454 rnYSiCAL geography of the sea, and its meteorology. 



the poles, is, in the northern hemisphere, between the parallels 

 of 25° and 50°. In the southern the field of battle is narrowed 

 down to a single belt (between 35° and 40°) ; here the two winds 

 exactly counterbalance each other. As the seaman proceeds from 

 this medial belt, the winds increase belt for belt very nearly pan 

 :pa88u; on the polar side, the polar winds— on the equatorial, 

 the equatorial winds, gaining more and more in days of annual 

 duration, and more and more in average velocity each. 



853. JiJxtent of the polar indraught.— The fact that the influence 

 of the polar indraught upon the winds should extend from the 

 antarctic to the parallel of 40° S., while that from the arctic is so 

 feeble as scarcely to be felt in 50° N., is indicative enough as to 

 difference in degree of aerial rarefaction over the two regions. 

 The significance of this fact is enhanced by the " brave^'west 

 winds," which, being bound to the place of greatest rarefaction, 

 rush more violently and constantly along to their destination 

 than do the counter-trades of the northern hemisphere. Why 

 should these polar-bound winds of the two hemispheres differ so 

 much in strength and prevalence, unless there be a much more 

 abundant supply of caloric, and, consequently, a higher degree of 

 rarefaction, at one pole than the other ? 



864. TJie rarefaction of the air over polar regions.— In the 

 sonthern hemisphere— and our attention is now directed exclu- 

 sively to that— the polar winds on the south side of 40° are very 

 much stronger than are the equatorial winds on the north side of 

 35° : a fact indicative of a greater degree of rarefaction about the 

 place^of polar calms than we have in the equatorial calm belt. 



855. Barometrical observations.— Th^t such is the case is also 

 suggested by the fact that the indraught into the antarctic calm 

 place is felt (§ 854) at the distance of 50° from the pole all round, 

 while the equatorial indraught is felt no farther than 35° from 

 the equator ; and that such is the case is proved by the barometer. 

 Lieutenant Andrau, of the Meteorological Institute of Utrecht* 

 has furnished us from the Dutch logs with 83,334 observations 

 on the height of the barometer between the parallels of 50° N. 

 and 36° S. at sea. Lieutenants Warley and Young have extracted 

 from the log-books in the Washington Obseivatory, taken at 

 random, 6,945 observations on the barometer south of the 

 parallels of 40° at sea. Dr. Kane has furnished us with the mean 

 height of the barometer in lat. 78° 37' N., according to 12,000 

 hourly obseivations made during his imprisonment of 17 months 



