39 



index for each apparent magnitude that is based on Parkhurst and 

 Seares' researches. To tliis objections may be raised, as for llie 

 cbister stars we have to deal willi absolute magnitudes. As, however, 

 the relation between colour index and luminosity is onijMnaccnrately 

 known as yet and as moreover, it cannot be decided whether a 

 given star belongs to the cluster oi- not. Van Rhi.tn's method is the 

 only one possible. Van Rhi.in found that the photographic magnitudes 

 (international scale) between iii = 7.5 and m = 14.5 wanted a constant 

 correction — 0"'.5 for reduction to the visual Potsdam scale. There- 

 fore by a correction — 0"*.7 they are reduced to the Harvard scale. 



The number of cluster stars of each magnitude we find by dimi- 

 nishing the nnmbers counted by the normal number, which was 

 determined for this cluster from Publ. Gron. W. 27, Table V. 



It appears at once that the Praesepe stars have faint luminosities. 

 The declivities that we observe in the frequency curve of the mag- 

 nitudes are partly smaller than the smallest declivity occurring in 

 Kapteyn's luminosity curve. That is why we could make only four 

 determinations of the parallax notwithstanding the great interval of 

 magnitudes. These give 



n = 0".024 ± 0".004. 



This parallax is considerably greater than the one which we 

 found for other stellar clusters. 



Messier 52. 



N. G. C. 7654; «,,„„== 23H9"'.8, d,,„„ =r -f 61°3', b = -\- 1° ; 

 I = 81°; class: D3. 



F. PiNGSDORF. Der Sternhaufen in der Cassiopeia. Diss. Bonn. 1909. 

 Measurements of three plates, taken by Küstner. The catalogue 

 contains 132 stars up to 15'". 0. The standard magnitudes have been 

 determined by visual observations by means of gauzes of 25 stars 



by ZURHELLEN. 



We find from 4 determinations : 



jT = 0".002 ± 0".0003. 



Messier 46. 



N. G. C. 2437; .^,„., = 7/' 37'" .2, r),^,„„ = - 14°35', b = + Q^ 

 /= 200°; class: l)i. 



W. Zurheli-en. Der Sternhaufen Messier 46. Ver()fientl. Kgl. Stern- 

 warte zu Bonn, N». 11, 1909. 



Measurements of three plates, taken by Küstner. The catalogue 



