30 



O. V. L. Charlier 



From the C du C we have available at the observatory 87 charts for C, and 

 61 for distributed as will be shown below (compare tab. 16 and 19). The mean 

 number of stars on a chart is 



Mean number of stars 404.45 3915, bo 



These are the numbers that will form the ground work for our investigation 

 of the constitution of our stellar system in the directions defined by the squares 

 Crj and C^. 



From the mean number of stars on a single chart we have to deduce the 

 corresponding number of stars in an entire » square >v Now a » square» is = Vis 

 of the sky = Vis X 41252.95 square-degrees (= n°) = 859.436 One chart of 



C du C covers 130' X 130' = 4.69445 Hence we get 



Number of stars per 86.155 834.072 



» » » » »Square» 74045 716 832 



which numbers we have to combine with the numbers from BD. 



Our first task now is to determine the value of the magnituds of BD ex- 

 pressed through an exact photometric scale. We have some guidance in this matter 

 from the numbers deduced by Pickering (Harvard Annals Vol. XXIII P. 179) from 

 his revision of the Durchmusterung magnitudes. Denoting the numbers of Pickering 

 with HR, he finds the following average scale of the 52)- magnitudes : 



Tab. 2. Average scale of Durchmusterung. 



BD 



HB. 



BD 



HR 



4.0 



4.1 



7.5 



7.5 



4.5 



4.5 



8.0 



8.0 



5.0 



5.0 



8.5 



8.6 



5.5 



5.4 



9.0 



9.3 



6.0 



5.8 



9.1 



9.5 



6.5 



6.4 



9.2 



9.7 



7.0 



7.0 







15. These average numbers are however of little use for our present purpose 

 as the scale of BD is very varialile in different squares as will be found beneath. 



The principal sources for photometric magnitudes that can be used here are 

 the following: 



iîD= Harvard Durchmusterung (Annals XLV) all stars to B/) = 7».5for — 40" < S < -|-90°, 

 PG = Potsdam General-Catalog (Pubb. XVII) » » » ,> , » 0" < 8 < +90°. 



HR^ = Harvard Revision (Annals XXIV) a number of stars » » = 9^.3 » —200 <; g < -j-go». 



