THE GULF STREAM. 37 



105. Current into the Caribbean Sea. — Now that we may form 

 some idea as to the influence which the salts left by the vapour 

 that the trade-winds, north-east and south-east, take up from sea- 

 water, is calculated to exert in creating currents, let us make a 

 partial calculation to show how much salt this vapour held in 

 solution before it was taken up, and, of com^se, while it was yet 

 in the state of sea- water. The north-east trade-wind regions of 

 the Atlantic embrace an area of at least three million square 

 miles, and the yearly evaporation from it is (§ 103), we will 

 suppose, fifteen feet. The salt that is contained in a mass of sea- 

 water covering to the depth of fifteen feet an area of three 

 million square miles in superficial extent, would be sufficient to 

 cover the British islands to the depth of fourteen feet. As this 

 water supplies the trade-winds with vapour, it therefore becomes 

 Salter, and as it becomes Salter, it becomes heavier ; and therefore 

 we may infer that the forces of aggregation among its particles 

 are increased. 



lOG. Amount of salt left by evaporation. — Whatever be the cause 

 that enables these trade-wind waters to remain on the surface, 

 whether it be from the fact just stated, and in consequence of 

 which the waters of the Gulf Stream are held together in their 

 channel ; or whether it be from the fact that the expansion from 

 the heat of the torrid zone is sufficient to compensate for this 

 increased saltness ; or whether it be from the low temperature 

 and high saturation of the submarine waters of the intertropical 

 ocean ; or whether it be owing to all of these influences together 

 that these waters are kept on the surface, suffice it to saj^, we do 

 know that they go into the Caribbean Sea (§ 103) as a surface 

 current. On their passage to and through it, the}' iirtermingle 

 with the fresh waters that are emptied into the sea from the 

 Amazon, the Orinoco, and the Mississippi, and from the clouds, 

 and the rivers of the coasts round about. An immense volume 

 of fresh water is supplied from these sources. It tends to make 

 the sea-water, that the trade-winds have been playing upon and 

 driving along, less briny, warmer, and lighter : for the waters of 

 these large intertropical streams are warmer than sea-water. 

 This admixture of fresh water still leaves the Gulf Stream a 

 br.ine stronger than that of the extratropical sea generally, but 

 not quite so strong (§ 102) as that of the trade-wind regions. 



107. Currents created by storms. — The dynamics of the sea con- 

 fess the power of the winds in those tremendous currents which 



