4 



C. V. L. Charlier 



observer is ßrst to be determined before the usual description of these objects may 

 be successfully applied to a discussion of their distribution in space. 



That a summary discussion eventually may be based directly on the description 

 given in the N. G. C. is, however, evident from the following table, obtained from 

 more detailed observations — nearer described below — of some of the clusters. 





Number 



Mean 





diametor 





3 



4.S 



p« 



S 



5.2 



pi 



23 



8.8 



cL 



9 



7.9 



L 





131 



vl. 



33 



21.1 



vvL 



2 



40 



eL 



2 



45 



The first column gives the si.ve of the clusters according to the scheme of 

 Herschel (S = small, L = large etc.), the second column the number in each class, 

 the third column the corresponding mean value of the diameter of the clusters 

 expressed in minutes of arc. The correlation between the apparent diameter and 

 the scale of Herschel is well pronounced, though some of the classes contain only 

 very few individuals. 



2. 1 have, however, not based my discussion of the distribution of the clusters 

 on all the clusters given by Dreyer, but preferred to use a smaller but more 

 homogeneous material. Such a material is afforded by the excellent charts prepared 

 by the late Franklin-Adams which represent the whole sky with approximately 

 uniform accuracy down to the stars of the 17:th magnitude.. This limit relates to 

 the original photographic plates (F. A. P.) now stored up at Greenwich. As to the 

 Franklin-Adams charts (= F. A. C), of which the Observatory at Lund possesses 

 a copy, their limiting magnitude, according to a not yet published investigation 

 made by Gyllenberg, amounts only to 15'", so that two whole magnitudes are lost 

 at the reproduction. 



The F. A. P. have been examined by P. I. Melotte in regard to stellar clusters 

 (»A catalogue of star clusters shown on Franklin- Adams Chart Plates» in M. A. S. 

 Vol. LX, 1915). This examination showed that 245 clusters were found on the 

 F. A. P. of which 14 are not noted in the catalogues of Dreyer. These 14 are 

 generally rather loose clusters though some of them are well defined. Of the 

 remaining 231 objects 79 are globular clusters or suspected to be such ones. In 

 this chapter I exclude the 79 globular clusters, the 14 clusters not in N. G. C. 

 (some of them could, indeed, have been considered) and moreover 9 very loose 

 clusters such as the Pleiades, the Hyades-Taurus cluster, Praesepe etc., for which 



