122 J. E. Hilgard—Tida!l Waves and Currents. 
ing still farther, the height somewhat declines in consequence 
of the changes of direction in the channel and its shallowness. 
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At Hell Gate this tide-wave is met by that which had entered 
at Sandy Hook, and had advanced more slowly owing to the 
narrowness and intricacies of the channel, especially in the East 
These two tides which meet and overlap each other at Hell 
Gate, differing from each other in times and heights, cause con- 
trasts of water elevations between the sound and harbor which 
call into existence the violent currents that traverse the Hast 
River. The conditions of the tidal circulation through Hell 
Gate are such that if there were a partition across it, the water 
would sometimes stand nearly five feet higher, and at other 
Sues gts feet lower, on one side than on the other. In the 
ase of the superposition or compounding of the two 
tides the d difference of level existing at any time, is, of pisses 
much less, but the difference of one foot is often ed 
within the space of 100 feet in the = sonra go of 
Hell Gate off Hallett’s Point. Referring, now, more particularly 
to the diagram representing New York bay - fartics (p. 125), 
it is important to pheerre that the entrance from Long Island 
Sound is : natural depression or arm of the sea which is not 
changed by the Sar ce now in operation. The tidal] currents 
