I 
Vol.. 6, 1920 INTERNATIONAL ASTRONOMICAL UNION 369 
5. Sources. — In order to obtain lines of constant wave-length and con- 
stant intensity-distribution, it is recommended that the modification of 
the Pfund arc employed at Mt. Wilson be adopted, namely, the Pfund 
arc operated between 110 and 250 volts as convenient, with 5 amperes or 
less, at a length of 12 millimeters, and used over a central zone, at right 
angles to the axis of the arc, not to exceed IV4 millimeters in width. 
6. Classification. — It is recommended that tables of wave-lengths be 
accompanied by at least two descriptive columns, one indicating the in- 
herent nature of the line (intensity, sharpness, asymmetry, etc.), the other 
indicating the character of the measures on the line. There is urgent need 
of some quantitative description of relative intensity as a function of wave- 
length. 
For indicating the intrinsic character of the line, the modification of 
Gale and Adams' groups, shortly to be defined at Mt. Wilson, is recom- 
mended. 
For indicating the degree of accuracy, the notation of Burns {Lick 
Ohs. Bulletin No. 247, p. 29 and Bulletin Bureau of Standards, No. 274, 
p. 251) is recommended. 
7. Tables of wave-lengths. — The time for an accurate and definitive 
determination of the wave-lengths of the different chemical elements does 
not yet seem to have arrived. 
It is recommended, however, that a Table of Stronger Lines in which wave- 
lengths of all elements shall be arranged in order of magnitude be prepared 
at the earliest practicable date. It is believed that present needs call 
for a table containing approximately twice as many lines as Kayser's 
Tabelle der Hauptlinien, which includes ten thousand wave-lengths and 
occupies one hundred octavo pages. 
8. Survey. — It is recommended that the conference at Brussels consider 
the possibility and advisability of making a survey of facilities, equipment, 
and opportunities for spectroscopic work in the various laboratories of 
the world, looking toward the avoidance of unnecessary duplication and 
the encouragement of cooperation in research. 
Hknry Crkw, Chairman, Harold D. Babcock, Ke:ivin Burns, W. W. 
CampbeivIv, Charlks E. St. John. 
REPORT OF THE COMMITTEE ON THE DETERMINATION OF SOLAR 
ROTATION BY THE DISPLACEMENT OF LINES 
Since the Bonn meeting of the International Union for Cooperation in 
Solar Research in 1913, results of investigations of the sun's rotation have 
been published by a number of observers, namely, J. S. Plaskett, Hubrecht, 
Schlesinger, DeLury, Evershed and Royds, H. H. Plaskett, and St. John 
and Ware. 
As the data relative to the linear velocity at the solar equator now cover 
