176 



KNOWLEDGE 



[Adocst, 1902. 



DISTANT WORLDS. 



U.— A KEVIf]\V OF SOME RECENT STUDIES 

 IN STELLAR DISTRIBUTION. 

 By C. Easton. 

 We have just seen by the aid of Stratonoff's charts 

 that if we consider the Arj^'ehiiider stars (mag. — 95) 

 projected on the Milky Way, the great majority of these 

 stars are not scattered in little groups irregularly spread 

 over the whole Galactic zone ; but tliat they are groujied 

 for the most part iu a few somewhat large condensations 

 (three or four in the northern hemisphere), whose 

 configuration is not much modified for stars below the 

 8th magnitude. But here an important question is pre- 

 sented. These great stellar condensations, in Cygnus, 

 Auriga, &e., are they not effaced as soon as we take into 

 consideration the innumerable numbers of stars fainter 

 than those in the " Durchmusterung," that is to say, the 

 multitude of stars of which the Milky Way, properly 

 speaking, is above all composed':' 



We have already an indication that it is not so ; the dis- 

 tribution of stars visible to the naked eye is quite different, 

 whilst a simple inspection of the charts of the Milky Way 

 shows a great analogy between the image formed by the 

 entiretv of the small stars and the distribution of the 

 lower classes of Argelander. An interesting research, 

 executed in 1893 by the German astronomer Plassmann, 

 also anticipates the results to which Stratonoff leads 

 us. And I had commenced an enquiry with the object 

 of elucidating this question of a possible " correlation " 

 between the distribution of stars of a medium brightness 

 and the very feeble ones, when Stratonoff's atlas appeared, 

 greatly facilitating my preliminary labours, whilst necessi- 

 tating the rehandling of tlie Russian astronomer's data to 

 make them comparable to the values indicating the distri- 

 bution of the "Galactic stars." 



In order to estimate, as precisely as these researches 

 admit, the distribution of the very small stars in the 

 Milky Way, I first constructed an isophotic chart of the 

 Galaxy, following the example of the Belgian astronomer, 

 J. C. Houzeau, in 1876, but working according to a 

 different method so as to obtain a much more detailed 

 chart. This chart for the part of the Milky Way which 

 extends from AquUa to Cassiopeia is published here for 

 the first time. Here the curves do not re]iresent, as on 

 the charts of Stratonoif, lines of equal stellar density, but 

 lines of equal brightness (isophotes) of the Galactic Ught. 

 From this chart I was able to deduce, by a method too 

 lengthy to give here,* numerical values representing the 

 intensity of the Galactic light for equal surfaces of a 

 given size, into which the Galactic zone had been divided, 

 and it is evident that when these values are compared with 

 those obtained for the stellar density of the Argelander 

 stars, calculated for the same surfaces, the divergences 

 which may appear should be attributed to extremely faint 

 stars. We have thus a means of evaluating the richness 

 of the Milky Way in feeble stars, and the particular 

 distribution of these small stars. 



But from such a comparison it appears, first of all, that 

 the great condensations of stars that begin to be seen in 

 those of the 8th magnitude are faithfully repnijuced — 

 taken as a whole— in the very faint "Galactic stars." 

 This agreement, made by the aid of numerical values, is 

 of much greater weight than the similar conclusion which 

 was already drawn iu a general way from the comparison 

 of the charts of the Milky Way with those of Stratonoff. 



What is the significance of this phenomenon ? 



* The detailed account of these researches will appear shortly in the 

 Proceedings of the Soi/al Academy of Hciences of the Netherlands. 



In the first place it is evident that it is not com|)atible 

 with the supposition that, in the parts of the universe 

 accessible to our observation, the stars, so to speak, form 

 islands in the ocean of space ; a great number of isolated 

 groups, separated from each other by intervals considerable 



Isophotic Chart of the Milky Way from Cassiopeia to Aquila. 



as compared with the dimensions of the groups, a 

 supposition which, according to many astronomers, agrees 

 best on the whole with what we know of the structure of 

 the universe. For, in this case, in proportion as the tele- 

 scope or the photographic camera penetrates deeper into 

 the stellar universe, new accumulations should make their 

 influence felt, and should destroy the image of the stellar 

 distribution produced by the stars nearest to us. and which 

 form but an insignificant fraction of the whole. (All of 

 Argelander's stars constitute but the huudredth part of 

 the whole of Herschel's stars.) On the contrary, we have 



