,,cl\d ,,/udies ,illu/ration3 ,a ,,sunset ,,sky4 ,frontispiece4 ,,cl\d ,,/udies ,by ,,ar?ur ,w4 ,,clayd51 ,m4,a4 ,,pr9cipal ,,( ,,! ,,royal ,,alb]t ,,memorial ,,college1 ,,exet] ,,london ,,john ,,murray1 ,,albem>le ,,/reet #aije ,,pr9t$ ,,by ,,william ,,cl[es ,,& ,,sons1 ,,limit$1 ,,london ,,& ,,beccles4 ,,preface ,to ! meteorologi/ ,i hope ! foll[+ pages may prove n only ( "s int]e/1 b ( practical value z a small /ep t[>ds t great] exactness ( language :i* is ess5tial be=e we c attempt to expla9 all ! details ( cl\d /ructure1 or ev5 int]*ange our ideas & obs]vations ) adequate precision4 ,! v>ieties depict$ & describ$ h be5 select$ f _m hundr$s1 z ^? :i* seem to me to %[ su* diff]5ces ( =m z to imply di/9ct diff]5ces 9 ! conditions to :i* !y are due4 ,i h n attempt$ to deal ) ! physical causes ( cond5sation except 9 a g5]al way1 be+ unwill+ to introduce diagrams ( iso!rmals & adiabatics & su* purely sci5tific me?ods into a "w also int5d$ = a wid] public4 ,= ^? :o wi% to pursue ?is "p ( ! subject ,i h app5d$ a li/ ( pap]s f ! ,qu>t]ly ,j\rnal ( ! ,royal ,meteorological ,society & o!r s\rces1 :i* may s]ve z ref]5ces4 ,i also hope t "s m vot>ies ( ! sci5ce may be induc$ to realize t meteorology does n consi/ solely ( ! tabulation ( long columns ( records1 b includes subjects = inve/igation z mu* m beautiful z !y are m difficult4 ,to ! arti/ ,i tru/ !y may also be ( "s use1 by call+ att5tion to ! v>iety & exquisite beauty ( ! sky4 ,no?+ is m extraord9>y 9 art ?an ! g5]al neglig5ce ( cl\d-=ms4 ,_m ( !m are q z wor?y ( c>eful draw+ z ! leaves ( a tree1 ! fl[]s ( a field1 ! ripples on a /ream1 or ! texture ( a c>pet1 or a m>ble pavem5t4 ,yet x is ! common rule to f9d pictures1 :i* are o!rwise m>vell\s examples ( skill & c>e1 disfigur$ by impossible skies ) vague1 %apeless cl\ds1 z untrue to nature z x w\ld be possible to make !m4 ,grace ( outl9e1 delicacy ( detail & texture1 ri*ness ( contra/1 beauty ( =m & light & col\r1 all are pres5t 9 ! skies1 & comb9e to make a :ole well wor?y ( ! be/ t art c give4 ,! illu/rations ,i (f] are n select$ = pictorial effect2 !y are *os5 f a purely sci5tific po9t ( view2 b !y are en\gh to indicate :at c\ld be done if ! facts ( nature 7 treat$ ) high arti/ic skill4 ,9 addition to ! meteorologi/ & ! arti/1 !re are a mu* l>g] numb] :o foll[ nei!r pr(ession1 b :o love ,nature 9 all h] moods2 & to !m also ,i hope ^! pages may be ( int]e/4 ,inde$1 if only a few ( !m %\ld be /imulat$ to take up a bran* ( nature /udy :i* has giv5 me _m an h\r ( quiet enjoym5t1 ! lab\r ( br++ ^! notes toge!r w n h be5 9 va94 ,,ar?ur ,w4 ,,clayd54 ,/4 ,john's1 ,exet]4 ,,cont5ts ,,*apt] ,,page ,i4 ,introductory #a ,,ii4 ,cirrus #ba ,,iii4 ,cirro-/ratus & ,cirro-cumulus #de ,,iv4 ,alto ,cl\ds #ei ,v4 ,l[] ,cl\ds #ga ,,vi4 ,cumulus #hd ,,vii4 ,cumulo-nimbus #aje ,,viii4 ,wave ,cl\ds #aai ,,ix4 ,cl\d ,altitudes #acg ,x4 ,cl\d ,nom5clature #aed ,,xi4 ,cl\d ,photography #afe ,ref]5ces #aha ,index #ahc ,,li/ ,,( ,,illu/rations ,,plate ,,page ,a ,sunset ,sky ,frontispiece #a4 ,"p ( a ,great ,halo #bb #b4 ,"p ( a ,sol> ,halo #bc #c4 ,cirro-nebula *ang+ to ,cirro-/ratus #bd #d4 ,cirro-nebula *ang+ to ,cirro-cumulus #bg #e4 ,high ,cirrus4 7,cirrus ,excelsus7 #ca #f4 ,w9dy ,cirrus4 7,cirrus ,v5tosus7 #cb #g4 ,?read ,cirrus4 7,cirro-filum7 #cd #h4 ,tail$ ,cirrus4 7,cirrus ,caudatus7 #ce #i4 ,hazy ,cirrus4 7,cirrus ,nebulosus7 #cf #aj4 ,*ange ,cirrus4 7,cirrus ,incon/ans7 #cg #aa4 ,common ,cirrus4 7,cirrus ,communis7 #dj #ab4 ,b& ,cirrus4 7,cirrus ,vittatus7 #da #ac4 ,b& ,cirrus4 7,cirrus ,vittatus7 #db #ad4 ,hazy ,cirro-/ratus4 7,cirro-/ratus ,nebulosus7 #df #ae4 ,cirro-/ratus #dg #af4 ,cirro-/ratus4 7,cirro-/ratus ,communis7 #dh #ag4 ,floccul5t ,cirro-/ratus4 7,cirro-/ratus ,cumulosus7 #di #ah4 ,cirro-/ratus & ,cirro-cumulus #ej #ai4 ,cirro-cumulus #ej #bj4 ,hazy ,cirro-cumulus4 7,cirro-cumulus ,nebulosus7 #ea #ba4 ,hazy ,cirro-cumulus4 7,cirro-cumulus ,nebulosus7 #ea #bb4 ,a ,sunset ,sky #eb #bc4 ,speckle ,cl\d 7,ley74 7,cirro-macula7 #ec #bd4 ,cirrus ,caudatus & ,cirro-macula #ee #be4 ,alto-cumulus ,in=mis #fd #bf4 ,hazy ,alto-cumulus4 7,alto-cumulus ,nebulosus7 #fe #bg4 ,flat ,alto-cumulus4 7,alto-cumulus ,/rati=mis7 #fe #bh4 ,high ,turret$ ,cl\d4 7,alto-cumulus ,ca/ellatus7 #ff #bi4 ,high ,ball ,cumulus4 7,alto-cumulus ,glom]atus7 #fg #cj4 ,mack]el ,sky4 7,alto-/ratus ,maculosus7 #fh #ca4 ,mack]el ,sky4 7,alto-/ratus ,maculosus7 #fi #cb4 ,alto-/rato-cumulus #gj #cc4 ,sunset4 7,alto-cumulus ,ca/ellatus ,fractus7 #gj #cd4 ,?ree ,lay]s ( ,/rati=m ,cl\d aft] ,ra9 #gc #ce4 ,ra9-,cl\d4 7,nimbus7 #ge #cf4 ,ra9-,cl\d4 7,nimbus7 #ge #cg4 ,/ratus ,communis #gg #ch4 ,/rato-cumulus #gg #ci4 ,/rato-cumulus #gh #dj4 ,/ratus ,maculosus #gh #da4 ,common ,/ratus4 7,/ratus ,communis7 #gi #db4 ,roll] ,cl\d4 7,/ratus ,radius7 #hj #dc4 ,small ,cumulus4 7,cumulus ,m9or7 #id #dd4 ,cumulus #ie #de4 ,l>ge ,cumulus4 7,cumulus ,major7 #if #df4 ,fracto-cumulus #ig #dg4 ,fall ,cl\d4 7,/ratus ,l5ticul>is7 #ih #dh4 ,?und]-cl\ds =m+ #aji #di4 ,?und]-cl\ds4 7,cumulo-nimbus7 #aaj #ej4 ,?und]-cl\ds4 7,cumulo-nimbus7 #aaa #ea4 ,?und]-cl\d4 7,cumulo-nimbus7 #aaa #eb4 ,?und]-cl\d4 7,cumulo-nimbus7 #aaa #ec4 ,! ,flank ( a ,great ,/orm #aab #ed4 ,cre/$ ,alto ,waves4 7,alto-cumulus ,undatus7 #abj #ee4 ,alto ,waves4 7,alto-/ratus ,undatus7 #aba #ef4 ,cirro ,ripples4 7,cirro-cumulus ,undatus7 #abb #eg4 ,wav$ ,cirro-/ratus4 7,cirro-/ratus ,undatus7 #acf #eh4 ,cam]a = measur+ ,altitudes #ada #ei4 ,pr9t f a ,negative us$ = measur+ ,altitude #add #fj4 ,pair ( ,pr9ts %[+ ! ,displacem5t ( ! ,cl\d #ade #fa4 ,cl\d ,cam]a = ,/udies #aga ,,cl\d ,,/udies ,,*apt] ,i ,,introductory ,,all :o h ! faculties prop] to man mu/ h be5 to "s ext5t /ud5ts ( cl\d =m4 ,g :]e we w1 d :at we w1 we _c easily escape f ! sky1 or avoid notic+ "s ( its features & c\pl+ !m ) ! v>y+ conditions ( wea!r4 ,we all sometimes want to "k if x is likely to ra91 or :e!r "s o!r *ange is probable2 & exp]i5ce soon %[s u t ! cl\ds give ! simple/ & mo/ obvi\s indication ( :at we may expect4 ,x is almo/ impossible to avoid notic+ t c]ta9 types ( cl\d1 or ! simultane\s appe>ance ( c]ta9 types1 is ! usual accompanim5t ( def9ite k9ds ( wea!r or ( p>ticul> *anges4 ,?us x is t mo/ p acquire "s small measure ( wea!r wisdom be=e _! s*ooldays are ov]4 ,g5]ation aft] g5]ation1 ?r\gh all human hi/ory1 ! same causes mu/ h l$ to ! same conclusions2 & ! /udy ( cl\ds mu/1 !re=e1 be "o ( ! olde/ ( all bran*es ( sci5tific inquiry4 ,yet1 old z x is1 x is /ill 9 its infancy1 hav+ made v little advance inde$ t[>ds ! precision ( an exact sci5ce4 ,!re are _m reasons = ?is want ( gr[?1 & s f> z ! !oretical aspects ( ! subject are conc]n$ x is easy en\gh to und]/&4 ,cl\ds are among ! mo/ inaccessible ( t]re/rial objects4 ,except by balloon asc5ts1 by s5d+ up kites be>+ record+ in/rum5ts1 or by mak+ obs]vations among ! m\nta9-tops1 we h no means ( gett+ at !m to /udy ! conditions "u :i* !y exi/4 ,temp]ature1 pressure1 humidity1 h g5]ally to be guess$ at1 ^? guesses be+ bas$ on ! scanty data :i* h be5 labori\sly obta9$ by "o or ano!r ( ^! cumbr\s me?ods4 ,moreov]1 _m cl\ds h su* va/ dim5sions t x is v difficult to grasp all t goes on 9 su* a space4 ,besides ! difficulty ( attack+ ! problems pres5t$ by cl\d =mation1 x is probable t ev5 if we c\ld h got among ! cl\ds at w1 we %\ld h und]/ood little m ?an we d1 f a want ( suffici5t c]ta9ty on _m ( ! purely physical que/ions involv$4 ,x is n _m ye>s s9ce ,mr4 ,j4 ,aitk5 discov]$ ! necessity = mat]ial nuclei z a fir/ /ep 9 ! =mation ( cl\d p>ticles1 & n _m mon?s h elaps$ s9ce ,mr4 ,c4 ,t4 ,r4 ,wilson %[$ t ^? p>ticles c be =m$ by ! action ( radiation on ! air itself4 ,!re is no?+ surpris+1 !re=e1 9 ! fact t our !oretical k ( ! :y & :]e=e ( ! facts reveal$ by a /udy ( cl\ds is limit$ to g5]al pr9ciples1 & q fails to say exactly :y ea* special =m %\ld be assum$4 ,! matt] = surprise is q diff]5t4 ,!oretical explanations are n ! fir/ /ep 9 ! work+ out ( a bran* ( sci5ce4 ,x beg9s ) ! acquisition1 by dilig5t & pa9/ak+ obs]vation1 ( a great mass ( facts4 ,?is may g on = c5turies1 ! accumulation gr[+ great] & great]1 until at la/ "s "o comes :o exam9es ! records1 classifies !m c>efully1 & f9ally makes a summ>y 9 ! =m ( a numb] ( g5]alizations1 :i* are ann\nc$ "u ! "n ( ,laws4 ,two examples ( su* 8,laws0 w suffice4 ,a/ronom]s = c5turies _h obs]v$ ! movem5ts ( ! planets1 always ) increas+ accuracy1 until ,ty*o ,brahe made 8 fam\s s]ies ( obs]vations on ! planet ,m>s4 ,^! mat]ials fell into ! h&s ( ,kepl]1 & ! result ( 8 "w 0 ! ann\ncem5t ( ,kepl]'s ,laws1 :i* /ate ! rules :i* gov]n ! movem5ts ( ! planets 9 _! orbits4 ,he f\nd t ! records c\ld n be acc\nt$ = unless ! planets mov$ 9 a c]ta9 way1 b he knew no?+ ( ! reasons = a me?od & ord] :i* cle>ly exi/$4 ,kepl]'s ,laws1 9 fact1 re/ ^u ano!r set1 namely1 ,newton's ,laws ( ,gravitation1 & ^! are !mselves a second example4 ,!y are ! summ>y ( accumulat$ exp]i5ce1 & ev5 at ! pres5t day we "k no?+ c]ta9 z to :y two bodies %\ld attract ea* o!r1 & no?+ z to :y t mutual attraction %\ld act z x 0 f\nd to act by ,newton4 ,! obs]vational "p ( cl\d /udy1 h[ev]1 is /ill 9 its infancy1 9 spite ( ! fact t x has be5 go+ on = su* c\ntless ages4 ,we are /ill 9 ! condition ( ! humble obs]v]s engag$ 9 ! comp>atively humdrum task ( ga!r+ facts = future arrangem5t & int]pretation4 ,cl\d obs]v]s1 9 all ages1 h suff]$ f a peculi> difficulty4 ,!y h _h no common language1 no code ( signs by :i* !y c\ld b5efit f ! "w ( ^? :o _h gone be=e !m1 no means ( transmitt+ _! own exp]i5ce to ea* o!r1 or to ^? :o w\ld come aft] !m4 ,no progress w\ld be possible 9 any /udy "u su* conditions1 = ea* p]son w\ld beg9 :]e ! previ\s g5]ation began1 in/ead ( tak+ up ! task :]e o!rs _h left x4 ,9 all languages !re is an extraord9>y sc>city ( cl\d names1 & su* z d exi/ are frequ5tly appli$ to q diff]5t =ms by diff]5t p4 ,s pron\nc$ is ?is lack ( t]ms1 t any "o :o tries to describe a sky )\t us+ any ( ! mod]n sci5tific names1 f9ds himself oblig$ to rely on long detail$ descriptions1 back$ ) ref]5ces to well-kn[n objects1 ^: outl9es or /ructures resemble ! cl\ds m or less vaguely2 & ev5 !n he has to be a ^w-pa9t] ( s+ul> skill if 8 description calls up 9 ! m9d ( ! read] a picture mu* l ! orig9al4 ,x 0 to meet ?is want ( a common tongue t ,luke ,h[>d1 9 #ahjc1 propos$ 8 s*eme ( cl\d names4 ,he recogniz$ ?ree ma9 types ( cl\d ar*itecture1 :i* he nam$ ,cirrus1 ,/ratus1 & ,cumulus4 ,cirrus includ$ all =ms :i* are built up ( delicate ?reads1 l ! fibres 9 a fragm5t ( wool2 ,/ratus 0 appli$ to all cl\ds :i* lie 9 level %eets2 & ,cumulus 0 ! lumpy =m4 ,by comb9ations ( ^! t]ms o!r cl\ds 7 describ$4 ,?us1 a quantity ( cirrus arrang$ 9 a %eet 0 call$ cirro-/ratus1 :ile high1 ?9 cl\ds l cirrus1 b made up ( deta*$ r\nd$ balls1 0 cirro-cumulus4 ,_m cumulus cl\ds1 arrang$ 9 a %eet ) little space betwe5 !m1 became cumulo-/ratus1 :ile ! great cl\ds f :i* our heavy ra9s desc5d p>take1 to "s ext5t1 ( all ?ree types1 & 7 !re=e di/+ui%$ by a special "n--,nimbus4 ,?is sy/em _h mu* to recomm5d x4 ,! ?ree fundam5tal types 7 obvi\s to all4 ,_! names 7 descriptive1 & 7 d]iv$ f a dead language1 s t no liv+ int]national jeal\sies 7 rais$4 ,x 0 suffici5tly detail$ to s]ve ! purposes ( ! "t1 :5 accurate obs]vation 0 9 its infancy4 ,h5ce x 0 univ]sally adopt$1 & w pretty c]ta9ly hold its own z ! broad basis ^u :i* any m detail$ sy/em mu/ necess>ily re/4 ,x has done excell5t s]vice2 b al?\gh obs]vation ( cl\ds 9 a g5]al way is f> f complete1 att5tion is n[ be+ giv5 to mu* small] details & mu* m m9ute diff]5ces ( =m1 & our vocabul>y mu/ be amplifi$4 ,precision ( description is ! fir/ ess5tial ( a satisfactory sy/em1 & ! "q is1 :at sort ( edifice c we build on ,luke ,h[>d's f\ndation4 ,! great difficulty is ! inf9ite v>iety ( cl\ds4 ,c]ta9 =ms may be arbitr>ily select$ z types1 & names may be giv5 to !m2 b h[ev] well !y are *os51 a v %ort p]iod ( obs]vation w %[ t !re are all mann] ( int]m$iate =ms1 :i* make a p]fect gradation f "o type to ano!r4 ,?is fact %\ld nev] be =gott54 ,!re is always a dang] t ! use ( any sy/em ( names bas$ on types %all lead to ! neglect ( ev]y?+ n typical4 ,a curi\s illu/ration is af=d$ by ! well-kn[n fact1 t 9 arrang+ collections ( fossil %ells1 x is frequ5tly f\nd t "s specim5s d n exactly mat* ! type examples to :i* names h be5 assign$4 ,9 =m] days x 0 ! cu/om to ?r[ aside su* 8bad specim5s10 z !y did n %[ pla9ly ! specific *>act]s4 ,x is n[ realiz$ t !y h a value ( _! own1 9 t !y are ! l9ks 9 ! evolution>y *a91 once suppos$ to be miss+4 ,inde$1 x is n unfrequ5t n[adays to see c>efully select$ s]ies1 %[+ ! gradual *ange :]eby "o species pass$ into ano!r1 display$ 9 ! place ( hon\r1 :ile ! type specim5s are relegat$ to humbl] places 9 ! g5]al collection4 ,types !re mu/ be1 no d\bt1 & :]e ! s]ies is cont9u\s1 "s "o mu/ make ! selection4 ,) cl\ds ! s]ies is absolutely cont9u\s4 ,! task is l *oos+ typical l9ks f a long *a9 9 :i* ea* l9k is almo/ exactly l its neighb\rs1 yet no two are alike1 & ! great] ! di/ance betwe5 !m ! less _! lik5ess4 ,cle>ly any sy/em put =w>d mu/ be accompani$ by illu/rations1 s t all may "k exactly :i* l9ks h be5 *os54 ,_m attempts h be5 made to meet ! want2 "s ( ! sy/ems propos$ be+ bas$ on ! =ms assum$ by ! cl\ds1 "s on _! suppos$ mode ( orig91 & "s on _! altitudes4 ,^? :i* 7 n f\nd$ on ,luke ,h[>d's types _h no *ance ( be+ accept$1 :ile k 0 n yet suffici5tly f> advanc$ to make classifications bas$ on orig9 ( =m at all possible4 ,b ! great reason :y none ( ! propos$ s*emes c\ld come into g5]al use 0 t !y 7 put =w>d )\t adequate illu/ration1 s t none b _! au?ors knew exactly :at !y meant4#a ,matt]s came to a head 9 #ahia1 :5 an ,int]national ,meteorological ,conf]5ce met at ,muni*4 ,"o object ( ?is ga!r+ 0 to promote inquiries into ! =ms & motions ( cl\ds1 by means ( conc]t$ obs]vations at ! v>i\s in/itutes & obs]vatories ( ! globe4 ,luke ,h[>d's sy/em 0 n en\gh = ! purpose 9 view1 & ! addition ( m detail$ t]ms _h to be settl$ be=e "w c\ld be begun4 ,pr(essor ,hildebr&sson1 ( ,upsala1 & ! ,hon4 ,ralph ,ab]cromby jo9tly submitt$ a revis$ s*eme1 ! ma9 feature ( :i* 0 ! introduction ( a new class ( cl\ds1 to be di/+ui%$ by ! prefix alto-be=e ! o!r "n4 ,su* alto cl\ds 7 less l(ty & d5s] ?an cirrus4 ,?is s*eme 0 ! be/ be=e ! ,conf]5ce1 & )\t wait+ to discuss1 & possibly improve x1 x 0 =mally adopt$1 & a committee appo9t$ to arrange & publi% an atlas %[+ pictures ( ! type-=ms4 ,?is atlas did n appe> until #ahif1 & 9 ! mean "t ! ,rev4 ,w4 ,clem5t ,ley _h publi%$ proposals ( 8 own1 "s ( :i* _h mu* to recomm5d !m4 ,b he 0 too late4 ,! ,int]national ,committee _h come to a decision1 &1 al?\gh x may be f> f ideal1 ! sy/em back$ by su* an au?ority mu/ be reg>d$ z ! /&>d until "s simil> ga!r+ has giv5 worldwide sanction to a *ange1 & ev5 !n x w\ld be bett] to modify by addition r ?an by sub/itution4 ,! subjects ( ! foll[+ pages are nam$ 9 g5]al accordance ) ?is ,int]national ,code1 b !y are by no means re/rict$ to types4 ,_! object is n to attempt any repetition ( ! "w :i* has already be5 well done by ! ,atlas ,committee1 b r to %[ ! *ief v>ieties )9 a type4 ,x w1 h[ev]1 become abundantly evid5t t ! /&>d sy/em is f> f complete1 & t any m9ute & detail$ /udy ( cl\d-=m mu/ take note ( ! precise v>iety4 ,?is at once raises ! "q :e!r _m ( ^! v>ieties are n suffici5tly di/9ct to be giv5 def9ite names4 ,if a meteorologi/ is told t cirrus cl\ds 7 se5 on a p>ticul> occasion1 he in/9ctively asks--,:at sort ( cirrus8 & is utt]ly unable to =m any m5tal picture ( ! cl\ds until ! "q has be5 answ]$ by a detail$ description4 ,a glance at a few ( ! plates fur!r on w %[ ! difficulty pla9ly1 & x occurs ) o!r =ms ( cl\d z well z cirrus4 ,is x n "t t ! ,int]national names 7 reg>d$ z ^? ( ! cl\d g5]a1 & to add specific names = ^? v>ieties :i* seem to imply "s diff]5ce 9 k9d 9 ! conditions :i* h l$ to _! =mation8 ,?is has be5 "h attempt$ by translat+ into ,lat9 ! ord9>y ,engli% t]m by :i* ! v>iety w\ld naturally be describ$4 ,m ext5d$ obs]vation w probably %[ t o!r species %\ld be introduc$1 & possibly "s ( ^? sugge/$ 9 ^! pages may h to be subdivid$4 ,:atev] ! names may be1 specific di/9ction ( "s sort is an ess5tial prelim9>y to detail$ /udy ( ! :y & :]e=e ( ! p>ticul> =ms4 ,! ,int]national sy/em is z foll[s3-- ,a4 ,upp] cl\ds4 7a7 ,cirrus4 7b7 ,cirro-/ratus4 ,b4 ,int]m$iate cl\ds4 7a7 ,cirro-cumulus & alto-cumulus4 7b7 ,alto-/ratus4 ,c4 ,l[] cl\ds4 7a7 ,/rato-cumulus4 7b7 ,nimbus4 ,d4 ,cl\ds ( diurnal asc5d+ curr5ts4 7a7 ,cumulus & cumulo-nimbus4 ,e4 ,high fogs4 7b7 ,/ratus4 ,9 ?is tabulation ! =ms m>k$ 7a7 are deta*$ & occur 9 dry wea!r1 :ile ^? m>k$ 7b7 are widely ext5d$4 ,! orig9al s*eme also gives ! mean heights ( ! v>i\s types1 b ^! values h be5 omitt$ "h because !y are extremely v>iable1 & impossible to asc]ta9 ) any approa* to accuracy by m]e eye e/imates4 ,!y v>y also ) ! season1 & probably also ) ! locality4 ,moreov]1 ! altitude is no guide to ! "n1 except t on ! :ole ! types occur 9 ! ord] giv51 tak+ gr\p ,a z ! highe/ & gr\p ,e z ! l[e/4 ,9 ! *apt] on cl\d altitudes ?is subject w be fur!r consid]$1 & "u ! descriptions ( cl\d-=ms _! av]age height or actual measurem5ts = ! p>ticul> specim5 figur$ w be giv5 :5ev] possible4 ,be=e com+ to ! description ( individual =ms1 x may n be out ( place to give brief consid]ation to ! be/ means ( obs]v+ !m 9 nature4 ,= eye obs]vation1 ( c\rse1 no directions are ne$$ :5 we are deal+ ) ! l[] & d5s] v>ieties2 b :5 we come to ! highe/ gr\ps x sometimes becomes necess>y to protect ! eye f ! brilliant gl>e :i* may make x impossible to detect ! real /ructure4 ,smok$ glass1 neutral-t9t$ spectacles1 or yell[ glass all h some?+ to recomm5d !m2 b by f> ! mo/ conv5i5t means is to look1 n at ! cl\ds !mselves1 b at _! images =m$ 9 a black mirror4 ,a lant]n cov] glass1 or a ?9 piece ( plate-glass1 black$ on ! back ) "s black pa9t1 s]ves admirably4 ,b all black pa9ts are n equally good4 ,! be/ are oil pa9ts :i* dry ) a glossy surface1 ! s-call$ enamels4 ,!y h ! advantage t ! v>ni% ) :i* !y are mix$ has an index ( refraction n v diff]5t f t ( ! glass4 ,! consequ5ce is t s little light is reflect$ f ! black5$ back1 comp>$ ) t :i* is reflect$ f ! front surface ( ! glass1 t ! second image c only be detect$ ) difficulty4 ,if ! mirror is a piece ( black or deeply col\r$ glass all trace ( ! second image is lo/4 ,) ?is simple appliance x is easy to /udy ! details ( ! ?9ne/ cl\ds "r up to ! sun1 & ev5 ! image ( ! sun itself may be glanc$ at )\t s]i\s discom=t4 ,nor is ! g5]al dim9ution ( brightness ! only ga94 ,if ! glass is s held t ! light f ! cl\d makes an angle ( ab\t #cc degrees ) ! surface1 "s ( ! blue light f ! sky is suppress$ altoge!r1 :ile t f ! cl\d is practically unaffect$4 ,! exact fraction suppress$ dep5ds ^u ! "p ( ! sky relative to ! sun1 & also on ! position ( ! mirror1 b a few m9utes' trial w %[ :5 ! maximum effect has be5 rea*$4 ,x is a/oni%+ to see = ! fir/ "t h[ ! delicate filam5ts ( cirrus or ! beautiful /ructures ( cirro-cumulus /& out %9+ :ite on ! deep blue backgr\nd2 & ! use ( ! black mirror is a revelation to mo/4 ,x also has "o indirect advantage1 :i* is really m important ?an x seems4 ,by gaz+ d[n into a mirror long-cont9u$ obs]vations c be made1 & "o =m ( cl\d may be wat*$ *ang+ into ano!r1 & possibly back aga9 into its orig9al %ape1 )\t any dang] ( incurr+ t unpleasant result ( mu* look+ upw>ds :i* is sometimes kn[n z exhibition heada*e4 ,su* a mirror may be q small1 s t x c be c>ri$ 9 a pocket-book1 a po9t ( "s mom5t1 z _m ( ! =ms ( cirrus are exce$+ly transi5t1 com+ & go+ 9 a few m9utes1 :ile o!rs are 9 a /ate ( cont9u\s *ange4 ,?is is p>ticul>ly (t5 ! case ) ! exquisite ripple cl\ds1 & ! delicate lacework ( ! high] k9ds ( cirrus4 ,/ill ano!r advantage possess$ by ! mirror is t x makes x easy to see ! sol> halos =m$ on ! v]ge ( a cyclone1 & to detect _! iridesc5t col\r+ 9 a way :i* is q beyond ! rea* ( ! nak$ eye or any protective spectacles4 ,e "o is famili> ) ! fa9t halos =m$ r\nd ! moon1 b ! correspond+ sol> ph5om5on is comp>atively little kn[n1 ?\gh x is f> common]1 mu* m brilliant1 & (t5 gl[s ) col\r4 ,its v brightness1 & t ( ! backgr\nd on :i* x is project$1 hides x f ! eye1 except on ^? r>e occasions :5 ! sun is conv5i5tly hidd5 by "s ?ick] cl\d4 ,if "s p]man5t record is desir$1 mu* c be done ) a few light /rokes ( a p5cil1 b m ambiti\s pictures are be/ secur$ by ! use ( s(t pa/els1 aid$ by a lib]al use ( ! f+] or lea!r /ump4 ,ord9>y pa9ts1 :e!r oil or wat]-col\r1 are ( little use = actual /udy ( cl\d detail1 except 9 ! h&s ( a highly skill$ arti/ :o kn[s h[ to get ! effect he wants 9 ! m9imum ( "t4 ,b no sket*+ or draw+ c make records ( cirrus or alto cl\ds ) ! spe$ & accuracy necess>y = c>eful /udy4 ,photography is really ! only way 9 :i* ! amaz+ weal? ( detail c be tru?fully portray$4 ,yet ev5 ! cam]a has its limitations4 ,x does n record col\r1 & completely fails to del9eate ! =ms ( alto-/ratus1 /ratus1 or nimbus1 if !y are pres5t 9 ! mo/ typical condition1 t is to say1 :5 !y cov] ! :ole sky ) a uni=m t9t4 ,x is only :5 ^! =ms are m or less brok5 up t a photograph1 or any?