Rappel de votre demande:

Format de téléchargement: : Texte

Vues 1 à 28 sur 28

Nombre de pages: 28

Notice complète:

Titre : Spectroscopic observation of the sun : N2, 3, 4, 5 / J. Norman Lockyer

Auteur : Lockyer, Joseph Norman. Auteur du texte

Éditeur : [Taylor and Francis] (London)

Date d'édition : 1869

Sujet : Spectre solaire

Notice du catalogue : http://catalogue.bnf.fr/ark:/12148/cb37298671n

Type : monographie imprimée

Langue : anglais

Format : 1 vol. ([ca 330 p.]) ; in-8

Format : Nombre total de vues : 28

Description : Collection numérique : Originaux conservés à la Bibliothèque de l'École polytechnique

Droits : Consultable en ligne

Droits : Public domain

Identifiant : ark:/12148/bpt6k949724

Source : Bibliothèque nationale de France

Conservation numérique : Bibliothèque nationale de France

Date de mise en ligne : 15/10/2007

Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour ce document est de 0%.

f7~! PROCEEDINUS OP THE ROYAL So(;H.:TV, No. 106, 86!).]

Thé readmg of Mr. Lu.kycr's Pa~r, Spcotrosco~c Ob~L-vat.i.m thé ~n, '). !L/' wns rcsumcd and concludcd.

(AL.stmct.)

THF author, after referring to bis inen'eetual atternpts since 18GG to observe the spectrum of thé pronnnences ~-ith an instrument oi smaU dise-sive powers, gave an accent of thé dclays .-h~ch had nnpedcd tlie onstruction of a larger on. (thc funds for which were supphed by thé ~r..nent-Gra.t Cun~ittee ea~.n 18o7),in order that the cou~dence in time between lus resuks and those obtamcJ by the Ind.an ob~ervers might not be nusinterpreted. t Duta'ds are given of the obsu-~tions made by the new instrumen ~hich ~ce.vedh~ ou ~.thcf October. Thèse obser.aUons u.ctude thé di.co.'e~ and ex~ct detenninaHon of thé lines, of thé pronunencesoectrum on the 20th of October, aud of the fact that the prominences are merely loc~ agrégations of a gaseoas médium whieh entirely envelopes the sun Thé term C'A~ is suggested for this envelope, in order to distinguish it from the cool absorbing atmosphère on the one hnnd, and from the ~h.tc light-giving photosphère on thé other. Thé possibility of variations in thé thickness of this envelope is snggested, and thé phenomena presented by the star in Corona are referred to.

It is statcd that. under proper instrumental and at.nosphenc cond~nons, thé snectnim of thé chromosphere is ah.ays visible in every part of the snn's ncriphery its height,and thé dimensions and shapes ofseveral prominences, obscrvcd at diuc.-cnt times, are given in the paper. One prominence hl'~h, was observed.on thé 20th Octoher.

~Two of thé lincs correspond ~Ith Fraunhofcr's C and F another lies 8° or 9° (of Kirchhorrs scah.) from D towards E. There is another br~ght Une which occasionaUy makcs its appcarance near (~ but shghtiy less re,n.~ible than that H' ît is rpmnrkc..I thnt thé line near I) bas no corre.ponding line ordinarUy visible in thé solar spcctrn.n. Ti.c aathor bas been tpd hv bis observations to ascrihe grcnt variation nt brdhancy to thé

)iucs. Un thc .)th <)t'N<n'onbcr a pronnncnce was obscrvcd in which ttic action \vas cvidcntty very intense and un this occasion t!)e light and coluur ufthc hm' nt F ~'t't'c must vivid. This was notobservcd n!l along the line visible ut thc <d ot' vicw oi' thc inst.rmuuut, but oniy at certain parts of the line \vhich appcared tu \vidcn ont.

Thé tatthur points out thut thchne F invat'iably expands (that the bnnd of i'~ht gets \Yi<)er and wider) as thé sun is appronciied, and that thc C line nnd thé I) line do uot and hc cn!:u'gcs npon the importance ofthis tact, taken in c'oum'xiuti \vith ~hc rcscm'che~ of Plucker, HiLtorf.andFranMaud on thé spcctt'um ot'hydt'(.'n--i:tati)!g at thé same timethathcisengagcd in re~earches un gaseuns spech'a which, it is possible, will enable us to det~nttine thé température and pressure at the surfaces of the chromosphere, aud t:r) ~i\'e a fuH expianation of thc varions colours of thé prommences w!)ich hâve ))cen obscrved at digèrent times.

T!)c paj~'t' jdso refers to certain bright régions in the sohu' speetrum Itsetf.

Evidence is addnccd t.o shu\ that possibty a chromosphere is, under certain cuuditi<jns~ a t'c~n.u' part of sttn'.t.'cunutny and thé outbm'st uf the star in (.'urona is <;spc('ia!!v' dwtt npuu.

[F/'O~ FKOCKMniNCS 0F T)!K ROYAL Soc-~TY, No. 110, 1869.J

SFECTROSCOPIC OBSERVATIONS 0F THE SUN.–No. 111.

NORMAN LOCKYHR, F.tLA.S.

J.

