MOUNT WILSON SOLAR OBSERVATORY. 217 



tically completed. At the urgent request of Professor Kapteyn, 

 however, an additional zone of 24 areas has been added, in order that 

 he might be supplied with standards at —15°. This increases the 

 number of regions to a total of 139. The table on the preceding 

 page refers to the enlarged plan. 



During the past year the extensive reductions involved in this inves- 

 tigation have been carried on by Miss Richmond, Miss Joyner, Miss 

 Carolyn Burns, and Miss Winn, with occasional assistance from Miss 

 Wolfe. With one or two exceptions, the measures of the diaphragm 

 photographs now available have been finished. For 102 of the areas 

 the reductions are complete up to and including the relative magni- 

 tudes; and for each of these regions Professor Kapteyn has been sup- 

 pUed with a sequence of standard magnitudes, which he is using for 

 the reduction of the Durchmusterung photographs of the Selected 

 Areas. 



Photovisual Magnitudes for the Selected Areas. 



The plans of Mr. Scares and Mr. Shapley for this investigation were 

 outhned in the preceding report. Photographs have been obtained 

 whenever the arrangement of the program for other photometric 

 investigations permitted. As indicated by the table, about one-third 

 of the photographic work has been finished. 



Distribution of Stars with Respect to the Galactic Plane. 



The increase in the number of the stars as the Milky Way is 

 approached from either side is a fact long established, and for objects 

 brighter than the eighth or ninth magnitudes there is substantial agree- 

 ment in the amount of the galactic condensation found by different 

 observers; for the fainter stars, however, the value of the concentra- 

 tion has until recently been affected with much uncertainty. 



The photometric results for the Selected Areas are still incomplete, 

 but those now^ available contribute materially to a more definite knowl- 

 edge of stellar distribution. From counts of about 40,000 stars on 

 photographs of 88 areas well distributed in galactic latitude, Mr. 

 Seares has derived the relation between stellar density and latitude 

 for the magnitude limit of the plates, which provisionally is placed at 

 17.5 on the Mount Wilson photographic scale. 



The data w^ere first compared with the density tables of Kapteyn. 

 The limiting magnitudes corresponding to the observed densities were 

 interpolated from these tables and combined to form the mean Umiting 

 magnitude of the counts on the scale used by Kapteyn. The result, 

 which is 16.3, deviates largely from the limit on the Mount Wilson 

 system and indicates an important divergence of scale, but this is 

 unimportant for the comparison. The differences between the loga- 

 rithms of the observed numbers of stars and the numbers interpolated 



