372 
INTERNATIONAL ASTRONOMICAL UNION Proc. N. A. S. 
duce line displacements at the sun's limb has been taken into considera- 
tion by all solar observers. Tests on Mount Wilson show that, under 
ordinary observing conditions, the integrated light just outside the solar 
image is not of sufficient intensity to affect the photographic plate during 
the exposure time employed for solar rotation plates ; that it requires con- 
siderable cloudiness over and around the sun, conditions never approxi- 
mated in regular work, to cause a measureable decrease in the line dis- 
placements at the limb; and that this large proportion of superpose 1 sky- 
light produces no differential effects between strong and weak lines. 
Recommendations for Program of Work 
1. In order to trace to their source the systematic differences that 
are found in the value of the solar rotation by different observers, it is 
desirable that further study be given to possible sources of systematic 
errors and to determining the source of the differences found by the same 
observer upon plates taken at frequent intervals, differences of the same 
order of magnitude as those between different observers. 
2. In the meantime it is desirable to carry on, when possible, continuous 
series of observations under constant instrumental conditions and by 
the same observer. 
3. As it seems increasingly probable that local conditions in the re- 
versing layer are frequent causes of divergent results, it is advisable to 
extend observations over a considerable period of time in investigation 
of such questions as variation with latitude or differences between the 
hemispheres. 
4. Simultaneous observation on the center and the limb is recommended 
as a valuable means of checking results and of investigating the hemi- 
spheres separately. 
We recommend the appointment of an International Committee on 
Solar Rotation determined by spectrographic methods, the four points 
above to be referred as suggestions to this committee. 
C. E. St. John, Chairman, W. S. Adams, Frank Schi^esingkr. 
REPORT OF THE COMMITTEE ON WIRELEvSS DETERMINATION 
OF LONGITUDE 
The Committee recommends : 
1. That the American delegation to the Brussels meeting of the Inter- 
national Astronomical Union urge the desirability of a Division of the 
Union which shall promote in the most practicable manner a world-wide 
program of accurate radio determinations of differences of longitudes, 
on the basis of one general program to be supported by the inter-allied 
nations concerned. 
2. That the American members of this Division or Committee of the 
Union should be selected by the American Delegation with reference 
