82 PROCEEDINGS OF THE CALIFORNIA 
navies of all countries are engaged in determining and mapping the topography 
of the water basins and channels of the earth. 
An accurate survey of waters adjacent to land is based upon a survey of the 
adjoining lands, by means of which the figure of the coast and the positions 
of a sufficient number of conspicuous and well-defined objects near the coast 
have been ascertained. These objects are the landmarks, by observations of 
which the positions of points on the surface of the water (and hence the 
soundings) are determined. The relative positions of the landmarks are 
ascertained with a degree of accuracy proportionate to the character and 
extent of information to be given by the chart. When perfect accuracy is 
aimed at; many stations on shore (and especially on island shoals and reefs) 
are first determined usually by a trigonometrical survey whose accuracy is 
tested by a base of verification. The stations in the triangulation being 
selected with reference to the ultimate ends in view (viz., the wants of the 
hydrographer and navigator), will be so chosen as to include or determine 
light-houses, headlands, and other remarkable objects—not allowing the 
triangles, however, to depart too much from the well conditioned forms. In 
making choice of stations, and thus giving shapes to the triangles, it is well 
to remember, that where all the angles are to be observed, the condition most 
favorable to the accuracy of computation—i. e., where instrumental errors 
and errors of observation will least affect the determination—is where each 
triangle is equilateral. But where, two angles only are to be observed, the 
unobserved angle should be a right angle, and the observed angles equal to 
each other and never less than twenty-five or thirty degrees. Experience 
proves that, in well conditioned triangles, the small errors made in* the 
measurement of the angles do not accumulate through each successive step 
in the operation, but on the whole tend to compensate each other. 
Whatever extent of coast may be surveyed, each series of hydrographic 
operations will be confined to comparatively limited spaces, and the whole 
will consist of numerous detailed charts correctly linked together and har- 
monized by means of the triangulation on shore; a description, therefore, of 
the modus operandi in making a hydrographic survey of a single harbor or 
short sea reach will apply equally to the system adopted in the survey of an 
extensive line of coast. 
Having made a reconnaissance of the region to be surveyed, and gathered 
a general idea of the facilities for, as well as the difficulties of doing the work, 
the next step is to locate tide gauges and tide observers. 
Judging from all information that can be gathered of the prevailing winds, 
currents, tides, shoals, and the configuration of the shore line, the hydrogra- 
pher will fix the number and sites of his tide gauges so as to get data for de- 
termining the figure of the surface of the water at any given instant. They 
should be more numerous the more the surface of the water at any instant 
deviates from the horizontal form. And the fewer the gauges used the greater 
the care to be exercised in deciding upon their locations. Placing a gauge 
within a bar, sand-bank or other impediment to the free action of the water, 
or within a lagoon which winds fill with water faster than it can escape, is to 
be especially guarded against. And in comparatively limited basins of water 
