Professor Qirsted o>i iraier-Spoutis. 65 



We can easily miderstand from all this the funnel-like shape 

 of the upper portion of the water-spout. On the other hand, 

 the great attenuation near the middle, may very easily give 

 rise to the descending stripes of cloud which we so often no- 

 tice in water-spouts. If the whu'l of air is immediately over 

 the sea, the water must ascend under it, partly owing to the 

 rarefaction of the air above it, and partly owing to the air 

 streaming in from all sides. Besides, the air contained in the 

 water must get out, and must force itself towards the less filled 

 space above, as always happens when the pressure of the at- 

 mosphere is diminished over water, and especially when there 

 is rapid motion. We therefore find that the water, Avhen the 

 whirlwind approaches, rises up, foams, and is agitated. The 

 gi'eater or less proximity of the vortex must have gi-eat in- 

 fluence on the extent of the action. 



When the whii'lwind comes entirely in contact with the sur- 

 face, whether it be on dry land or water, the particles of air 

 must be sent outwards by the centrifugal force, and the cm*- 

 rents towards the spout must consequently cease. The mo- 

 tion of the air. is also communicated to all easily moved solid 

 as well as liquid particles which come in contact with the 

 vortex. They thus acquire, not only a movement outwards, 

 but also a movement inwards. This occurs in the following 

 manner : The circular motion extends itself downwards, and 

 thus throws outwards towards the circumference, solid parti- 

 cles or water, according as the water-spout is over land or 

 water ; but, on the direct course outwards, such particles ex- 

 perience great resistance from the surrounding mass, so that 

 they must ascend as they retire from the middle. This is 

 shewn in the excavation left when the water-spout passes over- 

 loose soil, and also by the imcovering of the bottom when it 

 traverses shallow water. It cannot be doubted, that a deepen-^ 

 ing of the sea also takes place, but this cannot be so easily 

 observed. 



On water, the comlnned movements upwards and outwards'- 

 can be seen in great perfection, for, round the foot of the 

 water-spout, water is thrown out in parabolic cm*ves ; nay,, 

 one observer has remarked water round the base in the form: 

 of a reversed basin. Upon the whole, it may be said that the' 



VOL XS.Vlf. NO. Mil. — rcr.v 183). B 



