112 



POPULAR SCIENCE MONTHLY 



Guarding the Grand Canal 



moment of high water and most rapid down-stream at low water. 

 Hence the tidal current " flows " for a long time after high water has 

 passed and when the water-level is falling, and " ebhs " for a long 

 time after low water and when the water-level is rising. But rivers 

 gradually broaden and become deeper as they approach the coast, and 

 tidal currents in actual estuaries are, therefore, intermediate between 

 those of an open seacoast and those in a uniform canal. 



A String-town on a Chinese " Pike." 



