426 PHILOSOPHY OF STORMS. 



formed many thousand times less in diameter than that of 

 the ascending spout of air. 



This column of hail, falling from so great a height, (for 

 it must have been carried up beyond the region of perpetual 

 congelation,) might well "carry off all the surface of the 

 ground, and leave nothing but the naked chalk, covering 

 four or five acres of land below, and rolling like the bay of 

 Biscay." It may easily be calculated, however, that the 

 descending column, on reaching the earth, could not, if it 

 was solid, have had a diameter of two poles, and therefore 

 its lower end must have wavered about as the columns did 

 in the Hollidaysburg storm, so as to cut out a space very 

 much larger than itself. 



This was probably the case also in that basin which 

 Mr. Alison describes in the TenerifTe storm, as being six 

 hundred yards in circumference, and thirty feet deep, with 

 furrows cut in concentric circles. 



The stationary character of all these storms is not a little 

 remarkable, especially as it is now known that tornadoes 

 in this country always travel towards the east, or in some 

 eastern direction. This anomaly may be explained in the 

 following manner. 



Let a b and a c be two mountains, of moderate height, 

 butting up against each other in the south west, and let the 

 circle d e /'represent the area of a storm moving along the 

 line k i, from south west to north east. When the centre 

 of the storm reaches the mountains the barometer will stand 



