Atmospherical Phenomena. 267 



inconsiderable, and become greater the more we approach the 

 poles. For there the temperature alters much less with the la- 

 titude than here, and violent movements of the atmosphere are 

 much rarer, owing to the regularity of the trade wind ; hence, 

 when, at the equator, air comes from a point at 20° Lat., it is 

 only a few degrees colder, and thus the barometer rises but 

 little. In our latitudes, on the contrary, air, which comes from 

 a point 20° to the south, is 10° warmer, or even more, than that 

 of our climate, and consequently a considerable depression of 

 the barometer must be the consequence. In winter, when this 

 difference of temperature of places lying in the same meridian, 

 but in different latitudes, is much more considerable than in 

 summer, the movements of the barometer are also much greater 

 than in the warm season of the year, as has been long known 

 to natural philosophers. 



We have thus seen on the one hand, that the temperature 

 and pressure of the air, and on the other the cloudiness and se- 

 renity of the sky, stand in connexion with the direction of the 

 wind ; and therefore it was an easily pardonable error of the 

 older natural philosophers, to ascribe the state of the barome- 

 ter to fine or bad weather. But the barometer is not low du- 

 ring rainy weather because it rains ; but because the south winds 

 blow, which are not only moist, but also at the same time warm. 

 If we had not the Atlantic Ocean to the south-west, but an ex- 

 tensive sandy desert in its stead, the barometer would under 

 these circumstances, still sink, but the sky would be clear. 



lujiuence of the various Winds on the Weather. — In order 

 to point out the influence of the various winds mi the 

 weather, we shall now again go through the points of the 

 compass. If the sky is serene, and a north-east wind is blow- 

 ing, the barometer rises ; the wind brings with it, it is true, dry 

 air, but this is at the same time cold ; and hence if the air was 

 very moist, the vapours would be precipitated, the sky would 

 in a short time be covered with clouds, and rain would fall, 

 and the blue of the sky would appear dark and pure through 

 the apertures in the clouds. If, on the contrary the air was 

 not very moist, it would not be saturated notwithstanding the 

 lowering of the temperature, and the sky would remain clear. 

 If the north-east wind has blown for some time, the vapours 



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