KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 60. N'.0 8- 



77 



this plate the outer parts of the nebula appear distinctly dissolved, and although 

 some nebulous stars make it difficult to distinguish the stars that belong to the 

 nebula, it is indubitable that we can here distinguish several thousands of the stars 

 that form a part of the väst stellar system represented by Messier 33. 



In the following Table XVII are given the parallaxes obtained by different 

 methods for some of the larger spiral nebulse. 



Table XVII. 



N.G.C. 



From står 

 counts 



From 



From 



From novas apparent . , 



/ r . magnitude 

 diameter 



221 ,r ,0000050 0",0000100 (0",0000050) (0",0000050j 



698 — ,0000032 ,0000023 ,0000023 



3031 — ,0000016 ,0000008 ,0000014 



6946 0,00000019 0,00000080 0,00000054 0,00000011 



2841 0,00000010 0,00000026 0,00000060 



4321 0,00000029 — 0,00000021 0,00000020 



As Mr. B. Lindblad has kindly pointed out to the present writer, the spectrum 

 of the Andromeda nebula, with regard to the intensity of the iron bands /. 382"" and 

 X 388 " /l , shows such great analogies with the spectra of giant stars that we may be 

 entitled to assume that the spectrum is generated by giants. 



If it were possible to determine the apparent magnitude at which the main 

 body of giants in a spiral nebula begin to appear separated, it would give us an 

 additional means of estimating its distance. 



It seems plausible that regarding the Andromeda nebula this separation ought 

 to appear at the 20th or 21st magnitude, and if we assume the absolute magnitude 

 of the giant series to be, in the average, =0 m , we obtain a value of the parallax 

 agreeing comparatively well with the other determinations. 



Photographs on a large scale of N. G. C. 224 and 598, that have been placed at the 

 disposal of von Zeipel by Mr. Adams, show a great number of rifts (caves) in the spirals. 

 These rifts, with regard to their external structure, are very similar to those forma- 

 tions in the Milky Way that have been investigated above all by the extensive 

 researches of Barnard. 



A catalogue, now including 560 objects, has been made of all nebulse that are 

 undoubtedly belonging to the class of spirals. Their distribution in the sky and in 

 space has been investigated, besides which some other statistical researches have been 

 made concerning such observational data as have been available regarding these objects. 



§ 4. 



In order to give a contribution to the question of the structure of the Milky 

 Way, I have during the låter years undertaken an investigation of the star-distribu- 



K. Sv. Vet. Akad. Handl. Band 60. N:o 8. 



10* 



