196 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



first through the twelfth hour after the moon's transit of Greenwich. 

 The semidaily cycle is complete in 12 lunar hours. 



It will be noted that a cotidal line for the twelfth hour follows the 

 general trend of the coast of North America from Halifax in Nova 

 Scotia to Cape Canaveral in Florida and then turns off to the Bahamas. 



Figure 6. — Cotidal lines in the Atlantic Ocean. 



It shows that high water occurs at the same time at widely separated 

 places from north to south, but approximately at the same distance 

 off the coast. This cotidal line appears off the Delaware and Mary- 

 land coasts in figure 7, which shows the cotidal lines in Chesapeake and 

 Delaware Bays at intervals of lunar hours. 



