§ G58-660. SEA ROUTES, CALM BELTS, ETC. 353 



ogy it may be regarded as a general law, that the tendency of all 

 winds on the surface is to blow from the place where the barom- 

 eter is higher to the place where the barometer is lower. This 

 meteorological law is only a restatement of the dynamical truism 

 about water seeking its own level. 



658. The mean height of the barometer in the calm belts of the 

 The barometer in the tropics is greater (Plate I.) than it is in any other 

 calm belts. latitude. The mean height of the barometer in the 

 equatorial calm belt is less than it is on any other parallel between 

 the tropical and equatorial calm belts. The difference for the 

 calm belt of Cancer is 0.25 inch. This difference is permanent. 

 It is sufficient to put both systems of trade-winds in motion, and 

 to create an indraught of air flowing perpetually toward the equa- 

 torial calm belt from the distance of two thousand miles on each 

 side of it. 



659. In like manner, as we go from either tropical calm belt to- 

 winds with nor;7an(7 ward the ucarcst pole, the barometric pressure be- 



and winds with soti^/i- _ ^ ^p,, ^ . ^ 



ing inthem. comcs Icss and Icss. inc meteorologicai law just 



announced requires the prevailing wind on the polar side of these 

 calm belts to be from them and in the direction of the poles ; and 

 observations (Plate I.) show that such is the case. Dividing the 

 winds in each hemisphere into winds with northing and winds 

 with southing in them, actual observation shows that they balance 

 each other in the southern hemisphere between the parallels of 

 35° and 40°, and in the northern between the parallels of 25° and 

 50° ; that between these parallels the average annual prevalence 

 (>f winds with northing and of winds with southing in them is the 

 same, the difference being so small as to be apparently accident- 

 al ; that, proceeding from the medial band toward the pole, polar- 

 bound winds become more and more prevalent, and proceeding 

 from it toward the equator, equatorial-bound winds become more 

 and more prevalent. Now, in each case, the prevailing winds 

 blow (§ 657) from the high to the low barometer (Plate I.). 



660. The fact of two barometric ridges encircling the earth, as 

 The barometric ridges, thc high baromctcr of the tropical calm belts do, 

 and as they may be called (Plate I.), suggests a place of low ba- 

 rometer on the polar side as naturally as the ascent of a hill on 

 one side suggests to the traveler a descent on the other ; and, had 

 not actual observations revealed the fact, theorv should have taught 



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