"No, you told me to think of a place A, and I am still thinking of it, because it is very hot there."
"Well, this is another place, where the pressure is simply frightful. When the air rises at A the air from B rushes over to A to fill up the gap, and that is what we call wind."
"I see."
"No, you don't. It isn't quite so simple as that. Now, the atoms of air rushing from B to A don't go straight there, but they travel in—in sort of circles."
"Why do they do that?"
"Well, the fact is that these atoms are so keen to get over to A, where there is plenty of room, that they jostle each other, and that makes them go round and round. If they go round and round against the clock, like that, they are called cyclones, or depressions, or low-pressure systems. If they go with the clock, like that, it is an anti-cyclone."
"Oh!"
"What do you mean—'Oh'?"
"What I said; but go on."
"Now suppose this air—"