132 Mayow 



come to the top of the aerial vortex, they, receding 

 from the centre of their spiral motion, are dispersed all 

 around, and, heaped up in great abundance, form the 

 dense and gloomy cloud widely spread for a short time 

 (</, d). This, after the motion of the vapours of which 

 it consists has ceased, breaks up in a storm of rain, and,, 

 pressing by its weight on the underlying air and push- 

 ing it out, causes the violent wind. But it is to be 

 observed that although at some distance from the 

 aforesaid mass of waters, boisterous winds blow and 

 the sea is very rough, yet near the phenomenon all is 

 calm, which I think may thus be explained. Since the 

 air is very dense at the outer edge of the vortex, as is 

 seen in the figure, and is thrust out all round from the 

 aerial vortex by the pressure of the superincumbent 

 cloud, the wunds carried towards the vortex are arrested 

 and turned back by the air, which is very dense and also 

 rushes in the opposite direction, so that their impulse 

 cannot reach the vortex, yet meanwhile these winds 

 driven backwards cause furious whirlwinds at some 

 distance from the said phenomenon. 



It also makes for this, that the sea near the column 

 of rising water is whirled round — a motion in water 

 very much opposed to the propagation of waves, which 

 advance only in straight lines. 



After the mass of water has again fallen, a certain 

 part of the said tube is usually broken off, and when 

 this happens a vast quantity of water descends from on 

 high, and if a ship happens to be under it she is in- 

 stantly overwhelmed and sunk. There can be no 

 doubt that the water is produced by the condensation 

 and collection of the vapours which have risen in the 

 tube. But such a heaping up of them comes from this 

 that when the motion of the aerial whirlwind has 

 abated, the vapours at the top of the tube, ceasing 



