300 THE ATMOSPHEEE AND METEOEOLOaY. 



America, the winds raise enormous quantities of dust, and cause them 

 to revolve in space. At Buenos- Ayres the whirlwinds of 1805 and 

 March, 1866, were powerful enough to render the atmosphere as 

 black as night, and to stifle pedestrians in the streets ; after the 

 passage of the storm, the rain which fell showered mud upon the 

 ground. Sometimes the masses of dust are columns rcvolvino' and 

 dancing in immense circles like the genii of the air; sometimes, too, they 

 are enormous cupolas whirling in space covering hundreds and even 

 thousands of yards in breadth, and developing their ellipses for days 

 together and to great distances. These whirlwinds render the atmo- 

 sphere completely dark and irrespirable. In order not to be stifled, 

 travellers are obliged to shut themselves up in all haste in their tents 

 and to throw themselves down with their faces to the earth, so 

 as to form a rampart of their own bodies against the storm of sand. 

 At the same time the friction of all these grains of dust revolving 

 round one another, disengages in a continuous manner real torrents of 

 electricity. Above the whirlwind large birds of prey wheel in circles, 

 either because they wish to enjoy the atmospheric equilibrium re- 

 established by the storm, or because various small animals which are 

 their food are carried along in the tourbillon.* 



In mountainous countries the whirlwinds can raise neither clouds 

 of animalcula nor masses of dust, but they carry into space those 

 heaps of snow so terrible for travellers ; more still, they remove even 

 the pebbles and fragments of schist, gneiss, and granite, making them 

 whirl in circles which move rapidly with the conflicting aerial cur- 

 rents. The geologist, Theobald, has seen some of these whirlwinds 

 of stones which were no less than from 15 to 20 yards wide ; it is not 

 impossible, therefore, that certain masses of slaty fragments, which 

 resemble piles raised by the hand of man, have been heaped up by 

 whirlwinds. t 



The marine whirlwinds being phenomena of the same nature as 

 the terrestrial whirlwinds, must likewise raise particles from the 

 surface that they traverse. The foam of the waves is sucked up 

 by the aerial eddy, and ascends with a whirling movement. Some- 

 times the water swells and rises in great bubbles in the vacuum 

 formed in the midst of the whirlwind by the attraction of the air 

 towards its circumference. In spite of popular accounts, it is very 

 rarely that the water is carried up to the low clouds which brood 

 over the sea so as to fall in a deluge at a great distance, but the showers 



* Dc KhanikofF, Voyn{/e dans h KJiorassan ; Baddcley, Alexander Buchan, Meteorology. 

 t Theobald, Jahrbuch des Schivcizer Alpcn-Club, p. 531. 



