THE PATH OF EVOLUTION 



other worlds, shown to us by the stars in the heavens 

 around us, all are composed of the grouping together 

 into molecules of two or more of the atoms of about, 

 sixty-eight different elements. Of these, fifty are 

 metals, one-half of them so rarely met with that 

 even most professional chemists have never seen them 

 or their compounds. In the inanimate world that 

 we are familiar with, not over twenty-five enter into 

 its composition. In the living animal or vegetable 

 world still fewer only about fifteens-are ever present. 

 It is very seldom that even one-half of this number 

 occur. 



In regard to the compounds constituting the in- 

 organic world we may be said to have a pretty ac- 

 curate knowledge of all that form the outer crust 

 thereof, though we may find and do find from year to 

 year some rare substance that we cannot prove to be 

 composed entirely of the known elements, or that 

 contains some substance with new properties that we 

 cannot separate into still simpler atoms. This dis- 

 tinction of properties between the elementary atoms 

 of one body and those of another is absolute and in- 

 variable. The atoms of each one kind are absolutely 

 the same, unchangeable and indestructible. It is 

 impossible tp create them by human means, and it is 

 impossible to destroy them. Each atom may group 

 itself with others like itself to form molecules of 



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