! h&le ( ! top has a gyratory motion1 :i* causes x to describe a curve4 ,! axis ( ! heav5s corresponds to ! h&le ( ! top4 ,,ii4 ,,! ,,moon4 ,di/ance1 ,size1 & ,motions4 #hg4 ,! ,di/ance ( ! ,moon4--,! moon is ! ne>e/ ( ! heav5ly bodies4 ,its di/ance f ! c5tre ( ! e>? is only ab\t sixty times ! radius ( ! e>?1 or1 9 r\nd numb]s1 two hundr$ & =ty ?\s& miles4 ,! ord9>y me?od ( f9d+ ! di/ance ( "o ( ! ne>] heav5ly bodies is fir/ to asc]ta9 its horizontal p>allax4 ,?is enables u to =m a "r-angl$ triangle1 ! l5g?s ( ^: sides are easily comput$1 & ! l5g? ( ^: hypo!nuse is ! di/ance ( ! body f ! c5tre ( ! e>?4 ,illu/ration3 ,fig4 #aja4 ,horizontal p>allax has already be5 def9$ 7#cb7 z ! displacem5t ( a heav5ly body :5 on ! horizon1 caus$ by its be+ se5 f ! surface1 in/ead ( ! c5tre1 ( ! e>?4 ,?is displacem5t is due to ! fact t ! body is se5 9 a diff]5t direction f ! surface ( ! e>? f t 9 :i* x w\ld be se5 f ! c5tre4 ,horizontal p>allax might be def9$ z ! diff]5ce 9 ! directions 9 :i* a body on ! horizon w\ld be se5 f ! surface & f ! c5tre ( ! e>?4 ,?us1 9 ,fig4 #aja1 ,c is ! c5tre ( ! e>?1 ,a a po9t on ! surface1 & ,b a body on ! horizon ( ,a4 ,,ab is ! direction 9 :i* ! body w\ld be se5 f ,a1 & ,,cb ! direction 9 :i* x w\ld be se5 f ,c4 ,! diff]5ce ( ^! directions1 or ! angle ,,abc1 is ! p>allax ( ! body4 ,! triangle ,,bac is "r-angl$ at ,a2 ! side ,,ac is ! radius ( ! e>?1 & ! hypo!nuse is ! di/ance ( ! body f ! c5tre ( ! e>?4 ,:5 ! p>allax ,,abc is kn[n1 ! l5g? ( ,,cb c easily by f\nd by trigonometrical computation4 ,we h se5 7#cb7 t ! p>allax ( a heav5ly body gr[s less & less z ! body passes f ! horizon t[>ds ! z5i?4 ,! p>allax ( a body & its altitude are1 h[ev]1 s relat$1 t1 :5 we "k ! p>allax at any altitude1 we c readily compute ! horizontal p>allax4 ,! usual me?od ( f9d+ ! p>allax ( "o ( ! ne>] heav5ly bodies is fir/ to f9d its p>allax :5 on ! m]idian1 z se5 f two places on ! e>? :i* diff] consid]ably 9 latitude3 !n to calculate :at w\ld be ! p>allax ( ! body z se5 f "o ( ^! places & ! c5tre ( ! e>?3 & !n f9ally to calculate :at w\ld be ! p>allax 7 ! body on ! horizon4 ,illu/ration3 ,fig4 #ajb4 ,?us1 we %\ld asc]ta9 ! p>allax ( ! body ,b 7,fig4 #ajb7 z se5 f ,a & ,d1 or ! angle ,,abd4 ,we %\ld !n calculate its p>allax z se5 f ,a & ,c1 or ! angle ,,abc4 ,f9ally we %\ld calculate :at its p>allax w\ld be 7 ! body on ! horizon1 or ! angle ,,ab',c4 ,! simple/ me?od ( f9d+ ! p>allax ( a body ,b 7,fig4 #ajb7 z se5 f ! two po9ts ,a & ,d is to comp>e its direction at ea* po9t ) t ( ! same fix$ /> ne> ! body4 ,! /> is s di/ant1 t x w be se5 9 ! same direction f bo? po9ts3 h5ce1 if ! direction ( ! body diff]s f t ( ! /> #b z se5 f "o po9t1 & #b #f' z se5 f ! o!r po9t1 ! two l9es ,,ab & ,,db mu/ diff] 9 direction by #f'2 9 o!r words1 ! angle ,,abd w\ld be #f'4 ,! me?od j describ$ is ! usual me?od ( f9d+ ! p>allax ( ! moon4 #hh4 ,! ,app>5t ,size ( ! ,moon4--,! app>5t size ( a body is ! visual angle subt5d$ by x2 t is1 ! angle =m$ by two l9es drawn f ! eye to two opposite po9ts on ! outl9e ( ! body4 ,! app>5t size ( a body dep5ds ^u bo? its magnitude & its di/ance4 ,! app>5t size1 or angul> diamet]1 ( ! moon is ab\t ?irty-"o m9utes4 ,?is is asc]ta9$ by means ( ! wire micromet] already describ$ 7#ai74 ,! in/rum5t is adju/$ s t its longitud9al wire %all pass ?r\gh ! c5tre ( ! moon1 & its transv]se wires %all be tang5t to ! limbs ( ! moon on ea* side1 at ! po9t :]e !y are cut by ! longitud9al wire4 ,! micromet] screw is !n turn$ till ! wires are br\ght toge!r4 ,! numb] ( turns ( ! screw ne$$ to accompli% ?is w indicate ! arc betwe5 ! wires1 or ! angul> diamet] ( ! moon4 ,illu/ration3 ,fig4 #ajc4 ,9 ord] to be c]ta9 t ! longitud9al wire %all pass ?r\gh ! c5tre ( ! moon1 x is be/ to take ! moon :5 its disc is 9 ! =m ( a cresc5t1 & to place ! longitud9al wire aga9/ ! po9ts1 or cusps1 ( ! cresc5t1 z %[n 9 ,fig4 #ajc4 ,illu/ration3 ,fig4 #ajd4 #hi4 ,! ,real ,size ( ! ,moon4--,! real diamet] ( ! moon is a little ov] "o-f\r? ( t ( ! e>?1 or a little m ?an two ?\s& miles4 ,! comp>ative sizes ( ! e>? & moon are %[n 9 ,fig4 #ajd4 ,illu/ration3 ,fig4 #aje4 ,! di/ance & app>5t size ( ! moon be+ kn[n1 h] real diamet] is f\nd by means ( a triangle =m$ z %[n 9 ,fig4 #aje4 ,c repres5ts ! c5tre ( ! moon1 ,,cb ! di/ance ( ! moon f ! e>?1 & ,,ca ! radius ( ! moon4 ,,bac is a triangle1 "r-angl$ at ,a4 ,! angle ,,abc is half ! app>5t diamet] ( ! moon4 ,) ! angles ,a & ,b1 & ! side ,,cb kn[n1 x is easy to f9d ! l5g? ( ,,ac by trigonometrical computation4 ,twice ,,ac w be ! diamet] ( ! moon4 ,! volume ( ! moon is ab\t "o-fiftie? ( t ( ! e>?4 #ij4 ,app>5t ,size ( ! ,moon on ! ,horizon & 9 ! ,z5i?44--,! moon is ne>ly f\r ?\s& miles f>!r f ! obs]v] :5 %e is on ! horizon ?an :5 %e is 9 ! z5i?4 ,?is is evid5t f ,fig4 #ajf4 ,c is ! c5tre ( ! e>?1 ,m ! moon on ! horizon1 ,m' ! moon 9 ! z5i?1 & ,o ! po9t ( obs]vation4 ,,om is ! di/ance ( ! moon :5 %e is on ! horizon1 & ,,om' ! di/ance ( ! moon f ! obs]v] :5 %e is 9 ! z5i?4 ,,cm is equal to ,,cm'1 & ,,om is ab\t ! l5g? ( ,,cm2 b ,,om' is ab\t f\r ?\s& miles %ort] ?an ,,cm'3 h5ce ,,om' is ab\t f\r ?\s& miles %ort] ?an ,,om4 ,illu/ration3 ,fig4 #ajf4 ,not)/&+ ! moon is mu* ne>] :5 at ! z5i? ?an at ! horizon1 x seems to u mu* l>g] at ! horizon4 ,?is is a pure illusion1 z we become conv9c$ :5 we measure ! disc ) accurate in/rum5ts1 s z to make ! result indep5d5t ( our ord9>y way ( judg+4 ,:5 ! moon is ne> ! horizon1 x seems plac$ beyond all ! objects on ! surface ( ! e>? 9 t direction1 & !re=e f>!r (f ?an at ! z5i?1 :]e no int]v5+ objects enable u to judge ( its di/ance4 ,9 any case1 an object :i* keeps ! same app>5t magnitude seems to u1 ?r\gh ! in/9ctive habits ( ! eye1 ! l>g] 9 proportion z we judge x to be m di/ant4 #ia4 ,! ,app>5t ,size ( ! ,moon increas$ by ,irradiation4--,9 ! case ( ! moon1 ! ^w app>5t means mu* m ?an x does 9 ! case ( o!r cele/ial bodies4 ,inde$1 its brightness causes our eyes to play u false4 ,z is well kn[n1 ! cresc5t ( ! new moon seems "p ( a mu* l>g] sph]e ?an t :i* x has be5 said1 "t out ( m9d1 to hold 9 its arms4 ,! bright portion ( ! moon z se5 ) our measur+ in/rum5ts1 z well z :5 se5 ) ! nak$ eye1 cov]s a l>g] space 9 ! field ( ! telescope ?an x w\ld if x 7 n s bright4 ,?is effect ( irradiation1 z x is call$1 mu/ be all[$ = 9 exact measurem5ts ( ! diamet] ( ! moon4 ,illu/ration3 ,fig4 #ajg4 #ib4 ,app>5t ,size ( ! ,moon 9 ,diff]5t ,p>ts ( h] ,orbit4--,ow+ to ! ecc5tricity ( ! moon's orbit1 h] di/ance f ! e>? v>ies some:at f "t to "t4 ,?is v>iation causes a correspond+ v>iation 9 h] app>5t size1 :i* is illu/rat$ 9 ,fig4 #ajg4 #ic4 ,! ,mass ( ! ,moon4--,! moon is consid]ably less d5se ?an ! e>?1 its mass be+ only ab\t "o-eightie? ( t ( ! e>?2 t is1 :ile x w\ld take only ab\t fifty moons to make ! bulk ( ! e>?1 x w\ld take ab\t eighty to make ! mass ( ! e>?4 ,"o me?od ( f9d+ ! mass ( ! moon is to comp>e h] effect 9 produc+ ! tides ) t ( ! sun4 ,we fir/ calculate :at w\ld be ! moon's effect 9 produc+ ! tides1 7 %e z f> (f z ! sun4 ,we !n =m ! foll[+ proportion3 z ! sun's effect 9 produc+ ! tides is to ! moon's effect at ! same di/ance1 s is ! mass ( ! sun to ! mass ( ! moon4 ,! me?od ( f9d+ ! mass ( ! sun w be giv5 f>!r on4 #id4 ,! ,orbital ,motion ( ! ,moon4--,if we wat* ! moon f night to night1 we see t %e moves ea/w>d q rapidly among ! />s4 ,:5 ! new moon is fir/ visible1 x appe>s ne> ! horizon 9 ! we/1 j aft] sunset4 ,a week lat] ! moon w be on ! m]idian at ! same h\r1 & ab\t a week lat] /ill on ! ea/]n horizon4 ,! moon completes ! circuit ( ! heav5s 9 a p]iod ( ab\t ?irty days1 mov+ ea/w>d at ! rate ( ab\t twelve degrees a day4 ,?is ea/w>d motion ( ! moon is due to ! fact t %e is revolv+ ar\nd ! e>? f we/ to ea/4 ,illu/ration3 ,fig4 #ajh4 #ie4 ,! ,aspects ( ! ,moon4--,z ! moon revolves ar\nd ! e>?1 %e comes into diff]5t positions ) ref]5ce to ! e>? & sun4 ,^! diff]5t positions ( ! moon are call$ ! aspects ( ! moon4 ,! f\r *ief aspects ( ! moon are %[n 9 ,fig4 #ajh4 ,:5 ! moon is at ,m1 %e appe>s 9 ! opposite "p ( ! heav5s to ! sun1 & is said to be 9 opposition2 :5 at ,m' & at ,m'''1 %e appe>s n9ety degrees away f ! sun1 & is said to be 9 quadrature2 :5 at ,m''1 %e appe>s 9 ! same "p ( ! heav5s z ! sun1 & is said to be 9 conjunction4 #if4 ,! ,sid]eal & ,synodical ,p]iods ( ! ,moon4--,! sid]eal p]iod ( ! moon is ! "t x takes h] to pass ar\nd f a /> to t /> aga91 or ! "t x takes h] to make a complete revolution ar\nd ! e>?4 ,?is is a p]iod ( ab\t tw5ty-sev5 days & a ?ird4 ,x is sometimes call$ ! sid]eal mon?4 ,! synodical p]iod ( ! moon is ! "t t x takes ! moon to pass f "o aspect ar\nd to ! same aspect aga94 ,?is is a p]iod ( ab\t tw5ty-n9e days & a half1 & x is sometimes call$ ! synodical mon?4 ,illu/ration3 ,fig4 #aji4 ,! reason :y ! synodical p]iod is long] ?an ! sid]eal p]iod w appe> f ,fig4 #aji4 ,s repres5ts ! position ( ! sun1 ,e t ( ! e>?1 & ! small circle ! orbit ( ! moon ar\nd ! e>?4 ,! arr[ 9 ! small circle repres5ts ! direction ! moon is revolv+ ar\nd ! e>?1 & ! arr[ 9 ! arc betwe5 ,e & ,e' indicates ! direction ( ! e>?'s motion 9 its orbit4 ,:5 ! moon is at ,m#a1 %e is 9 conjunction4 ,z ! moon revolves ar\nd ! e>?1 ! e>? moves =w>d 9 its orbit4 ,:5 ! moon has come r\nd to m#a1 s t m#cm#a is p>allel ) ,m#c,m#a1 %e w h made a complete or sid]eal revolution ar\nd ! e>?2 b %e w n be 9 conjunction aga9 till %e has come r\nd to ,m1 s z aga9 to be betwe5 ! e>? & sun4 ,t is to say1 ! moon mu/ make m ?an a complete revolution 9 a synodical p]iod4 ,illu/ration3 ,fig4 #aaj4 ,! great] l5g? ( ! synodical p]iod is also evid5t f ,fig4 #aaj4 ,t repres5ts ! e>?1 & ,l ! moon4 ,! arr[s indicate ! direction 9 :i* ea* is mov+4 ,:5 ! e>? is at ,t1 & ! moon at ,l1 ! latt] is 9 conjunction4 ,:5 ! e>? has rea*$ ,t'1 & ! moon ,l'1 ! latt] has made a sid]eal revolution2 b %e w n be 9 conjunction aga9 till ! e>? has rea*$ ,t''1 & ! moon ,l''4 #ig4 ,! ,phases ( ! ,moon4--,:5 ! new moon appe>s 9 ! we/1 x has ! =m ( a cresc5t1 ) its convex side t[>ds ! sun1 & its horns t[>ds ! ea/4 ,z ! moon advances t[>ds quadrature1 ! cresc5t gr[s ?ick] & ?ick]1 till x becomes a half-circle at fir/ qu>t]4 ,:5 x passes quadrature1 x beg9s to become convex also on ! side away f ! sun1 or gibb\s 9 =m4 ,z x approa*es opposition1 x becomes m & m ne>ly circul>1 until at opposition x is a full circle4 ,f full moon to la/ qu>t] x is aga9 gibb\s1 & at la/ qu>t] a half-circle4 ,f la/ qu>t] to new moon x is aga9 cresc5t2 b ! horns ( ! cresc5t are n[ turn$ t[>ds ! we/4 ,! successive phases ( ! moon are %[n 9 ,fig4 #aaa4 ,illu/ration3 ,fig4 #aaa4 #ih4 ,cause ( ! ,phases ( ! ,moon4--,take a globe1 half ( :i* is color$ :ite & ! o!r half black 9 su* a way t ! l9e :i* sep>ates ! :ite & black portions %all be a great circle :i* passes ?r\gh ! poles ( ! globe1 & rotate ! globe sl[ly1 s z to br+ ! :ite half gradually into view4 ,:5 ! :ite "p fir/ comes into view1 ! l9e ( sep>ation betwe5 x & ! black "p1 :i* we may call ! t]m9ator1 appe>s concave1 & its projection on a plane p]p5dicul> to ! l9e ( vision is a concave l9e4 ,z m & m ( ! :ite portion comes into view1 ! projection ( ! t]m9ator becomes less & less concave4 ,:5 half ( ! :ite portion comes into view1 ! t]m9ator is project$ z a /raight l9e4 ,:5 m ?an half ( ! :ite portion comes into view1 ! t]m9ator beg9s to appe> z a convex l9e1 & ?is l9e becomes m & m convex till ! :ole ( ! :ite half comes into view1 :5 ! t]m9ator becomes circul>4 ,illu/ration3 ,fig4 #aab4 ,! moon is ( itself a d>k1 opaque globe2 b ! half t is t[>ds ! sun is always bright1 z %[n 9 ,fig4 #aab4 ,?is bright half ( ! moon corresponds to ! :ite half ( ! globe 9 ! prec$+ illu/ration4 ,z ! moon revolves ar\nd ! e>?1 diff]5t portions ( ?is illum9$ half are turn$ t[>ds ! e>?4 ,at new moon1 :5 ! moon is 9 conjunction1 ! bright half is turn$ entirely away f ! e>?1 & ! disc ( ! moon is black & invisible4 ,betwe5 new moon & fir/ qu>t]1 less ?an half ( ! illum9$ side is turn$ t[>ds ! e>?1 & we see ?is illum9$ portion project$ z a cresc5t4 ,at fir/ qu>t]1 j half ( ! illum9$ side is turn$ t[>ds ! e>?1 & we see ?is half project$ z a half-circle4 ,betwe5 fir/ qu>t] & full1 m ?an half ( ! illum9$ side is turn$ t[>ds ! e>?1 & we see x z gibb\s4 ,at full1 ! :ole ( ! illum9$ side is turn$ t[>ds u1 & we see x z a full circle4 ,f full to new moon aga91 ! phases occur 9 ! rev]se ord]4 #ii4 ,! ,=m ( ! ,moon's ,orbit4--,! orbit ( ! moon ar\nd ! e>? is an ellipse ( slight ecc5tricity4 ,! =m ( ?is ellipse is %[n 9 ,fig4 #aac4 ,c is ! c5tre ( ! ellipse1 & ,e ! position ( ! e>? at "o ( its foci4 ,! ecc5tricity ( ! ellipse is only ab\t "o-eighte5?4 ,x is impossible = ! eye to di/+ui% su* an ellipse f a circle4 ,illu/ration3 ,fig4 #aac4 #ajj4 ,! ,incl9ation ( ! ,moon's ,orbit4--,! plane ( ! moon's orbit is incl9$ to ! ecliptic by an angle ( ab\t five degrees4 ,! two po9ts :]e ! moon's orbit cuts ! ecliptic are call$ h] nodes4 ,! moon's nodes h a we/w>d motion correspond+ to t ( ! equ9oxes1 b mu* m rapid4 ,!y complete ! circuit ( ! ecliptic 9 ab\t n9ete5 ye>s4 ,! moon's latitude ranges f #e nor? to #e s\?2 & s9ce1 ow+ to ! motion ( h] nodes1 ! moon is1 dur+ a p]iod ( n9ete5 ye>s1 #e nor? & #e s\? ( e "p ( ! ecliptic1 h] decl9ation w range f #bc-a_/b #e #bh-a_/b nor? to #bc-a_/b #e #bh-a_/b s\?4 #aja4 ,! ,m]idian ,altitude ( ! ,moon4--,! m]idian altitude ( any body is its altitude :5 on ! m]idian4 ,9 our latitude1 ! m]idian altitude ( any po9t on ! equ9octial is =ty-n9e degrees4 ,! m]idian altitude ( ! summ] sol/ice is #di #bc-a_/b #gb-a_/b1 & t ( ! w9t] sol/ice is #di - #bc-a_/b #be-a_/b4 ,! greate/ m]idian altitude ( ! moon is #gb-a_/b #e #gg-a_/b1 & its lea/ m]idian altitude1 #be-a_/b - #e #bj-a_/b4 ,:5 ! moon's m]idian altitude is great] ?an ! elevation ( ! equ9octial1 x is said to run high1 & :5 less1 to run l[4 ,! full moon runs high :5 ! sun is s\? ( ! equ9octial1 & l[ :5 ! sun is nor? ( ! equ9octial4 ,?is is because ! full moon is always 9 ! opposite "p ( ! heav5s to ! sun4 #ajb4 ,wet & ,dry ,moon4--,at ! "t ( new moon1 ! cusps ( ! cresc5t sometimes lie 9 a l9e :i* is ne>ly p]p5dicul> ) ! horizon1 & sometimes 9 a l9e :i* is ne>ly p>allel ) ! horizon4 ,9 ! =m] case ! moon is popul>ly describ$ z a wet moon1 & 9 ! latt] case z a dry moon4 ,illu/ration3 ,fig4 #aad4 ,! great circle :i* passes ?r\gh ! c5tre ( ! sun & moon w pass ?r\gh ! c5tre ( ! cresc5t1 & be p]p5dicul> to ! l9e jo9+ ! cusps4 ,n[ ! ecliptic makes ! lea/ angle ) ! horizon :5 ! v]nal equ9ox is on ! ea/]n horizon & ! autumnal equ9ox is on ! we/]n4 ,9 our latitude1 z we h se51 ?is angle is #be-a_/b3 h5ce 9 our latitude1 if ! moon 7 at new on ! ecliptic :5 ! sun is at ! autumnal equ9ox1 z %[n at ,m#c 7,fig4 #aad71 ! great circle pass+ ?r\gh ! c5tre ( ! sun & moon w\ld be ! ecliptic1 & at ,new ,york w\ld be incl9$ to ! horizon at an angle ( #be-a_/b4 ,if ! moon happ5$ to be #e s\? ( ! ecliptic at ?is "t1 z at ,m#d1 ! great circle pass+ ?r\gh ! c5tre ( ! sun & moon w\ld make an angle ( only #bj-a_/b ) ! horizon4 ,9 ei!r ( ^! cases ! l9e jo9+ ! cusps w\ld be ne>ly p]p5dicul> to ! horizon4 ,illu/ration3 ,fig4 #aae4 ,if ! moon 7 at new on ! ecliptic :5 ! sun is ne> ! v]nal equ9ox1 z %[n at ,m#a 7,fig4 #aae71 ! great circle pass+ ?r\gh ! c5tres ( ! sun & moon w\ld make an angle ( #gb-a_/b ) ! horizon at ,new ,york2 & 7 ! moon #e nor? ( ! ecliptic at t "t1 z %[n at ,m#b1 ?is great circle w\ld make an angle ( #gg-a_/b ) ! horizon4 ,9 ei!r ( ^! cases1 ! l9e jo9+ ! cusps w\ld be ne>ly p>allel ) ! horizon4 ,at diff]5t times1 ! l9e jo9+ ! cusps may h e possible incl9ation to ! horizon betwe5 ! extreme cases %[n 9 ,figs4 #aad & #aae4 #ajc4 ,daily ,ret>dation ( ! ,moon's ,ris+4--,! moon rises1 on ! av]age1 ab\t fifty m9utes lat] ea* day4 ,?is is ow+ to h] ea/w>d motion4 ,z ! moon makes a complete revolution ar\nd ! e>? 9 ab\t tw5ty-sev5 days1 %e moves ea/w>d at ! rate ( ab\t ?irte5 degrees a day1 or ab\t twelve degrees a day fa/] ?an ! sun4 ,7 ! moon1 !re=e1 on ! horizon at any h\r to-day1 %e w\ld be "s twelve degrees bel[ ! horizon at ! same h\r to-morr[4 ,n[1 z ! horizon moves at ! rate ( "o degree 9 f\r m9utes1 x w\ld take x "s fifty m9utes to come up to ! moon s z to br+ h] ^u ! horizon4 ,h5ce ! daily ret>dation ( ! moon's ris+ is ab\t fifty m9utes2 b x v>ies consid]ably 9 diff]5t p>ts ( h] orbit4 ,!re are two reasons = ?is v>iation 9 ! daily ret>dation3-- 7#a7 ,! moon moves at a v>y+ rate 9 h] orbit2 h] spe$ be+ greate/ at p]igee1 & lea/ at apogee3 h5ce1 o!r ?+s be+ equal1 ! ret>dation is greate/ :5 ! moon is at p]igee1 & lea/ :5 %e is at apogee4 ,illu/ration3 ,fig4 #aaf4 ,illu/ration3 ,fig4 #aag4 7#b7 ,! moon moves at a v>y+ angle to ! horizon4 ,! moon moves ne>ly 9 ! plane ( ! ecliptic1 & ( c\rse %e passes bo? equ9oxes e lunation4 ,:5 %e is ne> ! autumnal equ9ox1 h] pa? makes ! greate/ angle ) ! ea/]n horizon1 & :5 %e is ne> ! v]nal equ9ox1 ! lea/ angle3 h5ce ! moon moves away f ! horizon fa/e/ :5 %e is ne> ! autumnal equ9ox1 & sl[e/ :5 %e is ne> ! v]nal equ9ox4 ,?is w be evid5t f ,figs4 #aaf & #aag4 ,9 ea* figure1 ,,sn repres5ts a portion ( ! ea/]n horizon1 & ,ec1 ,e'c'1 a portion ( ! ecliptic4 ,,ae1 9 ,fig4 #aaf1 repres5ts ! autumnal equ9ox1 & ,,aem ! daily motion ( ! moon4 ,,ve1 9 ,fig4 #aag1 repres5ts ! v]nal equ9ox1 & ,,vem' ! motion ( ! moon = "o day4 ,9 ! fir/ case ?is motion w\ld c>ry ! moon away f ! horizon ! di/ance ,,am1 & 9 ! second case ! di/ance ,a',m'4 ,n[1 x is evid5t t ,,am is great] ?an ,a',m'3 h5ce1 o!r ?+s be+ equal1 ! greate/ ret>dation ( ! moon's ris+ w be :5 ! moon is ne> ! autumnal equ9ox1 & ! lea/ ret>dation :5 ! moon is ne> ! v]nal equ9ox4 ,! lea/ ret>dation at ,new ,york is tw5ty-?ree m9utes1 & ! greate/ an h\r & sev5te5 m9utes4 ,! greate/ & lea/ ret>dations v>y some:at f mon? to mon?2 s9ce !y dep5d n only ^u ! position ( ! moon 9 h] orbit ) ref]5ce to ! equ9oxes1 b also ^u ! latitude ( ! moon1 & ^u h] ne>ness to ! e>?4 ,illu/ration3 ,fig4 #aah4 ,! direction ( ! moon's motion ) ref]5ce to ! ecliptic is %[n 9 ,fig4 #aah1 :i* %[s ! moon's motion = "o day 9 ,july1 #ahgf4 #ajd4 ,! ,h>ve/ ,moon--,! long & %ort ret>dations 9 ! ris+ ( ! moon1 ?\gh !y occur e mon?1 are n likely to attract att5tion unless !y occur at ! "t ( full moon4 ,! long ret>dations = full moon occur :5 ! moon is ne> ! autumnal equ9ox at full4 ,z ! full moon is always opposite to ! sun1 ! sun mu/ 9 ?is case be ne> ! v]nal equ9ox3 h5ce ! long ret>dations = full moon occur 9 ! spr+1 ! greate/ ret>dation be+ 9 ,m>*4 ,! lea/ ret>dations = full moon occur :5 ! moon is ne> ! v]nal equ9ox at full3 ! sun mu/ !n be ne> ! autumnal equ9ox4 ,h5ce ! lea/ ret>dations = full moon occur 9 ! mon?s ( ,augu/1 ,septemb]1 & ,octob]4 ,! ret>dation is1 ( c\rse1 lea/ = ,septemb]2 & ! full moon ( ?is mon? rises night aft] night less ?an half an h\r lat] ?an ! previ\s night4 ,! full moon ( ,septemb] is call$ ! ,h>ve/ ,moon1 & t ( ,octob] ! ,hunt]'s ,moon4 #aje4 ,! ,rotation ( ! ,moon4--,a c>eful exam9ation ( ! spots on ! disc ( ! moon reveals ! fact t %e always pres5ts ! same side to ! e>?4 ,9 ord] to d ?is1 %e mu/ rotate on h] axis :ile mak+ a revolution ar\nd ! e>?1 or 9 ab\t tw5ty-sev5 days4 #ajf4 ,librations ( ! ,moon4--,! moon appe>s to rock sl[ly to & fro1 s z to all[ u to see alt]nately a little f>!r ar\nd to ! "r & ! left1 or above & bel[1 ?an we o!rwise c\ld4 ,?is app>5t rock+ ( ! moon is call$ libration4 ,! moon has ?ree librations3-- 7#a7 ,libration 9 ,latitude4--,?is libration enables u to see alt]nately a little way ar\nd on ! nor!rn & s\!rn limbs ( ! moon4 ,?is libration is due to ! fact t ! axis ( ! moon is n q p]p5dicul> to ! plane ( h] orbit4 ,! deviation f ! p]p5dicul> is six degrees & a half4 ,z ! axis ( ! moon1 l t ( ! e>?1 ma9ta9s ! same direction1 ! poles ( ! moon w be turn$ alt]nately six degrees & a half t[>d & f ! e>?4 7#b7 ,libration 9 ,longitude4--,?is libration enables u to see alt]nately a little f>!r ar\nd on ! ea/]n & we/]n limbs ( ! moon4 ,illu/ration3 ,fig4 #aai4 ,x is due to ! fact t ! moon's axial motion is uni=m1 :ile h] orbital motion is n4 ,at p]igee h] orbital motion w be 9 advance ( h] axial motion1 :ile at apogee ! axial motion w be 9 advance ( ! orbital4 ,9 ,fig4 #aai1 ,e repres5ts ! e>?1 ,m ! moon1 ! l>ge arr[ ! direction ( ! moon's motion 9 h] orbit1 & ! small arr[ ! direction ( h] motion ( rotation4 ,:5 ! moon is at ,m1 ! l9e ,,ab1 drawn p]p5dicul> to ,,em1 repres5ts ! circle :i* divides ! visible f ! invisible portion ( ! moon4 ,:ile ! moon is pass+ f ,m to ,m'1 ! moon p]=ms less ?an a qu>t] ( a rotation1 s t ,,ab is no long] p]p5dicul> to ,,em'4 ,an obs]v] on ! e>? c n[ see some:at beyond ,a on ! we/]n limb ( ! moon1 & n q up to ,b on ! ea/]n limb4 ,:ile ! moon is pass+ f ,m' to ,m''1 h] axial motion aga9 ov]takes h] orbital motion1 s t ! l9e ,,ab aga9 becomes p]p5dicul> to ! l9e jo9+ ! c5tre ( ! moon to ! c5tre ( ! e>?4 ,exactly ! same side is n[ turn$ t[>ds ! e>? z :5 ! moon 0 at ,m4 ,:ile ! moon passes f ,m'' to ,m'''1 h] axial motion gets 9 advance ( h] orbital motion1 s t ,,ab is aga9 incl9$ to ! l9e jo9+ ! c5tres ( ! e>? & moon4 ,a portion ( ! ea/]n limb ( ! moon beyond ,b is n[ br\ght into view to ! e>?1 & a portion ( ! we/]n limb at ,a is c>ri$ out ( view4 ,:ile ! moon is pass+ f ,m''' to ,m1 ! orbital motion aga9 ov]takes ! axial motion1 & ,,ab is aga9 p]p5dicul> to ,,me4 7#c7 ,p>allactic ,libration4--,:ile an obs]v] at ! c5tre ( ! e>? w\ld get ! same view ( ! moon1 :e!r %e 7 on ! ea/]n horizon1 9 ! z5i?1 or on ! we/]n horizon1 an obs]v] on ! surface ( ! e>? does n get exactly ! same view 9 ^! ?ree cases4 ,:5 ! moon is on ! ea/]n horizon1 an obs]v] on ! surface ( ! e>? w\ld see a little f>!r ar\nd on ! we/]n limb ( ! moon ?an :5 %e is 9 ! z5i?1 & n q s f> ar\nd on ! ea/]n limb4 ,on ! contr>y1 :5 ! moon is on ! we/]n horizon1 an obs]v] on ! surface ( ! e>? sees a little f>!r ar\nd on ! ea/]n limb ( ! moon ?an :5 %e is 9 ! z5i?1 & n q s f> ar\nd on h] we/]n limb4 ,illu/ration3 ,fig4 #abj4 ,?is w be evid5t f ,fig4 #abj4 ,e is ! c5tre ( ! e>?1 & ,o a po9t on its surface4 ,,ab is a l9e drawn ?r\gh ! c5tre ( ! moon1 p]p5dicul> to a l9e jo9+ ! c5tres ( ! moon & ! e>?4 ,?is l9e m>ks (f ! "p ( ! moon turn$ t[>ds ! c5tre ( ! e>?1 & rema9s ess5tially ! same dur+ ! day4 ,,cd is a l9e drawn ?r\gh ! c5tre ( ! moon p]p5dicul> to a l9e jo9+ ! c5tre ( ! moon & ! po9t ( obs]vation4 ,?is l9e m>ks (f ! "p ( ! moon turn$ t[>ds ,o4 ,:5 ! moon is 9 ! z5i?1 ,,cd co9cides ) ,,ab2 b1 :5 ! moon is on ! horizon1 ,,cd is incl9$ to ,,ab4 ,:5 ! moon is on ! ea/]n horizon1 an obs]v] at ,o sees a little beyond ,b1 & n q to ,a2 &1 :5 %e is on ! we/]n horizon1 he sees a little beyond ,a1 & n q to ,b4 ,b is on ! we/]n limb ( ! moon1 & ,a on h] ea/]n limb4 ,s9ce ?is libration is due to ! po9t f :i* ! moon is view$1 x is call$ p>allactic libration2 &1 s9ce x occurs daily1 x is call$ diurnal libration4 ,illu/ration3 ,fig4 #aba4 #ajg4 ,portion ( ! ,lun> ,surface br\ght into ,view by ,libration4--,! area br\ght into view by ! fir/ two librations is betwe5 "o-twelf? & "o-?irte5? ( ! :ole lun> surface1 or ne>ly "o-six? ( ! hemisph]e ( ! moon :i* is turn$ away f ! e>? :5 ! moon is at h] /ate ( mean libration4 ,( c\rse a precisely equal portion ( ! hemisph]e turn$ t[>ds u dur+ mean libration is c>ri$ out ( view by ! lun> librations4 ,if we add to ea* ( ^! areas a fr+e ab\t "o degree wide1 due to ! diurnal libration1 & :i* we may call ! p>allactic fr+e1 we %all f9d t ! total area br\ght into view is almo/ exactly "o-elev5? "p ( ! :ole surface ( ! moon4 ,a simil> area is c>ri$ out ( view2 s t ! :ole region ?us sway$ out ( & into view am\nts to two-elev5?s ( ! moon's surface4 ,?is area is %[n 9 ,fig4 #aba1 :i* is a side view ( ! moon4 ,illu/ration3 ,fig4 #abb4 #ajh4 ,! ,moon's ,pa? ?r\gh ,space4--,7 ! e>? /ation>y1 ! moon w\ld describe an ellipse ar\nd x simil> to t ( ,fig4 #aac2 b1 z ! e>? moves =w>d 9 h] orbit at ! same "t t ! moon revolves ar\nd x1 ! moon is made to describe a s9u\s pa?1 z %[n by ! cont9u\s l9e 9 ,fig4 #abb4 ,?is feature ( ! moon's pa? is greatly exagg]at$ 9 ! upp] portion ( ! diagram4 ,! =m ( h] pa? is giv5 ) a great] degree ( accuracy 9 ! l[] "p ( ! figure 7! brok5 l9e repres5ts ! pa? ( ! e>?72 b ev5 "h !re is consid]able exagg]ation4 ,! complete s]p5t9e pa? ( ! moon ar\nd ! sun is %[n1 greatly exagg]at$1 9 ,fig4 #abc1 ! brok5 l9e be+ ! pa? ( ! e>?4 ,illu/ration3 ,fig4 #abc4 ,! pa? describ$ by ! moon ?r\gh space is mu* ! same z t describ$ by a po9t on ! circumf]5ce ( a :eel :i* is roll$ ov] ano!r :eel4 ,if we place a circul> disk aga9/ ! wall1 & c>efully roll along its edge ano!r circul> disk 7to :i* a piece ( lead p5cil has be5 fa/5$ s z to m>k ^u ! wall71 ! curve describ$ w some:at resemble t describ$ by ! moon4 ,?is curve is call$ an epicycloid1 & x w be se5 t at e po9t x is concave t[>ds ! c5tre ( ! l>g] disk4 ,9 ! same way ! moon's orbit is at e po9t concave t[>ds ! sun4 ,illu/ration3 ,fig4 #abd4 ,! exagg]ation ( ! s9uosity 9 ,fig4 #abc w be m evid5t :5 x is /at$1 t1 on ! scale ( ,fig4 #abd1 ! :ole ( ! s]p5t9e curve w\ld lie )9 ! bread? ( ! f9e circul> l9e ,,mm'4 #aji4 ,! ,lun> ,day4--,! lun> day is tw5ty-n9e times & a half z long z ! t]re/rial day4 ,ne> ! moon's equator ! sun %9es )\t int]mission ne>ly fifte5 ( our days1 & is abs5t = ! same l5g? ( "t4 ,consequ5tly1 ! vicissitudes ( temp]ature to :i* ! surface is expos$ mu/ be v great4 ,dur+ ! long lun> night ! temp]ature ( a body on ! moon's surface w\ld probably fall l[] ?an is ev] kn[n on ! e>?1 :ile dur+ ! day x mu/ rise high] ?an any:]e on our planet4 ,illu/ration3 ,fig4 #abe4 ,x might seem1 t1 s9ce ! moon rotates on h] axis 9 ab\t tw5ty-sev5 days1 ! lun> day ought to be tw5ty-sev5 days long1 in/ead ( tw5ty-n9e4 ,!re is1 h[ev]1 a sol>1 z well z a sid]eal1 day at ! moon1 z on ! e>?2 & ! sol> day at ! moon is long] ?an ! sid]eal day1 = ! same reason z on ! e>?4 ,dur+ ! sol> day ! moon mu/ make bo? a synodical rotation & a synodical revolution4 ,?is w be evid5t f ,fig4 #abe1 9 :i* is %[n ! pa? ( ! moon dur+ "o complete lunation4 ,e1 ,e'1 ,e''1 etc41 are ! successive positions ( ! e>?2 & #a1 #b1 #c1 #d1 #e1 ! successive positions ( ! moon4 ,! small arr[s indicate ! direction ( ! moon's rotation4 ,! moon is full at #a & #e4 ,at #a1 ,a1 at ! c5tre ( ! moon's disk1 w h ! sun1 :i* lies 9 ! direction ,,z1 ^u ! m]idian4 ,be=e ,a w aga9 h ! sun on ! m]idian1 ! moon mu/ h made a synodical revolution2 &1 z w be se5 by ! dott$ l9es1 %e mu/ h made m ?an a complete rotation4 ,! rotation :i* br+s ! po9t ,a into ! same relation to ! e>? & sun is call$ a synodical rotation4 ,x w also be evid5t f ?is diagram t ! moon mu/ make a synodical rotation dur+ a synodical revolution1 9 ord] always to pres5t ! same side to ! e>?4 #aaj4 ,! ,e>? z se5 f ! ,moon4--,to an obs]v] on ! moon1 ! e>? w\ld be an imm5se moon1 go+ ?r\gh ! same phases t ! moon does to u2 b1 in/ead ( ris+ & sett+1 x w\ld only oscillate to & fro ?r\gh a few degrees4 ,on ! o!r side ( ! moon x w\ld nev] be se5 at all4 ,! peculi>ities ( ! moon's motions :i* cause ! librations1 & make a spot on ! moon's disk seem to an obs]v] on ! e>? to oscillate to & fro1 w\ld cause ! e>? z a :ole to appe> to a lun> obs]v] to oscillate to & fro 9 ! heav5s 9 a simil> mann]4 ,x is a well-kn[n fact1 t1 at ! "t ( new moon1 ! d>k "p ( ! moon's surface is p>tially illum9$1 s t x becomes visible to ! nak$ eye4 ,?is mu/ be due to ! light reflect$ to ! moon f ! e>?4 ,s9ce at new moon ! moon is betwe5 ! e>? & sun1 x foll[s1 t1 :5 x is new moon at ! e>?1 x mu/ be full e>? at ! moon3 h5ce1 :ile ! bright cresc5t is enjoy+ full sunlight1 ! d>k "p ( its surface is enjoy+ ! light ( ! full e>?4 ,fig4 #abf repres5ts ! full e>? z se5 f ! moon4 ,illu/ration3 ,fig4 #abf4 ,! ,atmosph]e ( ! ,moon4 #aaa4 ,! ,moon has no ,appreciable ,atmosph]e4--,!re are sev]al reasons = believ+ t ! moon has little or no atmosph]e4 7#a7 ,_h ! moon an atmosph]e1 x w\ld be indicat$ at ! "t ( a sol> eclipse1 :5 ! moon passes ov] ! disk ( ! sun4 ,if ! atmosph]e 7 ( any consid]able d5sity1 x w\ld absorb a "p ( ! sun's rays1 s z to produce a dusky bord] 9 front ( ! moon's disk1 z %[n 9 ,fig4 #abg4 ,9 reality no su* dusky bord] is ev] se52 b ! limb ( ! moon appe>s %>p1 & cle>ly def9$1 z 9 ,fig4 #abh4 ,illu/ration3 ,fig4 #abg4 ,illu/ration3 ,fig4 #abh4 ,if ! atmosph]e 7 n d5se en\gh to produce ?is dusky bord]1 its refraction w\ld be suffici5t to di/ort ! delicate cusps ( ! sun's cresc5t 9 ! mann] %[n at ! top ( ,fig4 #abe2 b no su* di/ortion is ev] obs]v$4 ,! cusps always appe> cle> & %>p1 z %[n at ! bottom ( ! figure3 h5ce x w\ld seem t !re c be no atmosph]e ( appreciable d5sity at ! moon4 7#b7 ,! abs5ce ( an atmosph]e f ! moon is also %[n by ! abs5ce ( twilight & ( diffus$ daylight4 ,^u ! e>?1 twilight cont9ues until ! sun is eighte5 degrees bel[ ! horizon2 t is1 day & night are sep>at$ by a belt twelve hundr$ miles 9 bread?1 9 :i* ! transition f light to d>kness is gradual4 ,we h se5 7#ff7 t ?is twilight results f ! refraction & reflection ( light by our atmosph]e2 &1 if ! moon _h an atmosph]e1 we %\ld notice a simil> gradual transition f ! bright to ! d>k portions ( h] surface4 ,su*1 h[ev]1 is n ! case4 ,! b\nd>y betwe5 ! light & d>kness1 ?\gh irregul>1 is %>ply def9$4 ,close to ?is b\nd>y ! unillum9$ portion ( ! moon appe>s j z d>k z at any di/ance f x4 ,! %ad[s on ! moon are also pit*y black1 )\t a trace ( diffus$ daylight4 ,illu/ration3 ,fig4 #abi4 7#c7 ,! abs5ce ( an atmosph]e is also prov$ by ! abs5ce ( refraction :5 ! moon passes betwe5 u & ! />s4 ,let ,,ab 7,fig4 #abi7 repres5t ! disk ( ! moon1 & ,,cd an atmosph]e suppos$ to surr\nd x4 ,let ,,sae repres5t a /raight l9e f ! e>?1 t\*+ ! moon at ,a1 & let ,s be a /> situat$ 9 ! direction ( ?is l9e4 ,if ! moon _h no atmosph]e1 ?is /> w\ld appe> to t\* ! edge ( ! moon at ,a2 b1 if ! moon _h an atmosph]e1 a /> beh9d ! edge ( ! moon1 at ,s'1 w\ld be visible at ! e>?2 = ! ray ,s',a w\ld be b5t by ! atmosph]e into ! direction ,,ae'4 ,s1 also1 on ! opposite side ( ! moon1 a /> might be se5 at ! e>?1 al?\gh really beh9d ! edge ( ! moon3 h5ce1 if ! moon _h an atmosph]e1 ! "t dur+ :i* a /> w\ld be conceal$ by ! moon w\ld be less ?an if x _h no atmosph]e1 & ! am\nt ( ?is effect mu/ be proportional to ! d5sity ( ! atmosph]e4 ,! moon1 9 h] orbital c\rse across ! heav5s1 is cont9ually pass+ be=e1 or occult+1 "s ( ! />s t s ?ickly /ud h] app>5t pa?2 & :5 we see a /> ?us pass beh9d ! lun> disk on "o side1 & come out aga9 on ! o!r side1 we are virtually obs]v+ ! sett+ & ris+ ( t /> ^u ! moon4 ,! moon's app>5t diamet] has be5 measur$ ov] & ov] aga91 & is kn[n ) great accuracy2 ! rate ( h] motion across ! sky is also kn[n ) p]fect accuracy3 h5ce x is easy to calculate h[ long ! moon w take to travel across a "p ( ! sky exactly equal 9 l5g? to h] own diamet]4 ,suppos+1 !n1 t we obs]ve a /> pass beh9d ! moon1 & out aga91 x is cle>1 t1 if !re is no atmosph]e1 ! int]val ( "t dur+ :i* x rema9s occult$ ought to be exactly equal to ! comput$ "t :i* ! moon w\ld take to pass ov] ! />4 ,if1 h[ev]1 f ! exi/5ce ( a lun> atmosph]e1 ! /> disappe>s too late1 & re-appe>s too soon1 z we h se5 x w\ld1 ^! two int]vals w n agree2 ! comput$ "t w be great] ?an ! obs]v$ "t1 & ! diff]5ce w repres5t ! am\nt ( refraction ! />'s light has su/a9$ or suff]$1 & h5ce ! ext5t ( atmosph]e x has _h to pass ?r\gh4 ,comp>isons ( ^! two int]vals ( "t h be5 repeat$ly made1 ! mo/ ext5sive be+ execut$ "u ! direction ( ! ,a/ronom] ,royal ( ,engl&1 sev]al ye>s ago1 & bas$ ^u no less ?an two hundr$ & n9ety-six occultation obs]vations4 ,9 ?is det]m9ation ! measur$ or telescopic diamet] ( ! moon 0 comp>$ ) ! diamet] d$uc$ f ! occultations2 & x 0 f\nd t ! telescopic diamet] 0 great] ?an ! occultation diamet] by two seconds ( angul> measurem5t1 or by ab\t a ?\s&? "p ( ! :ole diamet] ( ! moon4 ,?is discrepancy is probably due1 9 "p at lea/1 to irradiation 7#ia71 :i* augm5ts ! app>5t size ( ! moon1 z se5 9 ! telescope z well z ) ! nak$ eye2 b1 if ! :ole two seconds 7 caus$ by atmosph]ic refraction1 ?is w\ld imply a horizontal refraction ( "o second1 :i* is only "o two-?\s&? ( ! e>?'s horizontal refraction4 ,x is possible t an atmosph]e compet5t to produce ?is refraction w\ld n make itself visible 9 any o!r way4 ,b an atmosph]e two ?\s& times r>] ?an our air c sc>cely be reg>d$ z an atmosph]e at all4 ,! cont5ts ( an air-pump receiv] c seldom be r>efi$ to a great] ext5t ?an to ab\t a ?\s&? ( ! d5sity ( air at ! e>?'s surface2 & ! lun> atmosph]e1 if x exi/s at all1 is ?us prov$ to be twice z att5uat$ z :at we commonly call a vacuum4 ,! ,surface ( ! ,moon4 ,illu/ration3 ,fig4 #acj4 #aab4 ,dusky ,pat*es on ! ,disk ( ! ,moon4--,) ! nak$ eye1 l>ge dusky pat*es are se5 on ! moon1 9 :i* popul> fancy has detect$ a resemblance to a human face4 ,) a telescope ( l[ p[]1 ^! d>k pat*es appe> z smoo? z wat]1 & !y 7 once suppos$ to be seas4 ,?is !ory 0 ! orig9 ( ! "n m>e 7,lat9 = sea71 :i* is /ill appli$ to ! l>g] ( ^! pla9s2 b1 if !re 7 wat] on ! surface ( ! moon1 x c\ld n fail to manife/ its pres5ce by its vapor1 :i* w\ld =m an appreciable atmosph]e4 ,moreov]1 ) a high telescopic p[]1 ^! pla9s pres5t a m or less unev5 surface2 &1 z ! elevations & depressions are f\nd to be p]man5t1 !y _c1 ( c\rse1 belong to ! surface ( wat]4 ,! *ief ( ^! pla9s are %[n 9 ,fig4 #acj4 ,!y are ,m>e ,crisium1 ,m>e ,foecunditatis1 ,m>e ,nect>is1 ,m>e ,tranquillitatis1 ,m>e ,s]5itatis1 ,m>e ,imbrium1 ,m>e ,frigoris1 & ,oceanus ,procell>um4 ,all ^! pla9s c easily be recogniz$ on ! surface ( ! full moon ) ! unaid$ eye4 #aac4 ,! ,t]m9ator ( ! ,moon4--,! t]m9ator ( ! moon is ! l9e :i* sep>ates ! bright & d>k portions ( its disk4 ,:5 view$ ) a telescope ( ev5 mod]ate p[]1 ! t]m9ator is se5 to be v irregul> & unev54 ,_m bright po9ts are se5 j outside ( ! t]m9ator 9 ! d>k portion ( ! disk1 :ile all along 9 ! neighborhood ( ! t]m9ator are bright pat*es & d5se %ad[s4 ,^! appe>ances are %[n 9 ,figs4 #aca & #acb1 :i* repres5t ! moon ne> ! fir/ & la/ qu>t]s4 ,!y indicate t ! surface ( ! moon is v r\gh & unev54 ,illu/ration3 ,fig4 #aca4 ,illu/ration3 ,fig4 #acb4 ,z x is always ei!r sunrise or sunset along ! t]m9ator1 ! bright spots outside ( x are cle>ly ! tops ( m\nta9s1 :i* cat* ! rays ( ! sun :ile _! bases are 9 ! %ade4 ,! bright pat*es 9 ! neighborhood ( ! t]m9ator are ! sides ( hills & m\nta9s :i* are receiv+ ! full light ( ! sun1 :ile ! d5se %ad[s ne> by are ca/ by ^! elevations4 #aad4 ,height ( ! ,lun> ,m\nta9s4--,!re are two me?ods ( f9d+ ! height ( lun> m\nta9s3-- 7#a7 ,we may measure ! l5g? ( ! %ad[s1 & !n calculate ! height ( ! m\nta9s t w\ld ca/ su* %ad[s ) ! sun at ! requir$ height above ! horizon4 ,! l5g? ( a %ad[ may be obta9$ by ! foll[+ me?od3 ! longitud9al wire ( ! micromet] 7#ai7 is adju/$ s z to pass ?r\gh ! %ad[ ^: l5g? is to be measur$1 & ! transv]se wires are plac$ "o at ea* end ( ! %ad[1 z %[n 9 ,fig4 #acc4 ,! micromet] screw is !n turn$ till ! wires are br\ght toge!r1 s z to asc]ta9 ! l5g? ( ! arc betwe5 !m4 ,we may !n =m ! proportion3 ! numb] ( seconds 9 ! semi-diamet] ( ! moon is to ! numb] ( seconds 9 ! l5g? ( ! %ad[1 z ! l5g? ( ! moon's radius 9 miles to ! l5g? ( ! %ad[ 9 miles4 ,illu/ration3 ,fig4 #acc4 ,! height ( ! sun above ! horizon is asc]ta9$ by measur+ ! angul> di/ance ( ! m\nta9 f ! t]m9ator4 7#b7 ,we may measure ! di/ance ( a bright po9t f ! t]m9ator1 & !n con/ruct a "r-angl$ triangle1 z %[n 9 ,fig4 #acd4 ,a solution ( ?is triangle w enable u to asc]ta9 ! height ( ! m\nta9 ^: top is j cat*+ ! level rays ( ! sun4 ,illu/ration3 ,fig4 #acd4 ,b is ! c5tre ( ! moon1 ,m ! top ( ! m\nta91 & ,,sam a ray ( sunlight :i* j grazes ! t]m9ator at ,a1 & !n /rikes ! top ( ! m\nta9 at ,m4 ,! triangle ,,bam is "r-angl$ at ,a4 ,,ba is ! radius ( ! moon1 & ,,am is kn[n by measurem5t2 ,,bm1 ! hypo!nuse1 may !n be f\nd by computation4 ,,bm is evid5tly equal to ! radius ( ! moon plus ! height ( ! m\nta94 ,by "o or ! o!r ( ^! me?ods1 ! heights ( ! lun> m\nta9s h be5 f\nd ) a great degree ( accuracy4 ,x is claim$ t ! heights ( ! lun> m\nta9s are m accurately kn[n ?an ^? ( ! m\nta9s on ! e>?4 ,comp>$ ) ! size ( ! moon1 lun> m\nta9s atta9 a great] height ?an ^? on ! e>?4 #aae4 ,g5]al ,aspect ( ! ,lun> ,surface4--,a cursory exam9ation ( ! moon ) a l[ p[] is suffici5t to %[ ! preval5ce ( crat]-l inequalities & ! g5]al t5d5cy to circul> %ape :i* is app>5t 9 ne>ly all ! surface m>k+s2 = ev5 ! l>ge seas & ! small] pat*es ( ! same "* repeat 9 _! outl9es ! r\nd =m ( ! crat]s4 ,x is along ! t]m9ator t we see ^! crat]-l spots to ! be/ advantage2 z x is !re t ! ris+ or sett+ sun ca/s long %ad[s ov] ! lun> l&scape1 & br+s elevations into bold relief4 ,!y v>y greatly 9 size2 "s be+ s l>ge z to be> a s5sible proportion to ! moon's diamet]1 :ile ! smalle/ are s m9ute z to ne$ ! mo/ p[]ful telescopes & ! f9e/ conditions ( atmosph]e to p]ceive !m4 ,illu/ration3 ,fig4 #ace4 ,! preval5ce ( r+-%ap$ m\nta9s & pla9s willbe evid5t f ,fig4 #ace1 :i* is f a photograph ( a model ( ! moon con/ruct$ by ,nasmy?4 ,?is same feature is ne>ly z m>k$ 9 ,figs4 #aca & #acb1 :i* are copies ( ,ru!rfurd's photographs ( ! moon4 #aaf4 ,lun> ,crat]s4--,! small] sauc]-%ap$ =mations on ! surface ( ! moon are call$ crat]s4 ,!y are ( all sizes1 f a mile to a hundr$ & fifty miles 9 diamet]2 & !y are suppos$ to be ( volcanic orig94 ,a high telescopic p[] %[s t ^! crat]s v>y rem>kably1 n only 9 size1 b also 9 /ructure & arrangem5t4 ,"s are consid]ably elevat$ above ! surr\nd+ surface1 o!rs are bas9s holl[$ out ( t surface1 & ) l[ surr\nd+ ramp>ts2 "s are l wall$ pla9s1 :ile ! majority h _! l[e/ depression consid]ably bel[ ! surr\nd+ surface2 "s are isolat$ ^u ! pla9s1 o!rs are ?ickly cr[d$ toge!r1 ov]lapp+ & intrud+ ^u ea* o!r2 "s h elevat$ peaks or cones 9 _! c5tres1 & "s are )\t ^! c5tral cones1 :ile o!rs1 aga91 conta9 sev]al m9ute crat]s in/ead2 "s h _! ramp>ts :ole & p]fect1 o!rs h !m brok5 or de=m$1 & _m h !m divid$ into t]races1 especially on _! inn] sides4 ,a typical lun> crat] is %[n 9 ,fig4 #acf4 ,illu/ration3 ,fig4 #acf4 ,x is n g5]ally believ$ t any active volcanoes exi/ on ! moon at ! pres5t "t1 ?