"Well, the whole thing started with it being very hot at A, you remember,
so that the air rose. If it had been hotter still at B just then the air
would have risen at B instead, and it couldn't have rushed over to A.
There'd have been a frightful muddle."

"There is."

"Well, it's your own fault for interrupting. This air, then--"

"Which air is this?"

"The air from B. The air from B cools the air at A--"

"But I thought the air at A had risen."

"Not all of it. And that makes it rain."

"Why?"

"Oh, well, I can't go into that. It's something to do with condensation.
Air absorbs more moisture when it is hot than when it is cold--"

"So do I. I understand that."

"When the air cools the water condenses."

"Is it fine then?"

"No, it rains, you fool."