November 1. 1898.1 



KNOWLEDGE 



extreme simplicity, and needmly care, system and per- 

 severance. Once an hour, oibetter once every half-hour, 

 observe and record the tim during which ten meteors 

 appear. This is most easily one by noting the time by a 

 watch and at exactly the bej: ning of a minute looking at 

 the sky, giving it undivided ttention and counting the 

 meteors seen, not including i ^se appearing outside of the 

 region covered by the map. f t;reat numbers of meteors 

 appear it may be better to co' t a larger number, as twenty 

 or even fifty. If the interva ic tween the meteors is long, 

 the number to be counted m be reduced. These obser- 

 vations should be repeated u il dawn, or over as long an 

 interval as possible. Bet en these observations the 

 observer may rest, or may ike epecial observations of 

 individual meteors. Thus, v en a meteor is seen, record 

 the hour and minute, the br jtness on a scale of stellar 

 magnitudes,- 2, equals the b^htness of Jupiter or Sirius ; 

 0, Arcturus or Vega ; 2, the 'ole Star ; 4, the Pleiades ; 

 6, the faintest starviiible; t colour, B=blue, G=green, 

 Y=yellow, W=wbii8, and j = red ; the class, L= Leonid, 

 if path prolonged wr ild passhrough centre of map, N = 

 other meteors. TL\>5 L 5 YI2h. 26m., indicates that a 

 Leonid, magnitude 5, yellow i colour, was seen at 12h. 20m. 

 Find by trial beforehand ho^ many seconds are required 

 to make each record. Agaii the path of each meteor may 

 be marked upon the map by oting its position in relation 

 to the adjacent stars. Such ork can be done equally well 

 elsewhere, and should not in rfere with the hourly count 

 mentioned above." 



PHOTOGRAPH OF TH NEBULOUS REGION 

 ROUND y ^ 37 CYGNI. 



By Isaac Robets, d.sc, k.r.s. 



THE region, to whic the photograph annexed 

 hereto refers, is omprised between E. A. 

 20h. 51m. 24s. am R.A. 21h. Om. 48s., and in 

 Declination betweei 42° 56-5' and 44° 51' north. 

 Epoch 1900. Soa — one millimetre to thirty 

 seconds of arc. In the N. ■ C, No. 7000, it is referred 

 to as faint, exceedingly largdiffused nebulosity. 



Some photographs of the 3gion have been taken with 

 portrait lenses, having ap cures up to six inches in 

 diameter and focal distance t thirty inches, but the scale 

 of such photographs is too mall for showing structural 

 details in a satisfactory man r ; two of these were taken 

 by Dr. Max Wolf in the latt half of the year 1891, and 

 were published in Kno\\xedg 



The photograph annexed vas taken with the twenty- 

 inch reflector, and exposure ■ the plate during two hours 

 and fifty-five minutes on th 10th October, 18'.)6, and it 

 will be seen that the struci ral details of the nebulosity 

 are delineated upon it on a^cale that will enable astro- 

 nomers in the future to dete., and correlate, any changes 

 that may take place in the r lulosity or in the stars that 

 surround or are involved in .. The whole extent of the 

 nebulosity that appears to be onnected, or is in proximity 

 to that shown on the photc aph would require a larger 

 plate than this to cover it, t; there is no indication of a 

 symmetrical aggregation oi the nebulosity such as is 

 visible in the majority of neilie that are known to exist 

 in many parts of the sky. 



There are several indicat as of fission, and also some 

 evidence of loci of vortical fsturbance in different parts 

 of the nebulosity, and thei''ore much matter of great 

 interest to the astronomers ■ the distant future is herein 

 recorded. 



It will be observed, on close 

 graph, that nearly the whole surfl 

 cloud of nebulosity is covered with/ 

 nitude between the ninth and thof 

 few of them can, with certainty, 

 actually involved in, and forming' part i 

 The hundreds of apparently finished i 

 placed between us and the nebulosity, i 

 true inference, what must be its dimet 

 from the solar system ? The answer, 

 given, would be bewildering, for, so far as it ii 

 to the present time, not one of the stars refer 

 sensible parallax, and therefore the distance firos 

 of the nearest of them would be practically in" 

 sequently, if the nebulosity is at a greater di 

 the stars, we are left entirely without data to 

 form even the crudest idea of the extent of thi 

 space. If the question should be asked : What e^ 

 is there for the assumption that the stars are betwi 

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

 were beyond the nebulosity, their photo-discs t 

 the negative, appear less bright, and their ma 

 more or less nebulous ; whereas only those stars wl 

 appear involved in the nebulositypresent these appearand 

 Of course it is a fair subject for argument that t" 

 nebulous stars which appear to be involved in 

 nebulosity are not so in reality, but seem thus bee 

 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 

 foUow 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 hes 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. 



fLetttxn, 



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

 statements of correspondents.] 



THE ECLIPSE THEORY OF VARIABLE STARS. 

 To the Editors of Knowledge. 



Sirs, — 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. Monck's second paragraph, I did 

 assume, for purposes of calculation, that the brightness of 

 the star (or stars) was imiform 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 



