36 KNUT LUNDMARK, GLOBULAR CLUSTERS AND SPIRAL NEBULJE. 



Of the above mentioned attempts to measure nebular parallaxes the conclusion 

 will be drawn, that the parallax of spiral nebulse is smaller tban 0",oos. The values 

 in the table also show that the parallaxes come forth smaller, the greater the instru- 

 ments used at the determination. 



2. Står Counts and Clusters, constituted by Nebulce. 



P. Götz, in his great investigation, Untersuchungen iiber den Andromedanebel 71 , 

 has measured positions for 1259 stars situated within and near the nebula. 

 Besides he has determined the position of a number of objects (knöts, condensa- 

 tions, holes, nebulous rays etc.) within the nebula. He has also, on a photographic 

 plate for a region all around the nebula, situated between a h 23 m — A 48 m and 



S + 38° 11' b 42° 41', counted the number of stars, whereat the part of the plate used 



at the counts has been devided up into 32 x 32 squares with a side of 8',4. 



Götz's Tables and Charts show 71 that the distribution of stars in the neighbour- 

 hood of the Andromeda nebula must be considered as purely accidential and not 

 showing a systematic arrangement of the kind that has heen observed about the 

 Orion-nebula and the nebulse about £ Persei, n Cygni, and 12 Monocerotis, and many 

 others 106 . On a more detailed examination of the står distribution within the 

 Andromeda nebula, G. finds, on the contrary, a connection indicated between the 

 nebula and the stars situated within its boundaries. Already at the counting of the 

 whole plate the står density proved to be increasing towards the central parts of 

 the nebula, but on account of the strong nebulosity on the plate the faintest stars 

 in these regions were löst. Hence the står numbers in Götz's Table II near the 

 centre are a little too small, while in this table the står density on an average is 

 32 per square with a side of 8 f ,4. Götz, in examining the star-distribution within the 

 nebula found a mean density of 38 expressed in the same surface unit. As, I 

 suppose, we must presume that the nebulous matter will, at any råte in the more 

 central parts of the nebula, excercise an absorbing effect upon stars situated beyond 

 the spiral, G:s result seems to speak against the supposition, that the nebula should 

 be near er than the faintest stars counted on the plate on an average, for in that 

 case a decrease of står density towards the centre of the nebula would be expected, 

 on account of the extinction of the faintest stars at the passage of the står light through 

 the nebulous matter. It is true, we may imagine that the occurence of a decrease 

 of the står density as due to this absorption could be compensated by an increase 

 of star-density within the nebula, and as no numerical suppositions regarding the 

 value of the absorption coefficient within the nebula will be possible we cannot yet 

 from Götz's counts draw any definitive positive conclusions about the relation of the 

 nebula to the stellar system. A survey of G:s chart regarding the distribution of 

 the stars about and in the nebula (loc. cit. Tafel II) seems, however, to speak 

 against the hypothesis, that the nebula should be nearer to us than the faintest of 

 the counted stars on an average seem to be. Under the supposition that the latter 

 is not the case, we shall derive an upper limit for its parallax. 



