Causes of Water Spouts. 51 



It may then be regarded as a certain fact tliat an ascending cur- 

 rent takes place along the axis of all whirlwinds, which are formed on 

 the surface of liquids. 



But this current would become descending if the whirl, instead of 

 forming itself on the surface of the liquid, was excited at the bottom 

 of the vessel, because in this ease, the fluid driven by the centrifu- 

 gal force could be replaced only at the superior extremity of the 

 axis of the whirl ; the following experiment will demonstrate this 

 truth. 



Third Experiment. — I adjusted the mill at the bottom of the ves- 

 sel of water (Fig. 2.) and turned it by a mechanism which left it to 

 act freely, as an inspection of the figure will show. There was soon 

 formed a depression at the center of the surface of the water of the 

 shape of a small funnel j and continuing the movements, the apex of 

 the funnel or inverted cone of air which filled it, was perceived to 

 extend itself by degrees, and approach the mill : bubbles of air were 

 separated from this point, which descended rapidly to the bottom of 

 the vessel ; and at length when the rotary movement had acquired 

 the ordinary velocity, a regular column of air extended throughout 

 the axis and entered among the vanes of the mill occasioning a regu- 

 lar whistling sound. 



This whirlwind was pointed below like a spindle, and the air di- 

 vided into bubbles escaped from the mill and rose rapidly along the 

 sides of the vessel. Light bodies, placed on the surface of the wa- 

 ter, such as cork, and small bits of paper, after revolving within the 

 gulf, were soon carried down to the bottom, whirling round with ra- 

 pidity, as they descend, until they reach the mill, whence they rise 

 along the sides. By regulating the movements, they may be retained 

 at different depths as long as may be desired. 



This experiment explains an extraordinary phenomenon which 

 regularly occurs on the coast of Norway. " When the tide is ri- 

 sing," says Mr. De Buch, " the ebb and flow are compressed within 

 narrow passages ; the water turns in whirlpools the violence of which 

 draws to the bottom boats which approach them ; the unfortunate 

 fishermen cling to their boats. Sometimes the whirlpool throws to 

 a great distance both men and boats, but often they are swallowed 

 up."* 



Travels in Norway and Lapland, by M. De Buch. 