+ o!r ?an a c>efully col\r$ picture1 w repres5t !m at all4 ,cl\d photography1 ev5 ( ! mo/ delicate & brilliant v>ieties1 is easy en\gh :5 ! "r me?ods are foll[$2 b ^! are n ! same z ^? :i* are "r = portraiture or l&scape "w ( ! usual k9d4 ,! backgr\nd ( blue sky produces almo/ ! same effect on ! plate z ! image ( ! cl\d itself1 & ! :ole art consi/s 9 an adequate exagg]ation ( ! m9ute diff]5ce s z to reveal ! details ( =m & /ructure4 ,a sl[ plate--! accompany+ illu/rations h all be5 tak5 on ,mawson & ,swan's photo-me*anical plates--extremely cauti\s developm5t1 & sometimes int5sification ( ! image1 are all t is necess>y2 b ! process becomes easi] if1 in/ead ( po9t+ ! cam]a to ! cl\d1 x is direct$ to ! image =m$ 9 a prop]ly con/ruct$ black mirror4 ,_m ( ! foll[+ /udies h be5 tak5 by ?is me?od1 & details ( ! cam]a & processes employ$ w be f\nd 9 a lat] *apt]1 = ! conv5i5ce ( any "o :o may be inspir$ to take up a fasc9at+ bran* ( photography4 ,x has be5 said t ref]5ce w be made to ! av]age altitudes ( ! diff]5t types ( cl\d1 & to ! actual altitude ( "s ( ! v>ieties %[n4 ,! "q w1 no d\bt1 h occurr$ to "s z to h[ ^? altitudes h be5 measur$4 ,! me?ods are all m or less complicat$1 involv+ r labori\s calculation4 ,!y g5]ally dep5d ^u simultane\s obs]vations made f two /ations at opposite ends ( a measur$ base l9e4 ,sometimes ! obs]vations are made directly by po9t+ an in/rum5t at ea* /ation to "s agre$ po9t ( ! cl\d4 ,x is obvi\s t ! two directions mu/ conv]ge to ?is po9t4 ,if ! conv]g5ce is measur$1 ! exact di/ance f ei!r /ation c be calculat$1 & if ! angle betwe5 ! cl\d-po9t & ! horizon b5ea? x is not$1 x is a simple matt] to d$uce ! actual altitude ( ! cl\d4 ,at o!r places ! obs]v]s h reli$ ^u ! comp>ison ( photographs simultane\sly tak5 f ! two /ations4 ,9 ?is me?od x is necess>y to "k ! exact direction 9 :i* ! cam]a is po9t$1 & ! position ( ! image ^u ! plate !n gives ! direction ( ! cl\d z se5 f t p>ticul> /ation1 & ! subsequ5t calculations are ! same4 ,measurem5ts by "o or ! o!r ( ! above me?ods h be5 made at sev]al places1 ! mo/ ext5sive s]ies be+ ^? :i* h be5 compil$ at ,upsala1 & at ! ,blue ,hill ,obs]vatory 9 ,massa*usetts4 ,! me?od employ$ by ! writ] at ,exet] has be5 r diff]5t1 & a description w be f\nd lat] on 9 ! *apt] on ,cl\d ,altitudes1 ! full] consid]ation ( :i* comes naturally aft] ! diff]5t =ms h be5 describ$ & comp>$4 ,,footnote3 #a ,see ref]5ce ,no4 #b on p4 #aha4 ,,*apt] ,,ii ,,cirrus ,a ,,cl\d is sometimes def9$ z any visible mass compos$ ( small p>ticles ( ice or wat] susp5d$ 9 ! air1 & =m$ by cond5sation f ! /ate ( vap\r4 ,z a g5]al rule ?is is exact en\gh1 b "u c]ta9 circum/ances x is possible to h ! p>ticles s small1 & s ?9ly scatt]$1 t x is n fully satisfi$4 ,! result+ mass may n be actually visible4 ,! pres5ce ( ! cond5s$ p>ticles may be indicat$ by no?+ m ?an a slight :it5+ ( ! blue sky1 or by ! =mation ab\t ! sun or moon ( bright circles ( light kn[n z halos4 ,if su* a halo appe>s1 x is g5]ally a ph5om5on ( brief duration4 ,sometimes ! circle breaks & becomes incomplete by ! pass+ away ( ! ?9 pat* ( cl\d1 sometimes ! cl\d increases 9 d5sity until ! r+s are de/roy$4 ,! ?9ne/ v>iety ( ?is halo-produc+ /ructure is q invisible to ! eye4 ,x is s ?9 z to h no di/9ctly noticeable effect ^u ! col\r ( ! sky1 b ! optical results ( its pres5ce may be v rem>kable4 ,highly complicat$ sy/ems ( r+s are sometimes produc$1 ! r+s1 z a rule1 fall+ into two gr\ps4 ,! commone/ =m has ! sun 7or moon7 9 ! c5tre1 & a circle ( pale light at a di/ance ( ab\t #bb degrees4 ,l>g] r+s are se5 less frequ5tly1 :i* h an angul> radius ( ab\t #df degrees1 & z a rule h ! sun situat$ on ! r+ itself4 ,9 ,plate #a we h a "p ( su* a great halo4 ,! cam]a 0 direct$ t[>ds ! ea/1 & tilt$ upw>ds at an angle ( ab\t #dj degrees4 ,! sun 0 beh9d ! cam]a1 9 ! s\?-we/1 & ! r+ c\ld be trac$ "r up to x on ei!r side4 ,at ! same "t ! sun 0 surr\nd$ p>tially by a halo ( ! m ord9>y type1 :i* 0 brightly col\r$1 mak+ an effective contra/ to ! dull :ite ( ! great] r+4 ,! ph5om5on did n la/ m ?an half an h\r1 & ! *anges 9 its appe>ance co9cid$ ) a gr[+ d5sity ( cl\d4 ,:5 fir/ notic$ ! great r+ 0 alone1 & ! sky 0 ( a full blue1 b a silv]y film came gradually up f ! s\?-we/1 & ! small] & bright] halo fla%$ out z ! delicate curta9 came ne> ! sun4 ,sl[ly ! cl\d spread to ! nor?-ea/1 ga!r+ d5sity f ! opposite po9t ( ! compass2 & by ! "t ! ord9>y halo 0 at its be/1 ! great :ite r+ _h completely vani%$4 ,illu/ration3 ,plate #a4 ,,"p ,,( ,a ,,great ,,halo4 ,illu/ration3 ,plate #b4 ,,"p ,,( ,a ,,sol> ,,halo4 ,^! circles1 & ! bright spots call$ mock-suns or mock-moons :i* (t5 accompany !m1 c all be expla9$ on ! assumption t _! cause is ! passage ( light ?r\gh a veil compos$ ( hexagonal cry/als ( ice4 ,! simple halo ( #bb degrees radius is common 9 mo/ p>ts ( ! _w1 be+ v g5]ally =m$ by ! film ( high cl\d :i* m>ks ! advanc+ edge ( a cyclonic cl\d sy/em4 ,a portion ( "o is %[n 9 ,plate #b1 9 :i* ! rudim5t>y fibr\s /ructure ( ! %eet ( cl\d is di/9ctly se54 ,halos ( ?is sort are frequ5tly col\r$1 (t5 mo/ brilliantly s2 b ! t9ts are seldom notic$ unless a black mirror is us$4 ,!y are sometimes q z bright z ^? ( an ord9>y ra9b[1 b in/ead ( be+ project$ ^u a backgr\nd ( d>k ra9-cl\ds1 !y are se5 aga9/ a "p ( ! sky :i* is ne> ! sun1 & !re=e exceptionally bright4 ,! r$ is always on ! inside ( ! r+1 ! violet outside1 !reby di/+ui%+ !m at once f ! s-call$ coron1 :i* are =m$ ar\nd ! sun or moon :5 %9+ ?r\gh a %eet ( alto or o!r l[] cl\d made up ( liquid p>ticles4 ,9 ^! ! radius ( ! r+s is mu* less1 & ! r$ is on ! outside1 ! violet actually t\*+ ! c5tral lum9>y4 ,! cl\d :i* produces halos is call$ cirro-nebula4 ,x is mu* ?9n]1 & on an av]age high] ?an cirro-/ratus4 ,mr4 ,ley nam$ x cirro-velum 7or cirro-veil71 b cirro-nebula has n[ got to be fairly well und]/ood4 ,x sometimes appe>s & disappe>s 9 a curi\s mann]1 %[+ t x occurs 9 pat*es1 :i* drift ab\t or :i* keep =m+ & melt+ away1 only to repeat ! process4 ,if1 h[ev]1 x =ms "p ( an advanc+ cyclone fr+e1 !n ! sky gets :it] & :it]1 until x is cov]$ ) a %eet ( und\bt$ cirro-/ratus4 ,?is process ( gr[+ d5sity is %[n 9 progress 9 ,plate #c4 ,illu/ration3 ,plate #c4 ,,cirro-,,nebula ,,*ang+ ,,to ,,cirro-,,/ratus4 ,cirro-nebula1 z we %all call x1 floats at v great altitudes 9 temp]ate regions2 b 9 pol> latitudes1 :]e ! optical ph5om5a peculi> to x are mo/ brilliant & div]sifi$1 x seems probable t ! ice du/ is mu* l[] d[n1 ev5 9 actual proximity to ! gr\nd4 ,9 ,engl& its height v>ies greatly ) ! "t ( ye>1 & o!r circum/ances1 b m\nts up 9 summ] to su* altitudes z n9e miles or m2 ! greate/ height yet record$ be+ #if miles1 or ab\t #ae1ejj metres1 at ,exet]4 ,! *ange f cirro-nebula to cirro-/ratus is g5]ally accompani$ by ! =mation ( a di/9ct fibr\s /ructure1 easily obs]vable by ! black mirror4 ,?is is n really a new feature1 b only a fur!r developm5t ( a /ructure already exi/+1 b too m9ute to be easily se54 ,true halo-produc+ cirro-nebula may usually be %[n to possess m or less ( a fibr\s texture 9 an indirect way1 :i* is wor? a brief description4 ,9 ord] to obs]ve ! spots on ! sun & o!r features ( ! sol> surface1 x is a common practice to hold a :ite scre51 say1 ab\t a foot f ! eyepiece ( a telescope1 :ile ! in/rum5t is po9t$ to ! sun4 ,an image1 consid]ably magnifi$1 is ?us project$ on to ! scre51 & ! sol> details c be /udi$ ) ease & safety4 ,if ?9 cl\ds drift be=e ! sun1 _! images are simil>ly project$ z !y pass across its disc1 & x is possible ?us to detect n only ! fibr\s texture b also ! movem5t ( cirro-nebula4#b ,! *ange into cirro-/ratus is also att5d$ by a m>k$ fall 9 altitude1 b :e!r ?is is due to an actual desc5t ( ! cl\d p>ticles1 or to a d[nw>d spread ( ! conditions :i* give rise to !m1 _c at pres5t be def9itely settl$4 ,! balance ( probability po9ts v /rongly t[>ds ! d[nw>d spread ( ! conditions4 ,x is likely t ! cl\ds1 p>ticul>ly ! cyclonic specim5s1 are w$ge-%ap$1 & t z !y pass ov]head we see fir/ ! ?9 edge1 & lat] on ! ?ick] p>ts1 :i* project mu* l[] d[n4 ,?is is j "o ( ^? _m m9or problems 9 cl\d me*anics :i* we are n able to solve f ! scanty data on record4 ,occasionally cirro-nebula breaks up into little deta*$ semi-transp>5t cl\dlets1 all ( !m exce$+ly ?91 & %[+ a complicat$ mottl+1 resembl+1 on a m9ute scale1 ! ripple cl\ds ( mu* l[] altitudes4 ,su* a sky is depict$ 9 ,plate #d1 b no reproduction c possibly d ju/ice to ! m9ute & delicate features ( ! real ?+4 ,! arrangem5t ( ! fa9t m>k+s 0 9 a /ate ( cont9ual flux1 curi\sly simil> to ! ev]-*ang+ aspect ( ! sun's photosph]e :5 se5 "u adequate p[]4 ,"s p>ts ( ! cl\d /ratum w\ld at "o mom5t break up into di/9ct granules arrang$ 9 complicat$ patt]ns1 o!r p>ts w\ld assume a fibr\s texture1 & yet o!r places w\ld %[ a cont9u\s smoo? %eet4 ,9 a m9ute or two all w\ld be *ang$--! smoo? "p granulat$1 ! fibres vani%$1 & ! granules fus$ toge!r1 & s on1 no two ( a s]ies ( photographs repres5t+ ! same details4 ,illu/ration3 ,plate #d4 ,,cirro-,,nebula ,,*ang+ ,,to ,,cirro-,,cumulus4 ,^! *anges ( =m cont9u$ until ! :ole 0 hidd5 f view by a veil ( mu* l[] /rati=m cl\d1 "o advance portion ( :i* is %[n4 ,plate #d does n repres5t a type or a di/9ct v>iety ( cl\d4 ,x is an int]m$iate =m1 or a tempor>y condition1 %[+ cirro-nebula 9 ! act ( *ang+ into cirro-cumulus1 or possibly cirro-/ratus4 ,cirro-nebula itself1 9 its simpl] =m1 is1 h[ev]1 a di/9ct type4 ,x is true t x nev] p]si/s ov] "o locality = m ?an an h\r or two )\t pass+ into "s d5s] =m1 b :ile x la/s its features are s di/9ctive1 & ! optical ph5om5a to :i* x gives rise are s /rik+ & significant1 t x is a matt] = surprise t x %\ld 9 ! ,int]national sy/em h be5 relegat$ to ! position ( a subord9ate v>iety ( cirrus4 ,x is m ne>ly relat$ to cirro-/ratus1 b is suffici5tly di/9ct f t to des]ve at lea/ specific rank4 ,true typical cirrus mu/ h a pla9ly %[n fibr\s /ructure4 ,! fibres may cross & int]lace1 !y may radiate 9 fan-l mann]1 or !y may curl & twi/ l a well-trimm$ o/ri* fea!r4 ,! cl\ds s =m$ mu/ n be arrang$ 9 a cont9u\s level %eet1 or !y at once become cirro-/ratus1 & x is impossible to inv5t a def9ition :i* w m>k ! exact limits ( ei!r type4 ,typical cirrus consi/s ( deta*$ cl\ds4 ,!y ca/ no %ad[s on ! l&scape1 = ! simple reasons t !y are semi-transp>5t & _! compon5t p>ts too n>r[4 ,if ! sun is %9+ d[n obliquely ?r\gh ! nak$ b\ghs ( a tall tree1 x w be se5 t ! l[e/ twigs ca/ fairly %>p %ad[s on ! gr\nd1 b t ev5 ^! are bord]$ by a fad+ rim2 ! twigs fur!r up ca/ no %>p %ad[s1 b broad] fa9t b&s ( %ade2 :ile ! topmo/ b\ghs ca/ no %ad[s :i* c cle>ly be id5tifi$4 ,9 o!r words1 ! m di/ant ! n>r[ twig is f ! gr\nd ! n>r[] ! real %ad[ or umbra1 & ! broad] ! p5umbra becomes1 until :5 ! di/ance is suffici5t ! %ad[ is all p5umbra4 ,cirrus filam5ts ?r[ no?+ b a fa9t p5umbra4 ,inde$1 x is only :5 !y lie 9 ! e>?'s %ad[1 & /& aga9/ ! backgr\nd ( a fa9tly light$ sky1 t !y %[ any sign ( %ad[ ev5 on !mselves4 ,!re is no d\bt t !y are compos$ ( p>ticles ( ice4 ,!y are =m$ at altitudes :]e ! !rmomet] mu/ be _m degrees bel[ freez+-po9t1 & n a few ( ! ?9n] examples %[ fragm5t>y halos l ^? ( cirro-nebula4 ,_! actual altitudes are v v>iable1 be+ great] 9 summ] ?an 9 w9t]1 & rea*+ a maximum = any giv5 /ation aft] a long spell ( hot wea!r4 ,exact measurem5ts h n yet be5 made 9 tropical latitudes or 9 pol> regions1 b !re is e reason to expect t ! upp] limit ( cirrus = equatorial di/ricts w be f\nd to be mu* high] ?an 9 ! temp]ate zones :]e actual obs]vations h be5 made4 ,9 places ne>] to ! ,arctic ,circle x is also almo/ c]ta9 t ! altitudes w be less4 ,9 ! ,new ,engl& /ates1 z %[n by ! ,blue ,hill obs]vations1 ! maximum altitude = summ] 0 f\nd to be little "u #ae1jjj metres4 ,at ,upsala1 9 ,sw$51 x 0 #ac1cjj metres4 ,! av]age altitudes at ! same obs]vatories 71 respectively1 ab\t #iijj & #hhjj metres4 ,at ,exet] ! writ]'s own measurem5ts give an av]age = ! summ] mon?s ( #aj1bjj metres1 ) a m9imum r l[] ?an 0 ! case 9 ,am]ica or ,sw$51 & ) a maximum f> above ! =eign values4 ,9 w9t] cirrus c]ta9ly comes mu* l[] d[n1 b ! numb] ( obs]vations is few]4 ,illu/ration3 ,plate #e4 ,,high ,,cirrus4 7,cirrus ,excelsus47 ,! l(tie/ v>iety ( cirrus appe>s 9 ! aft]noon 9 v hot wea!r1 sometimes q late 9 ! ev5+2 & 9 autumn x is by no means a r>e ev5t = x to sudd5ly =m j :5 ! sunset col\rs are fad+1 or ev5 aft] !y h pal$ into twilight4 ,"u su* circum/ances x /&s out ( a %9+ silv]y grey col\r aga9/ ! backgr\nd ( ! d>k5+ sky4 ,a specim5 ( x is %[n 9 ,plate #e1 :i* %[s its extreme slightness ( =m & delicacy ( texture4 ,sometimes x rema9s visible s long aft] ! />s h begun to %[ z to give ! idea t x is self lum9\s1 & ! illusion is c]ta9ly v /rong4 ,! writ] has not$ sev]al in/ances 9 :i* x 0 pla9ly visible1 l a silv]y curta91 ?\gh ! sky z a :ole 0 s d>k t />s l ! five brighte/ po9ts ( ! ,great ,be> c\ld be se5 ?r\gh ! cl\d1 & mu* small] />s d[n to ! ?ird & f\r? magnitude 7 pla9ly visible 9 ! cle> int]vals4 ,x has sometimes be5 call$ lum9\s cl\d1 & ,mr4 ,ley e/imat$ its altitude at upw>ds ( #ij1jjj metres2 b if we ?9k ( x z reflect+ ! light ( ! di/ant col\rless twilight !re is no ne$ to reg>d x z any?+ fundam5tally diff]5t f o!r cl\ds1 or to assume a great] altitude ?an we "k to h be5 ! case4 ,! specim5 figur$ occurr$ 9 ! e>ly aft]noon on ,june #ab1 #ahii1 at ,exet]1 & c>eful measurem5ts ( its altitude 7 made4 ,?is work$ out z #agjb miles1 or m ?an #bg1jjj metres1 a value s mu* great] ?an all o!r measurem5ts ( ! k9d t x 0 only aft] mo/ c>eful v]ification & ref]5ce to duplicate records t x c\ld be accept$4 ,x diff]s 9 sev]al ways f ! l[] v>ieties1 be+ ?9n]1 m gli/5+1 & 9 e way m delicate4 ,a suitable di/9ctive "n w\ld be high cirrus1 or cirrus excelsus4 ,illu/ration3 ,plate #f4 ,,w9dy ,,cirrus4 7,cirrus ,v5tosus47 ,l[] d[n by ?\s&s ( metres come ! fea!ry masses ( typical w9dy cirrus1 su* z are %[n 9 ,plate #f4 ,inde$1 9 cold w9t] wea!r !y occur )9 ?ree or f\r ?\s& metres ( ! gr\nd4 ,9 ! in/ance figur$ ! w9d 0 bl[+ f left to "r1 & ! cl\ds 7 travell+ swiftly4 ,! upp] filam5ts appe>$ to be repeat$ly torn away f ! ma9 masses1 :ile ! long fa9t /reaks :i* trail bel[ & beh9d are evid5tly due to /reams ( f9e p>ticles fall+ f ! ma9 c5tres ( cond5sation into a less rapidly mov+ /ratum bel[4 ,!re is no room = d\bt t ^! cl\ds1 l o!rs ( a simil> ord]1 are =m$ by a direct passage f ! vap\r to ! solid1 or t ! fibres are made ( m9ute sn[flakes4 ,! cond5sation is evid5tly att5d$ by rapid movem5ts1 :i* draw out ! cl\d1 z fa/ z x is =m$1 into long curv+ l9es :i* m>k l9es ( motion4 ,! v>iety is always1 !re=e1 an indication ( /rong w9ds & rapid eddy+ movem5ts 9 ! region 9 :i* x occurs4 ,su* /rong di/urbances ov]head almo/ always accompany simil> b less int5se movem5ts at ! gr\nd-level1 & :5 !y d n accompany !m !y prec$e !m4 ,! cl\d is well nam$ w9dy cirrus1 :i* may be conv]t$ into a specific "n1 cirrus v5tosus4 ,! next v>iety we come to 7,plate #g7 is 9 "s ways r simil>4 ,x is1 h[ev]1 ?9n]1 m delicate1 & is entirely compos$ ( f9e ?reads1 :i* are m sy/ematically arrang$4 ,g5]ally !re is a bundle1 or sev]al bundles1 ( long p>allel fibres1 :i* =m1 s to say1 ! quill ( ! fea!r1 ) numb]s ( %ort] ?reads bran*+ out f !m at v>i\s angles4 ,cirrus v5tosus 0 indicative ( irregul> movem5ts 9 v>i\s directions2 ?is v>iety po9ts also to complicat$ movem5ts1 b execut$ 9 accordance ) "s sort ( sy/em1 /rangely complex & wond]fully ord]$4 ,! specim5 figur$ is ! type ( :at ,mr4 ,ley call$ cirro-filum1 or ?read cirrus1 & 8 "n c h>dly be bett]$4 ,x is a cl\d ( summ]1 & occurs r high up 9 ! cirrus zone1 b no actual measurem5ts c be quot$4 ,x is fairly common1 b n ne>ly s frequ5t z ! la/4 ,illu/ration3 ,plate #g4 ,,?read ,,cirrus4 7,cirro-filum47 ,a some:at m famili> v>iety is %[n 9 ,plate #h4 ,little irregul> fea!rs ( cirrus1 f :i* long tap]+ /ream]s po9t d[nw>ds 9 graceful curves1 or else lag beh9d 9 ! direction f :i* ! cl\ds h travell$4 ,if cl\ds ( ?is type are c>efully wat*$1 x w soon be se5 t ea* fea!ry head is a c5tre ( cond5sation1 & t ! tails or /ream]s are no?+ else ?an fall+ p>ticles1 :i* dw9dle sl[ly away by evaporation1 & :i* gradually s9k bel[ ! level ( ! heads4 ,x is usual1 9 deal+ ) cl\d-=ms l ^!1 to speak ( air-curr5ts ( diff]5t velocities almo/ z if ! w9ds at diff]5t levels 7 z cle>ly sep>at$ z oil & wat]1 or ev5 air & wat]4 ,?is c h>dly be ! case1 = if su* a ?+ %\ld occur z an air-curr5t ( "o velocity fl[+ ov] ano!r ( less spe$1 or ( a curr5t 9 "o direction ov] ano!r mov+ 9 a diff]5t c\rse1 ! two mu/ inevitably mix at _! junction1 & 9 a v %ort "t ! passage f ! l[] curr5t to ! upp] "o w\ld be q gradual4 ,no d\bt we c (t5 obs]ve two1 ?ree1 or m lay]s ( cl\d mov+ 9 diff]5t directions2 b if we 7 to s5d up a balloon1 x w\ld be r>e inde$ to f9d its direction ( horizontal movem5t *ang$ 9 a few metres ( asc5t4 ,diff]5t & di/9ct air-curr5ts are (t5 invok$ to expla9 cl\d-=ms q unnecess>ily4 ,x is f> m likely t ! diff]5tial movem5ts involv$ 9 ! explanation ( ! features ( ^! cirrus v>ieties are due to increas$ velocity ) great] altitude1 to progressive *ange ( direction1 to irregul> eddies1 or to ! int]action ( asc5d+ & desc5d+ convection curr5ts4 ,inde$1 x is probable t c>eful /udy ( ! gr[? & decay ( ^! cl\ds w1 9 "t1 lead to a cle>] und]/&+ ( atmosph]ic movem5ts1 & s enable u to say m precisely :y !y are z we see !m to be4 ,! v>iety %[n 9 ,plate #h is r>e except 9 comb9ation ) o!r =ms4 ,x might well be t]m$ tail$ cirrus or cirrus caudatus4 ,illu/ration3 ,plate #h4 ,,tail$ ,,cirrus4 7,cirrus ,caudatus47 ,! =m ( cirrus %[n 9 ,plate #i is f> m frequ5tly se5 ?an ei!r ( ^? :i* h be5 describ$4 ,9 ?is ! fibr\s texture is v imp]fect1 & ! cl\dlets %[ a t5d5cy to arrange !mselves 9 a k9d ( ribb$ /ructure 9 two directions almo/ at "r angles to ea* o!r4 ,b ?is la/ is an accid5tal feature ( ! p>ticul> example1 & n 9 any way a specific "* ( ! cl\d4 ,! reason = reg>d+ x z a di/9ct v>iety is ! total abs5ce ( %>ply def9$ l9es1 n only ! heads ( cond5sation1 b ev5 ! long /ream]s atta*$ to !m be+ uni=mly hazy & ill-def9$4 ,x is a =m ( cirrus :i* comes at all seasons1 b mo/ frequ5tly 9 summ]2 x moves always ) great sl[ness1 indicat+ a quiet atmosph]e free f di/urbance ( any k9d4 ,! conditions necess>y = its appe>ance are a ne>ly uni=m di/ribution ( pressure ov] a consid]able area1 *equ]$ by little %all[ depressions ( "s trifl+ fraction ( an in*4 ,9 hot wea!r ^! are ! conditions "u :i* ?und]-/orms develop1 & ?is hazy cirrus1 or cirrus nebulosus1 may be tak5 z a c]ta9 sign ( su* an atmosph]ic /ate4 ,illu/ration3 ,plate #i4 ,,hazy ,,cirrus4 7,cirrus ,nebulosus47 ,s f> z p]man5cy ( =m is consid]$1 hazy cirrus is "o ( ! mo/ p]si/5t1 & af=ds a m>k$ contra/ to ! species %[n 9 ,plate #aj1 :i* repres5ts ! mo/ fugitive4 ,five m9utes be=e ! photograph 0 tak5 ! same "p ( ! sky 0 a deep1 cle> blue1 )\t any trace ( cl\d4 ,sudd5ly a few %ort curl+ wisps made _! appe>ance4 ,^! rapidly increas$ 9 numb]1 until a delicate filmy network ext5d$ ov] ! great] "p ( ! field ( view4 ,b :ile ! cam]a 0 be+ adju/$ = an exposure1 "p ( ! net _h brok5 up into ! granul> /ructure %[n 9 ! l[] "p ( ! photograph4 ,! granulation rapidly spread ?r\gh ! net1 almo/ z if ! fibres _h be5 curdl$1 & five m9utes lat] ! :ole _h be5 conv]t$ into a pat* ( cirro-cumulus :i* soon fus$ into a uni=m %eet4 ,mean:ile ! same s]ies ( ph5om5a 7 tak+ place 9 o!r p>ts ( ! sky4 ,illu/ration3 ,plate #aj4 ,,*ange ,,cirrus4 7,cirrus ,incon/ans47 ,on o!r occasions exactly ! same set ( ev5ts h be5 se5 to foll[ ea* o!r 9 ! inv]se ord]4 ,beg9n+ ) a fairly ev5 %eet1 ?is broke up into granules1 & !y 9 turn seem$ to be fray$ out into %ort hazy & wavy fibres :i* sl[ly melt$ away4 ,cle>ly we h "h to d1 n ) a di/9ct type ( cl\d1 b r ) ! fir/ /ep t[>ds ! =mation ( "o1 or ! la/ /age 9 ! life ( "o :i* is dry+ up4 ,b sometimes ! life ( ! cl\d is s %ort t x nev] passes beyond ?is fir/ /age2 & x is by no means a univ]sal rule = a gr[+ %eet ( cirrus to pass ?r\gh ?is /age at all4 ,x !re=e repres5ts a peculi> /ate ( in/ability1 & requires a "n ( its own4 ,sometimes pat*es ( x w come & g 9 an app>5tly caprici\s mann] = an h\r or m be=e p]man5t cond5sation is effect$ or be=e ! sky f9ally cle>s4 ,b ?is is a r>e ev5t1 s9ce ! sl[ *ange ( conditions :i* has br\ght ! /ratum ( air to ! un/able condition is g5]ally progressive1 & in/ead ( /opp+ at ! critical po9t1 goes beyond x1 ) ! result t ! cond5sation gr[s or ! cl\d disappe>s entirely4 ,*ange cirrus1 or cirrus incon/ans1 w\ld be an appropriate "n = a k9d ( cl\d :i* is s pla9ly indicative ( in/ability4 ,! critical condition ref]r$ to is1 ( c\rse1 t 9 :i* a p>ticul> /ratum ( air is j saturat$1 or is j on ! po9t ( =m+ visible cl\d4 ,if any cause is br\ght to be> on su* a /ratum :i* br+s ab\t ev5 slight cool+1 cl\d mu/ be produc$2 &1 conv]sely1 any?+ :i* results 9 ! slighte/ heat+ mu/ cause x to disappe>4 ,! %ortness & haz9ess ( ! fibres1 & ! fact t !y ga!r !mselves into granules1 %[s t ! cl\d is =m$ 9 a /ratum ( air :i* is ei!r /ill1 or is mov+ z a :ole1 )\t any ( ^? diff]5tial movem5ts :i* seem to be necess>y = ! long] fibr\s details4 ,! causes :i* may br+ ab\t ! local cool+ & heat+ are easy to und]/& :5 we rememb] h[ ! air w be affect$ by ! unev5 cont\rs ( ! gr\nd4 ,z x passes ov] hill & valley ! up-&-d[n movem5ts ( ! l[] lay]s1 or ev5 ! di/urbances caus$ by pass+ ov] a wood or clump ( trees1 all mu/ be propagat$ upw>ds4 ,ea* di/urbance mu/ sl[ly spread lat]ally & dim9i% v]tically1 s t x w rea* ! cirrus zone z a broad & g5tle dome-l oscillation4 ,suppose n[ a s]ies ( su* slight upheavals to rea* ! critical level4 ,! passage ( ! waves w mean alt]nate expansion & compression4 ,expansion means cool+1 & !re=e cl\d-production2 compression means heat+1 & !re=e ! de/ruction ( cl\d4 ,f ! mo/ transi5t =m ( cirrus we pass1 9 ,plate #aa1 to ! mo/ p]si/5t & probably ! mo/ frequ5t4 ,x occurs 9 deta*$ masses :i* h v v>iable =ms b are :olly fibr\s1 ) ! details arrang$ 9 a v irregul> mann]4 ,! example figur$ 0 tak5 9 ! ev5+ dur+ a long spell ( f9e wea!r4 ,if su* a cl\d is wat*$1 its p]man5ce ( detail is v /rik+1 & mu/ be due to a p]si/5ce ( sl[ eddy+ movem5ts & to a cont9ual r5ewal & wa/e ( ! compon5t p>ticles ( ea* wisp4 ,?is is ! k9d ( cirrus select$ g5]ally z ! type ( cirrus1 & ! selection is a good "o4 ,common cirrus1 or cirrus communis1 x %\ld be call$4 ,settl$ conditions & f9e wea!r are its usual att5dants4 ,illu/ration3 ,plate #aa4 ,,common ,,cirrus4 7,cirrus ,communis47 ,we next come to a v>iety :i* is any?+ b a h>b+] ( good1 namely1 ! long /ripes or b&s ( cirrus :i* /ret* outw>ds f ! m>g9 ( ! cl\d canopy ( a cyclonic /orm4 ,9 "s ways ^! app5dages to ! great nimbus resemble ! /rips ( cirri=m cl\d :i* fr+e ! summit ( a ?und]-cl\d4 ,!y look z if !y mu/ h be5 =m$ by ! bl[+ away1 by a rapid w9d1 ( ! top ( an upris+ column ( vap\r-*>g$ air4 ,_! ma9 outl9e may ?us be easily acc\nt$ =1 b we h only to /udy _! detail$ /ructure = a few m9utes to feel t !y really pres5t a problem ( a v high ord]4 ,plate #ab %[s a fairly simple example1 b ,plate #ac repres5ts a cl\d ( v great complexity4 ,to take ?is la/ ! cam]a 0 tilt$ upw>ds at an angle ( #de degrees1 s t ! top ( ! picture is n f> f ! z5i?4 ,! wond]ful plume ( cl\d rose f ! s\!rn horizon1 & end$ 9 a great %eaf ( fibres & films spread out l a p>tly op5$ fan ^: edge 0 only ab\t #ej degrees above ! nor!rn horizon4 ,its l5g? z x pass$ ov]head lay betwe5 a po9t a little ea/ ( s\? to a little we/ ( nor?2 & ! broad b& mov$ z a :ole1 )\t any m>k$ int]nal *anges1 f ! s\?-we/ t[>ds ! nor?