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Lorsqua la document ast trap grand pour *tra raproduit an un saul clich*. il ast film* A partir da I'angia supiriaur gaucha. da gaucha A droita, at da haut an bas. an pranant la nombra d'imagaa n^cassaira. Las diagrammas suivants illustrant la m«thoda. 1 2 3 1 2 3 4 5 6 hrr^r^ II." \^ ' THE NATURE OF A SUPPOSED VARIATION IN THE SOLAR ROTATION IN 1915 "a KM I'll I DiirUN [ JA\ 1 -^ Kr;.tint,'.l i " P•'^ >" ' I III \~iK-.ii'ii.-l' M J"' ^■■^' ^' '■'" 1, ,;l.l''..!l It. 'in \l.\ III \.. , ( 1, lot I't I.il ■ s^Sii^^m^:r,^sm^^^^ijmm'^^^^^^ ,'■ f: ■ -1.. 'v 1 ,■':' ' ' ■" 1* i ' ■ / « ■v «S;^'''-. r. ' -.• ' . i- .- '■ ' . K*«^' ?-■ .'*■'. , ■ t_ I ;rf' "' ^ ■•! '>• -,,, -^ v^;:"v ■I lUK x.vrrKK OF A SI iMM)si:i) \ AKi.viniN i\ im: SOLAR KolAlloN IN i.n^ U\ KM.I'II I, IM I IKS In ;i l)riif note' ividtiuc \va> |)r(>inti(l wliiili imlit.itdl ili it the C(inilu>ion' drawn hy Mr. II. II. iMa>kilt 'tliat the >un. ■hiriiiu Ihf suninu-r i>l 11)15. undrrwint a ivilic variation in it~ rotation rate of 0.15 km .... loinpktol in al>out .1 month," \\a> not jii.'^tififd, ant! that this variation in ^luctro-ioiiic nua^urcmcnt^ of thi- vi'loiitv of rotation of the svm's e<|uatoriai linil» mij-lu Ik- due to ihan>;e> in terrestrial ha/e. Mr IMa>ketl ha> critiei/ed' this e.\j)lanation without testing; my su),'^;e>tion tliat renua-ure ments or an analvsis of old measurement> sliould >how ion anount of he presence of blended sjiei truni of ha/e in the ol)r.er\ ation■^ in (jue>tion) smaller di-plaeement> of weak than of ^troni; >i)eitrvim lines, partieularl) on the day- when the lowe-t value- of the rate of rotation were obtained, i.e.. on the day- 01 ^jreate-t ha/ine-s. In what follows new e\ idinee eonl'irmini; this e\i)laiiation i- i^ivi 11 alon^ with an eku illation of the eritiu-m-. whieh .ire rel'e d to hy their numlxrs. 1. I'rom a lonsiderahU numiier of oh-ervations with respei t to ha/e Mr. I'laskett selected three of my oh-ervation-. implyiui; that these were all I had made, lie plaee- the-e oh-ervation- of obviously ehanj;ed eondition- be-ide hi> mea-ureimnts of i)lates made >ome hours pre\'ou,-ly, implyinj; in the wonls "low" and "high" that the ha/e e.xplanation has been eontradii ted. tlui-: During llic iHritiil umler niri-iiliratioii, ii.iiiuly Jiiiu' ji lo .\u(;ii-t ifi, beLury nuide three ciitrie- in the iil)serv.ilii)ii Imuk uilli relirciue In li.i/e; June -M, "HriKht" I'" 1 'H 1 (l<>«^ July II, "Wry hazy" I' 1 '(7 ^ 'hinh) .\uKiist i(). ■"Hrinht, some walirva|«)r ha/i" l' i 077 (hiK'h) ' A^lrofiliysii.il Jiuiriuil. 44, it('a he >l)(iiil follows hi> own ol)MT\ation-- with nfiTcmc to lia/i' and the ri>|H'ttivi' \aiiiis of liu- viloiity of rotation, inulin); in aironlanci- with tlu' lia/.f t-xplanation that low \aluis of the inrasurrnuiits of >olar rotation arc as>oi iatcd with ha/c and hi^;htr vaiiu-s with "no ha/r." thu>: \ in kn( i-^T *#■( Juiif .'J, ■■ H. < 4, A lilllr li;i/i mar >un" i S46 July 4. " H. t 4. Ilazf" 1 .Hijs July :o. " H, 4. No ha/c " .• ojO July .',(. ■■ \\. 4 5. I'i)>ili\tly iid lia/o" .• cx)< .\uKu>l 1(1, '• |{. 