1914] Sumner, et al.: Physical Conditions in San Francisco Bay 49 
latter from the water. It is likely, therefore, that they are not very 
exact. We have, however, tested the thermometers used and corrected 
the figures accordingly. 
TABLE 11 
TEMPERATURE READINGS AT Two BEDS OF THE MORGAN OYSTER COMPANY, 
MARCH TO SEPTEMBER, 1913 
Millbrae Dumbarton 
Dates Fahr. Cent. Fahr. Cent. 
March 21 =. toe.0 alu lei 49.0 9.4 
April 4, 18 58.5 - 14.7 57.5 14.2 
May 2, 16 61.2 16.2 62.5 16.9 
June I} 15 ... 64.2 17.9 66.5 19.2 
July 15 ... 19.2 70.0 21.1 
August 15 = 17.8 68.0 20.0 
September 15) -----_- 66.0 18.9 67.0 19.4 
It is interesting to compare these figures with some given by Town- 
send (1893, p. 348) for ‘‘oyster beds, 1 mile from Dumbarton Point,’ 
during the summer and fall of 1891. The mean of Townsend’s figures 
for the period from July 12 to September 27 is 69°8 F, the extremes 
being 58° and 74°. For the same three months of the later year the 
mean of our figures for the Dumbarton beds is 68°3 F, the extremes 
recorded being 65° and 71°. 
The temperature relations between the air and the water in the 
neighborhood of San Francisco deserve some attention. In the absence 
of disturbing factors, the relations between air and water temperature 
on an island, or along the coast of a continent, are comparatively simple 
in our latitudes. The mean annual temperatures for the two are ap- 
proximately the same, though a considerably greater range is recorded 
for the air than for the water. In the summer the air temperature 
is higher than that of the water, in the winter the converse is the case, 
while at two points, in the spring and in the fall, the two curves cross 
one another. As an illustrative case, in which these conditions are 
realized, the reader is referred to the Bulletin of the Bureau of Fish- 
eries for 1911, chart 219. 
In San Francisco Bay these simple relations are disturbed by two 
special factors, which work in opposition to one another. 
(1) Considerable quantities of fresh water are continually dis- 
charged into the bay by the Sacramento and San Joaquin rivers. This 
water comes immediately from the Great Valley region of California, 
