PHYSIOGRAPHY (Greek, physis = na ture +graphic = description), has been vari ously defined. By many it is considered to be synonymous with geomorphology or geomorph cgeny. In this sense it may be defined as the science which treats of land forms and their origin. On the other hand it is considered by many as equivalent to physical geography, and a recent authority has defined it as that sci ence which investigates the physical features of the earth and their influence on life, espe daily man." The geologists in general tend to favor the former idea; the geographers the lat ter. In the modern development of the subject there is a strong tendency to emphasize the more purely geographic aspects of the science; or, as some one has said, to humanize it.
Physiography has been called the latest chap ter in geology, a very apt phrase when applied to geomorphology proper. It covers largely the same subject matter treated in dynamical geol ogy, namely, the processes and forces now operating to modify the earth. Physiography, however, investigates these facts, as a key to the study of human progress; dynamical geol ogy because it is only in the light of the proc esses now in operation that we can interpret the history of the past, as locked up in the rocks.
Change of seasons, tides, wind circulation and their geographic relations are so directly dependent on astronomic considerations that a preliminary study of the earth in its relations to the universe is essential to physiography. Because of the activity of atmospheric agents in shaping land forms, physiography is often pref aced with a brief study of meteorology and climatology, with special reference to wind, temperature and rain, their cause and distri bution. A brief study of rocks and minerals is also necessary, since it is possible to under stand the activities shaping the earth's crust only when we know something of the nature of the materials upon which these forces act. The subject is not infrequently divided under the headings of the atmosphere, the hydro sphere and the lithosphere.
The For a discussion of the composition and direct geologic activity of the atmosphere as a weathering agent see the sec tion on Work of the Atmosphere in the arti cle on GEOLOGY. In addition to these factors more important considerations to the geog rapher are winds, temperature and rainfall.
The great wind belts are shown to be the result of excessive heating in the equatorial regions, causing the air drifts from the poles toward the equator, and this is modified by the earth's rotation giving belts of winds and calms. Un equal heating of land and water and the trend of mountain ranges modify the planetary wind belts and give local variations. Temperature depends primarily on latitude, but temperature belts are modified by proximity to oceans or large lakes, and by the effect of mountain ranges on wind direction. Precipitation is largely dependent on wind movements. In the equatorial belts of calms where the air is rising and cooling, rain is abundant. Deserts are the rule in the horse latitudes, where the air is descending and becoming warmer. Winds blowing over high mountains are forced to give up their moisture on the windward side, and are dry winds beyond the mountain ranges. The physiographer is concerned with all these facts in their effect on man and his activities, both directly as the sum total of climate, and indirectly in shaping land forms. See Ant; WIND; CLIMATE; GEOGRAPHY and GEOLOGY.
The The geologic aspects of the waters of the earth's crust have been discussed in the sections on Work of Oceans and Work of Lakes, in the article on GEOLOGY. See also OCEANS and LAKES.
The ocean as an equalizer of climate is of interest to the physiographer, since it is a well known fact that regions near the ocean do not have the extremes of temperature that exist in the interior of continents. Ocean currents are important in this respect. The warm Gulf stream and the cold Labrador current account ing respectively for the equable climate of England and the bleakness of Labrador. The ocean as a highway for human traffic and as a source of human food are within the scope of physical geography. The smoothness or irregu larity of shore lines, which results from geo logic processes, determine the nature of har borage. Still within the scope of the physiog rapher's research but less directly, so are the processes of sedimentation going on in the ocean, since these control in part the types of rocks with which man has to deal on the earth's surface.