The Mighty Deep 



great height. Probably in central regions of the 

 Pacific it rises only some three or four feet above 

 the usual sea-level. But when the flow enters 

 narrowing bays and channels, a very different 

 result is seen ; and the waters are often piled 

 up in a wonderful manner, — as in the Bristol 

 Channel, where the level at high tide is some- 

 times nearly forty feet above that at low tide. 



A marked contrast to this is seen in the 

 Mediterranean. There, as already said, practic- 

 ally no tides exist. The rise and fall amount 

 at most to only a few inches. Instead of a 

 wide entrance and a narrowing estuary, we have 

 just the opposite — a narrow entrance and a 

 widening sea beyond. Connection with the out- 

 side ocean is too restricted to admit of any full 

 flow of the tidal wave. 



Solar tides, or tides brought about by the sun's 

 attraction, are much the same in cause and effect 

 as lunar tides, only far smaller in degree. When 

 Sun and Moon happen to be on the same side of 

 the Earth, or on diff"erent sides but in the same 

 line, so that their combined pull is exerted in 

 one direction, we have Spring Tides. These 

 are always at the time of New Moon and Full 

 Moon. Sun and Moon then work together, each 

 helping the other in a common aim ; and the 



34 



