ASTRONOMY: F. H. SEARES 
559 
Further confirmatory evidence of the large value of the galactic 
condensation for the faint stars, which is so striking a feature of Kapteyn's 
conclusions, is available from two different sources. The first is a series 
of counts made at Groningen on photographs of 54 Selected Areas 
taken with the Bruce telescope of the Harvard station at Arequipa in 
Peru. The results for these including 127,315 stars, are given by Kap- 
teyn in his First and Second Reports on the Progress of the Plan of Selected 
Areas ."^ The second source of data for a comparison is the collection of 
counts recently published by Turner for nearly 600,000 stars in zones of 
the Astrographic Catalogue.^ 
The durchmusterung photographs of the southern Selected Areas 
extend from +62° to —76° galactic latitude, and are well distributed 
throughout this interval. The exposure time was two hours. We 
assume that the different plates are comparable, in limiting magnitude, 
and a reference to Professor Kapteyn's tabulation^ indicates that the 
agreement in this particular is satisfactory. The calculated limits of 
brightness given by him show considerable irregularity, but it should 
be noted that these have been derived from the observed density in each 
field, and are thus affected by local variations in the distribution of the 
stars, as well as by changes in atmospheric transparency and in the photo- 
graphic conditions of exposure and development. For example, area 
No. 110, galactic latitude +1°, lies between the two branches of the 
Milky Way, and is known to include an abnormally small number of 
stars. This accounts for the unusually bright limit of 13.2 given by 
Kapteyn. 
The photographs of areas in southern latitudes are richer in stars than 
those north of the Galaxy; but since the evidence from other sources as to 
the reality of this difference is conflicting, no distinction has been made 
between northern and southern latitudes in forming the mean curve 
connecting latitude with stellar density (number of stars per square 
degree to the limiting magnitude m, denoted by Nm). 
After the counts had been arranged in the order of increasing latitude, 
overlapping means for groups of ten areas were formed, with the results 
shown in the first two columns of table 1. These define a smooth curve 
whose ordinates and corresponding abscissae for equidistant intervals 
are in the third and fourth columns of the table. The value in paren- 
theses is an extrapolation. The fifth column contains the densities from 
Kapteyn's table in Groningen Publication, No. 18, p. 54, for magnitude 
16.0, which is adopted as the mean limit for the whole series of plates. 
In the column following are the densities from the Mount Wilson photo- 
graphs of 88 northern Selected Areas. These are the values given in 