SîN(;K my second pappr undcr tbc abovc title was eommnnicntcd to thc Royal Society, the wcatherhas been unfnvonrable to o))scrvatory work to an almust unprccedented degrec and, as a conséquence, thc number of observations 1 hâve been enabicd to rnake during thé last four months is very nuich smaUer than 1 had hopcd it would be.

Fortunately, l~wever, thc time has not been wholly lost in conséquence of the weather for, by thé kmdness of Dr. FranMand, 1 hâve hccn able in the intérim to farniharixe myself at thé Royal Collège of Chemistry with thé spcctra of gases and vapours under prcviousiy untried conditions, and, in addition to thé results aiready commnnicated to thc Roya! Society by Dr. Frankiand and mysel~, thé expérience 1 have gaincd at thé College of Chcmistry bas guided me greatly in my observations at thé télescope. tn my former paper it wns stated that a ditigent search after thé known third line of hydrogen in the spectrum of thé chromosphere had not met with success. AVhen, howevcr, Dr. Frankiand and mysdfhad deterrnined that thé pressure in thé chromosphere even was small, and that thé widening out of thé hydrogen lines was due in thé main, if not entirely, to pressure, 1 determined to seek for it agfun under bctter atmospheric conditions and 1 succccdcd after some failurcs. Thé position of this third line is at 279H of Kh-chboiTs scale. It is gencrally cxeessively faint, and much more care is rcquired to sec it than is necessary in thé case of thé other lines the least baxe in thé sky pnts it out altogether.

Renée, then, with thé exception of thc bright yellow line, the observcd spcctra of the promincnces and of thé chromosphere correspond exactly with thé spectrnm of hydrogen nnder different conditions of pressure-a tact not only important in itself, but as pointing to what may be hoped for in thé future.

With regard to the yellow line which Dr. Frankiand and myself have stated may possibly be due to thé radiation of a gréât thickness of hydrogen, it becamc a matter of importance to détermine whether, hkc thé red and grccnlincs (0 & F), it couldbeseen extending on to thé hmb. 1 have ïMt observed this it bas aiways in my instrument appeared as a very fine sharp line resting absolutely on t!te solar spectrum, nnd never encroacinng on it.

Dr. Frankiand and myself hâve pointed out that, although the chromosphère nnd thé prominences give out thé spectrum of hydrogen, it does not follow that they are composed merely of that substance supposing others to he mixed up with hydrogen, we might présume that they would be indicatcd by thcir selective absorption near thc sun's limb. In this case tlie spcctrum of the limb would contain additional Fraunhofcr Unes. 1 hâve pnrsued this investigation to some extent, with, at présent, négative results but 1 find that spécial instrumental appliances are necessary to settle thé question, and these are now being constructed.

If we assume, as aiready suggested by Dr. Frankiand and myself that no other extensive atmosphère besides thé chromosphere overlies thé photosphere, thé darkening of thé limb being due to thé général absorption of thc chromosphere, it will follow

I. That an additional selective absorption near thé lirnb is extremely probable.

II. That thé hydrogen Frannhofer lines indicating thé absorption of the outer shell of thé chromosphere will vary somewlmt in thickness this 1 find to be thé case to a certain extent.

III. That it is uot probable that the prominences will be visible on thc sun's disk.

In connexion with thé probable chromospheric darkening of thé limb, an observation of a spot on February 20th is of importance. Thé spot ohserved \vas near tbc limb, and thé absorption was much greater than auytbing 1 had seen bcfore so great, in tact, was thé ~c~ absorption, that thé several lines could only be disti~1gnisI~ed with dimculty, except in thé very brightest région. 1 ascribe this to thé greater length of thé absorbing médium in thé spot itself in thé line of sight, \vl)en the spot is observed near the limb, than when it is observed in thé centre of the diskanother indication of thé grcat gcne~a~ nbsorbing power of a comparatively thin layer, on rays passilg throngh it obliquely.

1 now corne to the sélective absorption in a spot. 1 hâve commenccd a map of the spot-spectrum, which, howcver, will require some time to complète. In thé iiitei-ini, 1 may state that thé rcsult of my work np to the present time ill this direction bas been to add magnésium nnd hariurn to thé matcrial (sodium) to which 1 referred in my paper in 186o, No. I. of tlie present series and 1 no longer regard a spot simply as a cavity, but as a place in which principally thé vapeurs of sodium, barium, and magnésium (owing to a downrush) occupy a lower position than they do ordinarily in thé pliotosphcrc.

1 do not make this assertion merely on thé strength of the lines observed to be thickest in thé spot-spectrum, but also upon thé following observations on thé chromosphere made on thé 21st and 2Sth ultimo. On both these days the brilliancy of the F line taught me that something unnsual was going on so 1 swept along thé spectrum to sec if any matcrials were being injected into tlie chromosphere.

