270 THE ATMOSPHERE AND METEOROLOGY. 



from the west and those from the east is much greater. According 

 to M. Liaisj it is as seven to three. In. the valley of the Saone 

 and Rhone, the general movement of the winds is from north to 

 south, as if the air were obliged to plunge in the kind of funnel 

 formed by the Yosges, the Jura, and the Alps to the east ; the heights 

 of the Cote d'Or, Beaujolais, and the Cevennes, to the west. It is 

 the same with every secondary valley. Thus the people of Yalais 

 scarcely know any winds but those from the east and west ; in the 

 high valley of the Rhone, the only winds which make themselves felt 

 are those from the north and south.* 



According to Kamtz, the mean direction of the wind in the whole 

 of France is S. 88" W., that is to say, that the resultant of all the 

 currents would blow from a point in the horizon situated at two degrees 

 to the south of west. This direction of the wind explains perfectly 

 why the large towns in France and the neighbouring countries tend 

 in general to increase on the side of the west ; they seek to breathe 

 pure air. It is for this reason that the rich inhabitants of the great 

 cities emigrate, from generation to generation, towards those portions 

 of the suburbs which look towards the setting sun. 



It is a remarkable fact, that the winds from the south-west increase in 

 intensity in proportion as they approach the pole, while the winds 

 from the noi'th-east diminish gradually in force as they approach 

 nearer the equator. The phenomenon is easily understood. The 

 space traversed by the masses of air, coming from the south, is 

 gradually restricted in the direction of the pole, and consequently 

 the flow of the whole aerial river cannot be effected save by an 

 acceleration of speed. The polar winds, on their side, traverse lati- 

 tudes where the space opens wider and wider before them, and their 

 force slackens gradually to the tropical zone, where they become the 

 peaceful and regular currents of the trade- winds. 



Already, for some centuries, savants have ascertained that, in the 

 northern hemisphere, the succession of the winds is accomplished 

 in a normal manner in the direction from south-west to north-east by 

 the west and north, and from the north-east to the south-west by the 

 east and south ; this is a rotatory movement similar to that which the 

 sun seems to describe in the heavens, when, after having risen in the 

 east, it proceeds towards the west, developing its vast curve around 

 the zenith. Aristotle made this observation more than two thousand 

 years ago in his Meteorology : " "When a wind ceases to blow, and 

 gives place to another wind of a neighbouring direction, the change 

 * Tschudi, Die Alpenwelt. 



