CHAPTER VII 



THE NATURE OF MATTER 



In Nature's infinite book of secrecy 



A little I can read. SHAKESPEARE, Antony and Cleopatra. 



As we noted in a previous chapter, the physicist believes that 

 every substance is made up of very tiny particles called molecules, 

 and that if these are broken up into their component atoms the 

 nature of the substance is completely changed except in the case 

 of elements. Thus a drop of water might be divided into smaller 

 drops and these into still tinier droplets. But such subdivision 

 cannot go on indefinitely. Ultimately a division would give mole- 

 cules of water. If these were again split, the product would no 

 longer be water but hydrogen and oxygen, the two elements that 

 make up water whose properties are entirely unlike those of 

 water. The physicist believes in molecules although he has 

 never seen them, because this molecular theory enables him to 

 explain and predict the many physical phenomena. Even ele- 

 ments exist in molecular form and while, when the molecules of 

 an element are split into the atoms, we have no new substance, 

 yet the properties of an element in its atomic state are usually 

 quite different from its properties in the molecular state. 



In spite of the fact that the molecule is so small it has never 

 been seen, yet its size has been calculated from experimental 

 data, with reasonable accuracy. A hydrogen molecule has a 

 diameter of about one eleven-billionth of an inch and weighs 

 about one ten-sextillionth of an ounce, figures that are meaning- 

 less, because they are so far removed from experience. It is 

 difficult to put them in terms that are comprehensible. A 

 bubble of hydrogen gas under ordinary conditions with a diam- 

 eter as great as that of the cross-section of a pin would contain 



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