186 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1930 



The corona gives a continuous spectrum in which absorption lines 

 show faintly and upon which a bright line spectrum is superposed. 

 The former is ascribed to reflected or scattered sunlight, the latter to 

 an unidentified gaseous element considered formerly to be a 

 hypothetical element, coronium, but now thought to be due to some 

 known element peculiarly excited. The periodic table of the elements 

 based upon atomic theory has no place for such a hypothetical gas. 

 The recent identification by Bowen of the hypothetical nebulium lines 

 with the " forbidden " lines of oxygen, nitrogen, and sulphur, whose 

 production is favored by the extremely low density in nebulae, points 

 to a similar explanation for coronium. 



RADIATION AND AGE OF THE SUN 



The solar radiation at the mean distance of the earth from the 

 sun is 1.94 calories per minute per square centimeter. It is subject 

 to variation over the 11-year spot-cycle, being about 2 per cent above 

 the mean when spots are most plentiful. Variations with periods 

 of a few days may reach 3 per cent (Abbot). The total radiation 

 from the sun is 38 X 10 ^^ ergs per second. Since pre-Cambrian times 

 the sun has been radiating at approximately this rate. This implies 

 a subatomic source of energy within the sun, the transformation of 

 hydrogen into helium, the annihilation of matter (Jeans), or radio- 

 active elements of higher atomic weight than uranium. In modern 

 theory the output of solar energy is equivalent to a loss in mass of 

 4,200,000 tons per second. Even at this enormous rate it would re- 

 quire fifteen thousand billion years for the transformation into en- 

 ergy of a mass equal to that of the sun. The widely accepted value 

 for the age of the earth derived from the radioactive content of the 

 oldest rocks is of the order of sixteen hundred million years. On the 

 assumption that the planets are the offspring of the sun's early years, 

 a minimum age of two thousand million years is found for the sun 

 (Nernst). 



Recently Milne has rediscussed the internal structure of stars and 

 finds that a star tends to generate a kind of " white dwarf " at its 

 center surrounded by a gaseous distribution of more familiar type; 

 the star being like the yolk in an egg. He concludes that in the in- 

 tensely hot, intensely dense, nucleus, the temperatures and densities 

 are high enough for the transformation of matter to take place with 

 ease and that in this nucleus we must look for the origin of stellar 



energy. 



SCHEMATIC SECTION 



A number of the factors bearing on the constitution of the solar 

 atmosphere may be advantageously assembled in a schematized dia- 



