Ocean rainfall : with charts and tables, 1864-1875 / by W.G. Black.

  • Black, William George, 1857-1932.
Date:
[1878]
Catalogue details

Licence: Public Domain Mark

Credit: Ocean rainfall : with charts and tables, 1864-1875 / by W.G. Black. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    10/28 (page 4)
    The month of April (South Autumn) had the least rainfall (17-68 inches), and the month of August (South Winter) 35 inches, the most wet days in the Southern Hemisphere. The least amount of rainfall in the Northern Hemisphere occurred in March, -68 inch (North Spring), and the least number of wet days, 5, in March, also. The least amount of rain in the Southern Hemisphere was •40 inch in October (South Spring), with only 1 wet day in October, also. The Spring may therefore be assumed to be the period of the minimum of rainfall at sea, and the Autumn that of its greatest prevalence, in either Hemisphere at different seasons, but at simultaneous periods of the whole year. The chart of the curves for the varying quantities of rainfall, wet days, and rates per diem showed that there was a greater convergence of the lines to minimum degrees for the four months — November, December, January, and February; but that in March they began to diverge remark- ably and to undergo maximum oscillations up and down till October, when they again subsided to an equilibrium of parallelism. The rates of rainfall seemed to vary according to the greater or lesser quantity of rain falling; and in the Northern Hemisphere was of least rate, -136 inch, in March (North Spring), and highest in September, *789 inch (North Autumn). In the Southern Hemisphere the rate was least in July, '167 inch (South Winter), and highest, -370 inch, in April (South Autumn). The curves of wet days seemed to oscillate even more than the curves of rainfall, and to vary in inverse proportion in either Hemisphere, so that when there were fewer wet days in the Northern Hemisphere, there were more in the Southern Hemisphere; and, on the other hand, when there were more wet days in any season in the Northern Hemisphere, there were fewer in the Southern Hemisphere at the corresponding period of the year. In reference to latitudes, the heaviest rainfall was found in the first 7° north of the equator, the demarcation being well defined north and south of this belt—the amounts being 41*72 inches of rain, 65 wet days, and -642 inch of rate per wet day, and 6-00 inches per degree of latitude, and this may be called the equatorial fain belt. The next belts or regions of prevalence fell between 12°-18° north, and the amounts were 18‘38 inches of rain, 22 wet days, and ’83 inch of rate, and 2-62 inches per degree of latitude ; and in the Southern Hemi- sphere the belt lay between 13°-20° south latitude, and the amounts were 23'94 inches of rain, 44 wet days and -540 inch of rate, and 2-99 inches per degree of latitude, and these may bo called the north and south tropical rain belts. These rains seemed chiefly to be dependent on the greater prevalence of storms, squalls, and cyclones in these regions in both Hemispheres; while the former were of the more special tropical nature, connected with condensation of the super-saturation of the air with vapour. An increase, again, of rain took placo in the regions of the Northern counter trades or brave west winds, but with more drizzly or continuous