REPORT OF COMMISSIONER OF FISH AISD FISIIERIES. 117 



tho eastern portiou, or perhaps ti better reference wonld be to the open sea either at 

 Block IsLind or Saudy Hook, whei-e the amplitude of the tide is 1.5 feet and 2.3 feet, 

 respectively. 



Having indicated briefly the tides of the Sound, we will now consider the other and 

 tar more imiiortant component in tho circulation, viz, the horizontal movement of 

 the water, or the tidal current. 



Beginning at the eastern cross section at the month of the Connecticut River, the 

 station located near t lie axial line of the Sound gave for the mean velocity of the maxi- 

 nnim flood vertical curve of velocities 3.2 feet per second, and for tho mean velocity 

 of the maximum ebb vertical curve of velocities 2.8 feet per second. 



The current station located similarly on the western cross-section at Matiuicock 

 Point, Long Island, gave for the mean velocity of the maximum flood vertical cui'vo 

 of velocities 0.86 of a foot per second, and /or the mean velocity of the maxinuim ebb 

 vertical curve of velocities 0.77 of a foot per second. 



The striking contrast in the ditference in the strength of the flood or ebb currents 

 of the eastern and western ends of the Sound indicated by the tigures given above 

 shows clearly what was to be expected from the tidal data, namely, that as we 

 approached the meeting-point of the two waves from opposite directions the hori- 

 zontal motion of the water should decrease. The series of current stations, located 

 at intervals of about 10 miles on the axial line of the Sound, when considered in con- 

 nection with the two mentioned above, illustrate very well this decrease and furnish 

 a knowledge of the horizontal movement throughout the Sound. Taking any sta- 

 tion in the series, its flood and ebb velocities will be greater or less than those given 

 above for the stations on the eastern or western cross-sections in almost direct pro- 

 portion to its distance from those cross-sections. 



By comparing the maximum flood and el)b velocities for the central stations on 

 each of the cross-sections, we lind that the flood velocitj'is to the ebb velocity as 1.15 

 is to 1.0 for the eastern cross-section; and that for the western cross-section the flood 

 velocity is to the ebb velocity as 1.12 to 1.0. These indicate clearly a resultant move- 

 ment to the westward, for in the diagram of current velocities, which can not well 

 be reproduced here, the duration of flood and ebb stream are seen to be about equal. 

 The maximum in the former takes place at the VIII luna:- hour and the maximum in 

 the latter at the II lunar hour, and at these times the stream is a continuous maxi- 

 nuim stream throughout the Sound. 



This excess of westerly over the easterly flow was to have been expected, for iu 

 Prof. Mitchell's report, "The circulation of the sea through New York Harbor," 

 Appendix No. 13 of the Report of the Coast and Geodetic Survey for 1886, are given 

 the results of a series of gaugings of East River at Nineteenth street, and in round 

 numliers there is as a mean value 448,000,000 cubic feet more water transferred to the 

 southward on every ebb tide of New York Harbor than is brought northward by the 

 flood tide.* This surplus of water must come through the eastern entrance of the 

 Souiul, hence from tho open sea, where it must be pure; and although small in 

 quantity in comparison with the volume in the Sound, it is a constant force to crowd 

 out at the western end stagnant or polluted water. 



Another interesting phenomenon l>rouglit out by our observations, and one which 

 ])lays a prominent part iu the circulation of the Sound, is the '■ underrun." Beginning 

 at the eastern entrance, the change from ebb to flood current takes place by the 

 tlenser sea water of the outside forcing its way iu along the bed of the Sound while the 

 surface is still running ebb. The l)eginning of this "underrun " was found to be about 

 one and a half hours previous to the surface reversal of the stream. The neutral 

 l)lane between the two currents running in opposite directions would gradually rise 

 (the "underrun" or flood current increasing while the ebb current was decreasing), 

 reaching the surface tinally when the ebb current disai)peared altogether. The 



* It must be hero noticed that the flood tide of Long Island Sound corresponds in 

 direction to the ebb tide of New York Harbor and rice versa. 



