IN STARRY SKIES

Evening Post, Volume CXIII, Issue 139, 16 June 1927, Page 19

IN STARRY SKIES

ASTROPHYSICS

A QttEAT NEW SCIENCE

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frothing in common. But each has grown ttntfl now their territories overlap. In the neutral ground a vast new science baa developed with astonishing rapidity; It haa already captured a large.part of chemistry, and; is at present transform-; ~3Bgeach-'qf the three ancient sciences'. This new science has an immense literature, but very few books. Its records Bare scattered throughout "the: scientific Journals of .th,^,; world. "■• Twenty-four :.^mm.ago -Miss Agnes ML; €lerke published hergreat 1-' book ; in ; , i^?*f.Pphyßi<3S,'?,. in 'which „ she; : gave ; an' Inspiring picture of the young science,ponscious; of its strength but still snore, jfrfiriifiy:. impressed by ;the' vast extent' and 'the' richness '.of the territories! it" was Betting out'to conquer. She t de--seribes-her object as not so much to in^ struct as to suggest, and adds: "It (i.e.. her book) represents'a 1 '"sort of Breconsaiaeanee, and embodies the informa-tion-collected byseoute and skirmisJjera regarding practicable 'line's of advance 1 and aeeessible points Of 'attack, with'a view to annexing for the realm of knowledge some further; strips and cor■u<skhfraJßi the territory' of ; ignoratfce.i!':. Blit the :book isSfar more "''impor-taiit" than might be expected from the mod-,-est deeeriptibn given inithe':'preface..Miss Clerke had a wide andt^eep^know"lei|ge:o"£ i-fKe*worTt*'ii^eady^ace i<Jmpiishii; ed, and a prophetic of .triumphs; that were yet to come. Her statement •^^"the^wutlookj-a- quarter- rof~ a-'«entury^ s^o, is well worth careful study in the light of recent advances, l^epler was _the: first to. recognise clearly;that;there:. is sneh a science as physical astronomyj and he speculated on the causes of celestial,motions.-.Bac_on, who f ajled. to Teepgnise theft great advances; ■lSade bjf. Cop^rniSus rand KS|l^.%ith -|trange.)iinagtnatiye :JiriSight"f picttired the-'scienee now known, as 'Astrophysics, in which inquiries are made into the patnre.xif the,...substance^pfj heavenly^ bodts(B,|theii p^altfiejjf pr6jter|ies'i:iandP |»fli)H|i«jij,sand;.thefsotocei ofiJthW moiiv^,! |Sting i^n'i;fiem.'l^se\iees.?thi^ science jpf tfie heavens advancing.,h'andii jn-hand with terrestrial science,'' each imparting novel truths to the other. Newton's establishment of the law of gravity in 1687 was the first step towards one practical realisation of sucKv a soience. In ISW2 Herschel 'discoY,erpd^l jystems of mutually/ 'liteyoi^ingi starswhieh showed the" lac*tio'n j;6f gravitattoa* jn sidereal worlds.' In 1852 the connection between sunspot. and terrestrial magnetic periods was detected. But the fllsoovery which led to the phenomenal .ididyince ofi'-.tji^'last half century took ijila^e :18t9,l'when:^ Kirchh'ptfij intS?l' preted the'dark lines' which-cross- thb solar spectrum. The spectroscope inijnediately placed new and uadreamt-of powers in man's hands, and these powers were enormously increased by the co-operation of photography. , Tile. photographic plate;- • • as* Miss: V Glerlfe" says, has three leading prerogatives Tit sees where the eye is blind, its impressions are cumulative, and they are permanent. Photographs thus produce documentary evidence Of -incontestibl'e Validity. iProm the moment that the Spectroscope and the.camera were lanited in the .spectrograph the yoiing S.tfienfte developed with astonishirig speed. The advances, of' tho'-'next quarter of a century were reebrded r by Miss Glerko, who pointed but the problems that still called for solution. * Another quarter of a century has passed. The number of worke^a" has' enormously increased." Discbveries~'sT:iir tome thick and fast. The time is ripo for another survey of. the position -chat has been reached and the work that now calls most urgently for attention. Professor . Dingle, F.R.A.S., FjP.Sj, Assistant: Professor of Astrophysics ajb the imperial College of Science ; -.;and Technology, ..has come forward. tb\- lipply what was wanted. Hifi work on ''Modern Astrophysics" was published by W, Colling, Sons, and.Co.. in 1924._ -The book has one -outstanding merit. that makes it pleasant to read. The author is an fenthusiast and feels the ehir'aneing 'interesi I of-.hiß sabject;; t He, has faith also that its appeal will be feK by others as it is by him. He states definitely that the book' is intended primarily for the general public: "We' cannot help. feeling .that he over-estimates the willingness of the public f to make the necessary mental effort. Astrophysics is undoubtedly as he says the most imaginative' of the "sciences. It deals with" subjects' of BUrpassing interest: The public likes imaginative works. Hero' it" has" onei Truth ife, indeed-; stranger }. than\ Action. But "unfortunately the title' "Modorh Astrophysics" is' hardly popular enough. It, suggests the study table rather than an' armchair before the fire.-^ Then again the price is hardly popular. Thirty shillings net becomes; thirty-six in New Zealand. Notwithstanding this wo can heartily recommend tho book.' One chapter, -it is true, we disagree- with completely. But that deals with what is/still a controversial subject.; The^ook generally gives the orthodox opinion at the present"day;pn-,,a 11;theisubjeqts-dis!-cu«sed.' "The bo*ok is really' p'bpuldr* in the sense that no specialised knowledge is required; and no technical or- unfamiliar language is used without, explana-, tiion.■.,': But it is assumed that the reader is prepared to think. We fear that . that.assumption.may limit.the.audience. Proctor, we have seen, had to pass from ''Saturn and its System" to "Other Wprldsthan Ours" in order to increase t^er number j)f Jhiel:rea fders.> i: fle>changed' his treatment of the. subject and ho chose a title with a greater appeal to popular taste. ■ "'*•;■

