66' Professor CErsted on Water-Spouts. 



water round the base of the water-spout forms a great wreath 

 of elevated water, with a bubbling and foaming surface. 



The particles carried up in the water-spout at the same 

 time acquire a spiral motion, owing to the whh-ling which is 

 combined with it. The falling particles, as, for example, drops 

 or minute solid substances, which, ere the water-spout reach- 

 ed the earth, had been driven 

 upwards, or descending rain-drops 

 and hailstones, must also enter 

 windings, which, however, cross 

 the windings already mentioned ; 

 for movements which are ascending and descending, and which 

 are directed to one and the same side, must cross each other 

 as ab and cd in the accompanying figure. 



Hence there are generally two spiral movements in a 

 transparent water-spout, one to the right and another to the 

 left. 



It has been said that water-spouts over water are for the 

 most part transparent, because they contain water ; but ex- 

 perience proves, as well as the very nature of the thing, that 

 in the interior there is no connected mass of water. It would 

 be more correct to say that water-spouts which come over the 

 sea are more rarely opaque, because they can contain no 

 dust, and hence can only be so far opaque that they include 

 numerous minute drops, or, what is most usual, a portion of 

 the fog-like cloudy mass. We can, therefore, easily under- 

 stand why the lower part of the middle portion of a water- 

 spout becomes generally transparent at last, viz. because the 

 whirling movement becomes weakened, and the cloud-funnel 

 is hence shortened. 



We have seen that the air which is immediately above a 

 water-spout, must descend into that portion of it in which the 

 air is attenuated, and, therefore, in the vicinity of the axis 

 more especially. If now, as we suppose, the whirlwind ex- 

 tends upwards, %r above the cloudy mass, in which mere ob- 

 servation would assign its commencement, the descending air, 

 coming from colder regions, must condense the vapours which 

 it meets with on its path, and partly produce large drops and 



