February 21, 1896.] 



SCIENCE. 



273 



lar coincidence may be noted in the general 

 character of the bed of that strait, it being 

 only suihciently deep to permit the passage 

 of the Gnlf Stream. It must not be sup- 

 posed, however, that the under-current 

 flowing into the Caribbean Sea entails a 

 permanent saline and thermal loss upon 

 the waters of the Gulf, as those abducted 

 quantities of salt and heat, by a system of 

 transfers, find their way.into consecutively 

 higher levels, and finally reach the surface 

 current and return with it to the Gulf. 



The current of the Yucatan Channel, 

 notwithstanding its being the strongest cur- 

 rent of the entire Gulf Stream system, 

 possesses no great depth, and owing to its 

 rapid spreading out it soon loses the best 

 part of its velocity. The only exception 

 in this respect is met with along the north- 

 ern edge of Campeche Bank, where its flow 

 shows considerable vitality, and it is here 

 that it has evidently taken the shortest 

 route to reach the western part of the Gulf. 



It also appears to be very variable in its 

 strength ; when flowing at its best some of 

 its waters are sent into the Strait of Florida, 

 but its main strength is directed against the 

 Gulf of Mexico with the effect of penning up 

 its waters above the level of the Atlantic. 

 Whenever the Yucatan current relaxes in 

 activity, the waters of the Gulf of Mexico, 

 in their reaction, frequently succeed in 

 cutting it off altogether from reaching the 

 Strait of Florida, and sometimes even in 

 partly forcing it back at its eastern and 

 weakest flank, into the Caribbean Sea. 



The Gulf Stream, as has been shown by 

 Lieutenant Pillsbury, is not the direct con- 

 tinuation of the Yucatan Channel current, 

 but originates about in the middle of the 

 western entrance to the Strait of Florida. 



As it first appears in the Strait it is com- 

 paratively an insignificant current, and we 

 are also disappointed in not finding it that 

 fiery furnace which, according to its reputa- 

 tion, transmits sufficient heat to the eastern 



part of the Atlantic to modify the climate 

 of the whole of western Europe. The fact 

 appears to be that it does not start upon its 

 journey at this point with more heat than 

 it requires for its own use until it reaches 

 Cape Florida, as it at once enters a contest 

 against the cold waters descending from 

 the Florida Bank, extending nearly half- 

 way across the Strait. During its progress 

 through the Strait these cold waters are 

 forced back into the vicinity of the reefs, 

 and by the time the Gulf Stream has 

 reached Cape Florida it is in full possession 

 of the Strait, from the surface to the bot- 

 tom, and from the Bahama Banks to the 

 Florida Reefs ; its axis being but 15 miles 

 distant from Cape Florida. 



This victory, however, has been obtained 

 at a great sacrifice of its supply of salt and 

 heat, leaving it in an inadequate condition 

 to engage unaided in another contest which 

 it must immediately enter upon. Fortu- 

 nately reinforcements are at hand, warm 

 and highly saline waters, which have been 

 slowly advancing along the Bahama Bank, 

 join the Gulf stream at its point of weak- 

 ness. Other and far more important succor 

 gathered by the northeast trade winds, joins 

 the Gulf stream on entering the ocean at 

 the eastern end of the strait. Yet all these 

 additions cannot account for the observed 

 fact that the waters of the Gulf stream ar€t 

 so much warmer and more saline than those 

 of the ocean, and in order to discover the 

 source of this great heat we must look in 

 a different direction than towards the Gulf 

 of Mexico, or towards the surface drift of 

 the Atlantic. 



What has been described as taking place 

 on the surface of the southeastern part of 

 the Gulf is reenacted on a much larger 

 scale on the entire surface of that part of 

 the Atlantic Ocean lying between the Ber- 

 mudas and the ' continental shelf,' off the 

 Southern States. A powerful evaporation 

 caused by the trade winds produces a con- 



