March 1, 1898.] 



KNOWLEDGE 



59 



and on photographs, will recognize, I believe, that the 

 clun-tiiin- of the Milky Way is not the same iu Sagittarius 

 and Scorpius, where brilliant and irregular masses — which 

 rather appear to be individually connected with parts of 

 the secondary branch (or with its brilliant stars) — alternate 

 with dark or poor regions ; in the region of Andromeda, 

 Lacerta, and about = Cygni, where an even stream 

 runs parallel to the galactic axis ; or in Cassiopeia, 

 Perseus, and Monoceros, where the tendency to duplica- 

 tion has been noticed in some cases independently by 

 Boeddicker, Easton, and Pannekoek ; or in the region 

 round Aquila to the west of Altair, where there is arranged 

 a series of fairly bright patches. 



A remarkable peculiarity of the general distribution of 

 the galactic light between a. and ; Aquibi? and (i Cassiopeia; 

 is that in the principal (following,') branch the brightness 

 decreases (iradualhj from the interior border to the exterior, 

 whilst the secondary (preceding) branch is much more 

 uniform. There is only one exception, but that is a 

 curious one : between y Sagittic and v Cygni it is the 

 principal branch that appears dull, whilst a great brilliant 

 patch stretches between /3 and 7 Cygni, on the interior 

 border of the secondary (preceding! branch ; it encroaches 

 a little on the dark interspace. A small, very brilliant 

 patch, a little distant, between x and 68 A Cygni, is 

 situated exactly on the galactic axis. 



I will only recall here the well-known argument of 

 Sir John Herschel on the ilark spaces with -well-defined 

 contours in the midst of a luminous zone (Coal-Sack): a 

 similar opening, in connection with a dark, large rift, 

 visible to the naked eye, passing between 68 A and p Cygni, 

 is found in a dim part of the zone between x Cygni 

 and a. Cephei — first drawn, I believe, by Heis. These two 

 are the chief. The probability is, in fact, very great that 

 we have here veritable holes in a " galactic band or 

 stream," fairly shallow, and fairly remote from us. 



We may add that the dark regions which often stretch 

 over large spaces, and which sometimes form veritable 

 intervals between two luminous streams, and occasionally 

 bear the character of fissures in a bed of luminous 

 matter (Mr. Kanyard and Mr. Maunder especially have 

 drawn attention to these curious dark lines in this same 

 magazine ), indicate that in several regions the Milky 

 Way is principally formed by a band or layer, relatively 

 shallow (which does not prevent another band or clusters 

 of stars being possibly projected upon this layer), but 

 fairly extensive in longitude and latitude. Sometimes, as 

 between 74, 68 A, and p Cygni, a large fissure crosses the 

 greatest part of the Milky Way in all its breadth. All 

 this does not easily fall in with the theory which only sees 

 in the Milky Way agglomerations, wholly chaotic, of stars 

 and clusters. 



The very extensive nebulosities, discovered lately by the 

 aid of photography, which sometimes envelop an entire 

 constellation (Orion, Scorpius), and which are certainly 

 related to the stars, furnish also a valuable argument for 

 the theory that certain extensive parts of the Milky Way 

 are in reality associated, and form each a more or less 

 complete whole. 



Thus, I believe, we must come back to this considera- 

 tion. In detail, the real distribution of the stars in the 

 Milky Way is very irregular. In the grouping of the 

 stellar agglomerations there is manifested, however, in a 

 certain degree, a systematic distribution. This organiza- 

 tion of the stellar matter does not, however, go so far 



» See Knowmdob, 1891, October, December; 1892, May ; 1S93, 

 April ; 1894, October ; 1895, January, Februarv, August, Norember ; 

 1896, February. 



as to produce a geometrical figure of any regularity what- 

 ever—ring, ellipse, or one or more rings, concentric or 

 interlaced. 



The undoubted connection between certain stars, nebu- 

 losities, and parts of the Milky Way, overthrows the theory 

 that the Milky Way is infinitely more distant from us than 

 the bright stars. Certain regions of the Milky Way may 

 be relatively near us. It follows from the researches of 

 Celoria that in all probability the Milky Way in Orion is 

 much nearer us than the opposite parts of it. But the 

 same conclusion is arrived at for other portions of the 

 Galaxy. I believe that " Holden's ellipses " * — stars ranged 

 in chaplets. etc. — are not, at least In certain cases, the 

 result of optical illusion (see the magnificent photo- 

 graphs published in Knowledge, 1891, October and 

 December — the region between a, f, and /' Cygni), and 

 that the dark fissures sometimes bordered by long ranges 

 of stars, and other phenomena of the same nature, are 

 undoubtedly real. Whatever may be the reason of these 

 strange peculiarities of distribution, it is indeed too difficult 

 to imagine that the regions where they are produced are 

 at incommensurable distances. 



Sir .John Herschel has already pointed out that the 

 "long lateral offsets which at so many places quit the 

 main stream of the Galaxy, and run out to great distances, 

 are either planes seen edgeways, or the convexities of 

 curved surfaces viewed tangent iaJli/, rather than cylindrical 

 or columnar excrescences, bristling up obliquely from the 

 general level." (" Outlines," j 792.) 



There is nothing, indeed, inadmissible in such trains of 

 stars — veritable branches of the Milky Way — lying across 

 the interior of our stellar system, and, in some cases, coming 

 near our sun. Combining this supposition (which gives a 

 plausible explanation of more than one question) with the 

 theorv of " segments of a ring," to which Celoria's theory 

 might be reduced, we find a system of spirals the most 

 simple figure that we can imagine the Milky Way to 

 assume according to this train of thought. 



As an analogy from what we see in the heavens, I will 

 take, not the nebula of Lyra, but rather the nebula Mess. 

 101 Ursae Maj. (Eoberts, " A Selection of Photogi-aphs," 

 1894, p. 32 ; also Knowledge, February, 1897, p. 54, Fig. 2), 

 or else the celebrated spiral nebula in Cines Venatici, 

 Mess. 51 Can. Venat. (Roberts, ihid., p. 30 ; and Know- 

 ledge, February, I8I17, p. 54, Fig. 4). 



This analogy also leads us to seek for a central nucleus 

 towards which the spirals may be directed. Now there 

 is one region in the Milky Way which, it indeed appears, 

 may occupy such a position. 



In discussing Celoria's theory we have seen that, to 

 explain the more general traits of the galactic problem, 

 we might place the sun excentrically in one great ring 

 (nearer to the Monoceros border), and inside a smaller 

 ring. As the points of intersection of these two hypo- 

 thetical rings, inclmed to each other at about nineteen 

 degrees, are distant from each other in the heavens about 

 one hundred and eighty degrees (Crux — Cassiopeia), it was 

 better to imagine the inner ring as fairly small. On the 

 other hand, the sun ought to be near that part of this 

 small ring which is iu the direction of Monoceros, since 

 this region is fairly well resolved into separate stars (see 

 my preceding article). If Celoria had made his counts, 

 not along the equator, but at about thirty-five degrees, he 

 would have found that this secondary " ring," very dim in 

 general, has one brilliant portion in Cygnu3 ; and this por- 

 tion, opposite to that region to which our sun is nearest, is 

 situated (in the smaller ring) at the middlf of the sysfim. 



* Holden, Puhlicafions Washburrt Observatori/ , II. 



