loo POPULAR SCIENCE MONTHLY. 



ing the very existence of man, favor or oppose his development. 

 IS^ations are under similar conditions. As only a man whose cor- 

 poral subsistence is assured can devote himself to research and the 

 cultivation of thought, so only a rich nation can produce a remark- 

 • able 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 crea- 

 tion 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 civiliza- 

 tion, 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 con- 

 fined 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 par- 

 ticular 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 



