50 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOEOLOGY. 



other as cold as ice. A familiar experiment shows that if two basins 

 of such water be brought in connection by oj)ening a w^ater-way 

 between them, the warm will immediately commence to flow to the 

 cold, and the cold to seek the place of the warm. But why this 

 warm flow in the Atlantic Ocean should seem to issue from the Gulf 

 of Mexico, as if by pressure, is not so clear. 



145. To satisfy ourselves that the trade-winds have little or 

 The trade-winds as nothing to do in causiug the Gulf Stream, we may by 



ji cause ol tu6 ijuii ^ . i*t' ii ti c* i i 



stream. a proccss 01 rcasomug, wnicn ignores all the tacts and 



circumstances abeady adduced, show that they cannot create a cm^- 

 rent to run when or where they do not blow. The north-east trade- 

 winds of the Atlantic blow between the parallel of 25^ and the 

 equator ; the Gulf Stream flows between the parallel of 25° and 

 the North Pole. 



146. A constantly acting power, such as the force of gTavitation, 

 Gulf stream impelled fg as necessarv (S 95) to keep fluids as it is to keep 



by a constantly act- tt • i- t -n n • l'i !> 



ing force. solids in motiou. In either case the projectile lorce 



is soon overcome by resistance, and unless it be renewed, the ciuTent 

 in the sea will cease to flow onward, as surely as a cannon-ball will 

 stop its flight through the air when its force is spent. When the 

 waters of Niagara reach Lake Ontario, they are no longer descend- 

 ing an inclmed plane ; there, gravity ceases to act as a propelling 

 force, and the stream ceases to flow on, notwithstanding the impulse it 

 derived from the falls and rapids above. A propelling povrer, hav- 

 ing its seat only in the Gulf of Mexico, or the trade-wind region, 

 could (§ 92) no more drive a jet of water across the ocean, than 

 any other single impulse could send any other trajectile that distance 

 through either air or water. The power that conveys the waters 

 of the Gulf Stream across the ocean is acting upon them (§ 95) 

 every moment, like gravity upon the current of the Mississippi 

 river ; with this diflerence, however, the Mississippi runs down 

 hill, the GuK Stream on the dead level of the sea. But if we 

 appeal (§ 80) to salt and vapour, to heat and cold, and to the 

 secreting powers of the insects of the sea, we shall find just such 

 som'ces of everlasting changes and just such constantly acting 

 forces as are requked (§ 108) to keep up and sustain, not only the 

 Gulf Stream, but the endless round of ciuTents in the sea, which 

 run from the equator to the poles, and from the poles back to the 

 equator; and these forces are derived from diflerence in specific 

 gravity between the flowing and reflowing water. 



147. The waters of the GuK as they go fi'om their fountain have 



