and Astronomical Notices. 173 



may doubtless tend to annihilate errors of this description, 

 but still there may be some of a constant nature, and much 

 valuable time is being lost meanwhile. 



Lieut. Maury's Generalization of the Trade-Wind. — But 

 although I have mentioned these charts to shew how greatly 

 the observed elements might be improved, yet I am happy to 

 be able to mention them as having been the means, even in this 

 imperfect state, of leading their indefatigable compiler, Lieut. 

 Maury, to an extensive generalization, if not, indeed, an import- 

 ant discovery, viz., the circulation of the atmosphere round the 

 whole world by the trade-winds crossing at the equator into 

 the opposite hemispheres, in place of returning to their own 

 poles ; a scheme of the grandest nature in meteorology, and 

 serving apparently to explain some of the hitherto most per- 

 plexing, but at the same time some of the most marked fea- 

 tures in the climate of the globe. 



Generally, then, and as long known, we have our world 

 surrounded on all sides with a film of atmosphere, the action 

 of the sun warming and consequently rarifying the equatorial 

 portion, gives it a tendency to rise up from the surface there, 

 while, to supply the vacuum tlius made, the colder air from 

 the poles rushes in, but the action of gravity preventing the 

 continued accumulation of hot air over the equator, necessi- 

 tates its falling down to the general level, and therefore 

 moving towards the poles from which the air has been drawn ; 

 thus the motions of the atmosphere to and from the equator 

 are explained. 



Secondly, The rotation of the earth being communicated to 

 the atmosphere, the polar body of air, in its passage to the 

 equator, will continually find itself in a parallel of greater 

 rapidity of movement, and will therefore seem to march in 

 the contrary direction, or to blow from the east, while the 

 reverse taking place with equatorial air on its way to the 

 poles, makes it seem to be coming from the west ; and these 

 directions being confounded with those previously existing, 

 give to the northern hemisphere a north-east current going to 

 the equator, and a south-west returning from it, and in the 

 southern hemisphere, similarly a south-reast ^nd north- 

 west. 



