TORRENTS OF THE HIGH ALPS. 29 



there is immediately poured a great mass of cold air over the whole extent of 

 this region. This, specifically heavier than the rest of the atmosphere, can 

 neither rise nor spread out, because it is imprisoned in a kind of funnel, which 

 constitutes always the form of the basin. It escapes then by the gorge, 

 following the line of greatest declivity, as every fluid must, and is precipitated 

 to the bottom of the medium of lesser density. The phenomena of this efflux 

 becomes in every respect similar to that of water. 



" But there are causes which must prodigiously accelerate the velocity. 

 The column of water carries with it a great volume of air incorporated with 

 it, which it pours with violence into the gullet. At the same time it does 

 not cease to press with all its weight on the volume of air, which has been 

 engulfed in the gorge as in a closed channel. There is there, then, a double 

 action, the force of which is extreme ; one may form some idea of it by com- 

 paring it to that exercised by the tromhes dJeau, which serve as blast-engines 

 to the works established in the mountains. It is necessary to imagine the air 

 escaping by the gorge of the mountains as by the nozzle of the bellows of a 

 gigantic forge, and then there will be no wonder that it produces the effects 

 I have described, which are all the consequences of excessive rapidity." 



This may require some explanation or illustration. 



Marsh, citing Wanderungen diireh Silicien und die Levant, by G. Parthey, 

 a work published in Berlin in 1834, gives the following singular instance of 

 unforeseen mischief, following from an interference with natural arrange- 

 ments, which may be considered a natural illustration of the application of 

 force referred to by Surell in his allusion to the application to blast- 

 furnaces of what is called a trombe d'eau : — " A land-owner at Malta 

 possessed a rocky plateau sloping gradually towards the sea, and terminating 

 in a precipice forty or fifty feet high, through natural openings in which the 

 sea water flowed into a large cave under the rock. The proprietor attempted to 

 estabhsh salt-works on the surface, and cut shallow pools in the rock for the 

 evaporation of the water. In order to fiU the salt-pans more readily he sank 

 a well down to the ocean beneath, through which he drew up water by a 

 windlass and buckets. The speculation proved a failure, because the water 

 filtered through the porous bottoms of the pans leaving little salt behind. 

 But this was a small evil compared with other destructive consequences 

 which followed. When the sea was driven into the cave by violent west or 

 north-west winds it shot a, jet d'eau through the well to the height of sixty 

 feet, the spray of which was scattered far and wide over the neighbouring 

 gardens, and blasted the crops. The well was now closed with stones, but 

 the next winter's storm hurled them out again, and spread the salt spray 

 over the grounds in the vicinity as before. Repeated attempts were made 

 to stop the orifice, but at the time of Parthey's visit the sea had thrice 

 burst through, and it was feared the evil was without remedy." 



Something similar to this is the action referred to by Surell. The 

 analogy holds only in the compression of air by the pressure of water 

 following upon it quicker than it can escape, and the force developed by its 

 elasticity where space is found for its subsequent expansion. 



M. Surell enters into several computations to determine the rapidity of 

 the flow of torrents, from which it appears that while the flow of the most 

 rapid rivers does not exceed 4 metres, or 13 feet, per second, both calcula- 

 tions and observations shew the flow of these torrents to be sometimes 

 about 14:'21 mfetres per second — ^nearly 15 mfetres, or 50 feet, — which is the 



