Dec. 7, 1871] 



NATURE 



"3 



rotation should acquire the preponderance necessary to produce 

 an enlargement of breadth towards the east ; and this elevation 

 of the level gives birth at the same time — from the middle of the 

 Gulf Stream to the polar current — to the surface current of warm 

 water which has been ascertained to exist by the American Com- 

 mission. 



It follows then from what precedes, that on the one hand the 

 polar current penetra'es at all points into the Gulf Stream, 

 nearly as far as iis surface, which sends to the polar current a 

 surface-current of warm water from twenty to fifty fathoms deep ; 

 and, on the other hand, that the Gulf Stream ought, throughout 

 the whole of its depth, to exercise upon the waters of the Atlantic 

 a pressure which forces them to give place to those which it 

 receives from the polar current, and which it draws along with it. 



The researches which have recently been made as to the Gulf 

 Stream all appear to confirm these conclusions, so that if we 

 suppose that the volume of the Gulf Stream is increased by all 

 the water which the polar current loses in its course, it will follow 

 that if we designate by Q the volume of the Gulf Stream at 

 Bernini, and by q that of the polar current in any section between 

 Newfoundland and Florida, the volume of the Gulf Stream, for 

 the same section, will be equal to (P -f q. After that, it is 

 necessary that the polar current — which, from the east coast of 

 Newfoundland, flows towards the Gulf Stream, and from Cape 

 Race takes a south-westerly direction along the American coast 

 — gives up in its passage towards Florida all its water to the 

 Gulf Stream. If, then, we assume the speed of the polar cur- 

 rent to the south of Newfoundland to be I 'S feet per second, 

 its breadth 50 miles, and its depth 900 feet, it will be found 

 that its delivery per second is 1,600,000.000 cubic feet, which 

 makes that of the Gulf Stream to the south of Newfoundland 

 3,200,000,000 cubic feet per second. 



From the southern part of the North Atlantic, then, between the 

 equator and 30° of latitude, itdischargesatthe rate of 1,600.000,000 

 cubic feet per second ; but besides the loss which has been accounted 

 for, there is anotlier which is due to evaporation ; the latter deprives 

 the Gulf Stream of a quantity of water greater than that which 

 falls into it in the form of rain, and which flows into it from the 

 neighbouring lands. To calculate this difference, we can make 

 use of the results of the researches which were made in 

 i860 at St. Helena by Lieut. Haughton. We thus find that 

 the excess of evaporation in the Atlantic, between 0° and 30° of 

 latitude, is equivalent toa mean height of water of o'22", which, 

 after deducting one-tenth for the water which comes from rivers, 

 gives a loss of 50,000,000 cubic feet per second. The total quan- 

 tity of water, then, which passes from the Atlantic between 

 o" and 30° of N. latitude, can be stated as equal to 1,650,000,000 

 cubic feet per second. 



If we then admit that two-thirds of all the surface of the lands 

 situated to the north of the 30th degi-ee of latitude send directly 

 or indirectly their waters to the Atlantic, and if we estimate the 

 quantity of rain which annually falls upon that surface, the north 

 part of the Atlantic will receive per second an addition of 

 50,000,000 cubic feet of water, or, about the same quantity 

 which is carried off by evaporation from the south part between 

 0° and 30' of N. latitude. 



But it follows hence that since the southern branch of the 

 Gulf Stream is formed by the water which flows from the south 

 part of the North Atlantic, it ought to have a delivery of 

 1,650,000,000 cubic feet per second ; and, as the delivery of 

 the entire current, after having passed Newfoundland, may be 

 staled at 3,250,000,000 cubic feet, it follows that that of the 

 northern branch is 1,600,000,000 cubic feet, while the united 

 polar currents ought to represent a volume of 1,650,000,000 

 cubic feet per second. At St. Augustine the depth of the Gulf 

 Stream is about 300 fathoms, which goes on diminishing regu- 

 larly, as far as Newfoundland, where it is 1,000 feet. From 

 Newfoundland, where it has a breadth of eighty miles and a 

 speed of two feet, the current proceeds E.N.E., with a decreas- 

 ing speed and an increasing breadth ; at the end of 300 miles it 

 has a depth of 200 and odd fathoms, a speed of o'6 feet, and a 

 breadth of 200 miles. Moreover, during this part of its course 

 it rises about 2 feet above its level at Newfoundland. Until it 

 attains this height, the Gulf Stream forms only a single current 

 maintained by the fall of i foot, which it presents from right to 

 left ; but as soon as it reaches that, its southern part presents 

 a slope sufficient to give birth to a branch which proceeds to 

 the south-east, towards the African coast, at a speed of 0'6 feet, 

 and with a delivery of 1,650,000,000 cubic feet per second. 

