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NATURE 



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189 = 



THE SUXS PLACE IN NATURE} 



VI. 



\\rF. come niiw id the third new |Kjint of vie«. Many 

 ' ap)>areiit stars are really centres of nebiiUv, i.e. of 



ulctcoritic swarms. 



In that vcf)' simple statement we have perhaps the very 

 greatest and the most fundamental change which hivs lieen sug- 

 gested by the new hypothesis. I am quite certain that all of 

 you who have rciid texlUiulcs of astronomy will t>e perfectly 

 familiar with the statement that all stars are distant suns. I 

 have written that myself several times, liut I now know that it 

 is not true. .Some stars, instead of being distant suns like our 

 sun. a condensed mass of gas with a crtisl gradually forming on 

 it, and a thick atmosphere over it, are simply the Ijrighter con- 

 denaitions, the central condensations of nebuhv, whether they 

 lie like that nf .\ndr<imcda, or planetary nebul.v, or such a 

 nebula as that of Oriim. Vou see the idea is perfectly new and 

 completely different from the old one, which taught us that all 

 -Stars were suns. Shortly after I made this as.sertion, photo- 

 graphv came to our aid. and I am so fortunate as to Ix; able to 



I . . -'1. .S- lail.i i-'iinil I) Ar^i!^ ( i 'r. * iiilj. 



prove to yiu the absolute truth of it by an appeal to Nature 

 herself; that is. I refer fur demonstration to autobiographical 

 records with which the heavens themselves have supplied us. 

 Among the tinesi anil most wonderful of the nebulx is one 

 which, unforlun.alely, we do nut see here, liecause it is in the 

 viuthern hemisphere : it is that surmunding the star ij in a 

 wonderful constellation. .\rgo, which it isipiite worth while to go 

 •inuth to sec, were there no other re;Lsons. Krom the photo- 

 Kraph you see that there is such an intimate connection, such 

 nn obvious relation, lietween st^ and nebula, that it is iinpos- 

 sible for us to inmgine for one moment that they arc not most 

 Clr«cly and mlimalely connected. 



I will now bring liefore you another case which we can, all of 

 u.%, .we, w> far as a certain (Kirt of the phenomena is concerned, 

 and especially al this lime of the year. I refer to those "stars," 

 the »ix I'lciads. which you will rememlier once lo.st a sister, 

 that one sees in the constellation of the Bull. Mere they are, 



• KcvimnJ from ^horlh.in'l note* of a course of I^cturcft to Workinjt Men 

 Al the Mutetmi of l'f;M;ii<:.'tl (Ecology during November and DcccmlM:r, 

 lB04. (Ojntinued from y*4,<: 14.) 



photographed by Dr. Roberts. You see they are not stars ; they 

 are nebula:. \\'hat we see in this photograph (see Kig. 25), in 

 the case of e.ich so-called " star," is obvious ; we see the centre 

 of condensation, and more than that, it is not a simple con- 

 densation, but there are stream-lines going in all directions, 

 and the maximum luminosity, where we locate the '* star." is 

 just at the place where, according tu this photograph, the 

 greatest number of the.se streams cut each other, antl where, 

 therefore, we. should get the greatest |xissible number of collisions 

 per second of time. The main point demonstrated by this 

 photograph, then, is that we are not dealing with stars anything 

 like our sun : we are simply dealing with nebidous condensa- 

 tions. I can show you the spectra of the lirighter parts of these 

 condensiitions, anil you will see tliat they resemble the spectra ot 

 ordinar)' stars. Broad dark lines of hydrogen are represented 

 in every one ; hence, although we are dealing not with a star 

 like the sun, but a meteoric condens.tlion - a place of inter- 

 section of streams of nebulous matter — we get a spectrum such 

 as is generally as.sociated with the spectrum of a star. And for 

 this there is very good reason. 



Mere an interesting ]K)int comes in. Suppose that we wished 

 to observe spectr< s-opically what was going on in these condensa- 

 tions, and that I allow the image of one of them to fall on the 

 slit of the spectroscope, so that we have the condensittion at the 

 centre, and the ends of the slit of the spectroscope beyond the 

 condensation. At the centre, where the slit crosses the con- 

 dcnsjition, of course we should have the spectrinn which you have 

 already seen on the .screen, a spectrum indicating that there is 

 something there which gives us a continuous spectrum, i.e. one 

 rich in all the colours of the rainbow ; liut thai some of the light 

 is absorbed here and there in consequence of the surrounding 

 atmosphere of hydrogen gas. So much for the centre. Next 

 consider what will hapjien when I observe, for instance, this or 

 thai part of the nebula where the condensation is absent ; we 

 shall not get absorption phenomena, but we shall get radiation 

 phenomena, and therefore a long bright line representing the 

 radiation of hydrogen over a large area, and al the middle of it 

 the ordinary spectrum of a star. I'rof. Canqibell, at the Lick 

 Observatory, has recently subjected another star to a similar 

 treatment, and you will .see (Fig. 26) what he has found. By 

 letting the .slit of the si)ectroscoi)e ui)on the image of the star, 

 lie finds that he gets the spectrum from one end to the other ; 

 but you .see that at the place occupied by one of the hydrogen 

 1 lines he gets a much longer image of the slit, showing that he 

 I had to deal there with a star immersed in something which was 

 ! competent to give a spectrum of hy<lrogeii. What was that 

 I something? N'ou can understand perfectly well thai, if one of 

 I the rieiads had been examined in the same way, it would be 

 I quite possible that we should get just such an ai)l>earance as 

 I I'rof. Campbell was fortunate enough lo obtain. This raises 

 i an interesting i|ue.stion, in which astronomic thought has been 

 going up and ilown now for the last foiirlecn or fifteen years, 

 and I think I can show you exactly liow llic mailer lies. The 

 diameter of the sun is very nearlya million miles. Now, supjiosc 

 Ihal Ihe iliameter of the solar atmosphere was ten million miles ; 

 then if we were by any means whatever lo speclroscopically 

 examine Ihe image of ihe sun under such condilions llial all the 

 light coming from these different regions could enter ihe slit of 

 the speclroscope al the same lime, and give us, aildcd logelher, 

 the whole light, we shoiiM be able lo ilelermine practically what 

 we might be able to see uniler these conditions by some such 

 considerations as these ; — 



Diameter of the sun, one milliim miles. 

 Diameter of the sun's atmosphere, ten million miles. 

 We shoulil therefore get the light from the sun in the ratio of 

 I to 99 'of Ihe light from the almosphere. Now suppose that 

 there is any chemical connection belween the absorplion in the 

 light of the sun and Ihe radialion in Ihe light of ihe sun's al- 

 mosphere, if we sweep the slit of the s|Krlr<iscope along ihced^e 

 of Ihe sun, the part of the spectrum which writes for us wh.at is 

 going im in the sc.lar phi>losphcre, gives us the speclriim crossed 

 by dark lines : Ihe eflecl of the almosphere is to absorb ihe light 

 of the more distant sun at which we look, and the result of ihe 

 absorplion is lo give us dark lines. 



Hul when we look al ihe almosphere which is resting on the 

 c.lge oflhe sun. an<l look at it where there is no brighler sun 

 behinil, absorplion no longer comes inio play, ami we get bright 

 lines. This is what happens when we look al the solar atmosphere 

 above Ihe sun's eilge and the solar atmosphere between us and 

 the sun. So long :is we are telling ihe slory of ihe sun, we get 



NO. 1337. VOL. 52] 