\gh "s obs]v]s h ?\ght !y disc]n$ indications ( su* volcanoes4 ,illu/ration3 ,fig4 #acg4 #aag4 ,cop]nicus4--,?is is "o ( ! gr&e/ ( lun> crat]s 7,fig4 #acg74 ,al?\gh its diamet] 7=ty-six miles7 is exce$$ by o!rs1 yet1 tak5 z a :ole1 x =ms "o ( ! mo/ impressive & int]e/+ objects ( its class4 ,its situation1 ne> ! c5tre ( ! lun> disk1 r5d]s all its wond]ful details conspicu\s1 z well z ^? ( objects imm$iately surr\nd+ x4 ,its va/ ramp>t rises to upw>ds ( twelve ?\s& feet above ! level ( ! plateau1 ne>ly 9 ! c5tre ( :i* /&s a magnific5t gr\p ( cones1 ?ree ( :i* atta9 a height ( m ?an tw5ty-f\r hundr$ feet4 ,_m ridges1 or spurs1 may be obs]v$ lead+ away f ! out] banks ( ! great ramp>t4 ,ar\nd ! crat]1 ext5d+ to a di/ance ( m ?an a hundr$ miles on e side1 !re is a complex network ( bright /reaks1 :i* div]ge 9 all directions4 ,^! /reaks d n appe> 9 ! figure1 nor are !y se5 ^u ! moon1 except at & ne> ! full phase4 ,!y %[ conspicu\sly1 h[ev]1 by _! unit$ lu/re on ! full moon4 ,?is crat] is se5 j to ! s\?-we/ ( ! l>ge dusky pla9 9 ! upp] "p ( ,fig4 #acb4 ,?is pla9 is ,m>e ,imbrium1 & ! m\nta9-*a9 se5 a little to ! "r ( ,cop]nicus is nam$ ! ,ap5n9es4 ,cop]nicus is also se5 9 ,fig4 #ace1 a little to ! left ( ! same range4 ,"u circum/ances specially favorable1 myriads ( comp>atively m9ute b p]fectly =m$ crat]s may be obs]v$ = m ?an sev5ty miles on all sides ar\nd ,cop]nicus4 ,! di/rict on ! s\?-ea/ side is specially ri* 9 ^! ?ickly scatt]$ crat]s1 :i* we h reason to suppose /& ov] or ^u ! bright /reaks4 #aah4 ,d>k ,*asms4--,d>k cracks1 or *asms1 h be5 obs]v$ on v>i\s p>ts ( ! moon's surface4 ,!y sometimes occur s+ly1 & sometimes 9 gr\ps4 ,!y are (t5 se5 to radiate f "s c5tral cone1 & !y appe> to be ( volcanic orig94 ,!y h be5 call$ canals & rills4 ,illu/ration3 ,fig4 #ach4 ,"o ( ! mo/ rem>kable gr\ps ( ^! *asms is t to ! we/ ( ! crat] nam$ ,triesnek]4 ,! crat] & ! *asms are %[n 9 ,fig4 #ach4 ,sev]al ( ^! great cracks obvi\sly div]ge f a small crat] ne> ! we/ bank ( ! great "o1 & !y subdivide z !y ext5d f ! app>5t po9t ( div]g5ce1 :ile !y are cross$ by o!rs4 ,^! cracks1 or *asms1 are ne>ly a mile broad at ! wide/ "p1 &1 aft] ext5d+ full a hundr$ miles1 tap] away till !y become invisible4 ,illu/ration3 ,fig4 #aci4 #aai4 ,m\nta9-,ranges4--,!re are comp>atively few m\nta9-ranges on ! moon4 ,! ?ree mo/ conspicu\s are ^? :i* p>tially enclose ,m>e ,imbrium2 namely1 ! ,ap5n9es on ! s\?1 & ! ,caucasus & ! ,alps on ! ea/ & nor?-ea/4 ,! ,ap5n9es are ! mo/ ext5d$ ( ^!1 hav+ a l5g? ( ab\t f\r hundr$ & fifty miles4 ,!y rise gradually1 f a comp>atively level surface t[>ds ! s\?-we/1 9 ! =m ( innum]able small elevations1 :i* increase 9 numb] & height t[>ds ! nor?-ea/1 :]e !y culm9ate 9 a range ( peaks ^: altitude & rugg$ aspect mu/ =m "o ( ! mo/ t]ribly gr& & romantic sc5es :i* imag9ation c conceive4 ,! nor?-ea/ face ( ! range t]m9ates abruptly 9 an almo/ v]tical precipice2 :ile ov] ! pla9 b5ea?1 int5sely black spire-l %ad[s are ca/1 "s ( :i* at sunrise ext5d full n9ety miles1 till !y lose !mselves 9 ! g5]al %ad+ due to ! curvature ( ! lun> surface4 ,_m ( ! peaks rise to heights ( f eighte5 ?\s& to tw5ty ?\s& feet above ! pla9 at _! nor?-ea/ base 7,fig4 #aci74 ,illu/ration3 ,fig4 #adj4 ,fig4 #adj repres5ts an ideal lun> l&scape ne> ! base ( su* a lun> range4 ,ow+ to ! abs5ce ( an atmosph]e1 ! />s w be visible 9 full daylight4 ,illu/ration3 ,fig4 #ada4 #abj4 ,! ,valley ( ! ,alps4--,! range ( ! ,alps is %[n 9 ,fig4 #ada4 ,! great crat] at ! nor? end ( ?is range is nam$ ,plato4 ,x is sev5ty miles 9 diamet]4 ,! mo/ rem>kable feature ( ! ,alps is ! valley ne> ! c5tre ( ! range4 ,x is m ?an sev5ty-five miles long1 & ab\t six miles wide at ! broade/ "p4 ,:5 exam9$ "u favorable circum/ances1 ) a high magnify+ p[]1 x is se5 to be a va/ flat-bottom$ valley1 bord]$ by gigantic m\nta9s1 "s ( :i* atta9 heights ( t5 ?\s& feet or m4 ,illu/ration3 ,fig4 #adb4 #aba4 ,isolat$ ,peaks4--,!re are comp>atively few isolat$ peaks to be f\nd on ! surface ( ! moon4 ,"o ( ! mo/ rem>kable ( ^! is t kn[n z ,pico1 & %[n 9 ,fig4 #adb4 ,its height exce$s eight ?\s& feet1 & x is ab\t ?ree times z long at ! base z x is broad4 ,! summit is cleft into ?ree peaks1 z is %[n by ! ?ree-peak$ %ad[ x ca/s on ! pla94 #abb4 ,bright ,rays4--,ab\t ! "t ( full moon1 ) a telescope ( mod]ate p[]1 a numb] ( bright l9es may be se5 radiat+ f sev]al ( ! lun> crat]s1 ext5d+ (t5 to ! di/ance ( hundr$s ( miles4 ,^! /reaks d n arise f any p]ceptible diff]5ce ( level ( ! surface1 !y h no v def9ite outl9e1 & !y d n pres5t any slop+ sides to cat* m sunlight1 & ?us %9e bright]1 ?an ! g5]al surface4 ,inde$1 "o great peculi>ity ( !m is1 t !y come out mo/ =cibly :5 ! sun is %9+ p]p5dicul>ly ^u !m3 h5ce !y are be/ se5 :5 ! moon is at full1 & !y are n visible at all at ^? regions ^u :i* ! sun is ris+ or sett+4 ,!y are n div]t$ by elevations 9 _! pa?1 b trav]se 9 _! c\rse crat]s1 m\nta9s1 & pla9s alike1 giv+ a slight additional brightness to all objects ov] :i* !y pass1 b produc+ no o!r effect ^u !m4 ,!y look z if1 aft] ! :ole surface ( ! moon _h assum$ its f9al configuration1 a va/ bru% *>g$ ) a :iti% pigm5t _h be5 drawn ov] ! globe 9 /raight l9es1 radiat+ f a c5tral po9t1 leav+ its trail ^u e ?+ x t\*$1 b obscur+ no?+4 ,illu/ration3 ,fig4 #adc4 ,! ?ree mo/ conspicu\s crat]s f :i* ^! l9es radiate are ,ty*o1 ,cop]nicus1 & ,kepl]4 ,ty*o is se5 at ! bottom ( ,figs4 #adc & #acj4 ,kepl] is a little to ! left ( ,cop]nicus 9 ! same figures4 ,x has be5 ?\ght t ^! bright /reaks are *asms :i* h be5 fill$ ) molt5 lava1 :i*1 on cool+1 w\ld af=d a smoo? reflect+ surface on ! top4 #abc4 ,ty*o4--,?is crat] is fifty-f\r miles 9 diamet]1 & ab\t sixte5 ?\s& feet deep1 f ! highe/ ridge ( ! ramp>t to ! surface ( ! plateau1 :5ce rises a c5tral cone five ?\s& feet high4 ,x is "o ( ! mo/ conspicu\s ( all ! lun> crat]s2 n s mu* on acc\nt ( its dim5sions z f its be+ ! c5tre f :5ce div]ge ^? rem>kable bright /reaks1 _m ( :i* may be trac$ ov] a ?\s& miles ( ! moon's surface 7,fig4 #adc74 ,ty*o appe>s to be an in/ance ( a va/ disruptive action :i* r5t ! solid cru/ ( ! moon into radiat+ fissures1 :i* 7 subsequ5tly fill$ ) molt5 matt]1 ^: sup]ior lum9osity m>ks ! c\rse ( ! cracks 9 all directions f ! crat] z _! common c5tre4 ,s num]\s are ^! bright /reaks :5 exam9$ by ! aid ( ! telescope1 & !y give to ?is region ( ! moon's surface su* increas$ lum9osity1 t1 :5 view$ z a :ole1 ! locality c be di/9ctly se5 at full moon by ! unassi/$ eye1 z a bright pat* ( light on ! s\!rn portion ( ! disk4 ,,iii4 ,,inf]ior ,,& ,,sup]ior ,,planets4 ,inf]ior ,planets4 #abd4 ,! ,inf]ior ,planets4--,! inf]ior planets are ^? :i* lie betwe5 ! e>? & ! sun1 & ^: orbits are includ$ by t ( ! e>?4 ,!y are ,m]cury & ,v5us4 ,illu/ration3 ,fig4 #add4 #abe4 ,aspects ( an ,inf]ior ,planet4--,! f\r *ief aspects ( an inf]ior planet z se5 f ! e>? are %[n 9 ,fig4 #add1 9 :i* ,s repres5ts ! sun1 ,p ! planet1 & ,e ! e>?4 ,:5 ! planet is betwe5 ! e>? & ! sun1 z at ,p1 x is said to be 9 inf]ior conjunction4 ,:5 x is 9 ! same direction z ! sun1 b beyond x1 z at ,p''1 x is said to be 9 sup]ior conjunction4 ,:5 ! planet is at su* a po9t 9 its orbit t a l9e drawn f ! e>? to x w\ld be tang5t to ! orbit1 z at ,p' & ,p'''1 x is said to be at its greate/ elongation4 ,illu/ration3 ,fig4 #ade4 #abf4 ,app>5t ,motion ( an ,inf]ior ,planet4--,:5 ! planet is at ,p1 if x c\ld be se5 at all1 x w\ld appe> 9 ! heav5s at ,a4 ,z x moves f ,p to ,p'1 x w appe> to move 9 ! heav5s f ,a to ,b4 ,!n1 z x moves f ,p' to ,p''1 x w appe> to move back aga9 f ,b to ,a4 ,:ile x moves f ,p'' to ,p'''1 x w appe> to move f ,a to ,c2 &1 :ile mov+ f ,p''' to ,p1 x w appe> to move back aga9 f ,c to ,a4 ,?us ! planet w appe> to oscillate to & fro across ! sun f ,b to ,c1 nev] gett+ f>!r f ! sun ?an ,b on ! we/1 or ,c on ! ea/3 h5ce1 :5 at ^! po9ts1 x is said to be at its greate/ we/]n & ea/]n elongations4 ,?is oscillat+ motion ( an inf]ior planet across ! sun1 comb9$ ) ! sun's motion among ! />s1 causes ! planet to describe a pa? among ! />s simil> to t %[n 9 ,fig4 #ade4 ,illu/ration3 ,fig4 #adf4 #abg4 ,phases ( an ,inf]ior ,planet4--,an inf]ior planet1 :5 view$ ) a telescope1 is f\nd to pres5t a succession ( phases simil> to ^? ( ! moon4 ,! reason ( ?is is evid5t f ,fig4 #adf4 ,z an inf]ior planet passes ar\nd ! sun1 x pres5ts sometimes m & sometimes less ( its bright hemisph]e to ! e>?4 ,:5 ! e>? is at ,t1 & ,v5us at sup]ior conjunction1 ! planet turns ! :ole ( its bright hemisph]e t[>ds ! e>?1 & appe>s full2 x !n becomes gibb\s1 half1 & cresc5t4 ,:5 x comes into inf]ior conjunction1 x turns its d>k hemisph]e t[>ds ! e>?3 x !n becomes cresc5t1 half1 gibb\s1 & full aga94 #abh4 ,! ,sid]eal & ,synodical ,p]iods ( an ,inf]ior ,planet4--,! "t x takes a planet to make a complete revolution ar\nd ! sun is call$ ! sid]eal p]iod ( ! planet2 & ! "t x takes x to pass f "o aspect ar\nd to ! same aspect aga91 its synodical p]iod4 ,illu/ration3 ,fig4 #adg4 ,! synodical p]iod ( an inf]ior planet is long] ?an its sid]eal p]iod4 ,?is w be evid5t f an exam9ation ( ,fig4 #adg4 ,s is ! position ( ! sun1 ,e t ( ! e>?1 & ,p t ( ! planet at inf]ior conjunction4 ,be=e ! planet c be 9 inf]ior conjunction aga91 x mu/ pass entirely ar\nd its orbit1 & ov]take ! e>?1 :i* has 9 ! mean "t pass$ on 9 its orbit to ,e'4 ,:ile ! e>? is pass+ f ,e to ,e'1 ! planet passes entirely ar\nd its orbit1 & f ,p to ,p' 9 addition4 ,n[ ! arc ,,pp' is j equal to ! arc ,,ee'3 h5ce ! planet has to pass ov] ! same arc t ! e>? does1 & #cfj m4 ,9 o!r words1 ! planet has to ga9 #cfj on ! e>?4 ,! synodical p]iod ( ! planet is f\nd by direct obs]vation4 #abi4 ,! ,l5g? ( ! ,sid]eal ,p]iod4--,! l5g? ( ! sid]eal p]iod ( an inf]ior planet may be f\nd by ! foll[+ computation3-- ,let a d5ote ! synodical p]iod ( ! planet1 ,let b d5ote ! sid]eal p]iod ( ! e>?1 ,let x d5ote ! sid]eal p]iod ( ! planet4 ,!n #cfj_/;b ! daily motion ( ! e>?1 ,& #cfj_/x ! daily motion ( ! planet1 ,& #cfj_/x - #cfj_/;b ! daily ga9 ( ! planet3 ,also #cfj_/;a ! daily ga9 ( ! planet3 ,h5ce #cfj_/x - #cfj_/;b #cfj_/;a4 ,divid+ by #cfj1 we h #a_/x - #a_/;b #a_/;a2 ,cle>+ ( fractions1 we h ab - ax bx3 ,transpos+ & collect+1 we h 7a b7x ab3 ,!re=e x ab_/ab4 #acj4 ,! ,relative ,di/ance ( an ,inf]ior ,planet4--,by ! relative di/ance ( a planet1 we mean its di/ance f ! sun comp>$ ) ! e>?'s di/ance f ! sun4 ,! relative di/ance ( an inf]ior planet may be f\nd by ! foll[+ me?od3-- ,illu/ration3 ,fig4 #adh4 ,let ,v1 9 ,fig4 #adh1 repres5t ! position ( ,v5us at its greate/ elongation f ! sun1 ,s ! position ( ! sun1 & ,e t ( ! e>?4 ,! l9e ,,ev w evid5tly be tang5t to a circle describ$ ab\t ! sun ) a radius equal to ! di/ance ( ,v5us f ! sun at ! "t ( ?is greate/ elongation4 ,draw ! radius ,,sv & ! l9e ,,se4 ,s9ce ,,sv is a radius1 ! angle at ,v is a "r angle4 ,! angle at ,e is kn[n by measurem5t1 & ! angle at ,s is equal to #ij- ! angle ,e4 ,9 ! "r-angl$ triangle ,,evs1 we !n "k ! ?ree angles1 & we wi% to f9d ! ratio ( ! side ,,sv to ! side ,,se4 ,! ratio ( ^! l9es may be f\nd by trigonometrical computation z foll[s3-- ,,vs 3 ,,es s9 ,,sev 3 #a4 ,sub/itute ! value ( ! s9e ( ,,sev1 & we h ,,vs 3 ,,es 4#gbc 3 #a4 ,h5ce ! relative di/ances ( ,v5us & ( ! e>? f ! sun are 4#gbc & #a4 ,sup]ior ,planets4 #aca4 ,! ,sup]ior ,planets4--,! sup]ior planets are ^? :i* lie beyond ! e>?4 ,!y are ,m>s1 ! ,a/]oids1 ,jupit]1 ,saturn1 ,uranus1 & ,neptune4 ,illu/ration3 ,fig4 #adi4 #acb4 ,app>5t ,motion ( a ,sup]ior ,planet4--,9 ord] to d$uce ! app>5t motion ( a sup]ior planet f ! real motions ( ! e>? & planet1 let ,s 7,fig4 #adi7 be ! place ( ! sun2 #a1 #b1 #c1 etc41 ! orbit ( ! e>?2 a1 b1 c1 etc41 ! orbit ( ,m>s2 & ,,cgl a "p ( ! />ry firmam5t4 ,let ! orbit ( ! e>? be divid$ into twelve equal p>ts1 ea* describ$ 9 "o mon?2 & let ab1 bc1 cd1 etc41 be ! spaces describ$ by ,m>s 9 ! same "t4 ,suppose ! e>? to be at ! po9t #a :5 ,m>s is at ! po9t a1 ,m>s w !n appe> 9 ! heav5s 9 ! direction ( #a a4 ,:5 ! e>? is at #c1 & ,m>s at c1 he w appe> 9 ! heav5s at ,c4 ,:5 ! e>? arrives at #d1 ,m>s w arrive at d1 & w appe> 9 ! heav5s at ,d4 ,:ile ! e>? moves f #d to #e & f #e to #f1 ,m>s w appe> to h advanc$ among ! />s f ,d to ,e & f ,e to ,f1 9 ! direction f we/ to ea/4 ,dur+ ! motion ( ! e>? f #f to #g & f #g to #h1 ,m>s w appe> to g backw>d f ,f to ,g & f ,g to ,h1 9 ! direction f ea/ to we/4 ,dur+ ! motion ( ! e>? f #h to #i & f #i to #aj1 ,m>s w appe> to advance f ,h to ,i & f ,i to ,k1 9 ! direction f we/ to ea/1 & ! motion w cont9ue 9 ! same direction until ne> ! succe$+ opposition4 ,! app>5t motion ( a sup]ior planet project$ on ! heav5s is ?us se5 to be simil> to t ( an inf]ior planet1 except t1 9 ! latt] case1 ! retrogression takes place ne> inf]ior conjunction1 & 9 ! =m] x takes place ne> opposition4 ,illu/ration3 ,fig4 #aej4 #acc4 ,aspects ( a ,sup]ior ,planet4--,! f\r aspects ( a sup]ior planet are %[n 9 ,fig4 #aej1 9 :i* ,s is ! position ( ! sun1 ,e t ( ! e>?1 & ,p t ( ! planet4 ,:5 ! planet is on ! opposite side ( ! e>? to ! sun1 z at ,p1 x is said to be 9 opposition4 ,! sun & ! planet w !n appe> 9 opposite p>ts ( ! heav5s1 ! sun appe>+ at ,c1 & ! planet at ,a4 ,:5 ! planet is on ! opposite side ( ! sun to ! e>?1 z at ,p''1 x is said to be 9 sup]ior conjunction4 ,x w !n appe> 9 ! same "p ( ! heav5s z ! sun1 bo? appe>+ at ,c4 ,:5 ! planet is at ,p' & ,p'''1 s t a l9e drawn f ! e>? ?r\gh ! planet w make a "r angle ) a l9e drawn f ! e>? to ! sun1 x is said to be 9 quadrature4 ,at ,p' x is 9 its we/]n quadrature1 & at ,p''' 9 its ea/]n quadrature4 ,illu/ration3 ,fig4 #aea4 #acd4 ,phases ( a ,sup]ior ,planet4--,m>s is ! only "o ( ! sup]ior planets t has appreciable phases4 ,at quadrature1 z w appe> f ,fig4 #aea1 ,m>s does n pres5t q ! same side to ! e>? z to ! sun3 h5ce1 ne> ^! p>ts ( its orbit1 ! planet appe>s slightly gibb\s4 ,else:]e 9 its orbit1 ! planet appe>s full4 ,all ! o!r sup]ior planets are s f> away f ! sun & e>?1 t ! sides :i* !y turn t[>ds ! sun & ! e>? 9 e "p ( _! orbit are s ne>ly ! same1 t no *ange 9 ! =m ( _! disks c be detect$4 #ace4 ,! ,synodical ,p]iod ( a ,sup]ior ,planet4--,dur+ a synodical p]iod ( a sup]ior planet ! e>? mu/ ga9 "o revolution1 or #cfj1 on ! planet1 z w be evid5t f an exam9ation ( ,fig4 #aeb1 9 :i* ,s repres5ts ! sun1 ,e ! e>?1 & ,p ! planet at opposition4 ,be=e ! planet c be 9 opposition aga91 ! e>? mu/ make a complete revolution1 & ov]take ! planet1 :i* has 9 ! mean "t pass$ on f ,p to ,p'4 ,illu/ration3 ,fig4 #aeb4 ,9 ! case ( mo/ ( ! sup]ior planets ! synodical p]iod is %ort] ?an ! sid]eal p]iod2 b 9 ! case ( ,m>s x is long]1 s9ce ,m>s makes m ?an a complete revolution be=e ! e>? ov]takes x4 ,! synodical p]iod ( a sup]ior planet is f\nd by direct obs]vation4 #acf4 ,! ,sid]eal ,p]iod ( a ,sup]ior ,planet4--,! sid]eal p]iod ( a sup]ior planet is f\nd by a me?od ( computation simil> to t = f9d+ ! sid]eal p]iod ( an inf]ior planet3-- ,let a d5ote ! synodical p]iod ( ! planet1 ,let b d5ote ! sid]eal p]iod ( ! e>?1 ,let x d5ote ! sid]eal p]iod ( ! planet4 ,!n w #cfj_/;b daily motion ( ! e>?1 ,& #cfj_/x daily motion ( ! planet2 ,also #cfj_/;b - #cfj_/x daily ga9 ( ! e>?4 ,b #cfj_/;a daily ga9 ( ! e>?3 ,h5ce #cfj_/;b - #cfj_/x #cfj_/;a #a_/;b - #a_/x #a_/;a ax - ab bx 7a-b7x ab x ab_/7a-b74 ,illu/ration3 ,fig4 #aec4 #acg4 ,! ,relative ,di/ance ( a ,sup]ior ,planet4--,let ,s1 e1 & m1 9 ,fig4 #aec1 repres5t ! relative positions ( ! sun1 ! e>?1 & ,m>s1 :5 ! latt] planet is 9 opposition4 ,let ,e & ,m repres5t ! relative positions ( ! e>? & ,m>s ! day aft] opposition4 ,at ! fir/ obs]vation ,m>s w be se5 9 ! direction em,a1 & at ! second obs]vation 9 ! direction ,,ema4 ,b ! fix$ />s are s di/ant1 t if a l9e1 e,a1 7 drawn to a fix$ /> at ! fir/ obs]vation1 & a l9e1 ,,eb1 drawn f ! e>? to ! same fix$ /> at ! second obs]vation1 ^! two l9es w\ld be s5sibly p>allel2 t is1 ! fix$ /> w\ld be se5 9 ! direction ( ! l9e e,a at ! fir/ obs]vation1 & 9 ! direction ( ! l9e ,,eb1 p>allel to e,a1 at ! second obs]vation4 ,b if ,m>s 7 se5 9 ! direction ( ! fix$ /> at ! fir/ obs]vation1 x w\ld appe> back1 or we/1 ( t /> at ! second obs]vation by ! angul> di/ance ,,bea2 t is1 ! planet w\ld h retrograd$ t angul> di/ance4 ,n[1 ?is retrogression ( ,m>s dur+ "o day1 at ! "t ( opposition1 c be measur$ directly by obs]vation4 ,?is measurem5t gives u ! value ( ! angle ,,bea2 b we "k ! rate at :i* bo? ! e>? & ,m>s are mov+ 9 _! orbits1 & f ?is we c easily f9d ! angul> di/ance pass$ ov] by ea* 9 "o day4 ,?is gives u ! angles ,,esa & ,,msa4 ,we c n[ f9d ! relative l5g? ( ! l9es ,,ms & ,,es 7:i* repres5t ! di/ances ( ,m>s & ( ! e>? f ! sun71 bo? by con/ruction & by trigonometrical computation4 ,s9ce ,,eb & e,a are p>allel1 ! angle ,,eas is equal to ,,bea4 ,,sea #ahj - 7,,esa ,,eas7 ,,esm ,,esa - ,,msa ,,ems #ahj - 7,,sea ,,esm74 ,we h !n ,,ms 3 ,,es s9 ,,sea 3 s9 ,,ems4 ,sub/itut+ ! values ( ! s9es1 & r$uc+ ! ratio to its l[e/ t]ms1 we h ,,ms 3 ,,es #a4ebd 3 #a4 ,?us we f9d t ! relative di/ances ( ,m>s & ! e>? f ! sun are #a4ebd & #a4 ,by ! simple obs]vation ( its greate/ elongation1 we are able to det]m9e ! relative di/ances ( an inf]ior planet & ! e>? f ! sun2 &1 by ! equally simple obs]vation ( ! daily retrogression ( a sup]ior planet1 we c f9d ! relative di/ances ( su* a planet & ! e>? f ! sun4 ,,iv4 ,,! ,,sun4 ,i4 ,,magnitude ,,& ,,di/ance ,,( ,,! ,,sun4 ,illu/ration3 ,fig4 #aed4 #ach4 ,! ,volume ( ! ,sun4--,! app>5t diamet] ( ! sun is ab\t #cb'1 be+ a little great] ?an t ( ! moon4 ,! real diamet] ( ! sun is #hff1djj miles1 or ab\t a hundr$ & n9e times t ( ! e>?4 ,z ! diamet] ( ! moon's orbit is only ab\t #dhj1jjj miles1 or "s sixty times ! diamet] ( ! e>?1 x foll[s t ! diamet] ( ! sun is ne>ly d\ble t ( ! moon's orbit3 h5ce1 7 ! c5tre ( ! sun plac$ at ! c5tre ( ! e>?1 ! sun w\ld completely fill ! moon's orbit1 & rea* ne>ly z f> beyond x 9 e direction z x is f ! e>? to ! moon4 ,! circumf]5ce ( ! sun z comp>$ ) ! moon's orbit is %[n 9 ,fig4 #aed4 ,! volume ( ! sun is #a1cje1jjj times t ( ! e>?4 #aci4 ,! ,mass ( ! ,sun4--,! sun is mu* less d5se ?an ! e>?4 ,! mass ( ! sun is only #ccj1jjj times t ( ! e>?1 & its d5sity only ab\t a f\r? t ( ! e>?4 ,to f9d ! mass ( ! sun1 we fir/ asc]ta9 ! di/ance ! e>? w\ld draw ! moon t[>ds itself 9 a giv5 "t1 7 ! moon at ! di/ance ( ! sun1 & !n =m ! proportion3 z ! di/ance ! e>? w\ld draw ! moon t[>ds itself is to ! di/ance t ! sun draws ! e>? t[>ds itself 9 ! same "t1 s is ! mass ( ! e>? to ! mass ( ! sun4 ,al?\gh ! mass ( ! sun is ov] ?ree hundr$ ?\s& times t ( ! e>?1 ! pull ( gravity at ! surface ( ! sun is only ab\t tw5ty-eight times z great z at ! surface ( ! e>?4 ,?is is because ! di/ance f ! surface ( ! sun to its c5tre is mu* great] ?an f ! surface to ! c5tre ( ! e>?4 ,illu/ration3 ,fig4 #aee4 #adj4 ,size ( ! ,sun ,comp>$ ) t ( ! ,planets4--,! size ( ! sun comp>$ ) t ( ! l>g] planets is %[n 9 ,fig4 #aee4 ,! mass ( ! sun is m ?an sev5 hundr$ & fifty times t ( all ( ! planets & moons 9 ! sol> sy/em4 ,9 ,fig4 #aef is %[n ! app>5t size ( ! sun z se5 f ! diff]5t planets4 ,! app>5t diamet] ( ! sun decreases z ! di/ance f x increases1 & ! disk ( ! sun decreases z ! squ>e ( ! di/ance f x increases4 ,illu/ration3 ,fig4 #aef4 #ada4 ,! ,di/ance ( ! ,sun4--,! mean di/ance ( ! sun f ! e>? is ab\t #ib1hjj1jjj miles4 ,ow+ to ! ecc5tricity ( ! e>?'s orbit1 ! di/ance ( ! sun v>ies some:at2 be+ ab\t #c1jjj1jjj miles less 9 ,janu>y1 :5 ! e>? is at p]ihelion1 ?an 9 ,june1 :5 ! e>? is at aphelion4 ,b1 ?\gh ! di/ance ( ! sun c easily be /at$ 9 figures1 x is n possible to give any real idea ( a space s enorm\s3 x is q beyond our p[] ( conception4 ,if "o 7 to try to walk su* a di/ance1 suppos+ t he c\ld walk f\r miles an h\r1 & keep x up = t5 h\rs e day1 x w\ld take sixty-eight ye>s & a half to make a s+le million ( miles1 & m ?an sixty-?ree hundr$ ye>s to trav]se ! :ole4 ,if "s cele/ial railway c\ld be imag9$1 ! j\rney to ! sun1 ev5 if our tra9s ran sixty miles an h\r day & night & )\t a /op1 w\ld require ov] a hundr$ & sev5ty-five ye>s4 ,s5sation1 ev51 w\ld n travel s f> 9 a human lifetime4 ,to borr[ ! curi\s illu/ration ( ,pr(essor ,m5d5hall1 if we c\ld imag9e an infant ) an arm long en\gh to enable him to t\* ! sun & burn himself1 he w\ld die ( old age be=e ! pa9 c\ld rea* him2 s9ce1 accord+ to ! exp]im5ts ( ,helmholtz & o!rs1 a n]v\s %ock is communicat$ only at ! rate ( ab\t a hundr$ feet p] second1 or #a1fcg miles a day1 & w\ld ne$ m ?an a hundr$ & fifty ye>s to make ! j\rney4 ,s\nd w\ld d x 9 ab\t f\rte5 ye>s1 if x c\ld be transmitt$ ?r\gh cele/ial space2 & a cannon-ball 9 ab\t n9e1 if x 7 to move uni=mly ) ! same spe$ z :5 x left ! muzzle ( ! gun4 ,if ! e>? c\ld be sudd5ly /opp$ 9 h] orbit1 & all[$ to fall unob/ruct$ t[>d ! sun1 "u ! accel]at+ influ5ce ( 8 attraction1 %e w\ld rea* ! c5tre 9 ab\t f\r mon?s4 ,i h said if %e c\ld be /opp$2 b su* is ! compass ( h] orbit1 t1 to make its circuit 9 a ye>1 %e has to move ne>ly n9ete5 miles a second1 or m ?an fifty times fa/] ?an ! swifte/ rifle-ball2 &1 9 mov+ tw5ty miles1 h] pa? deviates f p]fect /raightness by less ?an an eigh? ( an in*4 ,& yet1 ov] all ! circumf]5ce ( ?is trem5d\s orbit1 ! sun ex]cises 8 dom9ion1 & e pulsation ( 8 surface receives its response f ! subject e>?4 7,pr(essor ,c4 ,a4 ,"y3 ,! ,sun47 #adb4 ,me?od ( ,f9d+ ! ,sun's ,di/ance4--,!re are sev]al me?ods ( f9d+ ! sun's di/ance4 ,! simple/ me?od is t ( f9d+ ! actual di/ance ( "o ( ! ne>] planets by obs]v+ its displacem5t 9 ! sky z se5 f widely sep>at$ po9ts on ! e>?4 ,z ! relative di/ances ( ! planets f ea* o!r & f ! sun are well kn[n1 we c easily d$uce ! actual di/ance ( ! sun if we c f9d t ( any ( ! planets4 ,! two planets usually *os5 = ?is me?od are ,m>s & ,v5us4 7#a7 ,! displacem5t ( ,m>s 9 ! sky1 z se5 f two obs]vatories :i* diff] consid]ably 9 latitude1 is1 ( c\rse1 greate/ :5 ,m>s is ne>e/ ! e>?4 ,n[1 x is evid5t ?an ,m>s w be ne>] ! e>? :5 9 opposition ?an :5 9 any o!r "p ( its orbit2 & ! planet w be lea/ di/ant f ! e>? :5 x is at its p]ihelion po9t1 & ! e>? is at its aphelion po9t1 at ! "t ( opposition4 ,?is me?od1 !n1 c be us$ to ! be/ advantage1 :51 at ! "t ( opposition1 ,m>s is ne> its p]ihelion1 & ! e>? ne> its aphelion4 ,^! favorable oppositions occur ab\t once 9 fifte5 ye>s1 & ! la/ "o 0 9 #ahgg4 ,illu/ration3 ,fig4 #aeg4 ,suppose two obs]v]s situat$ at ,n' & ,s' 7,fig4 #aeg71 ne> ! poles ( ! e>?4 ,! "o at ,n' w\ld see ,m>s 9 ! sky at ,n1 & ! "o at ,s' w\ld see x at ,s4 ,! displacem5t w\ld be ! angle ,,nms4 ,ea* obs]v] measures c>efully ! di/ance ( ,m>s f ! same fix$ /> ne> x4 ,! diff]5ce ( ^! di/ances gives ! displacem5t ( ! planet1 or ! angle ,,nms4 ,^! obs]vations 7 made ) ! greate/ c>e 9 #ahgg4 7#b7 ,v5us is ne>e/ ! e>? at ! "t ( inf]ior conjunction2 b x c !n be se5 only 9 ! daytime4 ,x is1 !re=e1 impossible to asc]ta9 ! displacem5t ( ,v5us1 z se5 f diff]5t /ations1 by comp>+ h] di/ances f a fix$ />4 ,occasionally1 at ! "t ( inf]ior conjunction1 ,v5us passes directly across ! sun's disk4 ,! la/ ( ^! transits ( ,v5us occurr$ 9 #ahgd1 & ! next w occur 9 #ahhb4 ,x w !n be ov] a hundr$ ye>s be=e ano!r w occur4 ,illu/ration3 ,fig4 #aeh4 ,suppose two obs]v]s1 ,a & ,b 7,fig4 #aeh71 ne> ! poles ( ! e>? at ! "t ( a transit ( ,v5us4 ,! obs]v] at ,a w\ld see ,v5us cross+ ! sun at ,v#b1 & ! "o at ,b w\ld see x cross+ at ,v#a4 ,any obs]vation made ^u ,v5us1 :i* w\ld give ! di/ance & direction ( ,v5us f ! c5tre ( ! sun1 z se5 f ea* /ation1 w\ld enable u to calculate ! angul> di/ance betwe5 ! two *ords describ$ across ! sun4 ,?is1 ( c\rse1 w\ld give ! displacem5t ( ,v5us on ! sun's disk4 ,?is me?od 0 fir/ employ$ at ! la/ transits ( ,v5us :i* occurr$ be=e #ahgd2 namely1 ^? ( #agfa & #agfi4 ,!re are ?ree me?ods ( obs]vation employ$ to asc]ta9 ! app>5t direction & di/ance ( ,v5us f ! c5tre ( ! sun1 call$ respectively ! contact me?od1 ! micrometric me?od1 & ! photographic me?od4 7a7 ,9 ! contact me?od1 ! obs]vation consi/s 9 not+ ! exact "t :5 ,v5us crosses ! sun's limb4 ,to asc]ta9 ?is x is necess>y to obs]ve ! exact "t ( ext]nal & int]nal contact4 ,?is obs]vation1 ?\gh app>5tly simple1 is really v difficult4 ,) ref]5ce to ?is me?od ,pr(essor ,"y says1-- ,! difficulties dep5d 9 "p ^u ! imp]fections ( optical in/rum5ts & ! human eye1 p>tly ^u ! ess5tial nature ( light lead+ to :at is kn[n z diffraction1 & p>tly ^u ! action ( ! planet's atmosph]e4 ,! two fir/-nam$ causes produce :at is call$ irradiation1 & op]ate to make ! app>5t diamet] ( ! planet1 z se5 on ! sol> disk1 small] ?an x really is2 small]1 too1 by an am\nt :i* v>ies ) ! size ( ! telescope1 ! p]fection ( its l5ses1 & ! t9t & brightness ( ! sun's image4 ,! edge ( ! planet's image is also r5d]$ slightly hazy & indi/9ct4 ,illu/ration3 ,fig4 #aei4 ,! planet's atmosph]e also causes its disk to be surr\nd$ by a n>r[ r+ ( light1 :i* becomes visible long be=e ! planet t\*es ! sun1 &1 at ! mom5t ( int]nal contact1 produces an appe>ance1 ( :i* ! accompany+ figure is int5d$ to give an idea1 ?\gh on an exagg]at$ scale4 ,! planet moves s sl[ly z to occupy m ?an tw5ty m9utes 9 cross+ ! sun's limb2 s t ev5 if ! planet's edge 7 p]fectly %>p & def9ite1 & ! sun's limb undi/ort$1 x w\ld be v difficult to det]m9e ! precise second at :i* contact occurs4 ,b1 z ?+s are1 obs]v]s ) precisely simil> telescopes1 & side by side1 (t5 diff] f ea* o!r five or six seconds2 &1 :]e ! telescopes are n simil>1 ! diff]5ces & unc]ta9ties are mu* great]4444 ,a/ronom]s1 !re=e1 at pres5t are pretty mu* agre$ t su* obs]vations c be ( little value 9 remov+ ! rema9+ unc]ta9ty ( ! p>allax1 & are dispos$ to put m reliance ^u ! micrometric & photographic me?ods1 :i* are free f ^! peculi> difficulties1 ?\gh1 ( c\rse1 beset ) o!rs1 :i*1 h[ev]1 x is hop$ w prove less =midable4 7b7 ,( ! micrometric me?od1 z employ$ at ! la/ transit1 ,pr(essor ,"y speaks z foll[s3-- ,! micrometric me?od requires ! use ( a heliomet]1--an in/rum5t common only 9 ,g]many1 & requir+ mu* skill & practice 9 its use 9 ord] to obta9 ) x accurate measures4 ,at ! late transit1 a s+le ,engli% p>ty1 two or ?ree ( ! ,russian p>ties1 & all five ( ! ,g]man1 7 equipp$ ) ^! in/rum5ts2 & at "s ( ! /ations ext5sive s]ies ( measures 7 made4 ,none ( ! results1 h[ev]1 h appe>$ z yet2 s t x is impossible to say h[ greatly1 if at all1 ?is me?od w h ! advantage 9 precision ov] ! contact obs]vations4 7c7 ,! foll[+ obs]vations1 ) ref]5ce to ! photographic me?od1 are also tak5 f ,pr(essor ,"y3-- ,! ,am]icans & ,fr5* plac$ _! ma9 reliance ^u ! photographic me?od1 :ile ! ,engli% & ,g]mans also provid$ = its use to a c]ta9 ext5t4 ,! great advantage ( ?is me?od is1 t x makes x possible to p]=m ! necess>y measurem5ts 7^u ^: accuracy e ?+ dep5ds7 at leisure aft] ! transit1 )\t hurry1 & ) all possible precautions4 ,! field-"w consi/s m]ely 9 obta9+ z _m & z good pictures z possible4 ,a pr9cipal objection to ! me?od lies 9 ! difficulty ( obta9+ good pictures1 i4e41 pictures free f di/ortion1 & s di/9ct & %>p z to be> high magnify+ p[] 9 ! microscopic app>atus us$ = _! measurem5t4 ,! mo/ s]i\s difficulty1 h[ev]1 is involv$ 9 ! accurate det]m9ation ( ! scale ( ! picture2 t is1 ( ! numb] ( seconds ( arc correspond+ to a l9e> in* ^u ! plate4 ,besides ?is1 we mu/ "k ! exact ,gre5wi* "t at :i* ea* picture is tak51 & x is also extremely desirable t ! ori5tation ( ! picture %\ld be accurately det]m9$2 t is1 ! nor? & s\?1 ! ea/ & we/ po9ts ( ! sol> image on ! f9i%$ plate4 ,!re has be5 a good deal ( anxiety le/ ! image1 h[ev] accurate & %>p :5 fir/ produc$1 %\ld alt]1 9 c\rse ( "t1 ?r\gh ! contraction ( ! collodion film on ! glass plate2 b ! exp]im5ts ( ,ru!rfurd1 ,hugg9s1 & ,pas*51 seem to %[ t ?is dang] is imag9>y4444 ,! ,am]icans plac$ ! photographic telescope exactly 9 l9e ) a m]idian in/rum5t1 & s det]m9$1 ) ! extreme/ precision1 ! direction 9 :i* x 0 po9t$4 ,kn[+ ?is & ! "t at :i* any picture 0 tak51 x becomes possible1 ) ! help ( ! plumb-l9e image1 to det]m9e precisely ! ori5tation ( ! picture1--an advantage possess$ by ! ,am]ican pictures alone1 & mak+ _! value ne>ly twice z great z o!rwise x w\ld h be54 ,! figure bel[ is a repres5tation ( "o ( ! ,am]ican photographs r$uc$ ab\t "o-half4 ,v is ! image ( ,v5us1 :i*1 on ! actual plate1 is ab\t a sev5? ( an in* 9 diamet]2 aa' is ! image ( ! plumb-l9e4 ,! c5tre ( ! reticle is m>k$ ) a cross4 ,illu/ration3 ,fig4 #afj4 ,! ,engli% photographs prov$ to be ( little value1 & ! results ( ! measurem5ts & calculations ^u ! ,am]ican pictures h n yet be5 publi%$4 ,!re is a gr[+ appreh5sion t no photographic me?od c be reli$ ^u4 ,! mo/ rec5t det]m9ations by v>i\s me?ods indicate t ! sun's di/ance is su* t 8 p>allax is ab\t eighty-eight seconds4 ,?is w\ld make ! l9e> value ( a second at ! surface ( ! sun ab\t f\r hundr$ & fifty miles4 ,illu/ration3 ,plate #a4 ,,ii4 ,,physical ,,& ,,*emical ,,condition ,,( ,,! ,,sun4 ,physical ,condition ( ! ,sun4 #adc4 ,! ,sun ,compos$ ma9ly ( ,gas4--,x is n[ g5]ally believ$ t ! sun is ma9ly a ball ( gas1 or vapor1 p[]fully cond5s$ at ! c5tre by ! weight ( ! sup]9cumb5t mass1 b kept f liquefy+ by its exce$+ly high temp]ature4 ,! gase\s int]ior ( ! sun is surr\nd$ by a lay] ( lum9\s cl\ds1 :i* con/itutes its visible surface1 & :i* is call$ its photosph]e4 ,"h & !re 9 ! photosph]e are se5 d>k spots1 :i* (t5 atta9 an imm5se magnitude4 ,^! cl\ds float 9 ! sol> atmosph]e1 :i* ext5ds "s di/ance beyond !m4 ,! lum9\s surface ( ! sun is surr\nd$ by a rose-color$ /ratum ( gase\s matt]1 call$ ! *romosph]e4 ,"h & !re great masses ( ?is *romosph]ic matt] rise high above ! g5]al level4 ,^! masses are call$ prom95ces4 ,outside ( ! *romosph]e is ! corona1 an irregul> halo ( fa9t1 pe>ly light1 ma9ly compos$ ( filam5ts & /ream]s1 :i* radiate f ! sun to enorm\s di/ances1 (t5 m ?an a million ( miles4 ,9 ,fig4 #afa is %[n a section ( ! sun1 accord+ to ,pr(essor ,"y4 ,! accompany+ li?ographic plate gives a g5]al view ( ! photosph]e ) its spots1 & ( ! *romosph]e & its prom95ces4 #add4 ,! ,temp]ature ( ! ,sun4--,^? :o h inve/igat$ ! subject ( ! temp]ature ( ! sun h come to v diff]5t conclusions2 "s plac+ x z high z f\r million degrees ,fahr5heit1 & o!rs z l[ z t5 ?\s& degrees4 ,pr(essor ,"y ?9ks t ,rosetti's e/imate ( eighte5 ?\s& degrees z ! effective temp]ature ( ! sun's surface is probably n f> f correct4 ,by ?is is meant ! temp]ature t a uni=m surface ( lampblack ( ! size ( ! sun mu/ h 9 ord] to radiate z mu* heat z ! sun does4 ,! mo/ int5se artificial heat does n exce$ f\r ?\s& degrees ,fahr5heit4 ,illu/ration3 ,fig4 #afa4 #ade4 ,! ,am\nt ( ,heat ,radiat$ by ! ,sun4--,a unit ( heat is ! am\nt ( heat requir$ to raise a p\nd ( wat] "o degree 9 temp]ature4 ,x takes ab\t a hundr$ & =ty-?ree units ( heat to melt a p\nd ( ice )\t *ang+ its temp]ature4 ,a cubic foot ( ice weighs ab\t fifty-sev5 p\nds4 ,accord+ to ,sir ,william ,h]s*el1 7 all ! heat radiat$ by ! sun conc5trat$ on a cyl9d] ( ice =ty-five miles 9 diamet]1 x w\ld melt x (f at ! rate ( ab\t a hundr$ & n9ety ?\s& miles a second4 ,pr(essor ,"y gives ! foll[+ illu/ration ( ! en]gy ( sol> radiation3 ,if we c\ld build up a solid column ( ice f ! e>? to ! sun1 two miles & a qu>t] 9 diamet]1 spann+ ! inconceivable abyss ( n9ety-?ree million miles1 & if !n ! sun %\ld conc5trate 8 p[] ^u x1 x w\ld dissolve & melt1 n 9 an h\r1 nor a m9ute1 b 9 a s+le second4 ,"o sw+ ( ! p5dulum1 & x w\ld be wat]2 sev5 m1 & x w\ld be dissipat$ 9 vapor4 ,illu/ration3 ,fig4 #afb4 ,?is heat w\ld be suffici5t to melt a lay] ( ice ne>ly fifty feet ?ick all ar\nd ! sun 9 a m9ute4 ,to develop ?is heat w\ld require ! h\rly consumption ( a lay] ( an?racite coal1 m ?an sixte5 feet ?ick1 ov] ! entire surface ( ! sun2 & ! me*anical equival5t ( ?is heat is ab\t t5 ?\s& horse-p[] on e squ>e foot ( ! sun's surface4 #adf4 ,! ,brightness ( ! ,sun's ,surface4--,! sun's surface is a hundr$ & n9ety ?\s& times z bright z a c&le-flame1 a hundr$ & =ty-six times z bright z ! calcium-light1 & ab\t ?ree times & a half z bright z ! voltaic arc4 ,! sun's disk is mu* less bright ne> ! m>g9 ?an ne> ! c5tre1 a po9t on ! limb ( ! sun be+ only ab\t a f\r? z bright z "o ne> ! c5tre ( ! disk4 ,?is dim9ution ( brightness t[>ds ! m>g9 ( ! disk is due to ! increase 9 ! absorption ( ! sol> atmosph]e z we pass f ! c5tre t[>ds ! m>g9 ( ! sun's disk2 & ?is increas$ absorption is due to ! fact1 t ! rays :i* rea* u f ne> ! m>g9 h to trav]se a mu* great] ?ickness ( ! sol> atmosph]e ?an ^? :i* rea* u f ! c5tre ( ! disk4 ,?is w be evid5t f ,fig4 #afb1 9 :i* ! arr[s m>k ! pa?s ( rays f diff]5t p>ts ( ! sol> disk4 ,! ,spectroscope4 ,illu/ration3 ,fig4 #afc4 #adg4 ,! ,spectroscope z an ,a/ronomical ,in/rum5t4--,! spectroscope is n[ cont9ually employ$ 9 ! /udy ( ! physical condition & *emical con/itution ( ! sun & ( ! o!r heav5ly bodies4 ,x has become almo/ z indisp5sable to ! a/ronom] z ! telescope4 #adh4 ,! ,disp]sion ,spectroscope4--,! ess5tial p>ts ( ! disp]sion spectroscope are %[n 9 ,fig4 #afc4 ,^! are ! collimator tube1 ! prism1 & ! telescope4 ,! collimator tube has a n>r[ slit at "o end1 ?r\gh :i* ! light to be exam9$ is admitt$1 & some:]e )9 ! tube a l5s = cond5s+ ! light4 ,! light is disp]s$ on pass+ ?r\gh ! prism3 x !n passes ?r\gh ! objective ( ! telescope1 & =ms )9 ! tube an image ( ! spectrum1 :i* is exam9$ by means ( ! eye-piece4 ,! p[] ( ! spectroscope is increas$ by increas+ ! numb] ( prisms1 :i* are arrang$ s t ! light %all pass ?r\gh "o aft] ano!r 9 succession4 ,su* an arrangem5t ( prisms is %[n 9 ,fig4 #afd4 ,"o end ( ! collimator tube is se5 at ! left1 & "o end ( ! telescope at ! "r4 ,sometimes ! prisms are made long1 & ! light is s5t twice ?r\gh ! same tra9 ( prisms1 once ?r\gh ! l[]1 & once ?r\gh ! upp]1 half ( ! prisms4 ,?is is accompli%$ by plac+ a rectangul> prism aga9/ ! la/ prism ( ! tra91 z %[n 9 ,fig4 #afe4 ,illu/ration3 ,fig4 #afd4 ,illu/ration3 ,fig4 #afe4 #adi4 ,! ,micromet] ,scale4--,v>i\s devices are employ$ to obta9 an image ( a micromet] scale 9 ! tube ( ! telescope beside t ( ! spectrum4 ,illu/ration3 ,fig4 #aff4 ,"o ( ! simple/ ( ^! me?ods is %[n 9 ,fig4 #aff4 ,a is ! telescope1 ,b ! collimator1 & ,c ! micromet] tube4 ,! op5+ at ! out] end ( ,c conta9s a piece ( glass :i* has a micromet] scale m>k$ ^u x4 ,! light f ! c&le %9es ?r\gh ?is glass1 falls ^u ! surface ( ! prism ,p1 & is !nce reflect$ into ! telescope1 :]e x =ms an enl>g$ image ( ! micromet] scale alongside ! image ( ! spectrum4 ,illu/ration3 ,fig4 #afg4 #aej4 ,! ,comp>ison ( ,spectra4--,9 ord] to comp>e two spectra1 x is desirable to be able to see !m side by side 9 ! telescope4 ,! images ( two spectra may be obta9$ side by side 9 ! telescope tube by ! use ( a little rectangul> prism1 :i* cov]s "o-half ( ! slit ( ! collimator tube1 z %[n 9 ,fig4 #afg4 ,! light f "o s\rce is admitt$ directly ?r\gh ! uncov]$ half ( ! slit1 :ile ! light f ! o!r s\rce is s5t ?r\gh ! cov]$ portion ( ! slit by reflection f ! surface ( ! rectangul> prism4 ,?is arrangem5t & its action w be readily und]/ood f ,fig4 #afg4 ,illu/ration3 ,fig4 #afh4 #aea4 ,direct-,vision ,spectroscope4--,a beam ( light may be disp]s$1 )\t any ultimate deflection f its c\rse1 by comb9+ prisms ( cr[n & fl9t glass ) equal refractive1 b unequal disp]sive p[]s4 ,su* a comb9ation ( prisms is call$ a direct-vision comb9ation4 ,"o ( ?ree prisms is %[n 9 ,fig4 #afh1 & "o ( five prisms 9 ,fig4 #afi4 ,illu/ration3 ,fig4 #afi4 ,illu/ration3 ,fig4 #agj4 ,a direct-vision spectroscope 7,fig4 #agj7 is "o 9 :i* a direct-vision comb9ation ( prisms is employ$4 ,c is ! collimator tube1 ,p ! tra9 ( prisms1 ,f ! telescope1 & r ! comp>ison prism4 ,illu/ration3 ,fig4 #aga4 #aeb4 ,! ,telespectroscope4--,! spectroscope1 :5 us$ = a/ronomical "w1 is usually comb9$ ) a telescope4 ,! comp\nd in/rum5t is call$ a telespectroscope4 ,! spectroscope is m\nt$ at ! end ( ! telescope 9 su* a way t ! image =m$ by ! object-glass ( ! telescope falls ^u ! slit at ! end ( ! collimator tube4 ,a telespectroscope ( small disp]sive p[] is %[n 9 ,fig4 #aga2 a be+ ! object-glass ( ! telescope1 cc ! tube ( ! telescope1 & e ! comp>ison prism at ! end ( ! collimator tube4 ,a m p[]ful in/rum5t is %[n 9 ,fig4 #agb4 ,a is ! telescope1 ,c ! collimator tube ( ! spectroscope1 ,p ! tra9 ( prisms1 & ,e ! telescope tube4 ,fig4 #agc %[s a /ill m p[]ful spectroscope atta*$ to ! great ,newall refractor 7#ah74 ,illu/ration3 ,fig4 #agb4 ,illu/ration3 ,fig4 #agc4 #aec4 ,! ,diffraction ,spectroscope4--,a diffraction spectroscope is "o 9 :i* ! spectrum is produc$ by reflection ( ! light f a f9ely rul$ surface1 or grat+1 z x is call$1 in/ead ( by disp]sion 9 pass+ ?r\gh a prism4 ,! ess5tial p>ts ( ?is in/rum5t are %[n 9 ,fig #agd4 ,?is spectroscope may be atta*$ to ! telescope 9 ! same mann] z ! disp]sion spectroscope4 ,:5 ! spectroscope is ?us us$1 ! eye-piece ( ! telescope is remov$4 ,illu/ration3 ,fig4 #agd4 ,spectra4 #aed4 ,cont9u\s ,spectra4--,light f an inc&esc5t solid or liquid :i* has suff]$ no absorption 9 ! m$ium :i* x has trav]s$ gives a spectrum consi/+ ( a cont9u\s color$ b&1 9 :i* ! colors1 f ! r$ to ! violet1 pass gradually & imp]ceptibly into "o ano!r4 ,! spectrum is entirely free f ei!r light or d>k l9es1 & is call$ a cont9u\s spectrum4 #aee4 ,bright-,l9$ ,spectra4--,light f a lum9\s gas or vapor gives a spectrum compos$ ( bright l9es sep>at$ by d>k spaces1 & kn[n z a bright-l9$ spectrum4 ,x has be5 f\nd t ! l9es 9 ! spectrum ( a sub/ance 9 ! /ate ( a gas or vapor are ! mo/ *>act]i/ic ?+ ab\t ! sub/ance1 s9ce no two vapors give exactly ! same l9es3 h5ce1 :5 we h once become acqua9t$ ) ! bright-l9$ spectrum ( any sub/ance1 we c ev] aft] recognize t sub/ance by ! spectrum ( its lum9\s vapor4 ,ev5 :5 sev]al sub/ances are mix$1 !y may all be recogniz$ by ! bright-l9$ spectrum ( ! mixture1 s9ce ! l9es ( all ! sub/ances w be pres5t 9 ! spectrum ( ! mixture4 ,?is me?od ( id5tify+ sub/ances by _! spectra is call$ spectrum analysis4 ,! bright-l9$ spectra ( sev]al sub/ances are giv5 9 ! frontispiece4 ,! numb] ( l9es 9 ! spectra ( ! elem5ts v>ies greatly4 ,! spectrum ( sodium is "o ( ! simple/1 :ile t ( iron is "o ( ! mo/ complex4 ,! latt] conta9s ov] six hundr$ l9es4 ,?