 When the latter current reaches the 30th degree of N, latitude, 



it meets the north-east trade-wind, which urges it towards the 

 south. 



But while the southern half of the Gulf Stream proceeds 

 towards the south, its northern half, whose delivery per second 

 is 1,600,000,000 cubic feet, pursues its course towards the north, 

 along the shores of Great Britain, as far as the 60th degree of 

 latitude in this passage, during which the current rises towards 

 the land and gradually increases in breadth from loo to 150 

 miles, while its speed diminishes from 06 to 03 of a foot per 

 second, it is subjected to the impulse of the earth's rotation, and 

 its western margin, which naturally blends with the surface of 

 the Atlantic, is raised from i^ foot through a course of 140 

 miles, so that at the 60th degree of latitude this side is 3 J- feat 

 above the level of the ocean at Newfoundland. 



After the Gulf Stream, which throughout this course has a 

 depth of from 200 to 300 fathoms, reaches the north coast of 

 Scotland, about two-thirds of its waters proceed eastwards 

 towards the Norwegian coast, while the other third runs against 

 Iceland, and afterwards continues its course to the north-west to 

 the polar current of Greenland. The latter branch, which the 

 force of rotation raises towards the land, has a depth of 200 

 and odd fathoms, and a breadth of about 50 miles ; in order to 

 be able to advance towards the polar current with a speed of 

 about 0'3 feet per second, a fall of nearly half a foot is neces- 

 sary. If next we remark that the northern Gulf Stream, towards 

 the north point of Scotland, presents an elevation of I '5 foot 

 towards the land, we shall easily see that the branch of the Gulf 

 Stream, which proceeds to the north-west, has, along the Icelandic 

 coast, a level which exceeds by half a foot the southern margin 

 of the same current. From this it follows that the waters which 

 skirt the coast of Iceland encounter the polar current on the 

 west of that island at a level higher by 35 feet than the surface of 

 the Atlantic at Newfoundland. But while these waters advance 

 towards the polar current in virtue of the above-mentioned fall, 

 those of the southern margin of the Gulf Stream have precisely 

 the same level as the polar current. The waters of the western 

 side of the north branch of the Gulf Stream, which are forced to 

 bend towards the west after having reached the 60th degi'ee 

 of north latitude, cannot then continue their course towards the 

 polar current ; they spread themselves over the surface of the 

 Atlantic and take a southerly course towards Newfoundland, on 

 account of the difference of level. With regard to those parts 

 of the current situated between the north and south boundaries 

 of this branch of the Gulf Stream, they are, according to their 

 position, drawn for a shorter or longer time still towards the 

 polar current, before taking their course towards the south ; and 

 it is thus evident that the warm current must spread itself over 

 the whole surface of the Atlantic between the Northern branch 

 of the Gulf Stream and the polar current which descends from 

 Greenland. 



If next we turn our attention to the progress of the polar 

 current from the east coast of Greenland, starting from the fol- 

 lowing data, viz., that the eastern margin of this current, about 

 65° north latitude, on the west of Iceland, has a level of 3j feet 

 higher than that of the Atlantic at Newfoundland, and that it 

 pursues a course to the south-west at the rate of \ of a foot per 

 second — we see clearly that it is obedient to the impulse com- 

 municated by the rotation of the earth. Moreover, let us esti- 

 mate, after Irminger, the breadth of the current at 40 miles, 

 and suppose that the half of the water which the Gulf Stream 

 carries into the icy sea, as well as the half of that which falls in 

 the form of rain or snow, returns towards the south with the 

 current, while the other half descends by Baffin's Bay ; we then 

 find that the force of rotation raises the polar current, whose depth 

 may be estimated at 1,000 feel, one foot above its eastern margin, 

 and, regarding the speed as constant as far as the south point of 

 Greenland, we arrive at the result that, along its eastern side, 

 which naturally blends with the Atlantic, its surface must con- 

 tinue to rise as far as Cape Farewell, from 35 to 5 feet above the 

 level of the ocean at Newfoundland. If, after having doubled 

 Cape Farewell, the Gulf Stream descended straight towards 

 Newfoundland, the water in Davis Strait ought to rise to a 

 height sufficient to hinder the current from moving in a more 

 westerly direction. But, as the water in Davis Strait cannot 

 have a higher level than is necessary to impel towards the south 

 the tributary bodies of water as rapidly as they join it, and, as 

 for this purpose, at the 63rd degree of north latitude, an 

 inclination of only y\ feet above the level of the sea at New- 

 foundland is required, the polar current, on arriving at Cape 

 Farewell, presents towards Davis Strait a slope of 2\ feet along 



