GENEEAL DIEECTION OF CYCLONES. 291 



Ocean, and are separated from one another by unequal and tortuous 

 straits, cannot fail greatly to disturb tbe normal condition of the 

 winds,* and to produce a great number of storms and hurricanes often 

 confounded under the general name of typhoons. On the other hand, 

 on the Eastern Pacific, where the trade-winds blow with so much regu- 

 larity, hurricanes properly so-called are very rare. They have only 

 been observed on the eastern coasts of Mexico. 



While the cyclone developes its vast curves in the equatorial 

 regions, the entire whirlwind must lean forward, for the upper strata 

 carried aw^ay in the hurricane find much less resistance in the air 

 than the lower strata find above the ground and the surface of the sea. 

 The whole of the storm may, therefore, be compared to an immense 

 wheel, revolving horizontally over the globe, and pressing the earth 

 most strongly with its anterior part. Nevertheless, in extending 

 themselves in large spirals in the two temperate zones of the north 

 and south, the hurricanes become gradually subject to such modifica- 

 tions in opposite directions, and present apparent irregularities so 

 considerable that they seem at first to obey other laws. Instead 

 of leaning forward, one would say, on the contrary, that a real 

 vacuum, incessantly enlarging, was opened on this side of the whirl- 

 wind. Thus, as is proved by more than 300,000 observations made in 

 the North Atlantic, on board American, English, and Dutch ships, 

 and carefully compared by Messrs Andrau and Yan Asperen,t the 

 winds from the north, which have passed the thirtieth degree of 

 north latitude, are almost always w^anting in the spirals of cyclones. 

 In proportion as the meteor is developed towards the pole, the tran- 

 quil zone of the hurricane increases. The winds from the south and 

 from the east diminish by degrees in frequency and in intensity, 

 they then disappear completely. Finally, from the 50th to the 

 60th degree of latitude the rotation of the cyclone is represented 

 only by winds from the north-west, west, and south-west. One 

 might say that only half the hurricane remains. To the south 

 of the equator similar phenomena occur in inverse order, and every 

 successive curve in the spiral of the storms presents in its southern 

 convexity a greater or smaller break according to the height of latitude. 

 Fig. 117 may explain the modifications which the cyclones experi- 

 ence while proceeding from the tropical regions towards the poles 

 severally. :J: 



The fact that in the northern hemisphere the partial winds of the 



♦ See above, p. 256. f Be Wet der Stromen. 1862. 



X Mittheilimgen von Fetermann, t. xi. 1862. 



u 2 