4, I'ratliially lillli' i>r no lia/c" 1 cj;; That hi- comiiuiti'd ;in error in sfltin;.' hi> mrasuri's of rotation ovrr against my ri'iorii> of rlianncd londitions inadi- latir in tlu- day is a|»|)arfnt from a con'>ilanation. IMtl.I, 1 i I'l v-kj rr XnU H\ l»\n Tiirc Hrin(ilni-»s km 1 tnu- HrichI t)t'-> A Km Junt- :i JuU 1 1 ^ i^ S 00 1 I tjll 10 1 ■•< 10 i.H Hriht ''oO 1 007 7 00 7 ly I, 'Ihi-n h.i/cil u|t" I u:=; 'J .'0 10 i^H \tr\ ha/v. tirru". .linui- ' ^•y.iO I iM I r \: II 1>J Hrik'tit' r. -.till hiizv s' 00 I So^ Augu-t !'• S to 1 I I'J 4. ■pruttHallv lilllf I U77 1 2 47 l-i M liri(.'ht . Htime vKalff- i ur ntr ha/.t' i \aiKrr hii/f 5tKX3 I yig It is sinnilkant that on Jmu' ;i. when lu' ohtainrd ;; valui- of 1 .1)1 1 kill piTsw. oiu'of till- low vahu's in thr"cyciic variati ins" 1 ohtaini'd a kw hours aftiTward j.007 km [kt si'i., a valuf about i-ijual to thi- maximum values in the supjxiscd variation. I'mh- ahly the record "Hrifjht" indicated a {greater hrij^htness than "H. 4" of that date. On account of the haze which developed after I'laskett's plates were taken on July 1 1 and which remained throuf^hout my observa- tions these l.ilttr (14 ])lates at X 5000 and 7 at X 5600' yield decidedlv lower values than his. (»V so/. lA' Hi>l \l l<>\ / V ;.;;,- M)7 (In Annual I'l, prill). il>l\ mi .nunint nl llic |iri>cni< mI "^ninr watiT vapor ha/c," my i>l>-.ir\alinii> •■• plati> at X ;'kx:i' yiclil a valiU' .' piT (tilt lower than i\i>. All tluM- riMill^ are aMrihaMc to ilitTtnni dc^'nt- oi ha/iiir-> in aiTorilaiur with the n.onl^. rurlhrr .l.laiU art n'wiu in lahlr II. kinanlin^; his rrconi ot l)ri«hliu-> Mr. IMa>kiti ^lati»; 5 ri'prtsitils ;i vrry lirilliaiit 'lay rare in (>ll.i«a. •l ripris«'nt> a liri^tit ila> imrmal nliv r\ii)i; "I'.iilur ( rfpriM'iil:. a il.iy -li^rlilly liaell on. taili 'ory. presuniint; that >iu h .lil'lVrent (le;;ree^ of hri^h' • -- pi>-tulaie ilil' rent «le>;rees of ha/i 'ime our reioriK of M' a ount was kejit >urini; tlie iia^t two he li" II the spei K ;(KX3 'lii' oriler, ;roj,'rapli. -■lit ■»ii>i. r>uaily l'lale> taken oti i- a nii^re.elinj; oi -ki ti were taki n ness. On no (la\- was h e aloeii' \' tt ohservinj; eomlitions \' .< ineompi ii in of liie strentith of the >i)eetrum oi lia/i years on no ilay has it heen iin|)o-.>il>'' -. trum from ha/e just out>iile the ^.ilar inv jm auto lollimatinK l^im-Siii'l '^\ o.o; mm, fed l>y the 4; em eoneave mirror the line> are distinetly vi-ihie. A^.iin iu- - (lays ha/.ier than ,^.5 were not mea-ured. the record, as 14 of the 1 1 1 plates mea>ured at recorded hri^ihtness •• ;. " IMaskett also assert. ■-: "'Ihe record, if it n vtl that in j;eneral hijih valui'> were ohtained "ii \. values on hri^jhter days, in diri'ct contraditti statement." That this miulusion i^ faliaiious is -een Irm (omplete >ummary of hi> ohMTvation- ithou;,'h it i have the adnii^Mon that tliere were ha/,y day>i. I ments of the 1 1 1 plates may he grouped with re>,'ard 1 "ahove normal," "normal," and "iHiow normal," u-i' delinition of a normal dav ^ivi'n above: - . . . iow '>el ur\ - K) plates. It. " ^" aiiil " .