20 U. S. COAST AND GEODETIC SURVEY 



group, to winds of 16 to 24 miles per hour; the third group, to winds 

 of 25 to 35 miles per hour, and so on. Observations taken when the 

 wind was less than 5 miles per hour were generally not used. An 

 average wind velocity of 10 miles per hour was assumed for the first 

 group, 20 miles per hour for the second group, 30 miles for the third 

 group, and so on. The north and east component velocities were 

 averaged separately for each velocity group for each of the sixteen 

 directions. The current velocity and direction corresponding to the 

 average north and east component velocities for each wind velocity 

 group were obtained for each of the sixteen wind directions. 



The directions of wind and current used in the reductions were 

 generally magnetic directions, but the results were modified to apply 

 to true directions of both wind and current. 



The averages of current velocity and direction for each station, 

 modified to a true-direction basis, were arranged in tabular form 

 and further averages obtained of all the tabular current velocities 

 and directions for each of the 16 wind directions, and of the current 

 velocity for each wind velocity for all 16 wind directions. The several 

 wind velocities for which the corresponding currents had been deter- 

 mined were also averaged for each wind direction. From the final 

 averages of current and wind velocities thus obtained the velocity 

 ratio of current to wind for all wind velocities was derived for each 

 of the 16 wind directions, and the same ratio — current to wind — 

 was obtained for all 16 wind directions for each wind velocity. From 

 the final averages of direction the deviation of current direction from 

 wind direction was obtained for each of the 16 wind directions. 



Further treatment of results for the purpose of obtaining general 

 relations of current to wind for the entire coast will be mentioned 

 later in this text. 



PRESENTATION OF THE RESULTS 



LOCATIONS OF STATIONS 



The locations of the lightship stations at which currents were 

 observed are indicated by red circles accompanied by the names of 

 the stations on figures 8 to 12. Approximate values for the depth 

 of water at each current station and its distance from land are given 

 in table 1, page 26. 



EXPLANATION OF THE TABULAR DATA 



The tabular material comprises a number of different kinds of 

 current information which is given in various forms for the different 

 stations. The characteristics of the current movement, the length ■ 

 of the observational series, and the methods of reducing the observa- 

 tions were factors which determined the nature and form of the data 

 presented for a given station. However, uniformity of presentation 

 was aimed at and accomplished wherever feasible. Table 2 contains 

 the results derived from series of current observations at a number 

 of lightships by the process described under the heading "Nonhar- 

 monic reduction of reversing tidal currents." The name of the 

 lightship station and its latitude and longitude to the nearest tenth 

 of a minute are given in the first column of the table. In the second 

 and third columns the month and year in which the series of observa- 

 tions began and ended and the length of the series in days are given. 

 Next are given the time of slack before flood, the time, direction and 



