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From the PuocEEDiNos of tiik Ameiucan AssoriATioN for the Advancement OF SCIENCE, Vol. XXXI, iMontrciil Meeting, August, 1882. PRINTED AT THE SALEM PRESS, SALEM, MASS. 1883. tu CO in tv\ tei tli( be up su va or ail CURRENTS OF AIR AND OCEAN ; BY J. b. HURLBERT. 367 Currents of Air and Ocean in connection with Climates, Regions of Summer Rains and Summer Droughts. By J. Beaufort IIurerert, of Ottawa, Canada. lABSTUACT] The prevailing winds in the north temperate zone are from southwest towards the nortlieast. This great ciu'ient of air may be said to he constant north of latitude 85°. In the upper roaion of the air it blows nearly every day in the year from some point near the southwest towards the northeast. With a constant movement of the air in high altitudes from the southwest there must be a return current from the north towards the southwest, as there are counter cnirents in tiie ocean ; but these polar winds near the surface of the earth blow from all the colder points of the compass. The warm currents of air and water falling upon westein coasts, and aerial currents passing over the continents, elevate the tem- l)eratures of the western parts of the continents, while the cold cu'-rents pressing upon eastern shores lower the temperatures tlicre. The mean temperature of the Gulf stream in the Gulf of Mexico is 80° Fahrenheit ; its maximum temperature is 86°, or 5)° al)ove the ocean temperature due the latitude. Increasing its latitude 10°, it loses two degrees of heat, and after running 3,000 miles towards the north still preserves the temperature of summer. With this temperature it crosses the fortieth degree of north lati- tude, and cpreading out for thousands of square leagues over the cold waters of the ocean, does much to mitigate the rigors of winter in Europe. When it strikes the British islands it divides into two parts, the main current going to the I'olar sea, the other en- tering the Bay of Bi.>icay. It has been estimated that tlie quantity of heat discliarged over the Atlantic, from the waters of tlio Gulf streau) in winter, would be sufficient to raise the whole column of atniosijhere which rests upon France and the British islands from the freezing j)oint to summer heat. Every western wind which blows (and the pre- vailing winds are from the west or from some {)oint near the west or southwest in this part of the ocean) crosses the Gulf stream and carries with it a i)ortion of its heat, discharging it in its pas- 3G8 CURRENTS OF AIR AND OCKAN ; sao-e ovor Europe. Tlie isotlierm.il linos of 60° tind 55°, starting from the parallel of 40° on the American coast, run in a north- easterly direction, retaining nearly the same oceanic temperature on the European side in latitude 55° and 60° as exists on the American coast in latitude 40°. In the Pacific there are tropic and arctic currents like those in the Atlantic, and from similar causes. The Japan stream, or Kuro-Sivvo — black stream — a name derived from the deep blue color of its waters, flows from the southeast of Asia in a north- easterly direction, falling upon the western coast of North Amer- ica. This stream, flowing many thousand miles further than the Atlantic tropic ciwrent, is not so hot nor its littoral waters so cold as those in the Atlantic, but it spreads over the entire racific coast (^f Canada. These two currents in the Pacific — the arctic and tropical — produce similar effects to those in the Atlantic; the one warming the western coast of North America, in high latitudes, and the other cooling the eastern shores of Asia. Through the agency of these two cuirents in the Atlantic, the western countries of En rope are much warmer than the eastern parts of America in simiUsr latitudes ; the difference being about eight degrees in latitude 41° ; eleven and a half in latitude 51°; and twenty-five in latitude 58°. Similar causes in operation in the Pacific ocean give an equal elevation of the temperature of the western coasts of America over the eastern coasts of Asia in the same latitudes — the arctic currents chilling the one and the tropi- cal currents warming the other. From Vancouver in latitude 49° to Sitka in 57°, the summer tem- peratures are as high and as uniform as in the west of Europe, ex'-ept where the vicinity of mountains may modify the normal conditions of climate. Sir John Kicliardson says " the climate of Sitka" (on the Pacific coast) " is much warmer than that of Eu- rope in the same parallel" (Arc. Ex., Vol. II, p. 279). The isothermal of G0° for the three summer months rises as high as latitude 68° east of the Rocky mountains in the valley of Mac- kenzie river. Youkon, west of Mackenzie river and within the Arctic circle, latitude 67°, has a July 65° 7', and an August of 60°. In comparing the well known regions of the old world with the less known corresponding parts ol" the new, western coasts with western, eastern with eastern, and interior divisions with interior, > BY .1. BEAUFOUT HURLBEUT. 