J 218 



wliile the foJlowing table gives these diffeieiices for the phites of 

 the old group III and tlie new group II 



30 50 70 90 ilO 130 



group III (old) — 6 —22 —46 —62 —87 —95 

 group 11 (new) - 10 —25 —48 —62 —83 —96 



In this new classification neither the plates of the first group nor 

 those of the second group have been corrected for galactic conden- 

 sation. This correction, if a|)plio(l, would have iib influence on the 

 distance-correction for the first group; for the second group it would, 

 of course, lead to numbers not inateriallj diffeiing from the numbers 

 given in the thiid row of the first table on page li I 7. Therefore the 

 distance-correction, freed from I he influence of galactic condensation 

 may be considered to be as follows. 



30 50 70 

 group I (new) -|- 3 — 13 — 32 

 group 11 (new) — 6 — 19 —40 



The results of this investigation may be summari/.ed in the follow- 

 ing conclusions: 



1. The plates of the Harvard Map of the Sky, with regard to the 

 decrease of the limiting magnitude from the centre towards the 

 margin should be arranged into two groups. As the criterion for 

 this classification the galactic latitude of the centres of the plates 

 and not their mean density must be chosen. 



2. On the plates which have their centres outs/j/e the Milky Way 

 the limiting magnitude increases to a distance of about J 6 milli- 

 metres from the centre arid decreases from there to the margin. On 

 the plates which have their centres in the Milky Way the limiting 

 magnitude is continually decreasing from the centre and this decrease 

 exceeds that for the plates outside the Milky Way. 



3. The effects, mentioned sub 1 and 2 probably result from the 

 so-called KAPTEYN-phenonjenon. 



Gouda, January 1919. 



