THE NATURE OF MATTER 165 



So it is quite commonly observed that a thunder shower does not 

 cool the air but makes the heat more oppressive, and that severe 

 winter temperatures are moderated by a snow storm. 



If the tiny bubble of hydrogen were to be magnified as indi- 

 cated above, you would not see the molecules as solid objects 

 like golf balls, for each molecule is made up of relatively small 

 particles traveling in orbits or possibly oscillating in pathways. 

 Just as we say that the solar system, the central sun and the 

 bodies revolving about it, has a diameter of nearly 560,000,000 

 miles, though only a minute portion of this space is actually 

 occupied by the sun, planets, and moons, so the bodies that com- 

 pose a molecule really occupy but a small part of the space 

 assigned to it. The molecule consists of atoms, two in the case 

 of elements (or rarely one atom), moving in pathways about 

 some center. In complex compounds a molecule may consist of 

 hundreds of atoms. Each atom of hydrogen consists of a cen- 

 tral mass carrying an excess of one charge of positive electricity 

 and revolving about it one charge of negative electricity a bit 

 of disembodied force. The latter is known as the electron, the 

 body that carries the positive charge, the proton. It is the path- 

 ways of these that occupy the space assigned to the atom, the 

 diameter of which, in the case of hydrogen, is about half that of 

 the molecule. 



Protons and electrons are so small that they would still be 

 invisible if the tiny bubble of hydrogen gas were only magnified 

 to be as large as the earth. Suppose it were enlarged to a sphere 

 with a diameter that of the orbit of the earth. Then the mole- 

 cules would be some two-fifths of a mile in diameter, the electron 

 about one-fourth inch in diameter while the proton would be one 

 eighteen-hundredth of that. In spite of this disparity in size 

 the mass of the proton is about 1,800 times that of the electron. 



Chemists used to believe that there are eighty or more ele- 

 ments such as copper, iron, oxygen, which enter into various com- 

 binations forming compounds. Common salt, for instance, is a 

 combination of the elements sodium and chlorine. And this 