On thé 21st 1 canght a trace of magnésium but it was !ate in the d~y, and 1 was compelled to cease observing by honses hiding the snn. Ou the 28th 1 was more fortunate. If anything, t!tc évidences of intense action were stronger than on thé 2)st, and after one giance at thé F Une 1 turncd at once to thé magnésium hnes. 1 sa\v them appearing sliort and faint at the base of thc chrornosphcre. Mv work on thé spots led me t.o imagine that 1 shon!d fmd sodium-vapuur associated with thé magnesinm and on tm'ning fron to D 1 fonnd this to he tlie case. 1 afterwat'ds reversed barinm in the same way. Thé spcctrnm of ~e chromosphcrc seemed to bc fnU of lines, and 1 do not think thé three substances J Iiave named aceounted for aU of them. Thé observation was one of excessive dchcacy, as thé lines werc short and very </<?!. Tl)e promnience was a smati one, about twice thé nsuat heigbt of thé chromosphece but thé hydrogen hues towcred high abovc those due to thé nc\v)y injeeted matcrifds. Thé lines of magnésium cxtcnded perl)aps one-sixth of t.hc height of tlie F line, barium a little less, and sodium least ofall.

We hâve, then, thé following tacts

I. Thé Unes of sodium, magnésium, and barium, when ohserved in a spot, are thickcr than their usual Fraunhofcr lines.

II. Tito Unes of sodium, maa;nestum, and barium, \vhen observed in thu chromosphere, are thinner than their usual Frauuhofer lincs. A series of experiments bcaring upon thèse observations is now l!i

progress at the College of Chemistry, and wiil form thé subject of a communication from Dr. Frankiand and myself. 1 may at once, however, remark that wc have here additional évidence of a fact 1 asscrtcd in 18C5 on tclcscopic evidence-the fact, narnely, that a spot is thc seat of a downrush, a downrush to a région, as we now know, \vhere the sélective absorption of thé upper strata is different from what it would be (and, indecd, is eisewhere) at a higher level.

Messrs. De La Rne, Stewart, and Loewy, who brought forward thé theory ofa downrush about thé same time as my observations were made in 1865, at once suggested as one advantage of this explanation that all thé gradations of darkness, from thé facalec to thé central umbra, are thus supposcd to be duc to thé same omsc, namely, thé présence to Il greater or less extent of a relatively coolcr ahsorbing atmospliere. This 1 think is now spectroscopicatly estahiished we hâve, in fact, two causes for thé darl\emng of a spot

I. Thé général absorption of thé chromosphere, thicker hère than elsewhcre, as thé spot is a cavity.

II. Tiicgreaterse!ecdve absorption of thé lower sodium, barium, magncsium stratum, thé surface of its last layer being below thé ordinary level.

Messrs. De La Rue, Stewart, and Locwy also suggested, in their Re-

searches cm Solar H)ysics/ that if thé photosphère of thé sun be thé phmc of condensation ofgascous matter, thé plane may be ibund to bc subjcct to

periodical elevations ami dépressions, and that at thé cpoch of minimum sun-spnt-frcquency thé plane migl~t he uplifted very high in thé solar atmospitere, so that there was comparativcly little co!d absorbing atmosphère above it, and therefore gréât dimculty in forming a spot.

This suggestion is oncof gréât value and, as 1 pointed out in my préviens papcr, its accuracy can fortunatcly now be testcd. It may Iiappen, however, that in similar periodical fluctuations thé chromosphere may be carried up and down with the photosphère and 1 hâve aircady évidence that possibly such a state of things may have occnrred since 1860, for 1 do not tind thé C and F Fraunhoier liues of thé same relative thickncss as they werc in tliat ycar~. 1 am waiting to make observations with thé large Stemhcil spcctroscope beforc 1 consider this question settled. But thé well-knûwn great thicknessofthe F line in Sirius and other stars will point ont thé excessive importance of such observations as a method of ascertaining not only tlie physical constitution, but tlie actual pressures of thé outer limits of stellar atmosphères, and of thé same atmosphère at different epochs. And when other spectra have bcen studied as we have nowstndicd hydrogen, additional mcans of continuing similar researehes will be at our command indeed a somewhat careful examination of thé spectra of the digèrent classes of stars, as defined by Father Secchi, leads me to believe that several broad conclusions are not far to seek and 1 hope soon to lay them before thé Royal Society.

For some time past 1 have been engaged in endeavouring to obtain a sight of thé prominences, by using a very rnpidly oscillating slit but although 1 believe this method will eventuany succeed, the spectroscope 1 employ does not allow me to apply it under sunieienfly good conditions, and 1 am not at present satisfied with thc results 1 have obtained. Hearing, however, frorn Mr. De La Rue, on February 27th, that Mr. Huggins had succeeded in anticipating me by using absorbing média and a wide slit (thé description forwarded to me is short and vague), it immediately struck me, as possibly it has struck Mr. Huggins, that thé wide slit is quite sufficient without any absorptive média and during the last few days I have been perfectly encllanted with the sight which my spectroscope has revealed to me. Thé solar and atmospheric spectra being hidden, and thé image of thé wide slit alone heing visible, thé telescope or slit is moved slowly, and the strange shadow-ibrms fiit past. Hère one is reminded, by thé neecy, innnitely délicate cloud-films, of an English hedgerow with luxuriant ehns hère of a densely intertwined tropical forest, thé intimatoly interwoven branches threading in ail directions, thé promincnces gcnerally cxpanding as tliey mount upwards, and changing slowly, indeed almost imperceptibly. By this method thé smallest détails of thé pro-

1 havn ~Mtrnt' nf~r h~iflinc <.his nnnn)' in <~ thn ~nyxl So''i''<hv~ <~t An~<

Map tho 0 nud liucs nre nc!u'!yof<,ho samcbreadLh this I hall gat.hcrcd from ubso'vaLiotis tnudc with my own spcct.roH(;o])u.

minences and of tlie chromosphere itself are rendered perfectly visible and casy of observation.