3fi9 starting a nortli- perature 3 on the thoKO, in ream, or eep blue a iiorth- th Anier- thau tlie ,uters so e Tacilic he arctic \.thintic ; , in higli a. mtic, the e eastern ng about ude 51° ; ration in ire of the ia in the tlie tropi- imer tein- Europe, e normal ;limate of it of Eu- ^s as high y of Mac - (ithin the August of with the asl.s vvitii 1 interior, we iiiid a remarlvul)le similarity in the climates of the two conti- nents. Canton, in China, latitude 23°, has a summer tempei-ature of 82°, and Key West, in Florida, latitude 24°, 32', a summer of 82°. Pekin, latitude 40°, has a summer of 70,° which is only two or three degrees above that of l'liiladel|)hia of the same latitude. JNIangas-aka, Japan, and Charleston, South Caiolina, in the same latitudes, have summers of 80°. London, in the west of Europe, and Vancouver, in the west of North America, in similar lati- tudes, have the same mean summei temperatures, about 6H° ; Sitka, in latitude 57°, Sir .John liichardson says, has a climate nnich warmei' than Europe in the same latitude. The climates of the interior are warmer in sunnner and colder in winter than those on eastern and western coasts, but are some- what similar on both continents, being, however, warmer on the Red, Saskatchewan, and Mackenzie rivers, than in the same par- allels on the eastern continent. The isothermal of 65°, for the three summer months, crosses the lied river ir latitude 50°, and rises on liie Mackenzie to latitude 60°. The summer rains, too, throughout Canada, are similar to those in Euiope in the same latitudes from the Mediterranean to the Arctic, being somewhat uniform during the agricultural months, l)ut more cop.ous in Canada. South of the boumlary between Canada and the United States, west of the Mississippi, are the areas of summer droughts — a rainless, treeless region, similar in position on this continent, and in the character of the country to the desert areas of the old world — the one beginning on the western coasts of Mexico and California, and extending to liritish America on the north, and over half the continent eastward ; the other beginning on the western coast of Africa near the same latitude as the American desert, and extending northeast waid or east by north over Africa, Palestine, Independent Tartary and Manshire Tartary, nine thou- sand miles in the direction of the i)revailing winds. That portion of the North American continent extending from the Atlantic westward more than 2,000 miles in the latitude of Canada, and from the Gulf of Mexico for 1,500 miles northward, is covered with a mixed foiest of conifene and deciduous trees, which is unparalleled in exleiil, and in the variety and value of its woods. These forests, so beautiful and grand in their primitive state, 370 CURUKNTS OK Allt AND OCEAN ; have a valuo qviito indopciidoiit of their inoiioy worth. Tliey have a most poworiul and favorable iiilliience upon the climates of the country, cheek evaporation, and keep the water Ioniser in the soil, thus supplying the roots of plants, feeding tin springs and streams, etc. West of this vast forest, south of the parnllel of 48° or 49°, is the treeless region. The INIississippi may he taken as near the boundary of these two zones marked with such different features, the forest in many places not reaching that river, in others ex- tending beyond it, and again reappearing on tlie l'a.!ilic coast. East of the Mississippi trees appear first along tlie water-courses and on soil--, retentive of moisture, being still abscjit on the up- lands and sandy plains. To the north this immense treeless re- gion runs, in the country of the Upiier INIissonri (longitude 110° west), north of latitude 50°. Tlirotighout these immense areas there is either a total absence of rain in summer, as in the desert parts, or an insuHu!iency, as on the prairies. The grnsses which cover parts of these (hy up in sunnner, but their roots, Ibrming a deep matted sod, have vitality enough to put forth fresh shoots under the rains of spring and autumn ; trees, however, which are withered up by the droughts and arid winds of summer, have no such vitality. Vast portions of America, Africa, Asia and Australi;i, are des- titute of trees, while other equally extensive regions are covered with forests. These treeless zones lie in similar positions on the continents, beginning near the same latitudes on the westcu'ii coasts and running northeastward in the northern hemisphere, and southeastward in the southern, in the direction of the pre- vailing winds. In the OKI World (for Europe, Asia and Africa nmst, on the question of climates, be taken as one body of land) these treeless and mainly desert regions begin on the west coast of Africa, north of the twentieth parallel, and run northeastward or east by north, 9,000 miles over Africa, Palestine, noi-thern Aral)ia, and Inde- pendent Tartary to latitude r)0° in Mongolia, ending in the great desert of Gobi or ]\Ianshire Tartary. In North America we have a similar desert-treeless region, be- o;inninff in old and new California and on the coasts of Mexico (in the same latitudes as the African desert), and extending to the l\[ississii»[)i and beyond it, on the east, and to JJritisii America HV J. BKAUKOItT IIUKLBEKT. 