SUN, MOON, AND TIDES — COLBERT 191 



oscillation corresponds to the period of the principal tide-producing 

 force. When the moon is the predominant force, this period is 12 

 hours and 25 minutes sun time or exactly 12 lunar hours. 



There are two large basins in the Atlantic that respond to the 

 action of the moon to produce the tides in that ocean. The larger 

 of these extends across the North and South Atlantic Oceans with 

 the eastern coasts of North America at one end and the Antarctic 

 Ocean at the other end. The lateral limits in the open ocean may 

 only be approximated, but in other areas natural geophysical features 

 can be recognized. Such natural boundaries are the east coast of 

 North America, including the islands and reefs extending from the 

 Florida coast to the Windward Islands, the west coast of Africa 

 from Portuguese Guinea to Liberia and from Cape Fria to the Cape 

 of Good Hope. (See fig. 3.) 



We may consider that this basin is made up of three sections, 

 in order to follow the movement of the stationary wave. The oscil- 

 lation that has been set up by the astronomic force will cause the 

 water to rise to its highest level at the ends and at junctions of the 

 sections, and there would be no change in water level across the axis 

 or the nodal line of each section. 



At the present time there are no means for measuring the tide 

 in open ocean areas. Tides can be observed along the coasts and 

 on the off-lying islands of the continents that encompass this basin. 

 Referring to the eastern end of this Atlantic basin, the nodal line 

 of this section touches the Windward Islands of the eastern Caribbean. 

 At this location there should be little or no change in the tide. From 

 tidal observations along the shores of these islands, we find this 

 to be true. 



If we proceed northwest along the shores of the West Indies to 

 the coast of Georgia, we should find increased ranges in the tide. 

 Tidal observations confirm this. For the coast of Puerto Rico, the 

 rise and fall is 1 foot; for the Bahamas, 2 feet; and for the Georgia 

 coast, 6 feet. 



The period of oscillation of the water checks with the observed 

 times of high water and low water along the various coasts of the 

 continents of this main Atlantic basin. Twelve hours after the moon 

 passed over the meridian of Greenwich, the oscillation of the water 

 brought high water to the east coast of North America. Six lunar 

 hours later there was low water along this coast. 



The tides observed along other shores of the Atlantic Ocean are 

 caused by the movement of water in a smaller basin, which consists 

 of two sections with two nodal lines. Eight hours after the moon's 

 transit of Greenwich, high water will occur on the coasts of Iceland, 

 Greenland, and Labrador at one end of this basin and on the coast 

 of South America, between Natal in Brazil and Trinidad. 



