SCIENCE UP TO DATE.

Lyttelton Times, Volume CXVI, Issue 16959, 11 September 1915, Page 5

SCIENCE UP TO DATE.

THE HOKE OF THE SUN. (By JAMES COLLIER.) Sonic .startling •dir.rorcrios- in tlic seventies mi the coirt>union,of;t ln' sun | ol.traftoci the atlejition, especially or . Hie Englbh-speoking world, ,to tho | Ivitliertu unknown name of Norman ILoekyer. lie was tlionv if 1 .rigbfly r ?* ; member, a clerk in the War Office* Rko I the organiser of our province of Lanj Embury, though doubt-loss • of lotrcr ' rank than J. R. Gndley. He must soon i have relinqui.shod distasteful duties ior 1 iroro important- tasks, and, still happily ! living, Bo Jins won the homage of all the world for the discoveries he has i made or is making on t!:e mighty luni- ■ nmry. Not. only on “ t he. eye of day, I lu;l also on its eye-lashes, so to speak. ! not only on the new chemical elements Hound in it, and its sudden and .amazing protuberances but, also on the. corona, i or crown, on the atmosphere by which. I in common with the earth and probably j every other coding celestial body, the sun is , pliero or robe .cf the. sun, so recently | discovered, and in whoso eqnstituf.nq discoveries are still being made, that the attention of the reader i:> here invited. ECLIPSES AND THE ATMOSPHERE* Mete analogy and. a. priori conjecture suggested, long before it was . really iound, that, the sun would be ascortmiiecl to have aii atmosphere cl its own, rmrl one of the earliest iniits of spectral analysis. Fraunhofer's dark lines, with the decreasing density of the sun near ifs edges, proved the existence of a stratum of gas comparatively cold, chemically defined by these rays. But it is the eclipses of the sun that have revealed to us most of what we know about the run’s atmosphere. .Usually,•• that atmosphere is as completely invisible as the stars liv day, and for the same reasons--the splendour of the. God of Day and the diffusion of the.azure. A vast, curtain, says Notdnmnn, bailors over the sky, anri the brighter it is. the Joss we see of the source of illumination. Total eclipses of the sou have alonebad the power to tear down this curtain. Twenty-four times' in thirtyeight yfnrs has it been rent, and :ui “ immense luminous glory ” whose streamers extend for several millions of utiles, bursts upon the vision. This glory lias (several layers, 'so to speak. First, all round the luminary lies a thin red-rose ring, of ruby-like brilliancy, which is tailed the chromosphere. l'Voin it lea pa out the rosy flames ol the protuberances. These are often some hundreds of thousands of I unles in extent, and in the .short dnrj a tic,u ol .ill eclipse they may be ebsorv- | cd io change then- positions and forms 1 with a velocity that would be incredible were it not proved by calculation : sometunes it exceeds oO.fXK) miles per second. AH round the chromosphere and its red protuberances stretches the' iminon.se corona! atmosphere, the immense, green “crown’’, that forms the outward - atmosphere of the suu. SPECTRUM OF THE CORONA. Ihe study oi those various strata bv moans ol the spectroscope* during total eclipses shows that both the chromosphere and its protuberances- aro composed of luminous hydrogen. It shown also,- and tin* result is striking, that the green tint of the corona arises from si gas that has never yet been found on this earth: the pas has neon called, eoronium. Perhaps, like helium, it will yet be iomul in the earth’s atmosphere. Not till long sitter the discovery ..of helium in the pun’s atmo,sphere) was .it found op earth. 1 The method that Inis enabled Us to make these and oihoj marvellous discoveries is still costly and imperfect. | It allows too little time for.observation. |and the observation- ;no.v .'bo .vitiated 1 ' by a single cloud. The .total eclipses of j the sun between ISfiS and 1906 number 1 twenty-four,. ar.d their average duraI Hon »was..