\gh no two vapors give id5tical spectra1 !re are _m cases 9 :i* "o or m ( ! spectral l9es ( "o elem5t co9cide 9 position ) l9es ( o!r elem5ts4 #aef4 ,me?ods ( r5d]+ ,gases & ,vapors ,lum9\s4--,9 ord] to /udy ! spectra ( vapors & gases x is necess>y to h "s means ( conv]t+ solids & liquids into vapor1 & also ( r5d]+ ! vapors & gases lum9\s4 ,!re are f\r me?ods ( obta9+ lum9\s vapors & gases 9 common use4 ,illu/ration3 ,fig4 #age4 7#a7 ,by means ( ! ,buns5 ,flame4--,?is is a v hot b an almo/ non-lum9\s flame4 ,if any readily volatiliz$ sub/ance1 su* z ! comp\nds ( sodium1 calcium1 /rontium1 etc41 is introduc$ into ?is flame on a f9e plat9um wire1 x is volatiliz$ 9 ! flame1 & its vapor is r5d]$ lum9\s1 giv+ ! flame its own peculi> color4 ,! flame ?us color$ may be exam9$ by ! spectroscope4 ,! arrangem5t ( ! flame is %[n 9 ,fig4 #age4 ,illu/ration3 ,fig4 #agf4 7#b7 ,by means ( ! ,voltaic ,arc4--,an electric lamp is %[n 9 ,fig4 #agf4 ,:5 ?is lamp is to be us$ = obta9+ lum9\s vapors1 ! l[] c>bon is made l>g] ?an ! upp] "o1 & holl[$ out at ! top into a little cup4 ,! sub/ance to be volatiliz$ is plac$ 9 ?is cup1 & ! curr5t is all[$ to pass4 ,! heat ( ! voltaic arc is mu* m int5se ?an t ( ! ,buns5 flame3 h5ce sub/ances t _c be volatiliz$ 9 ! flame are readily volatiliz$ 9 ! arc1 & ! vapor =m$ is rais$ to a v high temp]ature4 7#c7 ,by means ( ! ,sp>k f an ,induction ,coil4--,! arrangem5t ( ! coil = obta9+ lum9\s vapors is %[n 9 ,fig4 #agg4 ,illu/ration3 ,fig4 #agg4 ,! t]m9als ( ! coil betwe5 :i* ! sp>k is to pass are br\ght q close toge!r4 ,:5 we wi% to vaporize any metal1 z iron1 ! t]m9als are made ( iron4 ,on ! passage ( ! sp>k1 a little ( ! iron at ! ends ( ! t]m9als is evaporat$2 & ! vapor is r5d]$ lum9\s 9 ! space trav]s$ by ! sp>k4 ,a cond5s] is usually plac$ 9 ! circuit4 ,) ! coil1 ! temp]ature may be v>i$ at pleasure2 & ! vapor may be rais$ ev5 to a high] temp]ature ?an ) ! electric lamp4 ,to obta9 a l[ temp]ature1 ! coil is us$ )\t ! cond5s]4 ,by us+ a l>g] & l>g] cond5s]1 ! temp]ature may be rais$ high] & high]4 ,by means ( ! induction coil we may also heat gases to inc&esc5ce4 ,x is only necess>y to all[ ! sp>k to pass ?r\gh a space fill$ ) ! gas4 ,illu/ration3 ,fig4 #agh4 7#d7 ,by means ( a ,vacuum ,tube4--,! =m ( ! vacuum tube commonly us$ = ?is purpose is %[n 9 ,fig4 #agh4 ,! gas to be exam9$1 & :i* is conta9$ 9 ! tube1 has v slight d5sity3 b ^u ! passage ( ! dis*>ge f an induction coil or a ,holtz ma*9e1 ?r\gh ! tube1 ! gas 9 ! capill>y "p ( ! tube becomes heat$ to a high temp]ature1 & is !n q brilliant4 #aeg4 ,rev]s$ ,spectra4--,if ! light f an inc&esc5t cyl9d] ( lime1 or f ! inc&esc5t po9t ( an electric lamp1 is all[$ to pass ?r\gh lum9\s sodium vapor1 & is !n exam9$ ) a spectroscope1 ! spectrum w be f\nd to be a bright spectrum cross$ by a s+le d>k l9e 9 ! position ( ! yell[ l9e ( ! sodium vapor4 ,! spectrum ( sodium vapor is rev]s$1 its bright l9es becom+ d>k & its d>k spaces bright4 ,) a spectroscope ( any consid]able p[]1 ! yell[ l9e ( sodium vapor is resolv$ into a d\ble l9e4 ,) a spectroscope ( ! same p[]1 ! d>k sodium l9e ( ! rev]s$ spectrum is se5 to be a d\ble l9e4 ,x is f\nd to be g5]ally true1 t ! spectrum ( ! light f an inc&esc5t solid or liquid :i* has pass$ ?r\gh a lum9\s vapor on its way to ! spectroscope is made up ( a bright gr\nd cross$ by d>k l9es2 !re be+ a d>k l9e = e bright l9e t ! vapor alone w\ld give4 #aeh4 ,explanation ( ,rev]s$ ,spectra4--,x has be5 f\nd t gases absorb & qu5* rays ( ! same degree ( refrangibility z ^? :i* !y !mselves emit1 & no o!rs4 ,:5 a solid is %9+ ?r\gh a lum9\s vapor1 ?is absorbs & qu5*es ^? rays f ! solid :i* h ! same degrees ( refrangibility z ^? :i* x is itself emitt+3 h5ce ! l9es ( ! spectrum receive light f ! vapor alone1 :ile ! spaces betwe5 ! l9es receive light f ! solid4 ,n[1 solids & liquids1 :5 heat$ to inc&esc5ce1 give a v mu* bright] light ?an vapors & gases at ! same temp]ature3 h5ce ! l9es ( a rev]s$ spectrum1 ?\gh receiv+ light f ! vapor or gas1 appe> d>k by contra/4 #aei4 ,effect ( ,increas+ ! ,p[] ( ! ,spectroscope ^u ! ,brilliancy ( a ,spectrum4--,an increase 9 ! p[] ( a spectroscope dim9i%es ! brilliancy ( a cont9u\s spectrum1 s9ce x makes ! color$ b& long]1 & !re=e spreads ! light out ov] a great] ext5t ( surface2 b1 9 ! case ( a bright-l9$ spectrum1 an increase ( p[] 9 ! spectroscope produces sc>cely any alt]ation 9 ! brilliancy ( ! l9es1 s9ce x m]ely sep>ates ! l9es f>!r )\t mak+ ! l9es !mselves any wid]4 ,9 ! case ( a rev]s$ spectrum1 an increase ( p[] 9 ! spectroscope dilutes ! light 9 ! spaces betwe5 ! l9es )\t dilut+ t ( ! l9es3 h5ce l9es :i* appe> d>k 9 a spectroscope ( slight disp]sive p[] may appe> bright 9 an in/rum5t ( great disp]sive p[]4 #afj4 ,*ange ( ! ,spectrum ) ! ,d5sity ( ! ,lum9\s ,vapor4--,x has be5 f\nd1 t1 z ! d5sity ( a lum9\s vapor is dim9i%$1 ! l9es 9 its spectrum become few] & few]1 till !y are f9ally r$uc$ to "o4 ,on ! o!r h&1 an increase ( d5sity causes new l9es to appe> 9 ! spectrum1 & ! old l9es to become ?ick]4 #afa4 ,*ange ( ! ,spectrum ) ! ,temp]ature ( ! ,lum9\s ,vapor4--,x has also be5 f\nd t ! appe>ance ( a bright-l9$ spectrum *anges consid]ably ) ! temp]ature ( ! lum9\s vapor4 ,9 "s cases1 an increase ( temp]ature *anges ! relative int5sities ( ! l9es2 9 o!r cases1 x causes new l9es to appe>1 & old l9es to disappe>4 ,9 ! case ( a comp\nd vapor1 an increase ( temp]ature causes ! color$ b&s 7:i* are peculi> to ! spectrum ( ! comp\nd7 to disappe>1 & to be replac$ by ! spectral l9es ( ! elem5ts ( :i* ! comp\nd is made up4 ,! heat appe>s to dissociate ! comp\nd2 t is1 to resolve x into its con/itu5t elem5ts4 ,9 ?is case1 ea* elem5t>y vapor w\ld give its own spectral l9es4 ,z ! comp\nd is n completely dissociat$ at once1 x is possible1 ( c\rse1 = "o or m ( ! spectral l9es ( ! elem5t>y vapors to co-exi/ 9 ! spectrum ) ! b&s ( ! comp\nd4 ,x has be5 f\nd1 t1 9 "s cases1 ! spectra ( ! elem5t>y gases *ange ) ! temp]ature ( ! gas2 & ,locky] ?9ks he has discov]$ conclusive evid5ce1 9 ! spectra ( ! sun & />s1 t _m ( ! sub/ances reg>d$ z elem5t>y are really resolv$ into simpl] sub/ances by ! int5se heat ( ! sun2 9 o!r words1 t our s-call$ elem5ts are really comp\nds4 ,*emical ,con/itution ( ! ,sun4 #afb4 ,! ,sol> ,spectrum4--,! sol> spectrum is cross$ transv]sely by a great numb] ( f9e d>k l9es1 & h5ce x belongs to ! class ( rev]s$ spectra4 ,^! l9es 7 fir/ /udi$ & mapp$ by ,fraunh(]1 & f him !y h be5 call$ ,fraunh(]'s l9es4 ,illu/ration3 ,fig4 #agi4 ,a r$uc$ copy ( ,fraunh(]'s map is %[n 9 ,fig4 #agi4 ,a few ( ! mo/ prom95t ( ! d>k sol> l9es are designat$ by ! lett]s ( ! alphabet4 ,! o!r l9es are usually designat$ by ! numb]s at :i* !y are f\nd on ! scale :i* accompanies ! map4 ,?is scale is usually drawn at ! top ( ! map1 z w be se5 9 "s ( ! foll[+ diagrams4 ,! two mo/ elaborate maps ( ! sol> spectrum are ^? ( ,kir*h(f & ,ang/rm4 ,! scale on ,kir*h(f's map is an arbitr>y "o1 :ile t ( ,ang/rm is bas$ ^u ! wave-l5g?s ( ! rays ( light :i* w\ld fall ^u ! l9es 9 ! spectrum4 ,illu/ration3 ,fig4 #ahj4 ,! appe>ance ( ! spectrum v>ies greatly ) ! p[] ( ! spectroscope employ$4 ,fig4 #ahj %[s a portion ( ! spectrum z x appe>s 9 a spectroscope ( a s+le prism3 :ile ,fig4 #aha %[s ! b gr\p ( l9es alone1 z !y appe> 9 a p[]ful diffraction spectroscope4 ,illu/ration3 ,fig4 #aha4 #afc4 ,! ,telluric ,l9es4--,!re are _m l9es ( ! sol> spectrum :i* v>y consid]ably 9 int5sity z ! sun passes f ! horizon to ! m]idian1 be+ mo/ int5se :5 ! sun is ne>e/ ! horizon1 & :5 8 rays are oblig$ to pass ?r\gh ! greate/ dep? ( ! e>?'s atmosph]e4 ,^! l9es are ( atmosph]ic orig91 & are due to ! absorption ( ! aque\s vapor 9 our atmosph]e4 ,!y are ! same l9es t are obta9$ :5 a c&le or o!r artificial light is exam9$ ) a spectroscope ?r\gh a long tube fill$ ) /eam4 ,s9ce ^! l9es are due to ! absorption ( our own atmosph]e1 !y are call$ telluric l9es4 ,a map ( ^! l9es is %[n 9 ,fig4 #ahb4 ,illu/ration3 ,fig4 #ahb4 #afd4 ,! ,sol> ,l9es4--,aft] d$uct+ ! telluric l9es1 ! rema9+ l9es ( ! sol> spectrum are ( sol> orig94 ,!y mu/ be due to absorption :i* takes place 9 ! sun's atmosph]e4 ,!y are1 9 fact1 ! rev]s$ spectra ( ! elem5ts :i* exi/ 9 ! sol> atmosph]e 9 ! /ate ( vapor3 h5ce we conclude t ! lum9\s surface ( ! sun is surr\nd$ ) an atmosph]e ( lum9\s vapors4 ,! temp]ature ( ?is atmosph]e1 at lea/ ne> ! surface ( ! sun1 mu/ be suffici5t to enable all ! elem5ts kn[n on ! e>? to exi/ 9 x z vapors4 ,illu/ration3 ,fig4 #ahc4 #afe4 ,*emical ,con/itution ( ! ,sun's ,atmosph]e4--,to f9d :e!r any elem5t :i* exi/s on ! e>? is pres5t 9 ! sol> atmosph]e1 we h m]ely to asc]ta9 :e!r ! bright l9es ( its gase\s spectrum are mat*$ by d>k l9es 9 ! sol> spectrum :5 ! two spectra are plac$ side by side4 ,9 ,fig4 #ahc1 we h 9 ,no4 #a a portion ( ! r$ end ( ! sol> spectra1 & 9 ,no4 #b ! spectrum ( sodium vapor1 bo? z obta9$ 9 ! same spectroscope by means ( ! comp>ison prism4 ,x w be se5 t ! d\ble sodium l9e is exactly mat*$ by a d\ble d>k l9e ( ! sol> spectrum3 h5ce we conclude t sodium vapor is pres5t 9 ! sun's atmosph]e4 ,fig4 #ahd %[s ! mat*+ ( a great numb] ( ! bright l9es ( iron vapor by d>k l9es 9 ! sol> spectrum4 ,?is mat*+ ( ! iron l9es e/abli%es ! fact t iron vapor is pres5t 9 ! sol> atmosph]e4 ,illu/ration3 ,fig4 #ahd4 ,! foll[+ table 7giv5 by ,pr(essor ,"y7 conta9s a li/ ( all ! elem5ts :i* h1 up to ! pres5t "t1 be5 detect$ ) c]ta9ty 9 ! sun's atmosph]e4 ,x also gives ! numb] ( bright l9es 9 ! spectrum ( ea* elem5t1 & ! numb] ( ^? l9es :i* h be5 mat*$ by d>k l9es 9 ! sol> spectrum3-- ,elem5ts4 ,bright ,l9es ,rev]s$4 ,obs]v]4 ,l9es4 #a4 ,iron #fjj #dfj ,kir*h(f4 #b4 ,titanium #bjf #aah ,?al54 #c4 ,calcium #hi #ge ,kir*h(f4 #d4 ,manganese #ge #eg ,ang/rm4 #e4 ,nickel #ea #cc ,kir*h(f4 #f4 ,cobalt #hf #ai ,?al54 #g4 ,*romium #ga #ah ,kir*h(f4 #h4 ,b>ium #bf #aa ,kir*h(f4 #i4 ,sodium #i #i ,kir*h(f4 #aj4 ,magnesium #g #g ,kir*h(f4 #aa4 ,copp]8 #ae #g8 ,kir*h(f4 #ab4 ,hydrog5 #e #e ,ang/rm4 #ac4 ,palladium #bi #e ,locky]4 #ad4 ,vanadium #ed #d ,locky]4 #ae4 ,molybd5um #bg #d ,locky]4 #af4 ,/rontium #gd #d ,locky]4 #ag4 ,lead #da #c ,locky]4 #ah4 ,uranium #ba #c ,locky]4 #ai4 ,alum9ium #ad #b ,ang/rm4 #bj4 ,c]ium #fd #b ,locky]4 #ba4 ,cadmium #bj #b ,locky]4 #bb4 ,oxyg5 a #db #ab bright ,h4 ,drap]4 ,oxyg5 b #d #d8 ,s*u/]4 ,9 addition to ! above elem5ts1 x is probable t sev]al o!r elem5ts are pres5t 9 ! sun's atmosph]e2 s9ce at lea/ "o ( _! bright l9es has be5 f\nd to co9cide ) d>k l9es ( ! sol> spectrum4 ,!re are1 h[ev]1 a l>ge numb] ( elem5ts1 no traces ( :i* h yet be5 detect$2 &1 9 ! cases ( ! elem5ts ^: pres5ce 9 ! sol> atmosph]e has be5 e/abli%$1 ! mat*+ ( ! l9es is f> f complete 9 ! majority ( ! cases1 z w be se5 f ! above table4 ,?is want ( complete co9cid5ce ( ! l9es is und\bt$ly due to ! v high temp]ature ( ! sol> atmosph]e4 ,we h already se5 t ! l9es ( ! spectrum *ange ) ! temp]ature2 &1 z ! temp]ature ( ! sun is f> high] ?an any t we c produce by artificial means1 we might reasonably expect t x w\ld cause ! disappe>ance f ! spectrum ( _m l9es :i* we f9d to be pres5t at our highe/ temp]ature4 ,locky] ma9ta9s t ! reason :y no trace ( ! spectral l9es ( c]ta9 ( our s-call$ elem5ts is f\nd 9 ! sol> atmosph]e is1 t ^! sub/ances are n really elem5t>y1 & t ! int5se heat ( ! sun resolves !m into simpl] con/itu5ts4 ,motion at ! ,surface ( ! ,sun4 #aff4 ,*ange ( ,pit* caus$ by ,motion ( ,s\nd+ ,body4--,:5 a s\nd+ body is mov+ rapidly t[>ds u1 ! pit* ( its note becomes some:at high] ?an :5 ! body is /ation>y2 &1 :5 su* a body is mov+ rapidly f u1 ! pit* ( its note is l[]$ some:at4 ,we h a good illu/ration ( ?is *ange ( pit* at a c\ntry railway /ation on ! passage ( an express-tra94 ,! pit* ( ! locomotive :i/le is consid]ably high] :5 ! tra9 is approa*+ ! /ation ?an :5 x is leav+ x4 #afg4 ,explanation ( ! ,*ange ( ,pit* produc$ by ,motion4--,! pit* ( s\nd dep5ds ^u ! rapidity ) :i* ! pulsations ( s\nd beat ^u ! drum ( ! e>4 ,! m rapidly ! pulsations foll[ ea* o!r1 ! high] is ! pit*3 h5ce ! %ort] ! s\nd-waves 7provid$ ! s\nd is all ! :ile travell+ at ! same rate71 ! high] ! pit* ( ! s\nd4 ,any ?+1 !n1 :i* t5ds to %ort5 ! waves ( s\nd t5ds also to raise its pit*1 & any ?+ :i* t5ds to l5g!n ^! waves t5ds to l[] its pit*4 ,:5 a s\nd+ body is mov+ rapidly =w>d1 ! s\nd-waves are cr[d$ toge!r a little1 & !re=e %ort5$2 :5 x is mov+ backw>d1 ! s\nd-waves are drawn out1 or l5g!n$ a little4 ,! effect ( ! motion ( a s\nd+ body ^u ! l5g? ( its sonor\s waves w be readily se5 f ! foll[+ illu/ration3 ,suppose a numb] ( p]sons /ation$ at equal int]vals 9 a l9e on a long plat=m capable ( mov+ backw>d & =w>d4 ,suppose ! m5 are f\r feet ap>t1 & all walk+ =w>d at ! same rate1 & t ! plat=m is /ation>y1 & t1 z ! m5 leave ! plat=m1 !y keep on walk+ at ! same rate3 ! m5 w evid5tly be f\r feet ap>t 9 ! l9e 9 front ( ! plat=m1 z well z on x4 ,suppose next1 t ! plat=m is mov+ =w>d at ! rate ( "o foot 9 ! int]val betwe5 two m5's leav+ ! plat=m1 & t ! m5 cont9ue to walk z be=e3 x is evid5t t ! m5 w !n be ?ree feet ap>t 9 ! l9e aft] !y h left ! plat=m4 ,! =w>d motion ( ! plat=m has ! effect ( cr[d+ ! m5 toge!r a little4 ,7 ! plat=m mov+ backw>d at ! same rate1 ! m5 w\ld be five feet ap>t aft] !y _h left ! plat=m4 ,! backw>d motion ( ! plat=m has ! effect ( sep>at+ ! m5 f "o ano!r4 ,! di/ance betwe5 ! m5 9 ?is illu/ration corresponds to ! l5g? ( ! s\nd-wave1 or ! di/ance betwe5 its two ends4 ,7 a p]son to /& beside ! l9e1 & c\nt ! m5 t pass$ him 9 ! ?ree cases giv5 above1 he w\ld f9d t m p]sons w\ld pass him 9 ! same "t :5 ! plat=m is mov+ =w>d ?an :5 x is /ation>y1 & few] p]sons w\ld pass him 9 ! same "t :5 ! plat=m is mov+ backw>d ?an :5 x is /ation>y4 ,9 ! same way1 :5 a s\nd+ body is mov+ rapidly =w>d1 ! s\nd-waves beat m rapidly ^u ! e> ( a p]son :o is /&+ /ill ?an :5 ! body is at re/1 & less rapidly :5 ! s\nd+ body is mov+ rapidly backw>d4 ,7 ! plat=m /ation>y1 & 7 ! p]son :o is c\nt+ ! m5 to be walk+ along ! l9e1 ei!r t[>ds or away f ! plat=m1 ! effect ^u ! numb] ( m5 pass+ him 9 a giv5 "t w\ld be precisely ! same z x w\ld be 7 ! p]son /ation>y1 & ! plat=m mov+ ei!r t[>ds or away f him at ! same rate4 ,s ! *ange 9 ! rapidity ) :i* pulsations ( s\nd beat ^u ! e> is precisely ! same :e!r ! e> is /ation>y & ! s\nd+ body mov+1 or ! s\nd+ body is /ation>y & ! e> mov+4 #afh4 ,*ange ( ,refrangibility due to ! ,motion ( a ,lum9\s ,body4--,refrangibility 9 light corresponds to pit* 9 s\nd1 & dep5ds ^u ! l5g? ( ! lum9\s waves4 ,! %ort] ! lum9\s waves1 ! great] ! refrangibility ( ! waves4 ,v rapid motion ( a lum9\s body has ! same effect ^u ! l5g? ( ! lum9\s waves t motion ( a s\nd+ body has ^u ! l5g? ( ! sonor\s waves4 ,:5 a lum9\s body is mov+ v rapidly t[>ds u1 its lum9\s waves are %ort5$ a little1 & its light becomes a little m refrangible2 :5 ! lum9\s body is mov+ rapidly f u1 its lum9\s waves are l5g!n$ a little1 & its light becomes a little less refrangible4 ,illu/ration3 ,fig4 #ahe4 #afi4 ,displacem5t ( ,spectral ,l9es4--,9 exam9+ ! spectra ( ! />s1 we (t5 f9d t c]ta9 ( ! d>k l9es are displac$ some:at1 ei!r t[>ds ! r$ or ! violet end ( ! spectrum4 ,z ! d>k l9es are 9 ! same position z ! bright l9es ( ! absorb+ vapor w\ld be1 a displacem5t ( ! l9es t[>ds ! r$ end ( ! spectrum indicates a l[]+ ( ! refrangibility ( ! rays1 due to a motion ( ! lum9\s vapor away f u2 & a displacem5t ( ! l9es t[>ds ! violet end ( ! spectrum indicates an increase ( refrangibility1 due to a motion ( ! lum9\s vapor t[>ds u4 ,f ! am\nt ( ! displacem5t ( ! l9es1 x is possible to calculate ! velocity at :i* ! lum9\s gas is mov+4 ,9 ,fig4 #ahe is %[n ! displacem5t ( ! ,f l9e 9 ! spectrum ( ,sirius4 ,?is is "o ( ! hydrog5 l9es4 ,,rv is ! spectrum1 ,r be+ ! r$1 & ,v ! violet end4 ,! long v]tical l9e is ! bright ,f l9e ( hydrog51 & ! %ort d>k l9e to ! left ( x is ! position ( ! ,f l9e 9 ! spectrum ( ,sirius4 ,x is se5 t ?is l9e is displac$ some:at t[>ds ! r$ end ( ! spectrum4 ,?is indicates t ,sirius mu/ be mov+ f u2 & ! am\nt ( ! displacem5t indicates t ! /> mu/ be mov+ at ! rate ( "s tw5ty-five or ?irty miles a second4 ,illu/ration3 ,fig4 #ahf4 #agj4 ,contortion ( ,l9es on ! ,disk ( ! ,sun4--,c]ta9 ( ! d>k l9es se5 on ! c5tre ( ! sun's disk (t5 appe> m or less di/ort$1 z %[n 9 ,fig4 #ahf1 :i* repres5ts ! contortion ( ! hydrog5 l9e z se5 at v>i\s times4 #a & #b indicate a rapid motion ( hydrog5 away f u1 or a d[n-ru% at ! sun2 #c & #d 79 :i* ! l9e at ! c5tre is d>k on "o side1 & b5t t[>ds ! r$ end ( ! spectrum1 & bright on ! o!r side ) a di/ortion t[>ds ! violet end ( ! spectrum7 indicate a d[n-ru% ( cool hydrog5 side by side ) an up-ru% ( hot & bright hydrog52 #e indicates local d[n-ru%es associat$ ) quiesc5t hydrog54 ,! contort$ l9es1 :i* indicate a viol5tly agitat$ /ate ( ! sun's atmosph]e1 appe> 9 ! mid/ ( o!r l9es :i* indicate a quiesc5t /ate4 ,?is is ow+ to ! fact t ! absorption :i* produces ! d>k l9es takes place at v>i\s dep?s 9 ! sol> atmosph]e4 ,!re may be viol5t commotion 9 ! l[] lay]s ( ! sun's atmosph]e1 & comp>ative quiet 9 ! upp] lay]s4 ,9 ?is case1 ! l9es :i* are due to absorption 9 ! l[] lay]s w\ld indicate ?is di/urbance by _! contortions2 :ile ! l9es produc$ by absorption 9 ! upp] lay]s w\ld be free f contortion4 ,x (t5 happ5s1 too1 t ! contortions are conf9$ to "o set ( l9es ( an elem5t1 :ile o!r l9es ( ! same elem5t are entirely free f contortions4 ,?is is und\bt$ly due to ! fact t diff]5t lay]s ( ! sol> atmosph]e diff] greatly 9 temp]ature2 s t ! same elem5t w\ld give "o set ( l9es at "o dep?1 & ano!r set at ano!r dep?3 h5ce commotion 9 ! sol> atmosph]e at any p>ticul> dep? w\ld be indicat$ by ! contortion ( ^? l9es ( ! elem5t only :i* are produc$ by ! temp]ature at t p>ticul> dep?4 ,a rem>kable case ( contortion witness$ by ,pr(essor ,"y is %[n 9 ,fig4 #ahg4 ,?ree successive appe>ances ( ! ,c l9e are %[n4 ,! second view 0 tak5 ?ree m9utes aft] ! fir/1 & ! ?ird five m9utes aft] ! second4 ,! contortion 9 ?is case indicat$ a velocity rang+ f two hundr$ to ?ree hundr$ miles a second4 ,illu/ration3 ,fig4 #ahg4 #aga4 ,contortion ( ,l9es on ! ,sun's ,limb4--,:5 ! spectroscope is direct$ to ! c5tre ( ! sun's disk1 ! di/ortion ( ! l9es indicates only v]tical motion 9 ! sun's atmosph]e2 b1 :5 ! spectroscope is direct$ to ! limb ( ! sun1 displacem5ts ( ! l9es indicate horizontal motions 9 ! sun's atmosph]e4 ,:5 a p[]ful spectroscope is direct$ to ! m>g9 ( ! sun's disk1 s t ! slit ( ! collimator tube %all be p]p5dicul> to ! sun's limb1 "o or m ( ! d>k l9es on ! disk are se5 to be prolong$ by a bright l9e1 z %[n 9 ,fig4 #ahh4 ,b ?is prolongation1 in/ead ( be+ /raight & n>r[1 z %[n 9 ! figure1 is (t5 wid5$ & di/ort$ 9 v>i\s ways1 z %[n 9 ,fig4 #ahi4 ,9 ! left-h& portion ( ! diagram1 ! l9e is deflect$ t[>ds ! r$ end ( ! spectrum2 ?is indicates a viol5t w9d on ! sun's surface bl[+ away f u4 ,9 ! "r-h& portion ( ! diagram1 ! l9e is deflect$ t[>ds ! violet end ( ! spectrum2 ?is indicates a viol5t w9d bl[+ t[>ds u4 ,9 ! middle portion ( ! figure1 ! l9e is se5 to be b5t bo? ways2 ?is indicates a cyclone1 on "o side ( :i* ! w9d w\ld be bl[+ f u1 & on ! o!r side t[>ds u4 ,illu/ration3 ,fig4 #ahh4 ,illu/ration3 ,fig4 #ahi4 ,! di/ortions ( ! sol> l9es indicate t ! w9d at ! surface ( ! sun (t5 bl[s ) a velocity ( f "o hundr$ to ?ree hundr$ miles a second4 ,! mo/ viol5t w9d kn[n on ! e>? has velocity ( a hundr$ miles an h\r4 ,,iii4 ,,! ,,photosph]e ,,& ,,sun ,,spots4 ,! ,photosph]e4 ,illu/ration3 ,fig4 #aij4 #agb4 ,! ,granulation ( ! ,photosph]e4--,:5 ! surface ( ! sun is exam9$ ) a good telescope "u favorable atmosph]ic conditions1 x is se5 to be compos$ ( m9ute gra9s ( int5se brilliancy & ( irregul> =m1 float+ 9 a d>k] m$ium1 & arrang$ 9 /reaks & gr\ps1 z %[n 9 ,fig4 #aij4 ,) a r l[ p[]1 ! g5]al effect ( ! surface is mu* l t ( r\gh draw+-pap]1 or ( curdl$ milk se5 f a little di/ance4 ,) a high p[] & excell5t atmosph]ic conditions1 ! gra9s are se5 to be irregul>1 r\nd$ masses1 "s hundr$s ( miles 9 diamet]1 spr9kl$ ^u a less brilliant backgr\nd1 & appe>+ some:at l sn[-flakes sp>sely scatt]$ ov] a grayi% clo?4 ,fig4 #aia is a repres5tation ( ^! gra9s accord+ to ,sec*i4 ,illu/ration3 ,fig4 #aia4 ,) a v p[]ful telescope & ! v be/ atmosph]ic conditions1 ! gra9s !mselves are resolv$ into granules1 or little lum9\s dots1 n m ?an a hundr$ miles or s 9 diamet]1 :i*1 by _! aggregation1 make up ! gra9s1 j z !y1 9 _! turn1 make up ! co>s] masses ( ! sol> surface4 ,pr(essor ,langley e/imates t ^! granules con/itute ab\t "o-fif? ( ! sun's surface1 :ile !y emit at lea/ ?ree-f\r?s ( its light4 #agc4 ,%ape ( ! ,gra9s4--,! gra9s diff] consid]ably 9 %ape at diff]5t times & on diff]5t p>ts ( ! sun's surface4 ,nasmy?1 9 #ahfa1 describ$ !m z will[-leaves 9 %ape1 sev]al ?\s& miles 9 l5g?1 b n>r[ & ) po9t$ ends4 ,he figur$ ! surface ( ! sun z a sort ( basket-"w =m$ by ! int]weav+ ( su* filam5ts4 ,to o!rs !y h appe>$ to h ! =m ( rice-gra9s4 ,on portions ( ! sun's disk ! elem5t>y /ructure is (t5 compos$ ( long1 n>r[1 blunt-end$ filam5ts1 n s mu* l will[-leaves z l bits ( /raw ly+ r\ghly p>allel to ea* o!r1--a ?at*-/raw =mation1 z x has be5 call$4 ,?is is specially common 9 ! imm$iate neighborhood ( ! spots4 #agd4 ,nature ( ! ,gra9s4--,! gra9s are1 und\bt$ly1 inc&esc5t cl\ds float+ 9 ! sun's atmosph]e1 & compos$ ( p>tially cond5s$ metallic vapors1 j z ! cl\ds ( our atmosph]e are compos$ ( p>tially cond5s$ aque\s vapor4 ,ra9 on ! sun is compos$ ( :ite-hot drops ( molt5 iron & o!r metals2 & ^! drops are (t5 driv5 ) ! w9d ) a velocity ( ov] a hundr$ miles a second4 ,z to ! =ms ( ! gra9s1 ,pr(essor ,"y says1 ,if "o 7 to speculate z to ! explanation ( ! gra9s & ?at*-/raws1 x might be t ! gra9s are ! upp] ends ( long filam5ts ( lum9\s cl\d1 :i*1 ov] mo/ ( ! sun's surface1 /& approximately v]tical1 b 9 ! neighborhood ( a spot are incl9$ s z to lie ne>ly horizontal4 ,?is is n c]ta91 ?\gh3 x may be t ! cl\d-masses ov] ! m quiet portions ( ! sol> surface are really1 z !y seem1 ne>ly globul>1 :ile ne> ! spots !y are drawn out into filam5t>y =ms by atmosph]ic curr5ts4 #age4 ,facul4--,! facul are irregul> /reaks ( great] brightness ?an ! g5]al surface1 look+ mu* l ! flecks ( foam on ! surface ( a /ream bel[ a wat]fall4 ,!y are sometimes f five to tw5ty ?\s& miles 9 l5g?1 cov]+ areas imm5sely l>g] ?an a t]re/rial cont95t4 ,^! facul are elevat$ regions ( ! sol> surface1 ridges & cre/s ( lum9\s matt]1 :i* rise above ! g5]al level ( ! sun's surface1 & protrude ?r\gh ! d5s] portions ( ! sol> atmosph]e4 ,:5 "o ( ^! passes ov] ! edge ( ! sun's disk1 x c be se5 to project1 l a little too?4 ,any elevation on ! sun to be p]ceptible at all mu/ measure at lea/ half a second ( an arc1 or two hundr$ & tw5ty-five miles4 ,! facul are mo/ num]\s 9 ! neighborhood ( ! spots1 & mu* m conspicu\s ne> ! limb ( ! sun ?an ne> ! c5tre ( ! disk4 ,fig4 #aib gives ! g5]al appe>ance ( ! facul1 & ! d>k5+ ( ! limb ( ! sun4 ,ne> ! spots1 ! facul (t5 und]go v rapid *ange ( =m1 :ile else:]e on ! disk !y *ange r sl[ly1 sometimes und]go+ little app>5t alt]ation = sev]al days4 ,illu/ration3 ,fig4 #aib4 #agf4 ,:y ! ,facul are mo/ ,conspicu\s ne> ! ,limb ( ! ,sun4--,! reason :y ! facul are mo/ conspicu\s ne> ! limb ( ! sun is ?is3 ,! lum9\s surface ( ! sun is cov]$ ) an atmosph]e1 :i*1 ?\gh n v ?ick comp>$ ) ! diamet] ( ! sun1 is /ill suffici5t to absorb a good deal ( light4 ,light com+ f ! c5tre ( ! sun's disk p5etrates ?is atmosph]e "u ! mo/ favorable conditions1 & is b slightly r$uc$ 9 am\nt4 ,! edges ( ! disk1 on ! o!r h&1 are se5 ?r\gh a mu* great] ?ickness ( atmosph]e2 & ! light is r$uc$ by absorption "s sev5ty-five p] c5t4 ,suppose1 n[1 a facula 7 suffici5tly elevat$ to p5etrate q ?r\gh ?is atmosph]e4 ,its light w\ld be undimm$ by absorption on any "p ( ! sun's disk2 b at ! c5tre ( ! disk x w\ld be se5 aga9/ a backgr\nd ne>ly z bright z itself1 :ile at ! m>g9 x w\ld be se5 aga9/ "o only a qu>t] z bright4 ,x is evid5t t ! light ( any facula1 ow+ to ! elevation1 w\ld be r$uc$ less rapidly z we approa* ! edge ( ! disk ?an t ( ! g5]al surface ( ! sun1 :i* lies at a l[] level4 ,sun-,spots4 #agg4 ,g5]al ,appe>ance ( ,sun-,spots4--,! g5]al appe>ance ( a well-=m$ sun-spot is %[n 9 ,fig4 #aic4 ,! spot consi/s ( a v d>k c5tral portion ( irregul> %ape1 call$ ! umbra1 :i* is surr\nd$ by a less d>k fr+e1 call$ ! p5umbra4 ,! p5umbra is made up1 = ! mo/ "p1 ( filam5ts direct$ radially inw>d4 ,illu/ration3 ,fig4 #aic4 ,!re is great v>iety 9 ! details ( =m 9 diff]5t sun-spots2 b !y are g5]ally ne>ly circul> dur+ ! middle p]iod ( _! exi/5ce4 ,dur+ ! p]iod ( _! developm5t & ( _! disappe>ance !y are mu* m irregul> 9 =m4 ,!re is no?+ l a gradual %ad+-(f ( ! p5umbra1 ei!r t[>ds ! umbra on ! "o side1 or t[>ds ! photosph]e on ! o!r4 ,! p5umbra is sep>at$ f bo? ! umbra & ! photosph]e by a %>p l9e ( dem>cation4 ,! umbra is mu* bright] on ! inn] ?an on ! out] edge1 & frequ5tly ! photosph]e is excessively bright at ! m>g9 ( ! p5umbra4 ,! brightness ( ! inn] p5umbra seems to be due to ! cr[d+ toge!r ( ! p5umbral filam5ts :]e !y ov]hang ! edge ( ! umbra4 ,!re is a g5]al anti!sis betwe5 ! irregul>ities ( ! out] & inn] edges ( ! p5umbra4 ,:]e an angle ( ! p5umbral matt] cr[ds 9 ^u ! umbra1 x is g5]ally mat*$ by a correspond+ outw>d ext5sion into ! photosph]e1 & vice v]sa4 ,! umbra ( ! spot is f> f be+ uni=mly d>k4 ,_m ( ! p5umbral filam5ts t]m9ate 9 little deta*$ gra9s ( lum9\s matt]2 & !re are also fa9t] veils ( a sub/ance less brilliant1 b sometimes rose-color$1 :i* seem to float above ! umbra4 ,! umbra itself is made up ( masses ( cl\ds :i* are really int5sely brilliant1 & :i* appe> d>k only by contra/ ) ! int5s] brightness ( ! sol> surface4 ,among ^! cl\ds are (t5 se5 "o or m m9ute circul> spots mu* d>k] ?an ! re/ ( ! umbra4 ,^! d>k] portions are call$ nuclei4 ,!y seem to be ! m\?s ( tubul> orifices p5etrat+ to unkn[n dep?s4 ,! fa9t veils m5tion$ above cont9ually melt away1 & are replac$ by o!rs 9 "s diff]5t position4 ,! bright granules at ! tips ( ! p5umbral filam5ts seem to s9k & dissolve1 :ile fre% portions break (f to replace !m4 ,!re is a cont9ual indraught ( lum9\s matt] ov] ! :ole ext5t ( ! p5umbra4 ,at times1 ?\gh v r>ely1 pat*es ( int5se brightness sudd5ly break out1 rema9 visible = a few m9utes1 & move ov] ! spot ) velocities z great z a hundr$ miles a second4 ,! spots *ange _! =m & size q p]ceptibly f day to day1 & sometimes ev5 f h\r to h\r4 #agh4 ,duration ( ,sun-,spots4--,! av]age life ( a sun-spot is two or ?ree mon?s3 ! longe/ on record is t ( a spot obs]v$ 9 #ahdj & #ahda1 :i* la/$ eighte5 mon?s4 ,!re are cases1 h[ev]1 :]e ! disappe>ance ( a spot is v soon foll[$ by ! appe>ance ( ano!r at ! same po9t2 & sometimes ?is alt]nate disappe>ance & re-appe>ance is sev]al times repeat$4 ,:ile "s spots are ?us long-liv$1 o!rs endure only a day or two1 & sometimes only a few h\rs4 #agi4 ,gr\ps ( ,spots4--,! spots usually appe> n s+ly1 b 9 gr\ps4 ,a l>ge spot is (t5 foll[$ by a tra9 ( small] ones to ! ea/ ( x1 _m ( :i* are apt to be irregul> 9 =m & v imp]fect 9 /ructure1 sometimes ) no umbra at all1 (t5 ) a p5umbra only on "o side4 ,9 su* cases1 :5 any consid]able *ange ( =m or /ructure %[s itself 9 ! pr9cipal spot1 x seems to ru% we/w>d ov] ! sol> surface1 leav+ its att5dants trail+ beh9d4 ,:5 a l>ge spot divides into two or m1 z (t5 happ5s1 ! p>ts usually seem to repel ea* o!r1 & fly ap>t ) great velocity4 #ahj4 ,size ( ! ,spots4--,! spots are sometimes ( enorm\s size4 ,gr\ps h (t5 be5 obs]v$ cov]+ areas ( m ?an a hundr$ ?\s& miles squ>e1 & s+le spots occasionally measure f =ty to fifty ?\s& miles 9 diamet]1 ! umbra be+ tw5ty-five or ?irty ?\s& miles across4 ,a spot1 h[ev]1 measur+ ?irty ?\s& miles ov] all1 may be consid]$ a l>ge "o4 ,su* a spot c easily be se5 )\t a telescope :5 ! brightness ( ! sun's surface is r$uc$ by cl\ds or ne>ness to ! horizon1 or by ! use ( color$ glass4 ,dur+ ! ye>s #ahga & #ahgb spots 7 visible to ! nak$ eye = a consid]able portion ( ! "t4 ,! l>ge/ spot yet record$ 0 obs]v$ 9 #aheh4 ,x _h a bread? ( m ?an a hundr$ & =ty-?ree ?\s& miles1 or ne>ly eighte5 times ! diamet] ( ! e>?1 & cov]$ ab\t a ?irty-six? ( ! :ole surface ( ! sun4 ,illu/ration3 ,fig4 #aid4 ,fig4 #aid repres5ts a gr\p ( sun-spots obs]v$ by ,pr(essor ,langley1 & drawn on ! same scale z ! small circle 9 ! upp] left-h& corn]1 :i* repres5ts ! surface ( half ( our globe4 ,illu/ration3 ,fig4 #aie4 #aha4 ,! ,p5umbral ,filam5ts4--,n unfrequ5tly ! p5umbral filam5ts are curv$ spirally1 indicat+ a cyclonic action1 z %[n 9 ,fig4 #aie4 ,9 su* cases ! :ole spot usually turns sl[ly ar\nd1 sometimes complet+ an entire revolution 9 a few days4 ,m frequ5tly1 h[ev]1 ! spiral motion la/s b a %ort "t2 & occasionally1 aft] cont9u+ = a :ile 9 "o direction1 ! motion is rev]s$4 ,v (t5 9 l>ge spots we obs]ve opposite spiral movem5ts 9 diff]5t portions ( ! umbra1 z %[n 9 ,figs4 #aif & #aig4 ,illu/ration3 ,fig4 #aif4 ,neighbor+ spots %[ no t5d5cy to rotate 9 ! same direction4 ,! numb] ( spots 9 :i* a decid$ cyclonic motion 7l t %[n 9 ,fig4 #aih7 appe>s is comp>atively small1 n exce$+ two or ?ree p] c5t ( ! :ole4 ,illu/ration3 ,fig4 #aig4 ,illu/ration3 ,fig4 #aih4 ,illu/ration3 ,plate #b4 ,plate ,,ii4 repres5ts a typical sun-spot z del9eat$ by ,pr(essor ,langley4 ,at ! left-h& & upp] portions ( ?is great spot ! filam5ts pres5t ! ord9>y appe>ance1 :ile at ! l[] edge1 & ^u ! great ov]hang+ bran*1 !y are arrang$ v diff]5tly4 ,! fea!ry bru% bel[ ! bran*1 closely resembl+ a fro/-cry/al on a w9d[-pane1 is z r>e z x is curi\s1 & has n be5 satisfactorily expla9$4 ,illu/ration3 ,fig4 #aii4 #ahb4 ,bir? & ,decay ( ,sun-,spots4--,! =mation ( a spot is sometimes gradual1 requir+ days or ev5 weeks = its full developm5t2 & sometimes a s+le day suffices4 ,g5]ally1 = "s "t be=e its appe>ance1 !re is an evid5t di/urbance ( ! sol> surface1 indicat$ especially by ! pres5ce ( _m brilliant facul1 among :i* pores1 or m9ute black dots1 are scatt]$4 ,^! enl>ge1 & betwe5 !m appe> grayi% pat*es1 9 :i* ! photosph]ic /ructure is unusually evid5t1 z if !y 7 caus$ by a d>k mass ly+ bel[ a ?9 veil ( lum9\s filam5ts4 ,?is veil seems to gr[ gradually ?9n]1 & f9ally breaks op51 giv+ u at la/ ! complete spot ) its p5umbra4 ,"s ( ! pores coalesce ) ! pr9cipal spot1 "s disappe>1 & o!rs =m ! att5dant tra9 be=e describ$ 7#agi74 ,! spot :5 once =m$ usually assumes a circul> =m1 & rema9s )\t /rik+ *ange until x disappe>s4 ,z its end approa*es1 ! surr\nd+ photosph]e seems to cr[d 91 & ov]:elm ! p5umbra4 ,bridges ( light 7,fig4 #aii71 (t5 mu* bright] ?an ! av]age ( ! sol> surface1 pu% across ! umbra2 ! arrangem5t ( ! p5umbra filam5ts becomes confus$2 &1 z ,sec*i expresses x1 ! lum9\s matt] ( ! photosph]e seems to tumble pell-mell into ! *asm1 :i* disappe>s1 & leaves a di/urb$ surface m>k$ ) facul1 :i*1 9 _! turn1 gradually subside4 ,illu/ration3 ,fig4 #bjj4 #ahc4 ,motion ( ,sun-,spots4--,! spots h a regul> motion across ! disk ( ! sun f ea/ to we/1 occupy+ ab\t twelve days 9 ! transit4 ,a spot g5]ally appe>s fir/ on or ne> ! ea/ limb1 &1 aft] twelve or f\rte5 days1 disappe>s at ! we/ limb4 ,at ! end ( ano!r f\rte5 days1 or m1 x re-appe>s at ! ea/ limb1 unless1 9 ! mean "t1 x has vani%$ f sight entirely4 ,?is motion ( ! spots is indicat$ by ! arr[ 9 ,fig4 #bjj4 ,! int]val betwe5 two successive appe>ances ( ! same spot on ! ea/]n edge ( ! sun is ab\t tw5ty-sev5 days4 ,illu/ration3 ,fig4 #bja4 #ahd4 ,! ,rotation ( ! ,sun4--,! spots are evid5tly c>ri$ ar\nd by ! rotation ( ! sun on its axis4 ,x is evid5t1 f ,fig4 #bja1 t ! sun w ne$ to make m ?an a complete rotation 9 ord] to br+ a spot aga9 ^u ! same "p ( ! disk z se5 f ! e>?4 ,s repres5ts ! sun1 & ,e ! e>?4 ,! arr[s indicate ! direction ( ! sun's rotation4 ,:5 ! e>? is at ,e1 a spot at a w\ld be se5 at ! c5tre ( ! sol> disk4 ,:ile ! sun is turn+ on its axis1 ! e>? moves 9 its orbit f ,e to ,e'3 h5ce ! sun mu/ make a complete rotation1 & turn f a to a' 9 addition1 9 ord] to br+ ! spot aga9 to ! c5tre ( ! disk4 ,to c>ry ! spot entirely ar\nd1 & !n on to a'1 requires ab\t tw5ty-sev5 days4 ,f ?is synodical p]iod ( ! spot1 z x might be call$1 x has be5 calculat$ t ! sun mu/ rotate on its axis 9 ab\t tw5ty-five days4 ,illu/ration3 ,fig4 #bjb4 #ahe4 ,! ,incl9ation ( ! ,sun's ,axis4--,! pa?s describ$ by sun-spots across ! sol> disk v>y ) ! position ( ! e>? 9 its orbit1 z %[n 9 ,fig4 #bjb4 ,we !re=e conclude t ! sun's axis is n p]p5dicul> to ! plane ( ! e>?'s orbit4 ,! sun rotates on its axis f we/ to ea/1 & ! axis leans ab\t sev5 degrees f ! p]p5dicul> to ! e>?'s orbit4 #ahf4 ,! ,prop] ,motion ( ! ,spots4--,:5 ! p]iod ( ! sun's rotation is d$uc$ f ! motion ( spots 9 diff]5t sol> latitudes1 !re is f\nd to be consid]able v>iation 9 ! results obta9$4 ,?us spots ne> ! equator indicate t ! sun rotates 9 ab\t tw5ty-five days2 :ile ^? 9 latitude #bj indicate a p]iod ab\t eighte5 h\rs long]2 & ^? 9 latitude #cj a p]iod ( tw5ty-sev5 days & a half4 ,/rictly speak+1 ! sun1 z a :ole1 has no s+le p]iod ( rotation2 b diff]5t portions ( its surface p]=m _! revolutions 9 diff]5t times4 ,! equatorial regions n only move m rapidly 9 miles p] h\r ?an ! re/ ( ! sol> surface1 b !y complete ! entire rotation 9 %ort] "t4 ,illu/ration3 ,fig4 #bjc4 ,!re appe>s to be a peculi> surface-drift 9 ! equatorial regions ( ! sun1 ! cause ( :i* is unkn[n1 b :i* gives ! spots a prop] motion2 t is1 a motion ( _! own1 indep5d5t ( ! rotation ( ! sun4 ,illu/ration3 ,fig4 #bjd4 #ahg4 ,di/ribution ( ! ,sun-,spots4--,! sun-spots are n di/ribut$ uni=mly ov] ! sun's surface1 b occur ma9ly 9 two zones on ea* side ( ! equator1 & betwe5 ! latitudes ( #aj & #cj1 z %[n 9 ,fig4 #bjc4 ,on & ne> ! equator itself !y are comp>atively r>e4 ,!re are /ill few] beyond #ce ( latitude1 & only a s+le spot has ev] be5 record$ m ?an #de f ! sol> equator4 ,fig4 #bjd %[s ! di/ribution ( ! sun-spots obs]v$ by ,c>r+ton dur+ a p]iod ( eight ye>s4 ,! irregul> l9e on ! left-h& side ( ! figure indicates by its height ! comp>ative frequ5cy ) :i* ! spots occurr$ 9 diff]5t latitudes4 ,9 ,fig4 #bje ! same ?+ is indicat$ by diff]5t degrees ( d>kness 9 ! %ad+ ( ! belts4 ,illu/ration3 ,fig4 #bje4 #ahh4 ,! ,p]iodicity ( ! ,spots4--,c>eful obs]vations ( ! sol> spots indicate a p]iod ( ab\t elev5 ye>s 9 ! spot-produc+ activity ( ! sun4 ,dur+ two or ?ree ye>s ! spots increase 9 numb] & 9 size2 !n !y beg9 to dim9i%1 & rea* a m9imum five or six ye>s aft] ! maximum4 ,ano!r p]iod ( ab\t six ye>s br+s ! return ( ! maximum4 ,! int]vals are1 h[ev]1 some:at irregul>4 ,illu/ration3 ,fig4 #bjf4 ,fig4 #bjf gives a graphic repres5tation ( ! p]iodicity ( ! sun-spots4 ,! height ( ! curve %[s ! frequ5cy ( ! sun-spots 9 ! ye>s giv5 at ! bottom ( ! figure4 ,x appe>s1 f an exam9ation ( ?is sun-spot curve1 t ! av]age int]val f a m9imum to ! next foll[+ maximum is only ab\t f\r ye>s & a half1 :ile t f a maximum to ! next foll[+ m9imum is six ye>s & six-t5?s4 ,! di/urbance :i* produces ! sun-spots is develop$ sudd5ly1 b dies away gradually4 #ahi4 ,connection betwe5 ,sun-,spots & ,t]re/rial ,magnetism4--,! magnetic ne$le does n po9t /eadily 9 ! same direction1 b is subject to v>i\s di/urbances1 "s ( :i* are regul>1 & o!rs irregul>4 7#a7 ,"o ( ! mo/ noticeable ( ! regul> magnetic *anges is ! s-call$ diurnal oscillation4 ,dur+ ! e>ly "p ( ! day ! nor? pole ( ! ne$le moves t[>d ! we/ 9 our latitude1 return+ to its mean position ab\t t5 ,p4,m41 & rema9+ ne>ly /ation>y dur+ ! night4 ,! ext5t ( ?is oscillation 9 ! ,unit$ ,/ates is ab\t fifte5 m9utes ( arc 9 summ]1 & n q half z mu* 9 w9t]2 b x diff]s v mu* 9 diff]5t localities & at diff]5t times1 & ! av]age diurnal oscillation 9 any locality increases & decreases pretty regul>ly dur+ a p]iod ( ab\t elev5 ye>s4 ,! maximum & m9imum ( ?is p]iod ( magnetic di/urbance are f\nd to co9cide ) ! maximum & m9imum ( ! sun-spot p]iod4 ,?is is %[n 9 ,fig4 #bjf1 9 :i* ! dott$ l9es indicate ! v>iations 9 ! int5sity ( ! magnetic di/urbance4 7#b7 ,occasionally s-call$ magnetic /orms occur1 dur+ :i* ! compass-ne$le is sometimes viol5tly di/urb$1 oscillat+ five degrees1 or ev5 t5 degrees1 )9 an h\r or two4 ,^! /orms are g5]ally accompani$ by an aurora1 & an aurora is always accompani$ by magnetic di/urbance4 ,a c>eful comp>ison ( aurora obs]vations ) ^? ( sun-spots %[s an almo/ p]fect p>allelism betwe5 ! curves ( auroral & sun-spot frequ5cy4 7#c7 ,a numb] ( obs]vations r5d] x v probable t e int5se di/urbance ( ! sol> surface is propagat$ to our t]re/rial magnetism ) ! spe$ ( light4 ,illu/ration3 ,fig4 #bjg4 ,fig4 #bjg %[s c]ta9 ( ! sol> l9es z !y 7 obs]v$ by ,pr(essor ,"y on ,aug4 #c1 #ahgb4 ,! contortions ( ! ,f l9e indicat$ an int5se di/urbance 9 ! atmosph]e ( ! sun4 ,!re 7 ?ree especially notable p>oxysms 9 ?is di/ortion1 occurr+ at a qu>t] ( n9e1 half-pa/ t51 & t5 m9utes ( twelve1 ,a4,m4 ,illu/ration3 ,fig4 #bjh4 ,fig4 #bjh %[s ! curve ( magnetic di/urbance z trac$ at ,gre5wi* on ! same day4 ,x w be se5 f ! curve t x 0 a day ( g5]al magnetic di/urbance4 ,at ! times ( ! ?ree p>oxysms1 :i* are giv5 at ! bottom ( ! figure1 x w be obs]v$ t !re is a peculi> %iv]+ ( ! magnetic curve4 #aij4 ,! ,spots are ,depressions 9 ! ,photosph]e4--,?is fact 0 fir/ cle>ly br\ght out by ,dr4 ,wilson ( ,glasg[1 9 #agfi1 f obs]vations ^u ! p5umbra ( a spot 9 ,novemb] ( t ye>4 ,he f\nd1 t :5 ! spot appe>$ at ! ea/]n limb1 or edge ( ! sun1 j mov+ into sight1 ! p5umbra 0 well m>k$ on ! side ( ! spot ne>e/ to ! edge ( ! disk2 :ile on ! o!r edge ( ! spot1 t[>ds ! c5tre ( ! sun1 !re 0 no p5umbra visible at all1 & ! umbra itself 0 almo/ hidd51 z if beh9d a bank4 ,:5 ! spot _h mov$ a day's j\rney t[>d ! c5tre ( ! disk1 ! :ole ( ! umbra came into sight1 & ! p5umbra on ! inn] edge ( ! spot began to be visible z a n>r[ l9e4 ,aft] ! spot 0 well advanc$ ^u ! disk1 ! p5umbra 0 ( ! same wid? all ar\nd ! spot4 ,:5 ! spot approa*$ ! sun's we/]n limb1 ! same ph5om5a 7 repeat$1 b 9 ! inv]se ord]4 ,! p5umbra on ! inn] edge ( ! spot n>r[$ mu* fa/] ?an t on ! out]1 disappe>$ entirely1 & f9ally seem$ to hide f sight mu* ( ! umbra ne>ly a :ole day be=e ! spot pass$ f view ar\nd ! limb4 ,?is is precisely :at w\ld occur 7z ,fig4 #bji cle>ly %[s7 if ! spot 7 a sauc]-%ap$ depression 9 ! sol> surface1 ! bottom ( ! sauc] correspond+ to ! umbra1 & ! slop+ sides to ! p5umbra4 ,illu/ration3 ,fig4 #bji4 ,illu/ration3 ,fig4 #baj4 #aia4 ,sun-,spot ,spectrum4--,:5 ! image ( a sun-spot is ?r[n ^u ! slit ( ! spectroscope1 ! spectrum is se5 to be cross$ longitud9ally by a cont9u\s d>k b&1 %[+ an increas$ g5]al absorption 9 ! region ( ! sun-spot4 ,_m ( ! spectral l9es are greatly ?ick5$1 z %[n 9 ,fig4 #baj4 ,?is ?ick5+ ( ! l9es %[s t ! absorption is tak+ place at a great] dep?4 ,new l9es & %ad+s (t5 appe>1 :i* indicate1 t1 9 ! cool] nucleus ( ! spot1 c]ta9 comp\nd vapors exi/1 :i* are dissociat$ else:]e on ! sun's surface4 ,^! l9es & %ad+s are %[n 9 ,fig4 #baa4 ,illu/ration3 ,fig4 #baa4 ,x (t5 happ5s t c]ta9 ( ! spectral l9es are rev]s$ 9 ! spectrum ( ! spot1 a ?9 bright l9e appe>+ ov] ! c5tre ( a ?ick d>k "o1 z %[n 9 ,fig4 #bab4 ,^! rev]sals are due to v bright vapors float+ ov] ! spot4 ,illu/ration3 ,fig4 #bab4 ,at times1 also1 ! spectrum ( a spot indicates viol5t motion 9 ! ov]ly+ gases by di/ortion & displacem5t ( ! l9es4 ,?is ph5om5on occurs (t5] at po9ts ne> ! out] edge ( ! p5umbra ?an ov] ! c5tre ( ! spot2 b occasionally ! :ole neighborhood is viol5tly agitat$4 ,9 su* cases1 l9es 9 ! spectrum side by side are (t5 affect$ 9 entirely diff]5t ways1 "o be+ greatly displac$ :ile its neighbor is n di/urb$ 9 ! lea/1 %[+ t ! vapors :i* produce ! l9es are at diff]5t levels 9 ! sol> atmosph]e1 & mov+ indep5d5tly ( ea* o!r4 ,illu/ration3 ,fig4 #bac4 #aib4 ,! ,cause & ,nature ( ,sun-,spots4--,accord+ to ,pr(essor ,"y1 ! arrangem5t & relations ( ! photosph]ic cl\ds 9 ! neighborhood ( a spot are su* z are repres5t$ 9 ,fig4 #bac4 ,ov] ! sun's surface g5]ally1 ^! cl\ds probably h ! =m ( v]tical columns1 z at aa4 ,j outside ! spot1 ! level ( ! photosph]e is ! mo/ "p1 ov]topp$ by eruptions ( hydrog5 & usually rais$ into facul1 z at bb4 ,^! facul are1 = metallic vapors1 z indicat$ by ! %ad$ cl\ds4444 ,:ile ! great cl\ds ( hydrog5 are f\nd ev]y:]e ^u ! sun1 ^! spiky1 vivid outbur/s ( metallic vapors seldom occur except j 9 ! neighborhood ( a spot1 & !n only dur+ its season ( rapid *ange4 ,9 ! p5umbra ( ! spot ! photosph]ic filam5ts become m or less ne>ly horizontal1 z at pp2 9 ! umbra at u x is q unc]ta9 :at ! true /ate ( affairs may be4 ,we h conjecturally repres5t$ ! filam5ts !re z v]tical also1 b depress$ & c>ri$ d[n by a desc5d+ curr5t4 ,( c\rse1 ! cavity is fill$ by ! gases :i* ov]lie ! photosph]e2 & x is easy to see1 t1 look$ at f above1 su* a cavity & arrangem5t ( ! lum9\s filam5ts w\ld pres5t ! appe>ances actually obs]v$4 ,pr(essor ,"y also sugge/s t ! spots may be depressions 9 ! photosph]e caus$ by ! dim9ution ( upw>d pressure f bel[1 9 consequ5ce ( eruptions 9 ! neighborhood2 ! spots ?us be+1 s to speak1 s9ks 9 ! photosph]e4 ,und\bt$ly ! photosph]e is n a /rictly cont9u\s %ell or cru/2 b x is heavy z comp>$ ) ! uncond5s$ vapors 9 :i* x lies1 j z a ra9-cl\d 9 our t]re/rial atmosph]e is heavi] ?an ! air2 & x is probably cont9u\s en\gh to h its upp] level affect$ by any dim9ution ( pressure bel[4 ,! gase\s mass bel[ ! photosph]e supports its weight & ! weight ( ! products ( cond5sation1 :i* mu/ always be desc5d+ 9 an inconceivable ra9 & sn[ ( molt5 & cry/alliz$ mat]ial4 ,to all int5ts & purposes1 ?