WIND. 5 



occurring in different localities, create currents, counter-currents, 

 and eddies, which resolve themselves into those cyclonic and anti- 

 cyclonic movements to which the atmosphere seems ever prone. 

 Associated with these we find V-shaped areas of low pressure, 

 " wedges " of high pressure, and so forth. 



Since an ascending current is composed of light air, which is 

 therefore indicated by a low barometer, wind always blows in 

 upon a centre of low pressure. This it does, with but few 

 exceptions, 1 in a spiral form. 



The reverse takes place around areas of high pressure or 

 anti-cyclones. 



Cyclones are analogous to upcast shafts, drawing the air 

 inwards at the bottom, and throwing it outwards at the top ; 



MILES 500 4OO 



Vertical scale one-half. 

 200 100 o 100 200 



400 500 MILES 



FIG. 3, Diagram 2 of mean barometric curve across the centre of the great Cuba hurricane, transversely 

 to its path, October 4 to 7, 1814. The mean barometric curve ou the centre line of the path of 

 the storm appears not to have differed essentially from the above. 



while anti-cyclones are analogous to downcast shafts, drawing 

 the air inwards at the top, and dispersing it outwards at the 

 bottom. 



Cyclones are indicative of bad weather and high winds, and, 

 in the northern hemisphere, revolve in the reverse direction to 

 the hands of a watch ; whereas anti-cyclones are associated 

 with fair, calm weather or light winds, and revolve in the 

 opposite direction. In the southern hemisphere, the direction 

 of rotation, both of cyclones and anti-cyclones, is reversed. 



In Fig. 3, a barometric section of a storm-basin, or cyclonic 

 depression, is indicated. 



The areas of storm-basins are sometimes very great, measur- 

 ing not unfrequently from 1000 to 1500 miles across, and seldom 



1 E.g. the trade winds, monsoons, electrical disturbances, and what are termed 

 " fctraight-line gales." 



2 Copied from Reid's "Law of Storms," p. 312. 



