160 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1933 



There is no clanger of burning in the well-tempered heat. Foods 

 may be left to cook for many hours without harm. All meats and 

 vegetables are most deliciously prepared. 



In short, the solar cooker is a delightful luxury. Whether im- 

 provements and simplifications may reduce it to less than a luxury 

 is still questionable. As an experiment in collecting solar heat, it 

 has served a very useful purpose. Several of the devices tried out 

 thereby seem likely to be of value for the greater problem of har- 

 nessing the sun rays for power. 



CONDITIONS IN THE SUN 



Before discussing the influence of the sun on climates and weather, 

 let us devote a few moments to the consideration of the sun itself. 

 As Dr. Russell stated 2 years ago, the sun is composed of the same 

 chemical elements as those found upon the earth, and roughly in 

 the same proportions. The temperature even at the surface of the 

 sun is observed to be of the order of 6,000° absolute centigrade, nearly 

 twice as hot as the arc light. All substances are not only melted, but 

 rendered gaseous, at such temperatures. At lower levels within the 

 sun's body there is every reason to believe that the temperature 

 rapidly rises. Dr. Eddington computes for the sun's central tem- 

 perature something like 20,000,000° C. The pressure there reaches 

 many millions of atmospheres. Though we have no examples of 

 such extreme conditions on the earth, we may surely infer that the 

 sun's substance except possibly near its center is wholly gaseous. 

 Elements like oxygen and hydrogen, which combine so avidly as 

 to explode together when burned on earth, would not unite at all 

 at solar temperatures. Not only are there no molecular compounds 

 formed there (except in sun spots, where lower temperatures pre- 

 vail), but even the atoms themselves are largely split to pieces, 

 throwing off electrons and the other recently discovered subatomic 

 constituents. 



MEASURING SOLAR RADIATION 



For many years the Smithsonian Institution has devoted much 

 attention to the measurement of the intensity of solar radiation. 

 We are concerned not only with its total heating power but with 

 the relative intensity of the rays of the different colors. [Here a 

 spectrum was thrown on the screen.] Not only the rays visible to 

 the eye, but others beyond the violet and beyond the red, which 

 we call ultraviolet and infrared, respectively, are plentifully emitted 

 by the glowing sun. 



All rays, whatever their color, or even if they are invisible ultra- 

 violet or infrared rays, give up their total energy to produce heat 



