now KAIN IS FOliMED. 295 



prevails to the north in (xermany, and the weather is stormy over some 

 l^art of western ]^]nrope. 



It is only since the general introdnetion ot telegraphic weather re- 

 ports and the construction ot daily weather charts, have enabled ns to 

 take a general survey of the simultaneous movemeTits of the atmosphere 

 over the greater portion of Europe, that this Fiihii wind has been satis- 

 factorily explained.* It is found that when a F<»hn wind blows on tlie 

 north of the Alps, the baronieter is low somewhere to the north or 

 northwest in Germany, nortliern France, or the F>ritish Isles, and 

 high to the southeast in the direction of Greece and the eastern Med- 

 iterraneati. Under these circumstances, since the winds always blow 

 from a place of high 1)arometer to one of low barometer, a strong south- 

 erly wind blows across the Alps. On their southern face it is forced to 

 ascend, and therefore, as just explained, it is cooled and gives rain in 

 Lombardy and V'enetia, and snow at higher elevations. IJut having 

 reached the crest of the mountains, it descends to the northern valleys, 

 and being by this time deprived of a large part of its vapor, it becomes 

 warmed in its <]escent, owing to comi)ression, absorbs and re-eva])orates 

 the cloud cairied with it, and is then further warmed at the rate of 1° 

 for everj" 1S3 feet of descent. Thus it reaches the lower levels as a 

 warm, dry wind, its warmth being the effect of dynamic heating. 



Other mountain chains afford examples of the same phenomenon. A 

 very striking instance, which much impressed me at the time, is one 

 that I witnessed many years ago in the mountains of Ceylon ; and it 

 was afterwards mentioned to me by Sir Samuel Baker, who had been 

 equally struck by it. My own ex})erience is as follows: In June, 1861, 

 I paid a week's visit to the hill sanitarium of Newara Eliya, at an ele- 

 vation of G,200 feet, on the western face of Pedro Talle Galle, the high- 

 est mountain in the island. The southwest monsoon was blowing 

 steadily on this face of the range; and during the whole time of my 

 stay it rained (as far as I am aware) without an hour's intermission, and 

 a dense canopy of cloud enveloped the hill face, and never lifted more 

 than a few hundred feet above the little valley in which Newara Eliya 

 is built. But on leaving the station by the eastern road that leads 

 across the crest of the range to Badulla, at a distance of 5 miles one 

 reaches the eol or dii) in the ridge near Hackgalle, and thence the road 

 descends some 2,000 feet to a lower table-land wdiich stretches away 

 many miles to the east. No sooner is this i)oint passed than all rain 

 ceases and clouds <lisappear, and one looks down on the rolling grassy 

 hills bathed in the sunshine of a tropical sun, and swept by the dry 

 westerly wind that descends from the mountain ridge. In little more 

 than a mile one passes from day-long and week-long cloud and rain to 

 constant sunshine and a cloudless sky. 



As an almost invariable rule, or at least one with few exceptions, 

 ascending air-currents are those that form cloud and rain, and descend- 



Tlio explauation was originally given by Prof. J. Haun, of Vienna. 



