The Hydrosphere 



be seen that although the attraction of the Sun upon 

 the Earth is enormously greater than 

 that of the Moon, the tide-raising 

 power of the latter is more effective 

 than that of the former in the pro- 

 portion of ii to 5, owing to its 

 greater proximity. 



At new and full Moon the Sun 

 and Moon are acting together, and 

 tend to produce high water at the 

 same places, and the Solar tide is 

 therefore added to the Lunar tide, 

 with the result that the waters rise 

 higher than at other times, and 

 what are known as " spring-tides" 

 are produced. 



At first and third quarter, how- 

 ever, the Solar tide is, so to speak, 

 subtracted from the Lunar tide, 

 and at such times there is little 

 rise and fall of the water, and thus 

 " neap-tides " result. 



The tidal wave in the open 

 ocean is only some 6 feet in height, 

 but as it approaches a coast -line 

 and enters narrow inlets and channels, 

 the friction of the water against the 

 sides and bottoms of these channels 

 retards the forward motion of the wave, 

 and thus the waters tend to be heaped 

 up, and in such places there is, there- 

 fore, a much greater rise and fall than in the open sea. 



55 



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