i 4 Introduction. 



cleared of woods, and that the whole southern upper elope of the vailey of 

 the Ubaye is devoid of forests ; in a word, that all the parts which beai 

 the dkect attacks of ih.e f<jehn — those which arrest it^-force it to ascend 

 them, and to pour upon them masses of water, ai'e all of them almost 

 entirely cleared of woods. Here we have no longer, as is the case abcrve 

 Menton, a tropical sun to warm the soil ; the wind has cooled down as it 

 rose higher from the sea, and is obliged with fatal effect to precipitate in the 

 form of rain the moisture it has borne thither ; and at that place where the 

 forests are an absolute necessity, and where the most considerable quantities 

 of water fall, there it is that they have completely disappeared. 



" This summary is incomplete, but it may sufi&ce to render intelligible the 

 general course of the orages, or storms of rain in the Alps, and the intensity 

 of these on certain parts, which are generally ttiose at which the fcehii is 

 compelled to rise considerably or to change its direction. The celebrated 

 torrent of Kiou-Bordoux, near Barcelonette, in face of the opening at Alios, 

 is exactly so situated. The portion of the Alps situated below the department 

 of the Is6re almost completely relieves the fcelm of its humidity, and this 

 is the classic region of the m-ages. 



" The fcelm does not confine itself to the production of ton-ential rains ; it 

 is not less terrible in its action on the snow, and on the glaciers. As has 

 been stated it blows sluggishly and warm for one, two, or three days before 

 the rain appears ; if at this time the ground be covered with snow this is 

 not slow to melt rapidly, and absorbing a great quantity of water it becomes 

 like a sponge ; then supervenes the rain which expedites the process and 

 brings on a kind of debdcle, or breaking up, and the water arrives in great 

 quantities in the valleys. If the rain do Jiot supervene the action of the 

 fwhn may suffice to cause all the snow to melt and to produce great conse- 

 quent disasters. Tn 1856 the inundations of the valley of Barcdonette had 

 no other cause of production ; the maximum of the flood was attained under 

 a magnificent sky, and aU the water came from the melting of the snow 

 which covered the mountain. In Switzerland the terrible inundations of 

 1868 had in general a double origin — with warm continuous rains were com- 

 bined the melting of the glaciers. It is always in the spring, or with the fiarst 

 snows of October, that the latter torrents are to be dreaded if the mountains he 

 not covered with glaciers ; where this is the case the danger is constant. 



" The/aAw sometimes produces general rains over the whole of thecountry 

 over Which it blows, but sometimes only local onit/es, or storms of rain. 

 This can easily be accounted for when it is considered that the contour of 

 the Alps admits of one current of air passing up a valley to be in its cause 

 and in its effects quite independent of a current passing up a neighbouring 

 valley, though they have had a common origin, — and that a difference in the 

 cooling of the currents of air may occasion a precipitation of rain in one vnltey, 

 while the neighbouring valleys, being warmer, are enjoying a cloudless s^." 



Thus can the immense quantities of water poured down by these ton-ents 

 be tiraced to their source, and thus can the immensity of the quantity of 

 water producing these devastations be accounted for. The inquii-y 

 brings into view the fact that it is the temporary deluges of rain, and not 

 the mean average annual rainfall, which occasion the torrential floods of the 

 Alps. And there are countries in which the mean average annual rainfall 

 may be very small, when an mnge, equalling or exceeding any in the Alps, 

 occurring, once in a decade, may prove not less destructive than any torrent 

 to-'thdt tovrew-ravaged region. 



