308 OUTLINES OF NATURAL PHILOSOPHY. 



in determining the motion to be wholly from the 

 east. 



417. The attractions of the sun and moon have 

 sometimes been considered as among the general 

 causes of the winds. They have no doubt a ten- 

 dency to produce in the atmosphere an undulation 

 backwards and forwards, like the tides which they 

 cause in the ocean. It does not appear, however, 

 that they could produce any continued progressive 

 motion of the air, similar to that of the Trade 

 Winds. Their effects also, are too minute to be 

 perceived, amid the action of so many more power- 

 ful causes. 



D'ALEMBERT in his Recherches sur les Causes Ge- 

 nerales des Vents, has treated of the forces of the 

 sun and moon to produce currents in the atmo- 

 sphere. His essay is more remarkable for the re- 

 source and ingenuity it displays in the management 

 of the calculus, than for the physical conclusions to 

 which it leads. 



418. The superior current above described, re- 

 stores the air carried from the higher latitudes to 

 the lower, with such a degree of equality, that the 

 average weight of the atmosphere, as measured by 

 the barometer, is nearly the same in all climates. 

 This restoration is, however, subject to great local 

 and temporary irregularities, from the different 



degrees 



