PHYSICAL OCEANOGRAPHY 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 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 lightship 
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 dominant 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 their 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. 58 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 miles per day 
(2.5 miles for 12 tidal hours) toward the N. 36° E. on the southern side of Stellwagen 
Bank, a few miles to the northward, on September 17, 1855 (Coast Pilot, 1911, p. 
151; lat. 42° 10', long. 70° 16'). 
“Information supplied by U. S. Coast and Geodetic Survey. 
