1914] Sumner, et al.: Physical Conditions in San Francisco Bay 83 
during approximately one complete tidal cycle, on July 18, 1913, gave 
a mean salinity of 31.07. For station 4967, the mean figure derived 
from the July samples of the preceding year was 31.53. 
It must here be remarked that both of the years in question were 
years of about equally deficient rainfall. For the year 1911-1912 
(July, 1911, to June, 1912), the mean precipitation at the three points 
considered on page 74. was 12.73 inches. For the year 1912-1913, 
the mean figure was 12.39 inches. 
Fortunately, we are able to insert, during the passage of this paper 
through the press, the results of some water analyses, based upon 
samples taken on March 5 and 6, 1914. Unlike the two preceding 
years, the season of 1913-1914 was one of exceptionally high rainfall. 
Up to the taking of these later samples (strictly speaking, from July 
1, 1913 to March 3, 1914), the mean precipitation, for the three points 
chosen as representing regions tributary to San Francisco Bay (p. 74), 
was 22.17 inches. That for the same period during the preceding 
year was 9.04, the ‘‘normal’’ being 13.78. 
The water samples, particularly the surface ones, show a strikingly 
low salinity for the later year, as compared with the same period in 
1912. For the surface waters, the later figures average only 36 per 
cent of the earlier ones, for the bottom waters they average 81 per cent 
of the earlier ones. The following table gives these figures by stations, 
permitting of a comparison between the water of the bay for March 5 
and 6, 1914, and that at corresponding phases of the tide from Febru- 
ary 13 to 27, 1912. 
TABLE 21a 
SALINITY OF WATER AT CERTAIN HypRoGRAPHIC STATIONS WHICH WERE REVISITED 
on MarcH 5 AND 6, 1914 
Station Reference 
No. Station Tide Surface Bottom 
1912 1914 1912 1914 
5351 4967 Ebb 29.53 12.81 31.01 29.04 
5357 4967 Flood 31.00 11.62 31.18 80.34 
5352 4970 Ebb 26.96 11.78 28.46 18.35 
5353 4974 UG UAT ae = 21.74 24.65 
5356 4975 exe TSO ae al 18.56 Dalit, 
5355 4978 Gs 14.19 4.02 21.47 13.42 
5354 4980 “S 19.02 7.65 21.28 11.04 
5362 5001 oe 28.38 12.27 28.33 23.17 
5361 5005 GG 27.79 11.85 27.75 20.32 
5360 5008 iad 27.37 12.32 28.84 30.07 
5363 5008 Flood 27.68 11.46 27.85 29.23 
Averages 23.94 8.71 26.04 21.22 
* Surface samples from these stations gave chlorine permillages so low that the salinities 
could not be obtained from Knudsen’s Hydrographic Tables. These samples have therefore 
been regarded as nearly pure river water. In computing the averages, their salinity has been 
considered as zero. 
