Physical Geography, that department of the science of geography which treats of the physical condition of the earth, describing its character and relations as a member of the solar system, explaining its great natural divisions of land and water, the atmosphere, and the great movements, as of oceanic and aerial currents, which variously affect and modify these features. The forms of continents and oceans and of their subdivisions, the heights and ranges of mountains, the phenomena of deserts and plains, and all the varying outlines from the highest mountain summits to the lowest depths of the sea, are among the first objects of its consideration. The geological structure of the earth and all meteorological phenomena belong to the broad field of its investigations; which also comprises the natural products of the earth, vegetable and animal. But comprehensive as is its range, it does not enter into individual descriptions of phenomena, localities, and species, but is concerned chiefly with general laws and principles, as they are manifested upon a grand scale, and in the organic kingdom with the existence of races and their distribution in certain zones or stations of habitation. The relations and adaptations of organic and inorganic nature to each other are specially treated in this science alone.

Its ultimate aim, as stated by Humboldt in his " Cosmos," the work which first gave to physical geography a special place among the sciences, "is to recognize unity in the vast diversity of phenomena, and by the exercise of thought and the combination of observations to discern the constancy of phenomena in the midst of apparent changes." - The first writers on physical geography were among the earliest geographers and writers on physical science, and have been referred to in the articles Earth and Geology. The broad views advanced by Thales, Pythagoras, Aristotle, Strabo, Pliny, and others of the ancient philosophers and geographers, entitle them to be regarded as the first cultivators of this science. In modern times its principles have been treated with great originality and ability by the Jesuit Jose de Acosta, in his Historia natural y moral de las Indias (Madrid, 1590). In 1650 was published the first edition of the work of Varenius, entitled Geographia Generalise in qua Affectiones Generales Telluris explicantur, which Humboldt says, " in the true sense of the words, is a physical description of the earth." A part of this is styled Geographia Comparativa, which is the term now generally applied to works on physical geography; and the leading subjects discussed are those of the most recent treatises.

The great advance made of late years in the auxiliary sciences furnished materials for more extended generalizations and a more complete delineation of comparative geography, which was treated in all its relations with the history of man by Karl Bitter in Die Erdkunde im Verhaltnisse zur Natur und zur Geschichte des Menschen (2d ed., 19 vols.,. Berlin, 1822-'59). The principles of the science are ably illustrated in the "Physical Atlas" of Alexander Keith Johnston, first published in 1848; and they are expounded, among others, in the writings of Sir John Herschel, Mrs. Somer-ville, Arnold Guyot, M. F. and A. Maury, Eeclus, and numerous other physicists. In this Cyclopaedia the topics more or less closely connected with physical geography are treated under their separate heads, as Clouds, Dew, Earthquake, Hail, Hurricane, Mountain, Tides, and Volcano, as well as under the more general heads of Climate, Earth, Geology, Meteorology, etc.