T* J 



On Water- y^pouis. 261 



vacant space which has been left by the particles of air proceed- 

 ing outwards. The air must therefore stream in anew from all 

 directions, so that, when it has no particularly great progressive 

 rapidity, those objects which are carried round by it must be di- 

 rected to a common centre; but when the progressive rapidity is 

 great, the influence of both forces on the direction must be per- 

 ceptible. . The rotatory movement does not affect those currents 

 flowing inwards, inasmuch as it is taken for granted in this case, 

 that the watcr-spout, although very near the earth, has not 

 touched it • for, in the latter case, the centriTugal force would also 

 di-ive outwards the particles of air near the earth. So long as the 

 water-spout does not reach the earth's surface, an ascending cur- 

 rent must prevail in its interior, which here constitutes the ele- 

 vating power. When it strikes buildings, it may very often 

 happen that the inward flowing currents from below become 

 either entirely or almost altogether stopped. There thus arises a 

 great rarefliction of the air around and over the building, so that 

 the included air must drive the windows and walls outwards, 

 and must at the same time force upwards roofs, and other objects 

 which have air under them. 



A tube of the length formed by the centrifugal force of the 



cannot be sufficiently fihed from below by the in- 

 ward flowing currents. A portion of the cloudy mass must 

 hence descend into the vortex. It is naturally the portions near- 

 est the middle which are driven with the greatest force down- 

 wards; nay, in a certain state of matters, the portions in sinking 

 will be altogether stopped by the centrifugal force. We can 

 easily understand from all this the funnel-like shape of the upper 

 portion of the water-spout. On the other hand, the great atten- 

 uation near the middle, may very easily give rise to the descend- 

 ing stripes of cloud which we so often notice in water-spouts. 

 If the whirl 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. Be- 

 sides, the air contained in the water must get out, and must force 



spout 



as 



the pressure of the atmosphere is diniinished over water, and es- 

 pecially when there is raoid motion. We therefore find that flip. 



foams, and is 



agitated. The greater or less proximity of the vortex must have 

 great influence on the extent of the action. 



