No\'EMBER 1, 1898.] \ 



KNOWLEDGE 



253 



•^reme simplicity, and nei only care, system and per- 



'•ance. Once an hour, r better once every balf-hour, 



ve and record the tie during which ten meteors 



This is most easi done by noting the time by a 



id at exactly the thinning of a minute looking at 



'iving it undividl attention and counting the 



n, not includin; those appearing outside of the 



ed by the map. If great nmnbers of meteors 



V be better to <unt a larger number, as twenty 



If the inter 1 between the meteors is long, 



le counted lay be reduced. These obser- 



e repeated ntil dawn, or over as long an 



h\e. Bween these observations the 



or majmake special observations of 



Thus vhen a meteor is seen, record 



-, the Mghtness on a scale of stellar 



'Is tbt Tightness of Jupiter or Sirius ; 



•2, tt Pole Star; 4, the Pleiades; 



4ble; he colour, B = blue, G=green, 



te, am ? = red ; the class, L Leonid, 



mid pa through centre of map, N = 



IS L 5 , 12h. :^6m., indicates that a 



, magnitu'' i, yellow n colour, was seen at 12h. "itim. 



, I by trial bef ■! --hand hv many seconds are required 



to make each reror 1. Ag! i, the path of each meteor may 



be marked upon tbo map I noting its position in relation 



to the adjacent stars. Sue work can be done equally well 



elsewhere, and should not terfere with the hourly count 



mentioned above." 



region, to wb 

 to refers, is 

 Im. 243. a] 

 tion betwe 

 1900. S< 

 In the N 

 ingly lar 

 hs of tt 

 aving a 

 distance 

 is to 

 ma 

 e la' 



iVLEI 



PHOTOGRAPH OF T E NEBULOUS REGION 

 ROUND i^f 37 CYGNI. 



By Isaac Boibts, d.sc, f.r.s. 



h the photograph annexed 

 comprised between R. A. 

 R.A. 21h. Cm. 4;5s., and in 

 42° .JG-")' and 44° 51' north, 

 e — one millimetre to thirty 

 T. C, No. 7000, it is referred 

 diffused nebulosity, 

 region have been taken with 

 rtures up to sis inches in 

 f thirty inches, but the scale 

 small for showing structural 

 ler ; two of these were taken 

 r half of the year 1891, and 



was taken with the twenty- 



f the plate during two hours 



3 10th October, 1896, and it 



ral details of the nebulosity 



Lcale that will enable astro- 



nd correlate, any changes 



osity or in the stars that 



"he whole extent of the 



icted, or is in proximity 



ould require a larger 



is no indication of a 



^bulosity such as is 



are known to exist 



|on, and also some 



different parts 



matter of great 



future is herein 



It will be observed, on close examination of the photo- 

 graph, that nearly the whole surface area of this vast 

 cloud of nebulosity is covered with stars, ranging in mag- 

 nitude between the ninth and the seventeenth ; but very 

 few of them can, with certainty, be pronounced as being 

 actually involved in, and forming part of, the nebulosity. 

 The hundreds of apparently finished stars are probably 

 placed between us and the nebulosity, and if this be the 

 true inference, what must be its dimensions and distance 

 from the solar system ? The answer, if one could be 

 given, would be bewildering, for, so far as it is known up 

 to the present time, not one of the stars referred to has a 

 sensible parallax, and therefore the distance from the earth 

 of the nearest of them would be practically infinite ; con- 

 sequently, if the nebulosity is at a greater distance than 

 the stars, we are left entirely without data to enable us to 

 form even the crudest idea of the extent of this part of 

 space. If the question should be asked : What evidence 

 is there for the assumption that the stars are between us 

 and the nebulosity ? my answer would be that, if the stars 

 were beyond the nebulosity, their photo-discs would, on 

 the negative, appear less bright, and their margins be 

 more or less nebulous ; whereas only those stars which 

 appear involved in the nebulosity present these appearances. 

 Of course it is a fair subject for argument that those 

 nebulous stars which appear to be involved in the 

 nebulosity are not so in reality, but seem thus because 

 they are beyond it in our line of sight. But this argument 

 is much weakened, if not entirely destroyed, when we find 

 on examination of the negative that those faint, star-like 

 condensations are not only nebulous themselves but they 

 follow the curvatures found in various parts of the nebu- 

 losity ; thus we are driven to infer that the stars are the 

 nearer bodies to us, and that the nebulosity lies beyond 

 the stars. 



Photography has now furnished a considerable amount 

 of evidence in support of the theory — first propounded I 

 think by Sir William Herschel — that the stellar universe 

 which is within the bounds of our aided vision, vast though 

 it be, forms only one unit in boundless space ; but this is 

 not the opportune time for presenting and discussing the 

 evidence furnished by photography bearing upon this 

 important theory. I may have an opening later on for its 

 discussion. 



Hfttfrs. 



[The Editors do not hold themselves responsible for the opinions or 

 statements of correspondents.] 



THE ECLIPSE THEORY OP VAKTABLE STARS. 

 To the Editors of Knowledge. 



SiKs, — With reference to Mr. Monck's remark (p. 182) 

 about the title of the article, as above, being misleading, 

 logically, perhaps it may be ; but a large majority of the 

 readers of Knowledge no doubt know that the eclipse 

 theory refers only to the Algol type of star, and the title 

 would not be misleading to such. No one, except perhaps 

 quite a stranger to the subject, supposes the eclipse theory 

 explains the long period variables such as Mira Ceti. 



With regard to Mr. ilonck's second paragraph, I dul 

 assume, for purposes of calculation, that the brightness of 

 the star (or stars) was uniform in all parts of the disc, as 

 seen by us. Later on, in the last paragraph but one, I 

 expressly anticipated his point that an obscuring atmo- 

 sphere would alter the character of the light curve. 



Mr. Whichells (p. 183) is quite correct in stating that 

 you can get a continuously varying light curve when the 



