104 



Notice of some Recent 



[Feb. 



From these tables it is obvious that the height of the 

 barometric column is increased as we recede from the equator, 

 at which part of the earth's surface it appears to assume a sta- 

 tionary elevation, which may be taken as a close approxima- 

 tion to the mean density at the level of the sea. The standard 

 barometric pressure for Britain has usually been considered 

 to be 29*820, while the mean of the lowest heights in the 

 observations previously stated is equivalent to 29*844. 



The mean of eight observations at the Cape of Good Hope 

 gives for the height of the barometer 29'861 inches. 



With regard to the Atlantic Ocean, Schouw sums up his 

 deductions under five heads : — 



1. There is a zone between 0° and 15° possessing an 

 elevated temperature where the rains are periodic, the 

 annual mean of the barometer lying between 337'" and 338". 



2. A zone between 15° and 30°, where steady winds pre- 

 serve the air dry, where rains seldom fall, the barometer 

 being 338 to 339. 



3. In the third zone, between 30° and 45°, the dry winds 

 are interrupted, especially in winter, by the S.E. wind, or 

 returning trade breeze, which takes up the moist and hot 

 air of the torrid zone, and produces aqueous precipitations. 

 The mean barometric pressure is between 339" and 337'". 



4. The fourth zone is comprised between 45° and the 

 polar circle. It receives during the whole year, and espe- 

 cially in summer, the returning trade wind, which, in 

 consequence of its meeting with colder winds, occasions 

 frequent rains. The barometer is 337" to 333*5'". 



5. Beyond the polar circle, in the fifth zone, the mean 

 barometric pressure increases. 



