124 G. F. BECKER RELATIONS OF RADIOACTIVITY TO COSMOGONY 



cold, so that the simplicity of their spectra is not surprising.^^ Their 

 luminosity is really as small as it appears, and few of them would be 

 visible to the human eye, even if they were as close to us as the moon is. 

 Langley determined the luminosity of the Owl nebula at a four-millionth 

 part of that of white-hot iron. The origin of their light is uncertain. 

 The glow may be due to electrical discharges, and thus analogous to the 

 light produced in highly exhausted tubes of hydrogen at the temperature 

 of liquid air, or possibly it is some unlniown variety of phosphorescence. 

 Though from association we incline to infer a high temperature when 

 luminosity makes its appearance, the aurora of the Arctic night affords 

 an instance of a glow vastly brighter than that of any nebula, and at the 

 very low temperature which prevails at altitudes of some 34 miles. 

 There is no proof that the gaseous nebulae are devoid of solid matter, 

 while it is strongly suspected that the white nebulae do contain solids. 



There does not seem to be the least doubt that stars are developed 

 from nebulae. The "helium" stars often have nebulous appurtenances 

 and show significant spectral relations to the gaseous nebulae. Helium 

 stars pass by the finest gradations into hydrogen stars of the Sirian type, 

 and these again into solar stars.^* 



In the table the known components of helium and Sirian stars, other 

 than helium and hydrogen, are marked by two accents, and it is interest- 

 ing to observe their distribution with reference to the periodic law. If a 

 straight line be drawn from barium to iron, not a single element below 

 the line is found in nebulae or the two groups of stars, and of all the 

 elements identified in these celestial bodies barium has the highest atomic 

 weight (137.4). About a third of the elements in or above this line are 

 found in these stars. Doubtless more stellar elements will be detected as 

 spectroscopic research advances, but it seems probable that the additional 

 elements will have atomic weights below that of barium rather than 

 above it. 



The chief components of the sun are shown in the table by one or 

 more accents. A few rare earths detected in its spectrum are omitted 

 because their positions in the periodic law are as yet unknown. It is 

 highly probable that some of the metalloids, as sulphur and chlorine, may 

 exist in the sun, although they are not spectroseopically evident. Even in 

 the laboratory the spectra of the metalloids are very much obscured when 

 metals are present in abundance. Of the 13 elements included in the last 

 three series of the table, lead -* alone is certainly found in the sun. The 



^ Of. A. M. Gierke : Problems of astrophysics, 1903, p. 535. 

 »= A. M. Gierke : Problems of astrophysics, 1903, p. 272. 



2* In Rowland's list of 1891 lead had but one line. In the great table, however, It 

 has two unquestioned lines and two questionable ones. 



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