Great wonders Nature seems to achieve by varying the arrangement of the same particles.  Arrange or unite the atoms of carbon in one way and you have charcoal; assemble the same atoms in another order, and you have the diamond.  The difference between the pearl and the oyster-shell that holds it is one of structure or arrangement of the same particles of matter.  Arrange the atoms of silica in one way and you have a quartz pebble, in another way and you have a precious stone.  The chemical constituents of alcohol and ether are the same; the difference in their qualities and properties arises from the way the elements are compounded—­the way they take hold of hands, so to speak, in that marriage ceremony which constitutes a chemical compound.  Compounds identical in composition and in molecular formulae may yet differ widely in physical properties; the elements are probably grouped in different ways, the atoms of carbon or of hydrogen probably carry different amounts of potential energy, so that the order in which they stand related to one another accounts for the different properties of the same chemical compounds.  Different groupings of the same atoms of any of the elements result in a like difference of physical properties.

The physicists tell us that what we call the qualities of things, and their structure and composition, are but the expressions of internal atomic movements.  A complex substance simply means a whirl, an intricate dance, of which chemical composition, histological structure, and gross configuration are the figures.  How the atoms take hold of hands, as it were, the way they face, the poses they assume, the speed of their gyrations, the partners they exchange, determine the kinds of phenomena we are dealing with.

There is a striking analogy between the letters of our alphabet and their relation to the language of the vast volume of printed books, and the eighty or more primary elements and their relation to the vast universe of material things.  The analogy may not be in all respects a strictly true one, but it is an illuminating one.  Our twenty-six letters combined and repeated in different orders give us the many thousand words our language possesses, and these words combined and repeated in different orders give us the vast body of printed books in our libraries.  The ultimate parts—­the atoms and molecules of all literature, so to speak—­are the letters of the alphabet.  How often by changing a letter in a word, by reversing their order, or by substituting one letter for another, we get a word of an entirely different meaning, as in umpire and empire, petrifaction and putrefaction, malt and salt, tool and fool.  And by changing the order of the words in a sentence we express all the infinite variety of ideas and meanings that the books of the world hold.