Since the physical forces upon which man is to rely act only upon matter, it becomes neces sary to consider the appearance of the mate rial world in and upon which they are to act. Of the earth's interior little is known, and even that little we may omit. Undoubtedly the inte rior is subject to the action of physical energy, and any radical changes in its condition might well be fatal to the existence of human society. Assuming its stability, however, we must re gard all speculations concerning its condition as beyond our present field of study. We need consider only the earth's surface, including everything that is so near the surface as to be within reach of the miner and the dredger, and also including the atmosphere. The physical forces act uniformly wherever they are to be found throughout the world; but those elements of the environment upon the examination of which we are now entering are variously arranged in different regions. It would be difficult to find any two spots on the earth in which the environments are identical ; and the primary differences are geographical.
The natural home of man is upon the land. The entire expanse of land area is a little more than one-fourth of the earth's surface, or about one-half as great as that of the sea, if we leave out of account the frozen oceans of the polar regions. Of this land area, three-fourths is in the northern half of the globe, and grouped into two great land masses, known as the Old World and the New. The Old World, consist ing of two distinct continents, of which Africa is one, and Europe and Asia the other, is more than twice as large as the New World of North and South America. Australia alone is entirely within the Southern Hemisphere. Asia is dis tinguished for her lofty plateaus, Europe for her mountains and indented coast-line, America for her plains and river The moun tains of the Old World stretch from east to west ; those of the New World, from north to south. The direction of the mountain ranges influences the direction of river courses, the distribution of moisture, the temperature, the Guyot, The Earth and Man, Chapters VIII. and IX.
character of the soils and of the crops, the movements of population, and the growth of industry. It is, therefore, a consideration of great importance. Yet, on the whole, the posi tion of mountain ranges is of less importance in the economic environment than the relative elevation of plains and plateaus, and the width of river basins. Thus it often happens that feat ures of the landscape which to the naturalist or artist are most striking, are of less interest to the student of human welfare than others that are less obvious. Another simple illustration of the same truth may be cited here, although it anticipates features of the enviroment upon which we have not yet touched. Every text
book of physical geography dwells upon the difference between the trees of different regions. No traveller can avoid noticing such differences, and they really are of some economic signifi cance. But they are of far less importance than differences in the grasses. All the cereals, or grains, are cultivated grasses, and both the vegetable and animal food of man are conse quently determined in large part by their character.
Of almost equal importance with the ele ments already noticed are climate, soil, mineral and vegetable products, and facilities for com munication. A writer describes the provinces which border on the basin of the Mediterranean Sea as enjoying—in healthfulness and equa bility of climate, in fertility of soil, in variety of vegetable and mineral products, and in natural facilities for the transportation and distribu tion of exchangeable commodities — advantages which have not been possessed in any equal degree by any other territory of like extent in the Old World or the The Roman Em pire, which encircled the Mediterranean and extended its sway far into three continents, thus rested upon the finest physical basis ever possessed by any single political power. If, then, we analyze the terms in which this supe rior physical environment has been described, we shall be in possession of nearly all the re maining features of the environment that need statement.
By the climate is meant the character of 1 George P. Marsh, The Earth as Modified by Human Action, P. I.
the atmosphere as regards temperature and moisture. Climate is affected by altitude, dis tance from the equator, proximity to the sea, oceanic and atmospheric currents, the presence of great forests, and the situation with refer ence to mountain ranges, plateaus, and plains. The equatorial regions are hot and moist. Islands and lands bordering upon the sea have a more equable climate, milder in winter and cooler in summer, than lands of equal latitude situated far inland. Since land absorbs and gives off heat more rapidly than water, there is an unequal heating of the air which causes an alternation of land and sea breezes daily, and a similar movement on a larger scale in consequence of the changes of These larger currents are of great economic signifi cance. They raise or lower the temperature according as they come direct from the sea or from continental areas. They bring with them moisture or drought. They have been known to carry fine particles of soil, as dust, in sufficient quantities to alter materially the character of the soil upon which it is deposited.