ÂDDENDUM.–Received March 17, 1869.

Since thé foregoing paper was written, 1 have had, thanks to thé somewhat better weather, some favourable opportunities for continuing two of thé lines of research more cspeeially alluded to ni it 1 refer to thé method 1 had adopted for viewing thé prominences, and to thé injection of sodium, magnésium, &c. into thc chromosphere.

With i -jgard to seeing thé prominences, 1 find that, when the sky is free from haze, the views 1 obtain ofthem are so perfect that 1 have not thought it worth ~vhile to remonnt thé osciMating slit. 1 am, however, collecting red and green and violet glass, of the rcquircd absorptions, to construct a rapidiy revolving wheel, in whieh thé percentages of light of each colour may be regniated. in this way 1 think it possible that we may in tirne be able to see the prominenees as they really are seen in an eclipse, with the additional advantage that we sliall be able to see thé sun at thé samc time, and test thé connexion or othcrwise between the prominences and thé snrface-phenomena.

Althongh 1 find it generally best for sketching.purposes to have tl)c open slit in a radial direction, 1 have lately placed it at a tangent to th c Ihnb, in ordcr to study the général outline of thé chromosphcre, which in a previous communication 1 stated to be pretty uniform, while M. Janssen bas characterized it as '<?~M/b~ e~ ~Mn/ïc~ My opinion is now that perhaps tlie mean of these two descriptions is, as nsnal, nearer thé truth, nnless thé surface changes its character to a large extent from time to tirne. 1 find, too, that in different parts thé outline varies here it is undulating and billowy therc it is ragged to a dcgrcc, Marnes, as it were, dart.h)g outof thc général surface, and forming a ragged, Meecy, interwoven outline, which in places is nearly even for some distance, and, like the billowy surface, becomes cxcessively uneven in thé neighbourhood of a prominence.

According to my present limited expérience of thèse exquisitely beautifui solar appendages, it is generally possible to see thé whole ofthcir structure but sornetimes they are of such dimensions along thé line of sight that they appear to be mnch denser than usual and as there is no longer under these circumstances any background to the central portion, only thc détails of the margins can be observed, in addition to thc varying brightnesses.

Moreover it does not at ail follow that thé largest prominences arc those in which the intensest action, or thé most rapid change, is going on, -the action as visible to us being generally confined to thé régions just in, or above, the chromosphere the changea arising from violent', nprnsh or rapid dissipation, the uprush and dissipation representing the birth and dcath of a prominence. As a ruie, thé attachment to tlie chromosphcre

is narrow and is net oftcn single Ingher up, thé stems, so to speak, intertwinc, and thé prominence expands and soars upward until it is lost in délicate filaments, winch are carried away in noating masses. Since last October, up to thé time of trying thé method of using tlie opcn slit, 1 had obtained évidence of considérable changes iu thé pronnncnccs from day to day. With thé open slit it is lit once evident that changes on thé small seale are continually going on it was only on thé !4th inst. tI~at 1 observed any change at ail comparable in magnitude and rapidity to those aiready observed by M. Janssen.

About 9'' 45'" on that day, with a tangential slit 1 observed il fine dense prominence ncar thé sun's cquator, on thé eastern limb. 1 tried to sketch it with thé slit in this direction but its border was so full of detail, and thé atmospheric conditions were so unfavourable, that 1 gave up thé attempt in dcspair. 1 turned thé instrument round 90° and narrowed thé slit, and my attention was at once taken by thé F line, a single look at it taught me that an injection into the chromosphere and intense action were taking place. Thèse phenomena 1 will refer to subsequently.

At 10~ 50' when the action was slackening, 1 opened the slit; saw at once that thé dense appearance had ail disappeared, and cloud-like filaments had taken its place. Thé first sketch, embracingan irregular prominence with a long perfectly straight one, which 1 ca'ilcd A, was nnished at 11" 5' thé height ofthe prominence heing 1' ô", or about 27,000 miles. 1 left thé Observatory for a few minutes and on returning, at 11~ 15'°, 1 was astonished to find that part oftiieprominenceA had entirely disappeared not even thé slightest rack appeared in its place whether it was entirely dissipated, or whether parts ofit had been wafted towards the other part, I do not know, although 1 think the latter explanation the more probable one, as thé other part had increased.

We now come to thé other attendant phenomena. First, as to the F line. In my second paper, under thé above title, 1 stated that thé F line widens as thé sun is approaehed, and that sometimes thé bright line scems to ex tend on to thé sun itself, sometimes on one side of thé F line, sometimes on thé other.

