1914} Sumner, et al.: Physical Conditions in San Francisco Bay 73 
These irregularities are perhaps related to the fact, already 
referred to, that the succeeding ebb and flood phases of the tide fre- 
quently do not agree with one another either in duration or in vertical 
range, and that the reversal of the current does not coincide with 
the commencing rise or fall of water level. We must likewise con- 
sider that the continued inflow, at the head of the bay, of water having 
23 l2m ipm 2 
Fig. R. Salinity of water samples taken at a point between Aleatraz 
Island and station H-4967, at hourly intervals, during one complete tidal cycle, 
on May 14, 1912. The continuous line is based on surface figures, the broken 
line on bottom ones. 
a much lower specific gravity than sea-water, probably results in pro- 
longing the duration of the ebb stream at the surface, as compared 
with that at the bottom. 
The results of the other series of observations, conducted through- 
out one tidal eyele, near the Golden Gate (station H—5329) are even 
more difficult to explain. While the salinity of the bottom water rose 
throughout the flood period, and began to decline at about the same 
time that the reversal of current was noted, that of the surface was 
subject to various irregularities, the highest point being reached about 
three hours after the commencement of the ebb stream. These facts 
suggest the occurrence of various cross-currents or eddies in the 
vicinity of the anchorage, a supposition for which we have other evi- 
dence. It is of significance to recall that during this last series of 
observations there was a (predicted) rise of 5.6 feet during the flood 
period, followed by a fall of only 1.3 feet during the ebb. 
In figure S we have compared our curve for annual salinity 
throughout the bay as a whole with that for the rainfall of the regions 
contributory to it. The latter curve is based not upon the average 
conditions for a long period, but upon the year covered by our hydro- 
graphic observations, together with the few months preceding the 
commencement of our work. The rainfall indicated for each month 
is the mean of that recorded by United States Weather Bureau 