*)iily ..three .minutes and six i seconds. Assume -that ,ibc same 'asfcro- ! nomer had. been present at. nil of them, I sind be would still have, bad the phenomenon under observation for tinly j cue liottr and a- half. I A, first step to remedy the precarious method of observation was taken by Sir Norman' Loekyer. and M. Janssen. Simultaneously or conjointly, they devised the celebrated method .now generally used. It has. almost mi pel's cried Hip .eclipse-! Man, audacious.mon, has virtually invented eclipses for his own private behoof! lie is henceforth independent of one. of the grandest, and most appalling; phenomena of nature. We. must discriminate., however. It. is only .the. chromosphere and its port nberances that can be independently observed. The corona..-cannot be thus observed. All the efforts made to examine it by an indonondent method have completely failed. As a consequence wo are unable to stave in what i the ■ “glory" that clothes as with a nimbus’the surfaces of the moon and: the .pun consist?. Still, wo know that the corona- is composed of gases extremely tenuous, which hold in suspense very fine dust, and yet ro transparent. though they are of enormous, thickness, that the; stars are risible through them. THE SPECTII OH EL TOG E A PH. Though the corona, of the suu cannot yet be scientifically observed save' during total solar eclipses, the various strata- of the atmosphere, which cannot be observed at si I even during eclipse?, because, they are concealed' behind the opaque disc* of the moon, can now be at all times observed on the whole surface of the sun. The means of making i udt ••observations wc owe to the speoi.rolieliogr.vph. This ingenious iust-ru- j ment is" tlio invention, at once independent and conjoint, of the Americau. astrophysicist, Hale and Mount "Wilson Ob.-ervatorv, and the French astronomer. l.V.slanches, '.successor to Janssen as director of the great, solar obsovvn- j tory at Mention. Me shall follow Nordmann’s account of ilie apparatus, which may be founded on a very simple idea, but- is not in itself very simple. At the focus of a mirror J. have*a fairly large image of the sun. There 1 set the slit of. a powerful spectroscope, adjusted to any diameter of that, image—say, to the. solar equator ; at the other end of the spectroscope 1 shall hare a. complete spectrum of the solar equator. Suppose now that I isolate a particular line of that spectrum—say, lhe red ray of hydrogen, and that 1 cover all the rest or that- spectrum by means of a sereei) pierced with, a fine slit, which coincides with that ray. Now. if I place «. ,photographic plate behind the screen, 1 shall have bn the plate » ray going from one end to the other of the solar equator. And the thickness and intensity of the ray will not Im uniform throughout,, hut- thesewill depend Vm the distribution over the solar equator’of the manses of hydrogen, whose absorption in the atmosphere of the sun produce i this ray. Next, leaving all the rest motionless."T displace the. image of- the sun on t-ho -slit, so as .to hrfyo it entirely and .yuce'CSMy'oiy swept- by. the ..latter. L.et .me,', .finally, give the other, cud cif the.photograph a corresponding-path and I. shall procure on -image- of thestm flint arises." solely from it-iFatniospberic hydrogen. . OTHER RESULTS. What is still more important; by the agency of the spoof rohoiiograph v.e can determine tlw vertical distribution of al , v chemical element or its distribution in the various layers of the solar atmosphere projected on the ani's disc; Here tiie astrophysicists' have far, surpassed thcr chemists. Wo have -no'" mean’s of determining by s simple optical obsem-