Dr. Frankiand and myself have pointed out, as a result of a long series ofexperiments, that thewidening out is due to pressure, and apparently not to température per se; thé P line near thcvacuum-pomtis thin, and it widens out on both sides (I do not say to thé same extent) as thé pressure is increased. Now, in thé absence of any disturbing cause, it would appear that wlien thé wider line shows itself on thé sun on one side of thé F line, it should at thé same time show itself on thé other this, howcvcr, it does Mo~ always <~o. 1 I)~ve now additional evidence to adduce on this point, and this time in the prominence line itself, off t-hesun. In the prominence to which 1 have refcrred, thé F briglit line underwent thé mnst strangc contortions, as if there were some disturbing cause which varied thé rcfrangibility of thé hydrogen-line under certain conditions and pressures.

Thé D line of hydrogen (?) also once bore a similar appenrance. Secondiy, as to thé other phcnomena whicti acconpanicd tins strange behaviourofthc F line, and werc apparent!y thé cause ofit. In tlie same ficld of view with F, 1 recognized thé barinm'tinc nt t~89- ofKirchhon"ssca)c.

Passing on, thé magnesinm-hnes and thé cnebsed nickel.iron-hnc werc visible in thé chromosphere. Themagncsinm was projt'cted higherinto thé chromosphet-G thau tlie harium, and the mckL'1 or ironwns projccted higher than thé magnpsinm. 1 carcfnlty cxamined \v!)e(:her thé other iron.lincs were visible ill the spcctrum ofthc chromosphL'rc thcy wcre not. 1 also scarchcd for the stronger barium-hues in the bri~htcr portion of thc spcetrum but 1 did not find them, probably owing to thé i'eebie et~vation of thé banum-vapour abovc thf ~-(.'nerai levct of the photosphère, which madc thé observation in this région a very dehcatc one. 1 detected another chromosphËre.line very near thé iron-line at 1569'~ (on thé east sicle ofit).

Thé sodium-lincs were also visible.

Unfortunatcly clouds prevcnted my contnnnng thèse interesting observa.tions but thé action was evidently toning do\vn.

Hère, then, we have an uprush of

Barium,

Magnésium,

? Nickel,

and an unkno\vn substance

from thé photosphère into thé chromosphere, and with thé uprnsh a dense promincnce accompanying thc uprnsh we have changes of an enormons magnitude in thé prominence and as the uprnsh ceases tlie prominencc melts away.

As stated in thé former part of thi.s papcr, thé barium- and magnesiumhncs wcre thinner titan thé corresponding Fraunhofer lines. In connexion with this subject, 1 bcg to be allowed to state that 1 hâve commenccd a carefui comparison of KIrchhon''s map wifli thé rccently published one of Angstrum. From \vhat 1 have ah'eady seen, 1 bchevc otbcr important conclusions, in addition to that before aUnded to, may be derived from this comparison but 1 hesitate to say more at présent, as 1 have not yr-t hecn able to compare Ângstrom'srnaps with thc sun itsc!f, or to examine thc angtilar diameters of thc snn registcrcd at Grccnwich during the présent century.

On thé Hth inst. 1 also succecded in dctecting thé hydrogen-Ime in thc extrême violet In thc spectrum ofthe chromosphere.

f~'OM the PROCEEDINGS 0F THE ROYAL SOCIETY, No. 111, 1869.]

SPECTROSCOPIC OBSERVATIONS 0F THE

SUN.-No. IV.

nv

J-. NORMAN LOCKYER, F.R.A.S.

Ï BEG to lay before thé Royal Society very brie~y the results of observa. tions made on the 11 Ith instant in thé neighbourliood ofanne spot, situated not very far from thé suu's limb.

I. Under certain conditions thé C and F lines may be observed ~'K/A~ on <A<? ~M~ and iti thé spot-spectrum also, as in prominences or in thc chromospherc.

II. Under certain conditions, although they are not observed as bright lines, thé corresponding Fraunhofcr lines are blotted out. HI. Thé accompanying changes of refrangibility of the lines in question

show that the absorbing materud movcs upwards and downwards as regards thé radinting material, and that these motions may be deterrmned with considérable accuracy.

IV. Thé bright Unes observable in tlie ordinary spcctrnm are somctimcs interrupted by thé spot-spectrum, i. c. they are only visible in those parts of thé solar spectrum near, and away from, spots.

V. Thé C and F lines varycxcessively in thickncss over and near a spot, and on thé lith in thé deeper portion of thé spot they were much thieker than usuaL

IV. Stars, in thé speetrum of which thé absorption-lines of hydrogen are absent, may either hâve their cliromosplieric light radiated from beyond thé limb just balanced by thé light absorbcd by thé chro. mosphere on thé disk, or they may corne under thé condition referred to in (II.), either absolutely or on thé average.

ÂDDENDUM.–Reeeived April 29, 1869.

Since thé date on which thé foregoing paper was written, 1 have ob.tained additional evidence on thé points referred to. 1 beg therefore to be perrnitted to make thé followiug additions to it.

Thé possibility of our being able to détermine the velocity of movements of uprush and downrush taking place in the chromospliei-e dépends upon thé alterations of wave-length observed.

