260 On Water-Spouts. 



On the actual nature of a Water-Spout. — If now, after all 

 this, we ask, Avhat a water-spout really is ; the answer would be : 

 it is a whirlwind (Luftwirbel.) By itself, a water-spout is not 

 more visible than air itself, but those portions which are mixed 

 either with vapor, drops of water, or solid matter, become vis- 

 ible. 



The source of this vortex is not to be sought in the lower re- 

 gions. There is no peculiarity of the earth's crust with which 

 the phenomena of water-spouts seems to be connected ; for, they 

 occur iu countries of the most diversified constitution, as, for ex- 

 ample, in volcanic, as well as in non-volcanic districts. In the 

 sea also, there seems to be no condition of the water or of the bot- 

 tom, on which their occurrence is dependent. Just as little can 

 these vortices be produced by the winds prevailing at the earth's 

 surface, for they take place most frequently in the midst of a se- 

 rene atmosphere. They must, therefore, have their origin in the 

 upper regions. 



Owing to the circular motion of water-spouts, all the parts ex- 

 hibit a centrifugal action towards the circumference. This force 

 is, as is well known, a necessary consequence of the nature of ro- 

 tatory motion. But any one even who is not acquainted with the 

 laws of circular motion, can form a perfect idea of this matter, by 

 taking a transparent vessel, as for example a flask, filled with a 

 mixture of sand and water, and by some means or other turning it 

 round on a perpendicular axis. The heavier portions will then 

 be observed on the outside, and the lighter in the middle. Those 

 portions which are carried to the greatest distance from the mid- 

 dle, are at the same time upwards ; this takes place because the 

 agency which drives them outwards finds a limit at the circum- 

 ference, which forces the particles that are in motion to ascend, 

 the only direction in which they can yield to the pressure. We 

 may be easily convinced that this action also takes place in the 

 open air, by distributing smoke in the air, from a tobacco pipe for 

 example, and then, at a distance of one or two feet, producing a 

 rapid rotatory movement, when the extension of the whirlwind 

 becomes apparent by means of the smoke. 



Owing to the rotatory motion, the particles in the middle 

 must also have a centrifugal action, and there must thus arise a 

 great rarefaction of the air at the centre. So long as the whirl- 

 wind does not reach the earth, the air must ascend, to fill up the 



