Perhaps the best general indication of the order in which a person who has no predilection for any one branch of science should take up the various parts is afforded by their historic development. This was a result of the natural reaction of man's mind to its surroundings. The things nearest to him, and most immediately important, first attracted his attention. The broadest division would be into the science of things on the earth's surface; the science of things above the earth, in the air and the sky; and the science of things within the earth, concealed from immediate view. If we take these in their order they naturally subdivide themselves as follows: 1--THINGS ON THE EARTH--EXPLAINED BY (a) Anthropology, the Science of Man and His Ancestors, treating of his nature, origin, development, division into races and tribes, society, industry, etc. (b) Zoölogy, the Science of Animal Life, treating of the "lower animals," and of animal life in general as distinguished from the kingdom of the plants, although the related science of biology deals with both plants and animals, its special subject being the phenomena of life in its widest sense. (c) Botany, the Science of Plant Life. (d) Geography, combined with Physiography, the Science of the Face, or Superficies, of the Earth, dealing with lands and seas, rivers and mountains, political divisions, etc. This is covered in our series by the volume on Physiography. (e) In this compartment several branches of science may be grouped, since they are all the product of study of things encountered on the earth's surface. They are: _Physics_, the Science of the Forces of Nature, dealing with the laws of the inanimate world around us, including the phenomena relating to solid, liquid, and gaseous bodies and substances. _Chemistry_, the Science of Matter and Its Changes, dealing with the atoms and their constituents, and with the combinations of atoms into molecules to form the various chemical elements, etc. _Electricity_ and _Magnetism_, the Science of Power, fundamentally underlying all other branches, and through its investigation of the nature of the constituents of atoms--the electrons--going deeper into the constitution of things than chemistry itself. In fact this science, in some respects, blends with chemistry, although it is quite separate when it deals with the mechanical developments of electromagnetism. _Medicine_, the Science of Health, _Physiology_, the Science of the Body, _Psychology_, the Science of Human Behavior, _Mechanics_, the Science of Machinery, etc., also naturally fall into this category of Things on the Earth. 2--THINGS ABOVE THE EARTH--EXPLAINED BY (a) Astronomy, the Science of the Heavenly Bodies.