\ 5," me.iii viloiity 50 plates, B. "4. ' i.e., ■norm.il." iiu-.iii velmily 4-' plates. H. " i 4" ami " i," nu-.iii vtloiity. . iqK AM/./7/ I: PeH KY It may \h- iiotid that 4.' of llu' 1 1 1 platts \s\u- madi 1 lay ,)|' l)ri),'htnf» hi low 'nomial." i.e., on days of ha/i- prisunial)l\ .../ovf normal Also 4^ of ilu' in iilalc^ wirr taki-n at l>ri^;ht noses riTonlcd as "4 5" ami 's 4- terms >o vamu- as to indiiatr tiilu-r unccriainty in tin- rstimati-s of hrinhtmss or varying tU-gnrs of ha/imss. Winn su( h una-rtainty in tin- riiords ixisls. tin- supiwirt wliiili tilt nummary j;ivis to tlu- ha/i- txplanation is as sati>fa(toiy as can hi- i-xpccted. 'Ihr K) plates of the first Kfup includi 15 at "H. 4 5," moan velocity i .()!S()kni per sec, and 4 at " H, 5," mean velocity r.oiijkm per sec. The accuracy of this hifjh record of hri>;htness (the only one of "H. 5") may l)e questioned, as it was the first made (on July ()) l>y I'la^ki It after the three mirrors of the coelostat telescope had been freshly plated (July 7), and it is prohalde that the much hri^hter ima^c of the sun produced as a conseijuence jjave the ohstrver an exai;f;erated impression of the clearness of the sky. If the day were in nality ha/y, then the i)lat' . should satisfy the criterion for blended sju-ctrum of ha/e. I have measured the 4 l)lates and find a dilTerenceof 0.054 km per sec. hetveen the values of the \elocity of rotation cleduced from nrou])s of weak and of stront; .■spectrum lines a dilTerence which may be interprete reasonable to sup])ose that record "H, 5" for the bri>;htness duriiif? his observations on July is too hi^h relative to the other ncords and for the lause indicated. I'rom the foreKoiiiL summary of his records and measurements it is (|uite evident that the following statement which appears in his original paper \\i. 147) is not justified: "Observations were never made exce|)t on days that were free from ha/,e." 2. Mr. riaskett states in his note: "DeLury bases his di.scus- .sion on plates made on two dates, June 24 and July 20, which are described as 'Ha/.y' and "Hright," apparently from memory, as it is not so recorded in the observation book." On June 24 he recorded "'H, .V4, ;i little hii/.e near sun," at 7:40.\.M. before his two observations, and "B, 3-4" at o:io.\.M. after these ob.servations. Memory need not be appealed to for the description "Ha/y" for these conditions. On July 20 he recorded i O.V .NO/ lA' KnI \l lii\ / V /u;-; UXI I ■■Hri^'lil 141 " tli.-fc linio lor inlirv.ilN ^:.<; j-.oS. S:o^ •*<■. ."l and .S:^S S:.}^ \ m.; aUo, " \i> li;i/c " I iiliNir\t'> -.\ 10: 1 1 AM, ,illiiwii>n tlu-^f rtiunl-- In -IawA until .1 » li.m^;r ok urn. i ju>t al'tiT llii>. wluM I rrmnUd llril il • .loinlrtl up " Hi luc ilic linii ■'Hritilit" i> ju-tilui! "4" rtpriMniint:. .uionliim to him, a "l)ri>;lit flaw normal olxcrxiii^; we; t her." In till' lollowinn two ini>^l,itt nicnt^ arc m.ulf; 'iin June .<4 Di'Lury- plalis \v»t»' takiii lhrou>;h cIoikIs whos,- pn^mff lir notis in till- ol)strvalion luiok. wlu-rras the writir'^ plat" -. tximNiil oariiiT, \v(Tf takin with a rUr • sky." On this dali- my mii^iiml piatis at X4-'io wiTi- takrn at 10: iS 10:54 \.m . ami ihoii'^'h I niadf olisi'ivations up to noon I did not ntord "iloudid up ' until afttrnoon. Ahsohitily no miiitioii of rloiids was made l)tlor( noon, so that the siatinu-nt that m\' "plati-s wi'i> 'aki'n tlirou;;h c'it)uds" is not corri'ct. Also, as