STL'DVIXG THE SUN AND STARS 



Bv C. G. ABBOT, 



Secretary of the S'niitlisoniaii Iiistittitio)i, and Director of the 

 S)iiitlisouiaii .Istropliysical Ol^scr^'atory 



It will be recalled that the Smithsonian Institution has two obser- 

 vatories, one in Chile and the other in Southern California, makinq- 

 daily measurements of the intensity of the sun's rays, on which all 

 life depends. The Institution also administers the similar solar ob- 

 serving station of the National Geogra]:)hic Society in South West 

 Africa. These three ol^servatories, situated on mountain tops in desert 

 localities, have cooperated for several years in observing the solar 

 rays on nearly every day. 



As anticipated a year ago from a study of regular periodicities 

 recently discovered in the variation of the intensity of the sun's rays, 

 the solar radiation rose to a feel)le maxinuim in the spring months, and 

 declined to a marked minimum in the autumn of 1928. Should these 

 observed periodicities continue to prevail in solar radiation, it may be- 

 come possible soon to forecast the general march of the sun's energy 

 for a year or more in advance, and also to forecast such climatic or 

 other terrestrial concerns as may be shown conclusively to depend 

 thereon. Short-interval irregular solar variations also seem to occur, 

 but in a manner not predictable. The daily results of solar radiation 

 measurements, through the kindl\- c()0|)eration of the Chief of the 

 U. S. Weather Bureau, are published on the Washington weather niajD. 



The writer and Mr. H. \\. Freeman of the Astrophysical Observa- 

 tory occupied the Smithsonian station on Mount Wilson, California, 

 from July to mid-September, 1928. They improved the somewhat 

 celebrated solar cooker, installed there some years ago, by employing 

 vacuuiu jackets for the heater tul)e, and by better protecting the 

 a])paratus in other ways from loss of heat. Series of measurements 

 were taken of temperatures in the ovens and elsewhere in the apparatus 

 at all hours of the day. The ovens remained for several weeks at 

 temperatures between 140° Centigrade at sunrise and 175° Centigrade 

 at mid-afternoon, so that baking and other operations of cooking could 

 be done at all hours of night as well as day, even though the exposure 

 to sun-rays was limited to about seven and one-half hours per day by 

 the shading of trees. 



Many years ago, under Secretary Langley's direction, the Astro- 

 physical Observatory made a study of the solar spectrum beyond the 



