368 THE PHYSICAL GEOGRAPHY OF THE SEA. 



1020. This reasoning is suggested not only by the facts and 

 circumstances already stated as well known, but it derives addi- 

 tional plausibility for correctness by the low barometer of these 

 regions. 



In the equatorial calm belts the mean barometric pressure is 

 about 0.2 inch less than it is in the trade-winds, and this diminu- 

 tion of pressure is enough to create a perpetual influx of the air 

 from either side, and to produce the trade-winds. Off Cape Horn 

 the mean barometric pressure* is 0.75 inch less than in the trade- 

 wind regions. This is for the parallel say of 57° — 8° S. Accord- 

 ing to the mean of 2472 barometric observations made along that 

 part only of the route to Australia which lies between the merid- 

 ians of the Cape of Good Hope and Melbourne, the mean baro- 

 metric pressure on the polar side of 42° S. has been shown by 

 Lieutenant Yan Gogh, of the Dutch navy, to be 0.33 inch less than 

 it is in the trade-winds. The mean pressure in this part of the 

 South Indian Ocean is, under winds with easting in them, 29.8 

 inches; ditto, imder winds with westing, 29.6 inches; this gives 

 a supposed mean pressure in the polar calms of 29.7 inches. 



To what, if not to the effects of the condensation of vapor borne 

 by those surcharged winds and to the immense precipitation in 

 the Austral regions, shall we ascribe this diminution of the at- 

 mospherical pressure in high south latitudes ? It is not so in high 

 north latitudes, except about the Aleutian Islands of the Pacific, 

 where the sea to windward is also wide, and where precipitation 

 is frequent but not so heavy. The steady flow of " brave" winds 

 toward the south would seem to call for a combination of phys- 

 ical conditions about their stopping-place exceedingly favorable 

 to rapid and heavy and constant precipitation. The rain-fall at 

 Cherraponjie and on the slopes of the Patagonian Andes reminds 

 us what those conditions are.. There, mountain masses seem to 

 perform in the chambers of the upper air the office which the jet 

 of cold water does for the exhausted steam in the condenser of 

 the engine. The presence of land, not water, about this S. polar 

 stopping-place is therefore suggested ; for the sea is not so flxvor- 

 able as the mountains are for aqueous condensation. 



By the terms in which our proposition has been stated, and by 



* Maury's Sailing Directions, Gth cd., 1854, p. 692; ditto, 8th ed,, 1859, vol. ii., p. 

 450. 



