862 
BULLETIN OF THE BUREAU OF FISHERIES 
It is natural to think of the wind as partly responsible for these variations in 
the direction and velocity of the drift, and this is borne out by the following table 
giving the wind movements and directions at Portland, Me., for each month, and 
the resultants calculated therefrom by traverse tables. 56 
Month 
Wind movement, miles 
Resultant 
N. 
NE. 
E. 
SE. 
S. 
SW. 
W. 
NW. 
October, 1913 
2,471 
449 
597 
813 
667 
574 
264 
1, 247 
N. 2° W., 2,030. 
November, 1913 
933 
132 
425 
442 
915 
1,736 
664 
1,701 
S. 84° W., 2, 274. 
December, 1913 
1,848 
443 
235 
232 
208 
1,422 
942 
2, 255 
N. 50° W., 3,697. 
June, 1919 
362 
464 
836 
400 
1, 904 
584 
348 
875 
S. 3° E„ 1,290. 
July, 1919 
382 
186 
551 
411 
2, 094 
826 
1, 013 
624 
S. 28° W., 2.279. 
August, 1919_ _ 
382 
382 
623 
505 
1,455 
863 
535 
983 
S. 33° W„ 1, 247. 
September, 1919 
690 
575 
485 
462 
2, 088 
638 
504 
1,097 
S. 27° W„ 1,118. 
October, 1919 
695 
407 
449 
679 
1, 116 
870 
758 
1, 020 
S. 73° W., 1,073. 
When the directions and velocities of winds and currents are compared for the 
individual months it becomes clear that the drift is not purely a wind current, though 
considerably affected by the wind. With winds prevailing from anywhere between 
north and west, the drift has a southerly component, driven eastward and offshore 
by strong west winds (as in November, 1913), but setting toward the southwest, 
when the average wind direction is between north and west. It is when drifting 
southward (whether with an easterly or a westerly component) during periods when 
winds prevail between west and north that the surface set attains its greatest daily 
velocities of 9 to 11 miles per day. By common knowledge this applies also during 
northeast winds. During the one month (June, 1919) when south winds prevailed, 
the current ran, none the less, toward the southwest, though held back by the head 
wind to an average rate of only about 4 miles per day. The dominant drift was also 
very slow (0.5 to 2.4 miles per day) during the three months when southwesterly 
winds prevailed, setting against the wind (WSW.) for one month, but with the wind 
(between north and east) during the other three. 
According to this correlation between current and wind, the direction of the 
nontidal current at this station is between WSW. and SE. and reaches a considerable 
velocity when westerly or northerly winds prevail; but its inherent stength is so 
small that southerly winds greatly reduce its velocity, or may even reverse it and 
produce a slow surface drift toward the northeast. 
The wind table for Portland (p. 965) shows that the average direction of the wind 
there, from early autumn until April, is between northwest and a few degrees south 
of west. 57 Consequently we may assume that the dominant sets recorded at the 
lightship for the months of October, November, and December are representative 
for autumn, winter, and for the first two months of spring. These combined (by 
the traverse tables) give a resultant movement toward the south and west (S. 15° 
W.) at an average rate of about 8 miles per day. In spite of the prevalence of south- 
west winds in summer the resultant of the combined drifts for June, July, August, 
» s From data supplied by the United States Weather Bureau. The directions are those from which the wind blows, as in 
every-day parlance. 
w Calculated on a time-percentage basis. 
