Vol.. 6, 1920 INTERNATIONAL ASTRONOMICAL UNION 
389 
partly in one volume and partly in another. It is, therefore, recommended 
that in future catalogs all data for a particular system be printed in one 
place. For catalogs printed in the near future the epoch 1950.0 is recom- 
mended for the R. A. and Decl. 
The material for each pair should include, in addition to measures indi- 
cating the character of the motion, the magnitude of the star (combined 
brightness of the components) on some consistent scale (which might well 
be that adopted in the photometric magnitudes of the Henry Draper 
Catalogue), the spectrum (when known), and the proper motion (in polar 
coordinates, not in R. A. and Decl.). For systems having known orbits 
all the elements, and not simply the period, should be recorded. It is 
not at all essential that all measures should be recorded, but references 
should be given to all published measures, orbits and notes. This, es- 
sentially, is Professor Doolittle's plan for the extension of Burnham's 
General Catalog. 
The ideal catalog would cover the entire sky. If this ideal cannot be 
attained, it is recommended that those who plan the publication of partial 
catalogs come to an agreement as to limiting declination so that unnecessary 
overlapping may be avoided. 
IV. WORK IN THE SOUTHERN HEMISPHERE 
The most important piece of observational double star work that can 
be undertaken at the present time is the extension to the South Pole of a 
survey of stars to about the 9th magnitude along lines similar to those of 
the survey of the northern sky completed at the Lick Observatory, and the 
systematic remeasurement of all the closer pairs in the southern sky 
which have already been cataloged. A careful examination of all pub- 
lished data indicates that at least 1800 double stars with angular separation 
under 5" remain to be discovered among the stars as bright as 9.0 magni- 
tude in the southern half of the sky — two thirds of them in the area south 
of - 30° declination. This assumes the southern sky to be as rich in such 
systems as the northern. Further, there is only one system (a Centauri) 
south of — 40 ° for which we have satisfactory orbit elements ; there are at 
least 18 such north of +40°. 
At present the only workers in this field are Mr. Innes, at Johannes- 
burg, using a 9-inch refracting telescope, and Mr. Dawson, at La Plata, 
using a 17-inch refractor. A larger telescope in a favorable position is 
urgently needed. Using a telescope of 20 to 25 inches aperture in a good 
location, a competent observer could extend to the South Pole such a 
survey as has been mentioned in about six years and could at the same time 
secure measures of all close known pairs south of -30° declination. "Any 
action that can be taken by the International Astronomical Union to en- 
courage and assist such an undertaking either through one of the observa- 
tories already existing in the southern hemisphere or through a special ex- 
pedition from the north is heartily to be recommended. 