\gh no?+ b a lay] ( cl\ds1 ! photosph]e ?us =ms a con/rict+ %ell1 & ! gases b5ea? are imprison$ & compress$4 ,moreov]1 at a high temp]ature ! viscosity ( gases is va/ly increas$1 s t q probably ! matt] ( ! sol> nucleus resembles pit* or t> 9 its consi/5cy m ?an :at we usually ?9k ( z a gas4 ,consequ5tly1 any sudd5 dim9ution ( pressure w\ld propagate itself sl[ly f ! po9t :]e x occurr$4 ,putt+ ^! ?+s toge!r1 x w\ld seem1 t1 :5ev] a free outlet is obta9$ ?r\gh ! photosph]e at any po9t1 ?us decreas+ ! inw>d pressure1 ! result w\ld be ! s9k+ ( a portion ( ! photosph]e some:]e 9 ! imm$iate neighborhood1 to re/ore ! equilibrium2 &1 if ! eruption 7 kept up = any l5g? ( "t1 ! depression 9 ! photosph]e w\ld cont9ue till ! eruption ceas$4 ,?is depression1 fill$ ) ! ov]ly+ gases1 w\ld con/itute a spot4 ,moreov]1 ! l9e ( fracture 7if we may call x s7 at ! edges ( ! s9k w\ld be a region ( weakness 9 ! photosph]e1 s t we %\ld expect a s]ies ( eruptions all ar\nd ! spot4 ,= a "t ! di/urbance1 !re=e1 w\ld gr[1 & ! spot w\ld enl>ge & deep51 until1 9 spite ( ! viscosity ( ! int]nal gases1 ! equilibrium ( pressure 0 gradually re/or$ b5ea?4 ,s f> z we "k ! spectroscopic & visual ph5om5a1 none ( !m contradict ?is hypo!sis4 ,!re is no?+ 9 x1 h[ev]1 to acc\nt = ! di/ribution ( ! spots 9 sol> latitudes1 nor = _! p]iodicity4 ,,iv4 ,,! ,,*romosph]e ,,& ,,prom95ces4 #aic4 ,! ,sun's ,out] ,atmosph]e4--,:at we see ( ! sun "u ord9>y circum/ances is b a fraction ( 8 total bulk4 ,:ile by f> ! great] portion ( ! sol> mass is includ$ )9 ! photosph]e1 ! l>g] portion ( 8 volume lies )\t1 & con/itutes a gase\s envelope ^: diamet] is at lea/ d\ble1 & its bulk !re=e sev5fold1 t ( ! c5tral globe4 ,?is out] envelope1 ?\gh ma9ly gase\s1 is n sph]ical1 b has an exce$+ly irregul> & v>iable outl9e4 ,x seems to be made up1 n ( regul> /rata ( diff]5t d5sity1 l our atmosph]e1 b r ( flames1 beams1 & /ream]s1 z transi5t & un/able z ^? ( ! aurora borealis4 ,x is divid$ into two portions by a b\nd>y z def9ite1 ?\gh n s regul>1 z t :i* sep>ates !m bo? f ! photosph]e4 ,! out] & f> m ext5sive portion1 :i* 9 texture & r>ity seems to resemble ! tails ( comets1 is kn[n z ! coronal atmosph]e1 s9ce to x is *iefly due ! corona1 or glory1 :i* surr\nds ! d>k5$ sun dur+ an eclipse4 #aid4 ,! ,*romosph]e4--,at ! base ( ! coronal atmosph]e1 & 9 contact ) ! photosph]e1 is :at resembles a %eet ( sc>let fire4 ,x appe>s z if c\ntless jets ( heat$ gas 7 issu+ ?r\gh v5ts ov] ! :ole surface1 clo?+ x ) flame1 :i* heaves & tosses l ! blaze ( a conflagration4 ,?is is ! *romosph]e1 or color-sph]e4 ,x owes its vivid r$ness to ! pr$om9ance ( hydrog5 9 ! flames4 ,! av]age dep? ( ! *romosph]e is n f> f t5 or twelve seconds1 or five ?\s& or six ?\s& miles4 #aie4 ,! ,prom95ces4--,"h & !re masses ( ?is hydrog51 mix$ ) o!r sub/ances1 rise f> above ! g5]al level into ! coronal regions1 :]e !y float l cl\ds1 or are torn to pieces by conflict+ curr5ts4 ,^! cl\d-masses are kn[n z sol> prom95ces1 or protub]ances4 #aif4 ,magnitude & ,di/ribution ( ! ,prom95ces4--,! prom95ces diff] greatly 9 magnitude4 ,( ! #b1gfg obs]v$ by ,sec*i1 #a1ifd atta9$ an altitude ( eighte5 ?\s& miles2 #gea1 or ne>ly a f\r? ( ! :ole1 rea*$ a height ( tw5ty-eight ?\s& miles2 sev]al exce$$ eighty-f\r ?\s& miles4 ,9 r>e in/ances !y rea* elevations z great z a hundr$ ?\s& miles4 ,a few h be5 se5 :i* exce$$ a hundr$ & fifty ?\s& miles2 & ,sec*i has record$ "o ( ?ree hundr$ ?\s& miles4 ,illu/ration3 ,fig4 #bad4 ,! irregul> l9es on ! "r-h& side ( ,fig4 #bad %[ ! proportion ( ! prom95ces obs]v$ by ,sec*i1 t 7 se5 9 diff]5t p>ts ( ! sun's surface4 ,! out] l9e %[s ! di/ribution ( ! small] prom95ces1 & ! inn] dott$ l9e t ( ! l>g] prom95ces4 ,by comp>+ ^! l9es ) ^? on ! opposite side ( ! circle1 :i* %[ ! di/ribution ( ! spots1 x w be se51 t1 :ile ! spots are conf9$ ma9ly to two belts1 ! prom95ces are se5 9 all latitudes4 #aig4 ,! ,spectrum ( ! ,*romosph]e4--,! spectrum ( ! *romosph]e is comp>atively simple4 ,!re are elev5 l9es only :i* are always pres5t2 & six ( ^! are l9es ( hydrog51 & ! o!rs1 ) a s+le exception1 are ( unkn[n elem5ts4 ,!re are sixte5 o!r l9es :i* make _! appe>ance v frequ5tly4 ,among ^! latt] are l9es ( sodium1 magnesium1 & iron4 ,:]e "s special di/urbance is go+ on1 ! spectrum at ! base ( ! *romosph]e is v complicat$1 consi/+ ( hundr$s ( bright l9es4 ,! majority ( ! l9es1 h[ev]1 are se5 only occasionally1 = a few m9utes at a "t1 :5 ! gases & vapors1 :i* g5]ally lie l[ 7ma9ly 9 ! int]/ices ( ! cl\ds :i* con/itute ! photosph]e71 & bel[ its upp] surface1 are elevat$ = ! "t be+ by "s eruptive action4 ,= ! mo/ "p1 ! l9es :i* appe> only at su* times are simply rev]sals ( ! m prom95t d>k l9es ( ! ord9>y sol> spectrum4 ,b ! selection ( ! l9es seems mo/ caprici\s3 "o is tak51 & ano!r left1 ?\gh belong+ to ! same elem5t1 ( equal int5sity1 & close beside ! fir/4 ,"s ( ! ma9 l9es ( ! *romosph]e & prom95ces are %[n 9 ,fig4 #bae4 ,illu/ration3 ,fig4 #bae4 #aih4 ,me?od ( ,/udy+ ! ,*romosph]e & ,prom95ces4--,until rec5tly1 ! sol> atmosph]e c\ld be se5 only dur+ a total eclipse ( ! sun2 b n[ ! spectroscope enables u to /udy ! *romosph]e & ! prom95ces ) ne>ly ! same facility z ! spots & facul4 ,! protub]ances are ord9>ily invisible1 = ! same reason t ! />s _c be se5 9 ! daytime2 !y are hidd5 by ! int5se light reflect$ f our own atmosph]e4 ,if we c\ld only get rid ( ?is a]ial illum9ation1 )\t at ! same "t weak5+ ! light ( ! prom95ces1 ! latt] w\ld become visible4 ,?is ! spectroscope enables u to accompli%4 ,s9ce ! air-light is reflect$ sun%9e1 x ( c\rse pres5ts ! same spectrum z sunlight1--a cont9u\s b& ( color cross$ by d>k l9es4 ,n[1 ?is sort ( spectrum is weak5$ by increase ( disp]sive p[] 7#aei71 because ! light is spread out into a long] ribbon1 & made to cov] a great] area4 ,on ! o!r h&1 ! spectrum ( ! prom95ces1 be+ compos$ ( bright l9es1 und]goes no su* dim9ution by increas$ disp]sion4 ,illu/ration3 ,fig4 #baf4 ,:5 ! spectroscope is us$ z a means ( exam9+ ! prom95ces1 ! slit is m or less wid5$4 ,! telescope is direct$ s t ! image ( t portion ( ! sol> limb :i* is to be exam9$ %all be tang5t to ! op5$ slit1 z 9 ,fig4 #baf1 :i* repres5ts ! slit-plate ( ! spectroscope ( its actual size1 ) ! image ( ! sun 9 ! prop] position = obs]vation4 ,illu/ration3 ,fig4 #bag4 ,if1 n[1 a prom95ce exi/s at ?is "p ( ! sol> limb1 & if ! spectroscope itself is s adju/$ t ! ,c l9e falls 9 ! c5tre ( ! field ( view1 !n "o w see some?+ l ,fig4 #bag4 ,! r$ portion ( ! spectrum w /ret* a?w>t ! field ( view l a sc>let ribbon ) a d>ki% b& across x2 & 9 t b& w appe> ! prom95ces1 l sc>let cl\ds1 s l our own t]re/rial cl\ds1 inde$1 9 =m & texture1 t ! resemblance is q />tl+4 ,"o might almo/ ?9k he 0 look+ out ?r\gh a p>tly-op5$ door ^u a sunset sky1 except t !re is no v>iety or contra/ ( color2 all ! cl\dlets are ( ! same pure sc>let hue4 ,along ! edge ( ! op5+ is se5 ! *romosph]e1 m brilliant ?an ! cl\ds :i* rise f x or float above x1 &1 = ! mo/ "p1 made up ( m9ute tongues & filam5ts4 #aii4 ,quiesc5t ,prom95ces4--,! prom95ces diff] z widely 9 =m & /ructure z 9 magnitude4 ,! two pr9cipal classes are ! quiesc5t1 cl\d-=m$1 or hydrog5\s1 & ! eruptive1 or metallic4 ,illu/ration3 ,plate #c4 ,! quiesc5t prom95ces resemble almo/ exactly our t]re/rial cl\ds1 & diff] among !mselves 9 ! same mann]4 ,!y are (t5 ( enorm\s dim5sions1 especially 9 horizontal ext5t1 & are comp>atively p]man5t1 (t5 und]go+ little *ange = h\rs & days4 ,ne> ! poles !y sometimes rema9 dur+ a :ole sol> revolution ( tw5ty-sev5 days4 ,sometimes !y appe> to lie ^u ! limb ( ! sun1 l a bank ( cl\ds 9 ! t]re/rial horizon1 probably because !y are s f> f ! edge t only _! upp] portions are 9 sight4 ,:5 fully se51 !y are usually connect$ to ! *romosph]e by sl5d] columns1 g5]ally smalle/ at ! base1 & (t5 app>5tly made up ( sep>ate filam5ts closely int]tw9$1 & exp&+ upw>d4 ,sometimes ! :ole "u surface is fr+$ ) p5d5t filam5ts4 ,sometimes !y float entirely free f ! *romosph]e2 & 9 mo/ cases ! l>g] cl\ds are att5d$ by deta*$ cl\dlets4 ,v>i\s =ms ( quiesc5t prom95ces are %[n 9 ,plate ,,iii4 ,o!r =ms are giv5 9 ,figs4 #bah & #bai4 ,illu/ration3 ,fig4 #bah4 ,_! spectrum is usually v simple1 consi/+ ( ! f\r l9es ( hydrog5 & ! orange ,d#c3 h5ce ! appellation hydrog5\s4 ,occasionally ! sodium & magnesium l9es also appe>1 ev5 ne> ! tops ( ! cl\ds4 ,illu/ration3 ,fig4 #bai4 #bjj4 ,eruptive ,prom95ces4--,! eruptive prom95ces ord9>ily consi/ ( brilliant spikes or jets1 :i* *ange v rapidly 9 =m & brightness4 ,z a rule1 _! altitude is n m ?an tw5ty ?\s& or ?irty ?\s& miles2 b occasionally !y rise f> high] ?an ev5 ! l>ge/ ( ! quiesc5t protub]ances4 ,_! spectrum is v complicat$1 especially ne> _! base1 & (t5 fill$ ) bright l9es4 ,! mo/ conspicu\s l9es are ^? ( sodium1 magnesium1 b>ium1 iron1 & titanium3 h5ce ,sec*i calls !m metallic prom95ces4 ,illu/ration3 ,fig4 #bbj4 ,!y usually appe> 9 ! imm$iate vic9ity ( a spot1 nev] v ne> ! sol> poles4 ,!y *ange ) su* rapidity1 t ! motion c almo/ be se5 ) ! eye4 ,sometimes1 9 ! c\rse ( fifte5 or tw5ty m9utes1 a mass ( ^! flames1 fifty ?\s& miles high1 w und]go a total trans=mation2 & 9 "s in/ances _! complete developm5t or disappe>ance takes no long] "t4 ,sometimes !y consi/ ( po9t$ rays1 div]g+ 9 all directions1 z repres5t$ 9 ,fig4 #bbj4 ,sometimes !y look l flames1 sometimes l %eaves ( gra91 sometimes l :irl+ wat]-sp\ts capp$ ) a great cl\d2 occasionally !y pres5t mo/ exactly ! appe>ance ( jets ( liquid fire1 ris+ & fall+ 9 graceful p>abolas2 frequ5tly !y c>ry on _! edges spirals l ! volutes ( an ,ionic column2 & cont9ually !y deta* filam5ts1 :i* rise to a great elevation1 gradually exp&+ & gr[+ fa9t] z !y asc5d1 until ! eye loses !m4 ,illu/ration3 ,fig4 #bba4 #bja4 ,*ange ( ,=m 9 ,prom95ces4--,fig4 #bba repres5ts a prom95ce z se5 by ,pr(essor ,"y1 ,sept4 #g1 #ahga4 ,x 0 an imm5se quiesc5t cl\d1 a hundr$ ?\s& miles long & fifty-f\r ?\s& miles high4 ,at a !re 0 a brilliant lump1 some:at 9 ! =m ( a ?und]-head4 ,on return+ to ! spectroscope less ?an half an h\r aft]w>ds1 he f\nd t ! cl\d _h be5 lit]ally bl[n into %r$s by "s inconceivable upru% f b5ea?4 ,! prom95ce !n pres5t$ ! =m %[n 9 ,fig4 #bbb4 ,! dbris ( ! cl\d _h already atta9$ a height ( a hundr$ ?\s& miles4 ,:ile he 0 wat*+ !m = ! next t5 m9utes1 !y rose1 ) a motion almo/ p]ceptible to ! eye1 till ! upp]mo/ rea*$ an altitude ( two hundr$ ?\s& miles4 ,z ! filam5ts rose1 !y gradually fad$ away l a dissolv+ cl\d4 ,illu/ration3 ,fig4 #bbb4 ,mean:ile ! little ?und]-head _h gr[n & develop$ into :at appe>$ to be a mass ( roll+ & ev]-*ang+ flame4 ,figs4 #bbc & #bbd give ! appe>ance ( ?is portion ( ! prom95ce at int]vals ( fifte5 m9utes4 ,o!r simil> eruptions h be5 obs]v$4 ,illu/ration3 ,fig4 #bbc4 ,illu/ration3 ,fig4 #bbd4 ,v4 ,,! ,,corona4 #bjb4 ,g5]al ,appe>ance ( ! ,corona4--,at ! "t ( a total eclipse ( ! sun1 if ! sky is cle>1 ! moon appe>s z a huge black ball1 ! illum9ation at ! edge ( ! disk be+ j suffici5t to br+ out its rotundity4 ,f beh9d x1 to borr[ ,pr(essor ,"y's vivid description1 /ream out on all sides radiant filam5ts1 beams1 & %eets ( pe>ly light1 :i* rea* to a di/ance sometimes ( sev]al degrees f ! sol> surface1 =m+ an irregul> /ellate halo1 ) ! black globe ( ! moon 9 its app>5t c5tre4 ,! portion ne>e/ ! sun is ( dazzl+ brightness1 b /ill less brilliant ?an ! prom95ces :i* blaze ?r\gh x l c>buncles4 ,g5]ally ?is inn] corona has a pretty uni=m height1 =m+ a r+ ?ree or f\r m9utes ( arc 9 wid?1 sep>at$ by a some:at def9ite outl9e f ! out] corona1 :i* rea*es to a mu* great] di/ance1 & is f> m irregul> 9 =m4 ,usually !re are sev]al rifts1 z !y h be5 call$1 l n>r[ beams ( d>kness1 ext5d+ f ! v edge ( ! sun to ! out] night1 & mu* resembl+ ! cl\d-%ad[s :i* radiate f ! sun be=e a ?und]-%[]2 b ! edges ( ^! rifts are frequ5tly curv$1 %[+ !m to be some?+ else ?an real %ad[s4 ,sometimes !re are n>r[ bright /ream]s1 z long z ! rifts1 or long]4 ,^! are (t5 incl9$1 occasionally are ev5 ne>ly tang5tial to ! sol> surface1 & frequ5tly are curv$4 ,on ! :ole1 ! corona is usually less ext5sive & brilliant ov] ! sol> poles1 & !re is a recognizable t5d5cy to accumulations above ! middle latitudes1 or spot-zones2 s t1 speak+ r\ghly1 ! corona %[s a disposition to assume ! =m ( a quadrilat]al or f\r-ray$ />1 ?\gh 9 almo/ e individual case ?is =m is greatly modifi$ by abnormal /ream]s at "s po9t or o!r4 ,illu/ration3 ,fig4 #bbe4 #bjc4 ,! ,corona z se5 at ,rec5t ,eclipses4--,! corona c be se5 only at ! "t ( a total eclipse ( ! sun1 & !n = only a few m9utes4 ,its =m v>ies consid]ably f "o eclipse to ano!r1 & app>5tly also dur+ ! same eclipse4 ,at lea/1 diff]5t obs]v]s at diff]5t /ations depict ! same corona "u v diff]5t =ms4 ,fig4 #bbe repres5ts ! corona ( #aheg z obs]v$ by ,liais4 ,9 ?is view ! petal-l =ms1 :i* h be5 notic$ 9 ! corona at o!r times1 are especially prom95t4 ,illu/ration3 ,fig4 #bbf4 ,fig4 #bbf %[s ! corona ( #ahfj z x 0 obs]v$ by ,temple4 ,illu/ration3 ,fig4 #bbg4 ,fig4 #bbg %[s ! corona ( #ahfg4 ,?is is int]e/+ z be+ a corona at ! "t ( sun-spot m9imum4 ,illu/ration3 ,fig4 #bbh4 ,fig4 #bbh repres5ts ! corona ( #ahfh4 ,?is is a l>g] & m irregul> corona ?an usual4 ,illu/ration3 ,fig4 #bbi4 ,! corona ( #ahfi is %[n 9 ,fig4 #bbi4 ,illu/ration3 ,fig4 #bcj4 ,fig4 #bcj is a view ( ! corona ( #ahga z se5 by ,capt4 ,tupman4 ,illu/ration3 ,fig4 #bca4 ,fig4 #bca %[s ! same corona z se5 by ,fo5&]4 ,illu/ration3 ,fig4 #bcb4 ,fig4 #bcb %[s ! same corona z photograph$ by ,davis4 ,illu/ration3 ,fig4 #bcc4 ,fig4 #bcc %[s ! corona ( #ahgh made up f sev]al views z comb9$ by ,pr(essor ,"y4 #bjd4 ,! ,spectrum ( ! ,corona4--,! *ief l9e 9 ! spectrum ( ! corona is ! "o usually designat$ z #adgd1 & n[ kn[n z ! coronal l9e4 ,x is se5 z a d>k l9e on ! disk ( ! sun2 & a spectroscope ( great disp]sive p[] %[s ?is d>k l9e to be closely d\ble1 ! l[] compon5t be+ "o ( ! iron l9es1 & ! upp] ! coronal l9e4 ,?is d>k l9e is %[n at x1 ,fig4 #bcd4 ,illu/ration3 ,fig4 #bcd4 ,besides ?is bright l9e1 ! hydrog5 l9es appe> fa9tly 9 ! spectrum ( ! corona4 ,! #adgd l9e has be5 sometimes trac$ ) ! spectroscope to an elevation ( ne>ly tw5ty m9utes above ! moon's limb1 & ! hydrog5 l9es ne>ly z f>2 & ! l9es 7 j z /rong 9 ! middle ( a d>k rift z any:]e else4 ,! sub/ance :i* produces ! #adgd l9e is unkn[n z yet4 ,x seems to be some?+ ) a vapor-d5sity f> bel[ t ( hydrog51 :i* is ! lighte/ sub/ance ( :i* we h any k4 ,x c h>dly be an allotropic =m ( any t]re/rial elem5t1 z "s sci5ti/s h sugge/$2 = 9 ! mo/ viol5t di/urbances 9 prom95ces & ne> sun-spots1 :5 ! l9es ( hydrog51 magnesium1 & o!r metals1 are contort$ & %att]$ by ! ru% ( ! cont5d+ elem5ts1 ?is l9e alone rema9s f9e1 %>p1 & /raight1 a little bright5$1 b n o!rwise affect$4 ,= ! pres5t x rema9s1 l a few o!r l9es 9 ! spectrum1 an unexpla9$ my/]y4 ,besides bright l9es1 ! corona %[s also a fa9t cont9u\s spectrum1 9 :i* h be5 obs]v$ a few ( ! m prom95t d>k l9es ( ! sol> spectrum4 ,?is %[s1 t1 :ile ! corona may be 9 ! ma9 compos$ ( gl[+ gas 7z indicat$ by ! bright l9es ( its spectrum71 x also conta9s consid]able matt] 9 su* a /ate z to reflect ! sunlight1 probably 9 ! =m ( du/ or fog4 ,v4 ,,eclipses4 ,illu/ration3 ,fig4 #bce4 #bje4 ,! ,%ad[s ( ! ,e>? & ,moon4--,! %ad[s ca/ by ! e>? & moon are %[n 9 ,fig4 #bce4 ,ea* %ad[ is se5 to be made up ( a d>k portion call$ ! umbra1 & ( a light] portion call$ ! p5umbra4 ,! light ( ! sun is completely exclud$ f ! umbra1 b only p>tially f ! p5umbra4 ,! umbra is 9 ! =m ( a cone1 ) its apex away f ! sun2 ?\gh 9 ! case ( ! e>?'s %ad[ x tap]s v sl[ly4 ,! p5umbra surr\nds ! umbra1 & increases 9 size z we rec$e f ! sun4 ,! axis ( ! e>?'s %ad[ lies 9 ! plane ( ! ecliptic1 :i* 9 ! figure is ! surface ( ! page4 ,z ! moon's orbit is incl9$ five degrees to ! plane ( ! ecliptic1 ! axis ( ! moon's %ad[ w sometimes lie above1 & sometimes bel[1 ! ecliptic4 ,x w lie on ! ecliptic only :5 ! moon is at "o ( h] nodes4 #bjf4 ,:5 !re w be an ,eclipse ( ! ,moon4--,! moon is eclips$ :5ev] x passes into ! umbra ( ! e>?'s %ad[4 ,x w be se5 f ! figure t ! moon c pass into ! %ad[ ( ! e>? only :5 %e is 9 opposition1 or at full4 ,ow+ to ! incl9ation ( ! moon's orbit to ! ecliptic1 ! moon w pass ei!r above or bel[ ! e>?'s %ad[ :5 %e is at full1 unless %e happ5s to be ne> h] node at ?is "t3 h5ce !re is n an eclipse ( ! moon e mon?4 ,:5 ! moon simply passes into ! p5umbra ( ! e>?'s %ad[1 ! light ( ! moon is some:at dimm$1 b n suffici5tly to attract att5tion1 or to be d5om9at$ an eclipse4 ,illu/ration3 ,fig4 #bcf4 #bjg4 ,! ,lun> ,ecliptic ,limits4--,9 ,fig4 #bcf ! l9e ,,ab repres5ts ! plane ( ! ecliptic1 & ! l9e ,,cd ! moon's orbit4 ,! l>ge black circles on ! l9e ,,ab repres5t sections ( ! umbra ( ! e>?'s %ad[1 & ! small] circles on ,,cd repres5t ! moon at full4 ,x w be se51 t1 if ! moon is full at ,e1 %e w j graze ! umbra ( ! e>?'s %ad[4 ,9 ?is case %e w suff] no eclipse4 ,7 ! moon full at any po9t ne>] h] node1 z at ,f1 %e w\ld pass into ! umbra ( ! e>?'s %ad[1 & w\ld be p>tially eclips$4 ,7 ! moon full at ,g1 %e w\ld pass ?r\gh ! c5tre ( ! e>?'s %ad[1 & be totally eclips$4 ,x w be se5 f ! figure t full moon mu/ occur :5 ! moon is )9 a c]ta9 di/ance f h] node1 9 ord] t !re may be a lun> eclipse2 & ?is space is call$ ! lun> ecliptic limits4 ,! f>!r ! e>? is f ! sun1 ! less rapidly does its %ad[ tap]1 & !re=e ! great] its diamet] at ! di/ance ( ! moon2 &1 ! ne>] ! moon to ! e>?1 ! great] ! diamet] ( ! e>?'s %ad[ at ! di/ance ( ! moon4 ,( c\rse1 ! great] ! diamet] ( ! e>?'s %ad[1 ! great] ! ecliptic limits3 h5ce ! lun> ecliptic limits v>y some:at f "t to "t1 accord+ to ! di/ance f ! e>? to ! sun & f ! e>? to ! moon4 ,! limits )9 :i* an eclipse is inevitable "u all circum/ances are call$ ! m9or ecliptic limits2 & ^? )9 :i* an eclipse is possible "u "s circum/ances1 ! major ecliptic limits4 ,illu/ration3 ,fig4 #bcg4 #bjh4 ,lun> ,eclipses4--,fig4 #bcg %[s ! pa? ( ! moon ?r\gh ! e>?'s %ad[ 9 ! case ( a p>tial eclipse4 ,! magnitude ( su* an eclipse dep5ds ^u ! ne>ness ( ! moon to h] nodes4 ,! magnitude ( an eclipse is usually d5ot$ 9 digits1 a digit be+ "o-twelf? ( ! diamet] ( ! moon4 ,illu/ration3 ,fig4 #bch4 ,fig4 #bch %[s ! pa? ( ! moon ?r\gh ! e>?'s %ad[ 9 ! case ( a total eclipse4 ,x w be se5 f ! figure t x is n necess>y = ! moon to pass ?r\gh ! c5tre ( ! e>?'s %ad[ 9 ord] to h a total eclipse4 ,:5 ! moon passes ?r\gh ! c5tre ( ! e>?'s %ad[1 ! eclipse is bo? total & c5tral4 ,at ! "t ( a total eclipse1 ! moon is n entirely invisible1 b %9es ) a fa9t copp]-color$ light4 ,?is light is refract$ into ! %ad[ by ! e>?'s atmosph]e1 & its am\nt v>ies ) ! quantity ( cl\ds & vapor 9 t portion ( ! atmosph]e :i* ! sunlight mu/ graze 9 ord] to rea* ! moon4 ,! duration ( an eclipse v>ies betwe5 v wide limits1 be+1 ( c\rse1 greate/ :5 ! eclipse is c5tral4 ,a total eclipse ( ! moon may la/ ne>ly two h\rs1 or1 includ+ ! p>tial portions ( ! eclipse1 ?ree or f\r h\rs4 ,e eclipse ( ! moon1 :e!r total or p>tial1 is visible at ! same "t to ! :ole hemisph]e ( ! e>? :i* is turn$ t[>ds ! moon2 & ! eclipse w h exactly ! same magnitude at e po9t ( obs]vation4 #bji4 ,:5 !re w be an ,eclipse ( ! ,sun4--,!re w be an eclipse ( ! sun :5ev] any portion ( ! moon's %ad[ is ?r[n on ! e>?4 ,x w be se5 f ,fig4 #bce t ?is c occur only :5 ! moon is 9 conjunction1 or at new4 ,x does n occur e mon?1 because1 ow+ to ! incl9ation ( ! moon's orbit to ! ecliptic1 ! moon's %ad[ is usually ?r[n ei!r above or bel[ ! e>? at ! "t ( new moon4 ,!re c be an eclipse ( ! sun only :5 new moon occurs at or ne> "o ( ! nodes ( h] orbit4 #baj4 ,sol> ,ecliptic ,limits4--,! di/ances f ! moon's node )9 :i* a new moon w\ld ?r[ "s portion ( its %ad[ on ! e>? s z to produce an eclipse ( ! sun are call$ ! sol> ecliptic limits4 ,z 9 ! case ( ! moon1 !re are major & m9or ecliptic limits2 ! =m] be+ ! limits )9 :i* an eclipse ( ! sun is possible "u "s circum/ances1 & ! latt] ^? "u :i* an eclipse is inevitable "u all circum/ances4 ,! limits )9 :i* a sol> eclipse may occur are great] ?an ^? )9 :i* a lun> eclipse may occur4 ,?is w be evid5t f an exam9ation ( ,fig4 #bce4 ,7 ! moon 9 t figure j outside ( ! l9es ,,ab & ,,cd1 x w be se5 t ! p5umbra ( h] %ad[ w\ld j graze ! e>?3 h5ce ! moon mu/ be some:]e )9 ! space b\nd$ by ^! l9es 9 ord] to cause an eclipse ( ! sun4 ,n[1 ^! l9es m>k ! prolongation to ! sun ( ! cone ( ! umbra ( ! e>?'s %ad[3 h5ce1 9 ord] to produce an eclipse ( ! sun1 new moon mu/ occur some:]e )9 ?is prolongation ( ! umbra ( ! e>?'s %ad[4 ,n[1 x is evid5t t ! diamet] ( ?is cone is great] on ! side ( ! e>? t[>d ! sun ?an on ! opposite side3 h5ce ! sol> ecliptic limits are great] ?an ! lun> ecliptic limits4 #baa4 ,sol> ,eclipses4--,an obs]v] 9 ! umbra ( ! moon's %ad[ w\ld see a total eclipse ( ! sun1 :ile "o 9 ! p5umbra w\ld see only a p>tial eclipse4 ,! magnitude ( ?is p>tial eclipse w\ld dep5d ^u ! di/ance ( ! obs]v] f ! umbra ( ! moon's %ad[4 ,illu/ration3 ,fig4 #bci4 ,illu/ration3 ,fig4 #bdj4 ,! umbra ( ! moon's %ad[ is j ab\t long en\gh to rea* ! e>?4 ,sometimes ! po9t ( ?is %ad[ falls %ort ( ! e>?'s surface1 z %[n 9 ,fig4 #bci1 & sometimes x falls ^u ! e>?1 z %[n 9 ,fig4 #bdj1 accord+ to ! v>y+ di/ance ( ! sun & moon f ! e>?4 ,! diamet] ( ! umbra at ! surface ( ! e>? is seldom m ?an a hundr$ miles3 h5ce ! belt ( a total eclipse is1 on ! av]age1 n m ?an a hundr$ miles wide2 & a total eclipse seldom la/s m ?an five or six m9utes1 & sometimes only a few seconds4 ,ow+1 h[ev]1 to ! rotation ( ! e>?1 ! umbra ( ! moon's %ad[ may pass ov] a long rea* ( ! e>?'s surface4 ,fig4 #bda %[s ! track ( ! umbra ( ! moon's %ad[ ov] ! e>? 9 ! total eclipse ( #ahfj4 ,illu/ration3 ,fig4 #bda4 ,illu/ration3 ,fig4 #bdb4 ,fig4 #bdb %[s ! track ( ! total eclipse ( #ahga across ,india & ! adjac5t seas4 ,illu/ration3 ,fig4 #bdc4 ,illu/ration3 ,fig4 #bdd4 ,9 a p>tial eclipse ( ! sun1 m or less ( "o side ( ! sun's disk is usually conceal$1 z %[n 9 ,fig4 #bdc4 ,occasionally1 h[ev]1 ! c5tre ( ! sun's disk is cov]$1 leav+ a bright r+ ar\nd ! m>g91 z %[n 9 ,fig4 #bdd4 ,su* an eclipse is call$ an annul> eclipse4 ,an eclipse c be annul> only :5 ! cone ( ! moon's %ad[ is too %ort to rea* ! e>?1 & !n only to obs]v]s :o are 9 ! c5tral portion ( ! p5umbra4 #bab4 ,comp>ative ,frequ5cy ( ,sol> & ,lun> ,eclipses4--,!re are m eclipses ( ! sun 9 ! ye> ?an ( ! moon2 & yet1 at any "o place1 eclipses ( ! moon are m frequ5t ?an ^? ( ! sun4 ,!re are m lun> ?an sol> eclipses1 because1 z we h se51 ! limits )9 :i* a sol> eclipse may occur are great] ?an ^? )9 :i* a lun> eclipse may occur4 ,!re are m eclipses ( ! moon visible at any "o place ?an ( ! sun2 because1 z we h se51 an eclipse ( ! moon1 :5ev] x does occur1 is visible to a :ole hemisph]e at a "t1 :ile an eclipse ( ! sun is visible to only a portion ( a hemisph]e1 & a total eclipse to only a v small portion ( a hemisph]e4 ,a total eclipse ( ! sun is1 !re=e1 a v r>e occurr5ce at any "o place4 ,! greate/ numb] ( eclipses t c occur 9 a ye> is sev51 & ! lea/ numb]1 two4 ,9 ! =m] case1 five may be ( ! sun & two ( ! moon1 or f\r ( ! sun & ?ree ( ! moon4 ,9 ! latt] case1 bo? mu/ be ( ! sun4 ,,vi4 ,,! ,,?ree ,,gr\ps ,,( ,,planets4 ,i4 ,,g5]al ,,*>act]i/ics ,,( ,,! ,,gr\ps4 #bac4 ,! ,inn] ,gr\p4--,! inn] gr\p ( planets is compos$ ( ,m]cury1 ,v5us1 ! ,e>?1 & ,m>s2 t is1 ( all ! planets :i* lie betwe5 ! a/]oids & ! sun4 ,! planets ( ?is gr\p are comp>atively small & d5se4 ,s f> z kn[n1 !y rotate on _! axes 9 ab\t tw5ty-f\r h\rs1 & !y are ei!r entirely )\t moons1 or are att5d$ by comp>atively few4 ,! comp>ative sizes & ecc5tricities ( ! orbits ( ?is gr\p are %[n 9 ,fig4 #bde4 ,! dots r\nd ! orbits %[ ! position ( ! planets at int]vals ( t5 days4 ,illu/ration3 ,fig4 #bde4 #bad4 ,! ,out] ,gr\p4--,! out] gr\p ( planets is compos$ ( ,jupit]1 ,saturn1 ,uranus1 & ,neptune4 ,^! planets are all v l>ge & ( slight d5sity4 ,s f> z kn[n1 !y rotate on _! axes 9 ab\t t5 h\rs1 & are accompani$ ) complicat$ sy/ems ( moons4 ,fig4 #bdf1 :i* repres5ts ! comp>ative sizes ( ! planets1 %[s at a glance ! imm5se diff]5ce betwe5 ^? ( ! inn] & out] gr\p4 ,fig4 #bdg %[s ! comp>ative sizes & ecc5tricities ( ! orbits ( ! out] planets4 ,! dots r\nd ! orbits %[ ! position ( ! planets at int]vals ( a ?\s& days4 ,illu/ration3 ,fig4 #bdf4 ,illu/ration3 ,fig4 #bdg4 #bae4 ,! ,a/]oids4--,betwe5 ! inn] & out] gr\ps ( planets !re is a great numb] ( v small planets kn[n z ! m9or planets1 or a/]oids4 ,ov] two hundr$ planets belong+ to ?is gr\p h already be5 discov]$4 ,_! orbits are %[n by ! dott$ l9es 9 ,fig4 #bdg4 ,! sizes ( ! f\r l>ge/ ( ^! planets1 comp>$ ) ! e>?1 are %[n 9 ,fig4 #bdh4 ,illu/ration3 ,fig4 #bdh4 ,! a/]oids ( ?is gr\p are di/+ui%$ f ! o!r planets1 n only by _! small size1 b by ! great ecc5tricities & incl9ations ( _! orbits4 ,if we except ,m]cury1 none ( ! l>g] planets has an ecc5tricity am\nt+ to "o-t5? ! diamet] ( its orbit 7#dc71 nor is any orbit incl9$ m ?an two or ?ree degrees to ! ecliptic2 b ! incl9ations ( _m ( ! m9or planets exce$ t5 degrees1 & ! ecc5tricities frequ5tly am\nt to an eigh? ( ! orbital diamet]4 ,! orbit ( ,pallas is incl9$ ?irty-f\r degrees to ! ecliptic1 :ile !re are "s planets ( ?is gr\p ^: orbits ne>ly co9cide ) ! plane ( ! ecliptic4 ,illu/ration3 ,fig4 #bdi4 ,fig4 #bdi %[s "o ( ! mo/ & "o ( ! lea/ ecc5tric ( ! orbits ( ?is gr\p z comp>$ ) t ( ! e>?4 ,illu/ration3 ,fig4 #bej4 ,! intricate complexity ( ! orbits ( ! a/]oids is %[n 9 ,fig4 #bej4 ,,ii4 ,,! ,,inn] ,,gr\p ,,( ,,planets4 ,m]cury4 #baf4 ,! ,orbit ( ,m]cury4--,! orbit ( ,m]cury is m ecc5tric ?an t ( any ( ! l>g] planets1 & x has also a great] incl9ation to ! ecliptic4 ,its ecc5tricity 7#dc7 is a little ov] a fif?1 & its incl9ation to ! ecliptic some:at ov] sev5 degrees4 ,! mean di/ance ( ,m]cury f ! sun is ab\t ?irty-five million miles2 b1 ow+ to ! great ecc5tricity ( its orbit1 its di/ance f ! sun v>ies f ab\t =ty-?ree million miles at aphelion to ab\t tw5ty-eight million at p]ihelion4 ,illu/ration3 ,fig4 #bea4 #bag4 ,di/ance ( ,m]cury f ! ,e>?4--,x is evid5t1 f ,fig4 #bea1 t an inf]ior planet1 l ,m]cury1 is ! :ole diamet] ( its orbit ne>] ! e>? at inf]ior conjunction ?an at sup]ior conjunction3 h5ce ,m]cury's di/ance f ! e>? v>ies consid]ably4 ,ow+ to ! great ecc5tricity ( its orbit1 its di/ance f ! e>? at inf]ior conjunction also v>ies consid]ably4 ,m]cury is ne>e/ to ! e>? :5 its inf]ior conjunction occurs at its own aphelion & at ! e>?'s p]ihelion4 ,illu/ration3 ,fig4 #beb4 #bah4 ,app>5t ,size ( ,m]cury4--,s9ce ,m]cury's di/ance f ! e>? is v>iable1 ! app>5t size ( ! planet is also v>iable4 ,fig4 #beb %[s its app>5t size at its extreme & mean di/ances f ! e>?4 ,its app>5t diamet] v>ies f five seconds to twelve seconds4 ,illu/ration3 ,fig4 #bec4 #bai4 ,volume & ,d5sity ( ,m]cury4--,! real diamet] ( ,m]cury is ab\t ?ree ?\s& miles4 ,its size1 comp>$ ) t ( ! e>?1 is %[n 9 ,fig4 #bec4 ,! e>? is ab\t sixte5 times z l>ge z ,m]cury2 b ,m]cury is ab\t "o-fif? m d5se ?an ! e>?4 #bbj4 ,greate/ ,elongation ( ,m]cury4--,m]cury1 be+ an inf]ior planet 7or "o )9 ! orbit ( ! e>?71 appe>s to oscillate to & fro across ! sun4 ,its greate/ app>5t di/ance f ! sun1 or its greate/ elongation1 v>ies consid]ably4 ,! f>!r ,m]cury is f ! sun1 & ! ne>] ! e>? is to ,m]cury1 ! great] is its angul> di/ance f ! sun at ! "t ( its greate/ elongation4 ,"u ! mo/ favorable circum/ances1 ! greate/ elongation am\nts to ab\t tw5ty-eight degrees1 & "u ! lea/ favorable to only sixte5 or sev5te5 degrees4 #bba4 ,sid]eal & ,synodical ,p]iods ( ,m]cury4--,m]cury accompli%es a complete revolution ar\nd ! sun 9 ab\t eighty-eight days2 b x takes x a hundr$ & sixte5 days to pass f its greate/ elongation ea/ to ! same elongation aga94 ,! orbital motion ( ?is planet is at ! rate ( ne>ly ?irty miles a second4 ,9 ,fig4 #bea1 ,p''' repres5ts elongation ea/ ( ! sun1 & ,p' elongation we/4 ,x w be se5 t x is mu* f>!r f ,p' ar\nd to ,p''' ?an f ,p''' on to ,p'4 ,m]cury is only ab\t =ty-eight days 9 pass+ f greate/ elongation ea/ to greate/ elongation we/1 :ile x is ab\t sixty-eight days 9 pass+ back aga94 #bbb4 ,visibility ( ,m]cury4--,m]cury is too close to ! sun = favorable obs]vation4 ,x is nev] se5 long aft] sunset1 or long be=e sunrise1 & nev] f> f ! horizon4 ,:5 visible at all1 x mu/ be s\ght = l[ d[n 9 ! we/ %ortly aft] sunset1 or l[ 9 ! ea/ %ortly be=e sunrise1 accord+ z ! planet is at its ea/ or we/ elongation4 ,x is (t5 visible to ! nak$ eye 9 our latitude2 b ! illum9ation ( ! twilight sky1 & ! excess ( vapor 9 our atmosph]e ne> ! horizon1 comb9e to make ! telescopic /udy ( ! planet difficult & unsatisfactory4 ,illu/ration3 ,fig4 #bed4 #bbc4 ,! ,atmosph]e & ,surface ( ,m]cury4--,m]cury seems to be surr\nd$ by a d5se atmosph]e4 ,"o pro( ( ! exi/5ce ( su* an atmosph]e is furni%$ at ! "t ( ! planet's transit across ! disk ( ! sun1 :i* occasionally happ5s4 ,! planet is !n se5 surr\nd$ by a bord]1 z %[n 9 ,fig4 #bed4 ,a bright spot has also be5 obs]v$ on ! d>k disk ( ! planet dur+ a transit1 z %[n 9 ,fig4 #bee4 ,! bord] ar\nd ! planet seems to be due to ! action ( ! planet's atmosph]e2 b x is difficult to acc\nt = ! bright spot4 ,illu/ration3 ,fig4 #bee4 ,illu/ration3 ,fig4 #bef4 ,s*rt]1 a celebrat$ ,g]man a/ronom]1 at ab\t ! beg9n+ ( ! pres5t c5tury1 ?\ght t he detect$ spots & %ad+s on ! disk ( ! planet1 :i* indicat$ bo? ! pres5ce ( an atmosph]e & ( elevations4 ,! %ad+ along ! t]m9ator1 :i* seem$ to indicate ! pres5ce ( a twilight1 & !re=e ( an atmosph]e1 are %[n 9 ,fig4 #bef4 ,x also %[s ! blunt$ aspect ( "o ( ! cusps1 :i* ,s*rt] notic$ at times1 & :i* he attribut$ to ! %ad[ ( a m\nta91 e/imat$ to be t5 or twelve miles high4 ,fig4 #beg %[s ?is m\nta9 ne> ! upp] cusp1 z ,s*rt] believ$ he saw x 9 ! ye> #ahjj4 ,by wat*+ c]ta9 m>ks ^u ! disk ( ,m]cury1 ,s*rt] came to ! conclusion t ! planet rotates on its axis 9 ab\t tw5ty-f\r h\rs4 ,mod]n obs]v]s1 ) m p[]ful telescopes1 h fail$ to v]ify ,s*rt]'s obs]vations z to ! indications ( an atmosph]e & ( elevations4 ,no?+ is kn[n ) c]ta9ty ab\t ! rotation ( ! planet4 ,illu/ration3 ,fig4 #beg4 ,! bord] ar\nd ,m]cury1 & ! bright spot on its disk at ! "t ( ! transit ( ! planet across ! sun1 h be5 se5 s9ce ,s*rt]'s "t1 & ! exi/5ce ( ^! ph5om5a is n[ well e/abli%$2 b a/ronom]s are f> f be+ agre$ z to _! cause4 #bbd4 ,intra-,m]curial ,planets4--,x has = "s "t be5 ?\ght probable t !re is a gr\p ( small planets betwe5 ,m]cury & ! sun2 & at v>i\s times ! discov]y ( su* bodies has be5 ann\nc$4 ,9 #ahei a ,fr5* obs]v] believ$ t he _h detect$ an intra-,m]curial planet1 to :i* ! "n ( ,vulcan 0 giv51 & = :i* c>eful se>* has s9ce be5 made1 b )\t success4 ,dur+ ! total eclipse ( #ahgh ,pr(essor ,watson obs]v$ two objects ne> ! sun1 :i* he ?\ght to be planets2 b ?is is /ill matt] ( controv]sy4 ,v5us4 #bbe4 ,! ,orbit ( ,v5us4--,! orbit ( ,v5us has b slight ecc5tricity1 diff]+ less f a circle ?an t ( any o!r l>ge planet4 ,x is incl9$ to ! ecliptic some:at m ?an ?ree degrees4 ,! mean di/ance ( ! planet f ! sun is ab\t sixty-sev5 million miles4 #bbf4 ,di/ance ( ,v5us f ! ,e>?4--,! di/ance ( ,v5us f ! e>? v>ies )9 mu* wid] limits ?an t ( ,m]cury4 ,:5 ,v5us is at inf]ior conjunction1 h] di/ance f ! e>? is n9ety-two million miles m9us sixty-sev5 million miles1 or tw5ty-five million miles2 & :5 at sup]ior conjunction x is n9ety-two million miles plus sixty-sev5 million miles1 or a hundr$ & fifty-n9e million miles4 ,v5us is consid]ably m ?an six times z f> (f at sup]ior conjunction z at inf]ior conjunction4 ,illu/ration3 ,fig4 #beh4 #bbg4 ,app>5t ,size ( ,v5us4--,ow+ to ! great v>iation 9 ! di/ance ( ,v5us f ! e>?1 h] app>5t diamet] v>ies f ab\t t5 seconds to ab\t sixty-six seconds4 ,fig4 #beh %[s ! app>5t size ( ,v5us at h] extreme & mean di/ances f ! e>?4 #bbh4 ,volume & ,d5sity ( ,v5us4--,! real size ( ,v5us is ab\t ! same z t ( ! e>?1 h] diamet] be+ only ab\t ?ree hundr$ miles less4 ,! comp>ative sizes ( ! two planets are %[n 9 ,fig4 #bei4 ,! d5sity ( ,v5us is a little less ?an t ( ! e>?4 ,illu/ration3 ,fig4 #bei4 #bbi4 ,! ,greate/ ,elongation ( ,v5us4--,v5us1 l ,m]cury1 appe>s to oscillate to & fro across ! sun4 ,! angul> value ( ! greate/ elongation ( ,v5us v>ies b slightly1 its greate/ value be+ ab\t =ty-sev5 degrees4 #bcj4 ,sid]eal & ,synodical ,p]iods ( ,v5us4--,! sid]eal p]iod ( ,v5us1 or t ( a complete revolution ar\nd ! sun1 is ab\t two hundr$ & tw5ty-five days2 h] orbital motion be+ at ! rate ( ne>ly tw5ty-two miles a second4 ,h] synodical p]iod1 or ! "t x takes h] to pass ar\nd f h] greate/ ea/]n elongation to ! same elongation aga91 is ab\t five hundr$ & eighty-f\r days1 or eighte5 mon?s4 ,v5us is a hundr$ & =ty-six days1 or ne>ly five mon?s1 9 pass+ f h] greate/ elongation ea/ ?r\gh inf]ior conjunction to h] greate/ elongation we/4 #bca4 ,v5us z a ,morn+ & an ,ev5+ ,/>4--,= a p]iod ( ab\t n9e mon?s1 :ile ,v5us is pass+ f sup]ior conjunction to h] greate/ ea/]n elongation1 %e w be ea/ ( ! sun1 & w !re=e set aft] ! sun4 ,dur+ ?is p]iod %e is ! ev5+ />1 ! ,hesp]us ( ! anci5ts4 ,:ile pass+ f inf]ior conjunction to sup]ior conjunction1 ,v5us is we/ ( ! sun1 & !re=e rises be=e ! sun4 ,dur+ ?is p]iod ( n9e mon?s %e is ! morn+ />1 ! ,phosphorus1 or ,lucif]1 ( ! anci5ts4 #bcb4 ,brilliancy ( ,v5us4--,next to ! sun & moon1 ,v5us is at times ! mo/ brilliant object 9 ! heav5s1 be+ bright en\gh to be se5 9 daylight1 & to ca/ a di/9ct %ad[ at night4 ,h] brightness1 h[ev]1 v>ies consid]ably1 ow+ to h] phases & to h] v>y+ di/ance f ! e>?4 ,%e does n appe> brighte/ :5 at full1 = %e is !n f>!