shown al)o\c, on June -'4 he dfscrilK'y iiisowu dei'mition i inoim t. In addition to tlie dirert statement ol" the re' r - as to the relative hrightness of the two -,elet ted dates, June . ,,i I Jul :o. rem. asurementsof my plalesat X i-' ;o and mea-urenun • liy n If of hi> jilates at X ,>i)00 yield further eontirmation of mv e\])lan,ition, for on June .'4 the dilYerenees ln-tween jjroups of measurements of weak and strong lines are j;reater than for tlie same lines on Julv :o. pointing; to a greater dej;ri-e of ha/ine-s on llie former dale i- i 1 1 I *ji.' r, i:;i July 1 1 10 J S 10 s"* \rr\ h.i/\ • I st>: J O."* 1 11: 17 II IQ Hri/htcr. >iitl h. :i;:v 7 (f-K) \ T 1, I 7'^i ^ > 1 ■*:'■ 'J -JXK July 20 6 ; J I So? Q > I t' II 1. im h.uf I 1 1 \ 7 I -i-H i 1 1 i ■-.'.■ •J .it Aue I'' i.v J7 i: w h.izc .il**»r • ;'KX) I ( 1 ') J <. I I •i','1 xyj Tahle II gi\es in di-tail the new measurements disc u>-t'd aliove. 'I"hey are all in harmony with [he ha/e (Xplaiiation. ( M\ 14 plates 20O RM.I'II /•:. IhlARY at X 5<)00, July ii, yifldi'd a vi^Iocity of — o.ooO km jK-r sec. for tlio nu-aiis of 4 atmospheric lim-s, showing that little error need l)e feared when the proper precautions in focusinfi the plate and in illuminatiii),' the j;ratinj{ evenly are taken.) Ki'j^ardin^ the jxissihility of errors of measurement in the results j;i\en in my note Mr. Plaskett says: "The dilViculties of measure- ment of hro.hl lines increase the errors and chances of preposses- sions, espicially with an observer whose last published measures show a probable error for even well-detined lines of o.c.km, i.e., of the same order as the dilTerences measured." 'I'here are no "chances of prepossessions," for in all of my spectroscopic measurements there is used a movable mask," which, l)y permittinj; only one strij) of spectrum to be seen at a time, keeps hidden not only the maj^nitude but also the direction of displace- ment of the spectrum lints beinjj measured. In the series referred to the averaj^e probable error was 0.052 km per sec. (not 0.06), and in tlii:^ \lar liiu'> un 1 1 1 platen, whii li wluti ri'pratfd yidtli-d an aviTajjc (lii'l'irri\< f lutwciii llif iman> m 0.055 km I"''' ^^'*'' "' wlii'li (lit"UT(iui> iS I'Xticdid 0.100 km |)ii sec. and () havr a mean of o. 1 5J km piT sit. of the ^ann- ma'^Miiludt as till- ■"ivclii- variation of o. 15 km per sci."' 'I'hf dilTcrcnci's diTivi-uremenl>' al X 5:00 to those of other lines at X 4J,^o without ])re\iou>ly comparing the extent of the chanfje in character of the two sets of lino in pa^in;; from the center of the solar disk to the iimhs): The measures show evideiue, adDnliiij; to ihe iritirion oi v.iryiii^: viloi ilv for (iilTerenl line intensity, of about S [kt cent haze. I'his. cm his ou n h\ |iiii h esis, should prixluii' ahout an S [ht cent (lilTtrciuc in velocity on tin- two dales. The (lilTereme in mean veltHity is ailually u |ht unl, h.iviii>r a 4 |HT cent change in velocity to lie accounted lor. ,v The arguments as to the dirfereiices in vahu- of the rotation for low sun and sii<;htly hij^her sun are hasi'd on "■ mi-a^jer and iiii on elusive" data, and the (juantitiis derive;e >ervation>. No such measurements couhl pos-ihly ca>t douht on the ha/e explanation unless at the same time contradictory e\ ideiK r of the chanj;es in haze were obtained by other reliable means. It may be said, in conclusion, that the facts presented above make the claim that the sun"s rate of rotation varied in i()i5 seem very unreasonable. All others who have made spectroMojiii investigations of the solar rotation have found varieiv in thiir measures", and some have suggested the possibility that the rate ' .