With mathematics as the tool, the classification of knowledge may proceed. All natural phenomena fall into two grand divisions: inorganic and organic. The inorganic are more general and should be considered first. Inorganic phenomena are of two classes: astronomical and terrestrial. Astronomical phenomena are the most general of all. The stars and planets appear under the least varied aspects.[XIII-12] Astronomy is the science by which the movements of the heavenly bodies, including the earth, are measured. How can we thoroughly understand any terrestrial phenomena without considering the nature of the earth and its relation to the other units of the solar system?[XIII-13] Terrestrial physics includes two fields: physics proper and chemistry. Material bodies may be regarded in either their physical or chemical aspects. Physics is more general than chemistry; it deals with masses rather than elements. Chemical phenomena depend upon the laws of physics, without being influenced by them in turn. Chemical action is conditioned by the laws of weight, heat, electricity. The study of inorganic phenomena thus falls under three scientific heads: astronomy, physics, and chemistry. Organic phenomena include two types: individual and group. The first refers to the function and structure of all individual forms in the plant and animal worlds. It is general physiology, or, in modern terms, biology. It involves the study of all life and the general laws pertaining to the individual units of life. Biology rests on chemistry, because it is in chemistry that all reliable knowledge about nutrition or secretion is found. Biology is indebted to physics for knowledge concerning the weight of, temperature of, and related facts about living organisms. Biological laws are partially determined by astronomical factors. If the earth were to rotate faster than it does, the course of physiological phenomena would be accelerated, and the length of life would be shortened.[XIII-14] If the orbit of the earth were to become as eccentric as that of a comet, changes of a fatal nature would occur to all life on the earth. If there were no inclination of the earth’s axis, the seasons would be unknown, and the geographical distribution of living species would be vastly different from the present situation. All accurate work in biological studies is mathematical in character. Thus biology, the science of organic phenomena, is dependent on all the preceding divisions on the scale of knowledge.