ft 2 



* KNOWLEDGE 



[Jan. 30, 1885. 



wonders of the solar system, is demonstrably incorrect. 

 From the observed size of those clusters we know that the 

 entire span is less than the thousandth part of the distance 

 separating us from them. Yet at the distance at which 

 they lie wo can discern separately thousands of stars. 

 Thus the average distance from star to star within .some of 

 these groups cannot be one millionth part of the distances 

 separating those groups from us. The splendour of seme 

 among those stars, as seen from the midst of those 

 groups, cannot therefore but exceed a billion* times 

 their lustre as seen by us. Since then these 

 stars can in the case of the more magnificent 

 clusters be seen with very small telescopes, it follows 

 that from the middle of those clusters they must 

 shine with a glory comparable with that of our own sun, 

 whose lustre at the distance of the nearest of our stars 

 would not be reduced to more than one .50,000 millionth 

 part. If then there are worlds circling round those suns, 

 there can then be no night for their inhabitants, but pro- 

 bably a constant daylight exceeding many times in glory 

 the most resplendent of our summer days. I should be 

 disposed for my own part to imagine rather, though I must 

 confess I know nothing on the subject, that if there be in- 

 habited worlds at all in connection with a glorious cluster 

 of this sort, they must be worlds circling round the whole 

 cluster, not round the individual stars composing it. But 

 more probably, I should say, there are no such worlds, but 

 those clusters will hereafter aggregate into suns which in 

 due course will l>ecome the centres of solar systems, more 

 or less (probably very little) like the family of planets to 

 whicli our earth belongs. 



These considerations may serve to show what interest 

 surrounds the inquiry into the architecture of the sidereal 

 heavens. If two varieties of stellar arrangement alone 

 suggest such diversity of condition, what might we not 

 expect to follow from the consideration of all the pecu- 

 liarities of stellar distribution which may be recognised 

 when the heavens are carefully surveyed 1 It is to such work 

 as is thus suggested that I referred in the opening remarks 

 of my former article. The failure- of the two methods of 

 gauging, devised by Sir W. Hersohel, should by no means 

 discourage astronomers from prosecuting diligent researches 

 into the noble problems dealt with by him. Not only, as 

 I have shown, did each failure involve an important and 

 quite unexpected discovery ; but both these failures helped 

 to show along what lines the inquiry may best be prose- 

 cuted, 



I propose now briefly to consider what these lines are, 

 touching somewhat on the work I have myself done in pur- 

 suance of this .special inquiry, and dealing somewhat more 

 fully with the work which has to be done (even in the 

 earliest stages of the inquiry) wherein also I hope to bear 

 a part, 



"Wilhelm Struve was led by his study of the papers of 

 Sir W. Hcrschel to recognise — but only indistinctly — the 

 importance of combining the principles which underlie the 

 two methods of star-gauging : — 



In any true survey of the star-depths it is manifestly 

 essential that the system of counting stars with the same 

 telescope, and as nearly as possible under the same condi- 

 tions, should bo carefully applied. And we shall not be led 

 astray by this system if we do not interpret our results on 

 an incorrect principle, as Sir William Herschel did in the 

 beginning of his work. Moreover, we can apply this system 



* By a IjillioLi I mean a million millions, by a trillion a million 

 million millions, rind so fortli, the English way of reckoning, by 

 which a billion, a trillion, a quadrillion and so fort;h, means a million 

 raised to the second power, the third power, the fourth power, and 

 so forth. 



in ways which at first he would have rejected as useless. He 

 supposed that the great gauging telescope which he applied 

 reached in all directions to the very limits of the sidereal 

 universe, and it is clear that nothing short of such a power 

 as he thus supposed himself to be applying could have 

 served his purpose if our galaxy were such a sy,'jtem as he 

 imagined. But that particular space- penetrating power, 

 though it did not do what Herschel had expected (because the 

 stellar universe is not what he supposed it), and though it 

 was unequal to the task of resolving all parts of the stellar 

 heavens, disclosed, as we have seen, important truths. It 

 is manifest that less telescopic power would have also given 

 important results, — seeing that the condition Herschel had 

 sujiposed essential to the validity of his survey had no real 

 existence. Nor can one see any reason to limit the diminu- 

 tion of telescopic power by which useful results might be 

 obtained. Without telescopic aid at all, the distribution of 

 stars numerically might be well worth studying. Nay, it 

 might be worth while to examine the distribution of stars 

 visible with less than ordinary powers of vision. 



It was the recognition of this (possibly a half-uncon- 

 scious recognition) which seems to have suggested Herschel's 

 second method of star gauging. In this he took only a very 

 small region for survey, and examined that with constantly 

 increasing telescopic power, under the idea that he was thus 

 lienetrating more and more deeply into space. Now this 

 kind of research, too, is manifestly essential in any true 

 survey of the star depths. Nor shall we be led astray by 

 this system unless we misunderstand what we are doing. 

 We mai/ be penetrating more deeply into space as we 

 increase our telescopic power, or we ma>/ simply be ana- 

 lysing more and more scrulinisingly a particular region of 

 stellar space : more probably we are doicg botli. But if we 

 keep our minds free from any bias one way or the other, our 

 results will always be available for the increase of our know- 

 ledge so soon as we can co-ordinate them properly together, 

 and combine them duly with results otherwi.se obtained. But 

 manifestly we must for this purpose extend this method of 

 survey to larger regions than Sir William Herschel dealt 

 with. If his principle of interpretation had been sound, 

 his plan of applying the method would have been all that 

 was needed. But so soon as we recognise the unsoundness 

 of the principle, and note how that unsonndness was shown 

 by the study of small regions of the heavens, and how im- 

 poitant in itself was the discovery thus made, we see that 

 results of great importance may be obtained by extending 

 the survey by this method. Nor can we see any reason to 

 limit the extent of the survey thus made. It may be 

 aj)plied to the whole heavens, if only a large enough array 

 of labourers can be persuaded to take part in the work. 



The study of the proper way of applying each method 

 points, then, to one and the same result, — viz., that the 

 whole star sphere requires to be surveyed with every order 

 of visual power (separately) from the unaided vision, or 

 even from visual powers lower than ours ordinarily are, to 

 the highest telescopic power that can be obtained. 



A colossal work truly : but then, fortunately, it is not 

 necessary that the whole work should be undertaken at 

 once. Any part of it, — the survey of any portion of the 

 heavens with such and such telescopic powers, or the 

 .survey with any definite telescopic power of the whole 

 heavens or any part of them, — means so much added 

 to our knowledge of the architecture of the complex system 

 of .stars of many orders, star-clusterings, star-clouds, and 

 other forms of matter, which we call the Galaxy. 



The elder Struve, recognising the importance of com- 

 bining both systems of survey, began the task by a piece 

 of work which cannot but be regarded as very rough 

 indeed, though it has been enthusiastically admired by the 



