REPORT OF THE SECRETARY. rey 
OBSERVATIONS AT WASHINGTON. 
Measurements for the determination of the “solar constant” of radiation 
were made whenever the atmospheric conditions permitted. These occasions 
are too infrequent to permit us to make at Washington a full record of the condi- 
tion of the sun, but in connection with and supplementary to the Mount Wilson 
work, the Washington results are of very great value. 
Measurements have been made frequently of the distribution of brightness 
over the solar disk, and the results of these measurements indicate, though 
perhaps not conclusively, that when the contrast in brightness between the 
center and edge of the solar disk is greater than usual, the intensity of solar 
radiation available to warm the earth is less than usual, and vice versa. This 
relation was suspected in former years. 
PREPARATION OF VOLUME II OF THE OBSERVATORY ANNALS. 
The reduction and preparation for publication of the results of the thousands 
of bolographic records made in the research on solar radiation has involved 
measurements and computations requiring the recording of upward of 2,000,000 
separate figures. The reductions have been chiefly in the care of Mr. Fowle, 
and he has been ably seconded by Miss Graves. Very useful and painstaking 
assistance has been rendered by Mr. Dwyer and by the temporary computers 
employed. The text and illustrations have been prepared under the care of the 
writer, in consultation with Mr. Fowle. The whole work was nearly completed 
at the conclusion of the fiscal year, and at this writing (September 15) is now 
ready for the press. As the story of the year’s work is chiefly the story of this 
volume, it will not be out of place to give here a summary of its principal 
contents. 
SUMMARY OF THE FORTHCOMING VOLUME OF ANNALS. 
The present volume is an account of the work of the Astrophysical Observa- 
tory from 1900 to 1907, with details of the investigations made, the apparatus 
and methods used, and the results obtained. 
Speaking broadly, the investigation relates to the intensity of the rays of the 
sun, and the dependence of the earth’s temperature thereon. The subject is here 
treated in three parts: First, the amount of the solar radiation as it would be 
found if measured outside the earth’s atmosphere, at mean solar distance, or, as 
it is often termed, “ The solar constant of radiation.” Second, the dependence 
of the earth’s temperature on the amount of solar radiation. Third, the differ- 
ence in brightness between the center and edge of the sun’s disk and its relation 
to the quantity of solar radiation received by the earth. 
The work is not limited to a determination of constants of nature, for the 
possibility was early recognized that the radiation of the sun might be far 
from uniform, so that the “solar constant of radiation” might prove to be 
a mean value about which the intensity of the solar beam would be found to 
fluctuate very perceptibly from time to time. A principal aim of the work has 
therefore been to prove whether such fluctuations of the quantity of solar 
rays do exist, and, if so, what may be the magnitude of the changes, their 
effects on climate, and their causes. For these purposes the measurement of 
the intensity of solar radiation and of the distribution of brightness over the 
disk of the sun have been made as often as possible for several years, and a 
study of the variation of temperature for the last thirty years at about fifty 
stations scattered as widely as possible over the inland areas of the world has 
also been made. 
