1217 



showed, that there exists still a pretty considerable diference between 

 the p/ates of group F and those of group III with regard to their 

 distance-corrections. This is shown in the following table in whit'h 

 for the groups I, III (before reduction) and III (after reduction) the 

 differences are given between the limiting magnitude at distances 

 of 30, 50, .... 130 milli-meti-es from the centre and that at the centre. 

 These numbers are expi-essed in hundredths of a magnitude. 



30 50 70 90 110 130 

 group I +2 —16 —37 —44 —50 -54 



group III (before red.) —6 —22 —46 -62 —87 —95 

 group III (after red.) —6 —19 —40 —52 —72 —79 

 From the fact that there remains a difference ^) between I and III 

 after they have been corrected for the influence of galactic conden- 

 sation it follows that this difference must originate in the colours 

 of the stars depending on their position with respect to the Milky 

 Way. If this is the true cause, it would be better not to divide the 

 plates into three groups according to their mean density, but 

 into two groups according to the galactic latitude of their 

 centres. We may, then, expect the plates of the first group (those 

 outside the Milky Way) to give a distance-correction showing the 

 characteristic properties of curve I in Fig. 1. The new curve for 

 this group would probably show a slower decline than the old one, 

 since now this group no longer contains plates whose centres have 

 a small galactic latitude. The new second group, which now would 

 contain only plates with small galactic latitude of the centres might 

 be expected to yield a curve almost identical with curve III of 

 Fig. 1. The results of the new classification proved to agree with 

 what had been expected. The new group I contains 34 plates, whose 

 centres have a galactic latitude ^20°; the remaining 21 plates form 

 the new group II. vSimilar to curve I of Fig 1 the new curve, 

 showing the variation of the limiting magnitude for the plates of the 

 new group I, has a pronounced maximum; but while the old curve 

 went down as far as — 54, the new one only descends to — 48. 

 The following table gives for the old and the new group I the differ- 

 ences found when the limiting magnitude at the centre is subtiacted 

 from that at distances of 30, 50 ... . 130 milii-metres from the centre 



30 50 70 90 110 130 



group I (old) +2 —16 —37 —44 —50 —54 

 group I (new) +3 —13 —32 —39 —46 —48 



*) Problably, this difference would still increase if we corrected the densities of 

 the plates of group I for the galactic latitude of the centre. In this group, loo, 

 a few plates occur whose centres have a small galactic latitude. 