-ea/4 ,! wea!r 0 v unsettl$4 ,a long procession ( cyclones _h be5 sweep+ along our we/]n %ores1 & ! b>omet] 0 j beg9n+ a fre% & rapid fall4 ,dur+ ! ensu+ night a heavy gale bur/ ov] ! s\? ( ,engl&4 ,illu/ration3 ,plate #ab4 ,,b& ,,cirrus4 7,cirrus ,vittatus47 ,illu/ration3 ,plate #ac4 ,,b& ,,cirrus4 7,cirrus ,vittatus47 ,! :ole ph5om5on 0 highly *>act]i/ic4 ,^! great b&s ) ! div]g5t /riation might well be kn[n z /orm b&s1 f _! almo/ inv>iable connection ) ! viol5t atmosph]ic movem5ts to :i* !y are mo/ probably due4 ,plate #ab %[s a mu* less dang]\s v>iety ( ! same species1 :i* is di/+ui%$ f x by ! comp>ative abs5ce ( int]nal detail & by ! curl$ ends4 ,cl\ds ( ?is "* h sometimes be5 call$ cirro-filum1 b a comp>ison ( ! plates ) ! typical cirro-filum ( ,plate #g w %[ t !re is little resemblance2 & ! att5dant wea!r is also 9 m>k$ contra/1 bo? ( :i* facts imply a fundam5tal diff]5ce 9 ! causes to :i* _! features are due4 ,b&$ or ribbon$ cirrus is ! "n :i* !y imm$iately sugge/1 & ?is may be r5d]$ cirrus vittatus4 ,?is ends our survey ( cirrus cl\ds4 ,any "o :o comp>es ! plates s f> giv5 w see t !y repres5t =ms s div]se t x is impossible to avoid ! conclusion t ! conditions "u :i* !y are produc$ mu/ diff] n only 9 degree b also 9 k9d4 ,:at ^? conditions are we h attempt$ "h & !re to sugge/1 b 9 no case c we feel t ! explanation has be5 at all complete4 ,9 "s cases1 notably ! la/1 we are face to face ) su* complicat$ details t x is hopeless to attempt to expla9 !m 9 ! pres5t /ate ( our k4 ,fact ^u fact mu/ be accumulat$ until we c give _! hi/ory f _! e>lie/ beg9n+s2 & f> m accurate & detail$ k ( ! att5dant atmosph]ic conditions mu/ be acquir$ be=e we c hope to rob su* elaborate /ructures ( _! pres5t my/]y4 ,?is requires ! co-op]ation ( _m eyes & _m m9ds1 & exact specific names mu/ be an ess5tial prelim9>y4 ,^? :i* h be5 sugge/$ 9 ^! pages are-- #a4 ,cirro-nebula1 or ,cirrus haze4 #b4 ,cirrus excelsus1 or ,high cirrus4 #c4 ,cirrus v5tosus1 or ,w9dy cirrus4 #d4 ,cirro-filum1 or ,?read cirrus4 #e4 ,cirrus nebulosus1 or ,hazy cirrus4 #f4 ,cirrus caudatus1 or ,tail$ cirrus4 #g4 ,cirrus vittatus1 or ,b& cirrus4 #h4 ,cirrus incon/ans1 or ,*ange cirrus4 #i4 ,cirrus communis1 or ,common cirrus4 ,,footnote3 #b ,! telescope ) :i* ^! obs]vations h be5 made is a #fh-;in* refractor equatorially m\nt$4 ,,*apt] ,,iii ,,cirro-,,/ratus ,,& ,,cirro-,,cumulus ,,sev]al ( ! v>ieties ( cirrus already discuss$ may ga!r s abundantly at "s giv5 level 9 ! atmosph]e1 t ! mo/ obvi\s feature comes to be ?is arrangem5t 9 a %eet4 ,! cl\d !n becomes cirro-/ratus1 & %\ld be s nam$4 ,we h describ$ h[ cirro-nebula frequ5tly gr[s 9 d5sity until x fails to produce halo ph5om5a1 & may ev5 r$uce ! sun to a hazy pat* ( light %[+ no outl9e4 ,?is is ! mo/ typical ( all =ms ( cirro-/ratus4 ,x has always a di/9ctly fibr\s or /reaky appe>ance1 :]eby x is at once di/+ui%$ f a simil> b l[] cl\d :i* w be describ$ lat] on4 ,a simil> %eet may be =m$ f ! fusion toge!r ( ! /reaks ( cirrus-nebulosus1 ! b&s ( cirrus vittatus1 or ! developm5t ( cirrus incon/ans4 ,b ! g5]al rule is t ! cirro-/ratus reta9s m or less ( ! specific *>act]s ( ! p>5t =m4 ,plate #ad %[s a hazy =m ( cirro-/ratus develop$ f ! nebul\s cirrus4 ,its altitude 0 great1 be+ ab\t #aj1jjj metres4 ,! processes ( gr[? & *ange c\ld be /udi$ easily4 ,fir/ w\ld appe> "s fa9t spots & /reaks2 ^! quickly fus$ toge!r into l>g] pat*es1 :i* aga9 jo9$ to _! neighb\rs4 ,9 a few m9utes ! cl\d s =m$ w\ld return to ! mottl$ or /reaky appe>ance1 & ei!r disappe> entirely or become v ?91 only to recomm5ce ! process4 ,?is w5t on = m ?an an h\r1 ! cl\dy pat*es gett+ l>g] & l>g]1 until ! critical condition 0 pass$1 & ! sky 0 cov]$ ) a g5]al veil ( typical cirro-/ratus4 ,illu/ration3 ,plate #ad4 ,,hazy ,,cirro-,,/ratus4 7,cirro-/ratus ,nebulosus47 ,9 ,plate #ae we h an example ( a cl\d :i* is cle>ly cirro-/ratus1 b ! %eet is brok5 up into long b&s1 & ea* ( ^! is made up ( common cirrus4 ,9 ! upp] "p ( ! picture ! sprays ( cirrus are =m+1 & z !y come into be+ !y are arrang$ 9 r[s4 ,we h "h to d ) a ph5om5on ( a v diff]5t ord] f ! "o pres5t$ by ! true b&$ cirrus4 ,! arrangem5t into belts mu/ "h be due to "s k9d ( wave-movem5t 9 ! air1 break+ up ! critical plane into long ribs transv]se to ! direction ( ! wave-movem5t4 ,! specim5 %[n 0 mov+ 9 a direction ne>ly at "r angles to ! b&s1 ?\gh ! surface w9d 0 ne>ly p>allel to _! l5g?4 ,! "q at once pres5t$ itself z to :e!r ! movem5t ( ! b&s 0 really a drift ( ! cl\d1 or :e!r x 0 n a case ( ! propagation ( cl\d production ) ! advanc+ wave4 ,?is 0 easily answ]$ by wat*+ ! details ( a b&4 ,! advanc+ side 0 always fea!ry1 & c>eful obs]vation %[$ t ! edge advanc$ by ?r[+ out new ?reads & curls4 ,a giv5 ?read or curl1 "o mom5t at ! edge1 w\ld 9 a few m9utes be well 9 ! b&4 ,q opposite ev5ts 7 tak+ place 9 ! re> ( ea* b&4 ,! cl\d 0 !re obvi\sly melt+ away4 ,inde$1 to sum ! matt] up1 ! cl\d b&s fl[$ pa/ _! details j z ! waves on ! sea fl[ pa/ ! float+ foam4 ,evid5tly we h 9 ,plate #ae ! result ( a plane ( comm5c+ cirrus =mation brok5 into a s]ies ( tr\ghs & waves by an undulatory movem5t ( ! air4 ,b1 z we h already said :5 speak+ ( cirrus incon/ans1 ! condition 9 :i* trifl+ up-&-d[n movem5ts c det]m9e :e!r cond5sation %all1 or %all n1 take place seldom la/s long4 ,x is usually only a /age 9 a cont9u\s *ange1 & 9 ?is p>ticul> in/ance ! b&$ /ructure 0 soon replac$ by a fairly cont9u\s %eet ( typical cirro-/ratus4 ,illu/ration3 ,plate #ae4 ,,cirro-,,/ratus4 ,! next plate1 ,no4 #af1 %[s a simil> process4 ,9 ! upp] "p we h cirrus incon/ans =m+ 9 pat*es out ( a deep cle>-blue sky4 ,its hazy fibres gr[ clos] & clos]1 betray+ a slight t5d5cy to ga!r 9 n>r[ ripple-l b&s1 b ! /ructure is soon lo/ 9 ! uni=m :ite %eet ( int]lac+ fibres1 :i* diff] f common cirrus 9 little else ?an _! numb] & clos5ess4 ,nev]!less1 ! /rati=m arrangem5t is q obvi\s en\gh to w>rant ! use ( ! t]m 8cirro-/ratus40 ,illu/ration3 ,plate #af4 ,,cirro-,,/ratus4 7,cirro-/ratus ,communis47 ,! *ange ( cirro-nebula into cirro-/ratus is %[n 9 ,plate #d1 to :i* ref]5ce has already be5 made4 ,! /ructures are rem>kably delicate1 %[+ 9 ! middle a di/9ct irregul> mottl+2 & r fur!r t[>ds ! top "r-h& corn] a ripple /ructure appe>s1 & 9 ! top left-h& corn] ! %eet is d5s] & :it]4 ,! altitude ( ?is cl\d 0 evid5tly great1 & actual measurem5t %[$ x to be #gf miles4 ,x did n la/ long1 & aft] its *ange into brok5 pat*es ( d5s] cirro-/ratus1 /ill high] cl\ds 7 reveal$ ?r\gh ! gaps4 ,cirro-/ratus (t5 =ms almo/ simultane\sly at m ?an "o level1 & :5 t happ5s ! full /rati=m appe>ance is g5]ally rea*$ fir/ by ! l[] lay]4 ,9 ,plate #ag we h two lay]s4 ,! fluffy bits ( cirrus nebulosus1 9 ! l[] "p ( ! picture1 are really ! high] cl\ds4 ,bel[ !m1 probably by _m ?\s&s ( feet1 floats ! d5s] cl\d %[n 9 ! upp] "p ( ! picture4 ,?is is an int]e/+ l9k betwe5 ! fibr\s & ! granul> =ms ( cirrus1 & is probably be/ describ$ z spott$ cirro-/ratus1 or cirro-/ratus maculosus4 ,x is a =m v frequ5tly met )1 b seldom %[+ any p]si/5ce4 ,x is indicative ( cond5sation 9 a calm atmosph]e1 & n unfrequ5tly m>ks ei!r ! small irregul>ities ( pressure :i* =m ! conditions = ?und]/orms1 or ! beg9n+ ( ! break up ( an anticyclone4 ,illu/ration3 ,plate #ag4 ,,floccul5t ,,cirro-,,/ratus4 7,cirro-/ratus ,cumulosus47 ,a co>s] texture & great] d5sity are %[n 9 ,plate #ah1 :]e we h cirro-/ratus 9 ! l[] "p ( ! picture1 & cirro-cumulus 9 ! upp]4 ,! altitude ( ?is cl\d 0 only ab\t #djjj metres1 "o ( ! lea/ values record$ at ,exet] = cirro-/ratus ( any k9d4 ,! intimate admixture ( ! fibr\s & granul> =ms is v cle>ly %[n4 ,illu/ration3 ,plate #ah4 ,,cirro-,,/ratus ,,& ,,cirro-,,cumulus4 ,?is close relation is equally obvi\s 9 ,plate #ai1 :]e ! cl\dlets are arrang$ 9 loosely m>%all$ r[s1 dimly resembl+ ! b&$ /ructure ( ,plate #ae4 ,b 9 ?is case ! direction ( movem5t 0 ) ! long l9es1 & ! propagation ( cl\d production foll[$ ! same c\rse4 ,"s ( ! little cl\dlets h an opacity1 & !re=e brilliancy1 q unusual = cirro-cumulus1 b _! intimate association evid5tly 9 ! same plane ) und\bt$ cirrus %[s t !y mu/ fall "u t g5]al description4 ,x is a cl\d indicative ( unsettl$ wea!r1 & ! exceptional brilliancy is d\btless due to an unusual quantity ( vap\r at ! cl\d plane1 :i* mu/ mean t ! *ange f ! dry /ratum above to ! damp "o bel[ mu/ be mu* m sudd5 ?an is ord9>ily ! case4 ,cl\ds ( ?is k9d might well be call$ cirro-/ratus cumulosus4 ,illu/ration3 ,plate #ai4 ,,cirro-,,cumulus4 ,we n[ come to two companion pictures1 ,plates #bj & #ba1 :i* 7 tak5 )9 half a m9ute ( ea* o!r4 ,9 ! fir/ ! cam]a 0 direct$ t[>ds ! we/1 & 9 ! second x 0 fac+ ! nor?-we/4 ,! sun 0 ne>+ ! horizon1 & 0 only j outside ! field ( view 9 ea* case1 s t ! two photographs =m a panorama ( ! we/]n sky4 ,a sol> halo _h disappe>$ ab\t half an h\r previ\sly1 & ! cirro-nebula _h *ang$ into ! rem>kable =ms ( cl\d depict$4 ,plate #ba %[s cirrus ripples 9 ! upp] "p1 & cirro-cumulus 9 s(t1 ill-def9$ balls 9 ! l[] "p2 b !y 7 at ! same level1 & are only diff]5t p>ts ( ! same cl\d plane4 ,9 ,plate #bb we see simil> ball-l cl\dlets rang$ 9 long l9es :i* run almo/ at "r angles to ! ripples ( ! companion picture4 ,cl\ds l ^! are r>e4 ,!y are almo/ unkn[n dur+ ! e>ly "p ( ! day1 &1 s f> z ! writ]'s exp]i5ce goes1 !y are only to be f\nd 9 ! aft]noon t[>ds sunset4 ,"s ( our mo/ gorge\s sunset skies are due to !m2 = _! altitude is consid]able1 & !y d n light up ) ! sunset col\rs until ! l[] cl\ds h become d>k %ad[s aga9/ ! gl[+ backgr\nd4 ,! hotte/ mon?s ( ! ye>1 ! /ill air & great evaporation :i* are ! contribut+ causes ( ?und]/orms1 are also ! conditions "u :i* su* skies may be se54 ,inde$1 :ile ^! photographs 7 be+ tak51 heavy ?und]/orms 7 9 progress )9 less ?an a hundr$ miles4 ,cirro-cumulus nebulosus1 or hazy cirro-cumulus1 describes ! =m correctly4 ,illu/ration3 ,plate #bj4 ,,hazy ,,cirro-,,cumulus4 7,cirro-cumulus ,nebulosus47 ,illu/ration3 ,plate #ba4 ,,hazy ,,cirro-,,cumulus4 7,cirro-cumulus ,nebulosus47 ,! next plate1 ,no4 #bb1 gives a view ( an ev5+ sky ab\t half an h\r aft] sunset4 ,! l[] cl\ds1 cirro-cumulus & cirro-/ratus1 ( a deep purple br[n1 /&+ out d>k aga9/ a gold-col\r$ %eet ( high] cirro-/ratus1 :i* comes out :ite 9 ! photograph1 :ile ! purple-t9t$ sky comes d>k4 ,we h "h ?ree di/9ct lay]s1 all cirrus4 ,fir/1 ! hazy cirro-cumulus1 =m+ two b>s across ! l[] "p ( ! picture2 !n long b&s ( cirrus or cirro-/ratus1 be/ se5 9 ! bottom "r-h& corn]2 &1 f> above bo?1 ! cirro-/ratus :i* 0 reflect+ ! yell[ sunlight4 ,su* a sky might be an indication ( ?und] conditions1 or x might be due to an unusual quantity ( vap\r 9 ! atmosph]e produc$ by "s o!r cause4 ,! actual conditions 7 ! g5tle fl[ ov] ,engl& ( vap\r-lad5 air f ! we/]n ocean1 h]ald+ ! *ange f a long spell ( f9e hot wea!r1 due to a ,july anticyclone1 to a mon? ( heavy ra9s & we/]n gales1 accompany+ ! passage ( a long procession ( cyclones along our we/]n %ores4 ,illu/ration3 ,plate #bb4 ,a ,,sunset ,,sky4 ,aga91 a m>k$ contra/ is %[n 9 ,plate #bc4 ,"h we h ! highe/ & ?9ne/ =m ( cirro-cumulus1 ! "o nam$ cirro-macula by ,mr4 ,ley4 ,x is r>ely1 if ev]1 se5 be=e elev5 o'clock 9 ! morn+1 & is f> common] 9 ! aft]noon4 ,! example %[n 0 photograph$ at sunset at ! close ( a day :i* _h be5 almo/ cl\dless4 ,cirro-macula =ms "h & !re 9 a cle> sky4 ,a hazy1 :iti% pat* appe>s1 :i* at fir/ %[s no def9ite /ructure1 b looks almo/ l a little bit ( cirro-nebula4 ,?is sudd5ly splits up by cle> blue lanes runn+ ?r\gh x1 & cutt+ ! pat* up into irregul> segm5ts1 :i* quickly r\nd !mselves (f into m9ute bits usually :it] on _! edges & semi-transp>5t 9 ! c5tre4 ,! process c be /rik+ly imitat$ by scatt]+ on wat] "s f9e p[d] :i* w float4 ,if left )\t di/urbance1 ! p>ticles draw toge!r into num]\s small gr\ps1 leav+ lanes ( cle> wat] betwe5 !m4 ,illu/ration3 ,plate #bc4 ,,speckle ,,cl\d 7,ley74 7,cirro-macula47 ,cirro-macula frequ5tly gives rise to ! fibr\s =m ( cirrus we h call$ cirrus caudatus4 ,! granules ( ! cirro-macula gr[ d5s]1 & beg9 to drop _! froz5 p>ticles z soon z !y become l>ge en\gh4 ,inde$1 a cl\dlet ( cirro-macula may sometimes be se5 to turn bodily into a f9e l9e ( fall+ cry/als1 :i* w be a curv+ l9e ( cirrus4 ,on ! o!r h&1 x w sometimes rema9 visible = an h\r or m )\t any trace ( desc5d+ /reaks or float+ fibres4 ,pure cirro-macula su* z ,plate #bc is n (t5 se52 x is f> m frequ5tly mix$ ) m solid-look+ cl\dlets & desc5d+ fibres1 su* z are %[n 9 ,plate #bd1 :i* gives ! same po9t ( view z #bc1 b a qu>t] ( an h\r lat]1 & photograph$ ) a long] focus l5s4 ,^! two photographs1 toge!r ) #bj & #ba1 give excell5t examples ( ! use ( ! black mirror4 ,9 none ( ! f\r c\ld ! nak$ eye detect all ( ! cl\d /ructures4 ,! :ole sky 0 a blaze ( dazzl+ light1 b by adju/+ exposure & developm5t ! details are fully br\ght out )\t ! lea/ difficulty4 ,illu/ration3 ,plate #bd4 ,,cirrus ,,caudatus ,,& ,,cirro-,,macula4 ,cirro-/ratus1 we see f ! examples :i* h be5 consid]$1 h>dly des]ves to be treat$ z a di/9ct g5us ( cl\d4 ,its =mation is id5tical ) t ( _m species ( cirrus1 or 9 "s cases ) t ( ! speckle cl\d1 cirro-macula1 or ev5 ! co>s] k9ds ( cirro-cumulus4 ,! diff]5t v>ieties :i* x %[s are be/ r5d]$ by ref]5ce to ! specific names ( ! deta*$ =ms :i* h simil> features4 ,cirro-cumulus1 on ! o!r h&1 does pres5t cle>ly m>k$ v>ieties4 ,cirro-macula is s di/9ct t x might well be giv5 ! "n aw>d$ to x by ,mr4 ,ley1 :ile ! t]m 8cirro-cumulus0 is res]v$ = ! co>s] & r\nd] =ms4 ,! hazy1 ripple-l /ructures ( ,plate #d & ,plate #bj %\ld also h "s di/9ctive appellation1 z w be sugge/$ lat] on :5 deal+ ) wave cl\ds z a :ole4 ,x is difficult to f9d any %ort way ( express+ ! v>i\s ideas :i* %\ld be summ$ up 9 ! "n ( a cl\d4 ,!re seems no alt]native to ! use ( additional words1 unless x be to foll[ ! example ( *emi/s1 & comp\nd appall+ names simil> to ^? :i* t]rify ! un9itiat$ :o ?9k !y w\ld l to read some?+ ab\t1 let u say1 ! coal-t> dyes4 ,if a cl\d belongs to ! ord] cirrus1 is 9 a level %eet1 & t %eet is compos$ ( int]lac+ or curl+ fibres1 l ^? ( common cirrus1 we c h>dly express ! facts m briefly ?an by call+ x cirro-/ratus communis1 or common cirro-/ratus4 ,if x consi/s ( cirrus b&s fus$ toge!r1 b /ill %[+ ! b&$ /ructure1 x is cirro-/ratus vittatus4 ,aga91 if x is f9ely speckl$1 l cirro-macula1 x may be describ$ z cirro-/ratus maculosus1 & if ! /ructure is co>s] x may be call$ cirro-/ratus cumulosus4 ,z a g5]al av]age1 cirro-/ratus lies some:at l[] 9 ! atmosph]e ?an ! deta*$ =ms1 probably because ! conditions :i* give rise to ! latt] rea* to great] altitudes 9 pat*es ?an x is possible = !m to rea* 9 a cont9u\s mann]4 ,vap\r becomes r>] ) increas$ height & ) dim9i%$ temp]ature1 s t x mu/1 on ! :ole1 be less frequ5tly pres5t 9 cl\d-produc+ quantity z ! height increases4 ,at great altitudes x w be seldom t ! quantity is great en\gh to produce a /rati=m cl\d1 ?\gh x may well be en\gh = cirro-macula1 or ! deta*$ =ms ( cirrus1 l cirrus excelsus4 ,! production ( cirro-cumulus & cirro-/ratus sometimes spreads across ! sky ) a/oni%+ spe$1 & ?is rapid advance ( ! edge ( ! cl\d may lead to q mi/ak5 ideas z to ! velocity ( ! w9d at t altitude4 ,9 ! case ( cirro-cumulus1 or cirro-macula1 x is easy to fix att5tion on a s+le cl\dlet4 ,if ?is has ! usual ball-l =m1 x c only be reg>d$ z float+ 9 ! air & mov+ ) x4 ,mean:ile new cl\dlets may be =m+ & gr[+ d5s]1 s t ! cl\d pat* z a :ole may be app>5tly advanc+ at a mu* great] rate4 ,c>eless obs]vation w\ld !n lead to ! idea t ! cl\d 0 mov+ mu* fa/] ?an x really is1 b if ! att5tion is rigidly fix$ on a p>ticul> cl\dlet ! mi/ake is impossible4 ,if ! cl\d is a v>iety ( cirro-/ratus1 x is n always easy1 or ev5 possible1 to di/+ui% betwe5 ! advance ( cond5sation & ! movem5t ( ! :ole1 b x c ne>ly always be done if ! cl\d %[s any def9ite features ^u :i* att5tion c be fa/5$4 ,sometimes none suffici5tly m>k$ c be se51 & :5 t happ5s x is /ill possible 9 mo/ cases1 by wat*+ ! edge ( ! cl\d-mass1 to see :e!r new cl\d is be+ add$ to t edge4 ,! wave-l =ms pres5t a special case1 :i* w be dealt ) 9 a lat] *apt]1 aft] ! g5]al pr9ciples ( cl\d =mation h be5 discuss$ 9 connection ) ! great cl\ds ( ! l[] air1 ^: causes & conditions are f> bett] und]/ood4 ,,*apt] ,,iv ,,alto ,,cl\ds ,,f cirro-cumulus & cirro-/ratus we pass ?r\gh almo/ ins5sible gradations to ! d5s] =ms class$ toge!r 9 ! alto gr\p4 ,^! cl\ds are fundam5tally diff]5t1 9 t !y are always compos$ ( liquid p>ticles1 ?\gh !re is no d\bt1 f _! great altitude1 t _! temp]ature mu/ (t5 be _m degrees bel[ ! ord9>y freez+-po9t ( wat]4 ,:5 ?is is ! case1 !y are n unfrequ5tly m or less mix$ ) /reaks & filam5ts exactly l ^? describ$ "u ! "n ( cirrus1 :i* h be5 expla9$ z due to sl[ly fall+ sn[flakes4 ,x is n imm$iately obvi\s h[ su* app>5tly contradictory /atem5ts c be reconcil$4 ,! explanation is t m9ute droplets ( wat] may be cool$ _m degrees bel[ freez+-po9t )\t *ang+ into ice1 & t su* sup]-cool$ droplets congeal in/antly if a few ( !m jo9 toge!r to =m a l>g] drop4 ,practically ! same process may be wat*$ any day :5 !re is a %>p fro/ & d5se fog drift+ sl[ly along4 ,! fog-p>ticles are liquid1 & produce optical effects 9 ! neighb\rhood ( any brilliant light1 l an arc lamp1 absolutely ! same z ^? :i* w\ld be produc$ if ! temp]ature 7 above freez+-po9t1 :ile !re are none ( ! diff]5t ph5om5a :i* might be expect$ if ! p>ticles 7 cry/all9e ice-du/4 ,z ^! liquid p>ticles drift along !y come 9 contact ) bran*es ( trees & o!r ob/acles1 ! surface /ratum :i* surr\nds !m & b9ds !m into sph]es is brok51 & ! drop in/antly solidifies4 ,x is to be not$1 moreov]1 t ! drop does n freeze z su*1 b m]ely adds "s m p>ticles to ! bran*+ cry/als ( ho> fro/1 :i* gr[ outw>ds always t[>ds ! direction f :i* ! fog is drift+4 ,mo/ liquids1 :5 fre$ f contact ) solid bodies1 or :5 surr\nd$ by a smoo? envelope ( uni=m "*1 c be cool$ bel[ _! normal freez+-po9t )\t solidification tak+ place2 b ! introduction ( a p>ticle ( ! solid1 or sometimes ( any =eign body1 in/antly br+s ab\t a rapid freez+ ( ! :ole4 ,^! ph5om5a ( surfusion1 z x is call$1 h long be5 kn[n1 & _m ( !m are v int]e/+ & difficult to und]/&4 ,inde$1 x is probable t we %all h to add l>gely to our k ( ! =ces :i* b9d ! molecules ( a body toge!r to =m a solid1 & :i* direct ! processes ( cry/allization be=e we %all be able to int]pret ) any c]ta9ty a s]ies ( facts dep5d+ on ! attributes ( ^? v =ces4 ,wat] is no exception4 ,if f9ely divid$1 z by plac+ x 9 f9e capill>y tubes1 9 ! pores ( wood1 or 9 ! n>r[ spaces ( a wick1 x may be cool$ sev]al degrees bel[ normal freez+-po9t4 ,9 a cl\d1 or fog1 all ! conditions necess>y = surfusion to take place are und\bt$ly pres5t4 ,! wat] is pure1 ! envelope is uni=m1 ! subdivision is exce$+ly m9ute1 & ! drops are free f mo/ ( ! me*anical di/urbances :i* br+ ab\t ! solidification ( l>g] masses 9 ! laboratory4 ,?us we see !re is no?+ at all surpris+ 9 ! fact t cl\ds compos$ ( liquid p>ticles may exi/ at temp]atures bel[ ! ord9>y freez+-po9t4 ,on ! contr>y1 we %\ld expect t ! solidification ( ! cl\d p>ticles w\ld n take place until ! temp]ature 0 _m degrees bel[ freez+1 z is c]ta9ly ! case ) cl\ds ( ! cirrus ord]4 ,at temp]atures betwe5 ?is unkn[n1 b l[ value1 & ! normal freez+-po9t1 ! cl\ds w be compos$ ( liquid2 b :5 ! p>ticles jo9 toge!r1 sn[flakes w result in/ead ( ra9drops2 & ?is w be j z true ( alto cl\ds z x is ( ! great vapor\s m\nta9s ( ! l[] regions ( ! air :i* br+ falls ( sn[4 ,! /reaks (t5 mix$ ) alto-cumulus are cirrus ?reads1 & are1 no d\bt1 ( exactly ! same nature z ! tails ( cirrus caudatus1 or ev5 ! fibres ( cirro-filum4 ,! simple/ alto cl\d is alto-/ratus4 ,:5 ?is is complete1 s z to cov] ! sky1 x c be di/+ui%$ f cirro-/ratus by ! abs5ce ( fibr\s /ructure1 & by ! facts t x nev] produces any halo or fragm5t ( a halo1 b in/ead surr\nds ! sun or moon ) a :ite blur1 or1 if x is ?9 en\gh1 ) a close r+ ( col\r$ light mu* ne>] ?an a halo1 & ) ! col\rs 9 ! inv]se ord]--t is1 ) ! r$ fur!/ f ! c5tre4 ,"s ( ^! s-call$ coron are v beautiful :5 se5 9 ! black mirror1 & "s ( ^? =m$ ar\nd a full moon %[ q brilliant t9ts to ! unaid$ eye4 ,( c\rse1 ^! meteorological coron h no relation :atev] to ! true sol> corona2 !y are simply =m$ by ! passage ( ! rays ( light ?r\gh ! veil ( small p>ticles1 & may be easily imitat$4 ,take a piece ( glass su* z a lant]n-cov] glass1 brea! on x1 & hold x close be=e ! eye :ile look+ at "s small s\rce ( light4 ,if ! dew deposit is ?91 bright col\rs are %[n 9 a lum9\s r+ surr\nd+ ! light1 & ! ?9n] ! deposit ( dew ! l>g] ! r+ w be4 ,brea! heavily s z to give a ?ick deposit1 & ! light w be se5 to be ! c5tre ( a pat* ( :ite brightness )\t any col\r4 ,! ph5om5a are due to :at is kn[n z diffraction1 & if ! o!r conditions are un*ang$ ! diamet] ( ! r+ is inv]sely proportional to ! size ( ! p>ticles4 ,purity ( col\r 9 ^! r+s is an indication ( uni=mity 9 ! size ( ! p>ticles4 ,:5 ! moon is %9+ ?r\gh a %eet ( alto-/ratus1 :i* ?9s (f to "o edge1 v beautiful effects may (t5 be notic$1 & ! *ange f ! col\rless blur1 :5 a ?ick] "p ( ! cl\d is int]pos$1 to ! brilliant col\rs ( ! corona =m$ by ! ?9n] edges is v /rik+4 ,simil> ph5om5a are %[n almo/ equally well by any ( ! alto cl\ds1 b cirrus ?9 en\gh to produce a col\r$ corona w g5]ally produce a halo4 ,alto-cumulus ( ! k9d mo/ ne>ly alli$ to cirro-cumulus is %[n 9 ,plate #be4 ,! upp] "p ( ! picture %[s ragg$1 irregul> pat*es1 ) slight indications ( fibr\s /reaks4 ,! l[] portion %[s r\nd]1 ball-l cl\dlets1 a few ( ! l>g] ( :i* h di/9ct %ad[s on ! side away f ! sun4 ,?is plate gives alto-cumulus 9 a p>tly =m$ condition1 b x is n a m]e passage =m4 ,sometimes exactly su* a cl\d w float ov]head = h\rs1 %[+ v little movem5t & only sl[ *anges ( detail4 ,x is !re=e a di/9ct v>iety1 & may be call$ alto-cumulus in=mis4 ,illu/ration3 ,plate #be4 ,,alto-,,cumulus ,,in=mis4 ,a less def9ite =m is %[n 9 ,plate #bf4 ,x may also be reg>d$ z only p>tly =m$1 b its con/ruction is q diff]5t1 e "p be+ mi/y & ill def9$4 ,x is a common cl\d1 especially 9 sultry summ] wea!r ) /ill air4 ,"u ^? circum/ances1 aft] a hazy morn+1 x may be se5 sl[ly =m+ dur+ ! aft]noon1 gr[+ 9 d5sity z ! h\rs g by1 until x rea*es a maximum ab\t five or six o'clock1 aft] :i* x melts away1 or settles d[n into small pat*es ( high /ratus4 ,mo/ frequ5t 9 summ]1 x is by no means r>e 9 autumn & w9t]1 b /ill air is ess5tial4 ,f its hazy appe>ance x may be call$ alto-cumulus nebulosus4 ,illu/ration3 ,plate #bf4 ,,hazy ,,alto-,,cumulus4 7,alto-cumulus ,nebulosus47 ,fixity ( detail & sl[ movem5t *>act]ize bo? ! =ego+ =ms1 & 9 t respect our next picture 7,plate #bg7 %[s a cl\d :i* is a great contra/4 ,its deta*$ cl\dlets are r flatt] & ?9n]1 & ?