22 G ON TIDES AND TIDAL ACTION IN HARBORS. 



current, usually called the ebb-stream, since it falls in with the ebb- 

 stream of New York Harbor, taking place when the sound-tide is 

 highest, starts from a level ot three and a half feet higher than the 

 easterly, and thus a much larger amount of water flows out through 

 the Sandy Hook channels than through the narrows at Throg's i!^eck. 

 It is apparent, then, that this portion of the ebb-stream, re-enforcing as 

 it does the ebb-stream of the harbor proper at the most favorable 

 times, performs a most important part in maintaining the channels 

 through the Sandy Hook bar. It may be estimated that the closing of 

 Hell Gate would cause the loss of certainly not less than three feet iu 

 the depth of those channels. 



From what has been said with regard to the meeting of the tides in 

 Hell Gate, it will be seen that the violent currents experienced in that 

 locality are due to causes beyond our control. The dangers to naviga- 

 tion arising from these currents, however, by their setting vessels upon 

 the rocks and reefs, may, in a great measure, be done away with by the 

 removal of the obstructions, in which work considerable progress has 

 already been made. The removal of the reef at Hallett's Point, the 

 work upon which is now iu ijrogress, will doubtless, in a great degree, 

 do away with the eddies and under-currents produced by the sharp turn 

 which the channel now takes at that point. It is not improbable that 

 the successful removal of those obstructions will yet cause the sound 

 entrance to be used iu preference to the other by the fleets idying 

 between European ports and the great commercial metropolis of America. 



Note. — The reader who wishes to enter upon the mathematical treatment of the subject 

 of tides is referred to Aii'y's treatise on tides and waves, and to the memoirs of Whewell 

 and Lubbock, in the Philosophical Transactions of the Royal Society ; and for investij^a- 

 tions of the laws of the tides on our own coasts, to the papers on that subject by Bache 

 and others in the annual reports of the Coast Survey. Among the latter, the lecturer is 

 particularly iudebtel to the "Report on the tides and currents of Hell Gate," by Henry 

 Mitchell, 1867, in which the complicated problem of the tidal circulation of New York Har- 

 bor is treated with great ability and success. 