It is clear therefore that a mere uprush or downrush at thé sun's IImb will not affect the wave-length, but that if we have at the limb cyclones, or backward or forward movements, thé wave-length will be altered so that we may have

1. An altération of wave-length near thé centre of the disk caused by upward or downward movements.

2. An altération of wave-length close to thé limb, caused by backward or forward movements.

If thé hydrogen-lines were invariably observed to broaden out on both suies, thé idea of movement would require to be received with great caution we might be in presence of phenomena due to greater pressure, both when thé Unes observed are bright or black upon thé sun but when they widen out sometimes on one side, sometimes on thé other, and sometimes on both, this explanation appears to be untenable, as Dr. Franidand and myself in our researches at tho College of Chemistry have never failed to observe a widening out on both sides thé F line when the pressure of the gas bas been incrensed.

On thé 21st I wfis cnabled to extend my former observations. On that day thé spot, observations of which form thé subject of thé paper, was very near the limb as this was thé first opportunity of

observing a fine spot under such circumstances 1 had been able to utilize, 1 at once commenced work upon it. Thé spot was so near the limb that its spectrum and that ofthe chromospliere were both visible in thé field of view.

Thé spot-spectrum was very narrow, as the spot itself was so greatly foreshortened but the spectrum of thé chromospherc showed me that thé whole adjacent limb was covered with prominences of various heights ail blended together.

Further, thé prominences seemed fed, so to speak,from, apparently, thé preceding edge of thé spot; for both F, and thé line near D, were ~c~~ o~ itself, the latter especially striking me with its tbickness and brillianey.

In the prommences C and F were observed to be strangely gnarled, knotty, and irregular, and 1 thought at once that some « injection must be taking place. 1 was not mistaken. On turning to thé magnésium lines 1 saw them far above the spectrum of the limb and uneoiinected with it.

A portion of the upper layer of the photosphère had in fact been lifted up beyond thé usual limits of the chromosphere, and was there floating cloud-like.

Thé vapeur of sodium was also present in the chromosphere, though not so high the magnésium, or unconnected with the spectrum of thé limb, and, as 1 expected, with such a tremendous uplifting force, 1 saw the iron lines (for the first time) in the spectrum of thé chromosphere.

My observations commenced at 7.30 A.M. by 8.30 there was comparative quiet.

At 9.30 the action had commenced afresh; there was now a single prominence. +

At the base of thé prominence 1 got this appearance –J~y–

–VT-

Higher up this t Hère 1 may be permitted to recall the obser.

vntion made on March 1~ in which a sli~ht movement of the slit gave

and finally

appcarances being due to cyclouic action.

On thé following side of the spot, at about 10 A.M., 1 observed that thc F line had disappeared, at the point of disappearance there appeared to be an elongated brilliantly ilinminated lozenge lying across it at right angles, as if thé spectroscope were analyzing thé light proceeding from a cyclone of hydrogen on the sun itself, but so near the limb that thc rotatory motion could be detected.

Thé next observations 1 have to lay before thé Royal Society were made on the 27th inst. Careful observations on thé 25 th and 2Gth reveded nothing remarkable except that the chromosphere was unusually uniform.

On the 27th a fine spot with a long train of smaller ones and facniee was well on the disk. Thé photosphère in advance of the spot, and the large spot itself, showed no altération from thé usual appearance of the hydrogenlines but in thé tails of the spot thé case waswidely different. Thé F line, at which 1 worked generally, as thé changes of wave-length are better seen, was as irregular as on the former occasions.

I. It often stopped short of one of thé small spots, swelling out prior to disappearance.

II. It was invisible in a facula between two small spots. III. It M?~ changed into a & line, and widened out o~ both sides two or <A?'CC ~ÎWM tN THE VERY SMALL SPOTS.

IV. Once 1 observed it to become bright ?tear a spot, and to expand over it on both sides.

V. Very many times near a spot it widened out, sometimes considerably, on thé less refrangible side.

VI. Once it exteiided as a bright line without any thickening ovor a small spot. !BMN

VII. Once it put on this appearance bright.

VIII. 1 observed in it ail gradations of darkness.

IX. When the bright and dark lines were alongside, the latter was always the less refrangible.

[~'OM ~e PROCRKDING8 OK THE RoyA.L SûCIETY, No. 115, 1869.]

SPECTROSCOPIC OBSERVATIONS 0F THE SUN.–No. V.

i)Y

J. NOtiM~N LOCKYEK, l'\K.S.

SïNCE thc datcofmy Inst communication nnder the ahnvetitte the wcathcr bas, if possible, bccn worse for telescopic wor~ than during tl)c winter and spring my opportuniticsof observation, therefore, have been very limited stiU the sun bas occasionaUy been in such a disturbcd state, and o~r atmosphère has at times been sopure, that several new facts of importancehave corne out.

1 will state them here as brieny as possible, rcserving a discussion of them and my detailed observations for a future occasion.

I. Thé extrême rates of movemcnt in the chromosphere observed ))p to t)te présent time are

Vertical movernent 40 miles a second

Horizontal or cyclonicmovement. 120

11.1 hâve carefully observed the chromosphere when spots have beeu near thé lirnb. Thé spots hâve sometimes been accompanied t)y prominences, at othcr times they have not becn so accompanied. Such observations s!io\< that we may Imve spots visible withont prominences in t!<e same regiox,

and prorninences without spots; but 1 do not say that a spot isnota.ccompanied by a prominence a~ some ~c o/ life, or that it does not resuit from somc action which, in the majority of cases, is accompanied by a protninence.

