26 University of California Publications in Zoology [ Vou. 14 
On the second of these occasions (station 5329), the mean flood 
current (first flood of day) was 1.09 knots per hour, the mean ebb 
current being 0.96 knot. Here, again, the ebb current was of lower 
average velocity, and for the same reason. The flood stream brought 
a rise of 5.6 feet, the ebb a fall of only 1.3 feet. 
It may be worth while here to refer to a series of tidal observations 
made in the strait connecting San Pablo Bay with the main body of 
San Francisco Bay (station 5330). Here, on July 21, 1913, the flood 
current had a mean velocity of 1.28 knots. The observations were not 
continued through the ebb period. 
The observations upon current velocity, during the present survey, 
were for the most part incidental to the study of other problems. 
Originally, they were made for the purpose of determining the stage 
of the tidal flow, in its relations to the temperature and salinity ob- 
servations and to the occurrence of plankton. The value of these 
figures is consequently somewhat limited. 
The current-meter readings were made only during the second, 
fourth, and fifth of the bimonthly periods, and a part of the sixth. 
They do not, therefore, cover the entire year. Again, our mode of 
procedure was not calculated to determine the mean rate of flow at 
the various stations. As stated above (p. 12), operations on any 
given date were commenced shortly after the turn of the tide, and 
the stations of each section of the bay were worked in a definite order. 
Thus stations at the beginning of the series would show an (appar- 
ently) lower current velocity than those which were reached later in 
the tidal eyele. As has already been stated, the meter was suspended 
from one of the gangways, at a distance of only four or five feet from 
the ship’s side, so that unless the vessel were exactly lined up with 
the current the rate of flow past the instrument must have been inter- 
fered with somewhat. 
Nevertheless, the following figures seem worth presenting, since 
they are based on 142 observations which were probably as accurate 
as the methods would permit. There are here included only the figures 
derived from the regular stations during the second, fourth, and fifth 
periods. 
The average of the readings for the ebb current was 1.68 knots 
(3.12 kilometers) per hour, the maximum figure (at station 5082) 
being 3.03 knots. The average of all the flood readings was 1.19 knots 
(2.21 kilometers), the maximum (at station 5112) being 2.90. 
