ELEMENTARY PHYSICS RELATING TO FRICTION AND LUBRICATION.
~15.~ Most of those who may read this work, are no doubt familiar with the laws of elementary physics; but as all may not be, for a better understanding of that which follows, it may be well to treat briefly of some of the physical laws bearing on the subject.
~16. The Molecule.~ Every visible body of matter is composed of exceedingly small particles called molecules. This is the basis of the theory of the constitution of matter which physicists have usually adopted. It is estimated that if we should attempt to count the number of molecules in a pin's head, counting at the rate of 10,000,000 per second, we should require 250,000 years.
~17. Porosity.~ The term pore in physics is restricted to the invisible space that separates molecules. All matter is porous; thus dense gold will absorb (24) liquid mercury, much as chalk will water; but the cavities to be see