152 Mr Lawson on the Trade-Winds at Bar dadoes. 



ESE., though slight, with a current above from E. ; at 3 P.M. 

 SE., with currents from ESE. and ENE., mixed up toge- 

 ther, overlying it. The north-easterly direction of the wind, 

 early in the morning, on these days, shewed the general ten- 

 dency of the lower portions of the atmosphere to move to the 

 southward ; and hence the operation of those causes which 

 could produce this. On each, towards 9 A.M., the direction 

 changed to SE. or ESE., and (except on the 15th) continued so 

 until towards evening, when it again backed to the north-east- 

 ward. Now the wind being from the NE. all night, an ac- 

 cumulation of the lower portions of the atmosphere to the 

 southward of the island must have been gradually taking place, 

 which was facilitated by the diminished velocity of the cur- 

 rents usually produced in it by the heat of the sun. Under 

 such circumstances, the rapid increase of temperature which 

 occurs after sunrise,* especially over the land, would soon 

 cause ascending currents in the atmosphere ; but these would 

 obviously take place at a point where the superincumbent 

 weight was least, and when there was least resistance to their 

 passing oif to the northward, or, in other words, towards the 

 outer margin of the accumulation rather than towards its 

 centre. To the southward of this point, the winds would be 

 from the south-eastward (21.) Such seems to be the ration- 

 ale of the above changes, which, though very complicated, and 

 apparently contradictory, nevertheless admit of complete ex- 

 planation by recognised physical laws. 



38. The sun's declination on the 17th and 18th September 

 was about 2° N. The moon's declination on these days 15° 

 and 20° S. respectively, and her hours of transit 1*^ 49™ P.M., 

 and 2^ 89^'^ a.m. The wind at 5 a.m. on the 17<^h was E., 

 with a current from SE. above ; at 9 NE.. a fine breeze ; at 

 3 P.M. ENE., fresh ; and at 9 ENE., fine. On the 18th it 

 was, at 5 A.M., E., fine, with a current from SSE. above; at 



* The diurnal curve of temperature, at Barbadoes, reaches its lowest 

 point about 6 A.M., and crosses the line of mean temperature about 7*" 

 46° A.M. See Observations on the Temperature, &c., of the Atmosphere 

 at Barbadoes, Edin. New Phil. Journal, June 1843. 