\gh ! cl\d z a :ole w (t5 p]si/ = h\rs1 x is und]go+ cont9ual *ange1 & is =m$ :5 ! air is f> f /ill4 ,cl\dlets =m & ga!r into /rati=m pat*es1 :i* soon break up aga9 & disappe>2 & ! process goes on "h & !re1 sometimes accompani$ by fairly rapid movem5t ( ! pat*es z a :ole4 ,?is cl\d may be describ$ z alto-cumulus /rati=mis4 ,illu/ration3 ,plate #bg4 ,,flat ,,alto-,,cumulus4 7,alto-cumulus ,/rati=mis47 ,we n[ come1 9 ,plate #bh1 to a cl\d ( s+ul> beauty4 ,x =ms rapidly 9 a cle> sky1 its fir/ traces be>+ a /rik+ resemblance to cirro-macula1 b ! floccules1 in/ead ( rema9+ semi-transp>5t or dropp+ cirrus ?reads1 rapidly become opaque balls ( cl\d :i* l5g!n upw>ds4 ,?is upw>d t5d5cy causes ! =m$ cl\dlets to h _! long] axes v]tical1 :i* is v *>act]i/ic4 ,x might be nam$ alto-cumulus ca/ellatus1 or high-turret$ cl\d4 ,mr4 ,ley nam$ x /ratus ca/ellatus1 or turret-cl\d1 b x c]ta9ly belongs to ! cumulus section ( ! alto gr\p4 ,?und] wea!r is ! inv>iable condition = its production4 ,if x is se51 at lea/ 9 ,engl&1 ?und]/orms are c]ta9 to be record$ n v f> away4 ,:5 ?is p>ticul> photograph 0 be+ tak5 9 ,s\? ,devon1 v de/ructive /orms 7 record$ 9 ,brittany & 9 ! ,engli% ,midl&s1 & ! anvil-%ap$ tops ( unmi/akable ?und]-cl\ds 7 visible above ! horizon :ile ! exposure 0 be+ made4 ,illu/ration3 ,plate #bh4 ,,high ,,turret$ ,,cl\d4 7,alto-cumulus ,ca/ellatus47 ,ano!r =m ( almo/ equal beauty is %[n 9 ,plate #bi4 ,! r\nd$ balls make _! appe>ance z semi-transp>5t spots ^u ! sky1 & 9 _! g5]al *>act]s might easily be mi/ak5 = cirro-macula4 ,b a few m9utes w be en\gh to decide ! "q4 ,! little spots rapidly gr[ d5s]1 frequ5tly becom+ ragg$ at ! edges2 !y nev] drop d[n ! sl5d] filam5ts :i* usually desc5d f cirro-macula1 & _! edges are nev] d5s] ?an _! c5tral p>ts1 :i*1 x w be rememb]$1 0 a frequ5t feature ( ! true speckle cl\d4 ,! cl\dlets are obvi\sly r\nd$ balls arrang$ 9 pat*es1 :i* may turn gradually into alto-/ratus by _! fusion1 or1 aft] an exi/5ce ( m9utes or h\rs1 ! :ole may disappe> by a dis9tegration ( ea* ball1 by its break+ up into a ragg$ mass & melt+ away4 ,! altitude at :i* ?is cl\d =ms is betwe5 #ejjj & #ijjj metres1 accord+ to measurem5ts made by ! writ]1 ! actual specim5 figur$ be+ ab\t #gjjj4 ,x is almo/ z *>act]i/ic ( ?und] wea!r z ! la/1 b :]eas ,plate #bh %[s a v>iety :i* is mo/ (t5 se5 be=e #c p4m41 s9ce x only occurs :ile ! cl\d planes are rapidly ris+1 ! "o be=e u may be =m$ at almo/ any "t ( day1 b mo/ frequ5tly occurs 9 ! aft]noon4 ,an imp]fect =m ( x is frequ5tly met ) ab\t sunset1 9 :i* ! r\nd$ balls are n usually s well def9$ z :5 ! sun is high above ! horizon4 ,alto-cumulus glom]atus w\ld be a suitably descriptive "n4 ,illu/ration3 ,plate #bi4 ,,high ,,ball ,,cumulus4 7,alto-cumulus ,glom]atus47 ,if x 7 possible to take a good typical example ( ! v>iety j describ$ & roll x flat1 s t ea* cl\dlet %\ld be r$uc$ to a l5ticul> %ape1 we get a type :i* seems seldom to appe> dur+ ! heat ( ! day1 & to be mo/ frequ5t ab\t sund[n4 ,x consi/s1 z %[n 9 ,plate #cj1 ( di/9ct cl\dlets1 ) consid]able spaces betwe5 !m1 & gives ! impression ( a discont9u\s level %eet4 ,b ! compon5t cl\dlets are mu* too def9ite1 & pres]ve _! individuality f> too well to sugge/ any idea ( a brok5 /ratus2 ! spott$ /ructure is ! pr$om9ant feature1 :ile ! /rati=m arrangem5t is almo/ equally pla94 ,alto-/ratus maculosus w\ld be a suitable t]m4 ,x is n s high a cl\d z ! glom]atus type1 ! "o %[n be+ at an altitude ( ab\t #efjj metres4 ,! plate %[s ! position ( ! sett+ sun1 :i* is p>tly hidd5 beh9d "s d>k pat*es ( brok5 alto-/ratus 7fracto-alto-/ratus71 ! hazy =m & b\nd>ies ( :i* =m an effective contra/ to ! %9+ cl\dlets #bjjj metres or s above !m4 ,_m ( our mo/ beautiful sunsets are due to ?is =m ( cl\d1 p>ticul>ly 9 ! late autumn4 ,x is a cl\d ( calm wea!r1 & (t5 floats app>5tly motionless1 & und]go+ little *ange1 l flakes ( gl[+ fire aga9/ ! backgr\nd ( a fad+ sky long aft] ! sun has disappe>$4 ,x is n indicative ( ?und] conditions1 & x may occur on ! m>g9s ( an anticyclone4 ,illu/ration3 ,plate #cj4 ,,mack]el ,,sky4 7,alto-/ratus ,maculosus47 ,a l[] & co>s] =m ( ! spott$ alto-/ratus is %[n 9 ,plate #ca1 :]e x is se5 ?r\gh ! gaps 9 a ?9 %eet ( brok5 /ratus4 ,9 ?is case also ! sun 0 gett+ l[ 9 ! sky1 be+ hidd5 by ! d5s] bit ( /ratus 9 ! bottom left-h& corn]4 ,illu/ration3 ,plate #ca4 ,,mack]el ,,sky4 7,alto-/ratus ,maculosus47 ,alto-/ratus does n (t51 if ev]1 gr[ f ! fusion ( ! cl\dlets ( ! maculosus type4 ,b x does come f alto-cumulus glom]atus1 & also f a =m %[n 9 ,plate #cb4 ,"h we h alto-/ratus 9 process ( gr[?4 ,small irregul> lumps ( cl\d =m+ on ! "r-h& side ( ! picture gr[ l>g] & m irregul>1 beg9 to fuse toge!r t[>ds ! c5tre1 & on ! left-h& side ! fusion is almo/ complete4 ,/ill1 al?\gh ! sky is cov]$ ) cl\d1 ! lumpy =m is pla9ly visible4 ,! t]m 8alto-/rato-cumulus0 is suitable1 z x diff]s f ! m frequ5t & mu* l[] cl\d1 :i* w be describ$ fur!r on z /rato-cumulus1 9 little else ?an altitude & g5]al massiv5ess ( texture4 ,?is high /rato-cumulus is common en\gh1 too common1 inde$1 9 ,engl&1 z x produces _m a dull grey sky bo? 9 summ] & 9 w9t]4 ,9 ! latt] season x is n unfrequ5t ) ! cold ea/ w9ds ( ,febru>y & ,m>*4 ,x is probably ! l[e/ ( ! alto cl\ds2 ! l[e/ measurem5t made by ! writ] be+ #ahbh metres at ,exet]1 b l[] altitudes seem to h be5 record$ else:]e4 ,illu/ration3 ,plate #cb4 ,,alto-,,/rato-,,cumulus4 ,alto-cumulus ca/ellatus1 :i* is break+ up & disappe>+1 is %[n 9 ,plate #cc4 ,x 0 photograph$ ) a long-focus l5s1 s t ! scale ( repres5tation is ab\t eight times z great z t ( ,plate #bg4 ,?is view 0 tak5 at ,exet] :ile a ?und]/orm 0 9 progress at ,bri/ol4 ,illu/ration3 ,plate #cc4 ,,sunset4 7,alto-cumulus ,ca/ellatus ,fractus47 ,,*apt] ,v ,,l[] ,,cl\ds ,,! cl\ds ( ! l[] portions ( ! atmosph]e are =m$ 9 regions :]e wat] vap\r is abundant1 & frequ5tly 9 easy rea* ( ! /rong asc5d+ & desc5d+ air curr5ts produc$ by ! v>y+ temp]atures & irregul> surface ( ! gr\nd4 ,x is suffici5t to recite ^! conditions to %[ t ^! l[] cl\ds w be d5s]1 l>g]1 co>s] 9 texture1 & *>act]iz$ by great] def9it5ess ( =m ?an ^? we h1 s f>1 consid]$4 ,9 ! ,int]national sy/em !y are classifi$ ?us-- ,gr\p ,c4 ,l[] cl\ds4 7a7 ,/rato-cumulus4 7b7 ,nimbus4 ,gr\p ,d4 ,cl\ds ( diurnal asc5d+ curr5ts4 ,cumulus & cumulo-nimbus4 ,gr\p ,e4 ,high fogs4 ,/ratus4 ,?is is c]ta9ly ! lea/ satisfactory "p ( ! :ole s*eme1 & x is n at all easy to see ^u :at gr\nds x 0 adopt$ by ! ,int]national ,committee4 ,gr\p ,d--cumulus & cumulo-nimbus--d %[ important diff]5ces f ! o!r gr\ps1 ?\gh x is (t5 difficult to say :e!r ! sky %\ld be describ$ z cov]$ ) /rato-cumulus or z cov]$ ) num]\s small cumulus4 ,x is ! sep>ation ( /ratus--plac+ x 9 a gr\p by itself1 & mak+ t ! l[e/--:i* is ! wor/ po9t4 ,z a matt] ( fact1 /ratus may exi/ at any altitude f sea-level up to su* heights t we %\ld n hesitate to call x alto-/ratus4 ,inde$1 !re is no ess5tial "* ( alto-/ratus :i* di/+ui%es x f "s ( ! l[] =ms4 ,:atev] its altitude1 its ?ickness & ! size ( its p>ticles may v>y 9 a precisely simil> mann]4 ,we may h ! p>ticles exce$+ly small1 :5 ! fog w be dry1 & su* a /ratus may be s ?9 z h>dly to dim ! sun2 or x may be s ?ick z to completely hide x4 ,on ! o!r h&1 ! fog may consi/ ( p>ticles easily visible to ! nak$ eye1 =m+ ! s-call$ ,scot* mi/1 or ! 8dry0 fog ( ,d>tmoor1 :i* w wet ?+s z rapidly & m ?or\ghly ?an a sm>t %[]4 ,:5 su* a fog accumulates to a suffici5t dep?1 ! p>ticles 9 _! fall pick up o!rs1 & ! result is a di/9ct f9e ra94 ,?is may occur n only ne> ! gr\nd1 b at almo/ any level bel[ t at :i* ! cl\d w\ld pass into ! region ( cirrus4 ,plate #cd %[s ?ree lay]s ( /ratus1 9 ea* case mu* brok5 up4 ,! highe/ lay] is a good example ( alto-/ratus maculosus4 ,l[] d[n1 by half a mile or m1 come p>ts ( a grey %eet consid]ably d5s] & ?ick]4 ,x is a matt] ( ta/e :e!r ?is %\ld be call$ high /ratus or l[ alto-/ratus4 ,!re is no te/ by :i* ! "o c be di/+ui%$ f ! o!r4 ,l[] aga9 come ! deta*$ d>k] cl\ds1 :i* are fragm5ts ( a %eet ( /ratus :i* is break+ up & disappe>+4 ,! photograph 0 tak5 9 ! aft]noon1 aft] a wet morn+1 & all ?ree lay]s 7 probably relics ( ! great ra9-cl\d sy/em1 or nimbus1 :i* produc$ ! ra9fall4 ,illu/ration3 ,plate #cd4 ,,?ree ,,lay]s ,,( ,,/rati=m ,,cl\d ,,aft] ,,ra94 ,we h ref]r$ to ! production ( f9e ra9 f a ?ick fog4 ,if n[ su* a ?ick lay] ( co>se-gra9$ fog--if we may use su* a phrase--is susp5d$ ov]head at a mod]ate altitude1 ! result is a drizzl+ ra9 und]nea?1 & ! cl\d at once becomes a nimbus4 ,:5 ,luke ,h[>d adopt$ ! t]m 8nimbus10 he propos$ to employ x1 app>5tly1 = a va/ mass ( cl\d su* z t :i* =ms ! ra9y region ( a cyclone2 a huge pile ( cl\ds conta9+ repres5tatives ( all 8 o!r types 9 "s unkn[n b close relation%ip4 ,x 01 9 fact1 a compreh5sive t]m1 & z su* !re 0 a good use = x4 ,at pres5t x is appli$ to any cl\d f :i* ra9 is fall+1 except :5 ! cl\d c be id5tifi$ z a v>iety ( cumulus :i* is call$ cumulo-nimbus4 ,b we h already said t a /ratus may be a ra9-cl\d1 & s may o!r v>ieties4 ,moreov]1 :5ev] a nimbus breaks suffici5tly = u to be able to see its upp] surface1 we inv>iably f9d t1 if x 7 view$ f above1 we %\ld1 )\t a mom5t's hesitation1 place x 9 "o ( ! o!r gr\ps4 ,x is only :5 we are und]nea? x we c see its ra9-produc+ "*1 & give x ! or?odox "n4 ,! real fact is t nimbus %\ld be an adjective1 mean+ ra9-produc+1 & n a sub/antive4 ,h[ev]1 x has its allott$ place 9 ! ,int]national sy/em1 & x is bett] to adh]e z f> z possible to a defective b widely recogniz$ sy/em until x c be au?oritatively am5d$1 r ?an to make an individual attempt to ignore x4 ,! facts are suffici5tly obvi\s1 & ! days ( nimbus z a type are numb]$4 ,! two plates1 ,nos4 #ce & #cf1 are fair typical repres5tations ( ! cl\ds usually kn[n z nimbus2 b !y are bo? ( !m only ! "u-surfaces ( o!r cl\ds1 ,plate #cf %[+ ! "u-surfaces ( a gr\p ( heavy cumulo-nimbus all jo9$ toge!r s z to cov] ! sky1 :ile ,plate #ce %[s a mass ( d5se /rato-cumulus4 ,! ra9-cl\d is always a =m ( ei!r /ratus or cumulus1 or a comb9ation ( ! two1 sometimes 9 fur!r comb9ation ) cl\ds ( ! alto class1 or ev5 ext5d+ upw>ds to cirro-/ratus & cirro-nebula4 ,:]e x consi/s ( a s+le lay]1 t lay] diff]s f its ra9less repres5tative only 9 great] ?ickness f base to summit1 or 9 great] d5sity2 & :5 !re are sev]al di/9ct lay]s ( cl\d1 s t ! l[e/ is %ad$ by ! high]1 ra9 may fall1 ev5 ?\gh !y diff] 9 no visible way f cl\ds :i* w\ld be ra9less if alone4 ,plate #cc is an example4 ,illu/ration3 ,plate #ce4 ,,ra9-,,cl\d4 7,nimbus47 ,illu/ration3 ,plate #cf4 ,,ra9-,,cl\d4 7,nimbus47 ,nimbus1 inde$1 is n a type-=m1 b is m]ely a typical condition1 & :5 us$ z a sub/antive is only a conv5i5t way ( express+ our ignorance z to ! real =m ( ! cl\d we s describe4 ,! altitude ( ! base ( a ra9-cl\d may v>y consid]ably4 ,x may be any?+ f sea-level up to heights :i* v>y ) ! geographical conditions & ) ! conditions ( temp]ature & pressure1 b probably 9 ?is c\ntry nev] great] ?an #gjjj or #hjjj metres4 ,ra91 or sn[1 (t5 falls f cl\ds at great] altitudes ?an ^!1 b unless 9 its desc5t x passes ?r\gh o!r l[] cl\ds1 ! drops1 z a rule1 w dry up & disappe>4 ,! au?or has (t5 se5 q heavy ra9 desc5d+ f a cl\d1 & disappe>+ completely )9 a ?\s& feet or s ( ! cl\d-base4 ,on r>] occasions a /ill m rem>kable ?+ may be se5--namely1 a %[] fall+ f an upp] cl\d into a l[]1 & none betwe5 ?is l[] cl\d & ! gr\nd4 ,?is curi\s ph5om5on c only be expla9$ by suppos+ t ! convection curr5ts :i* make ! l[] cl\d are /rong en\gh to support ! small ra9drops4 ,pure /ratus is a level %eet ( cl\d ) little v>iation ( ?ickness1 n asc5d+ e "h & !re into r\nd$ lumps4 ,its mo/ typical =m cov]s ! :ole sky ) a uni=m grey pall1 :i* may or may n completely hide ! sun4 ,su* a cl\d does n l5d itself to pictorial repres5tation4 ,a frequ5t =m1 9 :i* ! %eet is m or less brok51 is %[n 9 ,plate #cg4 ,?is is a v>iety :i* is frequ5t 9 ! summ] morn+s1 & g5]ally breaks up & cle>s away be=e elev5 o'clock4 ,if1 h[ev]1 x appe>s 9 autumn & w9t] ) lay]s ( alto cl\d above1 x may gr[ d5s]1 & turn into a /rati=m nimbus1 or x may g on drift+ ov]head = sev]al days )\t sign ( *ange4 ,illu/ration3 ,plate #cg4 ,,/ratus ,,communis4 ,break up su* a %eet ( cl\d by num]\s me&]+ cracks1 & r\nd (f ! deta*$ pieces s z to give !m a m or less r\nd$ or pyramidal section1 & ! cl\d becomes /rato-cumulus1 typical repres5tations ( :i* are %[n 9 ,plates #ch & #ci1 :i* depict diff]5t p>ts ( ! same sky4 ,9 ,plate #ch ! cam]a 0 po9t$ due we/1 & 9 ,plate #ci x 0 turn$ r\nd to ! nor?-we/1 s t ! two views d n q meet4 ,illu/ration3 ,plate #ch4 ,,/rato-,,cumulus4 ,illu/ration3 ,plate #ci4 ,,/rato-,,cumulus4 ,plate #dj is a diff]5t v>iety4 ,x is /rati=m1 ea* compon5t cl\dlet be+ r ragg$ at ! edges4 ,9 "s ways x resembles cirro-macula & ! speckl$ v>ieties ( alto cl\d1 b x is co>s] 9 texture & obvi\sly at no great altitude4 ,! ,int]national sy/em w\ld call x /rato-cumulus1 b ,mr4 ,ley gives a repres5tation f ano!r negative tak5 at ! same "t z ! type ( :at he calls /ratus maculosus1 a "n :i* seems f> m suitable1 s9ce ! cl\d be>s a mu* clos] relation to /ratus ?an to cumulus4 ,9 ! p>ticul> in/ance figur$1 ! brok5 /ructure did n la/ long2 ! spaces gradually clos$ 91 & a complete /ratus 0 ! result4 ,illu/ration3 ,plate #dj4 ,,/ratus ,,maculosus4 ,/rato-cumulus (t5 la/s = h\rs1 ) little or no p]ceptible *ange1 b /ratus maculosus r>ely p]si/s = m ?an half an h\r4 ,! fir/ is a cl\d ( fairly /able conditions1 ! latt] is dep5d5t = its exi/5ce ^u ! ne> approa* to critical conditions at "o p>ticul> level1 &1 z we h said 9 o!r cases1 su* a critical /ate is almo/ always soon pass$1 ) ! result t ! cl\d ei!r masses into a d5s] =m1 or else breaks up & disappe>s4 ,if ! up & d[n curr5ts are /rong en\gh to p]si/1 ! result w be /rato-cumulus & n /ratus maculosus4 ,a k9d ( /ratus :i* is frequ5tly se5 9 ! daytime is %[n 9 ,plate #da4 ,?is is lit]ally a lift$ fog1 hav+ be5 =m$ ab\t midday1 aft] gr\nd fog 9 ! e>ly morn+4 ,x w\ld be call$ common /ratus1 or /ratus communis4 ,:5 x appe>s x is a fairly p]si/5t =m1 sometimes break+ up or swell+ up into /rato-cumulus1 b m (t5 splitt+ into long rolls ( cl\d1 ) m>g9s l ^? ( cumulus4 ,?is ph5om5on is %[n 9 ,plate #db1 :i* 0 tak5 9 ,decemb] at #aa a4m41 on a day :i* op5$ ) a ?ick gr\nd fog4 ,a precisely simil> cl\d is frequ5t 9 ! e>ly h\rs ( a summ] morn+1 z a /age 9 ! disp]sal ( a radiation gr\nd fog4 ,! fog fir/ lifts f ! gr\nd1 until x rea*es a height ( a few hundr$ metres1 :5 x splits into ! long rolls ^: axes are at "r angles to ! direction ( drift4 ,! consequ5ce is v /range if y /& on a hilltop close "u ! drift+ mass1 & look t[>ds ! horizon 9 ! direction ( drift4 ,! *ang+ %ad[s give ! impression t ! cl\ds are actually roll+ along1 ?\gh ( c\rse no su* ?+ is really tak+ place4 ,z "t goes on ! rolls gr[ l>g] & ! int]spaces wid]2 !n transv]se fissures appe>1 & gradually ! rolls break up into small deta*$ cumulus4 ,cumulus radius1 f ! ,lat9 = a roll+-p91 might be a suitably descriptive "n1 b x %\ld n be =gott5 t x is only an int]m$iate l9k betwe5 /ratus & cumulus1 &1 inde$1 is m ne>ly relat$ to ! =m]1 s9ce x is nev] produc$ except on ! break up ( /ratus1 :ile x may dry up & disappe> )\t rea*+ ! cumulus /age at all4 ,/ratus radius w\ld !re=e be a bett] "n4 ,illu/ration3 ,plate #da4 ,,common ,,/ratus4 7,/ratus ,communis47 ,illu/ration3 ,plate #db4 ,,roll] ,,cl\d4 7,/ratus ,radius47 ,cumulus is closely relat$ to ano!r =m ( /ratus1 :i* ,mr4 ,ley has nam$ /ratus l5ticul>is1 b ?is appe>s to be s frequ5tly ! la/ /age 9 a disappe>+ cumulus t its hi/ory w come bett] lat] on4 ,x is m5tion$ "h z x is1 aft] all1 "o ( ! commone/ ( all =ms ( /ratus1 ! =m :i* appe>s at1 or aft]1 sunset1 & is "o ( ! few cl\ds :i* h an ,engli% popul> "n--,fall cl\d4 ,plate #dg gives a repres5tation ( x1 /&+ out d>k aga9/ an ev5+ sky1 ) a %eet ( alto-/ratus f> above x 9 ! upp] "p ( ! photograph4 ,to sum up1 !n1 we h among ! l[] cl\ds ( m or less /rati=m patt]n-- ,/ratus communis1 or ,common /ratus4 ,/ratus l5ticul>is1 ! ,fall cl\d4 ,/ratus radius1 or ,roll cl\d4 ,/ratus maculosus1 or ,mottl$ /ratus4 ,/rato-cumulus1 or ,%eet cumulus4 ,! la/ leads naturally to ! consid]ation ( cumulus & cumulo-nimbus1 :ile ! t]m 8nimbus0 does n belong to any "o type-=m1 b sometimes to "o1 sometimes to ano!r1 & g5]ally to a mixture ( two or m4 ,a good _m ye>s ago ! writ] made a s]ies ( measurem5ts ( ! ?ickness ( deta*$ cl\ds ( ! /ratus & cumulus types1 su* z ^? :i* may produce a %[]4 ,! conclusions rea*$ 9 consequ5ce ( ^? det]m9ations h s9ce be5 amply confirm$ by subsequ5t obs]vations4 ,9 w9t] no ra9 w fall f a cl\d unless x rea*es a m9imum ?ickness ( at lea/ #ajj metres1 :ile 9 summ] x mu/ h r great] ?ickness4 ,!re is "o exception1 & t is 9 w9t]1 :5 ! temp]ature is s l[ t ! drop />ts on its d[nw>d j\rney z a flake ( sn[4 ,:5 ?is is ! case1 ra9 may fall f a lay] ( ?9 lift$ fog1 n q ?ick en\gh to hide ! blue col\r ( ! sky4 ,b "u ord9>y conditions ( temp]ature1 if ! cl\d has a ?ickness less ?an #bjjj feet1 or #faf metres1 ra9 is unlikely1 b if x does come1 ! drops w be small & ! fall ( ra9 q trifl+4 ,above ?is ?ickness ! heav9ess ( ! ra9 & size ( ! drops increases1 s t if ! di/ance f base to summit be betwe5 #bjjj & #cjjj feet1 or #fjj to #ajjj metres1 ! fall w be g5tle4 ,a ?ickness ( #djjj to #fjjj feet1 or #abjj to #ahjj metres1 gives l>ge drops & a fairly heavy %[]1 :ile1 9 summ] "t at lea/1 cold heavy ra9 & hail come f cl\ds measur+ #fjjj to #aj1jjj feet1 or 9 r\nd numb]s #ahjj to #cjjj metres or m4 ,9 w9t] ! necess>y dim5sions seem to be less1 b ! rule /ill holds equally good1 t ! ra9-cl\d does n necess>ily diff] 9 any way f ! ra9less "o1 except 9 ?ickness1 & t :5 ! requisite ?ickness is pres5t ra9 is n always ! result4 ,,*apt] ,,vi ,,cumulus ,,"u ! g5]al t]m cumulus !re are gr\p$ ! mo/ common1 ! be/ kn[n1 & ! gr&e/ =ms ( cl\d4 ,inde$1 beautiful z ! cirrus & alto cl\ds may be1 !re is a solid gr&eur ab\t ! great] =ms ( cumulus :i* gives !m a beauty ( _! own q comp>able ) ! *>m af=d$ by ! delicate trac]y ( _! m l(ty rivals4 ,cumulus c be divid$ into sev]al types1 :i* are be/ consid]$ 9 ! ord] ( gr[?4 ,!y are all =m$ 9 ! l[] "p ( ! atmosph]e1 _! "u-surfaces v>y+ 9 altitude f ab\t #fjj metres1 or ev5 less1 up to #cjjj metres1 or slightly m4 ,! writ]'s own measurem5ts v>y f a m9imum ( #ehd metres to a maximum ( #bbhf metres1 ) an av]age ( a little m ?an #ajjj metres4 ,!y are describ$ 9 ! ,int]national sy/em z 8cl\ds 9 a ris+ curr5t10 & !re is no d\bt ! description is correct4 ,ea* cumulus mu/ be look$ ^u z simply ! visible top ( an asc5d+ pill> ( damp air4 ,! vap\r :i* makes its appe>ance 9 ! cl\d is pres5t 9 ! transp>5t air b5ea?1 & ! base ( ! cl\d is simply ! level at :i* t vap\r beg9s to cond5se into visible liquid p>ticles4 ,s9ce cumulus cl\ds are caus$ by asc5d+ curr5ts1 ^! curr5ts mu/ be br\ght ab\t ei!r by ! g5]al di/urbance ( ! air due to a cyclonic movem5t1 or by ! local irregul>ities ( temp]ature on ! gr\nd produc$ by ! sun's heat4 ,z a matt] ( fact1 we d get cumulus produc$ 9 great abundance 9 ! re> ( e cyclone1 & we get !m also "u ! conditions ( /ill air & hot sun1 :i* specially fav\r evaporation & ! developm5t ( diff]5ces ( temp]ature4 ,! cyclone cumulus may come at any h\r ( ! day or night1 ?