178 



NATURE 



[June 2 2, 1876 



flow in an easterly direction ; and, on the other hand, currents 

 of both air and water flowing from the poles towards the equator 

 must for the same reason lag behind, ard consequently appear to 

 flow in a westerly direction. From this I argue that the cold 

 currents from the Arctic regions to the equator do hug the 

 western shores, and therefore cannot possibly supply the cold 

 streams on the eastern side of the North Atlantic Ocean, south, 

 at all events, of 50° of lat. ; but that the supply must come from 

 the Antarctic Ocean ; and, on the other hand, from the same 

 cause, that the cold water on the eastern side of the South 

 Atlantic Ocean is water from the Arctic Ocean which underflows 

 the equatorial stream, and as it approaches the African coast, 

 has a portion of its stream thrown upwards towards the surface, 

 which accounts for the surface-water of the equatorial stream 

 near this coast being some degrees colder than that of the Guinea 

 current to the northward of it. 



I need not say that every gallon of water that flows into the 

 North Atlantic from the South Atlantic Ocean must be returned 

 to it in some way, either by a surface or an under-current ; and I 

 think I may safely argue that there are no surface- currents suffi- 

 cient to account frr the return of the volume of Antarctic water, 

 and that, therefore, a large portion of the water returned must 

 be from the Arctic basin, and must flow in the manner which I 

 have previously indicated. 



The surface-water in these warm regions is lifted by the inflow 

 below it of colder and therefore heavier water from the two polar 

 seas, it then flows off" as a surface-current, and the poi tion of it 

 flowing towards the north pole is deflected by the constant 

 easterly trade winds and obliged to flow westward along the 

 nor;h coast of South America ; a large portion of it flowing 

 through the Carribbean Sea into the Gulf of Mexico, and thence 

 through the Gulf of Florida. If we estimate the width of this 

 part of the stream to occupy in the narrows thirty-two miles out 

 of a total breadth of forty-two miles, and its depth at 200 

 fathoms, its velocity at an average rate of four miles per hour, 

 i.e., in the narrows, it is equal to a stream 2,650 miles wide, 60 

 feet deep, and running at the rate of one mile per hour, which 

 shows that it is not the mere rivulet it is sometimes described to 

 be. I am aware that its average rate is now said to be less than 

 four miles per hour ; but I myself travelled through the Gulf of 

 Florida twice a month for two years, once a month when bound 

 to the northward, keeping in the strength of the stream, and I 

 cannot help thinking that its strength is now very much under- 

 valued, probably in consequence of its rate, as noted, not being 

 strictly confined to the narrows. 



This stream is uplifted as it flows out of the northern entrance 

 of the Gulf of Florida by the inflow beneath it of colder and 

 heavier water flowing in the contrary direction from the Arctic 

 Pole ; and this, in my opinion, accounts for the arched form of 

 the surface of the Gult Stream as noted by Maury. Off Hatteras 

 it is only 100 fathoms deep, and being beyond the influence of 

 the trade winds, its easterly momentum, due to its northerly 

 flow, inclines its course to the northward and eastward. When 

 it gets to the northward of 40° of lat., which it does in about 50° 

 of W. long., it appears to spread itself out over the ocean. Now 

 this warm stream has been giving out volumes of vapour during 

 the whole of its northward course, and has from this cause been 

 gradually getting Salter and Salter ; and as it gets shallower, this 

 effect mubt naturally be greatly increased, besides which the 

 temperature of the stream begins rapidly to decrease. It, in my 

 opinion, then flows onwards towards the pole, gradually losing 

 temperature until it meets with Polar water, which, though 

 colder, has, owing to its admixture with glacial water, a less 

 specific gravity than itself; it then dips below the surface, and, 

 getting colder and colder, runs with great rapidity to the bottom 

 of the Polar basin. 



I must now try and prove that this is what takes place, and 

 for this purpose I shall quote from Maury and Capt. Nares. 



Maury, vol. ii. pp. 184 and 185. — "Capt. Duncan says, Dec. 

 18, 1826 :— 



" It was awful to behold the immense icebergs working away 

 to the nouh-east from us, and not one drop of water to be seen ; 

 they were working themselves right through the middle of the 

 ice. 



"Feb. 23, lat. 68° 37' N. long., about 63" W., about 3 p.m., 

 the iceberg came into contact with our floe, and in less than one 

 minute it broke the ice. Again he says, the berg was drifting at 

 the rate of about four knots, and by its force on the mass of ice 

 was pushing the ship before it, as it appeared, to inevitable 

 destruction. 



