PHYSICAL OCEANOGEAPHY OF THE GULF OF MAINE 863 



and September (similarly representative of that season) is a very slow set toward 

 the southwest at less than 1 mile per day. If all the sets for all the months be 

 combined, the resultant drift is toward the south by west Yi west (S. 18° W.) and 

 its average daily rate about ZYi miles per day. 



The underlying dominant drift at Portland lightship is thus shown to be south- 

 erly, so far as the general transference of water is concerned, and it is so shown on 

 the chart. Westerly winds may give it an offshore (easterly) component; and per- 

 sistent southwesterly winds, such as prevail in summer, may reverse the drift, driv- 

 ing the surface water to the northward and eastward. Such reversals, however, are 

 only temporary, and while operative produce drifts much slower than the dominant 

 southerly movement. It is only while the nontidal current is setting toward the 

 southern half of the compass that it has velocities of 4 miles per day or greater. 



No measurements have been made of the currents between Portland Ughtship 

 and Cape Ann, but observations taken by the United States Coast Survey at a point 

 10 miles southward from Cape Ann, on September 27 and 28, 1877 (U. S. Coast 

 Pilot, 1911, p. 151), showed a dominant set of about 3 miles per day toward the 

 WNW. (N. 66° W.) for that particular 24 hours. Fourteen miles to the south- 

 eastward of this we found a domtuant set of about 5.4 miles per day toward the SSE. 

 (S. 26° E.) at a depth of 5 meters (with the Ekman meter) on March 1 and 2, 1920 

 (station 20051, p. 857). These drifts, approximately at right angles to each other, 

 probably represent the dominant tendency at then- respective locations more closely 

 than might have been expected of one-day sets, because drift-bottle experiments also 

 indicate a tendency inshore and into Massachusetts Bay from the inner of these two 

 stations (Coast Guard station), southerly across the mouth of the bay from the 

 outer (p. 890). 



At Boston lightship (situated near the head of Massachusetts Bay, about 9 

 miles off the mouth of Boston Harbor) there is a very slow dominant drift toward 

 the eastward, a 29-day series of observations (from September 24 to October 22, 

 1913) giving a resultant of about 2.6 miles per 24 hours toward the S. 6° E., while a 

 second 58-day set (October 28 to December 19, 1913) showed a dominant drift of about 

 1 mile per day toward the N. 24° E.'^* These two combined point to a general 

 dominant movement of the surface stratum toward the SSE. (S. 25° E.) at the rate 

 of slightly less than 1 mile per day, and it is so shown on the chart (fig. 173). A 

 dominant set outward from the head of the bay toward its mouth is thus indicated 

 in its southern side, but one governed so much by the direction of the wind that the 

 surface water may make but a short distance good in this general direction over a 

 considerable period. 



The dominant drift at a station in the channel, between the tip of Cape Cod and 

 Stellwagen Bank, where the tidal currents were measured by the Coast Survey on 

 August 24 and 25, 1877 (Coast Pilot, 1911, p. 151; lat. 42° 07', long. 70° 15'), was 

 toward the N. 53° E. at a rate of about 4 miles per day, with about 5 mUes per day 

 (2.5 miles for 12 tidal hours) toward the N. 36° E. on the southern side of Stellwagen 

 Bank, a fev/ mUes to the northward, on September 17, 1855 (Coast Pilot, 1911, p. 

 151; lat. 42° 10', long. 70° 16'). 



5s Information supplied by U. S. Coast and Geodetic Survey. 