\gh comp>atively r>e betwe5 midnight & ! morn+4 ,heat cumulus is g5]ally =m$ dur+ ! aft]noon1 & x is only "u relatively uncommon conditions t x p]si/s dur+ ! night4 ,if ! cl\d has n gr[n to v great size x usually beg9s to break up & disappe> ab\t sunset1 b if x has gr[n to ! enorm\s dim5sions ( a summ] ?und]-cl\d x may g on gr[+1 pil+ mass on to mass1 until x g5]ates a ?und]/orm1 ev5 9 ! h\rs ( e>ly morn+4 ,9 ! case ( "s ( ! high] k9ds ( cl\d1 we are n able to give any c]ta9 acc\nt ( ! me*anics ( _! production f a /udy ( ^? cl\ds !mselves4 ,we h already ref]r$ incid5tally to "s ( ! speculations z to _! orig9 & "s ( ! facts def9itely kn[n1 b consid]able light c be ?r[n on ! g5esis ( all ! v>ieties ( cirro-cumulus & alto-cumulus by a c>eful /udy ( _! l>g] & m accessible repres5tatives ( l[] regions4 ,! cyclone cumulus does n diff] 9 any ess5tial f ! cl\ds ( calm wea!r4 ,! only diff]5ce is t ! upris+ curr5ts are p]haps p>tly eddies1 & ! rate ( fall ( temp]ature ) asc5t is (t5 m rapid4 ,giv5 any mass ( air at a p>ticul> temp]ature1 x c take up & hold 9 ! =m ( invisible vap\r a fix$ quantity ( wat]1 & no m4 ,:5 x holds ! maximum possible x is said to be saturat$4 ,if x is ne>ly saturat$ x w\ld be call$ damp2 if f> f saturat$1 dry4 ,n[1 ! w>m] ! air ! l>g] ! quantity ( vap\r necess>y to saturate x1 s t if a quantity is saturat$ at a high temp]ature1 & is !n cool$1 x w no long] be able to reta9 all its moi/ure 9 ! invisible =m1 b ! surplus quantity w make its appe>ance z liquid p>ticles1 t is to say1 z mi/ or cl\d4 ,simil>ly1 if a quantity ( air is n fully saturat$ at its p>ticul> temp]ature1 & is !n cool$1 x w approa* ne>] & ne>] to saturation1 & if ! process is cont9u$ long en\gh ! result w be cl\d =mation4 ,all cl\ds1 )\t exception1 are produc$ by exactly su* cool+ ( air conta9+ wat] vap\r1 fir/ to ! temp]ature at :i* ! quantity x conta9s is ! maximum possible1 & !n beyond t po9t4 ,n[1 if we />t ) v w>m air1 & cool x #a degree1 we decrease its vap\r-hold+ p[]1 & ! decrease p] degree gr[s less & less z ! temp]ature falls4 ,suppose1 = in/ance1 we h air saturat$ at #fa degrees & cool x to #fj degrees1 ! quantity ( vap\r cond5s$ w be equal to ! diff]5ce ( hold+ p[]4 ,suppose1 aga91 we h air saturat$ at #ca degrees & we cool x to #cj degrees1 ! quantity ( vap\r cond5s$ w aga9 be equal to ! diff]5ce ( hold+ p[]2 b ?is quantity w be v greatly less ?an 9 ! =m] case4 ,cool+ air saturat$ at #fa degrees to #fj degrees might produce a d5se cl\d2 b apply+ a simil> r$uction ( #a degree to air saturat$ at #ca degrees1 if we take ! same volume ( air1 w only produce a v mu* ?9n] result4 ,"h we see "o good reason :y ! highe/ cl\ds are ! ?9ne/ & ! alto cl\ds ( int]m$iate d5sity4 ,! necess>y cool+ may be br\ght ab\t 9 sev]al ways4 ,fir/ly1 ! air is capable ( radiat+ its heat into space1 & !re=e ( cool+4 ,b we "k little ( ! laws :i* gov]n atmosph]ic radiation1 & presumably1 if cl\d c\ld be produc$ by su* means1 x ought to make its appe>ance mo/ frequ5tly 9 ! small h\rs ( ! morn+ be=e sunrise4 ,we are1 h[ev]1 unaw>e ( any v>iety ( cl\d :i* answ]s ^? conditions1 unless x be ! gr\nd fogs :i* s (t5 =m dur+ ! night2 & ^!1 we "k1 are c]ta9ly due to ! *ill+ ( ! air by contact ) ! gr\nd1 :i* has be5 cool$ by radiat+ away its heat4 ,on ! contr>y1 x is well kn[n to a/ronom]s t ! sky is1 on ! :ole1 cle>] & fre] f cl\ds aft] midnight ?an 9 ! e>li] h\rs ( ! night--a circum/ance :i* is p>ticul>ly un=tunate = ! amateur />-gaz]1 :o has to be up & ab\t at ! same "t z ! re/ ( ! work+ _w4 ,cool+ by radiation we may !n dismiss z a cause ( cl\d =mation ( no great efficacy1 & c]ta9ly "o :i* has little to d ) ! production ( cumulus4 ,cool+ by contact ) a cold body is ano!r & m pot5t cause4 ,we (t5 see x 9 a m\nta9 di/rict1 :]e a fro/-b\nd peak /&s fac+ ! w9d ) glitt]+ sn[-slopes on :i* ! sun is %9+1 :ile a long tongue ( cl\d hangs l a bann] on its leew>d side4 ,9 su* a case x is easy to und]/& h[ ! air sweep+ by ! icy mass is *ill$ bel[ its saturation po9t2 b z x passes on1 ! *ill$ portions become mix$ ) ! re/1 & ! cl\d evaporates aga94 ,x is n q s easy to see h[ f> ?is cause is responsible = ! cl\ds :i* are =m$ :5 ! w>m damp air ( ! ocean drifts ov] a comp>atively cold l&4 ,x is probable t ! contact *ill+ is 9 ?is case only "p ( ! explanation1 & t o!r causes co-op]ate4 ,! mix+ ( w>m damp air ) cold has (t5 be5 adduc$ z a cause ( cl\ds4 ,no d\bt x might be1 & "s ( ! /rati=m types may possibly be =m$ at ! junction betwe5 a w>m damp /ratum ( air & a cold "o1 b no example is c]ta9ly kn[n4 ,x may also be a contribut+ cause 9 produc+ ! %>ply def9$ upp] surfaces ( "s cumulus or /rato-cumulus cl\ds1 b ^! are 9 ! ma9 mo/ c]ta9ly due to ! *ief cause ( cl\d production--namely1 :at is kn[n z dynamic cool+4 ,if a quantity ( air exi/s "u a c]ta9 pressure & at a c]ta9 temp]ature1 on r$uc+ ! pressure x w exp&1 & 9 ! act ( exp&+ x w become cool]4 ,?is may easily be illu/rat$ ) an air-pump4 ,let a damp sponge or a piece ( wet blott+-pap] /& "u a glass receiv] ov] an air-pump until ! air has become damp4 ,if ! app>atus is 9 a d>k5$ room1 & a p[]ful beam ( light f a lant]n is s5t ?r\gh ! receiv]1 ! damp air w be se5 to be q cle>2 b a /roke or two ( ! pump removes "s ( ! air1 ! rema9d] is *ill$ by its own expansion1 & a d5se cl\d is precipitat$4 ,if ?is cl\d be view$ closely1 x w be se5 to be compos$ ( m9ute p>ticles1 :i*1 on look+ t[>ds ! light1 gl[ ) ! col\rs ( a corona4 ,9 a few m9utes ! cl\d w disappe>1 b x c be recall$ aga9 & aga9 by successive /rokes ( ! pump1 gett+ ?9n] & ?9n] z ! air gets m & m r>efi$2 an illu/ration ( a second reason :y ! high cl\ds are ?9n] ?an ! l[]4 ,"s ye>s ago ,mr4 ,john ,aitk5 %[$ t if ! damp air us$ 9 ?is exp]im5t 7 c>efully filt]$1 s z to remove all =eign p>ticles1 no cl\d 0 produc$1 & ! introduction ( a puff ( unfilt]$ air 0 att5d$ by imm$iate cond5sation4 ,! d$uction 0 t vap\r1 ev5 bel[ its saturation temp]ature1 _c produce cl\d unless nuclei ( "s sort are already pres5t1 presumably du/ p>ticles4 ,lat] on x 0 %[n by ,mr4 ,%el=d ,bidwell & o!rs t gase\s p>ticles1 su* z ^? produc$ by ! burn+ ( sulphur1 w\ld s]ve ! purpose1 & t ! bru% dis*>ge f an electrifi$ po9t 0 9 "s my/]i\s way p>ticul>ly effective4 ,x has rec5tly be5 %[n by ,mr4 ,c4 ,t4 ,r4 ,wilson t causes su* z ! radiations ( radium1 or ! impact ( ultra-violet rays1 act+ on ! air itself1 splits up "s ( its p>ticles into ! small] bodies kn[n z ions1 & t ^! are effici5t nuclei4 ,^! exp]im5ts op5 up _m mo/ int]e/+ que/ions1 b1 unless x is to expla9 ! extreme d5sity & d>kness ( a ?und]-cl\d1 !y d n seem to play any important "p 9 det]m9+ ! =ms to be assum$4 ,nuclei 9 suffici5t abundance are probably always pres5t at any height :i* c be rea*$ by en\gh vap\r to =m a cl\d4 ,n[1 if we h a quantity ( air1 say at sea-level1 damp b n saturat$1 & x is caus$ to asc5d1 ei!r because x is w>m] & !re=e light] ?an ! surr\nd+ air1 or = "s o!r reason1 z x moves upw>ds ! pressure ^u x w decrease1 x w exp&1 & 9 ! act x w be /eadily cool$4 ,?is cool+ may aft] a "t br+ x d[n to ! same temp]ature z ! re/ ( ! air at its p>ticul> level4 ,if s1 x w no long] be light]1 & ! asc5t w come to an end4 ,b be=e ?is /ate ( affairs is atta9$ x may h rea*$ its saturation po9t1 & cl\d production w beg94 ,x is true t ! r>efaction ( ! air t5ds to enable x to reta9 m vap\r ?an x c\ld if x 7 cool$ )\t *ange ( d5sity4 ,! temp]ature ( ! air be+ fix$1 its hold+ p[] increases ) decrease ( pressure4 ,b ?is increase is mu* less ?an ! dim9ution due to cool+1 & ! result 9 nature mu/ be simil> to :at we c see happ5 "u ! receiv] ( ! air-pump4 ,! cond5sation ( wat] introduces ano!r factor ( great importance4 ,x has j be5 said t ! asc5d+ air may be cool$ s rapidly z to be r$uc$ to ! same temp]ature z ! re/ ( ! air at t level1 & if s ! asc5t w end4 ,cle>ly ! cessation or p]si/5ce ( ! upw>d motion dep5ds ^u :e!r ! dim9ution ( temp]ature p] #ajj metres ( asc5t is mo/ rapid 9 ! ris+ column or 9 ! air outside x4 ,z long z ! asc5d+ air is w>m] ?an t outside1 b at its own level1 s long w asc5t cont9ue4 ,n[1 z long z no cond5sation 0 tak+ place1 ! rate ( cool+ w\ld foll[ a simple law :i* produces a cool+ ( #a degree = ab\t #ajj metres ( asc5t2 b z soon z wat] vap\r beg9s to pass into ! liquid =m1 a l>ge quantity ( heat is set free1 & ! rate ( cool+ is consequ5tly greatly less5$4 ,cl\d production t5ds1 !re=e1 to accel]ate asc5t1 & ! great] ! am\nt ( cond5sation1 ! m important w ?is consid]ation become2 ?\gh1 on ! o!r h&1 :5 once ! cl\d is =m$1 x t5ds to /op ! ris+ curr5t by %ad+ ! air & gr\nd b5ea? x4 ,on an ord9>y day ! rate ( decrease ( temp]ature z we asc5d is r less ?an ! value giv5 above1 & upris+ curr5ts are soon *eck$4 ,if !y d ext5d f> en\gh to rea* cl\d production1 ! cl\ds w be small1 =m+ ! smalle/ v>iety ( cumulus4 ,?is is %[n 9 ,plate #dc4 ,small irregul> upris+ curr5ts h j be5 able to rea* f> en\gh up to h _! summits tipp$ ) cl\d4 ,illu/ration3 ,plate #dc4 ,,small ,,cumulus4 7,cumulus ,m9or47 ,aft] ! =ego+ explanation1 x is easy to see :y at a giv5 "t ! float+ cl\dlets %\ld h a common base level4 ,?is is ! height to :i* ! air mu/ atta9 be=e rea*+ its saturation temp]ature4 ,ea* cl\dlet m>ks an upris+ curr5t1 & ! int]vals %[ ! position ( ! c\nt]balanc+ desc5d+ /reams4 ,a l>g] v>iety is %[n 9 ,plate #dd4 ,9 ?is ! level base & g5]ally pyramidal %ape is %[n1 & also ! h>d1 r\nd$ upp] surface4 ,! ?ickness ( ?is cl\d 0 ab\t #ejj metres4 ,:5 cl\ds l ^! are visible1 !y may be ! beg9n+ ( l>g] ones1 & ! only way to judge :e!r !y are likely to develop into ra9- or %[]-cl\ds is to wat* !m4 ,if !y are se5 to be gr[+ l>g]1 & p>ticul>ly if deta*$ fragm5ts are develop+ into cl\ds1 fur!r gr[? is almo/ c]ta91 & ra9 is probable4 ,illu/ration3 ,plate #dd4 ,,cumulus4 ,if great t[]+ masses are mak+ _! appe>ance ) little d>k fragm5ts betwe5 !m1 z %[n 9 ,plate #de1 !n sm>t %[]s may be confid5tly expect$4 ,! cl\d figur$ 0 a %[]-cl\d1 & ! di/ance is se5 ?r\gh ! veil ( fall+ ra94 ,! height & ?ickness ( ?is p>ticul> cl\d 7 measur$ j aft] its photograph _h be5 tak54 ,its base 0 #abjj metres above ! gr\nd1 & its summit 0 #aejj metres fur!r4 ,its ?ickness f summit to base 01 !re=e1 n mu* %ort ( a mile1 & ! total cont5ts ( ! cl\d 7 probably betwe5 "o & a half & two cubic miles4 ,! upp] cont\r is h>d & r\nd$1 z 9 ! small] cl\d ( ,plate #dd1 b ! :ole cl\d is mu* l>g]4 ,illu/ration3 ,plate #de4 ,,l>ge ,,cumulus4 7,cumulus ,major47 ,we h already expla9$ t !re seems to be a def9ite connection betwe5 ! ?ickness ( su* cl\ds & ! am\nt ( precipitation f !m4 ,small cumulus1 less ?an #abj metres ?ick1 r>ely produces ra91 & no?+ l a heavy %[] is likely unless ! ?ickness exce$s #djj metres4 ,9 w9t]1 especially 9 h>d fro/1 sn[ cry/als may fall f ! smalle/ cl\d1 ev5 f little fragm5ts only a few metres ?ick1 b ! quantity ( wat] s precipitat$ w1 ( c\rse1 be small4 ,z long z ! top ( ! cumulus is r\nd$ & cle>ly def9$1 ! conditions ( arial equilibrium are /able1 & ! gr[? ( ! cl\d has be5 br\ght to an end by a /oppage ( ! asc5d+ curr5t4 ,9 ,plate #de ! asc5t has be5 h9d]$ bo? by ! me*anical action ( ! fall+ ra9drops & by ! cool+ ( ! l[] p>ts ( ! asc5d+ column by ! desc5t into x ( ! cool drops f its cold] upp] "p4 ,?is is probably "o ( ! *ief reasons :y a %[]-cl\d nev] ma9ta9s its activity z a ra9 produc] = m ?an a v limit$ p]iod4 ,z ! cl\d drifts ov] ! l&scape1 x seldom ma9ta9s its %[]y "* = m ?an t5 or tw5ty miles1 (t5 = mu* less4 ,cumulus1 l any ( ^! ?ree1 is a cl\d ( ! daytime4 ,x g5]ally beg9s ab\t t5 or elev5 o'clock 9 ! morn+1 gr[s l>g] until ab\t f\r o'clock1 & !n beg9s to break up & disappe>4 ,aft] ! asc5d+ curr5ts h ceas$1 ! compon5t cl\d p>ticles sl[ly settle d[n into ! w>m] air b5ea?1 until ! mass has lo/ its prop] pyramidal =m1 & has become an irregul> cl\d1 su* z is %[n 9 ,plate #df4 ,?is is kn[n z degrad$ or fracto-cumulus4 ,illu/ration3 ,plate #df4 ,,fracto-,,cumulus4 ,"o consequ5ce ( ! arre/ ( ! upris+ curr5ts is ! =mation ( l5ticul> pat*es ( /ratus1 call$ by ,mr4 ,ley /ratus l5ticul>is4 ,?is is (t5 =m$ ab\t sunset1 & has be5 nam$ fall cl\d1 f its appe>ance at ! fall ( night4 ,! "n is appropriate 9 ano!r way4 ,! asc5d+ curr5ts hav+ ceas$1 ! cl\d p>ticles sl[ly subside until !y dry up 9 "s w>m] /ratum4 ,! wat] vap\r does n cont9ue its desc5t1 b sl[ly diffuses 9 all directions1 & if ! fall ( cl\d p>ticles is suffici5t1 ?is /ratum1 :i* is approximately co9cid5t ) ! base ( ! orig9al cumulus1 soon becomes saturat$1 & fur!r p>ticles :i* fall into x rema9 visible4 ,?is saturat$ zone w sl[ly s9k l[] & l[] ) ! desc5t ( ! p>ticles1 until x rea*es regions 9 :i* ! temp]ature is high en\gh = ! :ole to be evaporat$ )\t rea*+ saturation po9t4 ,ev5+ /ratus 9 calm wea!r always goes ?r\gh ?is sequ5ce ( *anges4 ,x usually =ms at1 or soon aft]1 sund[n1 & beg9s to break up & disappe> z ! />s are becom+ visible 9 ! d>k5+ sky4 ,plate #dg %[s a specim5 ( ?is ev5+ /ratus4 ,illu/ration3 ,plate #dg4 ,,fall ,,cl\d4 7,/ratus ,l5ticul>is47 ,a curi\s feature is sometimes %[n on ! und]side ( a ?ick cl\d1 :i* is probably due to ! upp] "p ( ! asc5d+ column hav+ be5 c>ri$ beyond its position ( equilibrium by its own in]tia1 & !n fall+ back aga9 9 ! tee? ( ! /ill ris+ l[] "p4 ,! result is to give ! base ( ! cl\d an appe>ance ( a numb] ( r\nd$ masses hang+ d[nw>ds bel[ ! cl\d1 v sugge/ive ( ! idea t ! cl\d is upside d[n4 ,su* an ev5t w n (t5 occur1 & :5 x does ! conditions are q want+ 9 /ability1 & ! consequ5t features w be v transi5t4 ,:5 ! base ( a cumulus or cumulo-nimbus is s affect$1 ! cl\d is kn[n z fe/oon$ cumulus1 or cumulus mammatus4 ,a precisely simil> /ructure may be se5 "u /rato-cumulus1 or ev5 ?ick /ratus4 ,9 "s c\ntries x seems to be frequ5tly obs]v$1 b 9 ,engl& x is s uncommon t ! writ] has only not$ x ab\t a doz5 times 9 tw5ty ye>s1 & on no "o ( ^! did x la/ long en\gh to all[ ( its portrait be+ tak54 ,x is an indication ( v di/urb$ conditions1 & is usually foll[$ by heavy ra94 ,:5 cumulus cl\ds are =m$ 9 air :i* is /eadily mov+ z a :ole1 t is to say1 :5 !re is a /eady breeze1 !y h a v decid$ t5d5cy to foll[ ea* o!r 9 long l9es4 ,x may (t5 be notic$ t 9 a p>ticul> place ) a c]ta9 direction ( w9d ^! long processions foll[ def9ite tracks 9 relation to ! geographical features4 ,! ph5om5on does n seem to h be5 record$ except 9 hilly c\ntry1 b has frequ5tly be5 obs]v$ by ! writ]4 ,x is n ! same ?+ z ! =mation ( /ation>y belts ( cl\d transv]se to ! w9d4 ,^! cumulus float along ) ! movem5t ( ! air1 & ! "q to be answ]$ is1 :y %\ld !y foll[ ea* o!r s p]si/5tly1 & :y %\ld ! int]v5+ belts ( sky be s cont9u\sly free f cl\d4 ,if we consid] t ! w>m damp air :i* supplies !m is drawn f ! gr\nd1 x seems t any cause :i* t5ds to direct ?is w>m /ratum into def9ite *annels1 z x is c>ri$ on by ! w9d1 w be a compet5t cause ( ! :ole ph5om5on4 ,?is we f9d 9 ! pres5ce ( l(ty hills :i* /& 9 ! way ( ! w>m surface w9ds1 caus+ !m to foll[ m or less ! g5]al tr5d ( ! valleys1 & s deliv]+ ! ris+ convection curr5ts ( cl\d-produc+ air at ! same spot4 ,x is easy to conceive t o!r causes1 su* z a diff]5ce 9 temp]ature or dampness ( neighb\r+ tracts1 result+ f :e!r !y are b>e or wood$1 m>%l& or s&y pla91 might equally suffice2 or might1 at lea/1 p[]fully co-op]ate )1 or c\nt]act1 ! effect ( hill & vale4 ,b 9 any case x is pla9 t ! geographical conditions to ! w9dw>d ( ! place ( obs]vation n only may affect ! occurr5ce & di/ribution ( cl\d1 b if ! w9d is /eady x is difficult to see h[ !y c\ld avoid affect+ x4 ,ano!r puzzl+ ph5om5on1 sometimes pres5t$ by cl\d & fog1 is t our in/rum5ts = detect+ humidity %[ t ! air )9 !m is n always fully saturat$4 ,x seems probable t ?is is due to su* cl\d or fog hav+ begun ! process ( dry+ up1 or t 9 "s way n fully und]/ood ! pres5ce ( ! cl\d p>ticles aft] !y h fir/ come into exi/5ce may cause ! )drawal ( "s ( ! moi/ure f ! int]v5+ damp air4 ,! surface ( ea* m9ute droplet ex]ts a pressure on its int]ior simil> to ! pressure ex]t$ by ! film ( a soap-bubble on ! air )9 x1 & x is conceivable t "s ( ! uncond5s$ vap\r f outside may diffuse ?r\gh ?is enclos+ surface film1 & be reta9$ !re 9 consequ5ce ( ! pressure4 ,if ?is is s1 & subsequ5t inve/igation c alone decide ! matt]1 x w foll[ t :5 once cl\d production has begun x w be cont9u$ until ! air betwe5 ! cl\d p>ticles is r$uc$ s f> bel[ its saturation po9t t ! t5d5cy ( ! drops to evaporate1 t is to say1 = ! imprison$ wat] to escape ?r\gh ! conf9+ film1 balances ! reta9+ pressure4 ,?is consid]ation1 h[ev]1 is q incompet5t to affect ! g5]al explanation ( cl\d =mation :i* has be5 giv54 ,its result w\ld be to c>ry cond5sation a little fur!r ?an ! exact saturation po9t1 & to ret>d equally slightly ! subsequ5t evaporation ( ! cl\d p>ticles4 ,we h spok5 ( ! typical cumulus z hav+ a r\ghly pyramidal %ape1 & if ! horizontal movem5t ( ! air is small1 ! l(tie/ po9t ( ! cl\d w be situat$ approximately above ! c5tre ( its base4 ,b if ! horizontal movem5t increases 9 velocity1 s t ! top is 9 a m rapidly mov+ /ratum ?an ! base1 x w lean =w>d 9 ! direction ( movem5t4 ,?is is a v common ph5om5on1 be+ g5]ally %[n by cumulus on a w9dy day4 ,on mu* r>] occasions ! conv]se occurs1 & ! top ( ! cl\d lags beh9d ! base1 ! explanation be+ a less5+ ( ! velocity ( ! w9d z ! height above gr\nd increases4 ,b su* conditions r>ely occur1 & :5 !y d !y are due to local eddies & affect only a limit$ area4 ,h5ce su* cl\ds are isolat$1 & indicate a di/urb$ /ate ( ! air & unc]ta9ty ( wea!r4 ,! cl\ds :i* lean =w>d are =m$ "u conditions :i* are spread ov] wide di/ricts1 su* z ! re> ( a l>ge cyclone1 & cumulus ( t k9d may foll[ "o ano!r across ! sky = h\rs or ev5 days z long z ! w9d p]si/s4 ,s f> we h consid]$ only ! r\nd-topp$ types ( cumulus--^? :i* m>k ! tops ( asc5d+ curr5ts ^: asc5t has be5 /opp$ at a comp>atively e>ly /age1 or ^? ^: asc5t is /ill 9 t e>ly /age1 ?\gh ! upw>d movem5t has n yet come to an end4 ,! full /ory ( ! gr[? ( a cumulus is id5tical ) t ( ! y\? ( a cumulo-nimbus1 ! lat] /ages ( :i* we w consid] 9 ano!r *apt]4 ,,*apt] ,,vii ,,cumulo-,,nimbus ,,gr&e/ ( all cl\ds are ! huge m\nta9s ( vap\r :i* are ! p>5ts ( summ] ?und]-/orms4 ,!y are at once di/+ui%$ f ord9>y cumulus by _! upp] p>ts1 :i* sometimes rea* beyond ! region ( ! alto cl\ds high into ! realm ( cirrus1 & ext5d outw>ds z a broad disc1 :i* is occasionally indi/+ui%able f ! cirro-nebula & cirro-/ratus :i* =m ! van ( a cyclone cl\d canopy4 ,inde$1 !re seems to be no ess5tial divid+ l9e betwe5 a l>ge cumulo-nimbus & ! cl\d pile ( a small cyclone1 & no real diff]5ce betwe5 !m except _! size4 ,z a matt] ( fact1 ! t]m cumulo-nimbus w\ld only be giv5 to ! cl\d :5 a l>ge fraction ( ! :ole c be se5 at once4 ,9 deal+ ) common cumulus1 x has be5 po9t$ out t ! cessation ( ! upris+ convection curr5ts :i* det]m9es ! maximum height to :i* ! cl\d w gr[ is due to ! rate ( cool+ )9 ! asc5d+ column be+ great] ?an ! rate ( cool+ outside x4 ,x foll[s t :5 ! asc5d+ curr5t has rea*$ a c]ta9 height x w1 z a :ole1 be j z heavy z an equal column outside4 ,asc5t mu/ !n cease4 ,! equilibrium ( ! air 9 su* a case is said to be /able1 & ! condition ( su* /ability is simply t ! g5]al rate ( fall ( temp]ature p] #ajj metres ( asc5t is less ?an ! rate ( cool+ dynamically produc$ 9 an asc5d+ curr5t4 ,if1 h[ev]1 ! g5]al rate ( fall ( temp]ature is great] ?an t produc$ dynamically1 ! consequ5ce w be t ! upw>d t5d5cy ( ! ris+ air w increase z x moves upw>d1 & ! tall] ! column becomes ! great] w be ! diff]5ce ( weight betwe5 ! inside & outside columns4 ,9 su* a case ! equilibrium is said to be un/able1 & ! result w be ! production ( cumulo-nimbus4 ,j z cumulus may be divid$ into heat cumulus & ! cl\ds ( ! re> ( a cyclone1 s cumulo-nimbus may be divid$ into ! same two gr\ps4 ,9 ! case ( ! heat ?und]-cl\ds ! in/ability ( ! air is effect$ by ! rapid heat+ ( its l[] lay]s 9 contact ) ! gr\nd1 ^? l[] lay]s be+ s quickly w>m$ t !re is n "t = !m to become mix$ ) ! ov]ly+ air 9 :i* ! rate ( decrease is normal4 ,if !re is mu* w9d we r>ely get cumulo-nimbus1 because ! heat$ air is mix$ me*anically ) ! ov]ly+ p>ts1 & ! rate ( decrease is approximately normal ?r\gh\t4 ,calm air & hot sun are !n "o set ( necess>y conditions = ! production ( in/ability4 ,b x is well kn[n t ?und]-%[]s & less] examples ( cumulo-nimbus are by no means infrequ5t 9 ! re> ( a cyclone1 & su* /orm cl\ds are usually att5d$ by consid]able w9d4 ,!y are1 z a rule1 mu* small] ?an ^? produc$ by heat1 b !y h ! same =m1 & are evid5tly due to in/ability 9 ! l[] "p ( ! air1 & ! "q is h[ c t condition be produc$4 ,9 ord] to f9d ! answ] x is necess>y to ref] to ! temp]ature ph5om5a ( a cyclonic area4 ,if a cyclone be divid$ into f\r quadrants by two l9es drawn ?r\gh its c5tre1 "o 9 ! direction 9 :i* ! sy/em is travell+ & ! o!r at "r angles to x1 !n ! front "r-h& quadrant is ! w>me/ & ! re> "r-h& quadrant mu* cold]4 ,! cumulo-nimbus cl\ds ( a cyclone are limit$ to ! fir/ "p ( ?is cold quadrant1 t is to say1 to ! portion ( ! /orm 9 :i* a great volume ( cold air is fl[+ ov] a di/rict :i* has j be5 w>m$ & wett$ by ! prec$+ "p4 ,! result is t1 ! air be+ w>m$ by contact ) damp gr\nd at a temp]ature _m degrees above t ( ! air itself1 we h produc$ exactly ! same un/able /ate at a l[ temp]ature z we h at a high temp]ature 9 ! case ( heat /orms4 ,! l[] temp]ature ( ! :ole is en\gh to acc\nt = ! small] volume ( ! cl\d1 & t 9 turn expla9s :y cyclone ?und]/orms are1 g5]ally speak+1 on a mu* small] scale ?an heat /orms4 ,! life hi/ory ( a cumulo-nimbus is easily /udi$ on a suitable day4 ,! rapid heat+ ( ! l[] lay]s ( air causes !m to exp& bodily1 & z !y d s !y lift ! ov]ly+ air1 frequ5tly 9 broad domes or waves4 ,! fir/ result is ! expansion ( ^! upp] zones1 :i* are light5$ by ! fl[+ away ( /ill high] lay]s4 ,expansion means *ill+1 & soon] or lat] its effects become visible 9 ! =mation ( cirro-/ratus1 cirro-cumulus1 or alto-cumulus4 ,simultane\sly ! heat$ air ne> ! gr\nd beg9s to rise up 9 tall columns1 :ile ! cool] air f a little high] desc5ds to take its place4 ,soon pat*es ( l[] cl\d appe>1 at fir/ hazy & indi/9ct1 b gradually %ap+ !mselves into cumulus ) hazy base & r\nd$ summits4 ,^! rapidly assume ! typical pyramidal %ape1 ) level base & %>ply cont\r$ top1 & s f> !re is little to di/+ui% !m f an ord9>y cumulus 7see ,plate #dh74 ,b wat* !m c>efully4 ,"h & !re "s w be gr[+ tall] ?an _! fell[s1 & z !y gr[ _! rate ( gr[? increases until ! top beg9s to %[ signs ( spread+ outw>ds4 ,rapidly ! bulg+ summit ?r[s out long f+]s ( cl\d1 radiat+ f ! c5tral column almo/ z if propell$ by "s repulsive =ce4 ,at fir/1 ^! f+]s are m]ely project+ lumps ( cl\d ) r\nd$ ends1 b 9 a few m9utes !y und]go a sudd5 & /rik+ *ange4 ,! :ole summit becomes fray$ out1 drawn out into long radiat+ l9es1 :i* ?9 (f aga9/ ! blue sky exactly l ! edges ( a %eet ( cirro-/ratus4 ,false cirrus is ! "n commonly giv5 to ?is1 b !re seems no valid reason :y x %\ld be reg>d$ z 8false40 ,! top ( ! cl\d rapidly spreads horizontally1 =m+ a disc ( cirri=m cl\d1 :i* sometimes spreads sev]al miles ahead ( ! re/ ( ! /orm4 ,mean:ile1 ! orig9al cumulus column loses all its deep folds & convolutions1 & o!r r\nd-topp$ cumulus arise ar\nd x until ! complet$ sy/em consi/s ( a m or less disc-%ap$ mass ( cumulus1 ) a common base1 ris+ high] & high] t[>ds "s c5tral po9t1 :]e ^! are connect$1 by an upru%+ column ( vap\r1 to an upp] disc ) cirri=m m>g9s4 ,illu/ration3 ,plate #dh4 ,,?und]-,,cl\ds ,,=m+4 ,9 ,plate #di we h on ! left h& a specim5 9 :i* ! outspread+ is j beg9n+1 & ! same cl\d is %[n half an h\r lat] on ! left ( plate #ej4 ,a complete cumulo-nimbus 9 full "w is %[n on ! "r ( ,plate #di1 & ! same appe>s on ! "r 9 ,plate #ej4 ,illu/ration3 ,plate #di4 ,,?und]-,,cl\ds4 7,cumulo-nimbus47 ,illu/ration3 ,plate #ej4 ,,?und]-,,cl\ds4 7,cumulo-nimbus47 ,^! cl\ds 7 ?und]-cl\ds1 ! l>g] "o be+ a sm>t ?und]/orm ) heavy hail4 ,!y 7 photograph$ 9 ! ev5+1 & 9 ! second picture ! sun 0 j bel[ ! horizon4 ,b1 to cont9ue ! /ory ( a ?und]-cl\d1 we always f9d t aft] a "t ! cirri=m top flatt5s out & gradually subsides1 & ?is is usually accompani$ by a desc5t ( ! cl\d base to a l[] level4 ,mean:ile1 x frequ5tly happ5s t ! :ole s]ies ( ph5om5a is repeat$ 9 "o ( ! att5dant cumulus4 ,plates #ea & #eb are also two views ( ! same cl\d at diff]5t times4 ,9 ,plate #ea we h ! ma9 "p ( ! /orm on ! "r1 :ile on ! extreme left a l[] "p ( ! cl\d is ris+ rapidly into a tall dome4 ,9 ,plate #eb ! c5tral top has lo/ its cirri=m m>g9 & has di/9ctly flatt5$1 :ile ! left-h& dome has ris5 mu* high] & is beg9n+ to ?r[ out ! project+ bits4 ,illu/ration3 ,plate #ea4 ,,?und]-,,cl\d4 7,cumulo-nimbus47 ,illu/ration3 ,plate #eb4 ,,?und]-,,cl\d4 7,cumulo-nimbus47 ,! h>d-topp$ cumulus :i* fr+e ! l[] disc1 & ! va/ pile ( cirri=m & hazy cl\d :i* =ms ! c5tre ( a cumulo-nimbus1 are %[n 9 ,plate #ec1 :i* repres5ts "p ( ! side ( a great ?und]-cl\d4 ,9 ?is case ! diamet] ( ! l[] disc 0 ab\t #ae miles1 & ! upp] disc 0 r l>g]4 ,! upris+ column 9 ! middle 0 ab\t #g miles across1 & ! height f base to summit ab\t #c miles4 ,! :ole sy/em conta9$ betwe5 #ajj & #aej cubic miles ( cl\d4 ,:5 photograph$ x 0 ov] ! nor!rn "p ( ,salisbury ,pla94 ,lightn+ play$ repeat$ly betwe5 ! back ( ! :ite cumulus & ! hazy mass beh9d x1 & ! rumble ( ?und] 0 all b cont9u\s = ne>ly half an h\r z ! great cl\d pass$ by4 ,illu/ration3 ,plate #ec4 ,,! ,,flank ,,( ,a ,,great ,,/orm4 ,?is 0 an unusually l>ge cl\d = ?is c\ntry1 b specim5s ( #aj1 #bj1 or #cj cubic miles are q common4 ,n[ = ! explanation ( ! s]ies ( ev5ts4 ,to beg9 )1 we h ! production ( an ord9>y cumulus1 b ! equilibrium is un/able1 ! gr[? ( ! cl\d1 !re=e1 becomes m & m rapid1 & ! rapid cond5sation adds to ! in/ability until ! ris+ column is s mu* light] ?an an equal column outside t a p[]ful updraught is creat$1 /rong en\gh = a "t to hold up ! ra9drops or ev5 hail/ones4 ,at l5g? ! cond5sation is complete1 ! upp] "p ( ! cl\d consi/+ ( sn[ cry/als exactly l ^? ( any o!r cirrus4 ,9 ! mean "t1 ! rapid asc5d+ curr5t necess>ily involves an indraught f ar\nd1 & consequ5t desc5d+ curr5ts to supply x4 ,! result is to set up a circulat+ sy/em1 mov+ inw>ds along ! gr\nd1 upw>ds 9 ! c5tral column1 & outw>ds 9 ! upp] disc4 ,! d[nw>d curr5ts are sometimes %[n by a curl+ ov] ( ! edges ( ! upp] disc1 b ! ph5om5on is n (t5 se51 z ! desc5d+ movem5t is g5]ally en\gh to dry up ! cl\d p>ticles4 ,! rapid ris+ ( damp air drawn f ! gr\nd br+s ab\t rapid cond5sation & heavy ra94 ,! l>ge size ( ?und]-drops is almo/ c]ta9ly due to ! fact t x is only ! l>g] drops :i* c fall 9 ! tee? ( ! /rong updraught4 ,b :5 ^! drops beg9 to fall1 & /ill m :5 cold hail/ones beg9 to fall ?r\gh ?is asc5d+ air1 x becomes *ill$ f top to bottom1 & ! column is brok5 or ev5 /opp$ altoge!r4 ,! froz5 p>ticles :i* make up ! top subside gradually1 & ! *ill+ ( ! air imm$iately bel[ ! cl\d br+s ! saturation level ne>] ! gr\nd1 & we say ! cl\d base desc5ds4 ,! arrangem5t ( a ?und]-cl\d into ! upp] & l[] discs ) a connect+ upru% gives to ! typical cl\d a %ape some?