Sub-Coelum: A Sky-Built Human World is an 1893 utopian fiction written by Addison Peale Russell.
The falling sky clause occurs in the passage of Terence, suggesting that it was a common saying in his time, "Quid si redeo ad illos qui aiunt, ‘Quid si nunc cœlum ruat?’" — "What if I have recourse to those who say, ‘What now if the sky were to fall?’".