28 University of California Publications in Zoology [ Vou. 14 
Allowing for all of these circumstances, we may make an estimate 
(which has no claim to exactness), and say that the mean rate of 
water flow for all phases of the tide, over the entire bottom of San 
Francisco Bay, is between two-thirds and three-quarters of a knot 
per hour. As regards the surface and intermediate layers, the rate 
is doubtless somewhat higher than this, perhaps reaching a mean rate 
of one knot per hour. 
V. TEMPERATURE 
Tables 3 to 8 give the water temperatures recorded for each station 
of the regular series at each of the six bimonthly periods during which 
our observations were made. The instruments used all bore the Fahr- 
enheit scale, but the centigrade equivalents have likewise been included 
in the tables. 
The air temperatures, as already stated, were not recorded by the 
scientific staff, but they have been supplied from the ship’s log-book. 
It can hardly be doubted that the thermometers used for this purpose 
were at times considerably influenced by the heat from the furnaces, 
so that no great importance can be attributed to these figures. More- 
over, those air temperatures only have been included in the tables 
which were recorded at approximately the same time as the water 
temperatures. Thus the figures are for the daytime only. They do 
not fairly represent the mean condition for the twenty-four hours, 
but are considerably higher than this. For water temperatures, the 
diurnal variations are of course comparatively slight, and they may 
be left out of consideration in our discussions. 
The ‘‘surface’’ figure for a given station at a given period is the 
mean of the surface figure recorded during the flood-tide observations 
and that recorded during the ebb-tide observations. Similarly, the 
““bottom’’ figure is the mean of the ebb and flood figures for the 
bottom. 
The ‘‘flood’’ figure for each station is the mean of the surface and 
bottom figures for the flood tide, the ‘‘ebb’’ figure being the mean of 
the surface and bottom figures for the ebb tide. 
The mean figure for each station for a given period is the mean 
of the surface and bottom means for that station and period. The 
mean of the flood and ebb figures would commonly have given the 
same result, though exceptions would have occurred, owing to the 
occasional omission of a record at one or the other phase of the tide. 
