56 Causes of Water Sjjouts. 



veral spouts appeared at their inferior extremities like tubes, through 

 which clouds of smoke were seen to rise. 



According as the particles which form the spout are heavier and 

 larger, they have a greater breadth, and are formed into a tube ; in 

 one experiment a tube of sand was observed, containing in its interior 

 a column of impalpable blue glass ; in the case just cited, it is proba- 

 ble that the bottom of the spout was composed of drops of water, 

 and that these formed the tube, into which a thinner vapour rose in 

 visible clouds. 



In the course of these experiments, in endeavoring to form spouts 

 with sand, I remarked a circumstance which appears worthy of being 

 stated. 



When the column of water which rested on the sand, was not very 

 high, and when a circular movement was given it, not only at the 

 center, but throughout the mass, in turning it quickly with a rod, un- 

 til the sand which is at the bottom of the vessel, is drawn in and min- 

 gled with the water, it setdes, by deposition, at the bottom of the ves- 

 sel in a cone as regular as if formed by the hand. 



The ascending current has no longer force enough to raise the 

 sand in a spout, though it has enough to collect it at the center. If 

 the point of the cone is destroyed with a rod, it may be formed anew 

 by gently circulating the water ; the grains of sand are then seen to 

 rise from the bottom on all sides of the little conical mountain, and by 

 degrees to reestablish the point. May we not explain by a • similar 

 cause, the formation of those little conical mountains, which are so 

 common in sandy plains, and in many places, where their regular 



the mechanism of the phenomenon is reversed ; instead of drawing the water from 

 below, the primitive whirl, which commences near the sea, draws the clouds from 

 above, downwards, and as the clouds oppose less resistance than water to the interior 

 current, which draws them, the spout is less pressed by the lateral columns of air ; 

 the centrifugal force must in consequence give it a greater diameter, especially near 

 the clouds, where a replacement along the axis is more easy. Experiment 3d, Fig. 

 2, represented this effect very exactly. 



An analogous mechanism is perceived in the currents of smoke which are some- . 

 times produced by the firing of a cannon. The circular cylinder which forms them, 

 revolves with such rapidity, that when it comes in contact with the trees, it visibly 

 agitates the foliage ; instead, however, of dispersing immediately, they retain their 

 form for 15 or 20 seconds. In this phenomenon, the replacement of the portions of 

 the surface, which have a tendency to remove from the centre of rotation, cannot ex- 

 ist anywhere, the cylinder being circular and continuous ; the current must there- 

 fore subsist as long as the impulse which it received on leaving the gun continues. 



