100 GENEEAL OBSERVATIONS ON THE WINDS. 



Verde Islands, and in the Mediterranean, where it is called scirocco dust 

 (as coming from the South). This red dust was found by Ehrenberg to 

 consist of microscopic infusoria and organizations, whose habitat, as far as 

 was knoivn, is in South America. But this argument may be demurred to 

 from the limited extent this dust falls upon compared with the vast area 

 from which it is said to be derived. 



(7.) There is another great difficulty in the reception of this theory, in 

 the great breadth, in some parts, of that intervening band of Calms where 

 these supposed currents are to cross each other. In the Eastern part of 

 the Atlantic it is from 300 to 600 miles in breadth. If this great inter- 

 change of directions were continually going on with such a vast amount of 

 atmosphere, we may safely conclude that the lower strata would not be 

 characterized as they are by the Calms or " Doldrums." 



(8.) The more reasonable argument, in the present state of our know- 

 ledge, is, that the Trade Winds reaching this belt of Calm, by far the 

 greater part of the indraught will rise on its own side, and revert towards 

 the Pole of its own denomination in a precisely opposite direction to that 

 by which it arrived. In the parts of the Equatorial regions where this 

 intervening Calm belt is much narrower, as on the East coast of America, 

 this crossing may take place, and the upper currents pass on towards the 

 Poles of contrary names. At all events, this view of the circulation of the 

 atmosphere will satisfy our present proposition — that every particle of air 

 has been so commingled with the rest, that it produces the universality of 

 character which is demonstrated to exist. As stated before, these theories 

 are practically unimportant to the sailor in his profession, but are highly 

 interesting to him as a subject for observation and reflection.*' 



(9.) It has been held by many that the solar heat, combined with the 

 revolution of the earth, is sufficient to account for the general phenomena 

 of the Winds ; but there are still some difficulties in the way of accounting 

 for some of the periodical winds which are found to recur with great 

 regularity. Mr. Hopkins points out that the Trade Wind at times blows 

 towards areas of great condensation, inferring that a great rain-fall occa- 

 sions a corresppnding indraught.f This view of Mr. Hopkins is modified 

 bv other observations, which lead to the inference that currents of air 

 move around areas of high or low pressure, the latter condition being 

 that which usually attends the greatest rain-fall. This is adverted to 

 presently. 



It is also contended by some that the lowest stratum of the air, having 

 its velocity kept down by friction, generally moves from the Tropical belts 

 of high barometer to the regions of low barometer at the Poles and Equator. J 

 Thus, th-e N.W. and S.W. Anti-Trades constitute under currents toward the 

 Poles, beneath an upper current, also toward the Pole, and a middle return 



• See further on these subjects, Maury's " Physical Geography of the Sea." 



t Mr. Hopkins: "The Atmospheric Changes that produce Rain and Wind ;" also see 



Journal of the Royal Geographical Society, 1856, pp. 158, et seq. See, also, D. Vaughan, 



U.S., in British Association Report, 1860, page ll. 



+ See Professor J. T. Thomson, in Report of the British Association, 1857 ; and Professor 



J. D. Everett, inthesame Journal, 1871, page 54. A vast mass of data is given in Prof essor 



James H. Gofan's "Winds of the Northern Hemisphere," hereafter quoted (page 107). 



