560 
ASTRONOMY: F. H. SEARES 
these Proceedings, 3, 1917, 219, after the application of a correction of 
— 0.10 to the logarithms to reduce them to the limiting magnitude of 
the durchmusterung plates. 
The significant feature of the table is the relation between the three 
series of results shown by the differences in the last two columns. These 
reveal no important systematic effect and show that the increase in 
stellar density with decreasing latitude is substantially the same for all 
three investigations. The differences MW-DM are noteworthy in that 
all of the Mount Wilson photographs are of regions on or north of the 
celestial equator, while the durchmusterung areas are on or south of 
the equator, with only seven regions in common. 
The average value for the ratio of the number of stars at 5° latitude to 
the number at 80° is 23, with deviations of —2, +4, and —2 for DM, 
Kapteyn, and MW, respectively. This result refers to magnitude 16.0 
on the scale of Groningen Publication No. 18. On the international 
photographic scale the limit would be approximately 17.0. 
The counts for the Astrographic zones, which constitute a very impor- 
tant collection of data, have been discussed with detail in an article 
that will appear in the Astro physical Journal. The salient features 
only need be touched upon here. The zones are ten in number, each 
2° wide, and well distributed in declination from 4-62° to —65°. The 
counts extend throughout the entire 24 hours of right ascension, so that 
each zone includes a wide range of galactic iatitude. We have here, for 
each hour of right ascension, not only the total number of stars to the 
faintest limit of the Catalogue, but also the totals to at least one, and 
usually two, other limits from one to three magnitudes brighter. We 
assume that each limit is constant for any given zone; although there 
are obvious irregularities, their influence is pretty thoroughly eliminated 
by the method of discussion, and it is improbable that the mean distri- 
bution is affected to any important degree. 
A curve connecting latitude and density was drawn, just as in the case 
of the durchmusterung counts above, for each separate limit of each 
zone. From these curves were read the stellar densities for each 10° 
latitude. With these and their respective latitudes as arguments, 
corresponding magnitudes were interpolated from Kapteyn's distribu- 
tion table in Groningen Publication No. 18. The mean of the magnitudes 
thus found for any curve was adopted as the limiting magnitude for that 
curve and for the series of counts to which it corresponds. The process 
is exactly that described in these Proceedings, 3, 1917, 217, and there 
used for the determination of the limiting magnitude, on the scale of 
Kapteyn's table, of the Mount Wilson photographs of the Selected Areas. 
