﻿and Fluctuations. 439 



endeavouring to fly from the centre of rotation ; far beyond the 

 limits of the storm the air is thus compressed, and has its elastic 

 force disturbed to an extent that is at once noticed as breaking 

 the general regularity of barometric readings within the tropics*. 

 A still more remarkable phenomenon is the formation of one 

 or several smaller whirlwinds in the body of the larger one. 

 The wind pressing onwards in confused violence, and being un- 

 able to drive some slower-moving mass before it, is turned to- 

 wards the centre of lowest pressure and thrown into a whirl 

 which rotates in the same direction as the parent storm, but in 

 which the force and velocity are intensified to an extreme 

 degree f. The velocity is indeed so great that the ascensional 

 motion generated is frequently communicated even to the water 

 of the sea, which rises in vertical and rapidly whirling columns; 

 these travel, for the most part, with the wind of the hurricane, 

 carried in its circling course along whichever quarter they are 

 formed in ; but in exceptional cases they have been known to 

 travel in the same direction as the body of the storm, irrespec- 

 tive of the particular and temporary wind at the place where 

 they originate. And the constancy with which cyclones or re- 

 volving storms in every known locality follow a specified track 

 from which they rarely deviate, such tracks leading in different 

 parts of the world to very different points of the compass, but 

 always in the direction of the prevailing wind, seems to me 

 the phenomenon which, more almost than any other, establishes 

 the value of what I would call the mechanical, in contradistinction 

 to the meteorological agencies. This, however, has been over- 

 looked by meteorologists, who, misled by the name North-East 

 Trade in the North Atlantic, or South-East Trade in the South 

 Indian Ocean, have described the cyclones of these districts as 

 travelling (towards the W.N.W. or W.S.W.) at right angles, or 

 nearly at right angles, to the course of the Trade- Winds, and 

 have therefore insisted on the necessity of some cause for the 

 progression quite independent of the prevailing wind ; and 

 though no such cause has been suggested as accounting for 

 this imaginary movement of tropical hurricanes athwart the 

 Trade-Winds, it has been maintained that in our own latitudes 

 the storms move from west to east entirely by reason of the 

 feeble pressure of the warm and moist air on the east side of 

 the revolution, where the wind is southerly, yielding to the 

 superior pressure of the denser, colder, drier air on the west 

 side, where the wind is northerly J. But in every revolving 



* See the barometric readings on board the ' Buzzard/ shown on the 

 Admiralty Chart of the Nassau hurricane of 1866. 



t Piddington, « Sailor's Horn Book/ 4th edit. pp. 313-315. 

 \ Atlas des Tempetes, p. 21. 



2G2 