"Processor' Dingle's book can bo read ii»'an armchair, but to onev.who knows no physics and no astronomy it will.not be altogether easy reading. ' "'A\ more select audience of those who keep abreast of the main waves of current thought will certainly - derive much pleasure from it. In the introduction we immediately recognise "Professor Dingle's enthusiasm. "Astrophysics," ho says, "perhaps alone b£ tho sciences, seems too wonderful to be fictitious." "The facts not merely equal anticipatiom, not merely transcend them, but are so astounding that, until they were discovered, they had no counterpart in imagination at all." Before defining this new science, tho author sketches briefly our place in the universe. Wo live on one of the smaller satellites of a rather small star which rules a system of eight major, and a multitude of minor planets. Most or tha . major planets have satellites, and there are innumerable: comets and meteors associated with the system, which spreads over an, approximately circular. area sis thoua» and million miles" in diameter. . Tho whole system is travelling- ceaselessly through a snico which is extremely sparsely populated with tho other' suns that we pall stars. At the distance of the very* nearest of these stars, our whole system would appear ,as a star less bright than some of those we see. The 1 stars appear to bo congregated chiefly near a singlo plane. We are thus within a hazy ring of light called the galaxy. Amongst the stars we find entirely different objects, the planetary and the diffused gaseous nebulae. Globnlsr clusters, in which thousands of atars appear in an approximately spherical space, are seen in some parts of tho ofey, and they'are believed to be at im ]flen«<9 distances from up. Far beyond iJB&B ud probably quite outside tho regfe-« HrVg<A*«/«tftfS^-hnßaied*

