Page:Physical Geography of the Sea and its Meteorology.djvu/202

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176
PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY.

Number of Observations and Mean Height of the Barometer between the Parallels of 78° 37’ N. and 74° S.[1]

North Baromoter. No. South. Barometer. No.
0° and 5°[fn 1] 29.915 5114 0° and 5° 29.940 3692
5° and 10° 29.922 5343 5° and 10° 29.981 3924
10° and 15° 29.964 4496 10° and 15° .30.028 4166
15° and 20° 30.018 3592 15° and 20° 30.060 4248
20° and 25° 30.081 3816 20° and 25° 30.102 4536
25° and 30° 30.149 4302 25° and 30° 30.095 4780
30° and 35° 30.210 4989 30° and 35°[fn 1] 30.052 6970
35° and 40° 30.124 5103 42° 53′ 29.90[fn 2]
40° and 45° 30.077 5898 45° 0′ 29.66[fn 3]
45° and 50° 30.060 8282 49° 08′ 29.47
51° 29' 29.99[fn 4]   51° 33' 29.50
59° 51′ 29.88[fn 5]   54° 26’ 29.35
78° 37’ 29.759[fn 6]   55° 52' 29.36
      60°0’ 29.11
      66° 0′ 29.08
      74°0′ 28.93  
  1. ↑ 1.0 1.1 From 50° N. to 36° S. the observations are the mean of 83,334 taken from " Maandelijksche Zeilaanwijzingen van Java naar Let Kanaal Koninklijk Nederlandsch Meteorologisch Instituut, 1859."
  2. ↑ Hobart Town; mean of 10 years' observations.
  3. ↑ Sir J. C. Ross ; " Erebus and Terror."
  4. ↑ Greenwich; mean of 4 years' observations.
  5. ↑ St. Petersburg; mean of 10 years' observations.
  6. ↑ Dr Kane; 12,000 observations (mean of 17 months' observation)

away from the austral regions, just as the vapour that is formed in the real steam-boiler expels the air from it. This difference of atmosphere over the two halves of the globe, as indicated by the barometer, is very suggestive.

364. A standard of comparison for the barometer at sea.—Admiral Fitzroy has also reduced from the abstract logs in the Meteorological Department of the Board of Trade in London a great number of barometrical observations. He has discovered the near the parallel of 5° N. in the Atlantic Ocean the pressure of the atmosphere is so uniform as to afford navigators a natural standard by which, out there at sea, they may, as they pass to and fro, compare their barometers. This pressure is said to be so uniform, that after allowing for the six-hourly fluctuations, the mariner may detect any error in his barometer amounting to the two or three thousandth part of an inch.

365. South-east trade-winds having no moisture traced over into

  1. ↑ Below the parallels of 50° N. and 36° S. the observations are reduced to the temp, of 32° Fahr.
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