COASTAL CURRENTS^ ATLANTIC COAST 25 



Stream as located on the above-mentioned chart. Actually, the posi- 

 tion of the Gulf Stream shifts and it has been reported that its inner 

 limit is at times farther from shore and at other times nearer to shore 

 than is the lightship. The lightship is, therefore, sometimes within 

 the stream and sometimes outside its limits. The results of table 12, 

 which are based upon a long series of observations and may be assumed 

 to reflect conditions near the inner edge of the stream, show that at 

 Diamond Shoal Lightship the average direction of the nontidal cur- 

 rent for each month of the year falls within the northeast quadrant. 

 They also show a definite seasonal variation with large northeastward 

 velocities during the summer months, reaching a pronounced maximum 

 in July, and considerably smaller velocities setting more to the east- 

 ward during the autumn, winter, and sprmg months. 



The long series of current observations at Diamond Shoal Lightship 

 appeared to offer an opportunity to investigate a supposed fluctuation 

 of the Gulf Stream, depending upon the declination of the m_oon. In- 

 asmuch as the fluctuation had been described as an expansion of the 

 stream at high declination and a contraction at low declination, the 

 location of the station near the edge of the stream seemed well suited 

 for such an investigation. Reductions designed to develop the declina- 

 tional effect were made of values from 9 years of observations. The 

 results show that any monthly or semimonthly variation in the velocity 

 of the Gulf Stream at Diamond Shoal Lightship due to changing 

 declination of the moon is less than 0.1 knot. In addition, two other 

 reductions of the same series of observations were made, one referring 

 the current to the phases of the moon and the other, to its distance. 

 As in the case of the declinational reduction, the results of both were 

 negative. 



It, therefore, appears certain that at Diamond Shoal Lightship there 

 is no appreciable variation in the velocity of the Gulf Stream due to 

 the changing declination, phases, or distance of the moon. 



CURRENT CHARTS, GEORGES BANK AND VICINITY 



In the area eastward of Cape Cod and Nantucket Island, Mass., 

 comprising Georges Bank and the eastern approaches to Nantucket 

 Sound, series of current observations have been secured at a consider- 

 able number of locations. As the currents in this region have large 

 velocities and vary in rotational characteristics from place to place, 

 current charts showing the details of the observed movement at the 

 various stations and in the area as a whole were considered desirable. 

 The charts, figures 23 to 35, depict the rotary current movement over 

 Georges Bank in its relation to the rotary and reversing movements in 

 Nantucket Sound and its eastern approaches. 



The observed directions and average velocities of the tidal current 

 at selected locations for each hour, from to 12 hours after the Green- 

 wich transit of the moon, are represented. The observations used in 

 preparing the charts were secured at various times by Coast and 

 Geodetic Survey parties and by the crews of lightships. They were all 

 taken within 14 feet of the surface. The locations at which the obser- 

 vations were taken are marked by small circles. The observed direc- 

 tions of flow for the designated hour of the tidal cycle are represented 

 by arrows drawn through the circles. The mean velocities for the 

 designated hour are shown to the nearest tenth of a knot by numerals 



