EEPORT OP THE SECRETARY. 91 



influence is attributable to the presence of volcanic haze; and that 

 a combination of the effects of sun spots and volcanic haze accounts 

 for all the principal outstanding irregularities in the temperature 

 of the earth for the last 30 years. 



4. VOLUME III or THE ANNALS OF THE ASTROPHYSICAL OBSERVATORY. 



The principal work of the year was the reduction of observations 

 and the preparation for publication of Volume III of the Annals of 

 the Astrophysical Observatory. (Quarto; pp. XI 4-241; tables, 70; 

 inserted plates, 7; text figures, 32.) The manuscript was forwarded 

 to the Public Printer on April 1, and the first completed copy of the 

 book was received on July 3, 1913. About 1,400 copies have been 

 distributed to libraries and individuals throughout the world. 



In brief, the experiments described therein, which include the 

 work of the observatory from 1907 to 1913, appear — 



(a) To have established the scale of measurement of radiation to 

 within 1 per cent. 



(h) To have established the solar constant of radiation to within 

 1 per cent. 



(c) To have shown by two independent methods that the sun's 

 emission is not uniform but varies with an irregular periodicity of 

 from 7 to 10 days on the average and with irregular amounts seldom 

 if ever exceeding 10 per cent. 



{d) To have shown that the sun also varies in connection with the 

 sun-spot cycle. The solar emission appears to be increased at the 

 earth's mean distance from the sun by about 0.07 of a calorie per 

 square centimeter per minute for an increase of 100 Wolff sun-spot 

 numbers. 



(e) A marked effect of volcanic dust in the upper atmosphere on 

 the radiation of the sun and on the temperature of the earth is 

 indicated. 



(/) Studies of the radiation of the sky, the effects of water vapor 

 on the solar radiation, the distribution of radiation over the sun's 

 disk, the probable temperature of the sun, and other subjects are 

 included. 



5. STUDIES or THE TRANSMISSION OF LONG WAVE RATS BY WATER VAPOR 

 IN THE earth's ATMOSPHERE. 



Mr. Fowle's experiments on the transmission of radiation through 

 long columns of air containing measured quantities of water vapor 

 were temporarily discontinued owing to the need of completing the 

 publication of Volume III of the Annals. He, however, published 

 a paper on the quantity of water vapor found above the Mount Wil- 

 son station.^ 



Toward the end of the fiscal year a vacuum bolometer was pre- 

 pared for use in continuing the experiments on the transmission of 



1 Astrophysical Journal, vol. 37, p. 359, 1913. 



