1117 



B. Messow. Die beiden Stern liaufen im Perseus N. G. C. 869 iind 

 884, Astron. Abhandl. der Hamburger Stern warte in Bergedorf, Bd. 

 II, N'. 2, 1913. 



The places and magnitudes of 649 stars were determined by the 

 measurement of two photographic plates taken in Potsdam by 

 Ebkrhard and Ludendorff. From the diameters the magnitude was 

 graphicallj' determined with the aid of the standard magnitudes from 

 ScHWARZSCHiLD. They are photographic and have been expressed in 

 the P.D. scale. 



The catalogues of Krüger, Oertel, Vogel, Schur, Bronsky et 

 Stebnitzky, Lindemann, Ball and Rambaut were found unfit for our 

 purpose, either on account of incompleteness or their inexact magnitudes. 



We tell off Van Maanen's catalogue and determine the number 

 of stars of the cluster for every apparent magnitude. The interval 

 between the magnitudes is sufficient for seven determinations ot 

 parallaxes. If we class them according to the decreasing magnitude 

 of the stars employed, we get : 



I n = 0".004 



Mean jt — 0".005 rb 0".0005 



The results show a systematic course with decreasing magnitudes. 

 The cause of this may be a mistake in the scale of magnitudes, or 

 the fact that the catalogue is not sufficiently complete for the fainter 

 magnitudes used. 



We now perform the same calculations for Messovv's catalogue. 

 Less value is to be set upon the results we shall (ind then, because 

 Messow's magnitudes are based upon Schwarzschild's photographic 

 scale and Kapteyn's luminosity-curve applies to visual magnitudes. 



We find from 7 determinations: 



.T = 0",003 ± 0",00n3. 



In order to find wliether the different results of Van Maanen and 

 Messow can be explained from the scales of magnitudes used, we 

 reduce Van Maanen's magnitudes to Schwarzchild's standards. For 

 this purpose the apparent magnitudes of 197 stars in Van Maanen's 

 catalogue and Schwarzschild's treatise are compared with each other. 

 The identification is facilitated by using Pihl, or Oertel and Bronsky 



