CYCLONES. 143 
inside one, it will press and run against it, and the next layer 
against the next lighter one, and so on, thus establishing a motion 
of the air from the outside towards the centre, which would show 
itself to our senses as a wind blowing towards this centre, and in 
a short time the pressure throughout the whole of these circles 
would be the same as the outside, and thus our built up con- 
struction of air would cease to exist. But now suppose we have 
made our construction again, and this time established a large 
Pe eg Ge | a 
29.8 
ve 29.8 
29-8 
Fic. 1.—DIAGRAMMATIC REPRESENTATION OF A CYCLONE. 
_air-pump in the centre, which is able to draw off the air as fast 
‘as it comes in from the outside, so keeping the weight of the air 
‘on these lines constant. This time, it is true, the air, or wind, 
-might commence to blow straight towards the centre, and so get 
sucked through our big air-pump; but mathematicians would 
tell you that this could not last long, as the whole system is in 
what is called “unstable equilibrium.” What would happen 
would be that the air or wind pressing in from the outside would 
commence to run round the centre of our circle in a spiral line 
