Jan 1871
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1871natur...3..227j&link_type=abstract
Nature, Volume 3, Issue 64, pp. 227 (1871).
Other
Scientific paper
ATTENTION has been much drawn of late to the subject of Ocean Currents and their causes, and it has occurred to me that there is a directing if not an originating cause of these streams, which has, so far as I am aware, been overlooked by physicists. It is known* that at some parts of the earth's surface there exists an atmospheric pressure capable of sustaining a column of mercury in the barometer of upwards of 30 inches in height; at the same time there are certain areas over which this pressure is only such as to raise the barometric column to a little over 29 inches. Now if we compare the difference of absolute weight sustained by two such areas, we shall see that in the space over which the higher atmospheric pressure exists, there is an excess of weight of air, amounting in round numbers to 1,000,000 of tons on each square mile. Applying this fact to the region of the ocean in which the surface currents are best known, the North Atlantic, we find from the isobaric chart that there is throughout the year over a large portion of the eastern side of this sea, next the coast of North Africa, a pressure (to use the convenient mode of expressing it) of upwards of 30.2 inches. To westward of this space, towards the Gulf of Mexico and the coast of the United States, the average pressure decreases; between Newfoundland and the British Isles the pressure is still diminished, till in the wide channel between Iceland, Norway, and Spitzbergen, we arrive at a yearly pressure of less than 29.6 inches. It is reasonable to believe that the waters which lie under the high pressure area have a tendency to escape from under the excessive weight, towards the space over which the pressure is less. But the high pressure area next the African coast is precisely that upon which the north-east trade winds descend, and the waters, aided in their choice of an exit, will naturally flow off to south-westward before the wind. Their continuance in this direction is barred, however; for across the whole of the southward passage between Africa and South America, there exists another belt of high pressure, out of which the south-easterly trade winds blow. The only course left for the escaping waters (allowing for the moment that the excess of pressure is a cause of their movement) is to westward, where the pressure is lessened, towards the Gulf of Mexico, and the east coast of America, and thence towards the low pressure space between Iceland and Norway. But this is exactly the course that the Gulf Stream, or rather the North Atlantic warm stream of which the Gulf Stream is the most prominent feature, is seen to take. Are we not then warranted in concluding that the difference of atmospheric pressure has some power both in originating and in directing the course of this ocean current?
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