ARTICLES 607 



based upon carbon is the only possible one in the universe, and 

 that a life based upon silicon cannot exist ? In short, what does 

 this grouping together of the most important elements mean ? 



EXPLANATION OF FIGURE 



THE IMPORTANCE AND DISTRIBUTION OF ELEMENTS 



The importance of the elements is shown in a heavy, double, or single 

 circle around the symbol and the atomic number. 



The distribution of the elements is shown by letters : 



A and a = occurrence in atmosphere, abundant and less abundant. 



H ,, h = ,, ,, hydrosphere, abundant and less abundant. 



L ,, I = ,, ,, lithosphere, abundant and less abundant. 



M ,, m= ,, ,, meteorites, abundant and less abundant. 



B ,, b = ,, ,, biosphere, abundant and less abundant. 



(For an explanation of the new periodic table, see also Journ. Amer .Chem. 

 Soc, 1918, vol. xi, p. 1023 ; Amer. Journ. Science, 1918, vol. xlvi, p. 481 ; 

 Astrophys. Journ., 1918, vol. xlviii, p. 241.) 



