Vol. 6, 1920 INTERNATIONAL ASTRONOMICAL UNION 
385 
magnitudes for these same regions determined at Mount Wilson. The 
color-sensibiUty of the two instruments — the 16-inch Metcalf and the 60- 
inch reflector — is so different that the comparison is meaningless except 
for the few stars whose colors are known. The differences in this instance 
are extreme, because of the exceptional behavior of the 16-inch Metcalf 
instrument. A similar situation must be met in comparing the magnitudes 
of the Polar Sequence determined at Greenwich with those of other investi- 
gators. The influence of the instrument is here also unusually large; 
nevertheless such differences always appear, to some extent at least, and, 
unless taken into account, vitiate the comparison of results with different 
instruments. This fact was recognized by Miss Leavitt in her investiga- 
tion of the Polar Sequence and allowed for wherever possible. The re- 
sulting color system in Harvard Circular 170 is not very different from that 
of the Mount Wilson photographic magnitudes; but the true relation of 
the results of these two investigations can be determined only by allowing 
for the difference in the two systems. Owing to the systematic difference 
in the color of bright stars and faint stars, there is a direct influence upon 
the scales, whose accumulated effect between the 6th and 10th magnitudes 
amounts to nearly a tenth of a magnitude. 
Before leaving these general considerations, and more or less as a sum- 
mary of them, it may finally be remarked that in our opinion the most 
effective cooperation is to be attained by granting to the individual in- 
vestigator the greatest freedom of initiative and operation consistent with 
the ends to be accomplished. What is desirable as an end can profitably 
be determined by consultation and mutual agreement; but a healthful 
development of research requires that the individual be responsible for the 
means by which its objects are to be attained. 
The organization of an International Committee will require a classifica- 
tion of the activities which it is to undertake and the appointment of various 
subcommittees. These naturally will find their origin in the questions 
which the committee must consider, hence it seems desirable that a few 
of the most important of these problems should be passed in review. 
1. Standards oj magnitude. — With proper allowance for differences in 
color systems and zero points, the photographic scales of Harvard, Green- 
wich (Chapman and Melotte), Potsdam (Dziewulski), and Mount Wilson 
are in satisfactory agreement between the 10th and 16th magnitudes. The 
interval including the brighter stars is fully covered only by the results 
of Harvard and Mount Wilson. Here there is a scale divergence of 6%. 
For the reconciliation of this difference further investigations will be re- 
quired, which, in part at least, should be in the hands of other observers. 
The question is, therefore, very definitely one for the consideration of an 
international committee. The observations should preferably be made 
on the stars of the Polar Sequence. In any event groups such as the 
Pleiades which contain no red stars that are bright should be avoided, owing 