{ilrop/iy^iiiil Joiiriitil, 44, 1S4, loi'i. 202 KM. I'll /•:. Dh.l.l RY varied. I'K-- ^- ■'^- Vouii};,' Halm.' Kvorshetl and Royds', St. John, Adams, and Wan-.' However, Halm'.s low values in iqo2 iqo.^ can i)e readily accounted for hy the haziness produced by the volcanoes in the West Indies in 1902. which caused a marked lessening in the values of solar radiaticm. The low values obtained in 1912- 1913 by livershed and Royds may have been due to the Katmai eruption in June 1912, which also caused a great lessening in the measures of solar radiation. The low values of rotation obtained at Mount Wilson and ( )ttawa in i c) 1 5 also seem to synchronize with low values of radiati(m. i.e., it may be presumed, with high values of haziness. Ajxirt trom haze \arious instrumental and physical causes produce variations in the measurements of solar rotatiim. When the effects of all known causes (haze, local convections in the sun, errors of measurement, etc.)^ are eliminated or accounted for, it probably will be ])ossible to assert that the rate of the sun"s rotation does not ap]ireciably vary. The foregoing may be summarized briefly as follows: 1. The arguments which Mr. H. H. Plaskett advances (in his note critic! ' my e.\i)lanation of his observations of a supposed "cvclic variation" in the sun's rate of rotation in 19 1.^, iis due to variations in terrestrial haze) are based on fallacious use, or inaccu- rate statement, of the records and the measurements. 2. A synopsis of Mr. Plaskett's record of observations and measurements of the solar rotation supports the conclusion that in general high values of the rotation were obtained during brighter conditions and low values during hazier ccmditions. V Measurements of Mr. Plaskelt's plates, as well as of mine, satisfy the criterion of blended s])ectrum of haze in agreement with the record of observational conditions. 4. 'l"he knoxi'n terrestrial sources of blended spectrum offer a reasonalile e.\i)lanation of the supposed variation in rotation, so ' ///(' Sun (!■'*•'*-'. P- 'oo- ' TriiiisiUlioiis of I lie Koyal Sociily of Edhibiirgh. 41, .Si). 1004; anil .1 ^Iroiiomisilif Xtiihriililiii, 173, 2H7, iQofj. > Mo,,, Illy .Xoliics, ij, 554, KMi- *Pol>iiliir .l>lroiion}y, 13, 041, U)I5- 5 hil.ury, Aslropliysicil Journal. 44, 17.S, iqiO. O.V Sor.AK KOIMIOX l\ /y/? 203 that it i> unnuccssary to employ the liyf>ntliiii<,il ilcmriit ol nn L'xphination, which sup))()si's an inti-qilant'tary or solar >ovirit.' of blended spectrum. 5. At i)resent there is no sound reaxm lor l)elitvinj; that the rate of the sun's rotation is variable. I wish here to thank the director. Dr. Klot/., lor his approval of the publication of this note. Soi.AR I'liYsu s Division I)i)MlNfOX OllSKRVATDkY, OTTAWA May KjiS