REPORT OF COMMISSIONER OF FISH AND: FISHERIES. 117 
the eastern portion, or perhaps a better reference would be to the open sea either at 
Block Island or Sandy Hook, where 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 
far more important component in vhe circulation, viz, the horizontal movement of 
the water, or the tidal current. 
Beginning at the eastern cross section at the mouth of the Connecticut River, the 
station located near the axial line of the Sound gave for the mean velocity of the maxi- 
mum flood vertical curve of velocities 3.2 feet per second, and for the 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 Matinicock 
Point, Long Island, gave for the mean velocity of the maximum flood vertical curve 
of velocities 0.86 of a foot per second, and for the mean velocity of the maximum ebb 
vertical curve of velocities 0.77 of a foot per second. 
The striking contrast in the difference in the strength of the flood or ebb currents 
of the eastern and western ends of the Sound indicated by the figures 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 ebb velocities for the central stations on 
each of the cross-sections, we find that the flood velocity is to the ebb velocity as 1.15 
isto 1.0 for the eastern cross-section; and that for the western cross-section the flood 
velocity is to the ebb velocity as 1.12to1.0. 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 lunar hour and the maximum in 
the latter at the II lunar hour, and at these times the stream is a continuous maxi- 
mum stream throughout the Sound. 
This excess of westerly over the easterly flow was to have been expected, for in 
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 
numbers 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 
fiood tide.* This surplus of water must come through the eastern entrance of the 
Sound, hence from the 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 brought out by our observations, and one which 
plays a prominent part in the circulation of the Sound, is the ‘‘underrun.” Beginning 
at the eastern entrance, the change from ebb to flood current takes place by the 
denser sea water of the outside forcing its way in along the bed of the Sound while the 
surface is stillrunning ebb. The beginning of this ‘‘underrun” was found to be about 
one and a half hours previous to the surface reversal of the stream. The neutral 
plane 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 finally when the ebb current disappeared altogether. The 
* It must be here noticed that the flood tide of Long Island Sound corresponds in 
direction to the ebb tide of New York Harbor and vice versa. 
