222 



ON TIDES AND TIDAL ACTION IN HARBOES. 



nine feet of water, where the iigure 3 indicates the present depth. The 

 vessels were placed checker-wise, in such a manner as to impede naviga- 

 tion, while interfering least with the discharge of the water. The effect, 

 nevertheless, was the formation of a shoal in a short time, and the 

 scouring out of two channels, one on each side of the obstructions, 

 through which twelve and fourteen feet can now be carried at low water. 

 The increased water-way thus given to the ebb-tide caused it to aban- 

 don the old nine-foot channel on the less direct course to deep water. 

 We have here the total obstruction of a channel which was of consider- 

 able importance to the southward trade by new conditions introduced 

 at a point four miles distant from where the effect was produced, and 

 we are warned how carefully all the conditions of the hydraulic system 

 of a harbor must be investigated before undertaking to make any 

 change in its natural conditions, lest totally unlooked-for results be pro- 

 duced at points not taken into consideration. 



NEW YORK HARBOR. 



Ai)proaching now more closely to the consideration of the tidal con- 

 ditions in New York Harbor, we will examine the progress of the tide- 

 wave through Long Island Sound from the eastward to its meeting with 

 that entering New York Bay at Sandy Hook. 



TIMES AND HEIGHTS OF TIDES IN LONG ISD. SOUND AND NEV/ YORK HARBOR 



BLOCK I. 



We see from the annexed diagram that about seven and a half hours 

 after the transit of the moon high water has advanced just within Block 

 Island with an elevation of two i'eet, and at the same time has just 

 passed Sandy Hook with an elevation of four and a half feet. Travers- 



