48 THE "ESTABLISHMENT" OF A PORT. 



the exciting body have had time to obey the full 

 amount of force imparted to them. The moon ap- 

 pears to move faster than the waters can follow her, 

 and begins to influence a new area of the ocean, while 

 the waters first acted on are still rising to her impulse. 

 Thus, instead of a quiet heaping up of waters under 

 the moon, we have a broad shallow tide-wave in mo- 

 tion, following the apparent course of the moon in the 

 heavens, but never flowing vertically under her. As 

 this tide-wave moves over the ocean, it successively 

 brings high-water to the coasts it meets in its pro- 

 gress. Its direction and its force are modified by the 

 obstacles in its way, such as the opposition of oceanic 

 currents, the irregularities of coast-line, and the shape 

 and bearing of the channels through which it flows. 

 The broader and deeper the channel, the greater is the 

 speed of the tide-wave ; thus it traverses thousands of 

 miles of open ocean in the same space of time as it 

 takes to flow through a narrow and shallow channel of 

 trifling length. 



In every seaport it is high water at a certain fixed 

 hour on the days of new and full moon, and this hour, 

 which must be ascertained by careful observation, is 

 called the " Establishment " of the Port. To find the 

 time of any other tide in the same port, it is only ne- 

 cessary to add the establishment to the time of the 

 moon's passage over the meridian on any particular 

 day. By connecting, on a map of the world, such 

 points as have the same " establishment," lines may be 

 drawn which represent the summit of a great tide-wave 

 at a particular hour. Another set of lines may, in like 



