1914] Sumner, et al.: Physical Conditions in San Francisco Bay 11 
II. PROCEDURE FOLLOWED AND APPARATUS USED IN 
THE HYDROGRAPHIC WORK OF THE SURVEY 
The principal hydrographic observations here to be discussed ex- 
tended through a period of one year, viz., from February, 1912, to 
January, 1913. Six complete series of observations were made 
throughout the entire bay. It was intended that these series should 
be at intervals of two months, and this plan was adhered to, so far 
as possible. Circumstances disturbed the regular programme some- 
what, however, and the actual periods of observation were as follows: 
(1) February 13 to 27, 1912; (2) April 23 to May 6, 1912; (3) July 
22 to 31, 1912; (4) October 7 to 12, 1912; (5) November 25 to De- 
cember 5, 1912, and (6) January 13 to 28, 1913. 
During each of these six periods the various stations were visited 
twice, once during the flood and once during the ebb tide. Since 
there were twenty-three regular hydrographic stations, there would 
thus have been 276 sets of observations in the regular series, had there 
been no gaps in the latter. As a matter of fact, the number was 
somewhat less than this, owing to certain unavoidable omissions. 
In addition to the data derived from this principal series of 
stations, hydrographic observations were made at a considerable num- 
ber of other points in the bay, notably at the oyster beds, and lke- 
wise outside of the Golden Gate, at most of the dredging stations in 
those waters. Furthermore, a rather extensive supplementary set of 
observations was made in the bay during July, 1913. Six of the earlier 
stations were then visited at flood and ebb tide, and twelve new ones 
were added in regions where the regular stations were lacking. 
On two occasions, also, the ship was anchored at a single point 
throughout approximately a complete tidal cycle of twelve hours, the 
observations being made hourly. 
For the purposes of the field operations, the stations of the regular 
series were divided into three groups, according to locality. These 
corresponded to the ‘‘upper middle’’, and ‘‘lower’’ sections of the 
bay, referred to below (p. 23}. It will be seen that the station num- 
IED ACS 
; 
bers do not form a single consecutive series. This resulted from 
circumstances which it is hardly worth while to explain. The num- 
bers which appear on the charts and in the temperature and density 
tables of the present report are the ones given at the time of the 
first visits to the respective stations. The repetitions of these same 
