You see, the air from B is colder than the air at A was
before the air came from B."
"I _don't_ see."
"Well, obviously it _must_ be."
"How 'obviously'?"
"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."
"When is it fine?"
"Wait a bit. The falling of the rain of course generates heat--"
"Why 'of course'?"
"I can't explain _exactly_, but you know perfectly well that it's always
warmer on a cold day after the rain."
"Yes, but not on a hot day."
"Yes, it is."
"No, it isn't."
"It is, really. Anyhow, this is a cold day."
"No, it isn't. You said it was very hot at A."
"I'm not going to argue. You must take it from me that rain generates
heat."
"All right. Is it fine then?"
"No. Heat being generated the air rises.
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