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CARNEGIE INSTITUTION OF WASHINGTON. 



from Kapteyn's tables for the average limit of 16.3 are in the second 

 column of the accompanying table. Although systematic, these dif- 

 ferences are small, and the Mount Wilson counts therefore agree with 

 the results of Kapteyn in showing for the faint stars a high value of the 

 galactic condensation. 



Additional evidence is as follows : In his First and Second Reports on 

 the Progress of the Plan of the Selected Areas, Kapteyn gives counts for 

 127,315 stars on 54 photographs of Southern Selected Ai'eas made at 

 Arequipa. The limiting magnitude for these photographs is practi- 

 cally the same as that for the Mount Wilson series. A comparison 

 gives the differences in the third column of the table; these also are 

 satisfactorily small. On the other hand, a similar comparison with the 

 densities of Chapman and Melotte reveals the discordant results in the 

 fourth column. 



(Unit=0.01 in logarithm.) 



A very valuable mass of data, including counts of about 600,000 stars 

 from zones of the Astrographic Catalogue, has recently been collected 

 by Turner. These also have been reduced to densities and compared 

 with Kapteyn, and the differences in the logarithms for various magni- 

 tude limits on the scale of Groningen Publication No. 18 are in the last 

 five columns of the table. The faintest limit is here only 12.5, but this 

 is well below the point at which Kapteyn's densities begin to diverge 

 from those of Chapman and Melotte; the astrographic counts are 

 especially valuable as evidence on the distribution of stars of inter- 

 mediate brightness. 



Although the magnitude scale of Groningen Publication No. 18 seems 

 to require some correction, these various comparisons afford a striking 

 confirmation to the sixteenth magnitude (Groningen scale) of the values 

 of the galactic condensation found by Kapteyn. It is a characteristic 

 feature of his results that the condensation increases rapidly with 

 increasing magnitude, so that for the hmit mentioned the number of 

 stars in the Milky Way is from 20 to 30 times that at the galactic poles. 



