388 
INTERNATIONAL ASTRONOMICAL UNION Proc. N. A. S. 
Class A. — Systems for which the measures show a definite curvature of 
the relative path, or a well-determined variation in velocity along the rela- 
tive path. Class A systems are to be indicated in catalogs by the use of 
small capitals; e.g., 61 cygni, S 483, 8 KQUUi^Ei. 
Class B. — Systems which do not come in Class A, but whose physical 
connection is probable, as shown by the fact that the components have 
the same proper motion. Since limits must be adopted to exclude stars 
belonging simply to a great cluster (e.g., Ursa Major) it is suggested that 
pairs be entered in Class B only if the angular separation is less than 100 
times the annual proper motion. Pairs under 1".0 separation which have 
been under observation, say, for a decade or more, and have shown no 
relative motion may be included in this class on the assumption that they 
are moving together at a rate less than ".01 per annum. Systems of Class 
B are to be indicated in catalogs by the use of bold faced type; e.g., 
S 110, OS 175, OS 424. 
Class C. — Systems whose components have from the measures apparently 
different proper motions. This class will include the purely optical pairs 
and also pairs which may later require transfer to Class A. In catalogs 
they are to be indicated by the use of italics; e.g., 6 HercuUs, S 2'/6o, 
S 742. 
Class D. — Systems about whose motions nothing is known. This 
class might be made to include the wide, faint pairs apparently simply of 
historic interest as well as new pairs of unknown proper or relative motion. 
It is evident that pairs entered in this class will ultimately be transferred 
to one of the three preceding classes or dropped entirely from our catalogs. 
They will be indicated in catalogs by the use of lower case Roman type; 
e.g., h 528, A 3000. 
II. COOPERATION 
It is highly desirable that double star observers work in closer coopera- 
tion than heretofore to insure (1) the sufficient observation of all double 
stars in need of measurement at any given epoch; and (2) the avoidance of 
unnecessary duplication of measures. Of course no action should be taken 
that would in any way discourage personal initiative in the choice of prob- 
lems or methods; but it is suggested that certain astronomers who have 
been specially interested in collecting all measures of double stars (e.g., 
Messrs. Brie Doolittle, Robert Jonckheere, R. T. A. Innes) might be 
asked to act as a "clearing committee," which would supply any observer 
wishing it with a list of double stars in need of measurement and, in prin- 
ciple, suited to the power of the telescope to be employed. 
III. GENERAIv CATAIyOGS 
Experience in using and handling Burnham's General Catalog has 
proved the inconvenience of having the data for any one system recorded 
