126 On the Climate of the Canary Islands, 



character of the zone without the tropics, by the general pre- 

 valence of south-westerly winds. 



These islands are just within that distance from the continent 

 of Africa, which enables them to present highly interesting 

 examples of the gradation in which the true direction of the 

 trade-wind (that is to say, the direction in which it ought 

 to blow, from the general causes wkich occasion it) is 

 deflected from the influence, and in proportion to the vicinity 

 of a great continent. Within sight of the coast of Africa the 

 wind is found N. by E. ; at Lancerote and Fuertaventura, 

 N.N.E.; at Canary, N.E.; at TenerifFe, N. E. by E. ; and 

 the influence of the continent ceases to be perceptible at Palma. 

 At all seasons of the year, even when the N.E. Trade is strongest 

 in the lower regions of the atmosphere, the S.W. current, or the 

 general flow of the atmosphere in the upper regions from the 

 equator towards the pole, is experienced by ascending the high 

 land of Teneriffe, and of other islands in the group. Evidence 

 is thus afforded of the steady prevalence of that upper current, 

 the cause of which has been so satisfactorily explained by Mr. 

 Daniell, and of which the existence had been also manifested 

 by the phenomena of the fall to windward of the ashes of the 

 volcano of St. Vincent's, quoted by M. von Buch, from Mr. 

 Daniell's Essays. In proportion as the sun advances to the 

 southward of the line in autumn, the limit of the trade-wind 

 towards the north progressively recedes, following the sun. 

 Thus, the N.E. trade, which, in the height of summer, reaches 

 even the coast of Portugal, fails there, while it yet prevails at 

 Madeira ; and, in like manner, fails at Madeira, while it still 

 blows at the Canaries. Several very remarkable phenomena ob- 

 served at the Canary Islands, appear to justify Mr. Von Buch's 

 opinion that the N. E. trade-wind does not flow parallel to the 

 surface of the earth, but that it has a gradual ascent in its 

 progress southwards. It seems difficult otherwise to ex- 

 plain the great extent of lee occasioned by the several islands, 

 which has been carefully and accurately examined at each. At 

 Canary the lee is from twenty to twenty-five sea miles ; at 

 Teneriffe, fifteen ; at Gomera, ten ; and at Palma, thirty sea 

 miles. The distance to which the lee extends is well defined 

 by the breaking of the sea upon the smooth water, with so 