of thousands of spiral and other nebulae. Prom the moving platform of our tiny earth, it is our problem to investigate ttitf iature of: each of -■ these distant bodies, to find out what changes are. -taking,place at present and then to infer the probable history of the universe in. thepasji.and its further development „Such a problem may well aeß,nl,quite insoluble. Of our senses, that of sigJbt'dßithe only one we can use'in r-gejfctirig:. definite:knowledge.of the sky. ■ThevhilStory off astronomy during the :^riod..when;the:;eye was the only optical instrument iemployed, shows, however, what incredible results may be obtained by the activity of the brain dealing with the evidence collected by the unaided sight. The telescope increased enormously the power of the eye by gathering the light which fell on its, lens :or mirror, but even before.the teJoßcope. had been invented, the apparent positions of the stars had been determined and the motions of the sun, -the moon, .and-the planets had been studied, with, regard to them. The precession;"nf the equinoxes had been detected 7 'By "Hipparches, the motions of .the earth and the other planets round .the stfn' fc&4 be£n shown by Copernicus ;*° -S^Jaill their apparent movements, and Kepler had discovered the laws of •planetary-motion. Even Newton's establishment' of the law of gravitation was? independent of the use of the telescope. The'chief advantage of the tele-scoge-iß.its:.power of collecting light so as to render visible objects that would <«.ther)Kdse.; have remained unseen.' It gives enlarged images of the sun, the moon, n and^ the planets. It reveals the presenceVof faint stars and nebulae. It T-esolveg " single points of light into binary or multiple systems, and sometimes into clusters consisting of thous;ands'of Separate bodies; but contrary to •popular' opinibn, *it does not magnify the.image^of a single star. Sir Wil-liSinK-Hersehel -introduced the ■'• use of the photometer by which the relative ■orightness>-of; t*b sources' of light can •be.rtleterminedi,- But until the invention of the spectroscope nothing could ■be -learnt? of the-physical or, chemical nature of the stars and nebulae. The spectroscope extends to the eye the $n-??ytical .power-possessed by the musician's ear. From the analysis of the light received from a distant star it is n ßw PP.s4ty?r:tb;. learn much about its cK'emicJt]. ■composition, its physical constitoiibn, :*jts ■ temperature, its velocity ai^;:pc^sibly many other things—guch asV'its.:?niiss, its; density, the pressure in its atmosphere. The achievements pl.th§.,.speetfoscppe are so marvellous and sd'aiiique tiatiwe may; Well date ■thei'brefli?'of astrppnysics front the flrßt uae. 6<t ■■ this instrument in: astronomy. Bjjt.ifcdoes not work.alone." The three instruments, the telescope, the spectroscope, and the camera, have been combined. The telescope "provides an enormously enlarged lens for the eye, the camera provides a retina on which imprejssibns v.'can be permanently stored. The jjipectrbscope:; adds- an entirely new power' in analysing the rays of light. The photographic plate is fortunately sensitive to radiation, which no eye can see, and this fact adds- largely to the value of the information collected by the spectrpgraph. ' '.' .. S Eecently'anpther.instrument has beea added to' the' equipment of the Astrophysicist. This is the interferometer, the most sensational achievement . of which is the measurement of the diameters of several! giant stars. There ;>r« altogether six iustruments riised^in astfophysics: -The naked eye, the telescope, the photometer, the spectroscope, the camera, and the interferometer; but by. far-the most important, of them all is the spectroscope. Thestar, as Professor Dingle points out, appears to throw the whole secret hiitory of its b-ing into its spectrum. If \te can only learn to decipher the cryp-, tic messages we shall be able to solve the most abstruse problems of the physical universe. The spectrum appears to be influenced by every change of chemical or physical condition. At first emphasis 'was laid on the'identification of elements by 4he spectroscope. But it was sbon 'realised that it is only 1 a small part of each heavenly body whose: composition is thus revealed. But at the same time it was discovered that the spectrum made available an extra-- > ordinary wealth of. physical data. A single.; substance'ean give a variety of spectre, but each is characteristic of its source. In the stars the behaviour of matter can be studied at temperatures and pressures unattainable on earth. By- studying the light sent to us by celestial bodies astronomers are thus learning their chemical composition, their .^temperatures, and their motions. ; Light is even being shown on their distances and their masseSi We have riot yet realised the full possibilities of this astonishing instrument.