390 
INTERNATIONAL ASTRONOMICAL UNION Proc. N. A. S. 
V. COMMITTEE ON DOUBLE STARS 
Finally, your Committee recommends the appointment of an inter- 
national committee on double stars to act under the authority of the In- 
ternational Astronomical Union. 
Robert G. Aitkkn, Chairman, Eric Doolittle, W. J. Hussey. 
Note. — As the committee's work was carried on by correspondence 
there was not time for a complete discussion in advance of the meeting 
of the Section. The following comments were added by Mr. Hussey: 
"1. Personally I do not attach very much importance to the formal 
definition of a double star. I am inclined to accept our heritage from the 
past and work according to our best judgment for the future. The at- 
tempts made to define a double star in terms of magnitude and distance 
have generally broken down by not being sufficiently inclusive, owing to 
the movements of the stars themselves. 
"2. It does not seem to me wise to complicate the printing of results 
by the use of different kinds of type for the different classes of double 
stars, such as capitals, small capitals, italics, lower case, and bold face, 
etc. Such attempts lead to unsightly printed pages, and to the necessity 
of keeping constantly in mind the nomenclature used. In my opinion 
it is better to follow the prevailing practice of using brief descriptive terms, 
which carry their own meaning, such as binary, optical, pair, fixed, etc. 
* 3. The visual double stars are evidently binaries or optical pairs. 
To which class a given star belongs can only be ascertained from a suffi- 
ciently extended series of micrometrical measures, and such a series may 
require many years. Until such measures are obtained the status of a 
pair remains undetermined. It is not justifiable, as is proposed in the 
section "Class B" of the Report, to regard all pairs whose distances are 
under 1".00 as having common proper motions when no change is shown 
by measurements extending over so brief a period as ten years. Longer 
series of measurements may shovv some such stars to be optical pairs, 
others binaries, and still others common proper motion pairs. 
"4. Pairs whose components have different proper motions are optical 
systems. No star of this class can be a binary, and, therefore, appropriate 
to be put in Class A, as suggested in the paragraph headed Class C of the 
report. 
"5. Northern Work. At the present time the most pressing need in 
the north is the remeasurement of the pairs discovered during the past 
twenty years, and especially the close pairs discovered at the Lick Ob- 
servatory. 
"6. Southern Work. In the south there is needed the measurement 
of the known pairs, not recently measured, and the examination under 
good conditions of the southern stars to the ninth magnitude for the dis- 
covery of new pairs. 