371 111. They (Oimatos of i<(or in the [)rings and ° or 49°, is s near the it features, otlicrs ex- cidc coast, ter-courses on the II p- tieeless re- ritnde 110° ense areas the desert sses which rorniiiiji a esh shoots wiiich are T, liave no ii, are des- ire covered ons on the le western leinisphere, ol' the pre- ust, on the L'se treeless frica, north t by north, and Inde- i the great region, be- of Mexico [tending to ■i\\ America on the north. The winds over tliese desert areas on both conti- nents blow almost invariably in summer from some point near the southwest towards the northeast. These portions of the continents are destitute mainly of summer rains, but have high summer tem- peratures. Upon the modifications caused in these desert areas by the high lands of Mexico and the vast Mediterranean sea we cannot here enter, but may merely state that the mountains of Mexico limit the deserts there, and that great sea north of Africa causes a more humid air in the south of Europe and limits the deserts in that direction ; yet Spain, Italy, Sicily, and the whole country nortlieastward into Hungary, frequently suffer from sum- int V droughts. The reason, as a permanent cause, often assigned for these por- tions of the continent being destitute of trees— namely, the prairie fires — cannot for a moment bear investigation. Fires were naturally suggested to the first rude settlers, to whom the evidence of sight is the chief guide, as the only cause. In many parts of the African, Asiatic and American deserts and prairies there are no fires, still they are treeless. In other coun- tries, fires are as frequent where forests are iiernianeh, or, if burned down, young trees immediately grow up again. The ex- istence of forests over a region 2,000 miles by 1,000, and their failure where, anrl onh/ where, the summer rains fail and the arid winds prevail, ought to have suggested the exi)lanation. That the prairie fires sweeping over extenes of history, desert and treeless on the borders of other equally extensive areas covered vvitli dense for- ests. The climates which have produced these two distinct re- sults over those regions have remained permanent for ages, and will remain permanent in the future, unless changes supervene in the entire solar system ; Init for the calculation of such imaginary phenomena astronomy furnishes no data. We may infer, there- fore, that those conditions of climate — heat and humidity in the one case, and heat and aridity in the other — remaining the same, their etfects — forests and treeless regions — will be permanent expressions of those fixed efficient causes. The attempts to account for the deserts of the Old and New 872 CURRKNTS OF AIR AND OCKAN ; BY J. B. IIURI-BKRT. World by the physical conligtinition of tho continents, have led to many ingenious thcorios. The chief of tliese is the jisstunption tliiit nionnliiiii cli.'iins to tlie west of those rtiinless regions con- dense the vapor brought in the southwest winds, causing lieavy rains on the western sides of tiie mountains, but leaving the winds without vapor east of these mountain chains. The phe- nomena of rain on the west, but none on the east of the Ghauts in Ilindostan and other places, have been taken as suiHcient bases for tiiis theory. Tliat those regions having no summer rains are on similar parts of the continents north and south of tlie equator, both in the eastern and western hemispheres, beginning on western coasts at about the same latitudes ; that there are no mountains west of tiie Desert of Saliara, and the rainless regions in Australia; that the entire coasts of Mexico, old and new California, west of the mountains, are quite as destitute of rain in summer as the regions east ; tiiat those west winds give heavy falls of rain to the north and northeast tliroughout Canada, and in autumn, winter, and early spring, deposit lieavy rain and snow on tiiose interior desert areas cast of tlie Rocky mountains, over which they are said to pass in summer, devoid of vapor, — these and other facts ought to have corrected the erroneous opinions on this subject. That the great southwest currents of air — the tropical currents bring the vapor which falls in rain and snow, is here assumed as admitted, for it is the basis of tiie theory which we are contro- verting. Those vast wastes are, at the season of the year when little or no rain falls, highly heated by the summer suns. The southwest winds passing over these become rarelied, and thus, being capable of sustaining even more vapor than at a lower temperature, retain the humidity with which they have come from the tropics so heavily charged, till they reach the cooler regions, north and northeast, where they are condensed into rain or snow. Hence in summer the line dividing the zones of rain from those of drought is farther to the northeast ; as autumn and winter approach, those highly heated plains gradually cool suillciently to condense the vapors in the southwest winds, which now give heavy depositions of rain and snow. nv. liiive led to [issiiinption ?gioii9 eon- si ii