/ f ! e>?1 at sup]ior conjunction2 nor does %e appe> brighte/ :5 ne>e/ ! e>?1 at inf]ior conjunction1 = h] phase is !n a ?9 cresc5t 7see ,fig4 #beh74 ,%e is mo/ conspicu\s :ile pass+ f h] greate/ ea/]n elongation to h] greate/ we/]n elongation4 ,aft] %e has pass$ h] ea/]n elongation1 %e becomes bright] & bright] till %e is )9 ab\t =ty degrees ( ! sun4 ,h] phase at ?is po9t 9 h] orbit is %[n 9 ,fig4 #bfj4 ,h] brilliancy !n beg9s to wane1 until %e comes too ne> ! sun to be visible4 ,:5 %e re-appe>s on ! we/ ( ! sun1 %e aga9 becomes m brilliant2 & h] brilliancy increases till %e is ab\t =ty degrees f ! sun1 :5 %e is aga9 at h] brighte/4 ,v5us passes f h] greate/ brilliancy z an ev5+ /> to h] greate/ brilliancy z a morn+ /> 9 ab\t sev5ty-?ree days4 ,%e has ! same phase1 & is at ! same di/ance f ! e>?1 9 bo? cases ( maximum brilliancy4 ,( c\rse1 ! brilliancy ( ,v5us :5 at ! maximum v>ies some:at f "t to "t1 ow+ to ! ecc5tricities ( ! orbits ( ! e>? & ( ,v5us1 :i* cause h] di/ance f ! e>?1 at h] phase ( greate/ brilliancy1 to v>y4 ,%e is mo/ brilliant :5 ! phase ( h] greate/ brilliancy occurs :5 %e is at h] aphelion & ! e>? at its p]ihelion4 ,illu/ration3 ,fig4 #bfj4 #bcc4 ,! ,atmosph]e & ,surface ( ,v5us4--,s*rt] believ$ t he saw %ad+s & m>k+s on ,v5us simil> to ^? on ,m]cury1 indicat+ ! pres5ce ( an atmosph]e & ( elevations on ! surface ( ! planet4 ,fig4 #bfa repres5ts ! surface ( ,v5us z x appe>$ to ?is a/ronom]4 ,by wat*+ c]ta9 m>k+s on ! disk ( ,v5us1 ,s*rt] came to ! conclusion t ,v5us rotates on h] axis 9 ab\t tw5ty-f\r h\rs4 ,illu/ration3 ,fig4 #bfa4 ,x is n[ g5]ally conc$$ t ,v5us has a d5se atmosph]e2 b ,s*rt]'s obs]vations ( ! spots on h] disk h n be5 v]ifi$ by mod]n a/ronom]s1 & we really "k no?+ c]ta9ly ( h] rotation4 #bcd4 ,transits ( ,v5us4--,:5 ,v5us happ5s to be ne> "o ( ! nodes ( h] orbit :5 %e is 9 inf]ior conjunction1 %e makes a transit across ! sun's disk4 ,^! transits occur 9 pairs1 sep>at$ by an int]val ( ov] a hundr$ ye>s4 ,! two transits ( ea* pair are sep>at$ by an int]val ( eight ye>s1 ! dates ( ! mo/ rec5t be+ #ahgd & #ahhb4 ,v5us1 l ,m]cury1 appe>s surr\nd$ ) a bord] on pass+ across ! sun's disk1 z %[n 9 ,fig4 #bfb4 ,illu/ration3 ,fig4 #bfb4 ,m>s4 #bce4 ,! ,orbit ( ,m>s4--,! orbit ( ,m>s is m ecc5tric ?an t ( any ( ! l>g] planets1 except ,m]cury2 its ecc5tricity be+ ab\t "o-elev5?4 ,! incl9ation ( ! orbit to ! ecliptic is some:at "u two degrees4 ,! mean di/ance ( ,m>s f ! sun is ab\t a hundr$ & =ty million miles2 b1 ow+ to ! ecc5tricity ( 8 orbit1 ! di/ance v>ies f a hundr$ & fifty-?ree million miles to a hundr$ & tw5ty-sev5 million miles4 ,illu/ration3 ,fig4 #bfc4 #bcf4 ,di/ance ( ,m>s f ! ,e>?4--,x w be se51 f ,fig4 #bfc1 t a sup]ior planet 7or "o outside ! orbit ( ! e>?71 l ,m>s1 is ne>] ! e>?1 by ! :ole diamet] ( ! e>?'s orbit1 :5 9 opposition ?an :5 9 conjunction4 ,! mean di/ance ( ,m>s f ! e>?1 at ! "t ( opposition1 is a hundr$ & =ty million miles m9us n9ety-two million miles1 or =ty-eight million miles4 ,ow+ to ! ecc5tricity ( ! orbit ( ! e>? & ( ,m>s1 ! di/ance ( ?is planet :5 9 opposition v>ies consid]ably4 ,:5 ! e>? is 9 aphelion1 & ,m>s 9 p]ihelion1 at ! "t ( opposition1 ! di/ance ( ! planet f ! e>? is only ab\t ?irty-?ree million miles4 ,on ! o!r h&1 :5 ! e>? is 9 p]ihelion1 & ,m>s 9 aphelion1 at ! "t ( opposition1 ! di/ance ( ! planet is ov] sixty-two million miles4 ,! mean di/ance ( ,m>s f ! e>? :5 9 conjunction is a hundr$ & =ty million miles plus n9ety-two million miles1 or two hundr$ & ?irty-two million miles4 ,x w !re=e be se5 t ,m>s is ne>ly five times z f> (f at conjunction z at opposition4 ,illu/ration3 ,fig4 #bfd4 #bcg4 ,! ,app>5t ,size ( ,m>s4--,ow+ to ! v>y+ di/ance ( ,m>s f ! e>?1 ! app>5t size ( ! planet v>ies almo/ z mu* z t ( ,v5us4 ,fig4 #bfd %[s ! app>5t size ( ,m>s at its extreme & mean di/ances f ! e>?4 ,! app>5t diamet] v>ies f ab\t f\r seconds to ab\t ?irty seconds4 ,illu/ration3 ,fig4 #bfe4 #bch4 ,! ,volume & ,d5sity ( ,m>s4--,among ! l>g] planets ,m>s is next 9 size to ,m]cury4 ,its real diamet] is some:at m ?an f\r ?\s& miles1 & its bulk is ab\t "o-sev5? ( t ( ! e>?4 ,its size1 comp>$ ) t ( ! e>?1 is %[n 9 ,fig4 #bfe4 ,illu/ration3 ,plate #d4 ,! d5sity ( ,m>s is only ab\t ?ree-f\r?s ( t ( ! e>?4 #bci4 ,sid]eal & ,synodical ,p]iods ( ,m>s4--,! sid]eal p]iod ( ,m>s1 or ! "t 9 :i* he makes a complete revolution ar\nd ! sun1 is ab\t six hundr$ & eighty-sev5 days1 or ne>ly tw5ty-?ree mon?s2 b he is ab\t sev5 hundr$ & eighty days 9 pass+ f opposition to opposition aga91 or 9 p]=m+ a synodical revolution4 ,m>s moves 9 8 orbit at ! rate ( ab\t fifte5 miles a second4 #bdj4 ,brilliancy ( ,m>s4--,:5 ne> 8 opposition1 ,m>s is easily recogniz$ ) ! nak$ eye by 8 fi]y-r$ light4 ,he is mu* m brilliant at "s oppositions ?an at o!rs1 = reasons already expla9$ 7#bcf71 b always %9es bright] ?an an ord9>y /> ( ! fir/ magnitude4 #bda4 ,telescopic ,appe>ance ( ,m>s4--,:5 view$ ) a good telescope 7see ,plate ,,iv471 ,m>s is se5 to be cov]$ ) dusky1 dull-r$ pat*es1 :i* are suppos$ to be cont95ts1 l ^? ( our own globe4 ,o!r portions1 ( a gre5i% hue1 are believ$ to be tracts ( wat]4 ,! ruddy color1 :i* ov]p[]s ! gre51 & makes ! :ole planet seem r$ to ! nak$ eye1 0 believ$ by ,sir ,j4 ,h]s*el to be due to an o*rey t+e 9 ! g5]al soil1 l t ( ! r$ s&/one di/ricts on ! e>?4 ,9 a telescope1 ,m>s appe>s less r$1 & ! high] ! p[] ! less ! int5sity ( ! color4 ,! disk1 :5 well se51 is mapp$ out 9 a way :i* gives at once ! impression ( l& & wat]4 ,! bright "p is r$ incl9+ to orange1 sometimes dott$ ) br[n & gre5i% po9ts4 ,! d>k] spaces1 :i* v>y greatly 9 dep? ( tone1 are ( a dull gray-gre51 hav+ ! aspect ( a fluid :i* absorbs ! sol> rays4 ,! proportion ( l& to wat] on ! e>? appe>s to be rev]s$ on ,m>s4 ,on ! e>? e cont95t is an isl&2 on ,m>s all seas are lakes4 ,long1 n>r[ /raits are m common ?an on ! e>?2 & wide expanses ( wat]1 l our ,atlantic ,ocean1 are r>e4 7,see ,fig4 #bff47 ,illu/ration3 ,fig4 #bff4 ,illu/ration3 ,fig4 #bfg4 ,fig4 #bfg repres5ts a *>t ( ! surface ( ,m>s1 :i* has be5 con/ruct$ f c>eful telescopic obs]vation4 ,! outl9es1 z se5 9 ! telescope1 are1 h[ev]1 mu* less di/9ct ?an !y are repres5t$ "h2 & x is by no means c]ta9 t ! light & d>k portions are bodies ( l& & wat]4 ,9 ! vic9ity ( ! poles brilliant :ite spots may be notic$1 :i* are consid]$ by _m a/ronom]s to be masses ( sn[4 ,?is conjecture is favor$ by ! fact t !y appe> to dim9i% "u ! sun's influ5ce at ! beg9n+ ( ! ,m>tial summ]1 & to increase aga9 on ! approa* ( w9t]4 #bdb4 ,rotation ( ,m>s4--,on wat*+ ,m>s ) a telescope1 ! spots on ! disk are f\nd to move 7z %[n 9 ,fig4 #bfh7 9 a mann] :i* indicates t ! planet rotates 9 ab\t tw5ty-f\r h\rs on an axis incl9$ ab\t tw5ty-eight degrees f a p]p5dicul> to ! plane ( its orbit4 ,! incl9ation ( ! axis is %[n 9 ,fig4 #bfi4 ,x is evid5t f ! figure t ! v>iation 9 ! l5g? ( day & night1 & ! *ange ( seasons1 are ab\t ! same on ,m>s z on ! e>?4 ,! *anges w1 ( c\rse1 be some:at great]1 & ! seasons w be ab\t twice z long4 ,illu/ration3 ,fig4 #bfh4 ,illu/ration3 ,fig4 #bfi4 ,illu/ration3 ,fig4 #bgj4 #bdc4 ,! ,satellites ( ,m>s4--,9 #ahgg ,pr(essor ,hall ( ! ,wa%+ton ,obs]vatory discov]$ t ,m>s is accompani$ by two small moons1 ^: orbits are %[n 9 ,fig4 #bgj4 ,! inn] satellite has be5 nam$ ,phobos1 & ! out] "o ,deimos4 ,x is e/imat$ t ! diamet] ( ! out] moon is f five to t5 miles1 & t ( ! inn] "o f t5 to =ty miles4 ,phobos is rem>kable = its ne>ness to ! planet & ! rapidity ( its revolution1 :i* is p]=m$ 9 sev5 h\rs ?irty-eight m9utes4 ,its di/ance f ! c5tre ( ! planet is ab\t six ?\s& miles1 & f ! surface less ?an f\r ?\s&4 ,a/ronom]s on ,m>s1 ) telescopes & eyes l ours1 c\ld readily f9d out :e!r ?is satellite is inhabit$1 ! di/ance be+ less ?an "o-sixtie? ( t ( our moon4 ,x w be se5 t ,phobos makes ab\t ?ree revolutions to "o rotation ( ! planet4 ,x w1 ( c\rse1 rise 9 ! we/2 ?\gh ! sun1 ! />s1 & ! o!r satellite rise 9 ! ea/4 ,deimos makes a complete revolution 9 ab\t ?irty h\rs4 ,,iii4 ,,! ,,a/]oids4 #bdd4 ,bode's ,law ( ,planet>y ,di/ances4--,!re is a v rem>kable law connect+ ! di/ances ( ! planets f ! sun1 :i* is g5]ally kn[n by ! "n ( ,bode's ,law4 ,att5tion 0 drawn to x 9 #aggh by ! a/ronom] ,bode1 b he 0 n really its au?or4 ,to express ?is law we write ! foll[+ s]ies ( numb]s3-- #j1 #c1 #f1 #ab1 #bd1 #dh1 #if2 ea* numb]1 ) ! exception ( ! fir/1 be+ d\ble ! "o :i* prec$es x4 ,if we add #d to ea* ( ^! numb]s1 ! s]ies becomes-- #d1 #g1 #aj1 #af1 #bh1 #eb1 #ajj2 :i* s]ies 0 kn[n to ,kepl]4 ,^! numb]s1 ) ! exception ( #bh1 are s5sibly proportional to ! di/ances ( ! pr9cipal planets f ! sun1 ! actual di/ances be+ z foll[s3-- ,m]cury4 ,v5us4 ,e>?4 ,m>s4 ---- ,jupit]4 ,saturn4 #ci #gb #aj #aeb #ebi #ied #bde4 ,! ,fir/ ,discov]y ( ! ,a/]oids4--,! great gap betwe5 ,m>s & ,jupit] l$ a/ronom]s1 f ! "t ( ,kepl]1 to suspect ! exi/5ce ( an unkn[n planet 9 ?is region2 b no su* planet 0 discov]$ till ! beg9n+ ( ! pres5t c5tury4 ,c]es 0 discov]$ ,jan4 #a1 #ahja1 ,pallas 9 #ahjb1 ,juno 9 #ahjd1 & ,ve/a 9 #ahjg4 ,!n foll[$ a long int]val ( ?irty-eight ye>s be=e ,a/ra1 ! fif? ( ^! m9or planets1 0 discov]$ 9 #ahde4 #bdf4 ,olb]s's ,hypo!sis4--,aft] ! discov]y ( ,pallas1 ,olb]s sugge/$ 8 celebrat$ hypo!sis1 t ! two bodies might be fragm5ts ( a s+le planet :i* _h be5 %att]$ by "s explosion4 ,if su* 7 ! case1 ! orbits ( all ! fragm5ts w\ld at fir/ int]sect ea* o!r at ! po9t :]e ! explosion occurr$4 ,he !re=e ?\ght x likely t o!r fragm5ts w\ld be f\nd1 especially if a se>* 7 kept up ne> ! int]section ( ! orbits ( ,c]es & ,pallas4 ,pr(essor ,newcomb makes ! foll[+ obs]vations conc]n+ ?is hypo!sis3-- ,! "q :e!r ^! bodies c\ld ev] h =m$ a s+le "o has n[ become "o ( cosmogony r ?an ( a/ronomy4 ,if a planet 7 %att]$1 ! orbit ( ea* fragm5t w\ld at fir/ pass ?r\gh ! po9t at :i* ! explosion occurr$1 h[ev] widely !y might be sep>at$ ?r\gh ! re/ ( _! c\rse2 b1 ow+ to ! secul> *anges produc$ by ! attractions ( ! o!r planets1 ?is co9cid5ce w\ld n cont9ue4 ,! orbits w\ld sl[ly move away1 & aft] ! lapse ( a few ?\s& ye>s no trace ( a common int]section w\ld be se54 ,x is !re=e curi\s t ,olb]s & 8 contempor>ies %\ld h expect$ to f9d su* a region ( int]section1 z x impli$ t ! explosion _h occurr$ )9 a few ?\s& ye>s4 ,! fact t ! requir$ conditions 7 n fulfill$ 0 no argum5t aga9/ ! hypo!sis1 because ! explosion might h occurr$ millions ( ye>s ago2 & 9 ! mean "t ! p]ihelion & node ( ea* orbit w\ld h made _m entire revolutions1 s t ! orbits w\ld h be5 completely mix$ up4444 ,a diff]5t explanation ( ! gr\p is giv5 by ! nebul> hypo!sis2 s t ,olb]s's hypo!sis is no long] consid]$ by a/ronom]s4 #bdg4 ,lat] ,discov]ies ( ,a/]oids4--,s9ce #ahde ov] two hundr$ a/]oids h be5 discov]$4 ,all ^! are s small1 t x requires a v good telescope to see !m2 & ev5 9 v p[]ful telescopes !y appe> z m]e po9ts ( light1 :i* c be di/+ui%$ f ! />s only by _! motions4 ,to facilitate ! discov]y ( ^! bodies1 v accurate maps h be5 con/ruct$1 includ+ all ! />s d[n to ! ?irte5? magnitude 9 ! neighborhood ( ! ecliptic4 ,a r$uc$ copy ( "o ( ^! maps is %[n 9 ,fig4 #bga4 ,illu/ration3 ,fig4 #bga4 ,furni%$ ) a map ( ?is k9d1 & ) a telescope p[]ful en\gh to %[ all ! />s m>k$ on x1 ! obs]v] :o is se>*+ = ^! small planets w place 9 ! field ( view ( 8 telescope six spid]-l9es at "r angles to ea* o!r1 & at equal di/ances ap>t1 9 su* a mann] t sev]al small squ>es w be =m$1 embrac+ j z mu* ( ! heav5s z d ^? %[n 9 ! map4 ,he w !n direct 8 telescope to ! region ( ! sky he wi%es to exam9e1 repres5t$ by ! map1 s z to be able to comp>e successively ea* squ>e ) ! correspond+ portion ( ! sky4 ,fig4 #bgb %[s at ! "r h& ! squ>es 9 ! telescopic field ( view1 & at ! left h& ! correspond+ squ>es ( ! map4 ,illu/ration3 ,fig4 #bgb4 ,he c !n assure himself if ! numb]s & positions ( ! />s mapp$1 & ( ! />s obs]v$1 are id5tical4 ,if he obs]ves 9 ! field ( view a lum9\s po9t :i* is n m>k$ 9 ! map1 x is evid5t t ei!r ! new body is a /> ( v>iable brightness :i* 0 n visible at ! "t ! map 0 made1 or x is a planet1 or p]haps a comet4 ,if ! new body rema9s fix$ at ! same po9t1 x is ! =m]2 b1 if x *anges its position ) reg>d to ! neighbor+ />s1 x is ! latt]4 ,! motion is g5]ally s s5sible1 t 9 ! c\rse ( "o ev5+ ! *ange ( position may be detect$2 & x c soon be det]m9$1 by ! direction & rate ( ! motion1 :e!r ! body is a planet or a comet4 ,,iv4 ,,out] ,,gr\p ,,( ,,planets4 ,jupit]4 #bdh4 ,orbit ( ,jupit]4--,! orbit ( ,jupit] is incl9$ only a little ov] "o degree to ! ecliptic2 & its ecc5tricity is only ab\t half ( t ( ,m>s1 be+ less ?an "o-tw5tie?4 ,! mean di/ance ( ,jupit] f ! sun is ab\t f\r hundr$ & eighty million miles2 b1 ow+ to ! ecc5tricity ( 8 orbit1 8 actual di/ance f ! sun ranges f f\r hundr$ & fifty-sev5 to five hundr$ & ?ree million miles4 #bdi4 ,di/ance ( ,jupit] f ! ,e>?4--,:5 ,jupit] is 9 opposition1 8 mean di/ance f ! e>? is f\r hundr$ & eighty million miles m9us n9ety-two million miles1 or ?ree hundr$ & eighty-eight million miles1 &1 :5 he is 9 conjunction1 f\r hundr$ & eighty million miles plus n9ety-two million miles1 or five hundr$ & sev5ty-two million miles4 ,x w be se5 t he is less ?an twice z f> (f 9 conjunction z 9 opposition1 & t ! ratio ( 8 greate/ to 8 lea/ di/ance is v mu* less ?an 9 ! case ( ,v5us & ,m>s4 ,?is is ow+ to 8 v mu* great] di/ance f ! sun4 ,ow+ to ! ecc5tricities ( ! orbits ( ! e>? & ( ,jupit]1 ! greate/ & lea/ di/ances ( ,jupit] f ! e>? v>y some:at f ye> to ye>4 ,illu/ration3 ,fig4 #bgc4 #bej4 ,! ,brightness & ,app>5t ,size ( ,jupit]4--,! app>5t diamet] ( ,jupit] v>ies f ab\t fifty seconds to ab\t ?irty seconds4 ,8 app>5t size at 8 extreme & mean di/ances f ! e>? is %[n 9 ,fig4 #bgc4 ,jupit] %9es ) a brilliant :ite light1 :i* exce$s t ( e o!r planet except ,v5us4 ,! planet is1 ( c\rse1 brighte/ :5 ne> opposition4 #bea4 ,! ,volume & ,d5sity ( ,jupit]4--,jupit] is ! giant planet ( our sy/em1 8 mass l>gely exce$+ t ( all ! o!r planets comb9$4 ,8 mean diamet] is ab\t eighty-five ?\s& miles2 b ! equatorial exce$s ! pol> diamet] by five ?\s& miles4 ,9 volume he exce$s our e>? ab\t ?irte5 hundr$ times1 b 9 mass only ab\t two hundr$ & ?irte5 times4 ,8 specific gravity is1 !re=e1 f> less ?an t ( ! e>?1 & ev5 less ?an t ( wat]4 ,! comp>ative size ( ,jupit] & ! e>? is %[n 9 ,fig4 #bgd4 ,illu/ration3 ,fig4 #bgd4 #beb4 ,! ,sid]eal & ,synodical ,p]iods ( ,jupit]4--,x takes ,jupit] ne>ly twelve ye>s to make a sid]eal revolution1 or a complete revolution ar\nd ! sun1 8 orbital motion be+ at ! rate ( ab\t eight miles a second4 ,8 synodical p]iod1 or ! "t ( 8 passage f opposition to opposition aga91 is ?ree hundr$ & n9ety-eight days4 #bec4 ,! ,telescopic ,aspect ( ,jupit]4--,!re are no really p]man5t m>k+s on ! disk ( ,jupit]2 b 8 surface pres5ts a v div]sifi$ appe>ance4 ,! e>li] telescopic obs]v]s descri$ d>k belts across x1 "o nor? ( ! equator1 & ! o!r s\? ( x4 ,) ! increase ( telescopic p[]1 x 0 se5 t ^! b&s 7 ( a m complex /ructure ?an _h be5 suppos$1 & consi/$ ( /ratifi$1 cl\d-l appe>ances1 v>y+ greatly 9 =m & numb]4 ,^! *ange s rapidly1 t ! face ( ! planet r>ely pres5ts ! same appe>ance on two successive nights4 ,!y are mo/ /rongly m>k$ at "s di/ance on ea* side ( ! planet's equator1 & ?us appe> z two belts "u a l[ magnify+ p[]4 ,bo? ! outl9es ( ! belts1 & ! color ( portions ( ! planet1 are subject to consid]able *anges4 ,! equatorial regions1 & ! spaces betwe5 ! belts g5]ally1 are (t5 ( a rosy t+e4 ,?is color is sometimes /rongly m>k$1 :ile at o!r times h>dly a trace ( x c be se54 ,a g5]al telescopic view ( ,jupit] is giv5 9 ,plate ,v4 ,illu/ration3 ,plate #e4 #bed4 ,! ,physical ,con/itution ( ,jupit]4--,f ! *angeability ( ! belts1 & ( ne>ly all ! visible features ( ,jupit]1 x is cle> t :at we see on t planet is n ! solid nucleus1 b cl\d-l =mations1 :i* cov] ! entire surface to a great dep?4 ,! planet appe>s to be cov]$ ) a deep & d5se atmosph]e1 fill$ ) ?ick masses ( cl\ds & vapor4 ,until rec5tly ?is cl\d-lad5 atmosph]e 0 suppos$ to be some:at l t ( our globe2 b at pres5t ! physical con/itution ( ,jupit] is believ$ to resemble t ( ! sun r ?an t ( ! e>?4 ,l ! sun1 he is bright] 9 ! c5tre ?an ne> ! edges1 z is %[n 9 ! transits ( ! satellites ov] 8 disk4 ,:5 ! satellite fir/ ent]s on ! disk1 x commonly seems l a bright spot on a d>k backgr\nd2 b1 z x approa*es ! c5tre1 x appe>s l a d>k spot on ! bright surface ( ! planet4 ,! c5tre is probably two or ?ree times bright] ?an ! edges4 ,?is may be1 z 9 ! case ( ! sun1 because ! light ne> ! edge passes ?r\gh a great] dep? ( atmosph]e1 & is dim9i%$ by absorption4 ,x has also be5 suspect$ t ,jupit] %9es p>tly by 8 own light1 & n :olly by reflect$ sunlight4 ,! planet _c1 h[ev]1 emit any great am\nt ( light2 =1 if x did1 ! satellites w\ld %9e by ?is light :5 !y are 9 ! %ad[ ( ! planet1 :]eas !y totally disappe>4 ,x is possible t ! bright] portions ( ! surface are f "t to "t slightly self-lum9\s4 ,illu/ration3 ,fig4 #bge4 ,aga93 ! int]ior ( ,jupit] seems to be ! seat ( an activity s enorm\s t x c be ascrib$ only to int5se heat4 ,rapid movem5ts are always occurr+ on 8 surface1 (t5 *ang+ its aspect 9 a few h\rs4 ,x is !re=e probable t ,jupit] is n yet cov]$ by a solid cru/1 & t ! fi]y int]ior1 :e!r liquid or gase\s1 is surr\nd$ by ! d5se vapors :i* cease to be lum9\s on ris+ into ! high] & cool] regions ( ! atmosph]e4 ,figs4 #bge & #bgf %[ ! disk ( ,jupit] z x appe>$ 9 ,decemb]1 #ahha4 ,illu/ration3 ,fig4 #bgf4 #bee4 ,rotation ( ,jupit]4--,spots are sometimes visible :i* are mu* m p]man5t ?an ! ord9>y m>k+s on ! belts4 ,! mo/ rem>kable ( ^! is ! great r$ spot1 :i* 0 fir/ obs]v$ 9 ,july1 #ahgh1 & is /ill to be se5 9 ,febru>y1 #ahhb4 ,x is %[n j above ! c5tre ( ! disk 9 ,fig4 #bge4 ,by wat*+ ^! spots f day to day1 ! "t ( ,jupit]'s axial rotation has be5 f\nd to be ab\t n9e h\rs & fifty m9utes4 ,! axis ( ,jupit] deviates b slightly f a p]p5dicul> to ! plane ( its orbit1 z is %[n 9 ,fig4 #bgg4 ,illu/ration3 ,fig4 #bgg4 ,,! ,,satellites ,,( ,,jupit]4 ,illu/ration3 ,fig4 #bgh4 #bef4 ,jupit]'s ,f\r ,moons4--,jupit] is accompani$ by f\r moons1 z %[n 9 ,fig4 #bgh4 ,! diamet]s ( ^! moons range f ab\t tw5ty-two hundr$ to ?irty-sev5 hundr$ miles4 ,! second f ! planet is ! smalle/1 & ! ?ird ! l>ge/4 ,! smalle/ is ab\t ! size ( our moon2 ! l>ge/ consid]ably exce$s ,m]cury1 & almo/ rivals ,m>s1 9 bulk4 ,! sizes ( ^! moons1 comp>$ ) ^? ( ! e>? & its moon1 are %[n 9 ,fig4 #bgi4 ,illu/ration3 ,fig4 #bgi4 ,! names ( ^! satellites1 9 ! ord] ( _! di/ance f ! planet1 are ,io1 ,europa1 ,ganym$e1 & ,calli/o4 ,_! times ( revolution range f ab\t a day & ?ree-f\r?s up to ab\t sixte5 days & a half4 ,_! orbits are %[n 9 ,fig4 #bhj4 ,illu/ration3 ,fig4 #bhj4 #beg4 ,! ,v>iability ( ,jupit]'s ,satellites4--,rem>kable v>iations 9 ! light ( ^! moons h l$ to ! supposition t viol5t *anges are tak+ place on _! surfaces4 ,x 0 =m]ly believ$1 t1 l our moon1 !y always pres5t ! same face to ! planet1 & t ! *anges 9 _! brilliancy are due to diff]5ces 9 ! lum9osity ( p>ts ( _! surface :i* are successively turn$ t[>ds u dur+ a revolution2 b c>eful measurem5ts ( _! light %[ t ?is hypo!sis does n acc\nt = ! *anges1 :i* are sometimes v sudd54 ,! satellites are too di/ant = exam9ation ( _! surfaces ) ! telescope3 h5ce x is impossible to give any c]ta9 explanation ( ^! ph5om5a4 ,illu/ration3 ,fig4 #bha4 #beh4 ,eclipses ( ,jupit]'s ,satellites4--,jupit]1 l ! e>?1 ca/s a %ad[ away f ! sun1 z %[n 9 ,fig4 #bha2 &1 :5ev] "o ( 8 moons passes into ?is %ad[1 x becomes eclips$4 ,on ! o!r h&1 :5ev] "o ( ! moons ?r[s its %ad[ on ,jupit]1 ! sun is eclips$ to t "p ( ! planet :i* lies )9 ! %ad[4 ,to ! inhabitants ( ,jupit] 7if !re are any1 & if !y c see ?r\gh ! cl\ds7 ^! eclipses mu/ be v famili> affairs2 = 9 consequ5ce ( ! small incl9ations ( ! orbits ( ! satellites to ! planet's equator1 & ! small incl9ation ( ! latt] to ! plane ( ,jupit]'s orbit1 all ! satellites1 except ! mo/ di/ant "o1 are eclips$ 9 e revolution4 ,a spectator on ,jupit] might !re=e witness dur+ ! planet>y ye> =ty-five hundr$ eclipses ( ! moons1 & ab\t ! same numb] ( ! sun4 ,illu/ration3 ,fig4 #bhb4 #bei4 ,transits ( ,jupit]'s ,satellites4--,:5ev] "o ( ,jupit]'s moons passes 9 front ( ! planet1 x is said to make a transit across 8 disk4 ,:5 a moon is mak+ a transit1 x pres5ts its bright hemisph]e t[>ds ! e>?1 z w be se5 f ,fig4 #bhb3 h5ce x is usually se5 z a bright spot on ! planet's disk2 ?\gh sometimes1 on ! bright] c5tral portions ( ! disk1 x appe>s d>k4 ,illu/ration3 ,fig4 #bhc4 ,x w be se5 f ,fig4 #bhb t ! %ad[ ( a moon does n fall ^u ! "p ( ! planet's disk t is cov]$ by ! moon3 h5ce we may obs]ve ! transit ( bo? ! moon & its %ad[4 ,! %ad[ appe>s z a small black spot1 :i* w prec$e or foll[ ! moon accord+ to ! position ( ! e>? 9 its orbit4 ,fig4 #bhc %[s two moons ( ,jupit] 9 transit4 #bfj4 ,occultations ( ,jupit]'s ,satellites4--,! eclipse ( a moon ( ,jupit] mu/ be c>efully di/+ui%$ f ! occultation ( a moon by ! planet4 ,9 ! case ( an eclipse1 ! moon ceases to be visible1 because ! mass ( ,jupit] is int]pos$ betwe5 ! sun & ! moon1 :i* ceases to be lum9\s1 because ! sun's light is cut (f2 b1 9 ! case ( an occupation1 ! moon gets into su* a position t ! body ( ,jupit] is int]pos$ betwe5 x & ! e>?1 ?us r5d]+ ! moon invisible to u4 ,! ?ird satellite1 m'' 7,fig4 #bhb71 is invisible f ! e>? ,e1 hav+ become occult$ :5 x pass$ beh9d ! planet's disk2 b x w n be eclips$ until x passes into ! %ad[ ( ,jupit]4 #bfa4 ,jupit] )\t ,satellites4--,x occasionally happ5s t e "o ( ,jupit]'s satellites w disappe> at ! same "t1 ei!r by be+ eclips$ or occult$1 or by be+ 9 transit4 ,9 ?is ev5t1 ,jupit] w appe> )\t satellites4 ,?is occurr$ on ! #ba/ ( ,augu/1 #ahfg4 ,! position ( ,jupit]'s satellites at ?is "t is %[n 9 ,fig4 #bhd4 ,illu/ration3 ,fig4 #bhd4 ,saturn4 ,,! ,,planet ,,& ,,8 ,,moons4 #bfb4 ,! ,orbit ( ,saturn4--,! orbit ( ,saturn is r m ecc5tric ?an t ( ,jupit]1 its ecc5tricity be+ some:at m ?an "o-tw5tie?4 ,its incl9ation to ! ecliptic is ab\t two degrees & a half4 ,! mean di/ance ( ,saturn f ! sun is ab\t eight hundr$ & eighty million miles4 ,x is ab\t a hundr$ million miles ne>] ! sun at p]ihelion ?an at aphelion4 #bfc4 ,di/ance ( ,saturn f ! ,e>?4--,! mean di/ance ( ,saturn f ! e>? at opposition is eight hundr$ & eighty million miles m9us n9ety-two million miles1 or sev5 hundr$ & eighty-eight million2 & at conjunction1 eight hundr$ & eighty million miles plus n9ety-two million1 or n9e hundr$ & sev5ty-two million4 ,ow+ to ! ecc5tricity ( ! orbit ( ,saturn1 8 di/ance f ! e>? at opposition & at conjunction v>ies by ab\t a hundr$ million miles at diff]5t times2 b he is s imm5sely f> away1 t ?is is only a small fraction ( 8 mean di/ance4 #bfd4 ,app>5t ,size & ,brightness ( ,saturn4--,! app>5t diamet] ( ,saturn v>ies f ab\t tw5ty seconds to ab\t f\rte5 seconds4 ,8 app>5t size at 8 extreme & mean di/ances f ! e>? is %[n 9 ,fig4 #bhe4 ,illu/ration3 ,fig4 #bhe4 ,! planet g5]ally %9es ) ! brilliancy ( a mod]ate fir/-magnitude />1 & ) a d+y1 r$di% light1 z if se5 ?r\gh a smoky atmosph]e4 #bfe4 ,volume & ,d5sity ( ,saturn4--,! real diamet] ( ,saturn is ab\t sev5ty ?\s& miles1 & its volume ov] sev5 hundr$ times t ( ! e>?4 ,! comp>ative size ( ! e>? & ,saturn is %[n 9 ,fig4 #bhf4 ,?is planet is a little m ?an half z d5se z ,jupit]4 ,illu/ration3 ,fig4 #bhf4 #bff4 ,! ,sid]eal & ,synodical ,p]iods ( ,saturn4--,saturn makes a complete revolution r\nd ! sun 9 a p]iod ( ab\t tw5ty-n9e ye>s & a half1 mov+ 9 8 orbit at ! rate ( ab\t six miles a second4 ,! planet passes f opposition to opposition aga9 9 a p]iod ( ?ree hundr$ & sev5ty-eight days1 or ?irte5 days ov] a ye>4 #bfg4 ,physical ,con/itution ( ,saturn4--,! physical con/itution ( ,saturn seems to resemble t ( ,jupit]2 b1 be+ twice z f> away1 ! planet _c be s well /udi$4 ,! f>!r an object is f ! sun1 ! less x is illum9at$2 &1 ! f>!r x is f ! e>?1 ! small] x appe>s3 h5ce !re is a d\ble difficulty 9 exam9+ ! m di/ant planets4 ,"u favorable circum/ances1 ! surface ( ,saturn is se5 to be div]sifi$ ) v fa9t m>k+s2 &1 ) high telescopic p[]s1 two or m v fa9t /reaks1 or belts1 may be disc]n$ p>allel to its equator4 ,^! belts1 l ^? ( ,jupit]1 *ange _! aspect f "t to "t2 b !y are s fa9t t ! *anges _c be easily foll[$4 ,x is only on r>e occasions t ! "t ( rotation c be det]m9$ f a /udy ( ! m>k+s4 #bfh4 ,rotation ( ,saturn4--,on ! ev5+ ( ,dec4 #g1 #ahgf1 ,pr(essor ,hall1 :o _h be5 obs]v+ ! satellites ( ,saturn ) ! great ,wa%+ton telescope 7#ah71 saw a brilliant :ite spot ne> ! equator ( ! planet4 ,x seem$ z if an imm5se eruption ( inc&esc5t matt] _h sudd5ly bur/ up f ! int]ior4 ,! spot gradually spread itself out into a long light /reak1 ( :i* ! brighte/ po9t 0 ne> ! we/]n end4 ,x rema9$ visible until ,janu>y1 :5 x became fa9t & ill-def9$1 & ! planet 0 lo/ 9 ! rays ( ! sun4 ,f all ! obs]vations on ?is spot1 ,pr(essor ,hall f\nd ! p]iod ( ,saturn to be t5 h\rs f\rte5 m9utes1 reckon+ by ! brighte/ "p ( ! /reak4 ,_h ! middle ( ! /reak be5 tak51 ! "t w\ld h be5 less1 because ! bright matt] seem$ to be c>ri$ along 9 ! direction ( ! planet's rotation4 ,if ?is motion 0 due to a w9d1 ! velocity ( ! curr5t mu/ h be5 betwe5 fifty & a hundr$ miles an h\r4 ,! axis ( ,saturn is incl9$ tw5ty-sev5 degrees f ! p]p5dicul> to its orbit4 ,illu/ration3 ,fig4 #bhg4 #bfi4 ,! ,satellites ( ,saturn4--,saturn is accompani$ by eight moons4 ,sev5 ( ^! are %[n 9 ,fig4 #bhg4 ,! names ( ^! satellites1 9 ! ord] ( _! di/ances f ! planet1 are giv5 9 ! accompany+ table3-- ,numb]4 ,"n4 ,di/ance ,sid]eal ,discov]]4 f ,p]iod4 ,planet #a ,mimas #abj1hjj #j #bb #cg #j4id ,h]s*el #b ,enceladus #aee1jjj #a #h #ec #a4cg ,h]s*el #c ,te?ys #aia1ijj #a #ba #ah #a4hh ,cass9i #d ,dione #bde1hjj #b #ag #da #b4gc ,cass9i #e ,rhea #cdc1djj #d #ab #be #d4ea ,cass9i #f ,titan #gif1ajj #ae #bb #da #ae4id ,huygh5s #g ,hyp]ion #ifc1cjj #ba #g #g #ba4bi ,bond #h ,japetus #b1cac1hjj #gi #g #ec #gi4cc ,cass9i ,! app>5t brightness or visibility ( ^! satellites foll[s ! ord] ( _! discov]y4 ,! smalle/ telescope w %[ ,titan1 & "o ( v mod]ate size w %[ ,japetus 9 ! we/]n "p ( its orbit4 ,an in/rum5t ( f\r or five in*es ap]ture w %[ ,rhea1 & p]haps ,te?ys & ,dione2 :ile sev5 or eight in*es are requir$ = ,enceladus1 ev5 at its greate/ elongation f ! planet4 ,mimas c r>ely be se5 except at its greate/ elongation1 & !n only ) an ap]ture ( twelve in*es or m4 ,hyp]ion c be detect$ only ) ! mo/ p[]ful telescopes1 on acc\nt ( its fa9tness & ! difficulty ( di/+ui%+ x f m9ute />s4 ,japetus1 ! out]mo/ satellite1 is rem>kable = ! fact1 t :ile1 9 "o "p ( its orbit1 x is ! brighte/ ( ! satellites except ,titan1 9 ! opposite "p x is almo/ z fa9t z ,hyp]ion1 & c be se5 only 9 l>ge telescopes4 ,:5 we/ ( ! planet1 x is bright2 :5 ea/ ( x1 fa9t4 ,?is peculi>ity has be5 acc\nt$ = by suppos+ t ! satellite1 l our moon1 always pres5ts ! same face to ! planet1 & t "o side ( x is :ite & ! o!r int5sely black2 b x is d\btful :e!r any kn[n sub/ance is s black z "o side ( ! satellite mu/ be to acc\nt = su* extraord9>y *anges ( brilliancy4 ,illu/ration3 ,fig4 #bhh4 ,titan1 ! l>ge/ ( ^! satellites1 is ab\t ! size ( ! l>ge/ satellite ( ,jupit]4 ,! relative sizes ( ! satellites are %[n 9 ,fig4 #bhh1 & _! orbits 9 ,fig4 #bhi4 ,illu/ration3 ,fig4 #bhi4 ,illu/ration3 ,fig4 #bij4 ,fig4 #bij %[s ! transit ( "o ( ! satellites1 & ( its %ad[1 across ! disk ( ! planet4 ,,! ,,r+s ,,( ,,saturn4 #bgj4 ,g5]al ,appe>ance ( ! ,r+s4--,saturn is surr\nd$ by a ?9 flat r+ ly+ 9 ! plane ( its equator4 ,?is r+ is probably less ?an a hundr$ miles ?ick4 ,! "p ( x ne>e/ ,saturn reflects little sunlight to u2 s t x has a dusky appe>ance1 & is n easily se51 al?\gh x is n q s d>k z ! sky se5 betwe5 x & ! planet4 ,! out] edge ( ?is dusky portion ( ! r+ is at a di/ance f ,saturn ( betwe5 two & ?ree times ! e>?'s diamet]4 ,outside ( ?is dusky "p ( ! r+ is a mu* bright] portion1 & outside ( ?is ano!r1 :i* is some:at fa9t]1 b /ill s mu* bright] ?an ! dusky "p z to be easily se54 ,! wid? ( ! bright] p>ts ( ! r+ is ov] ?ree times ! e>?'s diamet]4 ,to di/+ui% ! p>ts1 ! out] "o is call$ r+ ,a1 ! middle "o r+ ,b1 & ! dusky "o r+ ,c4 ,betwe5 ,a & ,b is an app>5tly op5 space1 ne>ly two ?\s& miles wide1 :i* looks l a black l9e on ! r+4 ,o!r divisions 9 ! r+ h be5 notic$ at times2 b ?is is ! only "o always se5 ) good telescopes at times :5 ei!r side ( ! r+ is 9 view f ! e>?4 ,! g5]al telescopic appe>ance ( ! r+ is %[n 9 ,fig4 #bia4 ,illu/ration3 ,fig4 #bia4 ,illu/ration3 ,fig4 #bib4 ,fig4 #bib %[s ! divisions ( ! r+s z !y 7 se5 by ,bond4 #bga4 ,phases ( ,saturn's ,r+4--,! r+ is incl9$ to ! plane ( ! planet's orbit by an angle ( tw5ty-sev5 degrees4 ,! g5]al aspect f ! e>? is ne>ly ! same z f ! sun4 ,z ! planet revolves ar\nd ! sun1 ! axis & plane ( ! r+ keep ! same direction 9 space1 j z ! axis ( ! e>? & ! plane ( ! equator d4 ,:5 ! planet is 9 "o "p ( its orbit1 we see ! upp] or nor!rn side ( ! r+ at an incl9ation ( tw5ty-sev5 degrees1 ! greate/ angle at :i* ! r+ c ev] be se54 ,?is phase ( ! r+ is %[n 9 ,fig4 #bic4 ,illu/ration3 ,fig4 #bic4 ,:5 ! planet has mov$ ?r\gh a qu>t] ( a revolution1 ! edge ( ! r+ is turn$ t[>ds ! sun & ! e>?2 &1 ow+ to its extreme ?9ness1 x is visible only 9 ! mo/ p[]ful telescopes z a f9e l9e ( light1 /ret*+ out on ea* side ( ! planet4 ,?is phase ( ! r+ is %[n 9 ,fig4 #bid4 ,illu/ration3 ,fig4 #bid4 ,all ! satellites1 except ,japetus1 revolve v ne>ly 9 ! plane ( ! r+3 consequ5tly1 :5 ! edge ( ! r+ is turn$ t[>ds ! e>?1 ! satellites seem to sw+ f "o side ( ! planet to ! o!r 9 a /raight l9e1 runn+ along ! ?9 edge ( ! r+ l beads on a /r+4 ,?is phase af=ds ! be/ opportunity ( see+ ! inn] satellites1 ,mimas & ,enceladus1 :i* at o!r times are obscur$ by ! brilliancy ( ! r+4 ,illu/ration3 ,fig4 #bie4 ,fig4 #bie %[s a phase ( ! r+ int]m$iate betwe5 ! la/ two4 ,:5 ! planet has mov$ n9ety degrees f>!r1 we aga9 see ! r+ at an angle ( tw5ty-sev5 degrees2 b n[ x is ! l[] or s\!rn side :i* is visible4 ,:5 x has mov$ n9ety degrees f>!r1 ! edge ( ! r+ is aga9 turn$ t[>ds ! e>? & sun4 ,illu/ration3 ,fig4 #bie4 ,! successive phases ( ,saturn's r+ dur+ a complete revolution are %[n 9 ,fig4 #bif4 ,x w be se5 t !re are two opposite po9ts ( ,saturn's orbit 9 :i* ! r+s are turn$ edgewise to u1 & two po9ts half-way betwe5 ! =m] 9 :i* ! r+ is se5 at its maximum incl9ation ( ab\t tw5ty-sev5 degrees4 ,s9ce ! planet p]=ms a revolution 9 tw5ty-n9e ye>s & a half1 ^! phases occur at av]age int]vals ( ab\t sev5 ye>s & f\r mon?s4 ,illu/ration3 ,fig4 #big4 ,illu/ration3 ,fig4 #bih4 #bgb4 ,disappe>ance ( ,saturn's ,r+4--,x w be se5 f ,fig4 #big t ! plane ( ! r+ may n be turn$ t[>ds ! sun & ! e>? at exactly ! same "t1 & also t ! e>? may sometimes come on "o side ( ! plane ( ! r+ :ile ! sun is %9+ on ! o!r4 ,9 ! figure1 ,e1 ,e'1 ,e''1 & ,e''' is ! orbit ( ! e>?4 ,:5 ,saturn is at ,s'1 or opposite1 at ,f1 ! plane ( ! r+ w pass ?r\gh ! sun1 & !n only ! edge ( ! r+ w be illum9$4 ,7 ,saturn at ,s1 & ! e>? at ,e'1 ! plane ( ! r+ w\ld pass ?r\gh ! e>?4 ,?is w\ld also be ! case 7 ! e>? at ,e'''1 & ,saturn at ,s''4 ,7 ,saturn at ,s or at ,s''1 & ! e>? f>!r to ! left or to ! "r1 ! sun w\ld be %9+ on "o side ( ! r+ :ile we %\ld be look+ on ! o!r4 ,9 all ^! cases ! r+ w disappe> entirely 9 a telescope ( ord9>y p[]4 ,) v p[]ful telescopes ! r+ w appe>1 9 ! fir/ two cases1 z a ?9 l9e ( light 7,fig4 #bih74 ,x w be se5 t all ^! cases ( disappe>ance mu/ take place :5 ,saturn is 9 ! p>ts ( 8 orbit int]cept$ betwe5 ! p>allel l9es ,,ac & ,,bd4 ,^! l9es are tang5t to ! e>?'s orbit1 :i* !y enclose1 & are p>allel to ! plane ( ,saturn's r+4 ,z ,saturn passes away f ^! two l9es on ei!r side1 ! r+s appe> m & m op54 ,:5 ! d>k side ( ! r+ is 9 view1 x appe>s z a black l9e cross+ ! planet2 & on su* occasions ! sunlight reflect$ f ! out] & inn] edges ( ! r+s ,a & ,b enables u to see traces ( ! r+ on ea* side ( ,saturn1 at lea/ 9 places :]e two su* reflections come ne>ly toge!r4 ,fig4 #bii illu/rates ?is reflection f ! edges at ! divisions ( ! r+s4 ,illu/ration3 ,fig4 #bii4 #bgc4 ,*anges 9 ,saturn's ,r+4--,! "q :e!r *anges are go+ on 9 ! r+s ( ,saturn is /ill unsettl$4 ,"s obs]v]s h believ$ t !y saw additional divisions 9 ! r+s f "t to "t2 b ^! may h be5 errors ( vision1 due p>tly to ! %ad+ :i* is kn[n to exi/ on portions ( ! r+4 ,pr(essor ,newcomb says1 ,z se5 ) ! great ,wa%+ton equatorial 9 ! autumn ( #ahgd1 !re 0 no great or sudd5 contra/ betwe5 ! inn] or d>k edge ( ! bright r+ & ! out] edge ( ! dusky r+4 ,!re 0 "s suspicion t ! "o %ad$ into ! o!r by ins5sible gradations4 ,no "o c\ld = a mom5t suppose1 z "s obs]v]s h1 t !re 0 a sep>ation betwe5 ^! two r+s4 ,all ^! consid]ations give rise to ! "q :e!r ! dusky r+ may n be gr[+ at ! exp5se ( ! inn] bright r+4 ,/ruve1 9 #ahea1 advanc$ ! />tl+ !ory t ! inn] edge ( ! r+ 0 gradually approa*+ ! planet1 ! :ole r+ spread+ inw>ds1 & mak+ ! c5tral op5+ small]4 ,! !ory 0 bas$ ^u ! descriptions & draw+s ( ! r+s by ! a/ronom]s ( ! sev5te5? c5tury1 especially ,huygh5s1 & ! measures made by lat] a/ronom]s up to #ahea4 ,?is suppos$ *ange 9 ! dim5sion ( ! r+ is %[n 9 ,fig4 #cjj4 ,illu/ration3 ,fig4 #cjj4 #bgd4 ,con/itution ( ,saturn's ,r+4--,! !ory n[ g5]ally held by a/ronom]s is1 t ! r+ is compos$ ( a cl\d ( satellites too small to be sep>ately se5 9 ! telescope1 & too close toge!r to admit ( visible int]vals betwe5 !m4 ,! r+ looks solid1 because its p>ts are too small & too num]\s to be se5 s+ly4 ,!y are l ! m9ute drops ( wat] t make up cl\ds & fogs1 :i* to our eyes seem l solid masses4 ,9 ! dusky r+ ! p>ticles may be s scatt]$ t we c see ?r\gh ! cl\d1 ! dusk9ess be+ due to ! bl5d+ ( light & d>kness4 ,"s believe1 h[ev]1 t ! dusk9ess is caus$ by ! d>k] color ( ! p>ticles r ?an by _! be+ f>!r ap>t4 ,uranus4 #bge4 ,orbit & ,dim5sions ( ,uranus4--,uranus1 ! smalle/ ( ! out] gr\p ( planets1 has a diamet] ( ne>ly ?irty-two ?\s& miles4 ,x is a little less d5se ?an ,jupit]1 & its mean di/ance f ! sun is ab\t sev5te5 hundr$ & sev5ty millions ( miles4 ,its orbit has ab\t ! same ecc5tricity z t ( ,jupit]1 & is incl9$ less ?an a degree to ! ecliptic4 ,uranus makes a revolution ar\nd ! sun 9 eighty-f\r ye>s1 mov+ at ! rate ( a little ov] f\r miles a second4 ,x is visible to ! nak$ eye z a /> ( ! six? magnitude4 ,z se5 9 a l>ge telescope1 ! planet has a decid$ly sea-gre5 color2 b no m>k+s h ) c]ta9ty be5 detect$ on its disk1 s t no?+ is really kn[n ) reg>d to its rotation4 ,fig4 #cja %[s ! comp>ative size ( ,uranus & ! e>?4 ,illu/ration3 ,fig4 #cja4 #bgf4 ,discov]y ( ,uranus4--,?is planet 0 discov]$ by ,sir ,william ,h]s*el 9 ,m>*1 #agha4 ,he 0 engag$ at ! "t 9 exam9+ ! small />s ( ! con/ellation ,gem9i1 or ! ,tw9s4 ,he notic$ t ?is object :i* _h attract$ 8 att5tion _h an appreciable disk1 & !re=e c\ld n be a />4 ,he also p]ceiv$ by its motion t x c\ld n be a nebula2 he !re=e conclud$ t x 0 a comet1 & ann\nc$ 8 discov]y z su*4 ,on attempt+ to compute its orbit1 x 0 soon f\nd t its motions c\ld be acc\nt$ = only on ! supposition t x 0 mov+ 9 a circul> orbit at ab\t twice ! di/ance ( ,saturn f ! sun4 ,x 0 !re=e recogniz$ z a new planet1 ^: discov]y ne>ly d\bl$ ! dim5sions ( ! sol> sy/em z x 0 !n kn[n4 #bgg4 ,! ,"n ( ! ,planet4--,h]s*el1 out ( complim5t to 8 patron1 ,george ,,iii41 propos$ to call ! new planet ,georgium ,sidus 7! ,georgian ,/>72 b ?is "n f\nd little favor4 ,! "n ( ,h]s*el 0 propos$1 & cont9u$ 9 use 9 ,engl& = a "t1 b did n meet ) g5]al approval4 ,v>i\s o!r names 7 sugge/$1 & f9ally t ( ,uranus 0 adopt$4 ,illu/ration3 ,fig4 #cjb4 #bgh4 ,! ,satellites ( ,uranus4--,uranus is accompani$ by f\r satellites1 ^: orbits are %[n 9 ,fig4 #cjb4 ,^! satellites are rem>kable = ! great incl9ation ( _! orbits to ! plane ( ! planet's orbit1 am\nt+ to ab\t eighty degrees1 & = _! retrograde motion2 t is1 !y move f ea/ to we/1 in/ead ( f we/ to ea/1 z 9 ! case ( all ! planets & ( all ! satellites previ\sly discov]$4 ,neptune4 #bgi4 ,orbit & ,dim5sions ( ,neptune4--,s f> z kn[n1 ,neptune is ! mo/ remote memb] ( ! sol> sy/em1 its mean di/ance f ! sun be+ tw5ty-sev5 hundr$ & sev5ty-five million miles4 ,?is di/ance is consid]ably less ?an twice t ( ,uranus4 ,neptune revolves ar\nd ! sun 9 a p]iod ( a little less ?an a hundr$ & sixty-five ye>s4 ,its orbit has b slight ecc5tricity1 & is incl9$ less ?an two degrees to ! ecliptic4 ,?is planet is consid]ably l>g] ?an ,uranus1 its diamet] be+ ne>ly ?irty-five ?\s& miles4 ,x is some:at less d5se ?an ,uranus4 ,neptune is invisible to ! nak$ eye1 & no telescope has reveal$ any m>k+s on its disk3 h5ce no?+ is c]ta9ly kn[n z to its rotation4 ,fig4 #cjc %[s ! comp>ative size ( ,neptune & ! e>?4 ,illu/ration3 ,fig4 #cjc4 #bhj4 ,! ,discov]y ( ,neptune4--,! discov]y ( ,neptune 0 made 9 #ahdf1 & is ju/ly reg>d$ z "o ( ! gr&e/ triumphs ( a/ronomy4 ,soon aft] ,uranus 0 discov]$1 c]ta9 irregul>ities 9 its motion 7 obs]v$1 :i* c\ld n be expla9$4 ,x is well kn[n t ! planets are all ! :ile di/urb+ ea* o!r's motions1 s t none ( !m describe p]fect ellipses4 ,^! mutual di/urbances are call$ p]turbations4 ,9 ! case ( ,uranus x 0 f\nd1 t1 aft] mak+ due all[ance = ! action ( all ! kn[n planets1 !re 7 /ill c]ta9 p]turbations 9 its c\rse :i* _h n be5 acc\nt$ =4 ,?is l$ a/ronom]s to ! suspicion t ^! might be caus$ by an unkn[n planet4 ,lev]ri] 9 ,france1 & ,adams 9 ,engl&1 indep5d5tly ( ea* o!r1 set !mselves ! difficult problem ( comput+ ! position & magnitude ( a planet :i* w\ld produce ^! p]turbations4 ,bo?1 by a mo/ labori\s computation1 %[$ t ! p]turbations 7 su* z w\ld be produc$ by a planet revolv+ ab\t ! sun at ab\t twice ! di/ance ( ,uranus1 & hav+ a mass some:at great] ?an t ( ?is planet2 & bo? po9t$ out ! same "p ( ! heav5s z t 9 :i* ! planet ought to be f\nd at t "t4 ,almo/ imm$iately aft] !y _h ann\nc$ ! conclusion to :i* !y _h arriv$1 ! planet 0 f\nd ) ! telescope4 ,! a/ronom] :o 0 se>*+ = ! planet at ! sugge/ion ( ,lev]ri] 0 ! fir/ to recognize x3 h5ce ,lev]ri] has obta9$ ! *ief cr$it ( ! discov]y4 ,! obs]v$ planet is prov$ to be ne>] ?an ! "o pr$ict$ by ,lev]ri] & ,adams1 & !re=e ( small] magnitude4 #bha4 ,! ,obs]v$ ,planet n ! ,pr$ict$ ,"o4--,pr(essor ,peirce always ma9ta9$ t ! planet f\nd by obs]vation 0 n ! "o ^: exi/5ce _h be5 pr$ict$ by ,lev]ri] & ,adams1 ?