NATIONAL RESEARCH COUNCIL 
445 
For statistical purposes, it is very desirable to include all stars brighter than 
a given magnitude. This limit is often that for which the desired observa- 
tions can be obtained. If not, stars of special interest should be included, 
and in some cases a fixed number of stars of each fainter magnitude. Prefer- 
ence should here be given to the standard regions adopted at Groningen and 
Harvard. 
1. The absolute positions of the stars from observations of the Sun, Mercury, 
and Venus. These objects are difficult to observe visually, and a trial of pho- 
tographic methods, either by direct measurement, or by a photographic transit 
circle, is suggested. 
2. Positions of all stars of the ninth magnitude, and brighter, with photo- 
graphic doublets. 
3. Precise positions of standard stars, generally of about the ninth magni- 
tude, needed for the reduction of No. 2. Each star should be observed with 
transit micrometers, attached to first class meridian circles, on at least three 
nights at two observatories, if feasible. The aid of national observatories 
should be secured in this work, since they are best qualified to undertake it. 
These stars should be selected whenever possible from the list of intermediary 
stars of the Comite International Permanent. Nos. 2 and 3 should be car- 
ried on simultaneously. 
4. Proper motions of all stars of the magnitude 7.5, or brighter. 
5. Proper motions of stars in spiral, and other, nebulae. 
6. Restoration of the stations for determining variations in latitude both 
visually and photographically. 
7. Sufficient measures of all known double stars to determine the relative 
positions of the components, and if they have perceptible motions to furnish 
adequate material for an orbit. In the first case, these observations should 
be made with three telescopes, with a computed probable error not exceeding 
±0'^.05. These observations should be repeated every ten years, or, in the 
case of known b'naries of short period, more frequently. For many stars, the 
material needed already exists. 
8. Parallaxes of all stars of the sixth magnitude, and brighter, and of a 
selected list including variables, stars having large proper motion or parallax, 
binaries, nebulae, etc. The same stars should be observed with several tele- 
scopes to eliminate systematic errors, as far as possible. Some clusters, and 
stars of Class B, whose parallaxes are presumably small, should therefore be 
included. 
9. Precise positions by modern methods, photography and transit microm- 
eter, of the Moon and major planets. 
10. Orbits and ephemerides of asteroids and comets so far as this is not 
provided for by the Rechen-Institut. The loss of a faint asteroid may some- 
times be avoided by promptly computing a circular orbit for it. 
11. Spectra of special stars too faint to be classified on existing photographs. 
They can probably be obtained by a focal plane spectroscope, or objective 
prism, attached to a large reflector. 
