132 Facts in Meteorology. 



no means subject to such extremes as the latter. The temperature 

 of the sea never, in any latitude, exceeds 86 or 87 degrees of 

 Fahrenheit. 



The existence of banks or shallows has a local effect in diminish- 

 ing the temperature of the ocean, but the great agents in modifying 

 it are currents, which mingle together, or, rather, change the locality 

 of waters of different regions. Thus, the gulf stream, as it is called, 

 which sets into the gulf of Mexico from the equatorial regions, is 

 much warmer than the neighboring parts of the sea ; the current of 

 Chili is just the reverse, being in its progress from die higher to the 

 equatorial latitudes, where it passes into the wide Pacific, and car- 

 ries the warmth which is subsequently acquired, again to the higher 

 latitudes. 



Of Tides. 



The influence of the moon in producing the tides, is supposed to 

 be greater than that of the sun, and evidently governs ihe time of 

 high water. As the moon crosses the meridian of a place about 

 every twenty-four hours and fifty minutes, the sea, in most parts of 

 the world, ebbs and flows twice in that space of lime. In large 

 portions of the Pacific Ocean, however, as well as in certain other 

 localities, the tides are exempt from the lunar influence. At Ta- 

 hiti and the Georgian group, near the center of the Pacific Ocean, 

 the tide rises but one or two feet, and it is high water at noon and 

 midnight throughout the year, and this too, in the very region where 

 the established theory would lead us to expect the lunar tides to be 

 the most regular and powerful. The tides upon the coast of Guate- 

 mala, in the Caribbean sea, afford a similar exception, while on the 

 opposite coast at Panama the tides of the Pacific rise to the height of 

 twenty feet. These facts serve to show that the modus operandi of 

 the causes which produce tides, is not thoroughly understood.* 



* Does net the course of the great semi-diurnal tide wave, in each of the great 

 oceans, main?y correspond to the great circuits of oceanic and atmospheric currents, 

 moving from west to east in the higher latitudes? Mr. Lubbock, who is engaged 

 iu an elaborate investigation of the facts in relation to the tides, can furnish us the 

 fneans of solving this question. If the aflEirmative be true, these several movements 

 would seem to originate in a common impulse or tendency. 