111. At thnes, when a prominence is seen bright on thé sun itself, tlie bright F line varies eonsiderabty, both in thickness and bri!hancy, within thé tluckness of thé dark une. Thé appearances presented arc exactly as if we wcre looking at thé pt'ominences through a gratina.

IV. Bright prominenccs, when scen above spots on thé disk, if built up ofoth'rsubst.aoccs besides hydrogen, areiodicated by thé bright linesof those substances in addition to the lines of hydrogen. Thé bright lines are thcn seen very thin, situated ccntraHy (or nuariy so) on the broad absorption.bauds caused by thé tmdcr!yh)g less-tuminous vapours of thé same substances.

V. 1 have ntlast detected an absorption-line correspondiug to thé orange line in thé chromosphere. Fnther Secchi states* that therc is a line corresponding to it much brightcr than thé rest of thé spectrum. My observation would seem to indicate that he bas ohserved a brig!)t line less refrangible than thé ~ne in question, which bright hue is at timps excessively briihant. Jt reqnircs absolutety perfect atmospheric conditions to see it in thé ordinary solar spectrum. It is best seen in a spot.spcctrmn when thé spot is partiaHy covered by a bright promiuence.

VI. In thé neighbourhood nf spots the F bright line is sometimes ohservcd considcrably widened eut in several places, as if the spectroseope wcre analyxing injections of hydrogen at great pressure in very timited regions into thé chrornosphcre.

VII. Thé briUiancy of thé bright hues visible in thé ordinary solar spectrum is extremely variabte. One ofthem, at 1871' and another, lit 1529'5 of Kirchhon"s scale, I have detected in thé chromosphere lit thé same time that thcy were briHiant in thé ordinary solnr spectrum.

VIII. Altérations of wave-!ength hâve bcen detected in thé sodium-, magnésium-, and irun-IInes ill a spot-spectrnm. In thé case of thf last suhstnncc, thé hnes in which thé alteration was detected were not those observed when iron (if we acccpt then) to be due to iron alone) is injected into thé chroniosphere.

IX. When thé cbromosphcre is observed with a tangentiat slit, the F hright line close to thé snn's limb shows traces of absorption, which gradnaiïy dinnnish as thé higher stt'ata of thé chromosphere are brought on to thé slit, until thé absorption-line finally thina ont alld entirely disappears. Thé lines of other substances thus ohserved donot show this absorption. X. During the most recent observations 1 have been able to detect traces of magnésium and iron in nearty ail solar latitudes in thé chromosphere. If this be not merely thé resutt of thé good définition lately, it would indicate an ino'cased gênerai photospheric disturbance as thé maximum snnIII Comptes Hpn(h)s, 1869, 1' sem. p. 358.

spot period is approached. Moreover 1 suspect that thé chromosphere bas lost somewhat of its height.

1 append a list of the bright Unes, the positions of winch in thé chromosphere 1 have determined absolutcly, with the dates of discovery, rernarking that in thé case of C and F my observations were anticipated by M. Janssen:–

? band or line near black nn~n ï,,i~ r.

line, very deltcate. i T t J r uuiy

1 have seen other lines besides thèse at diffcrent times but 1 do not include them, as their positions have not been determined absolutely. 1 refrain from dwelllng on this list at présent, except to point out that, taking iron as an instance, and assuming that thé iron-lines mapped by Angstrom and Kirchhoff are due to iron only, 1 have only been able, up to thé present time, to detect 3 lines out of thé total number (460) in the speetrum of the lower regions of thé chromosphere,-a fact full of promise as [/o~ ?–&. G. S.]

~o~cyt.

C. October 20, 1868.

F. October 20, 1868.

near D. October 20, I868*.

near G. Dccember 22,1808.

/<. March 14, 1869.

)S'C~Ï'MW.

D. Febrnary 28, 1869.

J3<?rïM~.

t')89-5t. March 14, 1869.

2031-2..Tuly 5, 1869.

~~MMt'MW and ÏMC/M~e~ ~~C.

&

-Febru~y21, 1869.

6'J rebruary 21, 1869.

O~Ae~ ZîMM.

h-an. 1474. June 6, 1869.

? 1515'5. June 6, 1869.

Br~htUne 1529-5. July5,1869.

? 1567'5. March 6, 186!)

? 1613-8. June 6.

h-on. 1867-0. June 26.

Bright line 1871-5.

Iron. 2001-5.

? 2003-4.

t This reference is to Kirchhoff's scale.

regards thé possible results of future laboratory work, Thé same remark appues to magnésium and barium.

Dr. Frankiand and myself have determined that thé widening out ofthe sodium-line in thé spectrum of a spot whieh 1 pointed out in 18(jo,and then stated to be possibly an évidence of greater absorption, indicates a greater absorption due to greater pressure.

Thé continuous widening out of thé sodium-line in a spot must therefore be regarded as furnishing an additional argument (if one were now leeded) in favour of the theory of thé physical constitution of thé sun first pntforward by Dr. Frankiand andmysen'–name!y, that thé chromosphere and thé photosphère form the true atmosphere of thé sun, and that under ordinarycircumstances the absorption is onotinnous from thé top ofthe chromosphere to thé bottom of thé photosphère, at whatever dcpt!i from the bottom of thé spot that bottom may be assumed to be.

