86 



KNOWLEDGE 



[May 1, 1891. 



Geminorum) also lie in a small cluster of stars, which 

 may also be well seen ■nnth a binocular. 



The well-kno\vn double cluster x Persei may be seen 

 with an opera-glass, but a telescope is necessary to see the 

 component stars, and the larger the instrument the greater 

 the number visible in these wonderful objects, which, 

 like many somewhat simDar clusters, lie in the Milky 

 Way. This twin cluster has been well photographed at 

 the Paris Observatory, and also by Mr. Roberts. On the 

 Paris photograph^ — at least, in the paper print in my 

 possession — the clusters are clearly resolved into stars 



with no trace of outstanding nebulosity, suggesting that 

 the component stars are probably at nearly the same 

 distance from the earth. 



The cluster 39 ilessier, between tt' and 71 Cygni, may 

 be well seen with a binocular, in which it somewhat 

 resembles the Pleiades as seen with the naked eye. 



Another fine open cluster will be found a little north, 

 following /3 Ophiuchi. Between fi and y Ophiucbi is a 

 remarkably blank spot. On August 15, 1800, I failed to 

 glimpse the faintest star with binocular in a clear, moon- 

 less sky, a striking contrast to the rich region north of /3. 

 A similar blank space will be found just north of the stars 

 IT and <t> Aquilie (north of Altair). On September 3, 1886, 

 I could only see glimpses of very faint stars with the 

 binocular in a sky clear and moonless, a remarkable 

 vacuity so close to a region of bright stars, and a good 

 example of an interesting stellar feature, namely, rich and 

 poor regions in close proximity. I may here mention 

 that a region of considerable extent, remarkably barren of 

 bright stars, will be noticed with the naked eye in the 

 northern hemisphere. This comparatively poor region, 

 which contains no star brighter than the 4th magnitude, 

 is bounded by Cepheus, Cassiopeia, Perseus, Auriga, 

 Gemini, Ursa Major, Draco, and Ursa Minor, and forms a 

 conspicuous feature in the north-eastern portion of the 

 sky in the early winter evenings. It will be noticed that 

 the bounding constellations all contain conspicuous stars. 



Examined with a telescope, the heavens aflbrd numerous 

 instances of stellar aggi'egatiou. The Milky Way forms, 

 of course, the most remarkable example, on a great scale, 

 but among comparatively isolated groups there are 

 numerous interesting objects. Of these, the cluster known 

 as 35 Messier — a little north of the variable star tj 

 Geminorum — is visible in an opera-glass, but a telescope 

 is required to see the component stars. A very beautiful 

 photograph of this cluster has been taken at the Paris 

 Observatory. A well-marked clustering tendency is 

 visible among the brighter stars of the gi-oup, two, three, 

 four, and sometimes five stars being grouped together in 

 subordinate clusterings. 



In the southern hemisphere a splendid cluster of small 

 stars surrounds the star k Crucis. Sir John Herschel 

 charted 110 stars to the 7th magnitude and fainter. Some 



of the component stars are coloured with red, greenish, 

 and bluish tints, which, he says, " give it the aspect of a 

 superb piece of fancy jewellery." It lies near the northern 

 edge of the well-known " Coal-sack," and Dr. Gould says 

 of it : " The exquisitely beautiful cluster k Cruciti contains 

 a large number of stars of various tints and hues, con- 

 trasting wonderfully with each other, when viewed with a 

 telescope of large aperture." A drawing by Mr. Russell of 

 this cluster, made in 1872, shows some well-marked star- 

 streams. 



Just north of ^ Scorpii is a bright cluster which I found 

 \-isible to the naked eye in the Punjab sky as a hazy star 

 of about 4i magnitude. With a 3-inch refractor the 

 components were well seen. 



The so-called "globular clusters" form excellent 

 examples of the clustering tendency, but here the com- 

 ponent stars lie so close together that their physical 

 connection cannot be doubted. 



Among groups of stars not usually classed as clusters 

 there are many examples of this aggregating tendency 

 \-isible on the stellar photographs taken at the Paris 

 Observatory. Photographs of portions of the Milky Way 

 in Cassiopeia, Gemini, and Lyra show the small stars to 

 be in many places not scattered uniformly, but with a 

 marked tendency to cluster into subordinate groups ad- 

 joining comparatively starless spaces. This is especially 

 noticeable on a photograph of a portion of the constella- 

 tion Gemini (R.A. 6h. 10m., N. 20° 20 ), a little south of 

 7] Geminorum. On these photographs many cases occur 

 in which three, four, or more stars are grouped together, 

 often in a straight line, or nearly so, and to all appearance 

 comparatively isolated from their surrounding neighbours. 

 On a photograph of a rich MUky Way region in Cygnus 

 (R.A. 19h. 45m., N. 35° 30') taken by Mr. Roberts at 

 Liverpool, with an exposure of 60 minutes, on which no 

 less than 10,200 stars may be counted (in an area of 

 about 4 degrees), similar features are noticeable. 



In his observations of the Milky Way in the southern 

 hemisphere Sir John Herschel says : " Here (R.A. 17h. 

 50m., S. 33°-36°) the Milky Way is composed of separate, 

 or slightly, or strongly connected clouds of semi -nebulous 

 Ught ; and as the telescope moves, the appearance is that 

 of clouds passing in a sciul, as the sailors call it." " I 

 could fill a catalogue with the clusters of the 6th class 

 which are here. The Milky Way is like sand, not strewn 

 evenly as with a sieve, but as if flung down by handfuls 

 (and both hands at once), leaving dark intervals, and all 

 consisting of stars 14 . . . 16 . . . 20m. down to nebu- 

 losity, in a most astonishing manner." 



No. 2,908. " Cluster 7th class. The second of two stars 

 9m. which may be considered the leading stars of the very 

 large and fine cluster of the Nubecula Major, which fills 

 many fields, is of all degrees of condensation and much 

 broken up into groups and patches. . . . The field full of 

 grouping stars." 



The tendency of the stars to rim in streams is pointed 

 out by Proctor in his Unircrse mul the Coiiiiiu/ Transits 

 (first two chapters). Among the lucid stars the most re- 

 markable instances of this stream-forming arrangement 

 are found in Pisces, Scorpio, " the river Eridanus," the 

 streams in Aquarius, and the festoon of stars formed by rj, 

 y, a, 8, and /x Persei. The stream forming the constella- 

 tion Eridanus was noticed by the ancients (as the name 

 " river " implies), but in this case the stars are so far 

 apart that the connection is probably more apparent than 

 real. Perhaps the same may be said of the streams form- 

 ing Scorpio and Pisces, but still they are sufficiently well- 

 defined to attract the eye of even a casual observer. 

 Other examples of the kind may be seen in Corona Borealis, 



