SECRETARY'S REPORT 61 



instruments are nearly completed. In addition, silver-disk SI#69 

 was repaired, recalibrated, and retm^ned to the Servicio Meteorologico 

 National, Buenos Aires,' Argentina, and modified Angstrom SI#12 

 was built, calibrated, and forwarded in March 1955 to the Meteorolo- 

 gisches Observatorium, Hamburg, Germany. Silver-disk SI#52 

 was received in March 1955 from the University of Miinster in dam- 

 aged condition. Repairs and recalibrations are in progress. In May 

 1955, modified Angstrom SI#13 was lent to Drs. P. R. Gast and 

 Ralph Stair for temporary use on Sacramento Peak, N. Mex. 



Work in the field. — The quality of the sines at our two field observ- 

 ing stations during the current year proved inferior to the average of 

 previous years. At Montezuma, our high-altitude station in north- 

 ern Chile, the sky pollution due to the smelting operations at nearby 

 copper mines, mentioned in last year's report, continued unabated. 

 A study of the average quality of the sky before and after starting the 

 smelters (in March 1953) shows the magnitude of the pollution. A 

 summary by months, covering the period 1940-55, shows that in each 

 of the 12 months, the direct solar beam (at solar altitude of 30°) has 

 been reduced between 1 and 7 percent since the smelters started. The 

 sky brightness around the sun on the same days increased between 1.3- 

 and 2.6-fold after the smelters started. A summary of long-method 

 observations during the same period indicates that the direct solar 

 beam after the smelters started decreased some 2 to 6 percent and the 

 sky brightness increased 1.6- to 2.5-fold. The atmospheric trans- 

 mission coefficients show the following change at the wavelengths 

 indicated : 



Wavelength 0.39/t, a decrease of 2 to 7.5 percent. 



Wavelength 0.61aj, a decrease of 1.5 to 4.5 percent. 



Wavelength 0.97/t, a decrease of 1 to 2 percent. 



As a result of the variable daily output of gas and smoke from the 

 smelters, Montezuma skies are now definitely less uniform than 

 formerly. 



At Table Mountain we have noted for some years a gradual increase 

 in the amount of smog from the Los Angeles area, which rises at in- 

 tervals above the level of Table Mountain. As civilization expands 

 it becomes increasingly difficult to find high-altitude locations that 

 combine clearness, dryness, and uniformity of skies with accessibility 

 and bearable living conditions. 



Publications. — During the current year the following publications 

 concerned with the work of the Division of Astrophysical Research 

 appeared : 



Annals of the Astrophysical Observatory, volume 7, [July 7], 19.54. 



Pyrheliometer calibration program of the U. S. Weather Bureau, by T. H. Mac- 

 Donald and Norman B. Foster. Month. Weather Rev., vol. 82, No. 8, August 

 1954. 



