142 Mr Lawson on the Trade-Winds at Barbadoes. 



periods of conjunction and opposition, and would vary between 

 these according to their differences in declination and angular 

 distance. But at all times, the effect of the sun's attraction 

 being less than that of the moon, and being complicated with 

 his calorific influence on the superior meridian at least, will 

 be more obscure, and will contribute less to the modification 

 of the winds. The influence of the moon, likewise, will be 

 greater in perigee than in apogee. 



19. The effect will differ considerably, according as the point 

 at which the accumulation takes place is situated, between the 

 equatorial limits of the trades, or within the trades themselves. 

 In the former case, especially about the time of new and full 

 moon, the trade will be at first accelerated, and the equatorial 

 current retarded, on her passing both the upper and lower 

 meridians, which is in accordance with the observations of Mr 

 Lefroy, noticed above (16) ; but, on the accumulation of air 

 between these limits becoming considerable, its gravity will 

 not only prevent any farther inflowing, but, when assisted by 

 the solar heat acting on the land and sea on either side, 

 actually cause a returning current from its outer margin to- 

 wards the poles. In the latter, supposing the moon's declin- 

 ation to be 20° N. for instance, her attraction would retard 

 the NE. trade-wind to the southward of that latitude, and ac- 

 celerate it to the northward of it ; and it would accelerate the 

 equatorial current to the southward, and retard it to the 

 northward, while it accelerated the SE. trade throughout, 

 and equally retarded the equatorial current on that side of the 

 equator. A similar arrangement would occur on the inferior 

 meridian, only it would be reversed, the NE. trade being 

 there affected as the SE. had been on the superior meridian, 

 and vice versa ; and this reversal would also occur on the upper 

 meridian, on the sun and moon passing the lower. 



20. If the attraction of the sun and moon have any influence 

 at all on the direction and force of the winds within the tro- 

 pics, these changes must be manifested whenever the distribu- 

 tion of temperature in the atmosphere is such as to admit of it. 

 Such was really found to be the case ; for, during the cooler 

 months in the West Indies, when the sun was to the south of 

 the equator, and the moon passed the meridian about the 



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