40 



Hans Henie 



As can be seen in this table the decrease of the star density is evident on 

 almost all the plates. The amount and the character of this decrease is, however, 

 not directly to be seen, because of the great irregularities in the distribution of 

 the stars. 



It is to be supposed that the decrease would be more continuous, if the figures 

 from more plates could be combined. It is, however, useless to take the mean 

 from more plates directly. A better mode of procedure is to use the relative 

 densities. By relative density I understand the quotient between the mean den- 

 sity of any zone and that of the entire plate. 



These quantities which are easily obtained from tab. IV are given in tab. V 

 and designated by d. 



By means of this table the decrease of the star density on the negatives may 

 be studied. 



Two questions are liere to be taken into consideration. 



1) The amount of the decrease. 



2) The connection between the amount of the star density and the amount 

 of the decrease. 



In order to solve these questions I divide the plates into three groups according 

 to the mean density of the plates. The groups are these: 



I Z)q < 20 including 25 plates 



II 20 < Do < 35 — 19 — 

 III Do > 35 — 11 — 



For each zone I now take the average I'elative density of all the plates be- 

 longing to the different groups, and also of the whole set of plates. The result is 

 the following: 



Group 





d^ 





'h 







d, 



I 



1,301 



1,319 



1 ,139 



0,933 





0,842 



0,826 



II 



1,311 



1,257 



1,129 



0,958 



0,911 



0,799 





in 



1,546 



1,449 



1,284 





0,829 



0,648 



0,533 



Mean 



1,353 



1,323 



1,157 



0,951 



0,884 



0,788 



0,720 



These series give a good idea of the decrease of tlie density. To illustrate 

 the amount of the decrease I suppose the average density of the groups to liave 

 the values given beneath and calculate the corresponding values of the density of 

 the centre and offthe margins of the negative. 