+ l t ( an anvil :5 se5 sideways1 b 9 ! l>g] cl\ds ! disc-l =m is m obvi\s4 ,9 any ord9>y ?und]/orm ! great majority ( ! dis*>ges ( lightn+ play betwe5 ! two discs1 & ! l>g] ! cl\d ! m frequ5t ^! are4 ,su* dis*>ges z pass betwe5 ! cl\d & ! e>? come exclusively f ! base ( ! l[] disc if ! cl\d is l>ge1 & g5]ally foll[ imm$iately aft] or simultane\sly ) "o betwe5 ! two discs4 ,! ph5om5a ( lightn+ are int5sely int]e/+1 b ! purpose ( ^! pages is conf9$ to ! /udy ( cl\ds & cl\d =ms1 & x w\ld be go+ beyond our scope to discuss ei!r lightn+ or hail4 ,bo? are1 h[ev]1 s closely relat$ to cumulo-nimbus t !y c h>dly be pass$ ov] 9 sil5ce4 ,"o ?+ is c]ta91 & t is t nei!r ! electrical developm5ts nor ! hail has any?+ to d ) ! gr[? ( ! cl\d4 ,on ! contr>y1 bo? are consequ5ces ( ! cl\d1 ! hail be+ due to ! great altitude1 & consequ5t l[ temp]ature ( ! upp] "p ( ! cl\d1 & also to ! viol5t upris+ curr5ts )9 x2 :ile ! electrical ph5om5a are due to ei!r ! enorm\s am\nt ( cond5sation1 or to friction due to ! rapid upru%1 or m probably to ! fact t consid]able diff]5ces ( electrical condition exi/ 9 ! di/ant p>ts ( ! air connect$ by ! cl\d1 & betwe5 :i* its circulat+ curr5ts move4 ,^! diff]5ces are kn[n to exi/ at all times1 & we _c "h discuss _! orig94 ,! =mation ( cumulo-nimbus & cumulus is dep5d5t ^u ! pres5ce ( a l>ge am\nt ( wat] vap\r4 ,x is wor? :ile to consid] :e!r ! atmosph]ic movem5ts :i* br+ ab\t ! cond5sation c\ld exi/ )\t moi/ure4 ,:]ev] we f9d diff]5ces ( temp]ature betwe5 neighb\r+ places we mu/ get curr5ts ( hot air ris+ f ! w>m] spots1 & comp5sat+ desc5d+ curr5ts ar\nd !m4 ,b we h po9t$ out t if ! rate ( cool+ z we asc5d 9 ! /ill air is less ?an ! rate at :i* an asc5d+ curr5t w be dynamically cool$1 su* a ris+ curr5t w come to re/4 ,if1 on ! o!r h&1 ! rate ( cool+ 9 ! asc5d+ curr5t be less ?an 9 ! /ill air1 ! equilibrium w be un/able1 & a viol5t upru% w result4 ,n[1 9 a climate su* z our own1 :]e ! l[] regions ( ! air conta9 l>ge quantities ( wat] vap\r1 any consid]able rise br+s ab\t m or less cond5sation1 & t cond5sation is att5d$ by a lib]ation ( v l>ge quantities ( heat1 :i* ret>d cool+ 9 ! asc5d+ curr5t1 & s facilitate ! production ( in/ability4 ,b if ?is cause is put aside x is /ill possible to h a simil> circulation4 ,:5 discuss+ ! causes ( in/ability1 x has be5 po9t$ out t ! prime condition 0 an unusually rapid rate ( fall ( temp]ature 9 /ill air1 su* z may be produc$ by hot sun%9e4 ,n[1 ^! conditions are exactly ^? :i* w give rise to ! ph5om5on ( ! mirage1 & :i* rea* _! fulle/ developm5t 9 great des]t di/ricts :5 ! air is /ill4 ,aga91 x has be5 po9t$ out t ! causes :i* br+ %[]s & ?und]/orms to an end include ! *ill+ ( ! l[] p>ts ( ! asc5d+ column by ! desc5t ( cold ra9 or hail f above4 ,we may also add ! %ad+ ( ! und]ly+ gr\nd by ! cl\d itself1 & ! absorption ( heat 9 ! p>tial evaporation ( "s ( ! ra9 dur+ ! l[] "p ( its fall4 ,9 a des]t di/rict ! aris+ curr5ts are s dry t ev5 a v great asc5t does n (t5 result 9 visible cl\d2 & :5 x does1 ! cl\d is produc$ at s great a height t ! air is too r>efi$ to produce any?+ mu* d5s] ?an ?9 alto-/ratus1 f :i* no fall+ droplets c\ld rea* ! e>?4 ,x seems1 !n1 t !re w be no su* automatic *eck on ! gr[? ( ! circulat+ sy/em1 & x w g on gr[+ 9 volume & int5sity indef9itely4 ,z a matt] ( fact1 ?is is n ! case4 ,a diff]5t *eck does come into op]ation1 b n until ! indraught & updraught h become s p[]ful z to draw up ! du/ & s& & g5]ate a s&/orm1 ! weight & %ade ( :i*1 9 "t1 de/roys ! circulat+ curr5ts :i* uplift$ !m4 ,s9ce1 h[ev]1 cond5sation is a consid]able factor 9 produc+ in/ability1 we %\ld expect t su* s&/orms w\ld be r>] ?an ?und]/orms are 9 an equally hot b well-wat]$ di/rict1 :i* is ! fact4 ,aga91 s9ce ra9 & cl\d are *ecks ^u su* sy/ems1 we %\ld expect ! s&/orm sy/ems to be l>g] & f> l(ti] ?an ?und]/orms1 & to consi/ ( f> m viol5t atmosph]ic movem5ts4 ,?is also is ! case1 & :5 we "k t "s ( ^! di/urbances h ! dim5sions ( a cyclonic /orm1 x is easy to und]/& h[ ! f9e/ du/ may be rais$ to va/ altitudes1 into ! great upp] curr5ts ( ! air1 by :i* x may be borne hundr$s ( miles be=e return+ to ! gr\nd4 ,x is ?us t ! du/ ( ! ,african des]ts is c>ri$ across ! ,m$it]ranean to ,europe1 & ! yell[ loess f ,mongolia ev5 to ! ea/w>d ( ,japan4 ,,*apt] ,,viii ,,wave ,,cl\ds ,,ref]5ce has already be5 made on m ?an "o occasion to ! rem>kable rippl$ or wavy /ructure sometimes assum$ by cl\ds4 ,! waves may be ( almo/ any dim5sions1 f ! broad b&s into :i* a %eet ( cirro-/ratus or ( alto-/ratus is sometimes divid$1 d[n to ! mo/ m9ute ripples4 ,sometimes !y are rang$ 9 long /raight l9es1 sometimes !y are b5t into %>p angles1 & sometimes curv$ 9 v elaborate patt]ns2 b :e!r !y be l>ge or small1 /raight or curv$1 no "o c see !m & fail to conclude t !y mu/ be due to an action m or less analog\s to ! causes :i* produce waves on ! sea or ripple m>ks ^u ! s&4 ,wave cl\ds occur at all heights :]e cl\ds are =m$4 ,! break-up ( a lift+ fog into roll] cl\ds is probably ! l[e/ example1 b x may m frequ5tly be se5 9 high] cl\ds ( ! alto or cirrus k9ds4 ,a l[ example is giv5 9 ,plate #dj1 :i* repres5ts /ratus maculosus1 & :i* has already be5 describ$4 ,a high] type is %[n 9 ,plate #ed1 :i* is a wave-l arrangem5t ( alto-cumulus4 ,r high] come ! long zig-zag b&s ( ,plate #ee1 9 :i* ! /rati=m arrangem5t is m obvi\s1 & :i* w\ld be be/ describ$ z a wave-=m ( alto-/ratus4 ,^! two plates =m /rik+ contra/s4 ,! cl\ds %[n 9 ! fir/ are di/9ctly ( ! cumulus ord]1 & a prom95t feature is ! way 9 :i* ! "r-h& side ( ea* wave has a cle>-cut r\nd$ cont\r l t ( ! upp] edge ( a small cumulus1 :ile ! left-h& edge ( ea* b& is fray$ out into a ragg$ fr+e4 ,! :ole cl\d 0 mov+ sl[ly 9 a direction ne>ly1 b n q1 at "r angles to ! waves1 & ! fr+$ edge =m$ ! re>4 ,x is evid5t t ?is peculi> /ructure mu/ be due to a s]ies ( n>r[ waves int]sect+ a plane 9 :i* ! air is j on ! po9t ( produc+ alto-cumulus4 ,if !re 7 no su* waves1 ! little upris+ curr5ts1 ) _! int]v5+ d[n curr5ts1 w\ld be irregul>ly di/ribut$1 & all ! wave di/urbances h _h to d is to arrange !m4 ,! consequ5ce is t z ! waves pass along ! /ratum ! air is alt]nately rais$ & l[]$4 ,:]e x is ris+ cond5sation takes place1 :]e x is fall+ evaporation results4 ,illu/ration3 ,plate #ed4 ,,cre/$ ,,alto ,,waves4 7,alto-cumulus ,undatus47 ,illu/ration3 ,plate #ee4 ,,alto ,,waves4 7,alto-/ratus ,undatus47 ,! cl\d1 l mo/ o!r wave cl\ds1 did n reta9 its features = any l5g? ( "t1 b ! gaps clos$ sl[ly 9 z ! cl\d-b&s increas$ 9 size1 until a %eet ( alto-/ratus 0 produc$4 ,s9ce ! "t ( day 0 ! morn+1 x is almo/ c]ta9 t ! plane ( saturation 0 ris+ 9 accordance ) ! g5]al law1 :i* is t ! planes ( cond5sation rise /eadily1 until ab\t two or ?ree o'clock 9 ! aft]noon1 & !n sl[ly desc5d4 ,9 ,plate #ee ea* b& is mu* flatt] & less d5se4 ,!y are j z evid5tly =m$ by wave movem5ts int]sect+ ! plane ( cond5sation2 b ?is 0 =m$ 9 ! ev5+ :5 ! sun 0 ne>+ ! horizon1 & at a "t :5 ! cl\d planes are z a rule rapidly desc5d+4 ,among ! alto cl\ds wave-=ms sometimes p]si/ = a fairly long "t1 & 9 ?is case ! b&s mov$ /eadily onw>d 9 a direction equally incl9$ to _! l5g? & bread?1 t is to say1 f ! bottom left-h& corn] ( ! photograph to ! top "r-h& corn]4 ,z !y pass$ across ! sky new b&s kept on mak+ _! appe>ance at ab\t ! same spot1 ea* b& p]si/+ ) little *ange until x _h pass$ out ( sight4 ,go+ mu* high] up into ! region ( cirrus1 we meet ) ! mo/ m9ute & delicate ripple cl\ds4 ,"s ( ^! h already be5 ref]r$ to4 ,!y are connect$ ) ei!r cirro-macula1 cirro-cumulus1 or cirro-/ratus1 j z ! co>s] textur$ waves we h be5 consid]+ are connect$ ) alto-cumulus or alto-/ratus4 ,9 ,plate #ef we h an example 9 :i* we c see ! /ages 9 ! process4 ,ne>e/ to ! z5i? we h cirro-cumulus1 :i* is "h & !re irregul>ly di/ribut$1 b is g5]ally arrang$ 9 delicate ripples1 :i* are v>i\sly curv$4 ,ne>] ! horizon ! tr\ghs ( ! waves are fill$ 91 & %eets ( cirro-/ratus are ! result4 ,"h1 aga91 ! wave-=m is evid5tly n typical4 ,x is an arrangem5t ( ei!r cirro-cumulus or cirro-/ratus1 produc$ by ! int]section ( ! plane ( cond5sation by a s]ies ( wave movem5ts4 ,illu/ration3 ,plate #ef4 ,,cirro ,,ripples4 7,cirro-cumulus ,undatus47 ,! arrangem5t is1 h[ev]1 s /rik+ a feature :5 x is well %[n t any description ( ! cl\d :i* conta9s no ref]5ce to ! waves is manife/ly incomplete1 & ?is w\ld be be/ effect$ by add+ ! ^w undatus or wav$ to ! "n ( ! cl\d4 ,plate #ed w !n be alto-cumulus undatus1 ,plate #ee alto-/ratus undatus1 & ,plate #ef w\ld be describ$ z cirro-cumulus undatus1 pass+ into cirro-/ratus undatus & cirro-/ratus4 ,9 popul> language ,plate #ee might be call$ alto waves1 ,plate #ed cre/$ alto waves1 & ,plate #ef cirro ripples4 ,if we are satisfi$ t ! wave cl\ds are due to a wave movem5t int]sect+ a plane ( incipi5t cl\d =mation1 ! :ole "q ( _! mode ( production resolves itself into two p>ts--h[ is t plane ( incipi5t cond5sation produc$8 & h[ c we acc\nt = ! int]sect+ waves8 ,! fir/ "q has by f> ! great] importance1 s9ce x am\nts to ask+ = a g5]al explanation ( ! production ( high cl\ds1 especially ! =ms ( cirro-cumulus1 cirro-/ratus1 cirro-macula1 & ! correspond+ alto v>ieties4 ,!re are1 aga91 two divisions also to ?is "q4 ,h[ does ! wat] vap\r rea* ! /ratum 9 suffici5t quantity to saturate x8 & :5 cond5sation takes place1 :y does x s frequ5tly assume ! *>act]i/ic mottl$ & granul> =ms l cr[ds ( little cumulus cl\ds arrang$ 9 "o level8 ,?is la/ s5t5ce gives ! clue4 ,!y are1 9 tru?1 little cumulus cl\ds1 & mu/ be =m$ 9 exactly ! same way z _! va/ly l>g] prototypes ( l[] regions4 ,x has be5 expla9$ t l[ cumulus is ! result ( l>ge upw>d mov+ air columns or convection curr5ts1 ea* "o be+ initially caus$ by ! heat+ ( ! vap\r-lad5 air ne> ! gr\nd1 & ea* upris+ column be+ suppli$ by cool] desc5d+ air :i* fl[s d[n 9 ! int]v5+ spaces4 ,x has also be5 expla9$ t ^! movem5ts result 9 *anges ( temp]ature1 :i* t5d to *eck ^? movem5ts & re/ore ! orig9al equilibrium4 ,suppose ?is to occur1 z x con/antly does1 )\t any column rea*+ suffici5tly high to produce a cl\d4 ,!re w be no visible effect1 b1 nev]!less1 an important *ange has tak5 place4 ,e asc5d+ curr5t has lift$ "s wat] vap\r ) x to a high] level1 & ! desc5d+ dri] air has come d[n 9 contact ) ! gr\nd or damp] air to become equally *>g$ ) moi/ure 9 its turn4 ,! process w be repeat$ aga9 & aga91 & at "o level aft] ano!r1 s t ! wat] vap\r travels ev] high] & high]4 ,?is process ( int]*ange betwe5 asc5d+ & desc5d+ air has be5 call$ by ,mr4 ,ley inv]sion1 b ! t]m does n seem v suitable1 & int]convection w\ld be bett]4 ,! two opposite curr5ts pass ?r\gh ea* o!r1 z if ! asc5d+ air ga!r$ itself into def9ite *annels1 & pass$ ?r\gh holes 9 ! desc5d+ mass l ! passage ( wat] upw>ds ?r\gh a desc5d+ plate ( p]=at$ metal4 ,moreov]1 j z ! holes 9 su* a desc5d+ plate might h any size1 s t ! asc5d+ /reams might v>y 9 bread? f ! f9e/ hair to a column ( huge diamet]1 9 exactly ! same way ! asc5d+ columns ( air may v>y f ! smalle/ imag9able size to ! great cumulo-nimbus curr5ts4 ,x is ! little curr5ts :i* acc\nt = ! con/ant quiv] ( ! m>g9s ( any object :i* is view$ ?r\gh a l>ge telescope by day1 & = ! haze1 s *>act]i/ic ( a hot day1 :i* makes di/ant objects seem ill-def9$ & 9 a /ate ( cont9ual tremble4 ,! rays ( light 9 pass+ ?r\gh ! int]sect+ /reams are b5t a little1 n[ ?is way1 n[ t1 z ! air curr5ts sway to & fro4 ,! ne> neighb\rhood ( ! gr\nd is n ess5tial4 ,z long z ! temp]ature ( ! air at any level is ris+1 s long int]convection mu/ occur4 ,! process w be indep5d5t ( ! pres5ce or abs5ce ( w9d4 ,all t w9d c d is to mix up ! air at diff]5t levels1 break+ ! sy/em ( curr5ts & r$uc+ x to1 s to say1 a f9] texture1 or produc+ eddies1 if /rong en\gh1 :i* direct ! curr5ts & ga!r !m into def9ite *annels4 ,! f9al result 9 any case is t1 ) ris+ temp]ature1 wat] vap\r is /eadily borne upw>ds f ! gr\nd4 ,z x asc5ds ! air becomes cool]1 & yet reta9s its wat] vap\r4 ,:5 ! ris+ curr5ts are l>ge !y mix little ) ! desc5d+ dry air1 & on rea*+ a c]ta9 level cond5sation takes place1 & we h ! beg9n+ ( a cumulus4 ,if !y are ( a m mod]ate size !y w asc5d less rapidly1 ! admixture ) desc5d+ air w be> a l>g] proportion to ! :ole1 & ! plane at :i* cond5sation w beg9 w be high]1 & !n ea* small column w be tipp$ ) a ball ( alto-cumulus4 ,make ! int]convection curr5ts small] /ill1 & ! cl\d plane w be lift$ yet high]1 & we %all h cirro-cumulus or cirro-macula4 ,n[1 ! m ev5 ! di/ribution ( temp]ature on ! gr\nd ! less ! probability ( co>se int]convection1 & ! same is true ( any high] /ratum ( air1 provid$ x is free f di/urb+ influ5ces f outside4 ,if1 !re=e1 we h l>ge curr5ts ne> ! gr\nd1 end+1 z !y mu/1 9 cumulus1 x has already be5 expla9$ t ^! cl\ds /op ! action1 & ! g5]al sy/em ( l>ge curr5ts w be re/rict$ to ! region 9 :i* !y occur4 ,at "s di/ance above ! l[] cl\ds ! only diff]5ce w be t wat] vap\r has be5 br\ght up to _! level 9 great abundance4 ,small] sy/ems ( int]convection c !n exi/1 & s we may h ! spectacle ( sev]al lay]s ( cl\d--cumulus capp+ ! great curr5ts ( l[] regions1 alto-cumulus =m+ ! summits ( ! small] curr5ts ( int]m$iate regions1 & cirro-cumulus float+ f> above bo?4 ,frequ5tly x happ5s t be=e ! asc5t ( vap\r has gone q f> en\gh to produce a cl\d1 o!r causes co-op]ate1 & ! cl\d makes its appe>ance sudd5ly ov] consid]able pat*es ( sky4 ,! mo/ pot5t ( ^! is a fall ( ! b>ometric pressure1 :i* is br\ght ab\t by "s ( ! air f> above ! region ( ev5 ! highe/ cl\ds fl[+ away to "s o!r di/rict4 ,! air at all l[] levels be+ ?us reliev$ ( ! sup]9cumb5t pressure1 imm$iately exp&s1 & is !reby cool$ ?r\gh\t4 ,consequ5tly1 if at any level x 0 ne> its po9t ( saturation1 x w be c>ri$ beyond t po9t1 & cl\d w rapidly make its appe>ance ov] a l>ge "p ( ! sky1 possibly at m ?an "o level4 ,/rati=m arrangem5ts w be ! rule2 b if int]convection is go+ on at ! "t1 its pres5ce w be betray$ by a granul> or cumuloid /ructure4 ,int]convection cl\ds %\ld !n be mo/ frequ5t1 & be/ =m$ :5 ! air z a :ole is /ill or mov+ sl[ly 7s z n to create great eddies71 :5 ! temp]ature is ris+ rapidly1 & :5 ! b>omet] is mak+ a sudd5 fall4 ,all ^! conditions are met 9 ?und] wea!r1 & at ! "t :5 a summ] anticyclone is giv+ way4 ,x w be rememb]$ t _m ( ! mo/ beautiful =ms h be5 describ$ z =m+ "u "o or ! o!r ( ^! v conditions4 ,a second contribut+ cause1 & "o :i* t5ds to make ! cond5sation 9 pat*es or long broad b&s rang$ r\ghly at "r angles to ! direction 9 :i* ! air is mov+1 has be5 ref]r$ to e>li]4 ,x is ! passage ( ! air ov] an undulat+ c\ntry2 ! up-&-d[n movem5ts ( ! l[] air be+ transmitt$ upw>ds to great altitudes1 z ev] broad5+ & flatt5+ waves4 ,if ! upp] air is fl[+ m rapidly ?an ! l[]1 ^! broad waves may be f> ahead ( _! real cause1 :i* w1 !re=e1 q escape recognition1 b ! ph5om5on is con/antly to be detect$ 9 ! arrangem5t ( ! l[] cl\ds4 ,two in/ances 9 ! writ]'s exp]i5ce w suffice4 ,x 0 desir$ "o morn+ to measure ! altitude ( "s small cl\ds :i* 7 pass+ f ! nor?-we/ at a height ( probably betwe5 #bjjj & #djjj metres1 ov] a hill only ab\t #aej metres high] ?an ! valley 9 :i* ! app>atus 0 fix$4 ,9 ord] to make ! measurem5t1 x 0 necess>y = ! cl\d to cross ! valley & appe> 9 ! same field ( view z ! sun1 accord+ to ! me?od t w be describ$ fur!r on4 ,b 9 ord] to cross ! valley ! air _h to desc5d1 & s1 ( c\rse1 _h ! cl\d /ratum1 ?\gh to a less ext5t4 ,b small z ! desc5t 01 x 0 en\gh to dry up ! cl\ds entirely1 & = m ?an a c\ple ( h\rs ! cl\ds came sail+ ov] ! hill1 disappe>+ entirely1 & !n re=m+ s f> beyond t no measurem5t 0 possible1 s9ce n "o s+le fragm5t came ne> en\gh to ! position ( ! sun1 :i* rema9$ %9+ brightly ?r\gh a broad cle> gap betwe5 two pat*es ( cl\d-/rewn sky4 ,on ano!r occasion consid]able prep>ations _h be5 made = "s photographic obs]vations dur+ an eclipse ( ! sun4 ,! obs]vatory /&s on ! ea/]n side ( ! valley ( ! ,exe1 :i* is flank$ on its we/]n side by a long ridge ( hills go+ up to #hjj feet above ! sea4 ,beyond ^! hills lies ! deep1 n>r[ valley ( ! ,teign1 & beyond t ! granite ramp>ts ( ,d>tmoor1 #ajjj feet above ! sea4 ,! w9d 0 bl[+ g5tly across ! two valleys1 & %ortly be=e ! eclipse began a broad /rip ( ?9 cl\d =m$ above & r t[>ds ! ea/]n side ( ! ,exe valley1 j :]e ! sun 01 :ile at ! same "t ! sky 0 practically cle> half a mile fur!r ea/1 & bright sunlight 0 /ream+ d[n on ! ridge betwe5 ! two riv]s a few miles t[>ds ! we/4 ,! cl\d 0 nev] ?ick en\gh to q hide ! sun1 s t ! eclipse 0 easy to wat* ) ! nak$ eye2 b 9 spite ( fairly rapid movem5t ( ! cl\d masses z !y drift$ be=e ! sun1 !y kept on =m+ 9 j ! same place1 & completely prev5t$ ! c>ry+ out ( ! programme plann$4 ,x is almo/ c]ta9 t ! ph5om5on 0 br\ght ab\t by an upw>d mov+ wave m>k+ ! place :]e ! level ( approa*+ saturation 0 upheav$ by ! di/urbance caus$ by cross+ ! two valleys & int]v5+ ridge4 ,^! two in/ances are n quot$ z examples ( a r>e occurr5ce1 b z def9ite simple in/ances ( a ph5om5on :i* may be con/antly obs]v$1 & z pro( t ! con=mation ( ! gr\nd does ex]cise an influ5ce ^u ! di/ribution ( cl\d4 ,b no irregul>ities ( ! gr\nd w suffice to expla9 ! m9ute waves & ripples :i* h be5 describ$ at ! beg9n+ ( ?is *apt]4 ,^! mu/ be due to wave di/urbances 9 ! air itself4 ,!y h be5 expla9$ z due to two diff]5t curr5ts ( air1 ei!r a w>m damp curr5t fl[+ ov] a cold "o1 or vice v]s4 ,n[1 su* an occurr5ce z a w>m damp curr5t fl[+ ov] a cold "o mu/ be v r>e1 ?\gh x is impossible to d5y t x might occur4 ,! imm$iate contact ( a cold curr5t above a w>m damp "o is equally unlikely1 unless ! g5]al atmosph]ic condition 7 greatly di/urb$1 :i* is ! same ?+ z say+ t wave cl\ds w\ld n occur4 ,!y are mo/ frequ5t at j ^? times :5 int]convection has free/ play1 & ?is is amply suffici5t to acc\nt = a plane ( saturation )\t any necessity = a hypo!sis ( two lay]s ( air at diff]5t temp]atures all b produc+ cl\d at _! junction4 ,no conv9c+ evid5ce ( cl\d production by su* means has yet be5 adduc$1 & x is bett] to rely ^u causes :i* we "k d op]ate ?an to call 9 !ories z to :at might possibly happ54 ,?is is "o ( ^? po9ts 9 ! /udy ( cl\ds :i* ne$ inve/igation1 & until pro( is =?com+ x is bett] to say t ! admixture ( two /rata ( air might conceivably produce cl\d1 b mo/ =ms c be acc\nt$ = by o!r causes ( :i* we h m positive evid5ce4 ,/ill1 ! wave cl\ds are due to waves1 & !re seems no o!r way ( acc\nt+ = !m ?an ! supposition ( g5tle diff]5tial curr5ts4 ,b if su* curr5ts occur ! ripples & waves w n be limit$ to a def9ite surface1 s to say1 ( contact1 b w be propagat$ upw>ds & d[nw>ds = consid]able di/ances f ! level ( greate/ di/urbance4 ,:e!r1 !re=e1 ! level at :i* ! natural op]ation ( int]convection has produc$ saturation is high or l[ 9 ?is region1 ! result w be ! m>%all+ ( ! asc5d+ & desc5d+ elem5ts ( ! convection sy/em 9 ! *>act]i/ic waves4 ,! diff]5tial curr5ts1 !n1 :i* cause ! waves mu/ n be conceiv$ z produc+ ^? waves at a surface ( contact1 nor mu/ ! curr5ts be ?\ght ( z sep>at$ by any def9ite surface1 b r by a region ( v>iable b usually consid]able dep?1 9 :i* ! air is di/urb$ by a s]ies ( small sl[ eddies & oscillatory movem5ts4 ,:5 ! waves are p>allel /raight l9es ! air curr5ts may be really portions ( a :ole1 hav+ ! upp] "p m rapid ?an ! l[]4 ,9 su* a case ! direction ( movem5t %\ld be at "r angles to ! cl\d l9es4 ,if ! upp] curr5t diff]s 9 direction z well z velocity1 ! direction ( movem5t ( ! cl\ds w be int]m$iate1 & w resemble t ( ! upp] or l[] curr5t1 accord+ to _! relative di/ances f ! plane at :i* ! cl\ds are =m$4 ,! behavi\r ( ! cl\ds w dep5d ^u ! relative %>es 9 _! production borne by int]convection pure & simple & by ! wave oscillations4 ,if ! /ratum is "o 9 :i* cl\d w\ld actually be =m$ indep5d5tly ( ! up-&-d[n movem5ts1 all ?is w be able to d w be to arrange ! cl\dlets at _! bir?1 & ^! w !n cont9ue to exi/1 drift+ ) ! g5]al horizontal movem5t ( ! air l any o!r cl\d ( ! same ord]4 ,on ! o!r h&1 if ! production ( cl\d is dep5d5t ^u ! v]tical oscillations1 ! cl\dlets or l9es ( cl\d w move ) ! air waves1 & _! rate ( motion & direction ( motion w be det]m9$ by ! rate & direction ( ! waves1 :i* may be q diff]5t f t ( ! air at t /ratum z a :ole4 ,! asc5d+ waves w be m>k$ by l9es ( cl\d g5]ally r\nd] & bett] def9$ on _! advanc+ sides1 :ile ! desc5d+ tr\ghs w be m>k$ by cle> int]vals4 ,wave movem5ts ( ! necess>y k9d are frequ5tly v complicat$1 & x is n by any means a r>e occurr5ce to see ! wave l9es 9 "o "p ( ! sky at all sorts ( angles ) simil> l9es 9 o!r p>ts1 or ev5 to see two or m sets ( waves at diff]5t altitudes cross+ "o ano!r4 ,ei!r ph5om5on is always accompani$ by rapid *anges 9 ! cl\d1 & ! rippl$ /ructure is %ort-liv$4 ,?is 0 ! case ) ! cl\ds %[n 9 ,plate #ed4 ,plate #ec1 on ! contr>y1 %[s great uni=mity 9 ! wave l9es1 & al?