may be defined, therefore, as that branch of learning which deals especially with energy and with inanimate matter.

It should be borne in mind by the student that physical and natural originally meant the same thing, the only difference being that the former is of Greek origin, while the latter comes from the Latin Accordingly, we still find a great diversity of usage. Lord Kelvin spoke of a certain physicist as a "distinguished naturalist." The distinction suggested by Maxwell is, however, being rapidly adopted.

The unprecedented growth of physical science during the 19th century had the effect of enormously subdividing the subject. Astronomy, which, in fact, is the simplest branch of physics, requires a peculiar set of instruments for its pursuit, and, therefore, is no longer studied under the head of physics. The same is true of chemistry, which is the physics of the molecule: it has become a large subject requiring a special equipment, and is a science separate from physics. Such, however, was not the case when Robert Boyle studied physics and chemistry. In like manner geology is the physics of the earth's crust; but it must be studied afield as well as in a special laboratory, and, hence, is a separate and very important science. Mineralogy also deals with the physics of a special group of bodies. But these bodies are so vast in number and so enormously important in commerce that they must be studied elaborately and carefully under a special head and with a special equipment.

Turning now from the pure physical sciences to the applied physical sciences, we find them grouped under the general head of engineering, which in turn has already been extensively subdivided. It is the rapid advance in physical science which has made possible the vast improvements in modern civilization, somewhat in the same manner that the rapid advances in natural science have made possible a more powerful and beneficent science of medicine and have introduced into modern thought the controlling principle of evolution.

Physics {fiz'tks), in its broad sense, is that science which deals with the properties of matter and of energy. In its narrow sense physics is defined in such a way as to exclude those properties of matter which depend upon its composition (referring them to chemistry), and those properties of matter which are exhibited only in living beings (referring them to biology). For many years, however, there has ceased to be any sharp distinction between physics and chemistry. Witness the new sciences of physical chemistry and electrochemistry. Popularly defined, physics is made up of the sciences of mechanics, heat, light, sound, electricity and magnetism. A sounder view is that which regards physics as the appli-

cation of dynamics to the phenomena of sound, heat, light, electricity and magnetism. See Acoustics, Dynamics, Elasticity, Electricity, Hbat, Light and Magnetism. Phys'iog'raphy.

Scope op the Subject

This term has but recently come into use, and its meaning is not yet clearly and uniformly defined. In England physiography is regarded as the introduction to physical science in general. It is made to include the elements of physics, chemistry, astronomy, physical geography, geology and, sometimes, even certain phases of botany and zoology. In America the term has a somewhat different meaning. It is sometimes used as a synonym for physical geography, but sometimes it is defined as the science which describes and explains the physical features of the earth's surface. In this sense it is the correlative of meteorology, which treats of the atmosphere, and of oceanography, which treats of the oceans. According to early usage physical geography meant a description of the earth's physical features; but physiography does not content itself with a mere description of physical features. It attempts also to explain how existing physical features originated. This indeed is the fundamental distinction between physiography, as the term is commonly used in America, and that part of physical geography which deals with the physical features of the earth's surface. In its attempt to explain the origin of the present features of the earth's surface physiography necessarily draws, to some extent, on the past history of the earth; that is, on geology. Between physiography and geology, therefore, there is no sharp line of division. The present features of the earth are the surface expression of the geological processes which have operated in the past. The relation of physiography to geology may be likened to the relation of political geography to history. Political geography is an expression, in one form, of history. The political geography of all stages of history would, from one point of view, be a summary of history. Similarly, if the physiography of each stage of the earth's history were known, this knowledge would, from one point of view, give us the complete history of the earth.

The atmosphere is as much a part of the earth as are the rocks. The study of the atmosphere is meteorology, but physiography, even in its narrowest meaning, includes the consideration of the atmospheric forces and processes which have shaped or helped to shape the present surface of the land. This includes the movements of the air (winds), the moisture of the air, especially precipitation, the changes of temperature and the chemical changes effected, directly or indirectly, through the influence of the atmosphere. While meteorology in-