28 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



ASTROPHYSICAL OBSERVATORY. 



The principal research carried on by the Astrophysical Observa- 

 tory during the year has been on the variability of the sun. Progress 

 has been made in the dissemination of standards of pyrheliometry 

 and on the absorption of radiation by atmospheric water vapor. 



The first of these investigations was in continuation of observations 

 taken during several years past to definitely determine the laws gov- 

 erning the apparent variability of the " solar constant.'" The solving 

 of this problem, it is expected, will be of much value in the probable 

 forecast of climatic conditions from year to year. In this research 

 it seemed important that simultaneous observations be made in widely 

 separated parts of the world. It was accordingly arranged to make 

 such observations at Mount Wilson, California, and at Bassour. 

 Algeria. The results of this work are discussed by Mr. Abbot in his 

 report on another page. 



For several years the Institution has been sending to observatories, 

 widely separated throughout the world, standardized copies of the 

 standard silver-disk secondary pyrheliometer designed by the director 

 of the Smithsonian Astrophysical Observatory. During the past 

 year about 10 such instruments have been prepared and sent out, 

 mostly to foreign governmental meteorological services. It is hoped 

 to thus secure not only uniformity of radiation measures, but also a 

 more exact knowledge of solar radiation and the influence of the 

 terrestrial atmosphere upon it. 



In carrying forward the research on the absorption of radiation 

 by atmospheric water vapor, there has been recently devised at the 

 observatory a method for determining spectroscopically the total 

 quantity of water vapor between the observer and the sun. Atmos- 

 pheric water vapor absorption work during the year was confined 

 to the upper infra-red spectrum bands. It is expected by the use of 

 a vacuum bolometer now in preparation to make considerable gain 

 in the sensitiveness of the apparatus and greatly promote the value 

 of the work at great wave lengths. 



INTERNATIONAL CATALOGUE OF SCIENTIFIC LITERA- 

 TURE. 



The cooperative enterprise known as the International Catalogue 

 of Scientific Literature is represented in the United States through 

 the Smithsonian Institution, an appropriation being made each year 

 by Congress to maintain a regional bureau in this country under 

 the auspices of the Secretary of the Institution. 



This bureau, in cooperation with thirty-one other regional bureaus, 

 through a central bureau in London, publishes yearly 17 volumes, 

 which form an index to current scientific literature. Each countrv 