\gh its action w\ld completely expla9 all ! irregul>ities 9 ! motion ( ,uranus4 ,8 la/ /atem5t on ?is po9t is z foll[s3 ,my position is1 t !re 7 two possible planets1 ei!r ( :i* might h caus$ ! obs]v$ irregul> motions ( ,uranus4 ,ea* planet exclud$ ! o!r2 s t1 if "o 01 ! o!r 0 n4 ,!y co9cid$ 9 direction f ! e>? at c]ta9 epo*s1 once 9 six hundr$ & fifty ye>s4 ,x 0 at "o ( ^! epo*s t ! pr$iction 0 made1 & at no o!r "t = six c5turies c\ld ! pr$iction ( ! "o planet h reveal$ ! o!r4 ,! obs]v$ planet 0 n ! pr$ict$ "o4 #bhb4 ,bode's ,law ,disprov$4--,! foll[+ table gives ! di/ances ( ! planets accord+ to ,bode's law1 _! actual di/ances1 & ! error ( ! law 9 ea* case3-- ,planet4 ,numb]s ( ,actual ,errors4 ,bode4 ,di/ances4 ,m]cury #j #d #d #c4i #j4a ,v5us #c #d #g #g4b #j4b ,e>? #f #d #aj #aj4j #j4j ,m>s #ab #d #af #ae4b #j4h ,m9or #bd #d #bh #bj to #ce planets ,jupit] #dh #d #eb #eb4j #j4j ,saturn #if #d #ajj #ie4d #d4f ,uranus #aib #d #aif #aia4i #d4a ,neptune #chd #d #chh #cjj4f #hg4d ,x w be se51 t1 be=e ! discov]y ( ,neptune1 ! agreem5t 0 s close z to indicate t ?is 0 an actual law ( ! di/ances2 b ! discov]y ( ?is planet completely disprov$ its exi/5ce4 ,illu/ration3 ,fig4 #cjd4 #bhc4 ,! ,satellite ( ,neptune4--,neptune is accompani$ by at lea/ "o moon1 ^: orbit is %[n 9 ,fig4 #cjd4 ,! orbit ( ?is satellite is incl9$ ab\t ?irty degrees to ! plane ( ! ecliptic1 & ! motion ( ! satellite is retrograde1 or f ea/ to we/4 ,,vii4 ,,comets ,,& ,,meteors4 ,i4 ,,comets4 ,g5]al ,ph5om5a ( ,comets4 #bhd4 ,g5]al ,appe>ance ( a ,bright ,comet4--,comets bright en\gh to be se5 ) ! nak$ eye are compos$ ( ?ree p>ts1 :i* run into ea* o!r by ins5sible gradations4 ,^! are ! nucleus1 ! coma1 & ! tail4 ,! nucleus is ! bright c5tre ( ! comet1 & appe>s to ! eye z a /> or planet4 ,! coma is a nebul\s mass surr\nd+ ! nucleus on all sides4 ,close to ! nucleus x is almo/ z bright z ! nucleus itself2 b x gradually %ades (f 9 e direction4 ,! nucleus & coma comb9$ appe> l a /> %9+ ?r\gh a small pat* ( fog2 & ^! two toge!r =m :at is call$ ! head ( ! comet4 ,! tail is a cont9uation ( ! coma1 & consi/s ( a /ream ( milky light1 gr[+ wid] & fa9t] z x rec$es f ! head1 till ! eye is unable to trace x4 ,illu/ration3 ,fig4 #cje4 ,! g5]al appe>ance ( "o ( ! small] ( ! brilliant comets is %[n 9 ,fig4 #cje4 ,illu/ration3 ,fig4 #cjf4 ,illu/ration3 ,fig4 #cjg4 #bhe4 ,g5]al ,appe>ance ( a ,telescopic ,comet4--,! great majority ( comets are too fa9t to be visible ) ! nak$ eye1 & are call$ telescopic comets4 ,9 ^! comets !re seems to be a developm5t ( coma at ! exp5se ( nucleus & tail4 ,9 "s cases ! telescope fails to reveal any nucleus at all 9 "o ( ^! comets2 at o!r times ! nucleus is s fa9t & ill-def9$ z to be b>ely di/+ui%able4 ,fig4 #cjf %[s a telescopic comet )\t any nucleus at all1 & ano!r ) a slight cond5sation at ! c5tre4 ,9 ^! comets x is g5]ally impossible to di/+ui% ! coma f ! tail1 ! latt] be+ ei!r entirely invisible1 z 9 ,fig4 #cjf1 or else only an elongation ( ! coma1 z %[n 9 ,fig4 #cjg4 ,_m comets appe> simply z pat*es ( foggy light ( m or less irregul> =m4 ,illu/ration3 ,fig4 #cjh4 #bhf4 ,! ,developm5t ( ,telescopic ,comets on _! ,approa* to ! ,sun4--,z a rule1 all comets look ne>ly alike :5 !y fir/ come )9 ! rea* ( ! telescope4 ,!y appe> at fir/ z little foggy pat*es1 )\t any tail1 & (t5 )\t any visible nucleus4 ,z !y approa* ! sun _! peculi>ities are rapidly develop$4 ,fig4 #cjh %[s su* a comet z fir/ se51 & ! gradual developm5t ( its nucleus1 head1 & tail1 z x approa*es ! sun4 ,illu/ration3 ,fig4 #cji4 ,illu/ration3 ,fig4 #caj4 ,illu/ration3 ,fig4 #caa4 ,if ! comet is only a small "o1 ! tail develop$ is small2 b ^! small app5dages h a great v>iety ( =m 9 diff]5t comets4 ,fig4 #cji %[s ! s+ul> =m into :i* ,encke's comet 0 develop$ 9 #ahga4 ,figs4 #caj & #caa %[ o!r peculi> developm5ts ( telescopic comets4 #bhg4 ,developm5t ( ,brilliant ,comets on _! ,approa* to ! ,sun4--,brilliant comets1 z well z telescopic comets1 appe> ne>ly alike :5 !y come into ! view ( ! telescope2 & x is only on _! approa* to ! sun t _! di/9ctive features are develop$4 ,n only d ^! comets1 :5 !y fir/ come into view1 resemble ea* o!r1 b !y also be> a close resemblance to telescopic comets4 ,z ! comet approa*es ! sun1 bright vapor\s jets1 two or ?ree 9 numb]1 are emitt$ f ! nucleus on ! side ( ! sun & 9 ! direction ( ! sun4 ,^! jets1 ?\gh direct$ t[>ds ! sun1 are soon m or less c>ri$ backw>d1 z if repell$ by ! sun4 ,fig4 #cab %[s a succession ( views ( ^! jets z !y 7 develop$ 9 ! case ( ,halley's comet 9 #ahce4 ,illu/ration3 ,fig4 #cab4 ,! jets 9 ?is case seem$ to h an oscillatory motion4 ,at #a & #b !y seem$ to be attract$ t[>ds ! sun1 & 9 #c to be repell$ by him4 ,9 #d & #e !y seem$ to be aga9 attract$1 & 9 #f to be repell$1 b 9 a rev]se direction to t 9 #c4 ,9 #g !y appe>$ to be aga9 attract$4 ,bessel lik5$ ?is oscillation ( ! jets to ! vibration ( a magnetic ne$le :5 pres5t$ to ! pole ( a magnet4 ,9 ! case ( l>g] comets ^! lum9\s jets are surr\nd$ by "o or m envelops1 :i* are ?r[n (f 9 succession z ! comet approa*es ! sun4 ,! =mation ( ^! envelops 0 a conspicu\s feature ( ,donati's comet ( #aheh4 ,a r\gh view ( ! jets & ! surr\nd+ envelops is giv5 9 ,fig4 #cac4 ,fig4 #cad gives a view ( ! envelops )\t ! jets4 ,illu/ration3 ,fig4 #cac4 ,illu/ration3 ,fig4 #cad4 #bhh4 ,! ,tails ( ,comets4--,! tails ( brilliant comets are rapidly =m$ z ! comet approa*es ! sun1 _! increase 9 l5g? (t5 be+ at ! rate ( sev]al million miles a day4 ,^! app5dages seem to be =m$ entirely out ( ! matt] :i* is emitt$ f ! nucleus 9 ! lum9\s jets :i* are at fir/ direct$ t[>ds ! sun4 ,! tails ( comets are1 h[ev]1 always direct$ away f ! sun1 z %[n 9 ,fig4 #cae4 ,illu/ration3 ,fig4 #cae4 ,x w be se5 t ! comet1 z x approa*es ! sun1 travels head =emo/2 b z x leaves ! sun x goes tail =emo/4 ,! app>5t l5g? ( ! tail ( a comet dep5ds p>tly ^u its real l5g?1 p>tly ^u ! di/ance ( ! comet1 & p>tly ^u ! direction ( ! axis ( ! tail ) ref]5ce to ! l9e ( vision4 ,! long] ! tail1 ! ne>] ! comet2 & ! m ne>ly at "r angles to ! l9e ( vision is ! axis ( ! tail1 ! great] is ! app>5t l5g? ( ! tail4 ,9 ! majority ( cases ! tails ( comets measure only a few degrees2 b1 9 ! case ( _m comets record$ 9 hi/ory1 ! tail has ext5d$ half way across ! heav5s4 ,! tail ( a comet1 :5 se5 at all1 is usually sev]al million miles 9 l5g?2 & 9 "s in/ances ! tail is long en\gh to rea* across ! orbit ( ! e>?1 or twice z f> z f ! e>? to ! sun4 ,! tails ( comets are app>5tly holl[1 & are sometimes a million ( miles 9 diamet]4 ,s great1 h[ev]1 is ! t5uity ( ! matt] 9 !m1 t ! fa9te/ />s are se5 ?r\gh x )\t any app>5t obscuration4 ,see ,fig4 #caf1 :i* is a view ( ! great comet ( #abfd4 ,illu/ration3 ,fig4 #caf4 ,illu/ration3 ,fig4 #cag4 ,illu/ration3 ,fig4 #cah4 ,illu/ration3 ,fig4 #cai4 ,illu/ration3 ,fig4 #cbj4 ,! tails ( comets are sometimes /raight1 z 9 ,fig4 #caf1 b usually m or less curv$1 z 9 ,fig4 #cag1 :i* is a view ( ,donati's comet z x appe>$ at "o "t4 ,! tail ( a comet is occasionally divid$ into a numb] ( /ream]s1 z 9 ,figs4 #cah & #cai4 ,fig4 #cah is a view ( ! great comet ( #agdd1 & ,fig4 #cai ( ! great comet ( #ahfa4 ,no4 #a1 9 ,fig4 #cbj1 is a view ( ! comet ( #aegg2 ,no4 #b1 ( ! comet ( #afhj2 & ,no4 #c1 ( ! comet ( #agfi4 ,illu/ration3 ,fig4 #cba4 ,fig4 #cba %[s "s ( ! =ms :i* ! imag9ation ( a sup]/iti\s age saw depict$ 9 comets1 :5 ^! heav5ly visitants 7 ?\ght to be ! =]unn]s ( w>s1 pe/il5ce1 fam9e1 & o!r dire calamities4 #bhi4 ,visibility ( ,comets4--,ev5 ! brighte/ comets are visible only a %ort "t ne> _! p]ihelion passage4 ,:5 ne> ! sun1 !y sometimes become v brilliant1 & on r>e occasions h be5 visible ev5 at mid-day4 ,x is seldom t a comet c be se51 ev5 ) a p[]ful telescope1 dur+ its p]ihelion passage1 unless its p]ihelion is ei!r inside ( ! e>?'s orbit1 or b little outside ( x4 ,motion & ,orig9 ( ,comets4 #bij4 ,recognition ( a ,telescopic ,comet4--,x is impossible to di/+ui% telescopic comets by _! appe>ance f ano!r class ( heav5ly bodies kn[n z nebul4 ,su* comets c be recogniz$ only by _! motion4 ,?us1 9 ,fig4 #cbb1 ! upp] & l[] bodies look exactly alike2 b ! upp] "o is f\nd to rema9 /ation>y1 :ile ! l[] "o moves across ! field ( view4 ,! upp] "o is ?us %[n to be a nebula1 & ! l[] "o a comet4 ,illu/ration3 ,fig4 #cbb4 #bia4 ,orbits ( ,comets4--,all comets are f\nd to move 9 v ecc5tric ellipses1 9 p>abolas1 or 9 hyp]bolas4 ,s9ce an ellipse is a clos$ curve 7#dh71 all comets t move 9 ellipses1 no matt] h[ ecc5tric1 are p]man5t memb]s ( ! sol> sy/em1 & w return to ! sun at int]vals ( great] or less l5g?1 accord+ to ! size ( ! ellipses & ! rate ( ! comet's motion4 ,p>abolas & hyp]bolas be+ op5 curves 7#dh71 comets t move 9 ei!r ( ^! orbits are only tempor>y memb]s ( our sol> sy/em4 ,aft] pass+ ! sun1 !y move (f into space1 nev] to return1 unless deflect$ hi!r by ! action ( "s heav5ly body :i* !y pass 9 _! j\rney4 ,illu/ration3 ,fig4 #cbc4 ,s9ce a comet is visible only :ile x is ne> ! sun1 x is impossible to tell1 by ! =m ( ! portion ( ! orbit :i* x describes dur+ ! p]iod ( its visibility1 :e!r x is a "p ( a v elongat$ ellipse1 a p>abola1 or a hyp]bola4 ,?us 9 ,fig4 #cbc are %[n two orbits1 "o ( :i* is a v elongat$ ellipse1 & ! o!r a p>abola4 ,! "p ab1 9 ea* case1 is ! portion ( ! orbit describ$ by ! comet dur+ its visibility4 ,:ile describ+ ! dott$ portions ( ! orbit1 ! comet is invisible4 ,n[ x is impossible to di/+ui% ! =m ( ! visible portion 9 ! two orbits4 ,! same w\ld be true 7 "o ( ! orbits a hyp]bola4 ,:e!r a comet w describe an ellipse1 a p>abola1 or a hyp]bola1 c be det]m9$ only by its velocity1 tak5 9 connection ) its di/ance f ! sun4 ,7 a comet n9ety-two & a half million miles f ! sun1 mov+ away f ! sun at ! rate ( tw5ty-six miles a second1 x w\ld h j ! velocity necess>y to describe a p>abola4 ,7 x mov+ ) a great] velocity1 x w\ld necess>ily describe a hyp]bola1 &1 ) a less velocity1 an ellipse4 ,s1 at any di/ance f ! sun1 !re is a c]ta9 velocity :i* w\ld cause a comet to describe a p>abola2 :ile a great] velocity w\ld cause x to describe a hyp]bola1 & a less velocity to describe an ellipse4 ,if ! comet is mov+ 9 an ellipse1 ! less its velocity1 ! less ! ecc5tricity ( its orbit3 h5ce1 9 ord] to det]m9e ! =m ( ! orbit ( any comet1 x is only necess>y to asc]ta9 its di/ance f ! sun1 & its velocity at any giv5 "t4 ,comets move 9 e direction 9 _! orbits1 & ^! orbits h e conceivable incl9ation to ! ecliptic4 #bib4 ,p]iodic ,comets4--,!re are q a numb] ( comets :i* are kn[n to be p]iodic1 return+ to ! sun at regul> int]vals 9 elliptic orbits4 ,"s ( ^! h be5 obs]v$ at sev]al returns1 s t _! p]iod has be5 det]m9$ ) great c]ta9ty4 ,9 ! case ( o!rs ! p]iodicity is inf]r$ f ! fact t ! velocity fell s f> %ort ( ! p>abolic limit t ! comet mu/ move 9 an ellipse4 ,! numb] ( kn[n p]iodic comets is increas+ e ye>1 ?ree hav+ be5 add$ to ! li/ 9 #ahha4 ,! velocity ( mo/ comets is s ne> ! p>abolic limit t x is n possible to decide1 f obs]vations1 :e!r x falls %ort ( x1 or exce$s x4 ,9 ! case ( a few comets ! obs]vations indicate a m9ute excess ( velocity2 b ?is _c be confid5tly ass]t$4 ,x is n1 !re=e1 absolutely c]ta9 t any kn[n comet revolves 9 a hyp]bolic orbit2 & ?us x is possible t all comets belong to our sy/em1 & w ultimately return to x4 ,x is1 h[ev]1 c]ta91 t1 9 ! majority ( cases1 ! return w be delay$ = _m c5turies1 & p]haps = _m ?\s& ye>s4 #bic4 ,orig9 ( ,comets4--,x is n[ g5]ally believ$ t ! orig9al home ( ! comets is 9 ! /ell> spaces outside ( our sol> sy/em1 & t !y are drawn t[>ds ! sun1 "o by "o1 9 ! long lapse ( ages4 ,7 ! sun unaccompani$ by planets1 or 7 ! planets immovable1 a comet ?us drawn 9 w\ld :irl ar\nd ! sun 9 a p>abolic orbit1 & leave x aga9 nev] to return1 unless its pa? 7 aga9 deflect$ by its approa* to "s />4 ,b1 :5 a comet is mov+ 9 a p>abola1 ! slighte/ ret>dation w\ld *ange its orbit to an ellipse1 & ! slighte/ accel]ation into a hyp]bola4 ,ow+ to ! motion ( ! sev]al planets 9 _! orbits1 ! velocity ( a comet w\ld be *ang$ on pass+ ea* ( !m4 ,:e!r its velocity w\ld be accel]at$ or ret>d$1 w\ld dep5d ^u ! way 9 :i* x pass$4 ,7 ! comet accel]at$ by ! action ( ! planets1 on its passage ?r\gh our sy/em1 m ?an x 0 ret>d$ by !m1 x w\ld leave ! sy/em ) a m ?an p>abolic orbit1 & w\ld !re=e move 9 a hyp]bola4 ,7 x1 on ! contr>y1 ret>d$ m ?an accel]at$ by ! action ( ! planets1 its velocity w\ld be r$uc$1 s t ! comet w\ld move 9 a m or less elongat$ ellipse1 & ?us become a p]man5t memb] ( ! sol> sy/em4 ,9 ! majority ( cases ! ret>dation w\ld be s slight t x c\ld n be detect$ by ! mo/ delicate obs]vation1 & ! comet w\ld return to ! sun only aft] ! expiration ( t5s or hundr$s ( ?\s&s ( ye>s2 b1 7 ! comet to pass v ne> "o ( ! l>g] planets1 ! ret>dation might be suffici5t to cause ! comet to revolve 9 an elliptical orbit ( q a %ort p]iod4 ,! orbit ( a comet ?us captur$ by a planet w\ld h its aphelion po9t ne> ! orbit ( ! planet :i* captur$ x4 ,n[1 x happ5s t ea* ( ! l>g] planets has a family ( comets ^: aphelia are ab\t its own di/ance f ! sun4 ,x is !re=e probable t ^! comets h be5 captur$ by ! action ( ^! planets4 ,z might be expect$ f ! gigantic size ( ,jupit]1 ! ,jovian family ( comets is ! l>ge/4 ,! orbits ( sev]al ( ! comets ( ?is gr\p are %[n 9 ,fig4 #cbd4 ,illu/ration3 ,fig4 #cbd4 #bid4 ,numb] ( ,comets4--,! numb] ( comets record$ z visible to ! nak$ eye s9ce ! bir? ( ,*ri/ is ab\t five hundr$1 :ile ab\t two hundr$ telescopic comets h be5 obs]v$ s9ce ! inv5tion ( ! telescope4 ,! total numb] ( comets obs]v$ s9ce ! ,*ri/ian era is !re=e ab\t sev5 hundr$4 ,x is c]ta91 h[ev]1 t only an insignificant fraction ( all exi/+ comets h ev] be5 obs]v$4 ,s9ce !y c be se5 only :5 ne> _! p]ihelion1 & s9ce x is probable t ! p]iod ( mo/ ( ^? :i* h be5 obs]v$ is reckon$ by ?\s&s ( ye>s 7if1 inde$1 !y ev] return at all71 our obs]vations mu/ be cont9u$ = _m ?\s& ye>s be=e we h se5 all :i* come )9 range ( our telescopes4 ,besides1 z already /at$ 7#bhi71 a comet c seldom be se5 unless its p]ihelion is ei!r inside ! orbit ( ! e>?1 or b little outside ( x2 & x is probable t ! p]ihelia ( ! great majority ( comets are beyond ?is limit ( visibility4 ,rem>kable ,comets4 #bie4 ,! ,comet ( #afhj4--,! great comet ( #afhj1 %[n 9 ,fig4 #cbj1 is "o ( ! mo/ celebrat$ on record4 ,x 0 by 8 /udy ( its motions t ,newton prov$ ! orbit ( a comet to be "o ( ! conic sections1 & !re=e t ^! bodies move "u ! influ5ce ( gravity4 ,?is comet desc5d$ almo/ 9 a direct l9e to ! sun1 pass+ ne>] to t lum9>y ?an any comet be=e kn[n4 ,newton e/imat$1 t1 at its p]ihelion po9t1 x 0 expos$ to a temp]ature two ?\s& times t ( r$-hot iron4 ,dur+ its p]ihelion passage x 0 exce$+ly brilliant4 ,halley suspect$ t ?is comet _h a p]iod ( five hundr$ & sev5ty-five ye>s1 & t its fir/ record$ appe>ance 0 9 #dc ,b4,c41 its ?ird 9 #aajf1 & its f\r? 9 #afhj4 ,if ?is is its real p]iod1 x w return 9 #bbee4 ,! comet ( #dc ,b4,c4 made its appe>ance j aft] ! assass9ation ( ,julius ,cs>4 ,! ,romans call$ x ! ,julian ,/>1 & reg>d$ x z a cele/ial *>iot s5t to convey ! s\l ( ,cs> to ! skies4 ,x 0 se5 two or ?ree h\rs be=e sunset1 & cont9u$ visible = eight successive days4 ,! great comet ( #aajf 0 describ$ z an object ( t]rific spl5dor1 & 0 visible 9 close proximity to ! sun4 ,! comet ( #afhj has become celebrat$1 n only on acc\nt ( its great brilliance1 & on acc\nt ( ,newton's inve/igation ( its orbit1 b also on acc\nt ( ! speculation ( ! !ologian ,:i/on 9 reg>d to x4 ,he accept$ five hundr$ & sev5ty-five ye>s z its p]iod1 & calculat$ t "o ( its e>li] app>itions mu/ h occurr$ at ! date ( ! flood1 :i* he suppos$ to h be5 caus$ by its ne> approa* to ! e>?2 & he imag9$ t ! e>? is doom$ to be de/roy$ by fire on "s future enc\nt] ) ?is comet4 ,illu/ration3 ,fig4 #cbe4 #bif4 ,! ,comet ( #ahaa4--,! great comet ( #ahaa1 a view ( :i* is giv5 9 ,fig4 #cbe1 is1 p]haps1 ! mo/ rem>kable comet on record4 ,x 0 visible = ne>ly sev5te5 mon?s1 & 0 v brilliant1 al?\gh at its p]ihelion passage x 0 ov] a hundr$ million miles f ! sun4 ,its tail 0 a hundr$ & tw5ty million miles 9 l5g?1 & sev]al million miles ?r\gh4 ,x has be5 calculat$ t its aphelion po9t is ab\t two hundr$ times z f> f ! sun z its p]ihelion po9t1 or "s sev5 times ! di/ance ( ,neptune f ! sun4 ,its p]iod is e/imat$ at ab\t ?ree ?\s& ye>s4 ,x 0 an object ( sup]/iti\s t]ror1 especially 9 ! ,ea/4 ,! ,russians reg>d$ x z presag+ ,napoleon's great & fatal w> ) ,russia4 ,illu/ration3 ,fig4 #cbf4 ,illu/ration3 ,fig4 #cbg4 #big4 ,halley's ,comet4--,halley's comet has become "o ( ! mo/ celebrat$ ( mod]n times4 ,x is ! fir/ comet ^: return 0 bo? pr$ict$ & obs]v$4 ,x made its appe>ance 9 #afhb4 ,halley comput$ its orbit1 & comp>$ x ) ^? ( previ\s comets1 ^: orbits he also comput$ f record$ obs]vations4 ,he f\nd t x co9cid$ s exactly ) t ( ! comet obs]v$ by ,kepl] 9 #afjg1 t !re c\ld be no d\bt ( ! id5tity ( ! two orbits4 ,s close 7 !y toge!r1 t1 7 !y bo? drawn 9 ! heav5s1 ! nak$ eye w\ld almo/ see !m jo9$ into "o l9e4 ,!re c\ld !re=e be no d\bt t ! comet ( #afhb 0 ! same t _h appe>$ 9 #afjg1 & t x mov$ 9 an elliptic orbit1 ) a p]iod ( ab\t sev5ty-five ye>s4 ,he f\nd t ?is comet _h previ\sly appe>$ 9 #aeca & 9 #adef2 & he pr$ict$ t x w\ld return ab\t #ageh4 ,its actual return 0 ret>d$ some:at by ! action ( ! planets on x 9 its passage ?r\gh ! sol> sy/em4 ,x1 h[ev]1 appe>$ aga9 9 #agei1 & a ?ird "t 9 #ahce4 ,its next appe>ance w be ab\t #aiaa4 ,! orbit ( ?is comet is %[n 9 ,fig4 #cbf4 ,fig4 #cbg %[s ! comet z x appe>$ to ! nak$ eye1 & 9 a telescope ( mod]ate p[]1 9 #ahce4 ,?is comet appe>s to be gr[+ less brilliant4 ,9 #adef x appe>$ z a comet ( great spl5dor2 & com+ z x did 9 a v sup]/iti\s age1 soon aft] ! fall ( ,con/ant9ople1 & dur+ ! ?reat5$ invasion ( ,europe by ! ,turks1 x caus$ great al>m4 ,fig4 #cbh %[s ! *anges und]gone by ! nucleus ( ?is comet dur+ its p]ihelion passage 9 #ahce4 ,illu/ration3 ,fig4 #cbh4 ,illu/ration3 ,fig4 #cbi4 ,illu/ration3 ,fig4 #ccj4 #bih4 ,encke's ,comet4--,?is telescopic comet1 two views ( :i* are giv5 9 ,figs4 #cbi & #ccj1 appe>$ 9 #ahah4 ,encke comput$ its orbit1 & f\nd x to lie :olly )9 ! orbit ( ,jupit] 7,fig4 #cbd71 & ! p]iod to be ab\t ?ree ye>s & a ?ird4 ,by comp>+ ! int]vals betwe5 ! successive returns ( ?is comet1 x has be5 asc]ta9$ t its orbit is cont9ually gr[+ small] & small]4 ,to acc\nt = ! ret>dation ( ?is comet1 ,olb]s ann\nc$ 8 celebrat$ hypo!sis1 t ! cele/ial spaces are fill$ ) a subtile resi/+ m$ium4 ,?is hypo!sis 0 adopt$ by ,encke1 & has be5 accept$ by c]ta9 o!r a/ronom]s2 b x has by no means ga9$ univ]sal ass5t4 #bii4 ,biela's ,comet4--,?is comet appe>$ 9 #ahbf1 & 0 f\nd to h a p]iod ( ab\t six ye>s & two ?irds4 ,on its return 9 #ahde1 x met ) a s+ul>1 & z yet unexpla9$1 accid5t1 :i* has r5d]$ ! o!rwise r insignificant comet fam\s4 ,9 ,novemb] & ,decemb] ( t ye> x 0 obs]v$ z usual1 )\t any ?+ rem>kable ab\t x2 b1 9 ,janu>y ( ! foll[+ ye>1 x 0 f\nd to h be5 divid$ into two di/9ct p>ts1 s z to appe> z two comets in/ead ( "o4 ,! two p>ts 7 at fir/ ( v unequal brightness2 b1 dur+ ! foll[+ mon?1 ! small] ( ! two increas$ 9 brilliancy until x equall$ its companion2 x !n grew fa9t] till x entirely disappe>$1 a mon? be=e its companion4 ,! two p>ts 7 ab\t two hundr$ ?\s& miles ap>t4 ,fig4 #cca %[s ^! two p>ts z !y appe>$ on ! #ai? ( ,febru>y1 & ,fig4 #ccb z !y appe>$ on ! #ba/ ( ,febru>y4 ,on its return 9 #aheb1 ! comets 7 f\nd /ill to be d\ble2 b ! two compon5ts 7 n[ ab\t a million & a half miles ap>t4 ,!y are %[n 9 ,fig4 #ccc z !y appe>$ at ?is "t4 ,sometimes "o ( ! p>ts appe>$ ! bright]1 & sometimes ! o!r2 s t x 0 impossible to decide :i* 0 really ! pr9cipal comet4 ,! two portions pass$ out ( view 9 ,septemb]1 & h n be5 se5 s9ce2 al?\gh 9 #ahgb ! position ( ! comet w\ld h be5 especially favorable = obs]vation4 ,! comet appe>s to h become completely brok5 up4 ,illu/ration3 ,fig4 #cca4 ,illu/ration3 ,fig4 #ccb4 ,illu/ration3 ,fig4 #ccc4 ,illu/ration3 ,fig4 #ccd4 #cjj4 ,! ,comet ( #ahdc4--,! great comet ( #ahdc1 a view ( :i* is giv5 9 ,fig4 #ccd1 0 favorably situat$ = obs]vation only 9 s\!rn latitudes4 ,x 0 exce$+ly brilliant1 & 0 easily se5 9 full daylight1 9 close proximity to ! sun4 ,! app>5t l5g? ( its tail 0 sixty-five degrees1 & its real l5g? a hundr$ & fifty million miles1 or ne>ly twice ! di/ance f ! e>? to ! sun4 ,?is comet is especially rem>kable on acc\nt ( its ne> approa* to ! sun4 ,at ! "t ( its p]ihelion passage ! di/ance ( ! comet f ! photosph]e ( ! sun 0 less ?an "o-f\rte5? ( ! diamet] ( ! sun4 ,?is di/ance 0 only "o-half t ( ! comet ( #afhj :5 at its p]ihelion4 ,:5 at p]ihelion1 ?is comet 0 plung+ ?r\gh ! sun's out] atmosph]e at ! rate ( "o million1 two hundr$ & eighty ?\s& miles an h\r4 ,x pass$ half way r\nd ! sun 9 ! space ( two h\rs1 & its tail 0 :irl$ r\nd ?r\gh a hundr$ & eighty degrees 9 t brief "t4 ,z ! tail ext5d$ almo/ d\ble ! e>?'s di/ance f ! sun1 ! end ( ! tail mu/ h trav]s$ 9 two h\rs a space ne>ly equal to ! circumf]5ce ( ! e>?'s orbit1--a di/ance :i* ! e>?1 mov+ at ! rate ( ab\t tw5ty miles a second1 is a :ole ye> 9 pass+4 ,x is almo/ impossible to suppose t ! matt] =m+ ?is tail rema9$ ! same ?r\gh\t ?is trem5d\s sweep4 #cja4 ,donati's ,comet4--,! great comet ( #aheh1 kn[n z ,donati's comet1 0 "o ( ! mo/ magnific5t ( mod]n times4 ,:5 at its brighte/ x 0 only ab\t fifty million miles f ! e>?4 ,its tail 0 !n m ?an fifty million miles long4 ,_h ! comet at ?is "t be5 directly betwe5 ! e>? & sun1 ! e>? mu/ h pass$ ?r\gh its tail2 b ?is did n occur4 ,! orbit ( ?is comet 0 f\nd to be decid$ly elliptic1 ) a p]iod ( ab\t two ?\s& ye>s4 ,?is comet is especially celebrat$ on acc\nt ( ! c>eful telescopic obs]vations ( its nucleus & coma at ! "t ( its p]ihelion passage4 ,att5tion has already be5 call$ 7#bhg7 to ! *anges x und]w5t at t "t4 ,its tail 0 curv$1 & ( a curi\s fea!r-l =m1 z %[n 9 ,fig4 #cce4 ,at times x develop$ lat]al /ream]s1 z %[n 9 ,fig4 #ccf4 ,fig4 #ccg %[s ! head ( ! comet z x 0 se5 by ,bond ( ! ,h>v>d ,obs]vatory1 ^: del9eations ( ?is comet h be5 ju/ly celebrat$4 ,illu/ration3 ,fig4 #cce4 ,illu/ration3 ,fig4 #ccf4 ,illu/ration3 ,fig4 #ccg4 #cjb4 ,! ,comet ( #ahfa4--,! great comet ( #ahfa is rem>kable = its great brilliancy1 = its peculi> fan-%ap$ tail1 & = ! probable passage ( ! e>? ?r\gh its tail4 ,sir ,john ,h]s*el decl>$ t x f> exce$$ 9 brilliancy any comet he _h ev] se51 n except+ ^? ( #ahaa & #aheh4 ,sec*i f\nd its tail to be a hundr$ & eighte5 degrees 9 l5g?1 ! l>ge/ b "o on record4 ,fig4 #cch %[s ?is comet z x appe>$ at "o "t4 ,fig4 #cci %[s ! position ( ! e>? at ,e1 9 ! tail ( ?is comet1 on ! #cj? ( ,june1 #ahfa4 ,fig4 #cdj %[s ! probable passage ( ! e>? ?r\gh ! tail ( ! comet on t date4 ,z ! tail ( a comet d\btless consi/s ( some?+ mu* less d5se ?an our atmosph]e1 x is n surpris+ t no noticeable effect 0 produc$ ^u u by ! enc\nt]1 if x occurr$4 ,illu/ration3 ,fig4 #cch4 ,illu/ration3 ,fig4 #cci4 ,illu/ration3 ,fig4 #cdj4 #cjc4 ,coggia's ,comet4--,?is comet1 :i* appe>$ 9 #ahgd1 look$ v l>ge1 because x came v ne> ! e>?4 ,x 0 n at all brilliant4 ,its nucleus 0 c>efully /udi$1 & 0 f\nd to develop a s]ies ( envelops simil> to ^? ( ,donati's comet4 ,figs4 #cda & #cdb are two views ( ! head ( ?is comet4 ,fig4 #cdc %[s ! sy/em ( envelops t 7 develop$ dur+ its p]ihelion passage4 ,illu/ration3 ,fig4 #cda4 ,illu/ration3 ,fig4 #cdb4 ,illu/ration3 ,fig4 #cdc4 #cjd4 ,! ,comet ( ,june1 #ahha4--,?is comet1 ?\gh f> f be+ "o ( ! l>ge/ ( mod]n times1 0 /ill v brilliant4 ,x w ev] be memorable z ! fir/ brilliant comet :i* has admitt$ ( c>eful exam9ation ) ! spectroscope4 ,connection betwe5 ,meteors & ,comets4 #cje4 ,%oot+-,/>s4--,on wat*+ ! heav5s any cle> night1 we frequ5tly see an appe>ance z ( a /> %oot+ rapidly ?r\gh a %ort space 9 ! sky1 & !n sudd5ly disappe>+4 ,?ree or f\r su* %oot+-/>s may1 on ! av]age1 be obs]v$ 9 ! c\rse ( an h\r4 ,!y are usually se5 only a second or two2 b !y sometimes move sl[ly1 & are visible mu* long]4 ,^! />s beg9 to be visible at an av]age height ( ab\t sev5ty-five miles1 & !y disappe> at an av]age height ( ab\t fifty miles4 ,!y are occasionally se5 z high z a hundr$ & fifty miles1 & cont9ue to be visible till )9 ?irty miles ( ! e>?4 ,_! visible pa?s v>y f t5 to a hundr$ miles 9 l5g?1 ?\gh !y are occasionally two hundr$ or ?ree hundr$ miles long4 ,_! av]age velocity1 relatively to ! e>?'s surface1 v>ies f t5 to =ty-five miles a second4 ,! av]age numb] ( %oot+-/>s visible to ! nak$ eye at any "o place is e/imat$ at ab\t a ?\s& an h\r2 & ! av]age numb] l>ge en\gh to be visible to ! nak$ eye1 t trav]se ! atmosph]e daily1 is e/imat$ at ov] eight millions4 ,! numb] ( telescopic %oot+-/>s w\ld ( c\rse be mu* great]4 ,occasionally1 %oot+-/>s leave beh9d !m a trail ( light :i* la/s = sev]al seconds4 ,^! trails are sometimes /raight1 z %[n 9 ,fig4 #cdd1 & sometimes curv$1 z 9 ,figs4 #cde & #cdf4 ,!y (t5 disappe> l trails ( smoke1 z %[n 9 ,fig4 #cdg4 ,illu/ration3 ,fig4 #cdd4 ,illu/ration3 ,fig4 #cde4 ,illu/ration3 ,fig4 #cdf4 ,illu/ration3 ,fig4 #cdg4 ,%oot+-/>s are se5 to move 9 all directions ?r\gh ! heav5s4 ,_! app>5t pa?s are1 h[ev]1 g5]ally incl9$ d[nw>d1 ?\gh sometimes upw>d2 & aft] midnight !y come 9 ! greate/ numb]s f t qu>t] ( ! heav5s t[>d :i* ! e>? is mov+ 9 its j\rney ar\nd ! sun4 #cjf4 ,meteors4--,occasionally ^! bodies are brilliant en\gh to illum9ate ! :ole heav5s4 ,!y are !n call$ meteors1 al?\gh ?is t]m is equally applicable to ord9>y %oot+-/>s4 ,su* a meteor is %[n 9 ,fig4 #cdh4 ,illu/ration3 ,fig4 #cdh4 ,sometimes ^! brilliant meteors are se5 to explode1 z %[n 9 ,fig4 #cdi2 & ! explosion is accompani$ ) a l\d detonation1 l ! dis*>ge ( cannon4 ,illu/ration3 ,fig4 #cdi4 ,ord9>y %oot+-/>s are n accompani$ by any audible s\nd1 ?\gh !y are sometimes se5 to break 9 pieces4 ,meteors :i* explode ) an audible s\nd are call$ detonat+ meteors4 #cjg4 ,a]olites4--,!re is no c]ta9 evid5ce t any deposit f ord9>y %oot+-/>s ev] rea*es ! surface ( ! e>?2 ?\gh a peculi> du/ has be5 f\nd 9 c]ta9 localities1 :i* has be5 suppos$ to be ( meteoric orig91 & :i* has be5 call$ meteoric du/4 ,b solid bodies occasionally desc5d to ! e>? f beyond our atmosph]e4 ,^! g5]ally p5etrate a foot or m into ! e>?1 &1 if pick$ up soon aft] _! fall1 are f\nd to be w>m1 & sometimes ev5 hot4 ,^! bodies are call$ a]olites4 ,:5 !y h a /ony appe>ance1 & conta9 b little iron1 !y are call$ meteoric /ones2 :5 !y h a metallic appe>ance1 & are compos$ l>gely ( iron1 !y are call$ meteoric iron4 ,!re are eighte5 well-au!nticat$ cases 9 :i* a]olites h fall5 9 ! ,unit$ ,/ates dur+ ! la/ sixty ye>s1 & _! aggregate weight is twelve hundr$ & fifty p\nds4 ,! entire numb] ( kn[n a]olites ! date ( ^: fall is well det]m9$ is two hundr$ & sixty-"o4 ,!re are also on record sev5ty-f\r cases ( :i* ! date is m or less unc]ta94 ,!re h also be5 f\nd eighty-six masses1 :i*1 f _! peculi> composition1 are believ$ to be a]olites1 ?\gh _! fall 0 n se54 ,! weight ( ^! masses v>ies f a few p\nds to sev]al tons4 ,! entire numb] ( a]olites ( :i* we h any k is !re=e ab\t f\r hundr$ & tw5ty4 ,a]olites are compos$ ( ! same elem5t>y sub/ances z occur 9 t]re/rial m9]als1 n a s+le new elem5t hav+ be5 f\nd 9 _! analysis4 ,( ! sixty or m elem5ts n[ recogniz$ by *emi/s1 ab\t tw5ty h be5 f\nd 9 a]olites4 ,:ile a]olites conta9 no new elem5ts1 _! appe>ance is q peculi>2 & ! comp\nds f\nd 9 !m are s peculi> z to enable u by *emical analysis to di/+ui% an a]olite f any t]re/rial sub/ance4 ,iron ores are v abundant 9 nature1 b iron 9 ! metallic /ate is exce$+ly r>e4 ,n[1 a]olites inv>iably conta9 metallic iron1 sometimes f n9ety to n9ety-six p] c5t4 ,?is iron is malleable1 & may be readily work$ into cutt+ in/rum5ts4 ,x always conta9s eight or t5 p] c5t ( nickel1 toge!r ) small quantities ( cobalt1 copp]1 t91 & *romium4 ,?is composition has nev] be5 f\nd 9 any t]re/rial m9]al4 ,a]olites also conta91 usually 9 small am\nt1 a comp\nd ( iron1 nickel1 & phosphorus1 :i* has nev] be5 f\nd else:]e4 ,meteorites (t5 pres5t ! appe>ance ( hav+ be5 fus$ on ! surface to a slight dep?1 & meteoric iron is f\nd to h a peculi> cry/all9e /ructure4 ,! ext]nal appe>ance ( a piece ( meteoric iron f\nd ne> ,lockport1 ,n4,y41 is %[n 9 ,fig4 #cej4 ,fig4 #cea %[s ! peculi> int]nal /ructure ( meteoric iron4 ,illu/ration3 ,fig4 #cej4 ,illu/ration3 ,fig4 #cea4 #cjh4 ,meteoroids4--,a/ronom]s n[ univ]sally hold t %oot+-/>s1 meteors1 & a]olites are all m9ute bodies1 revolv+1 l ! comets1 ab\t ! sun4 ,!y are mov+ 9 e possible direction ?r\gh ! cele/ial spaces4 ,!y may n av]age m ?an "o 9 a million ( cubic miles1 & yet _! total numb] exce$s all calculation4 ,( ! nature ( ! m9ut] bodies ( ?is class no?+ is c]ta9ly kn[n4 ,! e>? is cont9ually enc\nt]+ !m 9 its j\rney ar\nd ! sun4 ,!y are burn$ by pass+ ?r\gh ! upp] regions ( our atmosph]e1 & ! %oot+-/> is simply ! light ( t burn+4 ,^! bodies1 :i* are invisible till !y plunge into ! e>?'s atmosph]e1 are call$ meteoroids4 #cji4 ,orig9 ( ! ,light ( ,meteors4--,:5 "o ( ^! meteoroids ent]s our atmosph]e1 ! resi/ance ( ! air arre/s its motion to "s ext5t1 & s conv]ts a portion ( its en]gy ( motion into t ( heat4 ,! heat ?us develop$ is suffici5t to raise ! meteoroid & ! air ar\nd x to inc&esc5ce1 & 9 mo/ cases ei!r to cause ! meteoroid to burn up1 or to dissipate x z vapor4 ,! lum9\s vapor ?us =m$ con/itutes ! lum9\s tra9 :i* occasionally accompanies a meteor1 & (t5 disappe>s z a puff ( smoke4 ,:5 a meteoroid is l>ge en\gh & refractory en\gh to resi/ ! heat to :i* x is expos$1 its motion is suffici5tly arre/$1 on ent]+ ! l[] lay]s ( our atmosph]e1 to cause x to fall to ! e>?4 ,we !n h an a]olite4 ,a brilliant meteor diff]s f a %oot+-/> simply 9 magnitude4 #caj4 ,! ,int5sity ( ! ,heat to :i* a ,meteoroid is ,expos$4--,x has be5 asc]ta9$ by exp]im5t t a body mov+ ?r\gh ! atmosph]e at ! rate ( a hundr$ & tw5ty-five feet a second raises ! temp]ature ( ! air imm$iately 9 front ( x "o degree1 & t ! temp]ature increases z ! squ>e ( ! velocity ( ! mov+ body2 t is to say1 t1 ) a velocity ( two hundr$ & fifty feet1 ! temp]ature 9 front ( ! body w\ld be rais$ f\r degrees2 ) a velocity ( five hundr$ feet1 sixte5 degrees2 & s on4 ,to f9d1 !re=e1 ! temp]ature to :i* a meteoroid w\ld be expos$ 9 pass+ ?r\gh our atmosph]e1 we h m]ely to divide its velocity 9 feet p] second by a hundr$ & tw5ty-five1 & squ>e ! quoti5t4 ,) a velocity ( =ty-f\r miles a second 9 our atmosph]e1 a meteoroid w\ld !re=e be expos$ to a temp]ature ( betwe5 ?ree & f\r million degrees4 ,! air acts ^u ! body z if x 7 rais$ to ?is int5se heat4 ,at su* a temp]ature small masses ( ! mo/ refractory or incombu/ible sub/ances kn[n to u w\ld fla% into vapor ) ! evolution ( int5se light & heat4 ,if "o ( ^! meteoric bodies is l>ge en\gh to pass ?r\gh ! atmosph]e & rea* ! e>?1 )\t be+ volatiliz$ by ! heat1 we h an a]olite4 ,z x is only a few seconds 9 mak+ ! passage1 ! heat has n "t to p5etrate f> into its int]ior1 b is exp5d$ 9 melt+ & vaporiz+ ! out] portions4 ,! resi/ance ( ! d5s] /rata ( ! atmosph]e to ! motion ( ! a]olite sometimes becomes s enorm\s t ! body is sudd5ly r5t to pieces ) a l\d detonation4 ,x seems l an explosion produc$ by "s disruptive action )9 ! mass2 b !re c be little d\bt t x is due to ! velocity--p]haps t51 tw5ty1 or ?irty miles a second--) :i* ! body /rikes ! air4 ,if1 on ! o!r h&1 ! meteoroid is s small z to be burn$ up or volatiliz$ 9 ! upp] regions ( ! atmosph]e1 we h a common %oot+-/>1 or a meteor ( great] or less brilliancy4 ,illu/ration3 ,fig4 #ceb4 #caa4 ,meteoric ,%[]s4--,on ord9>y nights only f\r or five %oot+-/>s are se5 9 an h\r1 & ^! move 9 e direction4 ,_! orbits lie 9 all possible positions1 & are seem+ly scatt]$ at r&om4 ,su* meteors are call$ sporadic meteors4 ,on occasional nights1 %oot+-/>s are m num]\s1 & all move 9 a common direction4 ,su* a display is call$ a meteoric %[]4 ,^! %[]s diff] greatly 9 brilliancy2 b dur+ any "o %[] ! meteors all appe> to radiate f "s "o po9t 9 ! heav5s4 ,if we m>k on a cele/ial globe ! app>5t pa?s ( ! meteors :i* fall dur+ a %[]1 or if we trace !m back on ! cele/ial sph]e1 we %all f9d t !y all meet 9 ! same po9t1 z %[n 9 ,fig4 #ceb4 ,?is po9t is call$ ! radiant po9t4 ,x always appe>s 9 ! same position1 :]ev] ! obs]v] is situat$1 & does n p>take ( ! diurnal motion ( ! e>?4 ,z ! />s move t[>ds ! we/1 ! radiant po9t moves ) !m4 ,! po9t 9 "q is purely an effect ( p]spective1 be+ ! vani%+ po9t ( ! p>allel l9es 9 :i* ! meteors are actually mov+4 ,^! l9es are se51 n 9 _! real direction 9 space1 b z project$ on ! cele/ial sph]e4 ,if we look upw>ds1 & wat* sn[ fall+ ?r\gh a calm atmosph]e1 ! flakes :i* fall directly t[>ds u d n seem to move at all1 :ile ! surr\nd+ flakes seem to div]ge f !m on all sides4 ,s1 9 a meteoric %[]1 a meteor com+ directly t[>ds ! obs]v] does n seem to move at all1 & m>ks ! po9t f :i* all ! o!rs seem to radiate4 #cab4 ,! ,augu/ ,meteors4--,a meteoric %[] ( no great brilliancy occurs annually ab\t ! #aj? ( ,augu/4 ,! radiant po9t ( ?is %[] is 9 ! con/ellation ,p]seus1 & h5ce ^! meteors are (t5 call$ ! ,p]seids4 ,! orbit ( ^! meteoroids has be5 pretty accurately det]m9$1 & is %[n 9 ,fig4 #cec4 ,illu/ration3 ,fig4 #cec4 ,x w be se5 t ! p]ihelion po9t ( ?is orbit is at ab\t ! di/ance ( ! e>? f ! sun2 s t ! e>? enc\nt]s ! meteors once a ye>1 & ?is takes place 9 ! mon? ( ,augu/4 ,! orbit is a v ecc5tric ellipse1 rea*+ f> beyond ,neptune4 ,z ! meteoric display is ab\t equally brilliant e ye>1 x seems probable t ! meteoroids =m a /ream q uni=mly di/ribut$ ?r\gh\t ! :ole orbit4 ,x probably takes "o ( ! meteoroids ab\t a hundr$ & tw5ty-f\r ye>s to pass ar\nd ?is orbit4 ,illu/ration3 ,fig4 #ced4 #cac4 ,! ,novemb] ,meteors4--,a some:at brilliant meteoric %[] also occurs annually1 ab\t ! #ac? ( ,novemb]4 ,! radiant po9t ( ^! meteors is 9 ! con/ellation ,leo1 & h5ce !y are (t5 call$ ! ,leonids4 ,_! orbit has be5 det]m9$ ) great accuracy1 & is %[n 9 ,fig4 #ced4 ,:ile ! ,novemb] meteors are n usually v num]\s or bright1 a rem>kably brilliant display ( !m has be5 se5 once 9 ab\t ?irty-?ree or ?irty-f\r ye>s3 h5ce we inf]1 t1 :ile !re are "s meteoroids scatt]$ ?r\gh\t ! :ole ext5t ( ! orbit1 ! great majority are mass$ 9 a gr\p :i* trav]ses ! orbit 9 a little ov] ?irty-?ree ye>s4 ,a conjectural =m ( ?is cond5s$ gr\p is %[n 9 ,fig4 #cee4 ,! gr\p is s l>ge t x takes x two or ?ree ye>s to pass ! p]ihelion po9t3 h5ce !re may be a brilliant meteoric display two or ?ree ye>s 9 succession4 ,illu/ration3 ,fig4 #cee4 ,! la/ brilliant display ( ^! meteors 0 9 ! ye>s #ahff & #ahfg4 ,! display 0 visible 9 ?is c\ntry only a %ort "t be=e sunrise1 & !re=e did n attract g5]al att5tion4 ,! display ( #ahcc 0 rem>kably brilliant 9 ?is c\ntry1 & caus$ great con/]nation among ! ignorant & sup]/iti\s4 ,illu/ration3 ,fig4 #cef4 #cad4 ,connection betwe5 ,meteors & ,comets4--,x has be5 f\nd t a comet :i* appe>$ 9 #ahff1 & :i* is designat$ z #ahff1 ,i41 has exactly ! same orbit & p]iod z ! ,novemb] meteors1 & t ano!r comet1 kn[n z ! #ahfb1 ,,iii41 has ! same orbit z ! ,augu/ meteors4 ,x has also be5 asc]ta9$ t a ?ird comet1 #ahfa1 ,i41 has ! same orbit z a /ream ( meteors :i* ! e>? enc\nt]s 9 ,april4 ,fur!rmore1 x 0 f\nd1 9 #ahgb1 t !re 0 a small /ream ( meteors foll[+ 9 ! tra9 ( ! lo/ comet ( ,biela4 ,^! v>i\s orbits ( comets & meteoric /reams are %[n 9 ,fig4 #cef4 ,! co9cid5ce ( ! orbits ( comets & ( meteoric /reams indicates t ^! two classes ( bodies are v closely relat$4 ,!y und\bt$ly h a common orig94 ,! fact t !re is a /ream ( meteors 9 ! tra9 ( ,biela's comet has l$ to ! supposition t comets may become gradually dis9tegrat$ into meteoroids4 ,physical & ,*emical ,con/itution ( ,comets4 #cae4 ,physical ,con/itution ( ,telescopic ,comets4--,we h no c]ta9 k ( ! physical con/itution ( telescopic comets4 ,!y are usually t5s ( ?\s&s ( miles 9 diamet]1 & yet ( su* t5uity t ! smalle/ />s c readily be se5 ?r\gh !m4 ,x w\ld seem t !y mu/ %9e 9 "p by reflect$ light2 yet ! spectroscope %[s t _! spectrum is compos$ ( bright b&s1 :i* w\ld indicate t !y are compos$1 9 "p at lea/1 ( inc&esc5t gases4 ,x is1 h[ev]1 difficult to conceive h[ ^! gases become suffici5tly heat$ to be lum9\s2 & at ! same "t su* gases w\ld reflect no sunlight4 ,x seems probable t ^! comets are really made up ( a comb9ation ( small1 solid p>ticles 9 ! =m ( m9ute meteoroids1 & ( gases :i* are1 p]haps1 r5d]$ lum9\s by electric dis*>ges ( slight int5sity4 #caf4 ,physical ,con/itution ( ,l>ge ,comets4--,9 ! case ( l>ge comets ! nucleus is ei!r a d5se mass ( solid matt] sev]al hundr$ miles 9 diamet]1 or a d5se gr\p ( meteoroids4 ,pr(essor ,peirce e/imat$ t ! d5sity ( ! nucleus is at lea/ equal to t ( iron4 ,z su* a comet approa*es ! sun1 ! nucleus is1 to a slight ext5t1 vaporiz$1 & out ( ?is vapor is =m$ ! coma & ! tail4 ,t "s evaporat+ process is go+ on f ! nucleus ( ! comet is prov$ by ! movem5ts ( ! tail4 ,x is evid5t t ! tail _c be an app5dage c>ri$ along ) ! comet1 z x seems to be4 ,x is impossible t !re %\ld be any cohesion 9 matt] ( su* t5uity t ! smalle/ />s c\ld be se5 ?r\gh a million ( miles ( x1 & :i* is1 moreov]1 cont9ually *ang+ its =m4 ,!n1 aga91 z a comet is pass+ its p]ihelion1 ! tail appe>s to be :irl$ f "o side ( ! sun to ano!r ) a rapidity :i* w\ld te> x to pieces if ! movem5t 7 real4 ,! tail seems to be1 n some?+ atta*$ to ! comet1 & c>ri$ along ) x1 b a /ream ( vapor issu+ f x1 l smoke f a *imney4 ,! matt] ( :i* x is compos$ is cont9ually /ream+ outw>ds1 & cont9ually be+ replac$ by fre% vapor f ! nucleus4 ,! vapor1 z x emanates f ! nucleus1 is repell$ by ! sun ) a =ce (t5 two or ?ree times z great z ! ord9>y sol> attraction4 ,! mo/ probable explanation ( ?is ph5om5on is1 t x is a case ( electrical repulsion1 ! sun & ! p>ticles ( ! comet>y mi/ be+ simil>ly electrifi$4 ,) ref]5ce to ?is electrical !ory ( ! =mation ( comets' tails1 ,pr(essor ,peirce makes ! foll[+ obs]vation3 ,9 its approa* to ! sun1 ! surface ( ! nucleus is rapidly heat$3 x is melt$ & vaporiz$1 & subject$ to frequ5t explosions4 ,! vapor rises 9 its atmosph]e ) a well-def9$ upp] surface1 :i* is kn[n to obs]v]s z an envelop4444 ,! electrification ( ! comet>y mi/ is analog\s to t ( our own ?und]-cl\ds4 ,any portion ( ! coma :i* has receiv$ ! opposite k9d ( electricity to ! sun & to ! repell$ tail w be attract$4 ,?is gives a simple explanation ( ! negative tails :i* h be5 sometimes se5 direct$ t[>ds ! sun4 ,9 cases ( viol5t explosion1 ! :ole nucleus might be brok5 to pieces1 & ! coma da%$ ar\nd s z to give v>ieties ( tail1 & ev5 multiple tails4 ,!re seems1 inde$1 to be no obs]v$ ph5om5on ( ! tail or ! coma :i* is n consi/5t ) a reasonable modification ( ! !ory4 ,pr(essor ,peirce reg>d$ comets simply z ! l>ge/ ( ! meteoroids4 ,!y appe> to %9e p>tly by reflect$ sunlight1 & p>tly by _! own prop] light1 :i* seems to be t ( vapor r5d]$ lum9\s by an electric dis*>ge ( slight int5sity4 ,illu/ration3 ,fig4 #ceg4 #cag4 ,collision ( a ,comet & ! ,e>?4--,x sometimes happ5s t ! orbit ( a comet int]sects t ( ! e>?1 z is %[n 9 ,fig4 #ceg1 :i* %[s a portion ( ! orbit ( ,biela's comet1 ) ! positions ( ! comet & ( ! e>? 