\gh ! v]tical oscillation is probably ! ma9 cause ( cond5sation1 ! =m 0 unusually p]si/5t4 ,irregul> pat*es ( wave di/urbance1 affect+ a plane occupi$ by cirro-/ratus vittatus1 are %[n 9 ,plate #eg4 ,9 ?is case ! wave sy/ems only t\* ! cl\d plane "h & !re1 & ! places ( contact v>i$ rapidly4 ,x is pretty cle> f ?is photograph t ! idea ( ! waves be+ =m$ at a surface ( contact betwe5 two div]se curr5ts w n suffice4 ,! b&s ( ! cirro-/ratus are = ! mo/ "p unbrok5 & unaffect$2 x is only "h & !re t ! wave region t\*es !m4 ,illu/ration3 ,plate #eg4 ,,wav$ ,,cirro-,,/ratus4 7,cirro-/ratus ,undatus47 ,! conclusions at :i* we h arriv$ are simple1 & !re is little room = d\bt z to _! ma9 correctness1 b !re are num]\s m9ute features pres5t$ by ^! beautiful cl\d patt]ns :i* await int]pretation1 & !y reveal complicat$ oscillatory movem5ts 9 ! air :i* are difficult to acc\nt =1 :e!r we seek _! orig9at+ causes or ! me*anics ( _! motions4 ,,*apt] ,,ix ,,cl\d ,,altitudes ,,dur+ an ext5d$ exp]i5ce ( cl\d photography1 x 0 f\nd t x 0 q possible to get pictures :i* %[$ ! cl\d detail ev5 :5 ! sun 0 9 ! field ( view4 ,sometimes ! sol> image 0 rev]s$1 b if ! exposure 0 v %ort ?is 0 n ! case4 ,9 su* photographs ! /ructure ( ! cl\d 0 exce$+ly cle> & %>ply def9$ q close to ! sun4 ,inde$1 ! int5se illum9ation seem$ to reveal m9ute details ( int]nal arrangem5t :i* c\ld n be detect$ 9 simil> cl\ds "s di/ance away4 ,! me?ods :i* _h be5 employ$ = ! measurem5t ( cl\d altitudes else:]e h already be5 briefly ref]r$ to4 ,"s ( !m requir$ two obs]v]s1 :o 7 equally responsible1 ea* ( !m hav+ to direct 8 app>atus or cam]a to ! same po9t ( ! cl\d1 & to record ! exact direction 9 :i* ! in/rum5t 0 po9t$4 ,! in/rum5ts1 if accurate1 7 co/ly1 & !re 7 _m opportunities = error 9 read+ ! graduat$ circles :i* gave ! directions4 ,moreov]1 9 mo/ ( ^! me?ods ! two obs]v]s 7 connect$ by telephone1 & _h to agree on ! exact po9t t[>ds :i* _! in/rum5ts %\ld be direct$2 ei!r ! exact po9t ( ! cl\d1 or ! precise direction z %[n by ! m\nt+ ( ! cam]a or o!r in/rum5t4 ,at ,kew "s ( ^! s\rces ( error 7 avoid$ by fix+ ! two cam]as ) ! axes ( ! l5ses & c5tres ( ! plates 9 a v]tical position & expos+ ! two plates simultane\sly4 ,! ,kew obs]vations 7 n long cont9u$1 & = "s ye>s ! only measurem5ts 9 progress 7 ^? c>ri$ out abroad1 p>ticul>ly at ! ,blue ,hill ,obs]vatory & at ,upsala4 ,! exp]i5ce ga9$ 9 photograph+ cl\ds 9 ord] to record _! =ms sugge/$ a way 9 :i* _m ( ! s\rces ( error 9 previ\s measurem5ts ( altitude c\ld be avoid$1 especially by simplify+ & r$uc+ ! op]ations at ! mom5t ( mak+ ! obs]vation4 ,if two cam]as are plac$ at ! opposite ends ( a measur$ base l9e1 ^: direction is kn[n1 & if !y are bo? po9t$ t[>ds ! sun1 on mak+ ! exposures by electrical means at ! same mom5t1 ! position ( ! image ( ! sun ^u ! plate gives ! direction 9 :i* ! cam]as are po9t$4 ,x w be 9 ! same direction z se5 f bo? ends ( ! l9e4 ,n[1 if we note ! "t at :i* ! exposure is made1 ?is ) ! date gives all t is requir$ = asc]ta9+ ! sun's position 9 ! sky1 & is1 !re=e1 ! only exact obs]vation :i* ne$ be made at ! "t ( tak+ ! photographs4 ,mi/akes are almo/ impossible1 z ea* plate conta9s its own record ( ! sun's position1 & ev5 if "s ( ! plates %\ld get mix$ ! images ( ! cl\ds w g5]ally suffice to pair !m prop]ly4 ,= g5]al measurem5ts !re is "o grave defect 9 ! me?od1 & t is t x c only be us$ :5 ! sun & cl\d c be got into ! same field ( view4 ,b ) ! high] v>ieties ( cl\d ?is is g5]ally possible1 & x 0 j ^! high] sorts ab\t :i* k 0 lea/ c]ta91 & :i* x 0 propos$ to /udy4 ,an initial difficulty 0 ! f9d+ ( a level site1 flat l& be+ v uncommon 9 ,devon%ire1 b =tunately a suitable place 0 f\nd 9 "s artificially levell$ gr\nd close to ,exet]1 belong+ to ! ,london & ,s\? ,we/]n ,railway ,company4 ,x 0 a /ret* ( gr\nd int5d$ to be cov]$ ) sid+s1 b _h n be5 f9i%$1 & _h become ov]gr[n ) grass1 /unt$ sall[s1 & o!r wild plants4 ,be+ railway gr\nd1 x 01 comp>atively1 ?\gh by no means entirely1 free f mis*iev\s & inquisitive p4 ,! next po9t 0 a suitable cam]a4 ,x mu/ h fairly long focus 9 ord] to give a l>ge image1 & !re=e l>ge displacem5t2 x mu/ be capable ( be+ po9t$ 9 any direction & clamp$ !re2 & x mu/ be capable ( /&+ consid]able extremes ( temp]ature & v>iations ( dampness1 z x 0 int5d$ t !y %\ld be kept on ! spot 9 wood5 /ructures1 :i* s]v$ = /&s z well z to conta9 ! app>atus4 ,! patt]n f9ally decid$ ^u is repres5t$ 9 ,plate #eh1 :i* %[s "o ( ! cam]as po9t$ up to ! sky & /&+ on "o ( ! /&s4 ,^! cam]as 7 to take plates ( :ole plate size1 two d\ble d>k slides ( ! ord9>y patt]n be+ atta*$ to ea*4 ,illu/ration3 ,plate #eh4 ,,cam]a ,,= ,,measur+ ,,altitudes4 ,! cam]a looks r complicat$1 b x is really simple4 ,its body consi/s ( front & back1 ea* atta*$ to a c5tral "p by a %ort bell[s & slid+ on a base bo>d1 to :i* x c be clamp$ by screws ( ! usual patt]n4 ,! c5tral "p c>ries trunnions1 su* z are us$ = look+-glasses1 :i* sw+ 9 sockets c>ri$ by two upright supports1 s z to give ! :ole free motion 9 a v]tical plane4 ,9 ord] to be able to fix x firmly at any angle1 ! base bo>d ( ! cam]a body c>ries on its und]side a ?9 bo>d project+ b5ea? x & =m+ a segm5t ( a circle ^: c5tre w\ld be ! horizontal axis ?r\gh ! trunnions4 ,! bo>d passes betwe5 ! jaws ( a small wood5 clamp+ vice 9 front1 :i* is c>ri$ by ! squ>e base to :i* ! uprights are fix$4 ,! :ole is firmly made ( well-season$ p9e1 & has /ood well ! h>d usage ( half a doz5 ye>s4 ,!re is no focus+ scre54 ,focus+ 0 done ) great c>e once = all1 & !n a coat ( h>d v>ni% 0 put ov] all ! adju/+ screws4 ,a small view-f9d] is atta*$ to "o side1 & x 0 by ?is t ! cam]a 0 po9t$ 9 ! desir$ direction4 ,9 ord] to less5 risk ( mi/ake1 x 0 s arrang$ t ! two slides belong+ to "o cam]a w\ld n fit ! o!r4 ,! l5ses1 ( #ah in*es focus1 & giv+ %>p detail all ov] ! plate1 7 c>efully mat*$1 & ! focus adju/$ until ! images giv5 by !m :5 plac$ side by side appe>$ to co9cide exactly4 ,!y 7 provid$ ) iris diaphragms1 :i* 7 %ut d[n to an ap]ture ( a qu>t] ( an in*1 & ) %utt]s :i* c\ld be releas$ at ! same mom5t by an electric curr5t1 act+ ?r\gh ! electro-magnet %[n "u ! l5s on ! front ( ! cam]a4 ,! %utt]s 7 ( ! k9d kn[n z ! 8,*ronolux10 :i* w give any exposure f ! sixty-f\r? ( a second up to ?ree seconds4 ,b x 0 f\nd 9 practice t ! highe/ spe$ 0 suffici5t & gave satisfactory results4 ,( c\rse1 !re 0 no idea ( adju/+ matt]s on ea* occasion s z to get ! be/ possible negatives capable ( yield+ good pr9ts4 ,measurem5t 0 ! object1 & if ! negative %[$ ! sun & suffici5t cl\d detail = ! id5tification ( cl\d po9ts1 t 0 all t 0 want$4 ,! %utt]s gave a good deal ( tr\ble at fir/4 ,_! slid+ p>ts 7 made ( ebonite1 & :5 ! cam]as 7 left 9 _! /&s ) an ,augu/ sun %9+ d[n ^u !m1 ev]y?+ inside got v hot & ! ebonite w>p$2 b ! difficulty 0 got ov] by sub/itut+ alum9ium4 ,! two cam]a /&s 7 plac$ #bjj y>ds ap>t1 & 7 connect$ by a l9e ( telegraph wire c>ri$ on %ort poles4 ,at ea* end ( ! wire an insulat$ connect+ piece 0 br\ght d[n to ! cam]a /&1 & to ! batt]ies & o!r app>atus4 ,! curr5t :i* 0 s5t ?r\gh ?is wire by press+ a contact at "o end ( ! l9e did n directly make ! exposures2 b two simil> relays 7 br\ght into action1 & ea* ( ^! s5t ! curr5t f a local batt]y ( ,leclan* cells ?r\gh ! electro-magnet on ! cam]a & made ! exposure4 ,aft] developm5t ! two negatives %[$ ! image ( ! sun1 n f> f ! c5tre ( ! field ( view1 & ! cl\d ^: altitude 0 requir$4 ,s9ce ?is 0 tak5 f two diff]5t po9ts ( view1 ! negatives 7 n alike1 b ! di/ances betwe5 ! c5tre ( ! sun's disc & any special po9t ( ! cl\d 7 diff]5t4 ,= in/ance1 if ! cl\d 7 ea/ ( ! sun1 ) its edge j app>5tly t\*+ ! sol> image z photograph$ f ! ea/]n /ation1 !n ! negative tak5 f ! we/]n end ( ! base w\ld %[ an int]val ( cle> sky betwe5 ! two1 :i* w\ld be great] z ! cl\d 0 l[]4 ,x (t5 happ5$ t aft] develop+ ! plates ! image ( ! sun 0 lo/ 9 a black blur1 b x 0 easy to r$uce ?is "p ( ! image by local application ( a r$uc+ ag5t#c by means ( a pa9t-bru%1 until ! disc became cle> en\gh4 ,two l9es 7 !n drawn on ! negative1 "o v]tical & ! o!r horizontal1 int]sect+ ea* o!r at ! c5tre ( ! sun's image4 ,^! l9es s]v$ z ! />t+-po9ts = exactly measur+ ! di/ance f _! po9t ( int]section to any select$ po9t ( ! cl\d4 ,! di/ances c\ld g5]ally be det]m9$ to a fiftie? or a hundr$? "p ( an in*1 & _! diff]5ce 01 ( c\rse1 dep5d5t ^u ! direction ( ! sun relative to ! base l9e & ! altitude ( ! cl\d1 b = l[ level cl\ds ! diff]5ce 0 sometimes s great t no pair ( correspond+ po9ts c\ld be detect$1 :ile x 0 (t5 z mu* z an in*4 ,) high] cl\ds ! diff]5ces 7 small]1 b unless ! sun 0 v l[ 9 ! sky1 ei!r ea/ or we/1 ! displacem5ts ( ! cl\d image 7 great en\gh to give reliable measures4 ,specim5 pr9ts f pairs ( negatives are %[n 9 ,plates #ei & #fj4 ,illu/ration3 ,plate #ei4 ,,pr9t ,,f ,a ,,negative ,,us$ ,,= ,,measur+ ,,altitude4 ,illu/ration3 ,plate #fj4 ,,pair ,,( ,,pr9ts ,,%[+ ,,! ,,displacem5t ,,( ,,! ,,cl\d4 ,! processes by :i* ! measurem5ts are work$ out are labori\s1#d & consi/ ( two p>ts1 ! fir/ be+ ! det]m9ation ( ! exact position ( ! sun f ! date1 h\r1 & latitude & longitude ( ! place1 & ! second1 ! det]m9ation ( ! position ( ! cl\d4 ,two po9ts :i* repres5t ! same "p ( ! cl\d are select$1 & _! respective di/ances f ! two l9es drawn ?r\gh ! sun are measur$ z accurately z possible4 ,n[1 a c]ta9 di/ance on ! negative corresponds ) a def9ite angul> displacem5t1 & a scale c be con/ruct$ %[+ h[ mu* %\ld be add$ to or subtract$ f ! sun's position to get ! exact position ( ! cl\d4 ,?is be+ done1 x is !n a simple piece ( trigonometry to d$uce ! actual height ( ! cl\d above ! place ( obs]vation4 ,! "w ( computation1 h[ev]1 0 greatly light5$ by ! fact t _m ( ! pairs ( negatives %[$ m ?an "o lay] ( cl\d2 ?us ,plate #ei1 :i* is a fair specim51 %[s ?ree lay]s1 &1 consequ5tly1 "o det]m9ation ( ! sun's position suffic$ = ?ree di/9ct results4 ,= ! highe/ cl\ds ! displacem5ts 71 ( c\rse1 small1 & c\ld only be made ) c]ta9ty ( a correct result )9 ab\t ?ree h\rs ( noon4 ,e>li] ?an #i a4m41 or lat] ?an #c p4m41 ! sun 0 too ne>ly 9 a l9e ) ! two /ations1 or too l[ 9 ! sky1 to give a suffici5t displacem5t ( image4 ,a base l9e ( #djj y>ds in/ead ( #bjj w\ld h be5 bett] = ! high cl\ds4 ,b1 on ! o!r h&1 :5 l[ level cl\ds are view$ f two diff]5t spots _! outl9es may seem s *ang$ t x may be impossible to id5tify a pair ( correspond+ po9ts1 & ! same difficulty may also arise :5 high cl\ds are se5 ?r\gh a gap 9 a l[] /ratum4 ,! long] ! base l9e ! m frequ5t & m obtrusive w\ld ?is p]spective difficulty become1 s ! di/ance ( #bjj y>ds betwe5 ! /ations 0 adopt$ z a conv5i5t mean4 ,! me?od ( mak+ ! obs]vations 0 simple4 ,ea* obs]v] 0 provid$ ) "s signal flags1 by :i* ! necess>y communications 7 made 9 accordance ) a simple code4 ,call ! two obs]v]s ,a & ,b1 & suppose ,a direct$ ! op]ations4 ,he wat*$ ! sky until a fav\rable opportunity seem$ to be approa*+4 ,he !n signall$ to ,b1 & bo? cam]as 7 turn$ to ! sun1 ! d>k slides 7 ins]t$1 ! %utt]s set1 & ev]y?+ made ready4 ,signals 7 !n int]*ang$1 to signify t prep>ations 7 complete1 & :5 ,a saw t ! edge ( ! cl\d _h rea*$ a suitable position to be 9 ! same field ( view ) ! sun1 ! contact key 0 press$ & ! plates simultane\sly expos$4 ,at ! mom5t :5 ?is 0 done ! "t 0 not$4 ,sev]al obs]vations 7 ?us made 9 a %ort "t4 ,measurem5ts 7 c>ri$ out z opportunity all[$ ov] f\r consecutive seasons1 f ! beg9n+ ( ,april until ! end ( ,octob]4 ,dur+ ! la/ ( ! f\r ye>s1 ! site _h become less conv5i5t ow+ to an ext5sion ( ! railway "w1 & e>ly 9 ,novemb] ! s]ies 0 br\ght to an abrupt conclusion by a heavy gale1 :i* snapp$ (f all ! poles c>ry+ ! connect+ wire4 ,b by t "t #dbc measurem5ts _h be5 obta9$1 ! great majority ( :i* ref]r$ to cl\ds ( ! cirrus & alto gr\ps4 ,! g5]al results may be tabulat$ ?us1 giv+ heights 9 metres3-- ---------------------------------------- ------------------- ,numb] ( ,maximum ,m9imum ,mean obs]vations4altitude4altitude4altitude4 ---------------------------------------- ,cirrus #eh #bg1dac #d1aad #aj1bcj ,cirro-/ratus #fd #ae1ejc #c1hdj #i1edj cumulus #fc #aa1fgi #c1feg #h1fbd ,alto-cumulus #hc #i1cij #a1hbh #e1cdh ,cumulus top #db #d1ehb -- #c1jjf base #dh #a1iei #ehd #a1bij ,/rato-cumulus #bg #f1ibf #hbc #b1bdh ,cumulo-nimbus top #ae #f1dji #b1jjd #h1jjb base #ae #b1bhf #gff #a1jde ---------------------------------------- ------------------- ,^! values are n v diff]5t1 on ! :ole1 f ^? :i* h be5 arriv$ at else:]e1 & 9 mak+ a comp>ison x mu/ be borne 9 m9d t !re is always a little want ( precision 9 cl\d nom5clature4 ,z a :ole1 ! ,exet] maxima are great] ?an ! =eign ones1 & ?is is v m>k$ly s 9 ! case ( cirrus1 = :i* ! ,am]ican highe/ record is #ad1icj metres1 ! ,sw$i% record is #ac1cgf1 :ile ! ,exet] value is #bg1dac metres1 or ab\t #ag miles4 ,b ?is extreme measurem5t1 & sev]al o!rs unusually l>ge1 7 made 9 "o morn+1 a day ( v hot damp wea!r1 :5 cl\d =m$ at sev5 diff]5t levels3 cumulus at a height ( #ai miles1 alto-cumulus at #ci miles1 cirro-cumulus at #dg miles1 cirro-/ratus 7,no4 #a7 at #h miles1 cirro-/ratus 7,no4 #b7 at #if miles1 cirrus at #aae miles1 & cirrus excelsus at #ag miles4 ,by ab\t half-pa/ "o 9 ! aft]noon ! sky 0 completely ov]ca/ ) dull grey cl\ds1 :i* cle>$ (f at half-pa/ f\r1 & at half-pa/ five 9 ! ev5+ ! cirrus _h fall5 to #gi miles1 & ! cirro-cumulus to #dc miles4 ,if ?is "o day's obs]vations _h be5 omitt$1 ! ,exet] maximum w\ld only h be5 little m ?an #ajjj metres above ! record f across ! ,atlantic1 b #ajjj metres is a height wor? not+4 ,:ile ! ,exet] maxima are all r great]1 we f9d ! m9ima = cirrus1 cirro-/ratus1 & cirro-cumulus are r less ?an at ! =eign /ations2 t is to say1 t cl\ds are =m$ ov] ,devon%ire bo? at l[] & at high] levels ?an seems to be ! case 9 ,massa*usetts or ,sw$54 ,x seems probable t ?is is due to a great] humidity on our we/]n coa/s1 su* z we %\ld suppose w\ld be ! case f _! position & ! prevail+ w9ds & ocean curr5ts4 ,if s1 we %\ld expect ! great convection cl\ds to be l>g]4 ,?us1 at ,exet]1 out ( only fifte5 examples ( cumulo-nimbus1 ! top v>i$ f #bjjd metres to #fdji1 ) an av]age base level ( #ajde4 ,at ,upsala ! maximum 0 #eigj & ! m9imum #adjj1 ) an av]age base level ( #adjj4 ,! mean ?ickness ( ! ,sw$i% cl\ds 0 only #adjj metres1 :ile t ( ! ,devon%ire specim5s 0 m ?an #bjjj metres4 ,aga9 & aga91 dur+ ! progress ( ^! measurem5ts1 x 0 f\nd t ! greate/ altitudes & ! ri*e/ developm5t ( ! high] v>ieties occurr$ t[>ds ! end ( a spell ( f9e calm wea!r1 :5 convection _h _h free play day aft] day4 ,a slight fall ( ! b>omet]1 only ! hundr$? "p ( an in*1 w\ld usually1 "u ^? circum/ances1 br+ ab\t abundant =mation ( high cl\ds1 frequ5tly ( ! undatus k9d4 ,all ! cumulus cl\ds1 by :i* we mean to include alto-cumulus & cirro-cumulus1 are mo/ frequ5t :5 ! levels ( cond5sation are ris+1 :ile ! /rati=m cl\ds are an indication ( no v]tical movem5t or ( active desc5t4 ,pure cirrus is indicative r ( movem5t 9 a horizontal direction1 & may occur :5 ! cond5sation levels are /ation>y1 or :5 !y are rapidly *ang+ ei!r way4 ,9 brok5 wea!r ! natural movem5ts ( ! atmosph]e & ( its vap\r are mask$ & di/urb$ by ! /rong eddies br\ght by ! cyclonic sy/ems4 ,x n unfrequ5tly happ5s t ! region ( di/urbance does n rea* up to ! level ( ! highe/ cirrus1 or1 :at is m probable1 ! cyclonic sy/em leans s f> =w>d t we may h 9 its re> ! upp] cl\ds float+ quietly f> above ! comp>atively %all[ region ( di/urbance1 :ile 9 front ! upp] "p ( ! /orm sy/em projects above undi/urb$ air4 ,! frequ5t appe>ance ( cl\d almo/ at ! same "t at m ?an "o level is at fir/ r difficult to und]/&1 b x w be notic$ t :5 ?is occurs ! b>omet] almo/ inv>iably falls4 ,n[1 if we suppose t ! air is ne>ly saturat$ at m ?an "o level1 & t ! :ole is !n bodily reliev$ ( "s ( ! sup]9cumb5t mass1 s t ! b>omet] falls1 ! mass ( air w at once swell up1 be+ cool$ f top to bottom simultane\sly1 & :]ev] x is damp en\gh cl\d w be =m$4 ,! conv]se is equally true4 ,if we h cl\d at sev]al levels1 & ! :ole is compress$ by ! addition ( m air above1 :i* is ! case :5 ! b>omet] rises1 t compression w be accompani$ by ! g5]ation ( heat & ! consequ5t dis9tegration & disappe>ance ( ! cl\ds4 ,,footnotes3 #c ,f]ricyanide ( potassium & hyposulphite ( soda4 #d ,f ! decl9ation ( ! sun correct$ = v>iation & f ! kn[n latitude1 ! m]idian z5i? di/ance is calculat$4 ,f ! ,gre5wi* "t1 ! longitude1 & ! equation ( "t1 ! h\r angle is obta9$4 ,n[1 if ,h be ! h\r angle1 ,d ! r$uc$ decl9ation1 & ,m ! m]idian z5i? di/ance1 ! sun's altitude may be calculat$ by ! =mula-- log v]s9 ,h ,l cos lat4 ,l cos ,d-#bj log n1 :]e n is a natural numb]1 & n v]s ,m cov]s alt4 ,aga91 to f9d ! azimu?-- v]s sup4 7lat4 alt47-v]s pol> di/4 m1 :]e m is ano!r natural numb]1 & log m ,l sec4 lat4 ,l sec4 alt4-#bj log v]s azim41 reckon$ f ! s\?4 ,h5ce ! position ( ! sun is asc]ta9$ = bo? negatives4 ,by actual measurem5ts on ! plates & ref]5ce to a previ\sly con/ruct$ scale ! position ( ! cl\d z se5 f ea* cam]a is next det]m9$1 & ! angle subt5d$ by ! base l9e at a po9t ,x v]tically b5ea? ! cl\d is calculat$4 ,if ,a & ,b are ! /ations1 & a & b ! angles f !m respectively1 ! di/ance ,,ax is giv5 ?us-- log ,,ax ,l s9 b-,l s9 ,,axb log ,,ab1 & ! height h ( ! cl\d above ,x is giv5 by-- log h log ,,ax ,l tan alt4-#aj4 ,,*apt] ,x ,,cl\d ,,nom5clature ,,s9ce a consid]able numb] ( new t]ms h be5 sugge/$ 9 ! =ego+ pages1 x may be conv5i5t to collect !m & tabulate !m1 s z to %[ _! relation to ^? already recogniz$ by ! ,int]national sy/em4 ,9 ! atlas put =w>d by ! committee1 sixte5 v>ieties are recogniz$ by di/9ct names1 & ^! are drawn up 9 tabul> =m ) appropriate abbreviations = use 9 mak+ records4 ,! names are-- ,cirrus4 ,ci4 ,cirro-/ratus4 ,ci4 ,s4 ,cirro-cumulus4 ,ci4 ,cu4 ,alto-cumulus4 ,a4 ,cu4 ,alto-/ratus4 ,a4 ,s4 ,/rato-cumulus4 ,s4 ,cu4 ,nimbus4 ,n4 ,cumulus4 ,cu4 ,cumulo-nimbus4 ,cu4 ,n4 ,/ratus4 ,s4 ,fracto-cumulus4 ,fr4 ,cu4 ,fracto-nimbus4 ,fr4 ,n4 ,fracto-/ratus4 ,fr4 ,s4 ,/ratus-cumuli=mis4 ,s4 ,cf4 ,nimbus-cumuli=mis4 ,n4 ,cf4 ,mammato-cumulus4 ,m4 ,cu4 ,dur+ our survey ( ^! gr\ps we h f\nd t "s ( !m include cl\ds ( _m %apes1 :i* mu/ be due to v div]se conditions4 ,x foll[s t if obs]vations are to be made on ! occurr5ce ( ^! special k9ds1 ) a view to arriv+ at a ?or\gh und]/&+ ( ! circum/ances to :i* !y owe _! =ms1 x becomes necess>y to devise a code ( names & symbols :]eby an int]*ange ( ideas & records may be r5d]$ possible4 ,specific names h be5 propos$ z ea* =m 0 consid]$1 & x only rema9s to sum !m up concisely4 ,subsequ5t obs]vation1 p>ticul>ly 9 o!r climates1 may %[ t fur!r additions %\ld be made2 b if ! pr9ciple ( specific names be once admitt$1 x w be easy to fill any omission4 ,,gr\p ,,cirrus4 ,"u ! g5]al head ( cirrus we h f\nd n9e di/9ct =ms-- #a4 ,cirro-nebula 7,ley7 7,plates #b & #c74 ,cirrus veil4 ,*>act]iz$ by comp>ative abs5ce ( /ructure & by ! =mation ( halo4 ,ci4 ,na4 #b4 ,cirro-filum 7,ley7 7,plate #g74 ,?read cirrus4 ,built up ( f9e long ?reads1 /raight1 curv$1 or cross+1 b free f hazy curl+ or floccul5t /ructures4 ,ci4 ,f4 #c4 ,cirrus excelsus 7,plate #e74 ,high cirrus4 ,*>act]iz$ by great altitude1 ?9ness1 irregul> bran*+ /ructure4 ,ci4 ,ex4 #d4 ,cirrus v5tosus 7,plate #f74 ,w9dy cirrus4 ,*>act]iz$ by curv+ bran*es lean+ =w>d 9 ! direction ( movem5t1 & o!r long curv+ /ream]s lagg+ beh9d & bel[4 ,fluffy p>ts are usually pres5t1 & m>k ! orig9s ( ! long curl+ fibres4 ,ci4 ,v4 #e4 ,cirrus nebulosus 7,plate #i74 ,hazy cirrus4 ,*>act]iz$ by ! abs5ce ( %>ply def9$ l9es1 fibres1 or /ream]s2 all p>ts ( ! cl\d be+ hazy1 & sugge/ive ( o!r v>ieties ( cirrus out ( focus4 ,ci4 ,neb4 #f4 ,cirrus caudatus 7,plate #h74 ,tail$ cirrus4 ,*>act]iz$ by small hazy or fluffy heads beh9d or bel[ :i* hang long /ream]s1 :i* tap] away m or less to a po9t4 ,! tails are %>ply def9$1 & s are ! edges ( ! heads4 ,ci4 ,ca4 #g4 ,cirrus vittatus 7,plates #ab & #ac74 ,ribbon cirrus4 ,*>act]iz$ by =mation 9 long b&s ( cl\d1 sometimes made ( p>allel long fibres ) cirrus haze l9k+ !m toge!r1 sometimes consi/+ ( a long bundle ( fibres1 f :i* o!rs div]ge at an angle z %[n 9 ! plate4 ,ci4 ,vt4 #h4 ,cirrus incon/ans 7,plate #aj74 ,*ange cirrus4 ,*>act]iz$ by a peculi> ragg$1 wavy appe>ance4 ,x is g5]ally only ! beg9n+ or ! end ( a mass ( cirro-/ratus or cirro-cumulus1 b occasionally x vani%es %ortly aft] its appe>ance1 )\t rea*+ ! fur!r /age4 ,ci4 ,94 #i4 ,cirrus communis 7,plate #aa74 ,type cirrus or common cirrus4 ,*>act]iz$ by %ort irregul>ly curl+ fibres collect$ toge!r 9 consid]able pat*es4 ,no def9ite arrangem5t into any ( ! =ms already describ$4 ,ci4 ,com4 ,,gr\p ,,cirro-,,/ratus4 ,"u ?is gr\p ! cl\d usually %[s "s /ructure1 be+ app>5tly built up f a mass+ toge!r ( deta*$ =ms at a common level4 ,:5 ?is is s x %\ld be describ$ by add+ ! specific "n ( ! deta*$ =m mo/ ne>ly relat$4 #a4 ,cirro-/ratus nebulosus 7,plates #c1 #d1 & #ad74 ,hazy cirro-/ratus4 ,*>act]iz$ by abs5ce ( visible /ructure4 ,ci4 ,s4 ,neb4 #b4 ,cirro-/ratus communis 7,plate #af74 ,common cirro-/ratus4 ,*>act]iz$ by ! pres5ce ( %ort curl+ fibres matt$ toge!r4 ,ci4 ,s4 ,com4 #c4 ,cirro-/ratus vittatus 7,plate #eg74 ,ribbon$ cirro-/ratus4 ,*>act]iz$ by be+ made up ( long /ripes or b&s ( cl\d4 ,ci4 ,s4 ,vt4 #d4 ,cirro-/ratus cumulosus 7,plate #ag74 ,floccul5t cirro-/ratus4 ,*>act]iz$ by an obscurely granul> /ructure4 ,ci4 ,s4 ,cu4 ,_m =ms ( cirro-/ratus are arrang$ 9 waves or ripples4 ,?is is indicat$ by atta*+ ! ^w undatus1 or wav$1 aft] ! ord9>y specific "n1 or ! lett] ,u aft] ! abbreviation4 ,,gr\p ,,cirro-,,cumulus4 ,divisible into ?ree species4 #a4 ,cirro-macula 7,ley7 7,plate #bc74 ,speckle cl\d4 ,*>act]iz$ by semi-transp>5cy1 by ! fact t ! p>ticles are frequ5tly :it] & m opaque on _! edges4 ,a pat* ( cirro-macula always looks l a ?9 %eet :i* has curdl$4 ,ci4 ,ma4 #b4 ,cirro-cumulus nebulosus 7,plates #bj & #ba74 ,hazy cirro-cumulus4 ,*>act]iz$ z r\nd$ balls ( semi-transp>5t cl\d1 b ill-def9$ & hazy4 ,no %ad[s4 ,ci4 ,cu4 ,neb4 #c4 ,cirro-cumulus 7,plates #ah & #ai74 ,*>act]iz$ z opaque r\nd$ balls cle>ly def9$1 b %[+ no %ad[s on _! "u sides4 ,ci4 ,cu4 ,com4 ,wave =ms aga9 are indicat$ by ! addition ( ! ^w undatus4 ,,gr\p ,,alto ,,cl\ds4 ,divisible into n9e species4 #a4 ,alto-/ratus4 ,high /ratus4 ,a uni=m veil ( cl\d %[+ no details ( /ructure except local v>iation 9 d5sity 9 pat*es4 ,r>ely d5se en\gh to completely hide ! sun1 or ev5 ! full moon4 ,a4 ,s4 #b4 ,alto-/ratus maculosus 7,plate #cj74 ,mack]el sky4 ,*>act]iz$ z num]\s ne>ly equal & small l5ticul> pat*es rang$ on a level & ab\t equi-di/ant f ea* o!r4 ,a4 ,s4 ,mac4 #c4 ,alto-/ratus fractus 7,plate #cd74 ,pat*es & bits ( cl\d ( irregul> %ape1 b resembl+ brok5 bits ( a level %eet4 ,a4 ,s4 ,fr4 #d4 ,alto-/rato-cumulus 7,plate #cb74 ,int]m$iate betwe5 alto-/ratus & alto-cumulus4 ,a4 ,s4 ,cu4 #e4 ,alto-cumulus in=mis 7,plate #be74 ,*>act]iz$ z m or less r\nd$ cl\dlets int]sp]s$ ) ragg$ bits ( cl\d & occasionally ) /reaks ( cirrus1 ! cl\dlets %[+ no cle>-cut outl9es1 b hav+ di/9ct %ad[s4 ,a4 ,cu4 ,94 #f4 ,alto-cumulus nebulosus 7,plate #bf74 ,hazy alto-cumulus4 ,a4 ,cu4 ,neb4 #g4 ,alto-cumulus ca/ellatus 7,plate #bh74 ,turret cl\d4 ,a high cl\d resembl+ a numb] ( tall n>r[ cumulus cl\ds on a v dim9utive scale4 ,! cl\dlets %[ di/9ct %ad[s1 are v opaque1 & _! upp] m>g9s are %>ply def9$4 ,v]tical axes long] ?an ! horizontal ones4 ,a4 ,cu4 ,ca4 #h4 ,alto-cumulus glom]atus 7,plate #bi74 ,*>act]iz$ by ! r\ndness & regul>ity ( ! cl\dlets1 :i* h %>p m>g9s1 ca/ di/9ct %ad[s1 & h _! axes ab\t equal 9 all directions4 ,a4 ,cu4 ,gl4 #i4 ,alto-cumulus communis4 ,small high cumulus ( ! ord9>y pyramidal patt]n4 ,a4 ,cu4 ,com4 #aj4 ,alto-cumulus /rati=mis 7,plate #bg74 ,flatt5$ cl\dlets ga!r+ into small deta*$ %eets4 ,a4 ,cu4 ,s4 ,l[] cl\ds4 ,,gr\p ,,/ratus4 #a4 ,/ratus communis 7,plates #cg & #da74 ,9 its mo/ typical /ate1 /ratus consi/s ( a %eet ( cl\d ( approximately uni=m ?ickness4 ,! mo/ common =m1 h[ev]1 does v>y consid]ably1 ?