6 1 4 THE AMERICAN JO URNAL OF SOCIOLOGY
tion of the climates in five zones : a torrid, comprised between the tropics ; two frigid, limited by the polar circles ; and two tem- perate zones, contained between the tropics and the polar circles. The structure and the movement of the earth also divide the year into four seasons. All these general limitations have in their turn relationships with the structure and the life of organized beings, including those organized into societies.
SECTION IV. PHYSICAL AND CHEMICAL LIMITS.
Nothing seems to limit the dimensions of inorganic com- pounds. They are, however, formed of particles. Thus, although water has no texture or visible structure, it is nevertheless formed of distinct molecules. There exists between these molecules a resistance which separates them. This resistance arises from their thermic state, for when one heats water or makes it cold it passes into vapor or becomes ice ; that is to say, its molecules acquire less or more cohesion. All unorganized bodies may take definite forms and augment their volume by the addi- tion of similar parts. Each crystallizable substance has its characteristic crystalline forms. It never deviates from certain clearly defined geometrical forms, whatever may be its mass. Enlargement is always effected by adding to the exterior of the body similar parts which previously existed apart from it. Crystals, the most perfect inorganic bodies, are composed exclusively of a homogeneous substance. All are limited by plane surfaces which break following straight lines and constant, measurable angles.
As examples of the law of physical limitation, we may cite in crystallography :
First, the law of symmetry: When a crystal presents upon one of its elements (angles or edges) a certain modification, all the other elements crystallographically similar are modified at the same time in the same way.
Second, the law of derivation: If a modifying face intercepts upon the edges of a crystal of the dimensions x, y, and z, every other face placed upon the same element will intercept upon these edges according to dimensions x* , y' , and z' , which wil
