WHAT THIS WORLD IS MADE OF 



Of course, this does not represent the limits of 

 divisibility for the air or the water, nor even the 

 fluorescein. It is very easy nowadays to produce 

 a vacuum of a millionth of an atmosphere that is, 

 containing only a millionth part of the air or other 

 gas that was there when the process of exhaus- 

 tion was begun. And the vacuum tube will still be 

 "full" of air. There will not be a space equal to 

 the millionth part of a hair's-breadth that will not 

 be occupied by whizzing molecules. What is true 

 of air is true of any substance. This extreme di- 

 visibility may be paralleled with common salt. It 

 is well known that perfectly pure water is a non- 

 conductor of electricity. A single gram of salt 

 dissolved in water suffices to carry electricity 

 through fifteen hundred tons of it. The theory of 

 conduction in liquids is that the electricity is fer- 

 ried across from one pole to the other by the in- 

 dividual atoms; each atom carries its own little 

 charge. We must suppose, in this case, that the 

 gram of salt is evenly distributed through every one 

 of fifteen thousand million cubic centimetres. In 

 each cubic centimetre there would have to be mill- 

 ions and millions of ferrying atoms. 



An experiment with this same substance, or 

 rather one of its two constituents sodium- 

 thrown into a flame, is equally amazing. A gram 

 is the weight of a thimbleful of water; a milligram, 

 8 113 



