KNOWLEDGE OF THE SUN — ST. JOHN 170 



Taiu.b I. — Elements idcniifled in the aun aud their position in the p< riudie tabic 

 [Unidentined elements in piireii theses) 



• HARE EARTHS 



Mount Wll.son Observntory 



Those in parentheses are as yet unidentified in the sun's atmos- 

 phere. This does not necessarily mean that these unidentified ele- 

 ments are absent. For some elements the lines of lowest excitation 

 potential, the resonance lines, are far in the ultra-violet beyond the 

 accessible regions in both stellar and solar spectra. A layer of 

 ozone situated some 50 miles above the earth's surface absorbs the 

 radiations to the violet of a2,975 A. The strong resonance lines of 

 the neon and fluorine groups are in this region. The question marks 

 mean that the evidence is not strong and that exact laboratory wave 

 lengths are wanting as in the case of osmium and iridium. Even- 

 tually such elements will be found to be definitely present or absent. 

 Ninety of the ninety-two possible elements have been found on the 

 earth. The heavy elements in the bottom line are all radioactive. 



