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SCIENCE. 



[N. S. Vol. III. No. 60. 



less to remove the other third we are led 

 to the conclusion that it flows back into the 

 Caribbean as an undercurrent. 



A study of the proportions of these cur- 

 rents has led to tlie conclusion that the 

 Yucatan Channel current owes its existence 

 mainly to the mechanical eifect of the 

 winds which produce an accumulation of 

 waters in the northwestern part of the 

 Caribbean Sea, but it is also, in part, due to 

 differences in temperature and density be- 

 tween the waters of the latter and those of 

 the Gulf. Hence, should the winds cease 

 to influence the level of the Caribbean Sea, 

 there would still be a surface current from 

 this sea into the Gulf and an undercurrent 

 in the opposite direction, similar to those 

 which actually exist in the Strait of Gi- 

 braltar from and to the Atlantic Ocean. 



The fresh water, which finds its way into 

 the southwestern part of the Gulf, remains 

 on the surface of the Gulf waters, but on ac- 

 count of its high temperature it readily as- 

 similates with the sea water, and by con- 

 tinuous absorption of salt and heat from 

 the lower strata reduces the latter to ab- 

 normally low temperatures. 



The river and rainwater entering the 

 northern parts of the Gulf also remains on 

 the surface, but it preserves its distinctive 

 character and low specific gravity for a 

 much longer time period, owing to its com- 

 paratively low temperature, for not until 

 it has reached the middle of the Gulf has 

 it gathered salt and heat to its full capacity. 

 Thus the course of the waters of the Missis- 

 sippi River can be traced by their lightness 

 for hundreds of miles into the Gulf of 

 Mexico. Instead of flowing directly south- 

 east towards the Strait of Florida, in ac- 

 cordance with the generally accepted sup- 

 position, these waters flow to the westward, 

 which deflection undoubtedly is influenced 

 by the existence of a lower water level in 

 the western part of the Gulf, due to the pil- 

 ing up of the v/ater in the eastern part by 



the flow from the Yucatan Channel. Not- 

 withstanding the fact that the tendency of 

 the Mississippi River waters, after entering 

 the Gulf, is towards the west, and regard- 

 less of the strength of the inflowing Yucatan 

 current, the predominent surface drift of 

 the Gulf is towards the Strait of Florida, 

 which phenomenon may be explained by 

 assuming that the Yucatan current in its 

 west and northward progress dips below the 

 surface waters and continues as an under- 

 current. 



The surface waters of the central and 

 eastern parts of the Gulf of Mexico, being 

 propelled against the direction of the pre- 

 vailing winds, are subjected to a powerful 

 influence of evaporation, by which their 

 specific gravity is increased to such an 

 extent that their weight can no longer 

 be borne on the surface, and sinking, they 

 carry larger amounts of salt and heat into 

 the deep strata than could reach such great 

 depths in any other way. Thus onlj- can 

 we account for such temperatures as 60° 

 and more at a depth of 250 fathoms, oc- 

 curring off Cape San Antonio, half way be- 

 tween the Florida and Campeche Banks, 

 against 44° in the western part of the Gulf 

 and 47° in the Caribbean Sea at correspond- 

 ing depths. 



In conformity with the direct eiiects, 

 known to result from decided differences of 

 temperature at considerable depths in com- 

 municating parts of the ocean, there will be 

 an undercurrent from the southeastern part 

 of the Gulf toward the western part and 

 another entering the Caribbean Sea, sup- 

 porting the views expressed when consider- 

 ing the volume of water. 



It is a remarkable phenomenon that the 

 temperature in the substrata of those parts 

 of the ocean adjacent to the Strait of 

 Florida should be so nearly the same as 

 that of the eastern part of the Gulf, thus 

 precluding the existence of a subsurface 

 counter-current in that strait; and a singu- 



