Causes of Water Spouts. 53 



I had attached to the middle of the rod a parallelogram of varnish- 

 ed pasteboard. (Fig. 3.) 



The vessel was filled with water to within two inches of the top. I 

 placed at the bottom, a layer of blue glass, and on the water a layer of 

 oil. The pasteboard, which was to form the whirl, was thus situated 

 obliquely in the middle of the water, at an equal distance from the 

 powder and the oil. I then turned the rod at the rate of about twice 

 in a second, and it was not long before two spouts were formed ; one 

 ascending from the blue glass, the other descending from the oil, and 

 uniting at the middle of the axis of the mill. 



From the facts which have just been described, we see that the 

 same mechanism, that is to say, the circular movement of a liquid, 

 can alone produce ascending or descending spouts separately, or si- 

 multaneously, following the position of the whirl ; the spout will be 

 ascending if it is excited on the surface ; it will be descending, if it is 

 formed at the bottom of the vessel ; and finally, a single whirl will pro- 

 duce an ascending spout, and another descending, if it is placed at the 

 centre of the liquid column. 



It is impossible not to see a striking analogy between the result of 

 the experiments which have just been described, and the grand natu- 

 ral phenomena ; in comparing them in the particular circumstances 

 which accompany them, this analogy becomes evident, and must 

 produce conviction. It results from the observations of travellers, 

 that spouts always take place in a calm, or at most when only a light 

 breeze is stirring, and that they are never observed during a great 

 storm, which would seem at first more likely to produce them. The 

 reason is, that the shock of winds, which produces the primitive whirl 

 is always very far from the point where the spout begins to appear. 



When we wish to raise a spout from the bottom of the vessel, we 

 create a whirl at the surface of the Hquid, and when we wish the spout 

 to descend, we form a whirl at the bottom of the vessel. 



In the natural phenomenon, the whirl which produces the ascending 

 spout is formed in the clouds, or near the clouds, and extends by de- 

 grees towards the sea, favored by the inferior calm ; if a rapid hori- 

 zontal wind existed on the surface of the sea, the whirl in extending 

 towards it, would be broken and scattered by the current. When 

 ascending water spouts have a progressive movement, the elevated 

 region of the atmosphere, where the whirl is commenced, must neces- 

 sarily have the same velocity as the inferior part where the spout is 

 produced ; otherwise the latter would become obHque and would soon 



