ing the very existence of man, favor or oppose his development. Nations are under similar conditions. As only a man whose corporal subsistence is assured can devote himself to research and the cultivation of thought, so only a rich nation can produce a remarkable literary or artistic movement. Civilization is the fruit of the leisure which material prosperity gives, and can not exist long of itself any more than a fire can continue to burn without being replenished. As a whole, the existence and development of man are subject to three series of conditions: for living, the realization of a certain minimum of indispensable natural requisites; for the creation of a particular civilization, a certain material abundance, which can be obtained only by utilizing the resources of the planet; and for the transformation of this local civilization into a general civilization, facilities for outside contact and mutual exchange.
The second term of this series is the earth, which is far from homogeneous in its different parts. Its surface is constituted of three elements of very different properties: a solid element, the land which incrusts the planetary spheroid; a fluid element, water, which occupies the cavities and depressions of the solid crust; and a gaseous element, the air, which envelops the land and the water. These elements, besides differing from one another, vary in their own qualities. Water is fresh or salt, stagnant or running; here spread out in wide, open oceans, there in interior basins or even confined in close ones; the air is warm or cold, moist or dry; and the solid crust is constituted of soils of different origin, composition, and aspect; level, moderately undulating, or bristling with mountains; formed of movable particles or of compact, hard masses.
The diversified shapes assumed by the constituent elements of our planet determine an infinite variety of aspects and resources. While the laws of human development remain the same everywhere, necessarily very unequal values attach to different regions in their relations to man. In fact, some parts of the earth are not at all adapted to human existence; others favor the development of a particular civilization; while other still more favored countries possess also the facilities for external communication indispensable for the growth of a brilliant civilization.
It is clearly evident that the earth does not furnish in all its parts even the minimum of. comforts necessary to human existence. Man can not live on the ocean except artificially and temporarily, and is consequently confined to the land. This is not adapted to the maintenance of man everywhere alike. In many places it only sparingly furnishes the food necessary to his life. In one place, as on the tops of high mountains, the air is too rarefied; at another, it is too cold or too arid, while in other places it is perniciously hot and
