262 On Water-Spouts. 



When the whirlwind comes entirely in contact with the siir- 

 facC; whether it be on dry land or water, the particles of air must 



be sent outwards by the centrifugal force, and the currents to- 



wards the spout must consequently cease. The motion 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 ac- 

 quire, not only a movement outwards, but also a movement in- 

 wards. This occurs in the following manner: The circular mo- 

 tion extends itself downwards, and thus throws outwards towards 

 the circumference, solid particles or water, according as the wa- 

 ter-spout is over land or water; but, on the direct course out- 

 wards, such particles experience great resistance from the sur- 

 rounding mass, so that they must ascend as they retire from the 

 middle. This is shown in the excavation left when the water- 

 spout passes over loose soil, and also by the uncovering of the 

 bottom when it traverses shallow water. It cannot be doubted, 



L 



that a deepening of the sea also takes place, but this cannot be so 



easily observed. 



On water, the combined movements upwards and outwards 

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

 spout, water is thrown out in parabolic curves ; nay, one observer 

 has remarked water round the base in the form of a reversed ba- 

 sin. Upon the whole, it may be said that the water round the 

 base of the water-spout forms 



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 whirling which is combined 

 with it* The falUng particles, as, for example, drops, or minlite 

 solid substances, which, ere the water-spout reached the earth, 

 had been driven upwards, or de- 

 scending rain-drops and hailstones, 



must also enter windings, which, 



however, cross the windings already 



mentioned; for movements which 



are Eiscending and descending, and 



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



other as ah and cd in the accompanying figure. 



Hence there are generally two spiral movements in a transpa- 

 rent water-spout 



water. 



