214 Mr. W. Brown on the Storms of Tropical Latitudes. 



in this state of continual change the storm progresses, or rather 

 recedes towards north. But air flowing with such rapidity 

 from slower to quicker moving circles of latitude, and its ve- 

 locity being gained in the upper regions of the atmosphere 

 where it is little exposed to friction, will arrive with a rate of 

 motion from west to east in the direction of that of the earth's 

 revolution, muchness than the surface of the earth upon which 

 it falls; that is with an impulse from east to west, and hence 

 the great easterly deflection of the north wind at the onset of 

 the hurricane. 



The effect of this latter force, however, on the progressive 

 motion of the storm is different from that just considered, be- 

 cause in this case there is a constantly sustained impulse 

 from east to west, causing it to advance in that direction, al- 

 though the resistance of the air on the west of the storm and 

 the rarefaction produced on the east of it occasion the rate of 

 its progress to be much less than the velocity of the wind at 

 the eastern portion of the hurricane, due to this impulse. 



Thus then the progressive motion being compounded of two 

 motions, the one towards north and the other towards west, — 

 the latter prevailing at first, the storm advances in a direction, 

 the resultant of these or towards west-north-west, as observed 

 by Redfield, and which continues to be its direction until it be- 

 gins to change its character on approaching the latitude of 30°. 



Supposing then the course of the wind to be that above 

 Fig. 2. 



w.N.w. 



E.S.E. 



described, its direction at the various parts of the hurricane 

 will be somewhat as represented in fig. 2, though the easterly 

 will be the predominating deflection of the northern current; 

 the resistance of the air on the west may cause the wind, after 

 some rarefaction has been produced, to become in some de- 

 gree westerly on that side ; an effect which will ensue in a yet 

 greater degree on the return of the air in the second portion 

 of the storm or southern current; to which the friction of the 

 earth in its first progress towards south, together with the re- 



