190 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



locations of high water and of low water, at the middle and at the 

 ends of the combined tank. It is evident that a further combination 

 of different tanks into one irregular-shaped basin would support a 

 stationary wave motion in sections and that there might be three or 

 more nodal lines. The water would come to rest eventually unless 

 the movement were continued by the original external force which 

 put it in motion. We know that when the force is continued to be 

 applied with the rhythm of the period of movement of the stationary 

 wave in that particular basin, the water will continue to oscillate. 



TIDE-PRODUCING FORCES 



In nature, the external force is astronomic. Tides are caused by the 

 attractions of the sun and the moon. The tide-producing forces are 

 the result of the difference in effects of the attraction of these heavenly 

 bodies on the waters of the sea and on the solid earth. The tide-pro- 

 ducing forces vary directly as the mass and inversely as the cube of 

 the distances of the heavenly bodies from the earth. Although the 

 mass of the sun is many times that of the moon, the inverse effect of 

 the cube of the vast distance to the sun, as compared with the nearness 

 of the moon to the earth, reduces the effect of the sun's tide-producing 

 force to less than one-half that of the moon. 



It is evident, under Newton's law, that the gravitational pull of 

 the earth mass would overcome any vertical pull of the sun and 

 moon which would tend to lift the sea directly below; but owing 

 to the great mobility of water, it is equally obvious that horizontal 

 movement could be induced into a body of sea water by the pulling 

 force of these rotating bodies. It is the horizontal component of 

 the combined attractive forces of the sun and moon that sets in 

 motion the waters of the ocean basins and gives rise to tidal movement. 



Dr. Rollin A. Harris, a tidal scientist of the United States Coast 

 and Geodetic Survey, proposed the stationary-wave theory for the 

 tidal movement and delineated various ocean basins that should prop- 

 erly respond to the tide-producing forces to maintain oscillating sys- 

 tems. Dr. Harris developed his tidal theory mathematically in 1900. 

 A study of tide observations at numerous places along the seacoasts 

 of the world has proved the correctness of Dr. Harris's theory and, 

 in a general way, the correctness of the marginal limits he had 



described. 



OCEAN TIDAL BASINS 



In most cases there are geographic land boundaries or submerged 

 bottom features that determine the configuration of the various ocean 

 tidal basins. The natural period of oscillation depends upon the 

 shape of the basin and the mean depth of water. The period of 



