ATOMIC EVOLUTION 



and we must therefore suppose, with Lord Kelvin, 

 that the atom is held together by a core of positive 

 electricity, which is now known as an ion. The 

 problem of atomic architecture is so to reconcile 

 the common attraction of the ion for all the elec- 

 trons, with the mutual repulsion of the electrons 

 themselves, as to produce a stable structure. By 

 the aid of mathematical theory, checked by actu- 

 al experiment with magnetized needles to repre- 

 sent electrons floating freely in water, under the 

 influence of a centrally placed electro - magnet, 

 Professor Thomson has been able to unravel the 

 architecture of the atom. The atoms of the differ- 

 ent "elements" vary only in the number and ar- 

 rangements of their electrons, every electron, 

 wherever observed, being absolutely identical with 

 every other. The electrons are found to be ar- 

 ranged in concentric rings within the atom, and 

 the presence of a certain number of them in each 

 ring is necessary for holding any given number in 

 place outside them. The stability of the atom, 

 therefore, depends on the number and arrange- 

 ment of the electrons it contains. No contempo- 

 rary physicist believes that such a thing as an 

 absolutely stable atom exists, though some may 

 undergo no apparent change in millions of years. 

 Thomson's theory clearly explains how atoms of one 

 element, by losing their outer ring or ring of elec- 

 trons, may be transformed into those of another, 

 and it also demonstrates the operation, among 

 atomic species, of the law of natural selection at 

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