GULF STEEAM— TEMPEEATUEE. 8 



better understood than tluit of tlie currents. The great tidal flow setting north- 

 wards, and reaching the opposite shores of the two hemispheres at the same time, 

 is divided into three distinct streams on reaching the south-western shores of the 

 British Isles. The main stream continues its northern course along the west coast 

 of Ireland, while the two others enter the St. George's and English Channels. 

 But after flowing round the west and north coasts of Ireland the first stream 

 passes through the I^orth Channel between Great Britain and Ireland, and there 

 meets the second on its way from the south. The main stream, after making the 

 circuit of Scotland, flows southwards along the east coast of England until it 

 meets the third from the English Channel about the Straits of Dover. At the 

 same time these streams are constantly modified according to the position of sun 

 and moon, the force and direction of the winds, the endless varieties of the 

 atmosphere, so that mean results alone can be given.* 



Gulf Stream. — Temperature. 



Like the tides, the main currents of the JSTorth-east Atlantic flow from the 

 south and south-west. To a depth of over 500 fathoms the surface waters on 

 the whole flow from south-west to north-east, and from south to north, from 

 the Bermudas and Azores to the British Isles, Iceland, Scandinavia, and 

 Spitzbergen. This is placed beyond all doubt by the tropical plants and 

 articles of human industry, bearing the marks of their origin, strewn along the 

 shores of JN^orthern Europe and the polar islands. But it is difiicult to say to what 

 extent the Gulf Stream, escaping through Florida Channel from the Gulf of 

 Mexico, is thus continued in the vast current traversing the entire breadth of the 

 North Atlantic. Carpenter,! Findltiy, and other physicists rightly regard this 

 current as the result of a general displacement occasioned by the tepid waters of 

 the torrid zone setting in towards the cold waters of the arctic seas. In fact, 

 Florida Channel is far too narrow to give egress to a stream spreading for a space 

 of at least 2,400,000 square miles between Scandinavia, Iceland, and Newfound- 

 land, and reaching a greater depth than 830 fathoms below the surface. The flow 

 of the Gulf Stream at the Bahamas is variously estimated at from 500,000+ to 

 3,000,000,000 § cubic yards per second by writers who have a theory to support. 

 But the approximate calculations of others give a nominal volume of about 

 52,000,000 cubic yards, which would take no less than ten years to fill the whole 

 space at present occupied by the tepid waters. Besides, the hydrographers who 

 have studied the Bermuda seas have ascertained that off" the United States coast 

 the Gulf Stream branches into a number of smaller currents, separated from each 

 other by masses of colder water, and all gradually merging in the main current of 

 the Atlantic. 



* The tidal systems are described in vol. iv. p. 7. 



t Lecture at the Royal Institution, Nature, March 10th, 1870. 



X James Croll, Fhilosophical Magazine, February, 1870. 



§ Y\ndlai,Y, Jotimal of tlie Geographical Society, 1853; T'roceedingx, 1869. 