lieu the! composition of the different strata of our atmosphere taken vertically. , . , • Pc.iinudres.'.was, moreover, the, first jo obtain..solar images produced by ,the black rays .of the spectrum—a . notable result. . .: .. To. diyc.iy.cr the distribution'.of. tin? raysi'.ot vajcinni; in the various layers tft9t.-sijirtcijt.-i the,sun is the work of a photographer.-. The ends, of rays fJ and K arc- ii.t ip.-'-d foi the lower strata ; the central part- for the . highest strata; and’l heir, intermediate portion' for the middle layers. Tho thing l litis not- vet l«c«n done, however, wc-are warned';

it is the task: 6f the future; though ! ihe first-series' of doeumems taken at I Mention and Mount Wilson have nl- ' ready'Ted -o , remarkable: results'. Ifc has been demoiistrated that the,greater number of the -30,000 black rays found in the solar spectrum arise solely from the 'ahnshc-? of an atmospheric layer that is comparatively - thin,' and is in immediate contact, with the; photosphere. The existence of this 1 reversing sttiituin ffevorsimj the colours of thy aolaivapecti-um) has been confirmed Ire .the photograph of its spectrum m-ado during eclipses. l That-spectrum shows ns. brilliant" rays all the rays that arc black in solar spectrum. This is' in perfect accordance with Kirchhof’s ideas. Further, our two astronomers have discovered in th..> solar atnibsphefie certain “ flocciili.” or cloudlets, filaments, and alignment.-?--a whole eencs ol stryigo phenomena- presented by the various gaseous masses in 'motion in the solar atufosnylicire. Thea- arc found: to be of vast importance for the study of solar physics. DesTandres has devised d speeip.l apparatus that instructs* in the speed of the atmospheric currents of the min—a. thing not yet- accomplished for our own .atmosphere. These velocities are seme time* fantastic. Recently si mass of ‘solar,hydrogen has been ibsorvod to Im*' attracted, --'or to “ asi>ire.'’ towards a sunspot at .a speed of mono miles an hour--the distance being that ot the moon irom t-no-earth. Such velocities. tog\ iliCr .with tiii. l -more existence of the luminescence of tho solar atmosphere and the characteristic curvature of the solar protuberances, have led astrophysicists to believe that the sun is the seat of powerful magnetic and electric phenomena. A recent discovery, or i'.erio.i of discoveries, which Nordmami cal!:- magnificent, the outcome of-helio-graph io researches, lends experimental support to the belief. It is. chiefly, the discovery that the bun spots are magnetic and the entire sun a magnetic field.

a -'magnificat -discovery.

Some time ago. examining tiie,heliograms ho-had obtained .with the spcq- : - trohcliogrnphic rays, Hale .noticed•tbit the gas showed itself above t-lio sunspots' in-curves-that regularly bent inwards towards: the sunspots, and also that those curves had the- appearance that-would bfeigiroh'them bv violent maelstrom movement that had its centre in tho .sunspot-. Further research proved the reality of the movement (of incandescent hydrogen). l and gaseous masses were sometimes surprised, as it were, in’ ihe violent rush towards the centre of any particular sunspot. The phenomena thus established assimilated the solar atmosphere above the sunspots to the vortices, tornadoes and cyclone of our "own atmosphere. Opt of this simple observation the American astroiiomei', by an 1 ingenious eonihinafioii of reasoning and experiment, lias elicited one of the most beautiful and suggestive of modern astronomical discoveries. It. is that of the magnetic character of the sunspot*—it is the discovery, of the whole fruii ax a- magnetic field.

If,, reasons: Mr. itale,, matter, rotates above a sunspot., and it..is.electrified, it nuiso engender an electric current, that is. an electric, field, of .which the ax’s is sensibly perpendicular, to. the sun. This is mere reasoning, so far, hut it can he proved. Halo applied to it the phenomenon discovered by the c-ele . brated Dritch physicist. Zeemann, who followed on '.lira track ,of Lorenz. f Fh<Zeemaun phenomenon is an effect produced on light- by magnetism and gerrorsflly by -all magnetic fields : and we know, or believe, that light is produced by electrons.' whose combination makes un atoms. •

Availing himself of resources only to be found in the’ United States, which furnished instruments of.a prodjgioir delicacy, and making a long series :o? costly, ingenious experiments.. Mr Hale. t length succeeded in proving to do nionstratioii that the. su,nsppta constitute 'powerful'magrot-ic fields, whose■'intensity -is more than 1 6CO0 1 times that! which attracts the needle to the. Pole. A:second discovery mede bv the same indefatigable savant is: that the magnetic polarity of the sunspots depends oir rhe direction in'which they; rotate. Thirdly, and little iroro than a- yeny ago. tlie sa-mo keen observer and misoner. discovered by analytic nicthoib that the entire surface'of the. sun is magnetic, like, the earth itself, with its North and -South' Poles, and these likewise, near the Poles of rotation... IXist&ndrcs has indepahoontly confirmed some of these results!

Filially, .for new and important discoveries crowd oil us, the German •physicist,. Stark, has proved that the rays of the . rays of the. sunspots, not only manifest the •existence*, of, magnetic but show the existence of. electric- Colds- that, act ~on the.■sources of light. The vistas, that these notable dise'everies open up,to speculation aijd research appear' dazzling • arid • bound-, less. ■ ■ ■ ....