Many of the field operations of the survey being geodetic in their nature, a system of pn mary triangulation, together with the determi nation of geographic positions by means of as tronomic methods, must furnish the foundation upon which the whole rests. On the Atlantic Coast a chain of triangles, beginning at the east ern boundary of Maine, stretches to the Gulf, constituting an oblique arc, which, besides serving as a basis for the coast triangulation, adds much to our knowledge of the figure of the earth. An extensive system of triangles ex tends across the continent along the 39th paral lel of latitude, connecting the surveys of the two coasts and furnishing a basis for the sur veys of the 13 States through which it passes. It is also one of the longest arcs now available for the determination of the figure of the earth. Another triangulation system is being executed along the 98th meridian. Its extension south ward through Mexico has already begun and there is a prospect of its extension northward through the Bntish possessions. Other import ant chains extend along the 112th meridian, the Canadian border and the Pacific Coast. In con nection•with these principal systems, the trian gulation has been considerably expanded in the New England States, New York and several Western States, including California, where some exceptionally large figures were intro duced. The longest line so far observed is from Mount Helena to Mount Shasta, over 190 miles.
A tertiary triangulation for topographic •and hydrographic purposes has been completed along the entire Atlantic and Gulf coasts and over most 'of the Pacific Coast, including much of Alaska. Much progress has been made in the latter territory by methods which possess a suf ficient degree of accuracy for immediate use and are capable of rapid execution. The coast of the Hawaiian Islands, of Porto Rico and of the greater part of the Canal Zone and the Philippine Islands has also been topographically surveyed.
In the determination of astronomic posi tions the exact methods originally developed in the survey have been adhered to and per fected. The methods of using the zenith tele scope for latitude and the telegraph for longi tude have been constantly improved.
The topographical operations have been mostly restricted to a narrow margin, not often over three to five miles wide, along the coast and surrounding harbors, bays and rivers up to the head of tide water. In some cases it has been somewhat more extensive, notably in the survey of the District of Columbia, where the scale was 1-4800 and the contour interval only five feet.
The hydrographic operations have extended as far out from the coast as was necessary for the interests of navigation and have included all harbors, channels, bays, etc., as far as the
work has gone. Much work has been done in the investigation of submerged rocks by the wire drag. Deep-sea soundings have been made extensively, especially in and about the Gulf Stream. Much attention has been given to tides, and continuous series of tidal -records have been obtained at several important points.
The results of the operations of the survey in connection with the study of terrestrial mag netism can be found on its charts and in its other numerous publications on the subject. In addition to the determination of the magnetic elements at many widely distributed points, and their frequent redetermination for secular vari ation, special observations are also made at certain base stations, with the aid of self-regis tering instruments, for the purpose of obtaining the record of the numerous variations of the earth's magnetism continually taking place.
The study of the force of gravity as a part of the great geodetic problem has received at tention for 30 years and the survey has of late years developed methods and instruments which will lead to a great extension of the work at a less cost than by older processes, but without lowering the standard of accuracy.
A network of precise levels has been ex ecuted covering in a general way the United States, connecting the Atlantic Ocean, the Gulf of Mexico, the Great Lakes and the Pacific Ocean.
Throughout its history the survey has con stantly been called upon to determine boundary lines, both State and national, which have been in dispute.
The office of standard weights and meas ures, charged with the maintenance of the stand ards of length, weight and capacity, which was under the direction of the superintendent of the Coast and Geodetic Survey until 30 June 1901, is now an independent organization under the title of the °National Bureau of Standards.° The principal publications of the survey con sist, among other things, of several hundred different charts; tide tables for all the princi pal and many minor ports; 'Coast Pilots,' con taining minute sailing directions for all navi gable waters along our coast; and the 'Report of the Coast and Geodetic Survey,' which con tains, besides the reports of the superintendent and his assistants on the conduct of the work, a series of special reports upon various tech nical and scientific operations of the service. For details of the work of the bureau see CHART; COAST PILOTS; GEODESY; GRAVITY; HY