" Passed Midshipman S. P. Giif&n, who cotnmanded the brig 



Rescue in the American searching expedition after Sir John 

 Franklin, informs me {i.e., Maury) that on one occasion the two 

 vessels were endeavouring to warp up to the northward in or 

 near Wellington Channel, against a strong surface-current, which 

 of cour.e wns setting to the south ; and that whilst so engaged, 

 an iceberg with its top many feet above the water came drifting 

 up from the south, and passed by them like a shot, although 

 they were stemming a surface- current both against the berg and 

 themselve*. Such was the force and velocity of the under- 

 current, that it carried the berg to the northward faster than the 

 crew could warp the vessel against a surface- but counter- 

 current." 



Capt, Nares, in the Report of the Challenger, No. 2, says : — 



"AH the observations, however, agree in denoting that at a 

 depth of from 80 to 200 fathoms there is a stratum of cold water 

 lying intermediate between the superheated surface-water and 

 the warm underlying layer, which is evidently the continuation 

 towards the cold regions of the main oceanic flow of water." 



If Capt. Nares had continued his investigations to the south- 

 ward of 65° 42' S., and it had been possible to trace this warm 

 layer as it gradually decreased its temperature, I have no doubt 

 that its course might be traced to the bottom. 



I could adduce further confirmation of these views if space 

 would allow me. If my readers will look at a globe, they will 

 readily see that the Arctic Ocean is comparatively a very small 

 sea, and that the effect of large volumes of salt water pouring 

 into the bottom of the Polar basin must elevate the lighter, 

 because fresher, surface-water, and consequently cause a constant 

 outflow towards the equator. A very large stream, known as 

 the Labrador current, runs off cs a surface-current through 

 Davis Strait, one fork dipping below the surface, at some sea- 

 sons of the year, as far to the southward as 42° N., and then 

 underrunning the Gulf Stream : and the other fork, running 

 over the tail of the great bank, and flowing in-shore of the Gulf 

 Stream, runs along the American coast as far south as Florida. 

 The velocity and boundaries of all these streams vary greatly at 

 different seasons, that is to say, the position of the sun affects 

 the ocean as much as it does the atmospheric currents. 



A further argument in favour of the cold currents flowing 

 from the surface at the poles is that this is exactly what happens 

 in the circulation of the atmosphere. The north-east and south- 

 east trades, which are generally admitted to be Polar currents, 

 descend on the equatorial side of 30° of lat. ; besides in no other 

 way that I can see can you obtain a sufficient motive power. A 

 primuni mobile defending on the lateral pressure of a column of 

 Polar water as opposed to the lesser weight of a column of tem- 

 perate or of equatorial water, assuming the length of the ocean 

 (counting say from 70° of lat. to the equator) to be 4, 200 miles, 

 and its mean depth to be 3 miles, i.e., a length of 1,400 times its 

 depth, appears to me to be a very insufficient power to move the 

 volumes of water which we know to be constantly circulating 

 between the equator and the poles. (An ordinary sheet of note 

 paper has a length equal only to 928 times its depth.) If, how- 

 ever, it is allowed that the cold streams flow from the surface, 

 and that they do not dip till they reach 70° of lat.' (the Labrador 

 current, as before stated, dips much further towards the equator, 

 sometimes in 42° N.), you have still a fall of nearly 3 feet 7 inches 

 per mile of lat. to the equator. ^ I have said sufficient to indicaie 

 very briefly my opinions. The arguments I have recently read 

 on this subject appear to be based on the idea that currents flow 

 in one lateral sheet from the pole to the equator. If they did 

 this, there would be no reason why the surface-currents should 

 not flow in a similar way. But they do not ; and, if of the depth 

 lately suggested, i.e., 3,000 feet, the Arctic basin could not receive 

 them if they did. The Challenger observations seem to me to 

 entirely disprove this view of the subject. 



There is a wonderful similarity between oceanic and atmo- 

 spheric circulation, which I propose more specially to point out 

 at some future time. If we wish to know how the N.E. trades 

 and the S.W. winds pass one another in the upper regions of the 

 atmosphere, let us question the currents of the ocean, and the 

 Labrador current will suggest an intelligible reply. If, on the 

 other hand, we want to know what is the system of ocean circu- 

 lation, let us ask the currents of the atmosphere ; and the Polar 

 currents {i.e., the trade-winds) and the equatorial currents {i.e., the 

 westerly winds of the temperate zones) will strongly suggest to 

 us the answer. It is quite true that there is no salt in the atmo- 

 sphere, but there is, instead, vapour, which plays as important a 



' They at most, if not at all, seasons dip in a much lower latitude, 

 2 Estimating the depth of the ocean as 2, 500. 



