November 1. 1898.] 



KNOWLEDGE, 



253 



extreme simplicity, and need only care, system and per- 

 severance. Once an hour, or better once every half-hour, 

 observe and record the time during which ten meteors 

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

 watch and at exactly the bcgincing of a minute looking at 

 the sky, giving it undivided attention and counting the 

 meteors seen, not including those appearing outside of the 

 region covered by the map. If great nimibers of meteors 

 appear it may be better to count a larger number, as twenty 

 or even fifty. If the interval between the meteors is long, 

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

 vations should be repeated until dawn, or over as long an 

 interval as possible. Between these observations the 

 observer may rest, or may make special observations of 

 individual meteors. Thus, when a meteor is seen, record 

 the hour and minute, the brightness on a scale of stellar 

 magnitudes,- 2, equals the brightness of Jupiter or Sirius ; 

 0, Arcturus or Vega ; 2, the Pole Star ; 4, the Pleiades ; 

 6, the faintest star visible ; the colour, B=blue, G=green, 

 Y = yellow, W=white, and R = red ; the class, L^ Leonid, 

 if path prolonged would pass through centre of map, N = 

 other meteors. Thus L 5 Y, 12h. 2Gm., indicates that a 

 Leonid, magnitude 5, yellow in colour, was seen at 12h. '26m. 

 Find by trial beforehand how many seconds are required 

 to make each record. Again, the path of each meteor may 

 be marked upon the map by noting its position in relation 

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

 elsewhere, and should not interfere with the hom-ly count 

 mentioned above." 



PHOTOGRAPH OF THE NEBULOUS REGION 

 ROUND y V 37 CYGNI. 



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



THE region, to which the photograph annexed 

 hereto refers, is comprised between R. A. 

 20h. 51m. 24s. and R.A. 21h. Om. 4:-5s., and in 

 Declination between 42= o(y'>' and 44° 51' north. 

 Epoch 1900. Scale — one millimetre to thirty 

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

 to as faint, exceedingly large diffused nebulosity. 



Some photographs of the region have been taken with 

 portrait lenses, having apertures up to sis inches in 

 diameter and focal distance of thirty inches, but the scale 

 of such photographs is too small for showing structural 

 details in a satisfactory manner ; two of these were taken 

 by Dr. Slax Wolf in the latter half of the year 1891, and 

 were published in Knowledge. 



The photograph annexed was taken with the twenty- 

 inch reflector, and exposure of the plate during two hours 

 and fifty-five minutes on the 10th October, 1896, and it 

 will be seen that the structural details of the nebulosity 

 are delineated upon it on a scale that will enable astro- 

 nomers in the future to detect, and correlate, any changes 

 that may take place in the nebulosity or in the stars that 

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

 nebulosity that appears to be connected, or is in proximity 

 to that shown on the photograph would require a larger 

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

 symmetrical aggregation of the nebulosity such as is 

 visible in the majority of nebulfe that are known to exist 

 in many parts of the sky. 



There are several indications of fission, and also some 

 evidence of led of vortical disturbance in different parts 

 of the nebulosity, and therefore much matter of great 

 interest to the astronomers of the distant future is herein 

 recorded. 



It wUl 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 Wilham Herschel — that the stellar universe 

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

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

 not the opportime 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. 



Hfttfts. 



[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 ilira 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 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 



