ASTRONOMICAL ASPECTS. The study of physi ography deals essentially with the earth—its spherical form, its envelopes of air and water, its cold crust and heated interior, and their in fluence on life. Yet no thorough appreciation of these conditons and influences is possible without a knowledge of the astronomical relations of the earth. The earth as a sphere, and as a member of the solar system in which it so moves as to give day and night and the seasons, are facts of fundamental importance to an under standing of changes in the earth; and the splwri cal form of the earth, and the presence of In-at among the members of the solar system. furnish adequate reason for a consideration of the hy potheses for the origin of the earth. This does not mean that the subject encromclies on astron omy: it is dealing with the' earth, but it, inquires of astronomy the reasons for terrestrial phenom ena of vital importance, and applies these to an interpretation of the phenomena in their relation to life.
'1'ItE AIR. The' influence of the air on life is universal. Its oxygen and carbon dioxide; the influence of its pressure; the effects of its density. for example. on the flight of birds; its water va por; its winds and their effects—these ae among the many reasons why a study of the air properly forms a part of physiography. The science of meteorology furnishes the explanations. and with these the physiographer needs to be familiar. In order that he may understand the distribution of life he should know why thene is vapor. why winds blow as they do, why there are rainy and desert regions. and why there are storms. The branch of physiography that deals especially with this phase of the subject is climatology. If the (climatologist studies only the causes of cli mate lie becomes a meteorologist ; but if his es pecial concern is the understanding of the laws of eflinate with reference to their influence on life, he is a physiographer. The study of the air has a bearing on other phases of physiography. Waves and ocean currents depend on air conditions. and to understand them calls for a knowledge of air movements. Rain, river floods. the difference be tween the timoonraphy of arid and moist lands, and the existence of glaciers. are among the tea
tures of the land that depend upon a knowledge of the air r their proper appreeiation. Each of these reacts on life. Thus, along several lines, It is evident that there is a phase of air study, for an appreciation I the seienee of i.tetwology, it is true, but with its main object the inle-f igation of the influence of the air on the environment of plant, animal, and human life.
oeF.AN. The temperature and movements of the wean. dependent upon sun's heat and air moocimlit-; the dependent on the attrac tion it the sun and moon; the composition of the ocean water, it, depth. and the characteristics of the ocean bottom are among the important physiographie of the ocean. Each of these has an influence on life. The ocean supplies vapor to the air; its vast expan-e and it, cur influence the temperature of the air and aid in those movements of the air by which the . . tem itur • rainfall of the lands are profoundly affected. Life in the ocean a, influenced by its environment: the effect of ocean influence on the life of the lank: the ocean as a barrier to the spread of life; and it- inmortanee to man in com merce 310 many other ways arc among the sub ject- with which a physiographie study of the ocean is concerned. The (weans and the lands are profoundly interrelated. The waste of the land is carried to the sea by r:t.n and rivers: and the rweanie agentsare attackivg the land its bor der, forming many varied coast features. 'Changes in level of the crust lower parts of the land be instill the sea. and raise ,ea bottoms to form dry hind. .No study of the muds can promise the he'st result- withont a knowledge and apprecia tion if the condition- of the coast line and sea bottom. From this it is evident that the physio graphic study of the ocean is broadly interrelated with the study of the lam l and air. The science of the study of the ocean is called oceanography; and. as in the ease of meteorology. while the physiographer must understand the principles, his concern is far less with the seienee of ocean ography than with the application of its princi ples to all understanding of their influence on life.