ATOMIC EVOLUTION 



is decomposed and produces another "element," 

 helium. Now the atomic weight of helium is 

 about 2.2, just about one-hundredth part of that 

 of radium, so that each atom, giving the lie to its 

 name, breaks up into about a hundred particles, 

 and when these have had a few weeks in which to 

 settle down, they are recognizable as atoms of 

 helium. Now it is these particles, flung out at a 

 speed nearly comparable to the speed of light, 

 from the specks of radium in the spinthariscope, 

 that strike the little screen of zinc-sulphide paper, 

 and thereby produce the never-ceasing shower of 

 sparks that are seen in the instrument. 



It is of no small interest that, after the comple- 

 tion of the synthetic philosophy, but just before 

 the death of its author, there should have been 

 discovered in radium a substance which proves 

 that the formula of evolution is as applicable to 

 atoms as it is to societies or solar systems. As I 

 have previously taken occasion to point out, the 

 definition of evolution, framed more than forty 

 years before the facts of radium were known, fits 

 those facts as well as if it had been framed to 

 describe them. This applicability to all circum- 

 stances, new and old, is the hall-mark of a universal 

 truth and of that alone. The most important 

 revelation of radium the revealer is this of atomic 

 evolution. Not even an atom is immune from the 

 universal law of unceasing change; and the reason 

 why every one should possess a spinthariscope is 

 that this simple little instrument demonstrates 

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