May 1, 1886.] 



♦ KNOWLEDGE ♦ 



225 



And here an important point presents itself to our con- 

 sideration. Admitting this fundamental hypothesis, it is 

 very obvious that we must jjay no attention to the signs of 

 special laws of association among the lucid stars. These 

 ctars are altogether dissociated from each other in reality, 

 however they may seem associated — if only that hypothesis 

 is correct. But when we are inquiring lohetJier that hypo- 

 thesis is correct, these signs of association are all-important 

 for our guidance. We are bound to inijuu-e whether they 

 can be accidental. And so we are no longer free to smooth 

 the star-groupings away bv taking averages. 



This bears in a very important manner on the problem 

 presented by the Milky Way. Sir John Herschel, follow- 

 ing very accurately the law of star gauging, comparts the 

 total number of lucid stars on the galactic zone with the 

 total number on the rest of the sky, and finds no trace of 

 any aggregation in the former region. Hence he concludes 

 (very justly, when once the fundamental law is accepted) 

 that there is no real association between the lucid and the 

 telescopic stars on the galactic zone.* 



But suppose that instead of con.sidering the galactic zone, 

 instead of spreading the galaxy over a belt which it does not 

 really cover, wo look at the galaxy itself. And suppose, 

 further, that as a first process of examination we compare 

 the number of lucid stars fivlling on the galaxy with the 

 number falling on the dark rifts and coal-sacks ui the 

 Milky Way, and on ihe space which separates the two 

 branches where tlie galaxy is double. Doing this, we find 

 at once the most striking evidence that the lucid stars are 

 closely associated with the telescopic galactic stars ; for we 

 find a marked disproportion between the number of stars 

 on the dark regions and the area covered by these regions. 

 In many places, especially in the southern heavens, we find 

 the very shape of the Milky Way indicated by the stars 

 which lie round the border of the dark regions, but with- 

 draw themselves, so to speak, from those vast ojisnings into 

 space. 



Take as an illustration the coal-sack in Crux. Is it an 

 accident that over this large dark space, covering about 

 50 square degrees, there is not a single lucid star, while all 

 round its borders lucid stars are strewn in plenty? The 

 whole surface of the heavens exceeds the co.il-sack some 

 eight hundred times in extent; and as there are about 

 G,000 lucid stars, one might expect seven or eight such 

 stars to be found in the coal-sack. But this is far from 

 being all. The neighbourhood of the coal-sack is much 

 richer in lucid stars than other regions in the heiivens ; so 

 that it is just where stars should be most richly distributed 

 that this vast black spot makes its appearance. The question 

 whether the absence of stars from the coal-sack and their 

 presence in great abundance in the Milky Way around that 

 vicinity are to be regarded as a mere coincidence can 

 scarcely be doubtful, I think, to anyone who studies 

 thoughtfully the portion of the galaxy depicted in fig. 2. 

 Nor, perhaps, is the way in which the sharply-defined 

 semicircular cavity on the right is associated with a 

 semicircular stream of stars less significant. No one who 

 examines this region thoughtfully can doubt, I should 

 imagine, that the lucid stars seen in it are mixed up with 

 the telescopic stars forming the Milky Way here. 



But if we admit that such evidence as this (and much 



* In his " Outlines of Astronomy " he uses expressions which 

 woulfi seem to indicite that lie had forgotten the facts very clearly 

 established and described on pages 381 and 383 of liis observations 

 made at the Cape of Go;d Hope. Nor can one wonder at this 

 when one considers the wonderful range and extent of the observa- 

 tions recorded in that most valaable treatise, second only (if 

 second) in value to the series of papers by liis father in the 

 Philosophical Transactions of the Koyal Society. 



more of the same kind might be adduced did space permit) 

 should lead us to regard the Milky Way as forming a stream 

 of really small stars, swayed into its present figure by the 

 large ones in its neighbourhood, it might seem that, so far 

 from showing that our sidereal system has no limits, we 

 should have gone far to prove that its dimensions are much 

 smaller than had been imagined. 



It is true that, according to these views, the small stars 

 in the Milky Way would be flu- nearer to us than has been 

 commonly supposed. But on the other hand, it would 

 follow with equal certainty that we could no longer imagine 

 we had even in any one direction pierced to the limits of the 

 sidereal system. If in searching into the depths of any part 

 of the Milky Way we are, in truth, merely searching more 

 and more closely within' a definite group of stai-s, be^'ond 

 that group there may lie at enormous distances other groups 

 which no telescope we can construct may even render visible. 

 It was only, indeed, whilst it was thought that the sidereal 

 system is continuous throughout its limits that astronomers 

 could hope to say where those limits lie. If, on the con- 

 trary, 1 am right in believing that the sidereal system 

 consists of aggregations of every conceivable form, those 

 aggregations may extend into space, millions on millions of 

 times beyond the limits of the most powerful instruments 

 man mav ever be able to construct. 



i^flu 35ook5 to I)f lAcatr (or aboiUfD)— 



lutke's Shrini>, by Graxt ALLE>f. Mr. Grant Allen's 

 new story is a vigorous example of the " scientific use of 

 the imagination ; " the license of fiction is nowhere re- 

 strained, but the accurate description which comes of 

 insight into, and .sympathy with, nature's least garish 

 scenes, is not lacking. The tale opens weirdly enough in the 

 scorching jungles of India, but is speedily transferred to a 

 humdrum watering place of old-fashioned type on the breezy 

 fiats of East Anglia. Tlie incidents are numerous and 

 original enough, however, to make the dry bones of the old 

 town live again ; and we can promise our readers an honest 

 shillingworth's excitement, not without safety-valve in 

 the se(iiiel. Mr. Allen has, in more than one of his deliglit- 

 ful fugitive sketches, laid stress on the unsuspected beautv 

 in mud, and in " Kalee's Shrine " that unstable compound 

 is made the scene of an episode which, for inducing an 

 " eerie " sensaticm in the reading, has not been excelled, if 

 equalled, in any of the now famous series in which the 

 s.tory is published. We must not risk spoiling the reader's 

 interest by telling it. 



Handbook of Mosses. By James E. Bagxall, A.L.S 



(London : Swan Sonnenscheiu, Le Bas, ct Lowrey. 1880.) — 

 The country reader who wishes for an introduction to a 

 living world of strange beauty and variety, as well as the 

 incipient student of bryology, may buy Mr. Bagnall's well- 

 wr.tten and equally well illustrated little volume with the 

 certainty of finding what he wants within its two covers. 

 Its author describes the few and simple appliances needed 

 for the collection and examination of the.se exquisite lowly 

 forms of vegetation ; describes their development, instructs 

 ns how, when, and whei-e to find them ; gives a classification 

 of the British species extensively illustrated ; furnishes 

 directions for their cultivation ; and winds up with a chapter 

 on their preparation for the .cabinet and herbarium. His 

 work is well and honestly done throughout. 



