?6 TWO NEW WORLDS 



of hydrogen atoms contains four atoms, forming 

 a tetrahedron or equilateral pyramid. Such a 

 structure we may identify with the helium 

 atom. 



Larger atoms are built up out of larger aggre- 

 gates of hydrogen atoms, and the manner of their 

 architecture is one of the most fascinating problems 

 awaiting the coming electric theory of crystals. 

 But we may well suppose that the helium atom 

 never loses its stability and predominance. It is 

 interesting to note that similar elements in the 

 periodic series are made up by adding 16, 32, or 48 

 hydrogen units to the atomic weight; in other 

 words, by adding four, eight, or twelve helium 

 atoms. These are probably disposed symmetrically, 

 on the principle of the tetrahedron, the octahedron, 

 and the dodecahedron. When the atom breaks up 

 these projecting helium atoms are the first to be 

 thrown off, as is done when radium and polonium 

 atoms break up. 



2. It would be an interesting task to endeavour 

 to follow up the influence of the configuration of 

 the compound atoms and their attendant electrons 

 on the building up of a crystalline or amorphous 

 solid. It will, no doubt, be a long time before a 

 complete mathematical theory is formulated which 

 accounts for the delicate balancing of the hydrogen 

 atoms within the positive atom and the molecules 

 within the crystal. The researches already made 



