24 THE METEOROLOGY OF JAMAICA 



by Admiral Beaufort. But if we were to adopt this scale in 

 Jamaica, all our land-breezes would be put down as calms ; 

 and indeed it is evident that this scale is not sufficiently 

 refined for wind on shore with regard to the smaller velocities. 

 The scale used in the United States of America has been 

 adopted in Jamaica ; it is given in Table XV. 



The explanation of the sea and land breezes is very 

 simple. During the daytime the land is heated by the sun, 

 while the sea hardly changes its temperature ; consequently 

 the air above the land rises and expands; the barometric 

 pressure is diminished; and the air from the sea flows in 

 from all directions to replace the ascending currents. During 

 the night the land is cooled by radiation, and the surface 

 currents of air move from the land outwards in all directions. 

 But these breezes in Jamaica are modified by the general 

 easterly drift of the air over the Caribbean Sea ; and the 

 results are strong north-east sea-breezes on the north side of 

 the island, and strong south-east sea-breezes on the south side. 



The sea-breeze sets in about 10 a.m. and lasts until about 

 5 p.m. It is strongest at the level of the sea, and diminished 

 with the elevation ; so that at an elevation of 1000 feet it is 

 hardly felt.* 



Table XVI. gives the diurnal variation of the wind at 

 Kingston from instruments placed on the roof of the Public 

 Works Office. The constancy from 9 p.m. through the night 

 to 8 a.m. is very remarkable, and there is no lull or calm at 

 all between the south-east sea-breeze and the north land- 

 breeze. Table XVII. gives the annual variation of the wind 

 at Kingston. 



The prevailing easterly winds over Jamaica and the West 

 Indies generally are due to the great anticyclone which 

 exists over the North Atlantic, and the position of whose 

 centre is on an average in lat. 30, long. 30 They are, of 

 course, part of the trade-wind system ; and to study them 

 we must get well above the sea-breeze limit. At both the 

 Kempshot observatory and at the Cinchona Plantation the 

 average direction is east ; but at the former place the 

 direction varies with the time of the year east-north-east or 

 even north-east in winter, and east-south-east or even south- 



* At Iver, St. Andrew, elevation 1700 or 1800 feet, it is distinctly felt. 



