Vol. 6, 1920 INTERNATIONAL ASTRONOMICAL UNION 
361 
Obviously, then, there is need for general agreement in respect to the 
units to be used. 
The following suggestions are offered for discussion : 
1. Distance. — So far as practicable let the unit distance be, a, the kilo- 
meter (in reference to dimensions of sun, planets, etc.). It can even be used 
in expressing stellar distances without employing larger numbers than the 
chemist and the physicist are accustomed to in speaking of the number of 
molecules in a cubic centimeter of gas), h, the "astronomical unit" (in 
reference to the solar system chiefly) , c, the light-year (especially in popular 
articles), and d, the parsec (wherever appropriate), or preferably a unit 
10 times as great, to be given a separate name. 
2. Absolute magnitude. — The meaning given to the expression "absolute 
magnitude" should be the magnitude at the distance of 10 parsecs, at which 
the star's parallax would be O.'^IO. 
3. Unit of heat. — Use the joule for the unit of heat instead of calorie, 
as the latter is not definite unless explained. 
4. Unit of wave-length. — Use the international angstrom. 
5. Unit of pressure. — One bar = 10^ dynes per square centimeter. 
This is in keeping with very general use in meteorology. 
II. NOTATION 
It is only right that considerable latitude should be allowed the author 
in the choice of notation, nevertheless some of the existing confusion could 
and should be avoided. There is no uniformity, for instance, in the nota- 
tion for the elements of a visual binary system. Also different methods 
are used in designating the brighter stars — by constellations and Greek 
letters, and by right ascension and declination. Again, the notation used 
in celestial mechanics, though difficult to standardize, appears to be more 
confused than necessary. 
Suggestions 
1. Binary systems. — Use a common notation — Aitken's, perhaps. 
2. System of units. — If metric units are used do not add the English 
equivalents; if English units are used add, generally, the metric equivalents. 
3. Wave-length system. — Use the abbreviations I S and R 5, and 
not I A and R A. Do not use the diacritical mark over either the ab- 
breviation A or the word angstrom. 
4. Unit of acceleration. — A short name is needed for the C. G. S. unit of 
acceleration. 
Additional suggestions in reference to notation will be made in connec- 
tion with "economy of publication." 
Ill, ECONOMY OF PUBUCATION 
That there is need for economy in amount of publication, in cost of pub ~ 
lication, and in manner of publication so as to save the time and effort 
