SEA ROUTES, CALM BELTS, AND VARIABLE WINDS. 



359 



the unknown as it does for tlie known regions, the mean height 

 of the barometer would be at the north pole about 29. G, at the 

 south about 28 inches. These lines, N and S, represent what 

 may be called the barometric descent of the counter-trades. 



672. The " brave west winds " — their barometric descent. — The 

 rarefaction of the air in the polar calms is, as we have seen 



LAT 40 



Diagram A. 

 50" 60' 



90 



(§ 667), sufficient to create an indraught all around to the dis- 

 tance of fifty degrees ol latitude from the south pole; also 

 {§ 662) the rarefaction in the belt of equatorial calms, is sufficient 



