266 COAST AND GEODETIC SURVEY CENTENNIAL 



Dr. Charles Lane Poor, Professor of Celestial Mechanics, Co- 

 lumbia University: Oceanic tides, with special reference to the work of 

 the United States Coast and Geodetic Survey. The mathematical theory 

 of the tides first assumes a solid Earth surrounded by a shallow, fric- 

 tionless ocean, in which the moon would cause waves to travel around 

 the earth from east to west. While this is apparently a simple problem, 

 conditions which actually exist, with the ocean varying in depth and 

 broken up by continents, present a most complex one. Yet scientists 

 for years considered the tides as an ideally simple wave, modified and 

 broken up by the continental barriers and the varying depths of the 

 ocean. Tins world wave theory, based on a study of European tides, 

 which are exceptionally simple, became the basis of all tidal work and 

 theories. Later the tides of the Pacific were studied; and although 

 they differed greatly from those of Europe, the discrepancy was ex- 

 plained away as a modification of the theory, due to some local condition. 



The Coast and Geodetic Survey has for a century collected and dis- 

 cussed an enormous amount of tidal data in the Pacific and Atlantic- 

 Oceans. These data revealed so many departures of the observed tides 

 from those predicated upon the world wave theory, that the accepted 

 general tidal wave would have to be so radically modified, in order to 

 represent the observed phenomena, as to lose all semblance to a single 

 uniform progressive wave. Gradually a feeling was evolved that the 

 tides were not a world phenomenon, but were strictly local in character; 

 that the tides of the Atlantic were due to oscillations in the waters of 

 the Atlantic, independent of what might be happening in the Pacific. 

 This idea has been developed by the Coast and Geodetic Survey into 

 a thoroughly consistent theory, and stands out as the great scientific 

 contribution of the survey to the theories of oceanic tides. 



Dr. Douglas Wilson Johnson, Associate Professor of Physiography, 

 Columbia University: The contribution of the United States Coast and 

 Geodetic Survey to physical geography. Every division of physical 

 geography has been enriched by the contributions of the Coast and 

 Geodetic Survey during the century of its existence. We are indebted 

 to this Bureau for notable additions to our knowledge of the size and 

 form of the Earth and associated phenomena as developed in its work 

 in latitude, variation of latitude, longitude, azimuth, triangulation, 

 gravity, and terrestrial magnetism. To the physical hydrography of 

 the ocean it has supplied data for detailed study of material and relief 

 of the bottom. Its studies of the Gulf Stream and other currentsPhave 

 produced notable results. The Survey's treatment of the subject of 

 the tides and tidal currents has been exhaustive, culminating in a monu- 

 mental expansion of the equilibrium theory of tides. Its charts record 

 the changes in coastal topography and exemplify the laws which govern 

 the action of wave and current. To the physical geography of the 

 atmosphere this organization has contributed a study of the winds and 

 related phenomena. 



