538 



KNOWLEDGE & SCIENTIFIC NEWS. 



[September, 1906. 



of Struve's grent catalogue, and on his work being sub- 

 mitted to the Royal Astronomical Society, tiic Council 

 decided to publish it as one of their Memoirs. In this 

 magnificent volume, 715 pages quarto, Jvlr. Lewis has 

 brought together the original olwervations made by 

 Struve, of each double star, the observations made on 

 the same by various observers throughout the world up 

 to the present time, and those made by himsell and his 

 co-workers at Greenwich. From these he has deduced 

 the orbits in which the pairs move about each other, 

 wherever the material available is sufficient for that 

 purpose, adding, wherever possible, particulars as to 

 their masses, sixes, colours, and spectra. 



There is no nationality in science, and yet there_ is a 

 legitimate source for gratification that so magnificent 

 a Memoir has been brought out by an English astro- 

 nomer; that the observations of the great English Ob- 

 servatory have contributed so much to its completeness; 

 and that it is published by the great English astronomi- 

 cal society. For, as has already been mentioned, it 

 was an Englishman who founded double star astro- 

 nomy, and some of the most distinguished workers in 

 the iield in its early days were also Englishmen. To- 

 wards the end of the nineteenth century, however, this 

 important department was falling into neglect amongst 

 English observers ; the present President of the Royal 

 Astronomical Society, Mr. W. H. Maw, being one of 

 the very few who were keeping up the traditions of the 

 Herschels, father and son, of the Rev. W. Dawes, and 

 other great names of the earlier part of the century. 

 The appearance of this Memoir is a proof that the sub- 

 ject has not lost its interest to English a.stronomers of 

 to-day, and that it is being followed up with an energy 

 and a skill in no way inferior to those of the very best 

 workers of earlier days. 



And the Memoir will tend to de\elop further activity 

 in this field, and to render that activity much more 

 efficient. It will be a great help to the double star 

 observer thus to be at once put in possession of the 

 observational history of any given star, without the 

 necessity for a long and arduous search through re- 

 cords; whilst he can here i-eadily learn what stars h:ive 

 been fully observed and what have been neglected, and 

 when it 'is needful that this or that binary should be 

 specially watched. The Memoir is not only a record of 

 past work; it will be an important basis for work in 

 the future. 



But Mr. Lewis's work has a significance quite apart 

 from the presentation of details respecting the re- 

 lative motions of certain close stars, and it affords 

 a remarkable example of the way in which the various 

 problems of astronomy are intermingled, the one with 

 the other. At first sight it would appear most unlikely 

 that the watch upon one member of a pair of stars as 

 it slowly gravitates round the other, should afford any 

 clue as to the general form of the stellar universe; yet, 

 as Mr. Lewis has shown in his Introduction, this alto- 

 gether unexpected information does come out from the 

 present Memoir. This important result partly follows 

 from the far-seeing and comprehensive character of 

 Struve's original work, and partly from the simple but 

 ingenious treatment to which Mr. Lewis has subjected 

 the material at his disposal. 



During the two years, February 11, 1825, to 

 February 11, 1827, Struve examined 120,000 stars from 

 the first to the eleventh magnitude, and found 3,112 

 double stars, whose distance apart did not exceed 32". 

 Several of these pairs were rejected from the final cata- 

 logue of 1837, the " Mensurae Micrometrica.- " and a 

 few fresh ones were added, so that the 1837 catalogue 



contains 2,640 pairs. Now in the seventy years which 

 separates us from the date of the " Mensurae Micro- 

 metricae," many of these objects show no clear evidence 

 of relative motion; others as unmistakably are moving 

 the one with respect to the other. Mr. Lewis, there- 

 fore, divides the items of the catalogue into two 

 classes — pairs in which the members are relatively lixed, 

 and pairs of which the members show a motion relative 

 the one to the other. 



Now if we examine the distribution of the stars of 

 the catalogue, certain facts become apparent. First of 

 all an examination of double stars in general — no dis- 

 tinction being made between fixed pairs and pairs with 

 relative motion — shows that their distribution follows 

 very closely the distribution of stars in general. But 

 quite a different state of things prevails if we inquire as 

 to the proportion which the fixed pairs bear to the rela- 

 tively moving pairs in different parts of the sky. The 

 natural expectation would be that the two classes would 

 show the same general law of distribution, and hence 

 that the ratio ~ would be much the same from what- 

 ever region of the sky it was derived. As a matter of 

 fact its value is about three times as great in one region 

 of the heavens as it is in the opposite. 



What can be the explajiatipn of this curious and 

 strongly marked relation? Mr. Lewis explains it as 

 follows : — 



"There is a very simple cause which mii;lit alter the 

 [jroportion between fixed and moving pairs in differ- 

 ent parts of the sky. 



" (liven a keen observer with an instrument of a cer- 

 tain power, and let him tabulate the stars which 

 appear double or multiple in a systematic search, 

 and suppose, for example, that he can find such a 

 triple as i' 2367, where 



A and B are separated c*' .4 and form a rapid 



binary ; 

 A and C are separated I4''.i and are relatively 

 fixed. 



" Now reduce the power of his instrument to one-third 

 and he can no longer see B, since i''.2 Is the smallest 

 separation he can perceive — he might elongate o ".8 

 The pair AC becomes a double star with no relative 

 motion. The same effect is obtained by retaining 

 his original instrument and removing the triple to 

 three times its former distance. The separating 

 power of his telescope is o ''.4, but B's distance from 

 A is now o".i3, and C's is 4''. 7, so that B is still 

 invisible, and C a fairly near companion without 

 relative motion. 



" I'ut in a different manner, my suggestion is : — 



'■ There is no apparent reason why distant stars should 

 not have close companions endowed with orbital 

 motion as frequently as those nearer to us, nor is 

 there any known reason why double stars should 

 not be evenly distributed in space. If we find this 

 distribution is not uniform it may be that in certain 

 regions the stars are, as a whole, more distant from 

 us than in others. Granting this, the proportion of 

 fixed pairs to pairs showing relative motion should 

 be a function of the distance of the stars from us." 



It will be remembered that some three years ago Dr. 

 .'\lfred Russel Wallace brought out a most interesting 

 book the purport of which was to show that the entire 

 trend of modern astronomy proved that the solar 

 system was in the centre of the entire visible universe. 

 It is one of life's little ironies that at that very time 

 Mr. Lewis's Memoir was ready for presentation to the 

 Royal Astronomical Society, with his demonstration 

 that the statistics of double stars appear to show that 

 the stars around us form a universe very much the 

 shape of an egg, and that we are not situated in the 



