F. GEOGRAPHY. 253 



bor is shown from the fact that the whole movement of water 

 which flows into New York Harbor in the course of each 

 tide through the East River is sufficient of itself to raise the 

 water of the harbor by one and one-tenth feet. The turn 

 of the tide in the East River occurs two hours after the ebb 

 begins in the harbor, and during these two hours the flow is 

 toward the East River instead of from it. As the result of 

 some calculations, it is shown that the whole of the flow 

 through, the Narrows corresponds to five and three-tenth 

 feet in elevation of the surface of the harbor, and this is the 

 amount which would run through if the East River were to 

 be cut off*. An additional nine tenths of a foot, however, is 

 to be added as due to that which comes from the East River 

 itself, giving a total of six and two-tenth feet, representing 

 the flow through the Narrows and over the bar. If, there- 

 fore, the East River were cut off*, the corresponding decrease 

 in the flow of water and decrease in the scouring of the bar 

 would involve a reduction of the depth of w T ater upon the 

 bar of about three and a half feet. Therefore the loss of this 

 river, or any obstruction to its flow or reduction of its ca- 

 pacity, become injurious to the harbor. B.ept. U. S. Coast 

 Survey, 1871,94. 



THE DIFFERENCE OF LEVEL BETWEEN RARITAN BAY AND 



THE DELAWARE RIVER. 



A line of leveling, seventy-seven miles long, has recently 

 been extended by the Coast Survey from mean tide on Rar- 

 itan Bay to mean tide at Gloucester City, on the Delaware 

 River. Tides were observed at each station for the purpose 

 of determining the true level of mean tide, which reference 

 planes were fixed by means of permanent bench-marks es- 

 tablished in the vicinity. These two bench-marks were made 

 the termini of the line of levels. Every precaution, even to 

 the extent of an entire re-leveling in an opposite direction, 

 was taken for the purpose of avoiding all sources of error. 

 The result has shown that the mean tide at Gloucester City 

 is three feet five inches above the mean tide at Raritan Bay, 

 which latter may be supposed to be the same as that of the 

 ocean. In connection with this accurate leveling a series of 

 barometric observations was made for the determination of 

 the altitudes of neighboring geodetic stations, of which the 



