108 PHYSICAL GEOGEAPHY OF THE SEA, AND ITS METEOROLOGY. 



slied receives about twice as much rain as the European. How 

 shall we account for this difference, except upon the supposition 

 that the winds from the Pacific carry (§ 171) more rain than the 

 winds from the Atlantic ? Why should they do this, except for the 

 icebergs and cool streaks already alluded to ? * 



284. It may well be doubted whether the south-westerly winds 

 iimis\'!>'tS''up ""^ — which are the prevailing winds in this part of 

 and transport, lor tho Atlantic — Carry into the interior of Europe 

 and America, va°^^ mucli morc moisturo than they bring with them 

 ^^^"'''^'^ into the Atlantic. They enter it with a mean 

 annual temperature not far from 60^, and with an average dew-point 

 of about 55^. They leave it at a mean temperatm^e varying from 

 60^ to 40^, according to the latitude in which they reach the shore, 

 and consequently with an average dew-point 7iot higher than the 

 mean temperature. Classifying the vrinds of this part of the ocean 

 according to the halves of the horizon as east and west, the mean 

 of 44,999 observations in the log-books of the Observatory shows 

 that, on the average, the Avest winds blow annually 230 and the 

 east v/inds 122 days. 



285. Taking all these facts and circumstances into considera- 

 The vapour-strings for tiou, and without pretending to determine how 

 the A^tlanti^J^ocean"^ much of the watcr whicli the rivers of America and 

 Em'ope carry into this part of the ocean, comes from it again, we 

 may with confidence assume that the A\^nds do not get vapour 

 enough from this part of the ocean to give rain to Europe, to the 

 Mississippi Valley, to om- Atlantic slopes, and the western half 

 of Asiatic Eussia. We have authority for this conclusion, just as 

 we have authority to say that the evaporation ffom the ]\Iediter- 

 ranean is greater in amount than the volume of water discharged 

 into it again by the rivers and the rains ; only in this case the re- 

 verse takes place, for the rivers empty more water into the At- 

 lantic than the w^inds carry from it. This fact also is confirmed by 

 the hydrometer, for it shows that the water of the North Atlantic 

 is, parallel for parallel, lighter than water in the Southern Ocean. 



286. The inference, then, from all this is, that the place in the 

 The places in the sea sca (§ 276) wlienco comc the watcrs of the Missis- 

 riverTonh^Vonh, sippi and other great rivers of the northern hemi- 

 S^crosSi^atThe^ sphoro is to be found in these southern oceans, and 

 calm belts. the chauuels by which they come are to be searched 

 out aloft, in the upper cmTents of the air. Thus we bring evi- 



♦ Keith Johnston, " Physical Atlas." 