9 #ahcb4 ,( c\rse1 7 a comet & ! e>? bo? to rea* ! int]section ( _! orbits at ! same "t1 a collision ( ! two bodies w\ld be inevitable4 ,) ref]5ce to ! probable effect ( su* a collision1 ,pr(essor ,newcomb rem>ks1-- ,! "q is frequ5tly ask$1 ,:at w\ld be ! effect if a comet %\ld /rike ! e>?8 ,?is w\ld dep5d ^u :at sort ( a comet x 01 & :at "p ( ! comet came 9 contact ) our planet4 ,! latt] might pass ?r\gh ! tail ( ! l>ge/ comet )\t ! slighte/ effect be+ produc$2 ! tail be+ s ?9 & airy t a million miles ?ickness ( x looks only l gauze 9 ! sunlight4 ,x is n at all unlikely t su* a ?+ may h happ5$ )\t ev] be+ notic$4 ,a passage ?r\gh a telescopic comet w\ld be accompani$ by a brilliant meteoric %[]1 probably a f> m brilliant "o ?an has ev] be5 record$4 ,no m s]i\s dang] w\ld be enc\nt]$ ?an t aris+ f a possible fall ( meteorites2 b a collision betwe5 ! nucleus ( a l>ge comet & ! e>? might be a s]i\s matt]4 ,if1 z ,pr(essor ,peirce supposes1 ! nucleus is a solid body ( metallic d5sity1 _m miles 9 diamet]1 ! effect :]e ! comet /ruck w\ld be t]rific beyond conception4 ,at ! fir/ contact 9 ! upp] regions ( ! atmosph]e1 ! :ole heav5s w\ld be illum9at$ ) a respl5d5ce beyond t ( a ?\s& suns1 ! sky radiat+ a light :i* w\ld bl9d e eye t beheld x1 & a heat :i* w\ld melt ! h>de/ rocks4 ,a few seconds ( ?is1 :ile ! huge body 0 pass+ ?r\gh ! atmosph]e1 & ! collision at ! e>?'s surface w\ld 9 an in/ant r$uce ev]y?+ !re exi/+ to fi]y vapor1 & bury x miles deep 9 ! solid e>?4 ,happily1 ! *ances ( su* a calamity are s m9ute t !y ne$ n cause ! slighte/ uneas9ess4 ,!re is h>dly a possible =m ( dea? :i* is n a ?\s& times m probable ?an ?is4 ,s small is ! e>? 9 comp>ison ) ! cele/ial spaces1 t if "o %\ld %ut 8 eyes1 & fire a gun at r&om 9 ! air1 ! *ance ( br++ d[n a bird w\ld be bett] ?an t ( a comet ( any k9d /rik+ ! e>?4 ,illu/ration3 ,fig4 #ceh4 ,illu/ration3 ,fig4 #cei4 #cah4 ,! ,*emical ,con/itution ( ,comets4--,fig4 #ceh %[s ! b&s ( ! spectrum ( a telescopic comet ( #ahgc1 z se5 by two diff]5t obs]v]s4 ,fig4 #cei %[s ! spectrum ( ! coma & tail ( ! comet ( #ahgd2 & ! spectrum ( ! bright comet ( #ahha %[$ ! same ?ree b&s = ! coma & tail4 ,n[1 ^! ?ree b&s are ^? ( c]ta9 hydroc>bon vapors3 h5ce x w\ld seem t ! coma & tails ( comets are compos$ *iefly ( su* vapors 7#cae74 ,,ii4 ,,! ,,zodiacal ,,light4 #cai4 ,! ,g5]al ,appe>ance ( ! ,zodiacal ,light4--,! ph5om5on kn[n z ! zodiacal light consi/s ( a v fa9t lum9osity1 :i* may be se5 ris+ f ! we/]n horizon aft] twilight on any cle> w9t] or spr+ ev5+1 also f ! ea/]n horizon j be=e daybreak 9 ! summ] or autumn4 ,x ext5ds out on ea* side ( ! sun1 & lies ne>ly 9 ! plane ( ! ecliptic4 ,x gr[s fa9t] ! f>!r x is f ! sun1 & c g5]ally be trac$ to ab\t n9ety degrees f t lum9>y1 :5 x gradually fades away4 ,9 a v cle>1 tropical atmosph]e1 x has be5 trac$ all ! way across ! heav5s f ea/ to we/1 ?us =m+ a complete r+4 ,! g5]al appe>ance ( ?is column ( light1 z se5 9 ! morn+1 9 ! latitude ( ,europe1 is %[n 9 ,fig4 #cfj4 ,illu/ration3 ,fig4 #cfj4 ,tak+ all ^! appe>ances toge!r1 !y indicate t x is due to a l5s-%ap$ app5dage surr\nd+ ! sun1 & ext5d+ a little beyond ! e>?'s orbit4 ,x lies ne>ly 9 ! plane ( ! ecliptic2 b its exact position is n easily det]m9$4 ,fig4 #cfa %[s ! g5]al =m & position ( ?is sol> app5dage1 z se5 9 ! we/4 ,illu/ration3 ,fig4 #cfa4 #cbj4 ,! ,visibility ( ! ,zodiacal ,light4--,! reason :y ! zodiacal light is m favorably se5 9 ! ev5+ dur+ ! w9t] & spr+ ?an 9 ! summ] & fall is evid5t f ,fig4 #cfb1 :i* %[s ! position ( ! ecliptic & ! zodiacal light ) ref]5ce to ! we/]n horizon at ! "t ( sunset 9 ,m>* & 9 ,septemb]4 ,x w be se5 t 9 ,septemb] ! axis ( ! light =ms a small angle ) ! horizon1 s t ! ph5om5on is visible only a %ort "t aft] sunset & l[ d[n :]e x is difficult to di/+ui% x f ! glimm] ( ! twilight2 :ile 9 ,m>*1 its axis be+ ne>ly p]p5dicul> to ! horizon1 ! light may be obs]v$ = "s h\rs aft] sunset & well up 9 ! sky4 ,fig4 #cfc gives ! position ( ! ecliptic & ( ! zodiacal light ) ref]5ce to ! ea/]n horizon at ! "t ( sunrise1 & %[s :y ! zodiacal light is se5 to bett] advantage 9 ! morn+ dur+ ! summ] & fall ?an dur+ ! w9t] & spr+4 ,x w be obs]v$ t "h ! angle made by ! axis ( ! light ) ! horizon is small 9 ,m>*1 :ile x is l>ge 9 ,septemb]2 ! conditions repres5t$ 9 ! prec$+ figure be+ ?us rev]s$4 ,illu/ration3 ,fig4 #cfb4 ,illu/ration3 ,fig4 #cfc4 #cba4 ,nature ( ! ,zodiacal ,light4--,v>i\s attempts h be5 made to expla9 ! ph5om5a ( ! zodiacal light2 b ! mo/ probable !ory is1 t x is due to an imm5se numb] ( meteors :i* are revolv+ ar\nd ! sun1 & :i* lie mo/ly )9 ! e>?'s orbit4 ,ea* ( ^! meteors reflects a s5sible portion ( sunlight1 b is f> too small to be sep>ately visible4 ,all ( ^! meteors toge!r w\ld1 by _! comb9$ reflection1 produce a k9d ( pale1 diffus$ light4 ,,iii4 ,,! ,,/ell> ,,univ]se4 ,i4 ,,g5]al ,,aspect ,,( ,,! ,,heav5s4 #cbb4 ,! ,magnitude ( ! ,/>s4--,! />s t are visible to ! nak$ eye are divid$ into six classes1 accord+ to _! brightness4 ,! brighte/ />s are call$ />s ( ! fir/ magnitude2 ! next brighte/1 ^? ( ! second magnitude2 & s on to ! six? magnitude4 ,! la/ magnitude includes ! fa9te/ />s t are visible to ! nak$ eye on ! mo/ favorable night4 ,/>s :i* are fa9t] ?an ^? ( ! six? magnitude c be se5 only ) ! telescope1 & are call$ telescopic />s4 ,telescopic />s are also divid$ into magnitudes2 ! division ext5d+ to ! sixte5? magnitude1 or ! fa9te/ />s t c be se5 ) ! mo/ p[]ful telescopes4 ,! classification ( />s accord+ to magnitudes has ref]5ce only to _! brightness1 & n at all to _! actual size4 ,a six? magnitude /> may actually be l>g] ?an a fir/ magnitude />2 its want ( brilliancy be+ due to its great] di/ance1 or to its inf]ior lum9osity1 or to bo? ( ^! causes4 ,none ( ! />s pres5t any s5sible disk1 ev5 9 ! mo/ p[]ful telescope3 !y all appe> z m]e po9ts ( light4 ,! l>g] ! telescope1 ! great] is its p[] ( reveal+ fa9t />s2 n because x makes ^! />s appe> l>g]1 b because ( its great] light-ga!r+ p[]4 ,?is p[] increases ) ! size ( ! object-glass ( ! telescope1 :i* plays ! "p ( a gigantic pupil ( ! eye4 ,! classification ( ! />s into magnitudes is n made 9 accordance ) any v accurate e/imate ( _! brightness4 ,! />s :i* are class$ toge!r 9 ! same magnitude are f> f be+ equally bright4 ,! />s ( ea* l[] magnitude are ab\t two-fif?s z bright z ^? ( ! magnitude above4 ,! ratio ( dim9ution is ab\t a ?ird f ! high] magnitude d[n to ! fif?4 ,7 ! ratio two-fif?s exact1 x w\ld take ab\t #b-a_/b />s ( ! #b;d magnitude to make "o ( ! #a/4 #f />s ( ! #c;d magnitude to make "o ( ! #a/4 #af />s ( ! #d? magnitude to make "o ( ! #a/4 #dj />s ( ! #e? magnitude to make "o ( ! #a/4 #ajj />s ( ! #f? magnitude to make "o ( ! #a/4 #aj1jjj />s ( ! #aa? magnitude to make "o ( ! #a/4 #a1jjj1jjj />s ( ! #af? magnitude to make "o ( ! #a/4 #cbc4 ,! ,numb] ( ! ,/>s4--,! total numb] ( />s 9 ! cele/ial sph]e visible to ! av]age nak$ eye is e/imat$1 9 r\nd numb]s1 at five ?\s&2 b ! numb] v>ies mu* ) ! p]fection & ! tra9+ ( ! eye & ) ! atmosph]ic conditions4 ,= e /> visible to ! nak$ eye1 !re are ?\s&s too m9ute to be se5 )\t telescopic aid4 ,fig4 #cfd %[s a portion ( ! con/ellation ( ! ,tw9s z se5 ) ! nak$ eye2 & ,fig4 #cfe %[s ! same region z se5 9 a p[]ful telescope4 ,illu/ration3 ,fig4 #cfd4 ,illu/ration3 ,fig4 #cfe4 ,/ruve has e/imat$ t ! total numb] ( />s visible ) ,h]s*el's tw5ty-foot telescope 0 ab\t tw5ty million4 ,! numb] t c be se5 ) ! great telescopes ( mod]n times has n be5 c>efully e/imat$1 b is probably some:]e betwe5 ?irty million & fifty million4 ,! numb] ( />s betwe5 ! nor? pole & ! circle ?irty-five degrees s\? ( ! equator is ab\t z foll[s3-- ,( ! #a/ magnitude ab\t #ad />s4 ,( ! #b;d magnitude ab\t #dh />s4 ,( ! #c;d magnitude ab\t #aeb />s4 ,( ! #d? magnitude ab\t #cac />s4 ,( ! #e? magnitude ab\t #hed />s4 ,( ! #f? magnitude ab\t #bjaj />s4 ---- ,total visible to nak$ eye #ccia />s4 ,! numb] ( />s ( ! sev]al magnitudes is approximately 9 inv]se proportion to t ( _! brightness1 ! ratio be+ a little great] 9 ! high] magnitudes1 & probably a little less 9 ! l[] ones4 #cbd4 ,! ,division ( ! ,/>s into ,con/ellations4--,a glance at ! heav5s is suffici5t to %[ t ! />s are n di/ribut$ uni=mly ov] ! sky4 ,! l>g] ones especially are collect$ into m or less irregul> gr\ps4 ,! l>g] gr\ps are call$ con/ellations4 ,at a v e>ly p]iod a my?ological figure 0 allott$ to ea* con/ellation2 & ^! figures 7 drawn 9 su* a way z to include ! pr9cipal />s ( ea* con/ellation4 ,! heav5s ?us became cov]$1 z x 71 ) imm5se hi]oglyphics4 ,!re is no hi/oric record ( ! "t :5 ^! figures 7 =m$1 or ( ! pr9ciple 9 accordance ) :i* !y 7 con/ruct$4 ,x is probable t ! imag9ation ( ! e>li] peoples may1 9 _m in/ances1 h discov]$ "s fanciful resemblance 9 ! configuration ( ! />s to ! =ms depict$4 ,! names are /ill reta9$1 al?\gh ! figures no long] s]ve any a/ronomical purpose4 ,! con/ellation ,h]cules1 = in/ance1 no long] repres5ts ! figure ( a man among ! />s1 b a c]ta9 portion ( ! heav5s )9 :i* ! anci5ts plac$ t figure4 ,9 />-maps int5d$ = s*ool & popul> use x is /ill cu/om>y to give ^! figures2 b !y are n g5]ally f\nd on maps design$ = a/ronom]s4 #cbe4 ,! ,nam+ ( ! ,/>s4--,! bright] />s h all prop] names1 z ,sirius1 ,procyon1 ,arcturus1 ,capella1 ,aldeb>an1 etc4 ,?is me?od ( designat+ ! />s 0 adopt$ by ! ,arabs4 ,mo/ ( ^! names h dropp$ entirely out ( a/ronomical use1 ?\gh _m are popul>ly reta9$4 ,! bright] />s are n[ g5]ally designat$ by ! lett]s ( ! ,greek alphabet1--alpha1 beta1 gamma1 etc41--to :i* is app5d$ ! g5itive ( ! "n ( ! con/ellation1 ! fir/ lett] ( ! alphabet be+ us$ = ! brighte/ />1 ! second = ! next brighte/1 & s on4 ,?us ,aldeb>an w\ld be designat$ z ,alpha ,tauri4 ,9 speak+ ( ! />s ( any "o con/ellation1 we simply designate !m by ! lett]s ( ! ,greek alphabet1 )\t ! addition ( ! "n ( ! con/ellation1 :i* answ]s to a p]son's surname1 :ile ! ,greek lett] answ]s to 8 ,*ri/ian "n4 ,! names ( ! sev5 />s ( ! ,dipp] are giv5 9 ,fig4 #cff4 ,:5 ! lett]s ( ! ,greek alphabet are exhau/$1 ^? ( ! ,roman alphabet are employ$4 ,! fa9t] />s 9 a con/ellation are usually designat$ by "s sy/em ( numb]s4 ,illu/ration3 ,fig4 #cff4 #cbf4 ,! ,milky-,way1 or ,galaxy4--,! ,milky-,way is a fa9t lum9\s b&1 ( irregul> outl9e1 :i* surr\nds ! heav5s ) a great circle1 z %[n 9 ,fig4 #cfg4 ,?r\gh a consid]able portion ( its c\rse x is divid$ into two bran*es1 & !re are v>i\s vacant spaces at diff]5t po9ts 9 ?is b&2 b at only "o po9t 9 ! s\!rn hemisph]e is x entirely int]rupt$4 ,illu/ration3 ,fig4 #cfg4 ,! telescope %[s t ! ,galaxy arises f ! light ( c\ntless />s too m9ute to be sep>ately visible ) ! nak$ eye4 ,! telescopic />s1 in/ead ( be+ uni=mly di/ribut$ ov] ! cele/ial sph]e1 are mo/ly cond5s$ 9 ! region ( ! ,galaxy4 ,!y are fewe/ 9 ! regions mo/ di/ant f ?is belt1 & become ?ick] z we approa* x4 ,! great] ! telescopic p[]1 ! m m>k$ is ! cond5sation4 ,) ! nak$ eye ! cond5sation is h>dly noticeable2 b ) ! aid ( a v small telescope1 we see a decid$ ?ick5+ ( ! />s 9 & ne> ! ,galaxy1 :ile ! mo/ p[]ful telescopes %[ t a l>ge majority ( ! />s lie actually 9 ! ,galaxy4 ,if all ! />s visible ) a twelve-in* telescope 7 blott$ out1 we %\ld f9d t ! great] "p ( ^? rema9+ 7 9 ! ,galaxy4 ,illu/ration3 ,fig4 #cfh4 ,! increase 9 ! numb] ( ! />s ( all magnitudes z we approa* ! plane ( ! ,milky-,way is %[n 9 ,fig4 #cfh4 ,! curve acb %[s by its height ! di/ribution ( ! />s above ! n9? magnitude1 & ! curve ,,acb ^? ( all magnitudes4 #cbg4 ,/>-,clu/]s4--,besides ?is gradual & regul> cond5sation t[>ds ! ,galaxy1 occasional aggregations ( />s into clu/]s may be se54 ,"s ( ^! are visible to ! nak$ eye1 sometimes z sep>ate />s1 l ! ,sev5 ,/>s1 or ,pleiades1 b m commonly z pat*es ( diffus$ light1 ! />s be+ too small to be se5 sep>ately4 ,! numb] visible 9 p[]ful telescopes is1 h[ev]1 mu* great]4 ,sometimes hundr$s or ev5 ?\s&s ( />s are visible 9 ! field ( view at once1 & sometimes ! numb] is s great t !y _c be c\nt$4 #cbh4 ,nebul4--,ano!r class ( objects :i* are f\nd 9 ! cele/ial spaces are irregul> masses ( s(t1 cl\dy light1 kn[n z nebul4 ,_m objects :i* look l nebul 9 small telescopes are %[n by m p[]ful in/rum5ts to be really />-clu/]s4 ,b _m ( ^! objects are n compos$ ( />s at all1 be+ imm5se masses ( gase\s matt]4 ,illu/ration3 ,fig4 #cfi4 ,! g5]al di/ribution ( nebul is ! rev]se ( t ( ! />s4 ,nebul are ?icke/ :]e />s are ?9ne/4 ,:ile />s are mo/ num]\s 9 ! region ( ! ,milky-,way1 nebul are mo/ abundant ab\t ! poles ( ! ,milky-,way4 ,?is cond5sation ( nebul ab\t ! poles ( ! ,milky-,way is %[n 9 ,figs4 #cfg & #cfi1 9 :i* ! po9ts repres5t1 n />s1 b nebul4 ,,ii4 ,,! ,,/>s4 ,! ,con/ellations4 ,illu/ration3 ,fig4 #cgj4 ,illu/ration3 ,fig4 #cga4 #cbi4 ,! ,great ,be>4--,! ,great ,be>1 or ,ursa ,major1 is "o ( ! circumpol> con/ellations 7#d71 & conta9s "o ( ! mo/ famili> a/]isms1 or gr\ps ( />s1 9 our sky2 namely1 ! ,great ,dipp]1 or ,*>les's ,wa94 ,! positions & names ( ! sev5 prom95t />s 9 x are %[n 9 ,fig4 #cgj4 ,! two />s ,alpha & ,beta are call$ ! ,po9t]s4 ,?is a/]ism is sometimes call$ ! ,but*]'s ,cleav]4 ,! :ole con/ellation is %[n 9 ,fig4 #cga4 ,a r fa9t /> m>ks ! nose ( ! be>1 & ?ree equidi/ant pairs ( fa9t />s m>k 8 feet4 #ccj4 ,! ,little ,be>1 ,draco1 & ,cassiopeia4--,^! are all circumpol> con/ellations4 ,! mo/ important /> ( ! ,little ,be>1 or ,ursa ,m9or1 is ,pol>is1 or ! ,pole ,/>4 ,?is /> may be f\nd by draw+ a l9e f ,beta to ,alpha ( ! ,dipp]1 & prolong+ x z %[n 9 ,fig4 #cgb4 ,?is expla9s :y ^! />s are call$ ! ,po9t]s4 ,! ,pole ,/>1 ) ! six o!r *ief />s ( ! ,little ,be>1 =m an a/]ism call$ ! ,little ,dipp]4 ,^! six />s are jo9$ ) ,pol>is by a dott$ l9e 9 ,fig4 #cgb4 ,illu/ration3 ,fig4 #cgb4 ,! />s 9 a s]p5t9e l9e betwe5 ! two ,dipp]s are ! *ief />s ( ,draco1 or ! ,dragon2 ! trapezium m>k+ its head4 ,fig4 #cgc %[s ! con/ellations ( ,ursa ,m9or & ,draco z usually figur$4 ,illu/ration3 ,fig4 #cgc4 ,to f9d ,cassiopeia1 draw a l9e f ,delta ( ! ,dipp] to ,pol>is1 & prolong x ab\t an equal di/ance beyond1 z %[n 9 ,fig4 #cgb4 ,?is l9e w pass ne> ,alpha ( ,cassiopeia4 ,! five pr9cipal />s ( ?is con/ellation =m an irregul> ,w1 op5+ t[>ds ! pole4 ,betwe5 ,cassiopeia & ,draco are five r fa9t />s1 :i* =m an irregul> ,k4 ,^! are ! pr9cipal />s ( ! con/ellation ,cepheus4 ,^! two con/ellations are %[n 9 ,fig4 #cgd4 ,illu/ration3 ,fig4 #cgd4 ,illu/ration3 ,fig4 #cge4 #cca4 ,! ,lion1 ,b]5ice's ,hair1 & ! ,hunt+-,dogs4--,a l9e drawn f ,alpha to ,beta ( ! ,dipp]1 & prolong$ z %[n 9 ,fig4 #cge1 w pass betwe5 ! two />s ,d5ebola & ,regulus ( ,leo1 or ! ,lion4 ,regulus =ms a sickle ) sev]al o!r fa9t />s1 & m>ks ! he>t ( ! lion4 ,d5ebola is at ! apex ( a "r-angl$ triangle1 :i* x =ms ) two o!r />s1 & m>ks ! end ( ! lion's tail4 ,?is con/ellation is visible 9 ! ev5+ f ,febru>y to ,july1 & is figur$ 9 ,fig4 #cgf4 ,illu/ration3 ,fig4 #cgf4 ,9 a /raight l9e betwe5 ,d5ebola & ,eta1 at ! end ( ! ,great ,be>'s tail1 are1 at ab\t equal di/ances1 ! two small con/ellations ( ,coma ,b]5ices1 or ,b]5ice's ,hair1 & ,canes ,v5atici1 or ! ,hunt+-,dogs4 ,^! are %[n 9 ,fig4 #cgg4 ,! dogs are repres5t$ z pursu+ ! be>1 urg$ on by ! huntsman ,botes4 ,illu/ration3 ,fig4 #cgg4 #ccb4 ,botes1 ,h]cules1 & ! ,nor!rn ,cr[n4--,arcturus1 ! pr9cipal /> ( ,botes1 may be f\nd by draw+ a l9e f ,zeta to ,eta ( ! ,dipp]1 & !n prolong+ x ) a slight b5d1 z %[n 9 ,fig4 #cgh4 ,arcturus & ,pol>is =m a l>ge isosceles triangle ) a fir/-magnitude /> call$ ,vega4 ,?is triangle encloses at "o corn] ! pr9cipal />s ( ,botes1 & ! head ( ! ,dragon ne> ! opposite side4 ,! side runn+ f ,arcturus to ,vega passes ?r\gh ,corona ,borealis1 or ! ,nor!rn ,cr[n1 & ! body ( ,h]cules1 :i* is m>k$ by a quadrilat]al ( f\r />s4 ,illu/ration3 ,fig4 #cgh4 ,botes1 :o is (t5 repres5t$ z a husb&man1 ,corona ,borealis1 & ,h]cules1 are del9eat$ 9 ,fig4 #cgi4 ,^! con/ellations are visible 9 ! ev5+ f ,may to ,septemb]4 ,illu/ration3 ,fig4 #cgi4 ,illu/ration3 ,fig4 #chj4 #ccc4 ,! ,lyre1 ! ,swan1 ! ,eagle1 & ! ,dolph94--,altair1 ! pr9cipal /> ( ,aquila1 or ! ,eagle1 lies on ! opposite side ( ! ,milky-,way f ,vega4 ,altair is a fir/-magnitude />1 & has a fa9t /> on ea* side ( x1 z %[n 9 ,fig4 #chj4 ,vega1 also ( ! fir/ magnitude1 is ! pr9cipal /> ( ,lyra1 or ! ,lyre4 ,betwe5 ^! two />s1 & a little f>!r to ! nor?1 are sev]al />s arrang$ 9 ! =m ( an imm5se cross4 ,! bright /> at ! head ( ?is cross is call$ ,d5eb4 ,! cross lies 9 ! ,milky-,way1 & conta9s ! *ief />s ( ! con/ellation ,cygnus1 or ! ,swan4 ,a little to ! nor? ( ,altair are f\r />s 9 ! =m ( a diamond4 ,?is a/]ism is popul>ly kn[n z ,job's ,c(f94 ,^! f\r />s are ! *ief />s ( ,delph9us1 or ! ,dolph94 ,^! f\r con/ellations are %[n toge!r 9 ,fig4 #cha4 ,! ,swan is visible f ,june to ,decemb]1 9 ! ev5+4 ,illu/ration3 ,fig4 #cha4 #ccd4 ,virgo4--,a l9e drawn f ,alpha to ,gamma ( ! ,dipp]1 & prolong$ ) a slight b5d at ,gamma1 w rea* to a fir/-magnitude /> call$ ,spica 7,fig4 #chb74 ,?is is ! *ief /> ( ! con/ellation ,virgo1 or ! ,virg91 & =ms a l>ge isosceles triangle ) ,arcturus & ,d5ebola4 ,illu/ration3 ,fig4 #chb4 ,virgo is repres5t$ 9 ,fig4 #chc4 ,to ! "r ( ?is con/ellation1 z %[n 9 ! figure1 !re are f\r />s :i* =m a trapezium1 & m>k ! con/ellation ,corvus1 or ! ,cr[4 ,?is bird is repres5t$ z /&+ on ! body ( ,hydra1 or ! ,wat]-,snake4 ,virgo is visible 9 ! ev5+1 f ,april to ,augu/4 ,illu/ration3 ,fig4 #chc4 ,illu/ration3 ,fig4 #chd4 ,illu/ration3 ,fig4 #che4 #cce4 ,! ,tw9s4--,a l9e drawn f ,delta to ,beta ( ! ,dipp]1 & prolong$ z %[n 9 ,fig4 #chd1 passes betwe5 two bright />s call$ ,ca/or & ,pollux4 ,! latt] ( ^! is usually reckon$ z a fir/-magnitude />4 ,^! are ! pr9cipal />s ( ! con/ellation ,gem9i1 or ! ,tw9s1 :i* is %[n 9 ,fig4 #che4 ,! con/ellation ,canis ,m9or1 or ! ,little ,dog1 is %[n 9 ! l[] "p ( ! figure4 ,!re are two conspicu\s />s 9 ?is con/ellation1 ! brighte/ ( :i* is ( ! fir/ magnitude1 & call$ ,procyon4 ,! region to :i* we h n[ be5 br\ght is ! ri*e/ ( ! nor!rn sky1 conta9+ no less ?an sev5 fir/-magnitude />s4 ,^! are ,sirius1 ,procyon1 ,pollux1 ,capella1 ,aldeb>an1 ,betelgeuse1 & ,rigel4 ,!y are %[n 9 ,fig4 #chf4 ,illu/ration3 ,fig4 #chf4 ,betelgeuse & ,rigel are 9 ! con/ellation ,orion1 be+ ab\t equally di/ant to ! nor? & s\? f ! ?ree />s =m+ ! belt ( ,orion4 ,betelgeuse is a r$ />4 ,sirius is ! brighte/ /> 9 ! heav5s1 & belongs to ! con/ellation ,canis ,major1 or ! ,great ,dog4 ,x lies to ! ea/ ( ! belt ( ,orion4 ,aldeb>an lies at ab\t ! same di/ance to ! we/ ( ! belt4 ,x is a r$ />1 & belongs to ! con/ellation ,taurus1 or ! ,bull4 ,capella is 9 ! con/ellation ,auriga1 or ! ,wagon]4 ,^! />s are visible 9 ! ev5+1 f ab\t ,decemb] to ,april4 #ccf4 ,orion & 8 ,dogs1 & ,taurus4--,orion & 8 ,dogs are %[n 9 ,fig4 #chg1 & ,orion & ,taurus 9 ,fig4 #chh4 ,aldeb>an m>ks "o ( ! eyes ( ! bull1 & is (t5 call$ ! ,bull's ,eye4 ,! irregul> ,v 9 ! face ( ! bull is call$ ! ,hyades1 & ! clu/] on ! %\ld] ! ,pleiades4 ,illu/ration3 ,fig4 #chg4 ,illu/ration3 ,fig4 #chh4 ,illu/ration3 ,fig4 #chi4 #ccg4 ,! ,wagon]4--,! con/ellation ,auriga1 or ! ,wagon] 7sometimes call$ ! ,*>iote]71 is %[n 9 ,fig4 #chi4 ,capella m>ks ! ,goat1 :i* he is repres5t$ z c>ry+ on 8 back1 & ! little "r-angl$ triangle ( />s ne> x ! ,kids4 ,! five *ief />s ( ?is con/ellation =m a l>ge1 irregul> p5tagon4 ,gamma ( ,auriga is also ,beta ( ,taurus1 & m>ks "o ( ! horns ( ! ,bull4 ,illu/ration3 ,fig4 #cij4 #cch4 ,pegasus1 ,&rom$a1 & ,p]seus4--,a l9e drawn f ,pol>is ne> to ,beta ( ,cassiopeia w lead to a bright second-magnitude /> at "o corn] ( a l>ge squ>e 7,fig4 #cij74 ,alpha belongs bo? to ! ,squ>e ( ,pegasus & to ,&rom$a4 ,beta & ,gamma1 :i* are connect$ ) ,alpha 9 ! figure by a dott$ l9e1 also belong to ,&rom$a4 ,algol1 :i* =ms1 ) ! la/-nam$ />s & ) ! ,squ>e ( ,pegasus1 an a/]ism simil> 9 configuration to ! ,great ,dipp]1 belongs to ,p]seus4 ,alg5ib1 :i* is rea*$ by b5d+ ! l9e at ,gamma 9 ! opposite direction1 is ! pr9cipal /> ( ,p]seus4 ,illu/ration3 ,fig4 #cia4 ,illu/ration3 ,fig4 #cib4 ,illu/ration3 ,fig4 #cic4 ,pegasus is %[n 9 ,fig4 #cia1 & ,&rom$a 9 ,fig4 #cib4 ,cetus1 ! ,:ale1 or ! ,sea ,mon/]1 %[n 9 ,fig4 #cic1 belongs to ! same my?ological gr\p ( con/ellations4 ,illu/ration3 ,fig4 #cid4 #cci4 ,scorpio1 ,sagitt>ius1 & ,ophiu*us4--,dur+ ! summ] mon?s a brilliant con/ellation is visible1 call$ ,scorpio1 or ! ,scorpion4 ,! configuration ( ! *ief />s ( ?is con/ellation is %[n 9 ,fig4 #cid4 ,!y be> "s resemblance to a boy's kite4 ,! brighte/ /> is ( ! fir/ magnitude1 & call$ ,ant>es 7f anti1 in/ead (1 & ,ares1 ! ,greek "n ( ,m>s71 because x rivals ,m>s 9 r$ness4 ,! />s 9 ! tail ( ! ,scorpion are visible 9 our latitude only "u v favorable circum/ances4 ,?is con/ellation is %[n 9 ,fig4 #cie1 toge!r ) ,sagitt>ius & ,ophiu*us4 ,sagitt>ius1 or ! ,ar*]1 is to ! ea/ ( ,scorpio4 ,x conta9s no bright />s1 b is easily recogniz$ f ! fact t five ( its pr9cipal />s =m ! outl9e ( an inv]t$ dipp]1 :i*1 f ! fact ( its be+ p>tly 9 ! ,milky-,way1 is (t5 call$ ! ,milk ,dipp]4 ,illu/ration3 ,fig4 #cie4 ,ophiu*us1 or ! ,s]p5t-,be>]1 is a l>ge con/ellation1 fill+ all ! space betwe5 ! head ( ,h]cules & ,scorpio4 ,x is difficult to trace1 s9ce x conta9s no v brilliant />s4 ,?is con/ellation & ,libra1 or ! ,balances1 :i* is ! zodiacal con/ellation to ! we/ ( ,scorpio1 are %[n 9 ,fig4 #cif4 ,illu/ration3 ,fig4 #cif4 ,illu/ration3 ,fig4 #cig4 #cdj4 ,capricornus1 ,aqu>ius1 & ! ,s\!rn ,fi%4--,! two zodiacal con/ellations to ! ea/ ( ,sagitt>ius are ,capricornus & ,aqu>ius4 ,capricornus conta9s ?ree pairs ( small />s1 :i* m>k ! head1 ! tail1 & ! knees ( ! animal4 ,aqu>ius is m>k$ by no conspicu\s />s4 ,an irregul> l9e ( m9ute />s m>ks ! c\rse ( ! /ream ( wat] :i* fl[s f ! ,wat]-,be>]'s ,urn into ! m\? ( ! ,s\!rn ,fi%4 ,?is m\? is m>k$ by ! fir/-magnitude /> ,fomalhaut4 ,^! con/ellations are %[n 9 ,fig4 #cig4 ,illu/ration3 ,fig4 #cih4 #cda4 ,pisces & ,aries4--,! rema9+ zodiacal con/ellations are ,pisces1 or ! ,fi%es1 ,aries1 or ! ,ram 7,fig4 #cih71 & ,canc]1 or ! ,crab4 ,! ,fi%es lie "u ,pegasus & ,&rom$a1 b conta9 no bright />s4 ,aries 7betwe5 ,pisces & ,taurus7 is m>k$ by a pair ( />s on ! head1--"o ( ! second1 & "o ( ! ?ird magnitude4 ,canc] 7betwe5 ,leo & ,gem9i7 has no bright />s1 b conta9s a rem>kable clu/] ( small />s call$ ,prsepe1 or ! ,beehive4 ,clu/]s4 #cdb4 ,! ,hyades4--,! ,hyades are a v op5 clu/] 9 ! face ( ,taurus 7#ccd74 ,! ?ree brighte/ />s ( ?is clu/] =m a lett] ,v1 ! po9t ( ! ,v be+ on ! nose1 & ! op5 ends at ! eyes4 ,?is clu/] is %[n 9 ,fig4 #cii4 ,! "n1 accord+ to ! mo/ probable etymology1 means ra9y2 & !y are said to h be5 s call$ because _! ris+ 0 associat$ ) wet wea!r4 ,!y 7 usually consid]$ ! daught]s ( ,atlas1 & si/]s ( ! ,pleiades1 ?\gh sometimes ref]r$ to z ! nurses ( ,bac*us4 ,illu/ration3 ,fig4 #cii4 #cdc4 ,! ,pleiades4--,! ,pleiades con/itute a celebrat$ gr\p ( />s1 or a m9iature con/ellation1 on ! %\ld] ( ,taurus4 ,hesiod m5tions !m z ! sev5 virg9s ( ,atlas born1 & ,milton calls !m ! sev5 ,atlantic si/]s4 ,!y are ref]r$ to 9 ! ,book ( ,job4 ,! ,spani>ds t]m !m ! little nanny-goats2 & !y are sometimes call$ ! h5 & *ick5s4 ,illu/ration3 ,fig4 #djj4 ,illu/ration3 ,fig4 #dja4 ,usually only six />s 9 ?is clu/] c be se5 ) ! nak$ eye1 & ?is fact has giv5 rise to ! leg5d ( ! lo/ ,pleiad4 ,on a cle>1 moonless night1 h[ev]1 a good eye c disc]n sev5 or eight />s1 & "s obs]v]s h di/+ui%$ z _m z elev54 ,fig4 #djj %[s ! ,pleiades z !y appe> to ! nak$ eye "u ! mo/ favorable circum/ances4 ,fig4 #dja %[s ?is clu/] z x appe>s 9 a p[]ful telescope4 ,) su* an in/rum5t m ?an five hundr$ />s are visible4 #cdd4 ,clu/] 9 ! ,sword-h&le ( ,p]seus4--,?is is a some:at d5se d\ble clu/]4 ,x is visible to ! nak$ eye1 appe>+ z a hazy />4 ,a l9e drawn f ,alg5ib1 or ,alpha ( ,p]seus 7#cch71 to ,delta ( ,cassiopeia 7#ccj71 w pass ?r\gh ?is clu/] at ab\t two-?irds ! di/ance f ! =m]4 ,?is d\ble clu/] is "o ( ! mo/ brilliant objects 9 ! heav5s1 ) a telescope ( mod]ate p[]4 ,illu/ration3 ,fig4 #djb4 #cde4 ,clu/] ( ,h]cules4--,! celebrat$ globul> clu/] ( ,h]cules c be se5 only ) a telescope ( consid]able p[]1 & to resolve x into di/9ct />s 7z %[n 9 ,fig4 #djb7 requires an in/rum5t ( ! v highe/ class4 ,illu/ration3 ,fig4 #djc4 #cdf4 ,o!r ,clu/]s4--,fig4 #djc %[s a magnific5t globul> clu/] 9 ! con/ellation ,aqu>ius4 ,h]s*el describes x z appe>+ l a heap ( s&1 be+ compos$ ( ?\s&s ( />s ( ! fifte5? magnitude4 ,illu/ration3 ,fig4 #djd4 ,fig4 #djd %[s a clu/] 9 ! con/ellation ,t\can1 :i* ,sir ,john ,h]s*el describes z a mo/ glori\s globul> clu/]1 ! />s ( ! f\rte5? magnitude be+ imm5sely num]\s4 ,!re is a m>k$ cond5sation ( light at ! c5tre4 ,illu/ration3 ,fig4 #dje4 ,illu/ration3 ,fig4 #djf4 ,fig4 #dje %[s a clu/] 9 ! ,c5taur1 :i*1 accord+ to ! same a/ronom]1 is beyond comp>ison ! ri*e/ & l>ge/ object ( ! k9d 9 ! heav5s1 ! />s 9 x be+ lit]ally innum]able4 ,fig4 #djf %[s a clu/] 9 ,scorpio1 rem>kable = ! peculi> arrangem5t ( its compon5t />s4 ,/> clu/]s are especially abundant 9 ! region ( ! ,milky-,way1 ! law ( _! di/ribution be+ ! rev]se ( t ( ! nebul4 ,d\ble & ,multiple ,/>s4 #cdg4 ,d\ble ,/>s4--,! telescope %[s t _m />s :i* appe> s+le to ! nak$ eye are really d\ble1 or compos$ ( a pair ( />s ly+ side by side4 ,!re are sev]al pairs ( />s 9 ! heav5s :i* lie s ne> toge!r t !y almo/ seem to t\* :5 se5 ) ! nak$ eye4 ,illu/ration3 ,fig4 #djg4 ,illu/ration3 ,fig4 #djh4 ,pairs ( />s are n consid]$ d\ble unless ! compon5ts are s ne> toge!r t !y bo? appe> 9 ! field ( view :5 exam9$ ) a telescope4 ,9 ! majority ( ! pairs class$ z d\ble />s ! di/ance betwe5 ! compon5ts ranges f half a second to fifte5 seconds4 ,illu/ration3 ,fig4 #dji4 ,epsilon ,lyr is a good example ( a pair ( />s t c b>ely be sep>at$ ) a good eye4 ,figs4 #djg & #djh %[ ?is pair z x appe>s 9 telescopes magnify+ respectively f\r & fifte5 times2 & ,fig4 #dji %[s x z se5 9 a m p[]ful telescope1 9 :i* ea* ( ! two compon5ts ( ! pair is se5 to be a truly d\ble />4 ,illu/ration3 ,fig4 #daj4 ,illu/ration3 ,fig4 #daa4 #cdh4 ,multiple ,/>s4--,:5 a /> is resolv$ into m ?an two compon5ts by a telescope1 x is call$ a multiple />4 ,fig4 #daj %[s a triple /> 9 ,pegasus4 ,fig4 #daa %[s a quadruple /> 9 ,taurus4 ,fig4 #dab %[s a sextuple />1 & ,fig4 #dac a septuple />4 ,fig4 #dad %[s ! celebrat$ septuple /> 9 ,orion1 call$ ,!ta ,orionis1 or ! trapezium ( ,orion4 #cdi4 ,optically ,d\ble & ,multiple ,/>s4--,two or m />s :i* are really v di/ant f ea* o!r1 & :i* h no physical connection :atev]1 may appe> to be ne> toge!r1 because !y happ5 to lie 9 ! same direction1 "o beh9d ! o!r4 ,su* accid5tal comb9ations are call$ optically d\ble or multiple />s4 ,illu/ration3 ,fig4 #dab4 ,illu/ration3 ,fig4 #dac4 #cej4 ,physically ,d\ble & ,multiple ,/>s4--,9 ! majority ( cases ! compon5ts ( d\ble & multiple />s are 9 reality comp>atively ne> toge!r1 & are b\nd toge!r by gravity into a physical sy/em4 ,su* comb9ations are call$ physically d\ble & multiple />s4 ,! compon5ts ( ^! sy/ems all revolve ar\nd _! common c5tre ( gravity4 ,9 _m in/ances _! orbits & p]iods ( revolution h be5 asc]ta9$ by obs]vation & calculation4 ,fig4 #dae %[s ! orbit ( "o ( ! compon5ts ( a d\ble /> 9 ! con/ellation ,h]cules4 ,illu/ration3 ,fig4 #dad4 #cea4 ,colors ( ,d\ble & ,multiple ,/>s4--,! compon5ts ( d\ble & multiple />s are (t5 highly color$1 & frequ5tly ! compon5ts ( ! same sy/em are ( diff]5t colors4 ,sometimes "o /> ( a b9>y sy/em is :ite1 & ! o!r r$2 & sometimes a :ite /> is comb9$ ) a blue "o4 ,o!r colors f\nd 9 comb9ation 9 ^! sy/ems are r$ & blue1 orange & gre51 blue & gre51 yell[ & blue1 yell[ & r$1 etc4 ,illu/ration3 ,fig4 #dae4 ,if ^! d\ble & multiple />s are accompani$ by planets1 ^! planets w sometimes h two or m suns 9 ! sky at once4 ,on alt]nate days !y may h suns ( diff]5t colors1 & p]haps on ! same day two suns ( diff]5t colors4 ,! effect ( ^! *ang+ color$ lights on ! l&scape mu/ be v rem>kable4 ,new & ,v>iable ,/>s4 #ceb4 ,v>iable ,/>s4--,!re are _m />s :i* und]go *anges ( brilliancy1 sometimes slight1 b occasionally v m>k$4 ,^! *anges are 9 "s cases app>5tly irregul>1 & 9 o!rs p]iodic4 ,all su* />s are said to be v>iable1 ?\gh ! t]m is appli$ especially to ^? />s ^: v>iability is p]iodic4 ,illu/ration3 ,fig4 #daf4 #cec4 ,algol4--,algol1 a /> ( ,p]seus1 ^: position is %[n 9 ,fig4 #daf1 is a rem>kable v>iable /> ( a %ort p]iod4 ,usually x %9es z a fa9t second-magnitude />2 b at int]vals ( a little less ?an ?ree days x fades to ! f\r? magnitude = a few h\rs1 & !n rega9s its =m] brightness4 ,^! *anges 7 fir/ notic$ "s two c5turies ago1 b x 0 n till #aghb t !y 7 accurately obs]v$4 ,! p]iod is n[ kn[n to be two days1 tw5ty h\rs1 =ty-n9e m9utes4 ,x takes ab\t f\r h\rs & a half to fade away1 & f\r h\rs m to recov] its brilliancy4 ,ne> ! beg9n+ & end ( ! v>iations1 ! *ange is v sl[1 s t !re are n m ?an five or six h\rs dur+ :i* an ord9>y obs]v] w\ld see t ! /> 0 less bright ?an usual4 ,?is v>iation ( light 0 at fir/ expla9$ by suppos+ t a l>ge d>k planet 0 revolv+ r\nd ,algol1 & pass$ ov] its face at e revolution1 ?us cutt+ (f a portion ( its light2 b !re are small irregul>ities 9 ! v>iation1 :i* ?is !ory does n acc\nt =4 #ced4 ,mira4--,ano!r rem>kable v>iable /> is ,omicron ,ceti1 or ,mira 7t is1 ! wond]ful />74 ,x is g5]ally invisible to ! nak$ eye2 b at int]vals ( ab\t elev5 mon?s x %9es =? z a /> ( ! second or ?ird magnitude4 ,x is ab\t =ty days f ! "t x becomes visible until x atta9s its greate/ brightness1 & is !n ab\t two mon?s 9 fad+ to invisibility2 s t its increase ( brilliancy is m rapid ?an its wan+4 ,its p]iod is q irregul>1 rang+ f t5 to twelve mon?s2 s t ! times ( its appe>ance _c be pr$ict$ ) c]ta9ty4 ,its maximum brightness is also v>iable1 be+ sometimes ( ! second magnitude1 & at o!rs only ( ! ?ird or f\r?4 ,illu/ration3 ,fig4 #dag4 #cee4 ,eta ,argus4--,p]haps ! mo/ extraord9>y v>iable /> 9 ! heav5s is ,eta ,argus1 9 ! con/ellation ,argo1 or ! ,%ip1 9 ! s\!rn hemisph]e 7,fig4 #dag74 ,! fir/ c>eful obs]vations ( its v>iability 7 made by ,sir ,john ,h]s*el :ile at ! ,cape ( ,good ,hope4 ,he says1 ,x 0 on ! #af? ( ,decemb]1 #ahcg1 t1 resum+ ! photometrical comp>isons1 my a/oni%m5t 0 excit$ by ! appe>ance ( a new c&idate = di/9ction among ! v brighte/ />s ( ! fir/ magnitude 9 a "p ( ! heav5s :]e1 be+ p]fectly famili> ) x1 ,i 0 c]ta9 t no su* brilliant object _h be=e be5 se54 ,aft] a mom5t>y hesitation1 ! natural consequ5ce ( a ph5om5on s utt]ly unexpect$1 & ref]r+ to a map = its configuration ) o!r conspicu\s />s 9 ! neighborhood1 ,i became satisfi$ ( its id5tity ) my old acqua9tance1 ,eta ,argus4 ,its light 01 h[ev]1 ne>ly tripl$4 ,:ile yet l[1 x equall$ ,rigel1 &1 :5 x atta9$ "s altitude1 0 decid$ly great]4 ,x cont9u$ to increase until ,jan4 #b1 #ahch1 !n fad$ a little till ,april foll[+1 ?\gh x 0 /ill z bright z ,aldeb>an4 ,9 #ahdb & #ahdc x blaz$ up bright] ?an ev]1 & 9 ,m>* ( ! latt] ye> 0 second only to ,sirius4 ,dur+ ! tw5ty-five ye>s foll[+ x sl[ly b /eadily dim9i%$4 ,9 #ahfg x 0 b>ely visible to ! nak$ eye2 & ! next ye> x vani%$ entirely f ! unassi/$ view1 & has n yet begun to recov] its brightness4 ,! curve 9 ,fig4 #dah %[s ! *ange 9 brightness ( ?is rem>kable />4 ,! numb]s at ! bottom %[ ! ye>s ( ! c5tury1 & ^? at ! side ! brightness ( ! />4 ,illu/ration3 ,fig4 #dah4 #cef4 ,new ,/>s4--,9 sev]al cases />s h sudd5ly appe>$1 & ev5 become v brilliant2 !n1 aft] a long] or %ort] "t1 !y h fad$ away & disappe>$4 ,su* />s are call$ new or tempor>y />s4 ,= a "t x 0 suppos$ t su* />s 7 actually new4 ,!y are n[1 h[ev]1 classifi$ by a/ronom]s among ! v>iable />s1 _! *anges be+ ( a v irregul> & fitful "*4 ,!re is sc>cely a d\bt t !y 7 all 9 ! heav5s z v small />s be=e !y blaz$ =? 9 s extraord9>y a mann]1 & t !y are 9 ! same places /ill4 ,!re is a wide diff]5ce betwe5 ^! irregul> v>iations1 or ! break+-=? ( light on a s+le occasion 9 ! c\rse ( c5turies1 & ! regul> & p]iodic *anges 9 ! case ( a /> l ,algol2 b a long s]ies ( c>eful obs]vation has result$ 9 ! discov]y ( />s ( ne>ly e degree ( irregul>ity betwe5 ^! two extremes4 ,"s ( !m *ange gradually f "o magnitude to ano!r1 9 ! c\rse ( ye>s1 )\t seem+ to foll[ any law :atev]2 :ile 9 o!rs "s slight t5d5cy to regul>ity c be trac$4 ,eta ,argus may be reg>d$ z a connect+ l9k betwe5 new & v>iable />s4 #ceg4 ,ty*o ,brahe's ,/>4--,an app>5tly new /> sudd5ly appe>$ 9 ,cassiopeia 9 #aegb4 ,x 0 fir/ se5 by ,ty*o ,brahe1 & is !re=e associat$ ) 8 "n4 ,its position 9 ! con/ellation is %[n 9 ,fig4 #dai4 ,x 0 fir/ se5 on ,nov4 #aa1 :5 x _h already atta9$ ! fir/ magnitude4 ,x became rapidly bright]1 soon rivall+ ,v5us 9 spl5dor1 s t good eyes c\ld disc]n x 9 full daylight4 ,9 ,decemb] x began to wane1 & gradually fad$ until ! foll[+ ,may1 :5 x disappe>$ entirely4 ,illu/ration3 ,fig4 #dai4 ,a /> %[$ itself 9 ! same "p ( ! heav5s 9 #ide & 9 #abfd4 ,if ^! 7 ?ree appe>ances ( ! same />1 x mu/ be reckon$ z a p]iodic /> ) a p]iod ( a little m ?an ?ree hundr$ ye>s4 #ceh4 ,kepl]'s ,/>4--,9 #afjd a new /> 0 se5 9 ! con/ellation ,ophiu*us4 ,x 0 fir/ notic$ 9 ,octob] ( t ye>1 :5 x 0 ( ! fir/ magnitude4 ,9 ! foll[+ w9t] x began to fade1 b rema9$ visible dur+ ! :ole ye> #afje4 ,e>ly 9 #afjf x disappe>$ entirely4 ,a v full hi/ory ( ?is /> 0 writt5 by ,kepl]4 ,"o ( ! mo/ rem>kable ?+s ab\t ?is /> 0 its brilliant sc9tillation4 ,accord+ to ,kepl]1 x display$ all ! colors ( ! ra9b[1 or ( a diamond cut ) multiple facets1 & expos$ to ! rays ( ! sun4 ,x is ?\ght t ?is /> also appe>$ 9 #cic1 #gih1 & #abjc2 if s1 x is a v>iable /> ) a p]iod ( a little ov] f\r hundr$ ye>s4 #cei4 ,new ,/> ( #ahff4--,! mo/ /rik+ case ( ?is k9d 9 rec5t times 0 9 ,may1 #ahff1 :5 a /> ( ! second magnitude sudd5ly appe>$ 9 ,corona ,borealis4 ,on ! #aa? & #ab? ( t mon? x 0 obs]v$ indep5d5tly by at lea/ five obs]v]s 9 ,europe & ,am]ica4 ,! fact t none ( ^! new />s 7 notic$ until !y _h ne>ly or q atta9$ _! greate/ brilliancy r5d]s x probable t !y all blaz$ up v sudd5ly4 #cfj4 ,cause ( ! ,v>iability ( ,/>s4--,! *anges 9 ! brightness ( v>iable & tempor>y />s are probably due to op]ations simil> to ^? :i* produce ! spots & prom95ces 9 our sun4 ,we h se5 7#ahh7 t ! frequ5cy ( sol> spots %[s a p]iod ( elev5 ye>s1 dur+ "o portion ( :i* !re are few or no spots to be se51 :ile dur+ ano!r portion !y are num]\s4 ,if an obs]v] s f> away z to see our sun l a /> c\ld f "t to "t measure its light exactly1 he w\ld f9d x to be a v>iable /> ) a p]iod ( elev5 ye>s1 ! light be+ lea/ :5 we see mo/ spots1 & greate/ :5 few are visible4 ,! v>iation w\ld be slight1 b x w\ld nev]!less exi/4 ,n[1 we h reason to believe t ! physical con/itution ( ! sun & ! />s is ( ! same g5]al nature4 ,x is !re=e probable1 t1 if we c\ld get a ne>] view ( ! />s1 we %\ld see spots on _! disks z we d on ! sun4 ,x is also likely t ! v>y+ physical con/itution ( ! />s might give rise to great diff]5ces 9 ! numb] & size ( ! spots2 s t ! light ( "s ( ^! suns might v>y to a f> great] degree ?an t ( our own sun does4 ,if ! v>iations _h a regul> p]iod1 z 9 ! case ( our sun1 ! appe>ances to a di/ant obs]v] w\ld be precisely :at we see 9 ! case ( a p]iodic v>iable />4 ,! spectrum ( ! new /> ( #ahff 0 f\nd to be a cont9u\s "o1 cross$ by bright l9es1 :i* 7 app>5tly due to gl[+ hydrog54 ,! cont9u\s spectrum 0 also cross$ by d>k l9es1 indicat+ t ! light _h pass$ ?r\gh an atmosph]e ( comp>atively cool gas4 ,mr4 ,hugg9s inf]s f ?is t !re 0 a sudd5 & extraord9>y outbur/ ( hydrog5 gas f ! />1 :i* by its own light1 z well z by heat+ up ! :ole surface ( ! />1 caus$ ! extraord9>y increase ( brilliancy4 ,n[1 ! spectroscope %[s t ! r$ flames ( ! sol> *romosph]e 7#aig7 are l>gely compos$ ( hydrog52 & x is n unlikely t ! blaz+-=? ( ?is /> arose f an action simil> to t :i* produces ^! flames1 only on an imm5sely l>g] scale4 ,di/ance ( ! ,/>s4 #cfa4 ,p>allax ( ! ,/>s4--,su* is ! di/ance ( ! />s1 t only 9 a comp>atively few in/ances has any displacem5t ( ^! bodies be5 detect$ :5 view$ f opposite p>ts ( ! e>?'s orbit1 t is1 f po9ts a hundr$ & eighty-five million miles ap>t2 & 9 no case c ?is displacem5t be detect$ except by ! mo/ c>eful & delicate measurem5t4 ,half ( ! above displacem5t1 or ! displacem5t ( ! /> z se5 f ! e>? in/ead ( ! sun1 is call$ ! p>allax ( ! />4 ,9 no case has a p>allax ( "o second z yet be5 detect$4 #cfb4 ,! ,di/ance ( ! ,/>s4--,! di/ance ( a /> ^: p>allax is "o second w\ld be #bjf1bfe times ! di/ance ( ! e>? f ! sun1 or ab\t n9ete5 million million miles4 ,x is q c]ta9 t no /> is ne>] ?an ?is to ! e>?4 ,light has a velocity :i* w\ld c>ry x sev5 times & a half ar\nd ! e>? 9 a second2 b x w\ld take x m ?an ?ree ye>s to rea* u f t di/ance4 ,7 all ! />s blott$ out ( exi/5ce to-night1 x w\ld be at lea/ ?ree ye>s be=e we %\ld miss a s+le "o4 ,alpha ,c5tauri1 ! brighte/ /> 9 ! con/ellation ( ! ,c5taur1 is1 s f> z we "k1 ! ne>e/ ( ! fix$ />s4 ,x is e/imat$ t x w\ld take its light ab\t ?ree ye>s & a half to rea* u4 ,x has also be5 e/imat$ t x w\ld take light ov] sixte5 ye>s to rea* u f ,sirius1 ab\t eighte5 ye>s to rea* u f ,vega1 ab\t tw5ty-five ye>s f ,arcturus1 & ov] =ty ye>s f ! ,pole-,/>4 ,9 _m in/ances x is believ$ t x w\ld take ! light ( />s hundr$s ( ye>s to make ! j\rney to our e>?1 & 9 "s in/ances ev5 ?\s&s ( ye>s4 ,prop] ,motion ( ! ,/>s4 #cfc4 ,:y ! ,/>s appe> ,fix$4--,! />s seem to reta9 _! relative positions 9 ! heav5s f ye> to ye>1 & f age to age2 & h5ce !y h come univ]sally to be d5om9at$ z fix$4 ,x is1 h[ev]1 n[ well kn[n t ! />s1 in/ead ( be+ really /ation>y1 are mov+ at ! rate ( _m miles a second2 b _! di/ance is s enorm\s1 t1 9 ! majority ( cases1 x w\ld be ?