This theory \vas based upon ail our observations made from 1866 np to thé time at which it was commun.icated to thé Royal Society and thé Paris Acndemy of Sciences, and bas been strengthencd by ail onr subséquent work; but several anuouncernents made by Father Secchi to tlie rans Academy of Sciences and other learned bodies are so opposed to it, nnd diû'er so nmch from myown observations, tliat itis necessary that 1 should rcfer to thein, nnd give my reasons for still thinking that thé theory abovc rcterred to is not in disaccurd with facts. At thé snmc time 1 must state that Father Secchi does not combat this theory indeed it is not to bc gathercdfrom any ofhis communications that hehasseenanyofthepapers communicated bv myself to thé Royal Society.

Father Secchi states that thé chromosphere is oftcn separated from thé photospho-e, and t))at between thé chromosphere and thé photosphère therc exists a stratum giving a contimiousspectrum, winch he considers to be thé base of thé solar atmosphère, and in which he thinks tliat thé inversion of thé speetrum takes place.

With regard to thé first assertion, 1 may first state that ail thé observations 1 have made have Icd me to a contrary conclusion. Secondly, in an instrument ofcomparatively small dispersive power, such as that employcd by Father Secchi, in whieh thé widening out of thé F Une at the base of thé chromosphere is not clearly Indieated, it is almost impossible to determine, by means of thc spectroscope, whether thé chromosphere rests on thé sun or not, as thé chrnmosphere is an envelope and we arc not dcaling merely with a section. But an instrument of gréât dispcrsive powcr can at once settle thé question for since thé F line widens out with pressure, and as thé pressure incrcases as the sun is approached, thé continuous curvature of the F line must indicate really the spectrum of a section and if thé chromosphere were suspended merely at a certain height above thé photosphere, we should not get a widening due to pressure but we always do get such a widening.

With regard to thé second assertion, 1 wou!d remark that if such a continnons-spectrnm-giving envelope existed, 1 entirely fail to sec how it could be regarded as a région of selective absorption. Seconde my observations have indicated no such stratum, aithougb injections of sodium, magnésium, &c. into the chromosphere not exceeding thé Hmit of thc sun's lirnb by 2" have been regularly observed for several months nast. To.day I have even detected a low ieve! of barium in thé ehromospherc not l"high. This indicates.Ithink, that my instrument is not laekin'~in delicac and as 1 have never seen anything approaching to a continuons spectrum when rny instrument I~as been in perfect adjnstrnent, 1 am inchned to attribute the observation to some instrumenta! error. Such a phenonenon might arise from a local iujcction of solid or iiquid part-ictes intu thé chromosphere, if such injection \vcre jtos~ible. liut 1 hâve never seen such au injection. H'snch an occnrrcttce conid be observed, it wouhi at once settle that part of Dr. Fraukhmd's and my own theory, which regards thé chromosphere as thé last layer of thé sotar atmosphère and it' it were possible to accept Father Secchi's observation, thé point wou!d bc settled in our favour,

Thé sodium experhnents to winch 1 have referred, however, and thé wtdening out of thé lines in thé spot-spectra, clearly indicate, 1 think, that tl)e base of thé atmosphère is below thé spot, and not above it. 1 therefore canuot accept Father Secehi's staternent as being final against another part of thf theory to which 1 have referrcd–a conclusion whieh Fat.!)er Secchi himself seellls to accept in uther cutmnunications.

Father St'echi remarks tilso timt thé F line is producedbv thé absorption of other bodies besides hydrogen, becausc it never disappears. This conchtsion is atso negatived by !ny observations for it bas very often becn ob. sen'ed to disappear attogethcr and to be replaced by a bright line. At tirnes, as 1 pointpd out to thé Roynl Society some rnonths ago, whett a violent storm is going on accompanied by rapid élévations and dépressions ofthe prominenees, there is a b!ack line on thé less-refrangibic side ofthc ))right one but this is a phenomenon due to a c!nmge of wave-Ieugt.h caused by thé rapid motion of thé hydrogen.

\Vith regard to the observation ofspot-spectra, 1 find that every incrensc ofdispersive power renders the phenomcnon much more dear, and at thc same time more simple. Thé sélective absorption 1 discovered in t8u(i cornes out in its most intense form, but without any ofthe more compncated accompaniments described by Father Secchi. 1 find, however, that by using three prisms this complexity vanishes to a grent ext.ent. We get portions of thé spectrum here and there abnormaUy bright, which have given rise doubtless to some of the statements ofthe distinguished Roman observer but thé bright lines, propcrly so-called, are as variable as they are in any other part ofthe disk, but not much more so. 1 quite agrée that thé "interprétation" of sun-spot phenomena to which Father Secchi bas referred* Comptes Rendus, 1869, 1~ sem. p. 76L

which ascrihcs the appearanccs to anything but selective plus gcnertd absorption, Is crrnncnus. But as 1 wns not j~ware that it had ever bc'ctt pro{)out)()u(t, 1 cfm onty rcfcr to my own }<rior papers in support oftny assertion, a))<) to Mr. Hu~ius's indorst'tm'nt of tuy observations, whic!) were Ct.xnnmnicntod to t.he l!oya! Socich' s')))K' thr~c years an'o.