THE TIDES 



529 



Atlantic-Ocean Tides 



A body of water resembling the artificial one just described is the 

 portion of the Atlantic Ocean (shown by one form of shading) ex- 

 tending from South America to southern Greenland and resting against 

 the western coast of Africa and Europe. A section of this basin or 



BRAZIL 

 GUIANA 



Near 



CAPE VERDE IDS. 



Off 



MOROCCO 



\N.of 

 IRELAND 



SOUTHERN 

 GREENLAND 



2 5 fms. 



1100 fms. 



35°ofQ:teat Circle 



^Zi' of Great Circle 



INDIAN 

 OCEAN 





BENGAL 



and 



PEGU 



I I O O fms. 



Fig. 2. This diagram shiows ttie binodal oscillation going on in the North 



Atlantic Ocean. When it is high water at either end, it is low water off Morocco 



and vice versA. The depth of the southern portion being greater than the depth of 



the northern, a half wave-length in the former exceeds a half wave-length in the 



latter — the period in each case being very nearly 12 lunar hours. 



system is shown by means of a diagram (Fig. 2). One nodal line 

 passes near the Cape Verde Islands and another lies westerly from Ire- 

 land. When it is high water on the coasts of Guiana and Brazil, it is 

 also high water around southern Greenland, and it is then low water 

 along the coast of Morocco, Spain and Portugal. The Roman numer- 

 als upon the small map of the world show that high water occurs at 

 eight o'clock, Greenwich lunar time, 

 for the South iVmerican and Green- 

 land ends of this basin and at two 

 o'clock for the central or Morocco 

 portion. On account of the extensive 

 openings to the eastward and north- 

 ward of this basin or system, pro- 

 gressive waves are formed which con- 

 tribute to the tides around the British 

 Isles and Arctic Archipelago, and are 

 chiefly responsible for the tides of 

 the Arctic Ocean. Since progressive 

 waves can not arise suddenly, their 

 effects are felt over a large portion of 



the system now under consideration, and they tend to obscure the 

 theoretical nodal lines which cross it. 



The tides along the Atlantic Coast of the United States are pro- 

 duced in the body of water which extends from this coast to the Ant- 

 arctic Continent by way of Cape of Good Hope. This is shown upon 



the smaller chart of the world (Fig. 4) by one of the types of shading. 



The northern portion of this region is not greatly influenced by pro- 

 gressive waves because the ■ openings through its northwestern, or 



M of Great Circle 



Fig. .3. This diagram shows 

 that the Bay of Bengal measures 

 a quarter of a wave-length to its 

 nodal line extending eastward 

 from Ceylon. Its tide depends 

 directly upon that tide of the 

 Indian Ocean which lies to 

 southward of the nodal line. 



the 



United-States, 



boundary are not large. 



Consequently, the theoretical 