\s&s ( ye>s be=e ?is rate ( motion w\ld produce a suffici5t displacem5t to be noticeable to ! unaid$ eye4 ,illu/ration3 ,fig4 #dbj4 #cfd4 ,secul> ,displacem5t ( ! ,/>s4--,?\gh ! prop] motion ( ! />s is app>5tly slight1 x w1 9 ! c\rse ( _m ages1 produce a m>k$ *ange 9 ! configuration ( ! />s4 ,?us1 9 ,fig4 #dbj1 ! left-h& portion %[s ! pres5t configuration ( ! />s ( ! ,great ,dipp]4 ,! small arr[s atta*$ to ! />s %[ ! direction & comp>ative magnitudes ( _! motion4 ,! "r-h& portion ( ! figure %[s ^! />s z !y w appe> ?irty-six ?\s& ye>s f ! pres5t "t4 ,illu/ration3 ,fig4 #dba4 ,fig4 #dba %[s 9 a simil> way ! pres5t configuration & prop] motion ( ! />s ( ,cassiopeia1 & also ^! />s z !y w appe> ?irty-six ?\s& ye>s h5ce4 ,illu/ration3 ,fig4 #dbb4 ,fig4 #dbb %[s ! same = ! con/ellation ,orion4 #cfe4 ,! ,secul> ,motion ( ! ,sun4--,! />s 9 all p>ts ( ! heav5s are f\nd to move 9 all directions & ) all sorts ( velocities4 ,:51 h[ev]1 ! motions ( ! />s are av]ag$1 !re is f\nd to be an app>5t prop] motion common to all ! />s4 ,! />s 9 ! neighborhood ( ,h]cules appe> to be approa*+ u1 & ^? 9 ! opposite "p ( ! heav5s appe> to be rec$+ f u4 ,9 o!r words1 all ! />s appe> to be mov+ away f ,h]cules1 & t[>ds ! opposite "p ( ! heav5s4 ,illu/ration3 ,fig4 #dbc4 ,?is app>5t motion common to all ! />s is held by a/ronom]s to be due to ! real motion ( ! sun ?r\gh space4 ,! po9t 9 ! heav5s t[>ds :i* our sun is mov+ at ! pres5t "t is indicat$ by ! small circle 9 ! con/ellation ,h]cules 9 ,fig4 #dbc4 ,z ! sun moves1 he c>ries ! e>? & all ! planets along ) him4 ,fig4 #dbd %[s ! direction ( ! sun's motion ) ref]5ce to ! ecliptic & to ! axis ( ! e>?4 ,fig4 #dbe %[s ! e>?'s pa? 9 space2 & ,fig4 #dbf %[s ! pa?s ( ! e>?1 ! moon1 ,m]cury1 ,v5us1 & ,m>s 9 space4 ,illu/ration3 ,fig4 #dbd4 ,illu/ration3 ,fig4 #dbe4 ,illu/ration3 ,fig4 #dbf4 ,:e!r ! sun is actually mov+ 9 a /raight l9e1 or ar\nd "s di/ant c5tre1 x is impossible to det]m9e at ! pres5t "t4 ,x is e/imat$ t ! sun is mov+ along 8 pa? at ! rate ( ab\t a hundr$ & fifty million miles a ye>4 ,?is is ab\t five-six?s ( ! diamet] ( ! e>?'s orbit4 #cff4 ,/>-,drift4--,9 sev]al in/ances1 gr\ps ( />s h a common prop] motion entirely diff]5t f t ( ! />s ar\nd & among !m4 ,su* gr\ps probably =m connect$ sy/ems1 9 ! motion ( :i* all ! />s are c>ri$ along toge!r )\t any great *ange 9 _! relative positions4 ,! mo/ rem>kable case ( ?is k9d occurs 9 ! con/ellation ,taurus4 ,a l>ge majority ( ! bright] />s 9 ! region betwe5 ,aldeb>an & ! ,pleiades h a common prop] motion ( ab\t t5 seconds p] c5tury t[>ds ! ea/4 ,proctor has %[n t five out ( ! sev5 />s :i* =m ! ,great ,dipp] h a common prop] motion1 z %[n 9 ,fig4 #dbg 7see also ,fig4 #dbj74 ,he proposes = ?is ph5om5on ! "n ( ,/>-,drift4 ,illu/ration3 ,fig4 #dbg4 #cfg4 ,motion ( ,/>s along ! ,l9e ( ,sight4--,a motion ( a /> 9 ! direction ( ! l9e ( sight w\ld produce no displacem5t ( ! /> t c\ld be detect$ ) ! telescope2 b x w\ld cause a *ange 9 ! brightness ( ! />1 :i* w\ld become gradually fa9t] if mov+ f u1 & bright] if approa*+ u4 ,motion along ! l9e ( sight has1 h[ev]1 be5 detect$ by ! use ( ! tele-spectroscope 7#aeb71 ow+ to ! fact t x causes a displacem5t ( ! spectral l9es4 ,z has already be5 expla9$ 7#afi71 a displacem5t ( a spectral l9e t[>ds ! r$ end ( ! spectrum indicates a motion away f u1 & a displacem5t t[>ds ! violet end1 a motion t[>ds u4 99 99 99 99 99 ,by means ( ^! displacem5ts ( ! spectral l9es1 ,hugg9s has detect$ motion 9 ! case ( a l>ge numb] ( />s1 & calculat$ its rate3-- ,,/>s ,,rec$+ ,,f ,,u4 ,sirius #bj miles p] second4 ,betelgeuse #bb miles p] second4 ,rigel #ae miles p] second4 ,ca/or #be miles p] second4 ,regulus #ae miles p] second4 ,,/>s ,,approa*+ ,,u4 ,arcturus #ee miles p] second4 ,vega #ej miles p] second4 ,d5eb #ci miles p] second4 ,pollux #di miles p] second4 ,alpha ,urs ,majoris #df miles p] second4 ,^! results are confirm$ by ! fact t ! am\nt ( motion indicat$ is ab\t :at we %\ld expect ! />s to h1 f _! obs]v$ prop] motions1 comb9$ ) _! probable di/ances4 ,aga93 ! />s 9 ! neighborhood ( ,h]cules are mo/ly f\nd to be approa*+ ! e>?1 & ^? :i* lie 9 ! opposite direction to be rec$+ f x2 :i* is exactly ! effect :i* w\ld result f ! sun's motion ?r\gh space4 ,! five />s 9 ! ,dipp]1 :i* h a common prop] motion1 are also f\nd to h a common motion 9 ! l9e ( sight4 ,b ! displacem5t ( ! spectral l9es is s slight1 & its measurem5t s difficult1 t ! velocities 9 ! above table are to be accept$ z only an approximation to ! true values4 ,*emical & ,physical ,con/itution ( ! ,/>s4 #cfh4 ,! ,con/itution ( ! ,/>s ,simil> to t ( ! ,sun4--,! /ell> spectra be> a g5]al resemblance to t ( ! sun1 ) *>act]i/ic diff]5ces4 ,^! spectra all %[ ,fraunh(]'s l9es1 :i* indicate t _! lum9\s surfaces are surr\nd$ by atmosph]es conta9+ absorb5t vapors1 z 9 ! case ( ! sun4 ,! positions ( ^! l9es indicate t ! /ell> atmosph]es conta9 elem5ts :i* are also f\nd 9 ! sun's1 & on ! e>?4 ,illu/ration3 ,fig4 #dbh4 #cfi4 ,f\r ,types ( ,/ell> ,spectra4--,! spectra ( ! />s h be5 c>efully obs]v$ by ,sec*i & ,hugg9s4 ,!y h f\nd t /ell> spectra may be r$uc$ to f\r types1 :i* are %[n 9 ,fig4 #dbh4 ,9 ! spectrum ( ,sirius1 a repres5tative ( ,type ,i41 v few l9es are repres5t$2 b ! l9es are v ?ick4 ,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>1 & 9 ,type ,,iv41 :i* is t ( ! r$ />s1 no?+ b flut$ spaces is visible2 & ?is spectrum %[s t some?+ is at "w 9 ! atmosph]e ( ^? r$ />s diff]5t f :at !re is 9 ! simpl] atmosph]e ( ,type ,i4 ,locky] holds t ^! diff]5ces ( spectra are due simply to diff]5ces ( temp]ature4 ,accord+ to him1 ! r$ />s1 :i* give ! flut$ spectra1 are ( ! l[e/ temp]ature2 & ! temp]ature ( ! />s ( ! diff]5t types gradually rises till we rea* ! fir/ type1 9 :i* ! temp]ature is s high t ! dissociation 7#afa7 ( ! elem5ts is ne>ly if n q complete4 ,,iii4 ,,nebul4 ,classification ( ,nebul4 #cgj4 ,planet>y ,nebul4--,_m nebul 7#cbh7 pres5t a well-def9$ circul> disk1 l t ( a planet1 & are !re=e call$ planet>y nebul4 ,specim5s ( planet>y nebul are %[n 9 ,fig4 #dbi4 ,illu/ration3 ,fig4 #dbi4 #cga4 ,circul> & ,elliptical ,nebul4--,:ile _m nebul are circul> 9 =m1 o!rs are elliptical4 ,! =m] are call$ circul> nebul1 & ! latt] elliptical nebul4 ,elliptical nebul h be5 discov]$ ( e degree ( ecc5tricity4 ,examples ( v>i\s circul> & elliptical nebul are giv5 9 ,fig4 #dcj4 ,illu/ration3 ,fig4 #dcj4 #cgb4 ,annul> ,nebul4--,occasionally r+-%ap$ nebul h be5 obs]v$1 sometimes )1 & sometimes )\t1 nebul\s matt] )9 ! r+4 ,!y are call$ annul> nebul4 ,!y are bo? circul> & elliptical 9 =m4 ,sev]al specim5s ( ?is class ( nebul are giv5 9 ,fig4 #dca4 ,illu/ration3 ,fig4 #dca4 #cgc4 ,nebul\s ,/>s4--,sometimes "o or m m9ute />s are envelop$ 9 a nebul\s haze1 & are h5ce call$ nebul\s />s4 ,sev]al ( ^! nebul are %[n 9 ,fig4 #dcb4 ,illu/ration3 ,fig4 #dcb4 #cgd4 ,spiral ,nebul4--,v _m nebul disclose a m or less spiral /ructure1 & are kn[n z spiral nebul4 ,!y are illu/rat$ 9 ,fig4 #dcc4 ,!re are1 h[ev]1 a great v>iety ( spiral =ms4 ,we %all h occasion to speak ( ^! nebul aga9 7#cha-chc74 ,illu/ration3 ,fig4 #dcc4 #cge4 ,d\ble & ,multiple ,nebul4--,_m d\ble & multiple nebul h be5 obs]v$1 "s ( :i* are repres5t$ 9 ,fig4 #dcd4 ,illu/ration3 ,fig4 #dcd4 ,fig4 #dce %[s :at appe>s to be a d\ble annul> nebula4 ,fig4 #dcf gives two views ( a d\ble nebula4 ,! *ange ( position 9 ! compon5ts ( ?is d\ble nebula indicates a motion ( revolution simil> to t ( ! compon5ts ( d\ble />s4 ,illu/ration3 ,fig4 #dce4 ,illu/ration3 ,fig4 #dcf4 ,irregul> ,nebul4 #cgf4 ,irregul> ,=ms4--,besides ! m or less regul> =ms ( nebul :i* h be5 classifi$ z indicat$ above1 !re are _m ( v irregul> %apes1 & "s ( ^! are ! mo/ rem>kable nebul 9 ! heav5s4 ,fig4 #dcg %[s a curi\sly %ap$ nebula1 se5 by ,sir ,john ,h]s*el 9 ! s\!rn heav5s2 & ,fig4 #dch1 "o 9 ,taurus1 kn[n z ! ,crab nebula4 ,illu/ration3 ,fig4 #dcg4 ,illu/ration3 ,fig4 #dch4 #cgg4 ,! ,great ,nebula ( ,&rom$a4--,?is is "o ( ! few nebul t are visible to ! nak$ eye4 ,we see at a glance t x is n a />1 b a mass ( diffus$ light4 ,inde$1 x has sometimes be5 v naturally mi/ak5 = a comet4 ,x 0 fir/ describ$ by ,m>ius 9 #afad1 :o comp>$ its light to t ( a c&le %9+ ?r\gh horn4 ,?is gives a v good idea ( ! impression x produces1 :i* is t ( a transluc5t object illum9at$ by a brilliant light beh9d x4 ,) a small telescope x is easy to imag9e x to be a solid l horn2 b ) a l>ge "o ! effect is m l fog or mi/ ) a bright body 9 its mid/4 ,unlike mo/ ( ! nebul1 its spectrum is a cont9u\s "o1 simil> to t f a heat$ solid1 indicat+ t ! light emanates1 n f a gl[+ gas1 b f matt] 9 ! solid or liquid /ate4 ,?is w\ld sugge/ t x is really an imm5se />-clu/]1 s di/ant t ! highe/ telescopic p[] _c resolve x2 yet 9 ! l>ge/ telescopes x looks less resolvable1 & m l a gas1 ?an 9 ^? ( mod]ate size4 ,if x is really a gas1 & if ! spectrum is cont9u\s ?r\gh\t ! :ole ext5t ( ! nebula1 ei!r x mu/ %9e by reflect$ light1 or ! gas mu/ be subject$ to a great pressure almo/ to its out] limit1 :i* is h>dly possible4 ,if ! light is reflect$1 we _c det]m9e :e!r x comes f a s+le bright />1 or a numb] ( small ones scatt]$ ?r\gh ! nebula4 ,) a small telescope ?is nebula appe>s elliptical1 z 9 ,fig4 #dci4 ,fig4 #ddj %[s x z x appe>$ to ,bond1 9 ! ,cambridge refractor4 ,illu/ration3 ,fig4 #dci4 ,illu/ration3 ,fig4 #ddj4 #cgh4 ,! ,great ,nebula ( ,orion4--,! nebula :i*1 above all o!rs1 has occupi$ ! att5tion ( a/ronom]s1 & excit$ ! wond] ( obs]v]s1 is ! great nebula ( ,orion1 :i* surr\nds ! middle /> ( ! ?ree :i* =m ! sword ( ,orion4 ,a good eye w p]ceive t ?is />1 in/ead ( look+ l a bright po9t1 has a hazy appe>ance1 due to ! surr\nd+ nebula4 ,?is object 0 fir/ describ$ by ,huygh5s 9 #afei1 z foll[s3-- ,!re is "o ph5om5on among ! fix$ />s wor?y ( m5tion1 :i*1 s f> z ,i "k1 has hi!rto be5 notic$ by no "o1 & inde$ _c be well obs]v$ except ) l>ge telescopes4 ,9 ! sword ( ,orion are ?ree />s q close toge!r4 ,9 #afef1 z ,i *anc$ to be view+ ! middle "o ( ^! ) ! telescope1 in/ead ( a s+le />1 twelve %[$ !mselves 7a n uncommon circum/ance74 ,?ree ( ^! almo/ t\*$ ea* o!r1 & ) f\r o!rs %one ?r\gh a nebula1 s t ! space ar\nd !m seem$ f> bright] ?an ! re/ ( ! heav5s1 :i* 0 entirely cle>1 & appe>$ q black2 ! effect be+ t ( an op5+ 9 ! sky1 ?r\gh :i* a bright] region 0 visible4 ,illu/ration3 ,fig4 #dda4 ,! repres5tation ( ?is nebula 9 ,fig4 #dda is f a draw+ made by ,bond4 ,9 brilliancy & v>iety ( detail x exce$s any o!r nebula visible 9 ! nor!rn hemisph]e4 ,9 its c5tre are f\r />s1 easily di/+ui%$ by a small telescope ) a magnify+ p[] ( =ty or fifty1 toge!r ) two small] ones1 requir+ a n9e-in* telescope to be well se54 ,besides ^!1 ! :ole nebula is dott$ ) />s4 ,9 ! w9t] ( #ahfd-fe ! spectrum ( ?is nebula 0 exam9$ indep5d5tly by ,sec*i & ,hugg9s1 :o f\nd t x consi/$ ( ?ree bright l9es1 & h5ce conclud$ t ! nebula 0 compos$1 n ( />s1 b ( gl[+ gas4 ,! position ( "o ( ! l9es 0 ne> t ( a l9e ( nitrog51 :ile ano!r seem$ to co9cide ) a hydrog5 l9e4 ,?is w\ld sugge/ t ! nebula is a mixture ( hydrog5 & nitrog5 gas2 b ( ?is we _c be c]ta94 ,illu/ration3 ,fig4 #ddb4 #cgi4 ,! ,nebula 9 ,argus4--,!re is a nebula 7,fig4 #ddb7 surr\nd+ ! v>iable /> ,eta ,argus 7#cee71 :i* is rem>kable z exhibit+ v>iations ( brightness & ( outl9e4 ,9 _m o!r nebul1 *anges h be5 suspect$2 b ! indi/9ctness ( outl9e :i* *>act]izes mo/ ( ^! objects1 & ! v diff]5t aspect !y pres5t 9 telescopes ( diff]5t p[]s1 r5d] x difficult to prove a *ange beyond a d\bt4 #chj4 ,! ,dumb-,bell ,nebula4--,?is nebula 0 nam$ f its peculi> %ape4 ,x is a good illu/ration ( ! *ange 9 ! appe>ance ( a nebula :5 view$ ) diff]5t magnify+ p[]s4 ,fig4 #ddc %[s x z x appe>$ 9 ,h]s*el's telescope1 & ,fig4 #ddd z x appe>s 9 ! great ,p>son/[n reflector 7#bj74 ,illu/ration3 ,fig4 #ddc4 ,illu/ration3 ,fig4 #ddd4 ,spiral ,nebul4 #cha4 ,! ,spiral ,nebula 9 ,canes ,v5atici4--,! great spiral nebula 9 ! con/ellation ,canes ,v5atici1 or ! ,hunt+-,dogs1 is "o ( ! mo/ rem>kable ( its class4 ,fig4 #dde %[s ?is nebula z x appe>$ 9 ,h]s*el's telescope1 & ,fig4 #ddf %[s x z x appe>s 9 ! ,p>son/[n reflector4 ,illu/ration3 ,fig4 #dde4 ,illu/ration3 ,fig4 #ddf4 #chb4 ,cond5sation ( ,nebul4--,! appe>ance ( ! nebula j m5tion$ sugge/s a body rotat+ on its axis1 & und]go+ cond5sation at ! same "t4 ,x is n[ a g5]ally receiv$ !ory t nebul are ! mat]ial out ( :i* />s are =m$4 ,accord+ to ?is !ory1 ! />s orig9ally exi/$ z nebul1 & all nebul w ultimately become cond5s$ into />s4 ,illu/ration3 ,fig4 #ddg4 ,illu/ration3 ,fig4 #ddh4 ,illu/ration3 ,fig4 #ddi4 #chc4 ,o!r ,spiral ,nebul4--,fig4 #ddg repres5ts a spiral nebula ( ! ,great ,be>4 ,?is nebula seems to h sev]al c5tres ( cond5sation4 ,fig4 #ddh is a view ( a spiral nebula 9 ,cepheus1 & ,fig4 #ddi ( a s+ul> spiral nebula 9 ! ,triangle4 ,?is also appe>s to h sev]al po9ts ( cond5sation4 ,figs4 #dej & #dea repres5t oval & elliptical nebul hav+ a spiral /ructure4 ,illu/ration3 ,fig4 #dej4 ,illu/ration3 ,fig4 #dea4 ,,! ,,magellanic ,,cl\ds4 ,illu/ration3 ,fig4 #deb4 #chd4 ,situation & ,g5]al ,appe>ance ( ! ,magellanic ,cl\ds4--,! ,magellanic cl\ds are two nebul\s-look+ bodies ne> ! s\!rn pole ( ! heav5s1 z %[n 9 ! "r-h& portion ( ,fig4 #deb4 ,9 ! appe>ance & brightness ( _! light !y resemble portions ( ! ,milky-,way4 ,illu/ration3 ,fig4 #dec4 ,! l>g] ( ^! cl\ds is call$ ! ,nubecula ,major4 ,x is visible to ! nak$ eye 9 /rong moonlight1 & cov]s a space ab\t two hundr$ times ! surface ( ! moon4 ,x is %[n 9 ,fig4 #dec4 ,! small] cl\d is call$ ! ,nubecula ,m9or4 ,x has only ab\t a f\r? ! ext5t ( ! l>g] cl\d1 & is consid]ably less brilliant4 ,x is visible to ! nak$ eye1 b x disappe>s 9 full moonlight4 ,?is cl\d is %[n 9 ,fig4 #ded4 ,! region ar\nd ?is cl\d is s+ul>ly b>e ( />s2 b ! magnific5t clu/] ( ,t\can1 already describ$ 7#cdf71 is ne>1 & is %[n a little to ! "r ( ! cl\d 9 ! figure4 ,illu/ration3 ,fig4 #ded4 ,illu/ration3 ,fig4 #dee4 #che4 ,/ructure ( ! ,nubecul4--,fig4 #dee %[s ! /ructure ( ^! cl\ds z reveal$ by a p[]ful telescope4 ,! g5]al gr\nd ( bo? consi/s ( l>ge tracts & pat*es ( nebulosity 9 e /age ( resolution1--f t :i* is irresolvable ) eighte5 in*es ( reflect+ ap]ture1 up to p]fectly sep>at$ />s1 l ! ,milky-,way & clu/]+ gr\ps4 ,!re are also nebul 9 abundance1 bo? regul> & irregul>1 globul> clu/]s 9 e /ate ( cond5sation1 & objects ( a nebul\s "* q peculi>1 & unlike any ?+ 9 o!r regions ( ! heav5s4 ,9 ! area occupi$ by ! nubecula major two hundr$ & sev5ty-eight nebul & clu/]s h be5 enum]at$1 besides fifty or sixty outli]s1 :i* ought c]ta9ly to be reckon$ z its app5dages1 be+ ab\t six & a half p] squ>e degree2 :i* v f> exce$s ! av]age ( any o!r "p ( ! nebul\s heav5s4 ,9 ! nubecula m9or ! conc5tration ( su* objects is less1 ?\gh /ill v /rik+4 ,! nubecul1 !n1 comb9e1 ea* )9 its own area1 *>act]s :i* 9 ! re/ ( ! heav5s are no less /rik+ly sep>at$2 namely1 ^? ( ! galactic & ! nebul> sy/em4 ,globul> clu/]s 7except 9 "o region ( small ext5t7 & nebul ( regul> elliptic =ms are comp>atively r>e 9 ! ,milky-,way1 & are f\nd congregat$ 9 ! greate/ abundance 9 a "p ( ! heav5s ! mo/ remote possible f t circle2 :]eas 9 ! nubecul !y are indiscrim9ately mix$ ) ! g5]al />ry gr\nd1 & ) irregul> ?\gh small nebul4 ,,! ,,nebul> ,,hypo!sis4 #chf4 ,! ,basis ( ! ,nebul> ,hypo!sis4--,we h se5 t ! planets all revolve ar\nd ! sun f we/ to ea/ 9 ne>ly ! same plane1 & t ! sun rotates on 8 axis f we/ to ea/4 ,! planets1 s f> z kn[n1 rotate on _! axes f we/ to ea/2 & all ! moons1 except ^? ( ,uranus & ,neptune1 revolve ar\nd _! planets f we/ to ea/4 ,^! common features 9 ! motion ( ! sun1 moons1 & planets1 po9t to ! conclusion t !y are ( a common orig94 #chg4 ,kant's ,hypo!sis4--,kant1 ! celebrat$ ,g]man philosoph]1 seems to h ! be/ "r to be reg>d$ z ! f\nd] ( ! mod]n nebul> hypo!sis4 ,8 reason+ has be5 concisely /at$ ?us3 ,exam9+ ! sol> sy/em1 we f9d two rem>kable features pres5t$ to our consid]ation4 ,"o is1 t six planets & n9e satellites ! entire numb] !n kn[n move ar\nd ! sun 9 circles1 n only 9 ! same direction 9 :i* ! sun himself revolves on 8 axis1 b v ne>ly 9 ! same plane4 ,?is common feature ( ! motion ( s _m bodies c\ld n by any reasonable possibility h be5 a result ( *ance3 we are !re=e =c$ to believe t x mu/ be ! result ( "s common cause orig9ally act+ on all ! planets4 ,on ! o!r h&1 :5 we consid] ! spaces 9 :i* ! planets move1 we f9d !m entirely void1 or z good z void2 =1 if !re is any matt] 9 !m1 x is s r>e z to be )\t effect on ! planet>y motions4 ,!re is1 !re=e1 no mat]ial connection n[ exi/+ betwe5 ! planets ?r\gh :i* !y might h be5 =c$ to take up a common direction ( motion4 ,h[1 !n1 are we to reconcile ?is common motion ) ! abs5ce ( all mat]ial connection8 ,! mo/ natural way is to suppose t !re 0 once "s su* connection1 :i* br\ght ab\t ! uni=mity ( motion :i* we obs]ve2 t ! mat]ials ( :i* ! planets are =m$ once fill$ ! :ole space betwe5 !m4 ,!re 0 no =mation 9 ?is *aos1 ! =mation ( sep>ate bodies by ! mutual gravitation ( p>ts ( ! mass be+ a lat] occurr5ce4 ,b1 naturally1 "s p>ts ( ! mass w\ld be m d5se ?an o!rs1 & w\ld ?us ga!r ar\nd !m ! r>e matt] :i* fill$ ! int]v5+ spaces4 ,! l>g] collections ?us =m$ w\ld draw ! small] ones into !m1 & ?is process w\ld cont9ue until a few r\nd bodies _h tak5 ! place ( ! orig9al *aotic mass4 ,kant1 h[ev]1 fail$ to acc\nt satisfactorily = ! motion ( ! sun & planets4 ,accord+ to 8 sy/em1 all ! bodies =m$ out ( ! orig9al nebul\s mass %\ld h be5 drawn to a common c5tre s z to =m "o sun1 in/ead ( a sy/em ( revolv+ bodies l ! sol> sy/em4 #chh4 ,h]s*el's ,hypo!sis4--,! idea ( ! gradual transmutation ( nebul into />s seems to h be5 sugge/$ to ,h]s*el1 n by ! /udy ( ! sol> sy/em1 b by t ( ! nebul !mselves4 ,_m ( ^! bodies he believ$ to be imm5se masses ( phosphoresc5t vapor2 & he conceiv$ t ^! mu/ be gradually cond5s+1 ea* ar\nd its own c5tre1 or ar\nd ! p>ts :]e x is mo/ d5se1 until x %\ld become a />1 or a clu/] ( />s4 ,on classify+ ! nebul1 x seem$ to him t he c\ld see ?is process go+ on be=e 8 eyes4 ,!re 7 ! l>ge1 fa9t1 diffus$ nebul1 9 :i* ! cond5sation _h h>dly begun2 ! small] b bright] ones1 :i* _h become s f> cond5s$ t ! c5tral p>ts w\ld soon beg9 to =m into />s2 yet o!rs1 9 :i* />s _h actually begun to =m2 &1 f9ally1 />-clu/]s 9 :i* ! cond5sation 0 complete4 ,! spectroscopic revelations ( ! gase\s nature ( ! true nebul t5d to confirm ! !ory ( ,h]s*el1 t ^! masses w all1 at "s "t1 cond5se into />s4 #chi4 ,laplace's ,hypo!sis4--,laplace 0 l$ to ! nebul> hypo!sis by consid]+ ! rem>kable uni=mity 9 ! direction ( ! rotation ( ! planets4 ,believ+ t ?is c\ld n h be5 ! result ( *ance1 he s\ght to inve/igate its cause4 ,?is1 he ?\ght1 c\ld be no?+ else ?an ! atmosph]e ( ! sun1 :i* once ext5d$ s f> out z to fill all ! space n[ occupi$ by ! planets4 ,he beg9s ) ! sun1 surr\nd$ by ?is imm5se fi]y atmosph]e4 ,s9ce ! sum total ( rot>y motion n[ se5 9 ! planet>y sy/em mu/ h be5 !re f ! beg9n+1 he conceives ! imm5se vapor\s mass =m+ ! sun & 8 atmosph]e to h _h a sl[ rotation on its axis4 ,z ! int5sely hot mass gradually cool$1 x w\ld contract t[>ds ! c5tre4 ,z x contract$1 its velocity ( rotation w\ld1 by ! laws ( me*anics1 con/antly increase2 s t a "t w\ld arrive1 :51 at ! out] b\nd>y ( ! mass1 ! c5trifugal =ce due to ! rotation w\ld c\nt]balance ! attractive =ce ( ! c5tral mass4 ,!n ^? out] portions w\ld be left beh9d z a revolv+ r+1 :ile ! next inn] portions w\ld cont9ue to contract until ! c5trifugal & attractive =ces 7 aga9 balanc$1 :5 a second r+ w\ld be left beh9d2 & s on4 ,?us1 in/ead ( a cont9u\s atmosph]e1 ! sun w\ld be surr\nd$ by a s]ies ( conc5tric revolv+ r+s ( vapor4 ,z ^! r+s cool$1 _! d5s] mat]ials w\ld cond5se fir/2 & ?us ! r+ w\ld be compos$ ( a mix$ mass1 p>tly solid & p>tly vapor\s1 ! quantity ( solid matt] con/antly increas+1 & t ( vapor dim9i%+4 ,if ! r+ 7 p]fectly uni=m1 ?is cond5sation w\ld take place equally all ar\nd x1 & ! r+ w\ld ?us be brok5 up into a gr\p ( small planets1 l ! a/]oids4 ,b if1 z w\ld m likely be ! case1 "s portions ( ! r+ 7 mu* d5s] ?an o!rs1 ! d5s] portions w\ld gradually attract ! r>] portions1 until1 in/ead ( a r+1 !re w\ld be a s+le mass compos$ ( a ne>ly solid c5tre1 surr\nd$ by an imm5se atmosph]e ( fi]y vapor4 ,?is cond5sation ( ! r+ ( vapor ar\nd a s+le po9t w\ld n *ange ! am\nt ( rot>y motion t _h exi/$ 9 ! r+4 ,! planet ) its atmosph]e w\ld !re=e be 9 rotation2 & w\ld be1 on a small] scale1 l ! orig9al sol> mass surr\nd$ by its atmosph]e4 ,9 ! same way t ! latt] =m$ itself fir/ into r+s1 :i* aft]w>ds cond5s$ into planets1 s ! planet>y atmosph]es1 if suffici5tly ext5sive1 w\ld =m !mselves into r+s1 :i* w\ld cond5se into satellites4 ,9 ! case ( ,saturn1 h[ev]1 "o ( ! r+s 0 s uni=m ?r\gh\t1 t !re 0 no d5s] portion to attract ! re/ ar\nd x2 & ?us ! r+ ( ,saturn reta9$ its annul> =m4 ,illu/ration3 ,fig4 #def4 ,su* is ! celebrat$ nebul> hypo!sis ( ,laplace4 ,x />ts1 n ) a purely nebul\s mass1 b ) ! sun1 surr\nd$ by an imm5se atmosph]e1 out ( :i* ! planets 7 =m$ by gradual cond5sation4 ,fig4 #def repres5ts ! cond5s+ mass accord+ to ?is !ory4 #cij4 ,! ,mod]n ,nebul> ,hypo!sis4--,accord+ to ! nebul> hypo!sis z held at ! pres5t "t1 ! sun1 planets1 & meteoroids orig9at$ f a purely nebul\s mass4 ,?is nebula fir/ cond5s$ into a nebul\s />1 ! /> be+ ! sun1 & its surr\nd+ nebulosity be+ ! fi]y atmosph]e ( ,laplace4 ,! orig9al nebula mu/ h be5 put into rotation at ! beg9n+4 ,z x contract$ & became cond5s$ ?r\gh ! loss ( heat by radiation into space1 & "u ! comb9$ attraction ( gravity1 cohesion1 & aff9ity1 its spe$ ( rotation increas$2 & ! nebul\s envelop became1 by ! c5trifugal =ce1 flatt5$ into a ?9 disk1 :i* f9ally broke up into r+s1 out ( :i* 7 =m$ ! planets & _! moons4 ,accord+ to ,laplace1 ! r+s :i* 7 cond5s$ into ! planets 7 ?r[n (f 9 succession f ! equatorial region ( ! cond5s+ nebula2 & s ! out] planets w\ld be ! old]4 ,accord+ to ! m mod]n idea1 ! nebul\s mass 0 fir/ flatt5$ into a disk1 & subsequ5tly brok5 up into r+s1 9 su* a way t !re w\ld be no m>k$ diff]5ce 9 ! ages ( ! planets4 ,! sun repres5ts ! c5tral portion ( ! orig9al nebula1 & ! comets & meteoroids its outly+ portion4 ,at ! sun ! cond5sation is /ill go+ on1 & ! meteoroids appe> to be /ill gradually drawn 9 to ! sun & planets4 ,! :ole /ore ( en]gy ) :i* ! orig9al sol> nebula 0 end[$ exi/$ 9 x 9 ! pot5tial =m4 ,by ! cond5sation & contraction ?is en]gy 0 gradually trans=m$ into ! k9etic en]gy ( mol> motion & ( heat2 & ! heat became gradually dissipat$ by radiation into space4 ,?is trans=mation ( pot5tial en]gy into heat is /ill go+ on at ! sun1 ! c5tre ( ! cond5s+ mass1 by ! cond5sation ( ! sun itself1 & by ! impact ( meteors z !y fall into x4 ,x has be5 calculat$1 t1 by ! %r9k+ ( ! sun to ! d5sity ( ! e>?1 ! trans=mation ( pot5tial en]gy into heat w\ld g5]ate en\gh heat to ma9ta9 ! sun's supply1 at ! pres5t rate ( dissipation1 = sev5te5 million ye>s4 ,a %r9kage ( ! sun :i* w\ld g5]ate all ! heat he has p\r$ into space s9ce ! inv5tion ( ! telescope c\ld n be detect$ by ! mo/ p[]ful in/rum5ts yet con/ruct$4 ,! lea/ velocity ) :i* a meteoroid c\ld /rike ! sun w\ld be two hundr$ & eighty miles a second2 & x is easy to calculate h[ mu* heat w\ld be g5]at$ by ! collision4 ,x has be5 %[n1 t1 7 en\gh meteoroids to fall into ! sun to develop its heat1 !y w\ld n increase 8 mass appreciably dur+ a p]iod ( two ?\s& ye>s4 ,! sun's heat is und\bt$ly develop$ by contraction & ! fall ( meteoroids2 t is to say1 by ! trans=mation ( ! pot5tial en]gy ( ! orig9al nebula into heat4 ,x mu/ be borne 9 m9d t ! nebul> hypo!sis is simply a supposition z to ! way 9 :i* ! pres5t sol> sy/em may h be5 develop$ f a nebula end[$ ) a motion ( rotation & ) c]ta9 t5d5cies to cond5sation4 ,( c\rse no?+ c\ld h be5 develop$ out ( ! nebula1 ! g]ms ( :i* _h n be5 orig9ally implant$ 9 x by ! ,creator4 ,,iv4 ,,! ,,/ructure ,,( ,,! ,,/ell> ,,univ]se4 #cia4 ,sir ,william ,h]s*el's ,view4--,sir ,william ,h]s*el assum$ t ! />s are di/ribut$ ) tol]able uni=mity ?r\gh\t ! space occupi$ by our /ell> sy/em4 ,he acc\nt$ = ! increase 9 ! numb] ( />s 9 ! field ( view z he approa*$ ! plane ( ! ,milky-,way1 n by ! supposition t ! />s are really clos] toge!r 9 & ab\t ?is plane1 b by ! supposition t our /ell> sy/em is 9 ! =m ( a flat disk clov5 at "o side1 & ) our sun ne> its c5tre4 ,a section ( ?is disk is %[n 9 ,fig4 #deg4 ,illu/ration3 ,fig4 #deg4 ,an obs]v] ne> ,s1 ) 8 telescope po9t$ 9 ! direction ( ,s b1 w\ld see comp>atively few />s )9 ! field ( view1 because look+ ?r\gh a comp>atively ?9 /ratum ( />s4 ,) 8 telescope po9t$ 9 ! direction ,s a1 he w\ld see _m m />s )9 8 field ( view1 ev5 ?\gh ! />s 7 really no ne>] toge!r1 because he w\ld be look+ ?r\gh a ?ick] /ratum ( />s4 ,z he direct$ 8 telescope m & m ne>ly 9 ! direction ,s f1 he w\ld be look+ ?r\gh a ?ick] & ?ick] /ratum ( />s1 & h5ce he w\ld see a great] & great] numb] ( !m 9 ! field ( view1 ?\gh !y 7 ev]y:]e 9 ! disk di/ribut$ at uni=m di/ances4 ,he assum$1 also1 t ! />s are all tol]ably uni=m 9 size1 & t c]ta9 />s appe> small] ?an o!rs1 only because !y are f>!r (f4 ,he suppos$ ! fa9t />s ( ! ,milky-,way to be m]ely ! mo/ di/ant />s ( ! /ell> disk2 t !y are really z l>ge z ! o!r />s1 b appe> small ow+ to _! great di/ance4 ,! disk 0 assum$ to be clov5 on "o side1 to acc\nt = ! division ( ! ,milky-,way ?r\gh ne>ly half ( its c\rse4 ,?is !ory ( ! /ructure ( ! /ell> univ]se is (t5 ref]r$ to z ! clov5 disk !ory4 ,illu/ration3 ,fig4 #deh4 #cib4 ,! ,clov5 ,r+ ,!ory4--,accord+ to ,mdl]1 ! />s ( ! ,milky-,way are entirely sep>at$ f ! o!r />s ( our sy/em1 belong+ to an outly+ r+1 or sy/em ( r+s4 ,to acc\nt = ! division ( ! ,milky-,way1 ! r+ is suppos$ to be clov5 on "o side3 h5ce ?is !ory is (t5 ref]r$ to z ! clov5 r+ !ory4 ,accord+ to ?is hypo!sis1 ! /ell> sy/em view$ f )\t w\ld pres5t an appe>ance some:at l t 9 ,fig4 #deh4 ,! outly+ r+ clov5 on "o side w\ld repres5t ! />s ( ! ,milky-,way2 & ! lum9\s mass at ! c5tre1 ! rema9+ />s ( ! sy/em4 #cic4 ,proctor's ,view4--,accord+ to ,proctor1 ! ,milky-,way is compos$ ( an irregul> spiral /ream ( m9ute />s ly+ 9 & among ! l>g] />s ( our sy/em1 z repres5t$ 9 ,fig4 #dei4 ,! spiral /ream is %[n 9 ! inn] circle z x really exi/s among ! />s1 & 9 ! out] circle z x is se5 project$ ^u ! sky4 ,accord+ to ?is view1 ! />s ( ! ,milky-,way appe> fa9t1 n because !y are di/ant1 b because !y are really small4 ,illu/ration3 ,fig4 #dei4 #cid4 ,newcomb's ,view4--,accord+ to ,newcomb1 ! />s ( our sy/em are all situat$ 9 a comp>atively ?9 zone ly+ 9 ! plane ( ! ,milky-,way1 :ile !re is a zone ( nebul ly+ on ea* side ( ! /ell> zone4 ,he believes t s mu* is c]ta9 ) ref]5ce to ! /ructure ( our /ell> univ]se2 b he consid]s t we are z yet comp>atively ignorant ( ! int]nal /ructure ( ei!r ! /ell> or ! nebul> zones4 ,! /ructure ( ! /ell> univ]se1 accord+ to ?is view1 is %[n 9 ,fig4 #dfj4 ,illu/ration3 ,fig4 #dfj4 ,,index ,a4 ,ab]ration ( light1 #ch4 ,a]olites1 #cjd4 ,aldeb>an1 /> 9 ,taurus1 #cdj1 #cdb4 ,algol1 a v>iable />1 #cdc1 #ceh4 ,almanac1 p]petual1 #hb4 ,alps1 lun> m\nta9s1 #abf4 ,altair1 /> 9 ,aquila1 #ccf4 ,alt-azimu? in/rum5t1 #ac4 ,altitude1 #ab4 ,&rom$a 7con/ellation71 #cdc1 #cdf4 nebula 91 #cgf4 ,ang/rm's map ( spectrum1 #afd4 ,ant>es1 /> 9 ,scorpio1 #cdg4 ,ap5n9es1 lun> m\nta9s1 #abb1 #abd4 ,aphelion1 #dg4 ,apogee1 #dd4 ,aqu>ius1 or ! ,wat]-,be>]1 #cej4 clu/] 91 #ced4 ,aquila1 or ! ,eagle1 #ccf4 ,arcturus1 /> 9 ,botes1 #cce1 #cfe1 #cgj4 ,argo1 or ! ,%ip1 #cfj4 nebula 91 #chc4 v>iable /> 91 #cfj4 ,aries1 or ! ,ram1 #cej4 ,a/]oids1 #bbc1 #bda4 ,a/ra1 an a/]oid1 #bda4 ,auriga1 or ! ,wagon]1 #cdb4 ,azimu?1 #ac4 ,b4 ,betelgeuse1 /> 9 ,orion1 #cdj1 #cgj4 ,b]5ice's ,hair 7con/ellation71 #ccd4 ,bode's law1 #bda4 disprov$1 #bgc4 ,botes 7con/ellation71 #ccd1 #cce4 ,c4 ,cal5d>1 !1 #hj4 ,calli/o1 moon ( ,jupit]1 #bej4 ,canc]1 or ! ,crab1 #cej4 tropic (1 #fa4 ,canes ,v5atici1 or ! ,hunt+-,dogs1 #ccd4 ,canes ,v5atici1 nebula 91 #chd4 ,canis ,major1 or ! ,great ,dog1 #cdb4 ,canis ,m9or1 or ! ,little ,dog1 #cdj4 ,capella1 /> 9 ,auriga1 #cdj1 #cdc4 ,capricorn1 tropic (1 #fa4 ,capricornus1 or ! ,goat1 #cej4 ,cassiopeia 7con/ellation71 #ccb4 new /> 91 #cfb4 ,ca/or1 /> 9 ,gem9i1 #cdj1 #cgj4 ,caucasus1 a lun> range1 #abd4 ,c5taurus1 />-clu/] 91 #cee4 ,cepheus 7con/ellation71 #ccd4 nebula 91 #chg4 ,c]es1 ! planet1 #bda4 ,cetus1 or ! ,:ale1 #cdf4 v>iable /> 91 #cei4 ,*>les's ,wa91 #ccj4 ,circles1 great1 #d4 diurnal1 #h4 h\r1 #af4 small1 #d4 v]tical1 #ab4 ,clock1 a/ronomical1 #ah4 "t1 #gh4 ,coma ,b]5ices1 or ,b]5ice's ,hair1 #ccd4 ,comet1 ,biela's1 #bic4 & e>?1 collision (1 #caf4 ,coggia's1 #big4 ,donati's1 #bif4 ,encke's1 #bic4 ,halley's1 #bia4 ( #afhj1 #bij4 ( #ahaa1 #bij4 ( #ahdc1 #bie4 ( #ahfa1 #big4 ( ,june1 #ahha1 #cjj4 ,comets1 appe>ance (1 #bgd4 & meteors1 #cac4 bright1 #bgd4 *emical con/itution (1 #cah4 developm5t (1 #bgg4 numb] (1 #bhh4 orbits (1 #bhb4 orig9 (1 #bhg4 p]iodic1 #bhf4 physical con/itution (1 #cad4 tails (1 #bgi4 telescopic1 #bge1 #bha4 visibility (1 #bha4 ,conic sections1 #dh4 ,conjunction1 #ia4 inf]ior1 #acj4 sup]ior1 #acj1 #acf4 ,con/ellations1 #cbe4 zodiacal1 #cb4 ,cop]nican sy/em1 !1 #dd1 #ec4 ,cop]nicus1 a lun> crat]1 #abj1 #abi4 ,corona ,borealis1 or ! ,nor!rn ,cr[n1 #ccf4 ,corona ,borealis1 new /> 91 #cfc4 ,corvus1 or ! ,cr[1 #cci4 ,cry/all9e sph]es1 #da4 ,cycles & epicycles1 #db4 ,cygnus1 or ! ,swan1 #cch4 ,d4 ,day & night1 #eg4 civil1 #gg4 lun>1 #ajh4 sid]eal1 #gd4 sol>1 #gd4 ,decl9ation1 #af4 ,deimos1 satellite ( ,m>s1 #bci4 ,delph9us1 or ! ,dolph91 #cch4 ,d5eb1 /> 9 ,cygnus1 #cch1 #cgj4 ,dione1 satellite ( ,saturn1 #bei4 ,dipp]1 ! ,great1 #ccj1 #cff1 #cfi1 #cgj4 ! ,little1 #cca4 ! ,milk1 #cdg4 ,dissociation1 #afc4 ,dom9ical ,lett]1 !1 #ha4 ,draco1 or ! ,dragon1 #cca4 ,e4 ,e>?1 d5sity (1 #he4 flatt5$ at poles1 #ee4 =m (1 #ec4 9 space1 #ef4 se5 f moon1 #aji4 size (1 #ee4 weight (1 #hc4 ,ecc5tric1 ! #dc4 ,ecc5tricity1 #df4 ,eclipses1 #baj4 annul>1 #bai4 lun>1 #baj1 #bad4 sol>1 #baf4 ,ecliptic1 !1 #bg4 obliquity (1 #bh4 ,ellipse1 !1 #de1 #di4 ,elongation1 ( planet1 #acj4 ,enceladus1 moon ( ,saturn1 #bei4 ,epicycles1 #db4 ,epicycloid1 #ajg4 ,epsilon ,lyr1 a d\ble />1 #cef4 ,equator1 ! cele/ial1 #g4 ,equ9octial1 !1 #g4 colure1 #af4 elevation (1 #i4 ,equ9ox1 autumnal1 #bi4 v]nal1 #af1 #bi4 ,equ9oxes1 precession (1 #ca1 #he4 ,eta ,argus1 a v>iable />1 #cfj1 #chc4 ,europa1 moon ( ,jupit]1 #bej4 ,f4 ,facul1 sol>1 #agg4 ,fomalhaut1 /> 9 ,s\!rn ,fi%1 #cej4 ,fraunh(]'s l9es1 #afd1 #cga4 ,g4 ,galaxy1 !1 #cbf4 ,ganym$e1 moon ( ,jupit]1 #bej4 ,gem9i1 or ! ,tw9s1 #cdj4 ,georgium ,sidus1 #bga4 ,h4 ,h]cules 7con/ellation71 #ccf4 clu/] 91 #cec4 orbit ( d\ble /> 91 #ceg4 sol> sy/em mov+ t[>ds1 #cfg4 ,h]s*el1 ! planet 7see ,uranus74 ,h]s*el's hypo!sis1 #cib1 #cif4 ,horizon1 !1 #e4 ,hyades1 !1 #cdb1 #cej4 ,hydra1 or ! ,wat]-,snake1 #cdj4 ,hyp]bola1 !1 #di4 ,hyp]ion1 moon ( ,saturn1 #bei4 ,i4 ,io1 moon ( ,jupit]1 #bej4 ,irradiation1 #ij1 #aac4 ,j4 ,japetus1 moon ( ,saturn1 #bei4 ,job's ,c(f9 7a/]ism71 #cch4 ,juno1 ! planet1 #bda4 ,jupit]1 app>5t size (1 #bde4 di/ance (1 #bde4 great r$ spot (1 #bdi4 orbit (1 #bdd4 p]iods (1 #bdf4 physical con/itution (1 #bdf4 rotation (1 #bdh4 satellites (1 #bej4 eclipses (1 #beb4 transits (1 #bed4 volume (1 #bde4 )\t satellites1 #bee4 ,k4 ,kant's hypo!sis1 #cia4 ,kepl]1 a lun> crat]1 #abi4 ,kepl]'s sy/em1 #dd4 laws1 #df4 />1 #cfb4 ,kir*h(f's map ( spectrum1 #afd4 ,l4 ,laplace's hypo!sis1 #cib4 ,latitude1 cele/ial1 #cj4 ,leap ye>1 #ha4 ,leo1 or ! ,lion1 #ccd4 ,leonids 7meteors71 #cab4 ,libra1 or ! ,balances1 #cdg4 ,libration1 #ajb4 ,longitude1 cele/ial1 #cj4 ,lyra1 or ! ,lyre1 #cch4 d\ble /> 91 #cef4 ,m4 ,magellanic cl\ds1 !1 #chi4 ,magnetic /orms1 #aij4 ,magnetism & sun-spots1 #aij4 ,m>s1 app>5t size (1 #bcf4 brilliancy (1 #bcg4 di/ance (1 #bce4 orbit (1 #bce4 p]iods (1 #bcg4 rotation (1 #bci4 satellites (1 #bci4 volume (1 #bcf4 ,m]cury1 app>5t size (1 #bbf4 atmosph]e (1 #bbh4 di/ance (1 #bbe4 elongation (1 #bbg4 orbit (1 #bbe4 p]iods (1 #bbg4 volume (1 #bbf4 ,m]idian1 !1 #ab4 ,m]idian circle1 #ag4 ,m]idians1 cele/ial1 #ca4 ,meteoric iron1 #cje1 #cjg4 %[]s1 #caj4 /ones1 #cje4 ,meteors1 #cjj4 ,augu/1 #caa4 light (1 #cji4 ,novemb]1 #cab4 sporadic1 #caj4 ,meteoroids1 #cjh4 ,micromet]s1 #bj1 #aec4 ,milky-,way1 !1 #cbf4 ,mimas1 moon ( ,saturn1 #bei4 ,mira1 a v>iable />1 #cei4 ,moon1 app>5t size (1 #hg1 #hi4 aspects (1 #ia4 atmosph]e (1 #aji4 *asms 91 #abc4 crat]s 91 #aai4 day (1 #ajh4 di/ance (1 #hf4 eclipses (1 #baj4 =m ( orbit1 #ig4 h>ve/1 #aja4 hunt]'s1 #ajb4 incl9ation ( orbit1 #ig4 kept 9 h] pa? by gravity1 #ea4 librations (1 #ajb4 mass (1 #ij4 m]idian altitude (1 #ih4 m\nta9s (1 #aaf4 orbital motion (1 #ia4 phases (1 #ic4 real size (1 #hh4 ris+ (1 #ii4 rotation (1 #ajb4 sid]eal p]iod (1 #ib4 surface (1 #aae4 synodical p]iod (1 #ib4 t]m9ator (1 #aae4 wet & dry1 #ih4 ,n4 ,nadir1 !1 #f4 ,neap-tides1 #gb4 ,nebula1 9 ,&rom$a1 #cgf4 crab1 #cgf4 dumb-bell1 #chc4 9 ,argus1 #chc4 9 ,canes ,v5atici1 #chd4 9 ,cepheus1 #chg4 9 ,orion1 #cgh4 9 ! ,triangle1 #chg4 9 ,ursa ,major1 #chf4 ,nebul1 #bha1 #ccj1 #cgc4 annul>1 #cgc4 circul>1 #cgc4 cond5sation (1 #che4 d\ble1 #cge4 elliptical1 #cgc4 irregul>1 #cgf4 multiple1 #cge4 spiral1 #cgc1 #chd4 ,nebul> hypo!sis1 !1 #cia4 ,neptune1 discov]y (1 #bga4 orbit (1 #bga4 satellite (1 #bgd4 ,new /yle1 #hj4 ,newcomb's !ory ( ! /ell> univ]se1 #cih4 ,newton's sy/em1 #dh4 ,nodes1 #ig4 ,nubecula1 ,major1 #chi4 ,m9or1 #chi4 ,nutation1 #cd4 ,o4 ,olb]s's hypo!sis1 #bda4 ,old /yle1 #hj4 ,ophiu*us 7con/ellation71 #cdg4 new /> 91 #cfb4 ,opposition1 #ia1 #acf4 ,orion1 #cda4 nebula 91 #cgh4 ! trapezium (1 #cef4 ,p4 ,pallas1 ! planet1 #bda4 ,p>abola1 !1 #di4 ,p>allax1 #cg4 ,pegasus 7con/ellation71 #cdc1 #cdf4 triple /> 91 #cef4 ,p]igee1 #dd4 ,p]ihelion1 #dg4 ,p]seids 7meteors71 #caa4 ,p]seus 7con/ellation71 #cdf4 clu/] 91 #cec4 ,phobos1 satellite ( ,m>s1 #bci4 ,pico1 a lun> m\nta91 #abg4 ,pisces1 or ! ,fi%es1 #cej4 ,piscis ,au/ralis1 or ! ,s\!rn ,fi%1 #cej4 ,planets1 #ci4 inf]ior1 #acj4 p]iods (1 #acb4 phases (1 #acb4 inn] gr\p (1 #bba4 intra-,m]curial1 #bcj4 m9or1 #bbc4 out] gr\p (1 #bbb1 #bdd4 sup]ior1 #acd4 motion (1 #acd4 p]iods (1 #acg4 phases (1 #acg4 ?ree gr\ps (1 #bba4 ,pleiades1 !1 #cbh1 #cdb1 #cea4 ,po9t]s1 !1 #ccj4 ,pol> di/ance1 #af4 ,pole ,/>1 !1 #g1 #ccj1 #cfe4 ,poles1 cele/ial1 #g1 #i4 ,pollux1 /> 9 ,gem9i1 #cdj1 #cgj4 ,prsepe1 or ! ,beehive1 #cej4 ,precession ( equ9oxes1 #ca1 #he4 ,prime v]tical1 !1 #ab4 ,proctor's !ory ( ! /ell> univ]se1 #cih4 ,procyon1 /> 9 ,canis ,m9or1 #cdj4 ,ptolemaic sy/em1 !1 #da4 ,q4 ,quadrature1 #ia1 #acg4 ,r4 ,radiant po9t 7meteors71 #caj4 ,radius vector1 #dg4 ,refraction1 #ce4 ,regulus1 /> 9 ,leo1 #ccd1 #cgj4 ,rhea1 moon ( ,saturn1 #bei4 ,rigel1 /> 9 ,orion1 #cdj1 #cgj4 ,"r asc5sion1 #af4 ,s4 ,sagitt>ius1 or ! ,ar*]1 #cdg4 ,saturn1 app>5t size (1 #bef4 di/ance (1 #bef4 orbit (1 #bee4 p]iods (1 #bef4 physical con/itution (1 #beg4 r+ (1 #bfa4 *anges 91 #bfh4 con/itution (1 #bfi4 phases (1 #bfc4 rotation (1 #beh4 satellites (1 #bei4 volume (1 #bef4 ,scorpio1 or ! ,scorpion1 #cdg4 clu/] 91 #cee4 ,seasons1 !1 #fd4 ,sirius1 ! ,dog-,/>1 #cdj1 #cdb1 #cfe1 #cgj1 #cga4 ,sol> sy/em1 !1 #da4 ,sol/ices1 #bi1 #ei1 #fj4 ,s\nd1 effect ( motion on1 #afh4 ,spectra1 bright-l9$1 #aeh4 comp>ison (1 #aed4 cont9u\s1 #aeh4 displacem5t ( l9es 91 #aga4 ( comets1 #cah4 rev]s$1 #afa4 sun-spot1 #aic4 types ( /ell>1 #cga4 ,spectroscope1 !1 #aeb4 diffraction1 #aeg4 direct-vision1 #aee4 disp]sion1 #aeb4 ,spectrum analysis1 #aei4 sol>1 #afd4 ,sph]e1 def9$1 #c4 ! cele/ial1 #e4 rotation (1 #g4 ,spr+-tides1 #gb4 ,/>s1 circumpol>1 #g4 clu/]s (1 #cbh1 #cej4 color (1 #ceg4 con/ellations (1 #cbe4 con/itution (1 #cga4 di/ance (1 #cfd4 d\ble1 #cee4 drift (1 #cfh4 f\r sets (1 #aj4 magnitude (1 #cbb4 motion (1 9 l9e ( sight1 #cfi4 multiple1 #cef4 names (1 #cbe4 nebul\s1 #cgc4 new1 #cfa4 numb] (1 #cbc4 p>allax (1 #cfd4 prop] motion (1 #cfe4 secul> displacem5t (1 #cff4 tempor>y1 #cfa4 v>iable1 #ceh4 ,sun1 atmosph]e (1 #adi4 brightness (1 #aea4 *emical con/itution (1 #afd4 *romosph]e (1 #adi1 #aif4 corona (1 #adi1 #aif1 #bjd4 di/ance (1 #adb4 facul (1 #agg4 heat radiat$ by1 #aej4 incl9ation ( axis (1 #ahg4 mass (1 #adj4 motion (1 among ! />s1 #bf4 at surface (1 #afh4 9 atmosph]e (1 #agb4 secul>1 #cff4 photosph]e (1 #adi1 #age4 prom95ces (1 #adi1 #aig4 rotation (1 #ahf4 spectrum (1 #afd1 #aga4 temp]ature (1 #adi4 volume (1 #adj4 w9ds on1 #agd4 ,sun-spots1 #agi4 & magnetism1 #aij4 bir? & decay (1 #ahe4 cause (1 #aid4 cyclonic motion 91 #ahb4 di/ribution (1 #ahh4 duration (1 #aha4 gr\ps (1 #aha4 p]iodicity (1 #ahi4 prop] motion (1 #ahg4 size (1 #aha4 spectrum (1 #aic4 ,t4 ,taurus1 or ! ,bull1 #cdb4 quadruple /> 91 #cef4 ,telescope1 ,cassegra9ian1 #bc4 equatorial1 #ai4 front-view1 #bb4 ,gregorian1 #bc4 ,h]s*elian1 #bb4 ,"l ,rosse's1 #be4 ,melb\rne1 #be4 ,newall1 #bj4 ,newtonian1 #bb4 ,p>is1 #bf4 reflect+1 #ba4 ,wa%+ton1 #bj4 ,vi5na1 #bj4 ,telespectroscope1 !1 #aee4 ,telluric l9es ( spectrum1 #afe4 ,te?ys1 moon ( ,saturn1 #bei4 ,tides1 #fg4 ,"t1 clock1 #gh4 sun1 #gh4 ,titan1 moon ( ,saturn1 #bei1 #bfa4 ,t\can1 /> clu/] 91 #ced1 #chi4 ,transit in/rum5t1 #ag4 ,transits ( ,v5us1 #ade4 ,triesnek]1 lun> =mation1 #abc4 ,tropics1 #fa4 ,twilight1 #fb4 ,ty*o ,brahe's />1 #cfa4 sy/em1 #dd4 ,ty*o1 a lun> crat]1 #abi4 ,u4 ,univ]se1 /ructure ( ! /ell>1 #cif4 ,uranus1 discov]y (1 #bga4 "n (1 #bgj4 orbit (1 #bfi4 satellites (1 #bga4 ,ursa ,major1 or ! ,great ,be>1 #ccj4 nebula 91 #chf4 ,ursa ,m9or1 or ! ,little ,be>1 #ccj4 ,v4 ,vega1 /> 9 ,lyra1 #ccf1 #cfe1 #cgj4 ,v5us1 app>5t size (1 #bca4 atmosph]e (1 #bcd4 brilliancy (1 #bcb4 di/ance (1 #bca4 elongation (1 #bca4 orbit (1 #bcj4 p]iods (1 #bcb4 volume (1 #bca4 transits (1 #ade1 #bcd4 ,v]ni]1 !1 #ae4 ,virgo1 or ! ,virg91 #cch4 ,ve/a1 ! planet1 #bda4 ,vulcan1 ! planet1 #bcj4 ,y4 ,ye>1 !1 #gh4 anomali/ic1 #gi4 ,julian1 #hj4 sid]eal1 #gi4 tropical1 #gi4 ,z4 ,z5i?1 !1 #f4 di/ance1 #ab4 ,zodiac1 !1 #cb4 ,zodiacal con/ellations1 #cb4 light1 #cah4 ,zones1 #fa4 99 99 99 99 99 99 ,transcrib]'s note3 ,miss+ or obscur$ punctuation 0 correct$4 ,typographical errors 7 sil5tly correct$4