\gh usually d5se en\gh to hide ! sun4 ,portions ( su* a %eet w\ld take ! same specific "n1 unless ! portions are v small & ragg$1 :i* w\ld be express$ by add+ ! ^w fractus4 ,s4 ,com4 #b4 ,/ratus maculosus 7,plate #dj74 ,=m$ ei!r by ! appe>ance ( cl\d 9 lumps1 :i* are always l5ticul> 9 %ape1 & ultimately jo9 toge!r to =m a /ratus1 or by ! break up ( ! typical /ratus4 ,s4 ,mac4 #c4 ,/ratus radius 7,plate #db74 ,roll cl\d4 ,=m$ dur+ ! break up ( a l[ /ratus1 :i* sep>ates up into a numb] ( p>allel l9es ( cl\d4 ,s4 ,r4 #d4 ,/ratus l5ticul>is 7,plate #dg74 ,fall cl\d4 ,=m$ by ! collapse ( cumulus or /rato-cumulus4 ,a cl\d ( ev5+1 easily recogniz$ z l5ticul> pat*es4 ,s4 ,l4 #e4 ,/rato-cumulus 7,plates #ch & #ci74 ,a t]m appli$ to ei!r a /ratus :i* has ?ick5$ e "h & !re into cumulus1 or a numb] ( cumulus :i* h jo9$ toge!r s z to %[ a ne>ly cont9u\s common base4 ,s4 ,cu4 ,,gr\p ,,cumulus4 #a4 ,cumulus m9or 7,plate #dc74 ,small cumulus4 ,cumulus cl\ds s small z to pres5t ! appe>ance ( r\nd$ lumps1 no def9ite pyramidal =m or flatt5$ base4 ,cu4 ,mi4 #b4 ,cumulus major 7,plates #dd & #de74 ,l>ge cumulus4 ,*>act]iz$ by a flatt5$ base & r\nd$ cle>-cut upp] surfaces4 ,cu4 ,ma4 #c4 ,cumulo-nimbus 7,plates #di to #eb74 ,/orm cl\d4 ,*>act]iz$ by ! exp&$1 anvil-%ap$1 or disc-%ap$ top1 cirrify+ at its edges4 ,,g5]al ,,t]ms ,nimbus1 a t]m appli$ to a cl\d f :i* ra9 is fall+4 ,:5 ! =m ( ! cl\d is visible1 ! t]m %\ld be atta*$ to t belong+ to ! cl\d4 ,x may1 h[ev]1 be us$ z a sub/antive alone :5 !re is no?+ to %[ f :at sort ( cl\d1 or comb9ation ( cl\ds1 ! ra9 is fall+ 7,plates #ce & #cf74 ,nimbus is ei!r heavy /ratus1 massive /rato-cumulus1 or a comb9ation ( ^! ) /rati=m cl\ds above1 & possibly ragg$ masses ( fracto-cumulus bel[4 ,n4 ei!r alone or aft] ! sign ( ! cl\d4 ,fracto- is a t]m plac$ z a prefix be=e ! "n ( a cl\d to indicate t ! cl\d has ragg$ irregul> m>g9s1 z if x _h be5 m or less torn to pieces4 ,x is sometimes less awkw>d to app5d ! ^w fractus aft] ! "n ( ! cl\d4 ,a conv5i5t abbreviation w\ld be to write ,f4 aft] ! "n ( ! cl\d4 ,undatus1 or wav$1 %\ld always be add$ to ! "n ( any cl\d :i* %[s ! arrangem5t s describ$4 ,,*apt] ,,xi ,,cl\d ,,photography ,,ref]5ce has be5 made 9 ! fir/ *apt] to ! fact t ^? :o wi% to make a photographic /udy ( cl\ds mu/ foll[ a special c\rse ( proc$ure4 ,= e photographic purpose !re is "s p>ticul> process or "s special k9d ( app>atus :i* is bett] fitt$ = ! end 9 view ?an any o!r1 & half ! difficulty 9 atta9+ success is to f9d out ! be/ tools & ! be/ me?ods4 ,!re is no difficulty :atev] 9 secur+ excell5t photographs ( heavy grey cl\ds1 or ( cl\ds :i* /& out d>k aga9/ a twilight sky4 ,any cam]a & any plate c be us$1 & 9 an exp]i5c$ h& w ensure success aft] a few trials1 b except "u ^! special conditions1 cirrus1 9 all its v>ieties1 ! alto cl\ds1 & ev5 _m ( ! l[] ones1 pres5t a real difficulty due to two causes4 ,9 ! fir/ place1 !y & _! surr\nd+s are s brilliant t a v %ort exposure is suffici5t1 f> %ort] ?an w\ld be ne$$ = a sunlit l&scape2 & 9 ! second place1 ! act9ic value ( ! light !y reflect is v little great] ?an t receiv$ f ! backgr\nd ( blue sky4 ,:5 s m9ute a diff]5ce comes to be repres5t$ 9 ! mono*rome ( ! ord9>y photograph1 ! eye fails to appreciate x1 & all ! f9] details are lo/4 ,n[1 if prop] c>e is tak5 9 ! developm5t ( a negative1 satisfactory results may be atta9$ ev5 if ! exposure is twice z great1 or only half z great1 z x %\ld h be5 to get ! be/ result4 ,b if ! exposure is f\r or m times ! be/ duration1 ! negative w g5]ally yield b poor contra/s1 if any result at all c be coax$ out4 ,aga91 if ! exposure is only a qu>t] or less ( ! ideal "t1 little or no image w come out4 ,suppose1 n[1 we h a brilliant object1 & ! correct exposure = ! plate & ap]ture ( l5s employ$ %\ld be "o-fiftie? ( a second2 if we make an error ei!r 9 judg+ or 9 effect+ ! exposure1 :i* am\nts to "o tw5ty-fif? ( a second too mu*1 we get ! negative expos$ ?ree times z mu* z x %\ld be4 ,suppose1 aga91 ! object is less brilliant1 & ! correct exposure %\ld be "o-fif? ( a second1 an equal error ( "o tw5ty-fif? w make little diff]5ce4 ,b 9 photograph+ cirrus & su* cl\ds1 if we us$ ! same plates & ! same l5s ap]tures z we employ = ord9>y l&scape "w1 we %\ld want exposures ( ! ord] ( ^? giv5 by a focal plane %utt]1 & a mi/ake ei!r 9 judg+ or 9 mak+ ! exposure1 ( ev5 ! hundr$? "p ( a second1 w\ld be fatal to good results1 & w\ld probably completely spoil ! plate4 ,evid5tly "o ( our fir/ /eps mu/ be to l5g!n ! correct exposure4 ,!re are f\r ways 9 :i* ?is c be done--by us+ a sl[-act+ plate1 by less5+ ! ap]ture ( ! l5s1 by putt+ "s transp>5t scre5 9 front ( ! l5s to %ut (f "s ( ! light1 &1 f9ally1 by po9t+ ! cam]a1 n at ! cl\d itself1 b at its image 9 a black mirror4 ,( ^!1 ( c\rse ! sl[ plate & small ap]ture are ! simple/ to adopt1 & all ! cl\d /udies %[n 9 ! illu/rations to ^! pages h be5 tak5 on plates prep>$ = photo-me*anical purposes or = transp>5cies4 ,!re seems to be no?+ to *oose betwe5 ^! two br&s4 ,or?o*romatic1 iso*romatic1 d\ble-coat$1 & _m o!r special types ( plate _h previ\sly be5 tri$1 bo? ) col\r$ filt]s 9 front ( ! l5s & )\t !m1 )\t %[+ any m>k$ sup]iority ov] an ord9>y plate ( l[ rapidity4 ,at la/ ! photo-me*anical plates 7 tri$1 & ! ef=ts made to get satisfactory cl\d portraits1 :i* _h previ\sly be5 m>k$ only n[ & !n ) satisfactory results1 became uni=mly & cont9u\sly successful4 ,if ! sl[ plates are expos$ 9 ! cam]a )\t ei!r a scre5 or ! black mirror1 ! diaphragm %\ld be r$uc$ to a small size & ! exposure suitably adju/$4 ,! l5g? ( exposure may g5]ally be judg$ by look+ at ! image on ! focus+ scre51 & r$uc+ ! ap]ture until ! picture %[s its detail easily4 ,!n1 reg>d+ ! picture z t ( a sunlit sea or di/ant l&scape1 judge ! necess>y exposure by ! brightness ( ! image4 ,no def9ite rule c be giv54 ,! light v>ies enorm\sly f day to day1 & h\r to h\r1 & especially ) ! position occupi$ by ! cl\d relative to ! sun4 ,?us1 work+ ) a l5s ( six in*es focus & an ap]ture ( a qu>t] ( an in*1 ! exposure may v>y f ! quicke/ snap ( a ,?ornton-,pick>d roll] bl9d to z mu* z a qu>t] ( a second1 or ev5 m4 ,aga91 us+ a l5s ( eighte5 in*es focus & an exposure ( a fiftie? ( a second1 ! necess>y ap]ture might v>y f an eigh? ( an in* up to an in* & a half4 ,b if we suppose t we are deal+ ) an ord9>y bright summ] sky betwe5 #i a4m4 & #e p4m41 & t ! cl\ds are cirrus or cirro-cumulus1 an ap]ture ( ab\t "o ?irty-second ( ! focal l5g? w probably give "s sort ( image ) a snap-%ot exposure4 ,at fir/ ! failures w be _m1 b a little practice w soon enable v respectable pictures to be tak5 by v>y+ ei!r ! diaphragm or ! spe$ ( %utt]4 ,heavi] cl\ds ( ! alto types w ne$ r long] exposure or l>g] ap]ture4 ,! l5s may be ( any k9d1 z long z x gives a well-def9$ image1 b !re are _m advantages 9 us+ "o ( ! rectil9e> type provid$ ) an iris diaphragm4 ,a rapid l5s is n ne$$2 inde$1 x has be5 po9t$ out t sl[ness is a v great desid]atum1 & if ! cam]a is provid$ ) a rapid l5s x mu/ be ru?lessly /opp$ d[n4 ,= g5]al cl\d purposes ! be/ k9d ( l5s is a wide-angle rectil9e>1 b _m occasions w pres5t !mselves on :i* a l5s ( long] focus w be want$ 9 ord] to give m insight into ! details ( "s specially delicate cl\ds4 ,if ! l5ses are good1 & ! focus+ is accurate1 enl>gem5ts w g a long way t[>ds reveal+ ! m9ut] /ructures1 b ! results c nev] be q s well def9$ z a direct photograph 9 a long cam]a4 ,a %utt] w be ess5tial1 & x %\ld be "o :i* op5s 9 ! middle1 or :i* travels across ! l5s4 ,! %utt]s :i* are +5i\sly contriv$ to give m exposure to ! l[] "p ( ! picture ?an to its upp] "p are useless = ! purpose 9 view4 ,x %\ld h "s latitude ( exposure1 f ab\t "o-sixtie? ( a second up to a full second or m4 ,!n z to ! cam]a4 ,any light-tight cam]a w d1 &1 z ! objects w all be at a great di/ance1 x may v well be a fix$-focus "o1 or may be kept set up & fix$ 9 focus = a di/ant object4 ,if n1 on sett+ x up x %\ld be focus$ on ! horizon or mo/ di/ant object possible1 & n on ! cl\d itself4 ,z1 h[ev]1 ! cl\ds pres5t !mselves at all heights above ! horizon1 ev5 9 ! z5i?1 x becomes necess>y to h "s means ( po9t+ ! cam]a 9 su* directions4 ,to a c]ta9 ext5t ! ord9>y /& does all[ ( tilt+1 b a special support :i* w all[ ! cam]a to be fix$ firmly 9 any position is ( ! greate/ conv5i5ce4 ,if ! /udy is meant to be at all prolong$1 ! be/ plan is to make a suitable cam]a1 once = all1 :i* c be left 9 fix$ focus1 s z to be always ready1 & :i* c be direct$ ) equal ease to any "p ( ! sky1 f ! horizon to ! z5i?4 ,if x is int5d$ to use a black mirror1 !n a special m\nt becomes almo/ ess5tial4 ,_m ( ! mo/ delicate ( ! photographs reproduc$ "h h be5 tak5 ) a cam]a ( peculi> patt]n1 ! /ructure ( :i* is %[n 9 ,plate #fa4 ,! l5s is an ord9>y rapid rectil9e>1 & ! /op us$ 0 g5]ally "o-sixte5? ( ! focal l5g?4 ,! %utt] is a light slip ( alum9ium1 :i* c be drawn across f side to side at any desir$ pace4 ,! body ( ! cam]a is mahogany1 ) a bell[s "p = gett+ correct focus1 b :5 once ?is 0 obta9$ ! back 0 clamp$ to ! tail-bo>d & a little v>ni% bru%$ ov] ! clamp+ screws4 ,illu/ration3 ,plate #fa4 ,,cl\d ,,cam]a ,,= ,,/udies4 ,! cam]a sw+s on a c\ple ( screws1 :i* act z trunnions4 ,^! pass ?r\gh two upright arms1 :i* spr+ on ei!r side f ! base bo>d1 :i* is atta*$ to ! ord9>y cam]a /&4 ,?is base bo>d c be rotat$ into any horizontal position desir$1 & ! cam]a c be tilt$ ?r\gh any v]tical angle by sw++ x betwe5 ! uprights1 & c be clamp$ by tight5+ ! two trunnion screws4 ,^! screws are s plac$ on ! front ( ! cam]a t ! l5s & its atta*m5ts on ! "o side ne>ly balance ! back "p ( ! cam]a on ! o!r side1 & s less5 ! dang] ( slipp+4 ,support$ 9 front ( ! l5s by light brass-"w is ! black mirror1 made ( a v d>k glass optically work$ on ! front face4 ,x is a curi\s fact t1 al?\gh bits ( plate-glass black5$ on ! back seem to ! nak$ eye to give a s+le image ( suffici5t tru?1 if su* a mirror is plac$ 9 front ( ! cam]a ! second fa9t image =m$ by reflection f ! black5$ surface is almo/ always to be detect$4 ,moreov]1 ! l5s ) its l>ge ap]ture at once detects irregul>ities 9 ! surface ( ! glass1 :i* are q imp]ceptible ?r\gh ! n>r[ limits ( ! pupil4 ,black glass1 ) a truly work$ surface1 is ess5tial !n1 b ! surface ne$ n be ( ! high ord] ( excell5ce requir$ = mirrors us$ = telescopic "w1 s9ce ! fir/ image is n1 z a rule1 int5d$ to be highly magnifi$4 ,! mirror is held s t its surface makes an angle ( ab\t #cc degrees ) ! axis ( ! l5s1 & ! block c>ry+ %utt] & mirror c be turn$ r\nd into any position by slipp+ x r\nd ! l5s m\nt z an axis4 ,! mirror ?us always reta9s ! correct angle4 ,! action ( ! mirror is to a l>ge ext5t due to m]e dim9ution ( brightness1 b x also p>tly ext+ui%es ! blue light ( ! sky )\t ex]t+ any su* influ5ce on ! :ite light f a cl\d4 ,?is is due to ! fact t ! blue light ( ! sky is p>tly pol>iz$1 :ile t reflect$ f ! cl\d is n4 ,n[1 pol>iz$ light :i* falls ^u a black mirror held 9 a p>ticul> position is n reflect$ by x4 ,?is position dep5ds ^u v>i\s circum/ances1 b "o condition is t ! reflect$ ray mu/ make an angle ( ab\t #cc degrees ) ! surface ( ! glass4 ,! am\nt ( ! pol>iz$ compon5t ( ! blue light v>ies greatly1 b is at a maximum at all po9ts #ij degrees away f ! sun4 ,?is1 !n1 is ! be/ possible position = photograph+ a cl\d1 z ! :ole ( ?is pol>iz$ compon5t may be suppress$ by adju/+ ! mirror to ! prop] position1 & !n ! mo/ delicate cirrus fibres /& out brilliant on an almo/ black backgr\nd4 ,! black mirror c\ld ) "s advantage be replac$ by a ,nicol's prism m\nt$ betwe5 ! compon5ts ( ! l5s1 s t x c\ld be turn$ 9 any position2 b ,nicol's prisms are exp5sive1 & su* an arrangem5t w\ld co/ _m times ! sum suffici5t = an excell5t mirror1 & !n w\ld n>r[ d[n ! field ( view 9 a v inconv5i5t way4 ,) ?is app>atus exposures ( a t5? to a fif? ( a second 7 usually requir$ = high cl\ds 9 bright daylight1 :ile long] times1 up to a second1 might be requir$ "u less actively act9ic conditions4 ,! exposure hav+ be5 made1 ! next /ep is developm5t4 ,n[1 e practical photograph] has 8 own pet =mula1 8 own p>ticul> fav\rite among ! num]\s develop+ comp\nds n[ on ! m>ket4 ,x is1 !re=e1 r a ?ankless task to (f] advice z to :i* %\ld be select$4 ,9 all probability z good results may be got by o!r me?ods & o!r =mul1 & ! description :i* foll[s mu/ be und]/ood r z an acc\nt ( ! process actually adopt$1 ?an advice z to t :i* %\ld be *os54 ,! develop] us$ has be5 always pyro & ammonia1 made up 9 accordance ) ! =mula-- ,pyro #cj gra9s ,potassium metabisulphite #cj ,ammonium bromide #cj ,wat] #aj ozs4 ,b if mu* "w 0 anticipat$ ! solution 0 made up 9 a m conc5trat$ =m1 & dilut$ to ?is /r5g? ( #c gra9s ( pyro p] ounce = actual use4 ,! ammonia solution is prep>$ by mix+ #c drams ammonia =tiss4 ) #bj ozs4 ( wat]4 ,9 develop+ x is necess>y to rememb] t our object is to make ! mo/ ( a v small diff]5ce 9 effect4 ,! plate is fir/ fl[$ ov] ) a mixture ( suffici5t develop]1 ) n m ?an a qu>t] ( its bulk ( ! ammonia4 ,if ! cl\d %\ld fla% out 9 a few seconds add m ( ! pyro solution1 b unless ! exposure has be5 mu* ov]done ?is w n happ54 ,if ! image beg9s to appe> aft] f ?irty to =ty seconds x is probable t ! be/ result w be rea*$ by leav+ x alone1 b if !re is any hang+ back ( ! detail ano!r qu>t] bulk ( ammonia %\ld be put into ! glass1 ! develop] mix$ ) x1 & ! :ole return$ to ! develop+ di%4 ,if no image appe>s aft] ab\t =ty seconds1 add m ammonia z above describ$1 & leave = ano!r =ty seconds1 & s on1 until by ?is me?od ( trial ! "r quantity ( alkali = ! p>ticul> exposure has be5 asc]ta9$4 ,! developm5t mu/ nev] be hurri$1 or ! backgr\nd ( sky w black5 too soon1 & 9 "s cases x may take a qu>t] ( an h\r or m to get en\gh d5sity on ! cl\d4 ,b z a g5]al rule ! image is fully out 9 ab\t two m9utes1 & ! plate is !n wa%$ & fix$ 9 ! usual way4 ,if a black mirror is us$ !re w seldom be any necessity = int5sification1 b if n1 x may frequ5tly be requir$1 especially = ! m delicate k9ds ( cirrus4 ,inde$1 ! image may sometimes be s ?9 t ! common process ( int5sification by m]cury & ammonia does n give d5sity en\gh4 ,if t seems at all likely to be ! case1 x is wis] to use ! =mula kn[n z ,monckhov5's1 s9ce t simply adds silv] to silv] in/ead ( replac+ ! silv] image by "s o!r body1 & ! process c consequ5tly be repeat$ m ?an once1 if suffici5t d5sity is n secur$ by ! fir/ application4 ,! =mula does n seem to be v (t5 us$1 s x may be be/ to quote x4 ,a4 ,potassium bromide #ajj gra9s ,m]curic *loride #ajj ,wat] #aj ozs4 ,b4 ,potassium cyanide 7pure7 #ajj gra9s ,silv] nitrate #ajj ,wat] #aj ozs4 ,place ! wa%$ negative 9 ,a until x has gone :ite1 !n r9se x well & transf] to ,b1 9 :i* ! image turns to a velvety black4 ,aft] wa%+1 ! process c be repeat$4 ,int5sification is1 h[ev]1 only a way ( sav+ photographs :i* _c be secur$ aga94 ,if ! fir/ photograph ( a p>ticul> v>iety ( cl\d is n satisfactory1 x ought at lea/ to tell ! op]ator :]e he _h gone wrong1 & a second attempt %\ld produce a bett] result ?an any image built up by *emical action on an imp]fect base4 ,!re is no?+ novel 9 any ( ^! me?ods1 & !re is no d\bt t o!r =mul w\ld be z good2 b ! "o ?+ ess5tial is to h a develop] ^: action c be held "u control1 & to apply t develop] 9 su* a way t v consid]able ov]-exposure w n result 9 ! ru9 ( ! plate4 ,if a numb] ( photographs h be5 tak5 9 ab\t ! same "p ( ! sky1 & )9 a %ort "t ( ea* o!r1 !n ! correct proportions ( develop] & alkali w be ne>ly ! same = all1 b ! fir/ ( su* a bat* w always h to be attack$ 9 ! cauti\s /ep-by-/ep me?od4 ,pati5ce & p]sev]ance1 back$ by a /eady refusal to be disc\rag$ by ! failures :i* are at fir/ inevitable1 are z c]ta9 to be cr[n$ by success z !y are 9 o!r /udies4 ,! work]s are few1 & !re is mu* to be done2 = x is ma9ly to ^? :o w photograph ! high] cl\ds1 & s trace ! /ages ( _! gr[? & decay1 t we mu/ look = ! data :i* w enable u to solve ! problems !y pres5t1 & s enl>ge ! n>r[ b\nd>ies ( our k ( "s ( ! mo/ beautiful ?+s 9 ,nature4 ,,ref]5ces #a4 8,int]national ,atlas ( ,cl\ds0 7,atlas ,int]national des ,nuages74 ,hildebr&sson1 ,rigg5ba*1 & ,teiss]5c de ,bort4 ,p>is4 #ahif4 ,?is is ! atlas ref]r$ to 9 ! text4 ,! lett]-press is %ort1 & is repeat$ 9 ,engli%1 ,fr5*1 & ,g]man4 #b4 8,annals ( ! ,a/ronomical ,obs]vatory ( ,h>v>d ,college40 ,vol4 ,,xxx4 ,obs]vations made at ! ,blue ,hill ,meteorological ,obs]vatory4 ,"p ,,iii4 ,measurem5t ( ,cl\d ,heights & ,velocities4 ,by ,h4 ,h4 ,clayton & ,s4 ,p4 ,f]gusson4 ,"p ,,iv4 ,discussion ( ! ,cl\d ,obs]vations4 ,by ,h4 ,h4 ,clayton4 ,?is la/ gives a v concise acc\nt ( all ! diff]5t proposals :i* h be5 made = ! sy/ematic nam+ ( cl\ds4 #c4 8tudes ,int]national des ,nuages40 #ahif-ahig4 ,obs]vations et ,mesures de la ,sude4 ,i41 ,,ii4 ,publication de l',obs]vatoire ,mtorologique de l',univ]sit ,roy4 d',upsala4 ,h4 ,h4 ,hildebr&sson4 ,an acc\nt ( ! ,upsala obs]vations ref]r$ to 9 ! text4 #d4 ,qu>t]ly ,j\rnal ( ! ,royal ,meteorological ,society4 ,helm ,w9d4 ,m>riott4 #ahhf & #ahhi4 ,! ,?ickness ( ,%[] ,cl\ds4 ,clayd54 #ahhf4 ,me?ods ( ,cl\d ,measurem5t4 ,ekholm4 #ahhh4 ,cirrus ,=mation4 ,clayton4 #ahij4 ,nom5clature ( ,cl\ds4 ,hildebr&sson4 #ahhg4 ,ab]cromby4 #ahhg4 ,wilson-,b>k]4 #ahij4 ,ga/]4 #ahic4 ,scott4 #ahie4 ,a ,new ,in/rum5t = ,cl\d ,measurem5t4 ,ekholm4 #ahic4 ,calculation ( ,photographic ,cl\d ,measurem5ts4 ,olsson4 #ahid4 ,! ,motion ( ,cl\ds4 ,%aw4 #ahie4 #e4 ,reports ( ! ,briti% ,association4 ,reports ( ! ,committee on ,meteorological ,photography4 ,clayd54 #ahia to #aijj4 ,! reports = #ahif & #aijj ref] ma9ly to ! measurem5ts describ$ 9 ! text4 #f4 8,cl\dl&40 ,clem5t ,ley4 ,! "w 9 :i* ,mr4 ,ley set =? 8 propos$ s*eme4 #g4 8,a ,popul> ,treatise on ! ,w9ds40 ,f]rel4 ,n a 8popul>0 "w 9 ! usual s5se1 b conta9s lucid descriptions ( ! me*anics ( ! atmosph]e4 #h4 ,!re are _m excell5t text-books on meteorology1 all ( :i* deal m or less ) ! movem5ts ( ! atmosph]e & ! =mation ( cl\ds4 ,,index ,ab]cromby1 #aj ,aitk51 #c1 #ia ,altitude ( cl\ds1 #ai1 #adi ---- ( ra9-cl\ds1 #gf ,alto cl\ds1 #ei1 #aei ,alto-cumulus communis1 #afa ---- ca/ellatus1 #ff1 #afj ---- glom]atus1 #fg1 #afa ---- in=mis1 #fd1 #afj ---- nebulosus1 #fe1 #afj ---- /rati=mis1 #fe1 #afa ,alto-/rato-cumulus1 #gj1 #afj ,alto-/ratus maculosus1 #fh1 #afj ,asc5t ( vap\r1 #abd ,atlas1 ,int]national1 #aa ,b& cirrus1 #da ,bidwell1 ,%el=d1 #ib ,black mirror1 #ad1 #agc ,blue ,hill1 #bj1 #ach ,cam]as1 #adj1 #aga ,*ange cirrus1 #cg ---- ( velocity1 #ce ,cirri=m top ( ?und]-cl\d1 #aaj ,cirro-cumulus1 #de1 #aei ---- nebulosus1 #eb1 #aei ,cirro-filum1 #cc1 #aef ,cirro-macula1 #ec1 #aei ,cirro-nebula1 #bf1 #bg1 #aee ,cirro-/ratus1 #de1 #aeg ---- communis1 #dg1 #aeh ,cirro-/ratus cumulosus1 #dh1 #aeh ---- nebulosus1 #de1 #aeh ---- vittatus1 #aeh ,cirro-velum1 #bd ,cirrus1 #ba1 #aee ---- altitudes1 #cj1 #adi ---- communis1 #dj1 #aeg ---- caudatus1 #cd1 #aef ---- excelsus1 #ca1 #aef ---- incon/ans1 #cg1 #aeg ---- nebulosus1 #cf1 #aef ---- ripples1 #ea ---- v5tosus1 #cb1 #aef ---- vittatus1 #da1 #aef ,cl\d altitudes1 #adi ---- nuclei1 #c ---- photography1 #ag1 #afe ,cond5sation1 #ic ,cool+ by contact1 #hi ---- by expansion1 #ib ---- by mixture1 #ij ---- by radiation1 #hh ,developm5t1 #age ,diff]5tial curr5ts1 #acc ,diffraction1 #fc ,dim5sions ( cl\ds1 #aab ,dry fog1 #gc ,equilibrium1 /able & un/able1 #ajf ,exet] measurem5ts1 #acg ,exposure1 #afg ,fall cl\d1 #ha1 #hh ,false cirrus1 #aaj ,fog p>ticles1 #fj ,fracto1 #afd ,gravitation1 #d ,great waves1 #abi ,halos1 #ba1 #bb1 #bc ,heat cumulus1 #he ---- ?und]/orms1 #ajg ,hildebr&sson1 #aj ,ho> fro/1 #fj ,h[>d1 ,luke1 #i1 #aj ,int5sification1 #agg ,int]convection1 #abe ,int]national ,code1 #aa ---- ,committee1 #aj ---- ,sy/em1 #ab1 #ga ,ions z nuclei1 #ib ,irregul>ities ( gr\nd1 #ci ,kepl]1 #d ,kew1 #ach ,ley1 ,clem5t1 #bd1 #cd1 #ee ,lightn+1 #aad ,l[] cl\ds1 #ga ,mammato-cumulus1 #ii ,meteorological ,conf]5ce1 #i ,me?ods ( comput+ altitudes1 #adc ,muni*1 #i ,newton1 #d ,nimbus1 #gd1 #afc ,nuclei1 #ib ,photographic me?ods1 #ag1 #afe ,ra9-cl\ds1 altitude1 #gf ----1 ?ickness1 #ha ,rate ( fall ( temp]ature1 #id ,s&/orms1 #aag ,saturation1 #hg ,scot* mi/1 #gc ,sl[ plates1 #afg ,spread ( cond5sation1 #eg ,/able equilibrium1 #ajf ,/rato-cumulus1 #gg ,/ratus1 #gb1 #afa ---- communis1 #gg1 #afa ---- l5ticul>is1 #hj1 #ih1 #afb ---- maculosus1 #gh1 #afb ---- radius1 #gi1 #afb ,subsid5ce ( cl\d top1 #aaa ,surfusion1 #fa ,sw+ /&1 #aga ,turret$ cl\d1 #ff ,ty*o ,brahe1 #d ,types1 #h ,umbra & p5umbra1 #bi ,undatus1 #afd ,unsaturat$ cl\d1 #aja ,upsala1 #aj1 #ach ,wave cl\ds1 #dg1 #aai1 #acc ,wilson1 ,c4 ,t4 ,r41 #ib ,,! ,,end ,,pr9t$ ,,by ,,william ,,cl[es ,,& ,,sons1 ,,limit$1 ,,london ,,& ,,beccles4 99 99 99 99 99 ,transcrib]'s ,note ,v>iations 9 hyph5ation 7i4e4 ?und]/orm & ?und]-/orm7 h be5 reta9$4 ,! foll[+ app>5t typographical errors 7 correct$3 ,page #aga1 8focuss$0 *ang$ to 8focus$40 7x %\ld be focus$ on ! horizon7 ,page #agc1 8ap]ature0 *ang$ to 8ap]ture40 7! l5s ) its l>ge ap]ture7