864 
BULLETIN OF THE BUREAU OF FISHERIES 
The directions and velocities given on the chart (fig. 173) for the stations off 
Cape Cod and in the region of Nantucket Shoals are copied direct from the Coast 
Pilot (1912, chart to face p. 9; based on observations taken by the U. S. Coast 
and Geodetic Survey). A south-southeasterly drift of about 12 miles a day at a 
station 7 miles off Nauset Light illustrates the general tendency toward a south- 
erly movement of the water along Cape Cod, mentioned in the Coast Pilot. Obser- 
vations taken at the Pollock Rip lightship and at Round Shoal lightship, at the 
entrance to Nantucket Sound, from June 20 to September 14, 1911, have also brought 
out dominant drifts toward the southeast at rates, respectively, of 9 to 10 and 2 to 3 
miles per 24 hours. By this evidence, corroborated by bottle drifts (p. 886), the sur- 
face water sets southerly across and out of the eastern end of Nantucket Sound, not 
into the latter. This is corroborated by an east-southeasterly set of about 7 miles per 
24 hours, recorded at a station 4 miles within the sound (2 miles south of Handker- 
chief Shoal lightship). 
Sets of varying duration, taken by the Coast and Geodetic Survey at 11 stations 
in the general region of Nantucket Shoals, show a general dominant set between 
south and east, roughly paralleling the chief axis of the shoal ground, at rates 
varying from about 2 miles per day to about 14 miles (average about 3 miles). 
However, this is complicated by evidence of subsidiary eddying movements, such 
as might be expected over this uneven bottom, where strong tidal currents are 
complicated by rips and deeper channels. 
Earlier studies pointed to the conclusion that the tidal currents at a point about 
16 miles to the eastward of Nantucket light vessel are not only rotary but run at 
an equal velocity at all hours (Coast Pilot, 1912, p. 10); and it seems to have been 
taken generally for granted that there is no dominant set at the lightship, which is 
situated about 10 miles to the southward of the 40-meter contour of the shoals and 
42 miles SSE. from Nantucket Island (lat. 40° 37', long. 69° 37'), but that the 
currents there are purely tidal. This, however, is contradicted by 19 sets of current 
measurements, each of 29 days’ duration, taken at this lightship by the United States 
Coast and Geodetic Survey in the months of June, July, August, September, October, 
November, December, February, March, April, and May of the years 1911, 1912, and 
and 1914, tabulated below. 69 In 13 cases a dominant set results toward the north 
and west; a set toward the south and east in four; and one series showed no appreciable 
set in either direction, as tabulated. 
Dominant set at Nantucket lightship for various months 
Month and year 
Direction of domi- 
nant set 
Drift per 
24 hours 
Month and year 
Direction of domi- 
nant set 
Drift per 
24 hours 
June, 1914 
N. 46° W 
2.2 
September-October, 1913. 
N. 89° W. 
5.3 
June-July,1914___ 
N. 55° W 
2.2 
Do. 
N. 80° W 
8.2 
June-July, 1911 
N. 5° E 
1. 1 
N. 86° W. 
5.3 
July, 1914. 
N. 53° W 
2.7 
November, 1913 
S. 68° E 
2.4 
July, 1911 — 
N. 25° W. 
1. 9 
December, 1913 
S. 44° E 
4.0 
August, 1914 
N. 45° W. 
4.8 
S. 51° E 
2.9 
August, 1911 
N. 53° W 
3.8 
S. 40° E___, 
1.0 
August-September, 1911 
N. 45° W 
2.4 
April, 1914 
N. 75° W 
1.4 
September, 1914 
N. 74° W 
7.4 
May, 1914 
N. 62° W 
4.3 
18 Data supplied by the U. S. Coast aud Geodetic Survey. 
