40 KNUT LUNDMARK, GLOBULAR CLUSTERS AND SPIRAL NEBULiE. 



The counts on the Upsala plate are performed twice with an interval of some time 

 and are certainly not so reliable as the står counts performed here concerning the 

 står cloud in Cygnus, at which the longest exposures have been double in order easily 

 to distinguish the faintest stars on the plates, but they will nevertheless be worth 

 some confidence. As the ratio betvveen aperture and focal length for the instru- 

 ment employed at Upsala is Vio, the distinguishing at the countings between stars 

 and small nebulse come off rather successfully, and the numbers given in Table IX 

 might therefore pretty well represent the real distribution of the stars. 



It appears from the said Table that the stars seem to be distributed at random 

 and that the peculiar distribution of the nebulse is not to be recognized. Nor can 









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Fig. 5. The Cluster of nebulse in Perseus (coordinates for centre: a = 3* 10"',0; o = + 40° 56'). 



a decrease of the står density towards the centre of the nebula be proved and thus 

 it will also in this case be justified to suppose that M 33 is more distant than the 

 faintest stars on our plate. 



From Table IX we find that the står density per square degree is 506. Since 

 the galactic latitude of the nebula is —31°, we obtain from van Rhijn's table the 

 limiting magnitude for the stars on the plate = 15 m .72. From this follows that if 

 7c 157 = 0",ooo498, the parallax of the nebula should be smaller than this valne. 



From the map drawn of the cluster of nebulse in Perseus found by Wolf, it 

 also results that we can distinguish a certain spiral arrangement of nebulse in this 

 cluster; in any case a certain regular distribution is prevailing. 



It deserves at last to be mentioned that Wolf has investigated the spectra of 

 some of the nebulse in the large nebulous cluster close to the pole of the Milky Way 



