488 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



violently and constantly along to their destination tlian do tlie 

 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 liigher degi^ee of rarefaction, at "^one 

 pole than the other ? 



854. In the southern hemisphere — and om- attention is now 

 The rarefaction of the directed oxclusively to that — the polar winds on the 

 airoverpoiarregions. gQ^^h sido 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. That such is the case is also suggested by the fact that the 

 Barometrical obsei-va- indraught into the autarctic 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 equa- 

 tor ; and that such is the case is proved by the barometer. Lieu- 

 tenant Andi'au, of the Meteorological Institute of Utrecht, has 

 fm-nished 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 Y/ashington Observatory, taken at ran- 

 dom, 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 m lat. 78° 37' N., accordmg to 12,000 hourly observa- 

 tions made during his imprisonment of 17 months in the ice there. 

 The annals of Greenmch and St. Petersbm-g give us the mean 

 height of the barometer in lat. 51° 29' N. according to three years' 

 observations, and in lat. 59° 51' N. according to ten years of ob- 

 servation. Such are the sources of the table, p. 466. 



856. Captains Wilkes, U. S. N., and Clarke Boss, E.N., both, 

 The low austral ba- duriug their cxpeditious to the South Seas in 1839-41, 

 rometer. ]^g^^ occasiou to remark upon the apparent defici- 

 ency of atmosphere over the extra-tropical regions of the southern 

 hemisphere ; and the low barometer off Cape Horn had attracted 

 the attention of navigators at an early day. I observed it in 

 1831 when doubling the Cape as master of the IT. S. S. " Falmouth," 

 and wrote a paper on it, which was published in the American 

 Joui'nal of Science in 1833-4. The more abundant materials which 

 the abstract lo,^s since placed within my reach have enabled me to go 

 more fully into this subject than it was possible to do while I was 



