Geography Physical

Geography, Physical, though sometimes taken as including those topics here alluded to as Astronomical or Mathematical Geography (q.v.), may be succinctly defined as that department of the general science of geography that deals with the scientific description and explanation of the present natural aspect of our earth and its inhabitants, and the changes that are now taking place on its surface. Since all the phenomena that we see around us to-day are but the results of countless series of changes that have been in progress during incalculable ages, physical geography is in some respects the last chapter of geology (q.v.); but, from the light which the investigation of causes now in operation throws upon the agencies at work in past times, its study forms practically a most important introduction to that of the dyneimical department of geology. Physical Geography includes the study of the atmosphere (q.v.); its temperature, moisture, pressure, and consequent movements or winds (q.v.), most of which conditions make up that which we term climate and form the subject of the special science of meteorology (q.v.). It also deals with the inner, aqueous envelope, which covers about eleven-fifteenths of the surface of the globe, the ocean (q.v.) or hydrosphere, with its waves, tides (q.v.), and currents (q.v.). In relation to the solid earth, or lithosphere, the science deals with its distribution in continents and islands; its horizontal contours, or coast-lines, and its vertical contours, or relief, in plains, plateaux, hills, mountains, and valleys; the agencies that have effected this earth-sculpture, such as frost (q.v.), rain (q.v.), underground waters, rivers (q.v.), glaciers (q.v.), and ocean-waves, the epigene or surface agencies, as they are termed; and those more obscure, because hyjjogene or subterranean, agencies, including the earthquake (q.v.) and the volcano (q.v.) and also probably other less violent agents which result in the tilting, folding, and crumbling of originally horizontally stratified rocks in the processes of mountain-building. Finally, Physical Geography is concerned with chorography or the distribution (q.v.) of vegetables and animals as affected by such natural causes as soil, temperature, light, moisture, altitude, proximity to the sea, and climate generally, together with their involuntary or instinctive migrations. One of the most interesting generalisations in this department of the science is that the successive altitudinal zones of vegetation on a snow-clad mountain near the equator from the sea-level to its summit present much similarity to the latitudinal zones met with at or near sea-level in going from the equator to the poles. The distribution of the various races of man, the subject of ethnoyraphy, and the physical causes which limit the dispersal and affect the concentration of the human species under the operation of its own freewill, form the transition from Physical to Political Geography. Whilst the intense cold and long winters of the north allow only of the scanty vegetation that furnishes pasture for the reindeer of a small nomadic population, the enervating heat of the luxuriant tropical regions proves equally fatal to human energy. The oldest civilisations of which we have any record arose in the warmer temperate zone, and were in some cases, as in those of Assyria, Babylon, and Egypt, promoted by the fertilising effects of periodical inundations of rivers, whose waters were available for irrigation. Later empires, such as much of that of Rome, Britain, Germany, and the United States, have originated in colder regions, where, forests have had to be cleared and fens to be drained. Natural facilities, such as good harbourage, a tidal or other navigable river, the confluence of two rivers, the possibility of bridging a river, the convergence of mountain passes, an oasis in a desert, a good supply of spring water, or the proximity of mineral wealth, such as coal and iron, have determined originally the position of most large towns. Even their expansion in modern times may be similarly influenced, as in the cases of the suburban villages on the patches of water-bearing gravel round London, which are only now being connected by buildings over the intervening waterless clay districts, and of the often-flooded meadows of the Lea that so obstruct the spread of the metropolis eastward.