REPORT OF THE SECRETARY. 95 
Omaha. Ascensions were not made until after July 1, 1914, but it 
may be said in anticipation that two ascensions by day and one by 
night were made. All three instruments were recovered. No unex- 
pected phenomena were disclosed by the night record. One day 
record appears to be excellent. Fortunately the instrument which 
recorded it came back uninjured, and further tests and calibrations 
with it are intended. The instrument reached a very great height, 
and recorded radiation successfully until after it began to descend. 
Preliminary reductions show that the values recorded fall below 
our adopted value of the solar constant of radiation. 
SUMMARY. 
Progress has been made in the measurement of the effects pro- 
duced by atmospheric water vapor on solar and terrestrial radia- 
tion. New apparatus for measuring sky radiation has been devised 
and perfected. Special pyrheliometers have been constructed and 
caused to record solar radiation ‘with considerable success at great 
altitudes when attached to free balloons. The results obtained tend 
to confirm the adopted value of the solar constant of radiation. 
Further results from balloon pyrheliometry are expected. A tower 
telescope has been erected and put in operation on Mount Wilson. 
By means of it the variability of the sun has been independently con- 
firmed, for it appears that changes of the distribution of radiation 
over the sun’s disk occur in correlation with the changes of the sun’s 
total radiation. 
Respectfully submitted. 
C. G. Assort, 
Director Astrophysical Observatory. 
Dr. Cuarutes D. Watcortt, 
Secretary of the Smithsonian Institution. 
