CHAPTER XLIV. 



TEMPERATURE, WINDS, WAVES, TIDES AND CURRENTS. 



THE forces active in early geological phenomena, had their 

 origin for the most part in the earth itself. But as the outer 

 portions cooled the initial heat became less effective, and the heat 

 of the sun, causing most of the phenomena of climate, became 

 an efficient geological agent, especially during the later stages of 

 the earth's history. 



The earth revolves around the sun and rotates on its axis. If 

 the axis was perpendicular to the plane of revolution there would 

 be no change in the distribution of heat over the surface of the 

 earth during the year; there would be no zones; no changes of 

 seasons. But the axis is declined from a perpendicular to the 

 plane of revolution about 23 1-2, and to this fact we owe the 

 zones, the long cold winters in the polar regions, the winter and 

 summer of the temperate zones, and the wet season and dry sea>- 

 son of the tropics. 



The crust of the earth is very uneven. The depressions filled 

 with water we call the sea; those portions above the sea we call 

 the land. The sea is divided into oceans and the land is divided 

 into continents, and these into grand divisions. 



Water is not a good absorber nor a good radiator of heat, 

 hence does not gain heat rapidly during the day or the summer, 

 and does not lose heat rapidly during the night or the winter, 

 maintaining quite a uniform temperature during the year. The 

 rough, dense land is a much better absorber and radiator than 

 the water, so that it gets much hotter during the day and sum- 

 mer, and much colder during the night and winter than the water. 

 The water, with its uniform temperature, tends to equalize the 

 varying temperatures of the land, so that climates along the sea- 

 shore are markedly different from inland climates. For this rea- 



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