THE SMITHSONIAN INSTITUTION. 189 



more common in summer than in winter ; the following are his reduo 

 tions : 



Between lat.320 and 330, 9 stations, 8 ^j^j^^ N. Avinds, 3.06. - S. to W.S.W. 7.77 days. 



year s average : S Carolina, Geor- \ j^^, j^_ ^.^^^ j g3_ _ g ^^ ^^ ^^ ^^ -^^ ^^^^_ 



gia, Alabama, and Mississippi. ) -^ 



Delaware, Maryland, and Eastern Vir- / Jan., N. winds, 2.81. — S. to W.S.W. 6.29 days. 



ginia. ^ July, N. winds, 1.05 — S. to W.S.W. 13.00 days. 



New England States south of latitude ) Jan., N. winds, 3.55. — S. to W.S.W. 6.60 days. 



450, 49 stations, 5 years. ) July, N. winds, 1.44. — S. to W.S.W. 15.74 days. 



Between 450 and 50O latitude : Iowa, 1 j^^ ^_ ^^.^^^ 4.17. - S. to W.S.W. 5.73 days. 



Wisconsin, Michigan Canada, and \ j^^, j^_ ^^,.^^^ ^ ^.^ _ g ^^ ^.S.W. 10.77 days. 



Maine, 10 stations, 17 years. ) 



Total north wind 19.74 Total south wind. 76.06 



I quite concur in the opinion^ first entertained by Yolney, that the 

 summer south winds of the United States are chiefly supplied from the 

 trade winds of the tropics. To this wind is to be ascribed the amazing 

 fertility of the climate for sugar, cotton, Indian corn, and tobacco. The 

 isthmus which connects North and South America is too high to allow 

 the trade winds to cross into the Pacific ocean ; and in summer they ap- 

 pear to be frequently directed northwards by this great natural wall, 

 and find their way across the Gulf of Mexico, and spread out as a 

 surface current loaded with moisture over the Mississippi valley and 

 the eastern seaboard States. If the isthmus which connects the two 

 continents had been sufficiently low to allow the trade winds to cross 

 into the Pacific, the valley of the Mississippi would have had, in all 

 probability, a much less productive summer climate, resembling that 

 of the south of Europe or the north of Africa. 



I may here mention that there is only an extremely limited area in 

 Europe which has sufficient summer rains, with the requisite tempera- 

 ture, to grow Indian corn, and that there are no cotton or sugar regions. 

 The summers of Spain, except on the northwest of the country, are 

 usually so very dry that little Indian corn can be grown without arti- 

 ficial watering. The productive powers of the soil are almost entirely 

 centred in the valleys, which are irrigated by the melting of the snow 

 of the mountains. 



The summers of Italy are also too dr}', and the melting of the snow 

 on the Alps is essential to the fertility of Lombardy. The largest and 

 best region for Indian corn in Europe is in the south and east of France. 

 Mr. Marsh, in his introductory lecture here, told us that for three 

 months rain did not fall in summer at Constantinople. In Palestine, 

 " rain in summer" is still as rare as the " snow in harvest." In the valley 

 of the lower Nile, a shower of rain is a remarkable phenomenon ; the 

 overflowings of the river serve for the growth of wheat, but no Indian 

 corn or millet can be had without laborious irrigation ; accordingly, fifty 

 thousand oxen are employed in summer to draw water for this purpose. 

 In upper Egypt no crops of any kind are obtained without the same 

 appliance ; and during a low current in the river the peasants are obliged 

 to raise the water upwards of forty feet. When we reflect on these 

 facts, the great fertility of the summer climate of North America, east 

 of the Rocky Mountains, is very surprising. The aridity of the Medi- 

 terranean shores is owing to the prevalence of northerly winds ; while 

 the fertility of the United Spates is owing to the prevalence of those 



