When was the origin of the "Nightfall" quotation found?

Question

”Nightfall”, a 1941 novelette by Isaac Asimov, is possibly his most well-known and acclaimed work. It was prompted by a discussion between Asimov and John W. Campbell concerning a quotation from Ralph Waldo Emerson:

If the stars should appear one night in a thousand years, how would men believe and adore, and preserve for many generations the remembrance of the city of God!

Asimov’s take, as detailed in Nightfall, was that in this situation men would instead go insane.

I read about the genesis of the story more than ten years ago in “The Early Asimov, Volume 2” (published in 1974), where Asimov wrote that he had never been able to actually track down the source of the quotation. From that, I assumed that it must either be really obscure, or that it had simply been mis-attributed to Emerson. Today, however, it seems to be well-known that the quotation comes from Emerson’s essay “Nature”. When did the source quotation become known to the sci-fi community - did Asimov live to see its identification?

Answer 1

The quotation wasn't really obscure. Once The Early Asimov was published, where Asimov said that he couldn't find its source, he was immediately informed about it by several readers:

A few years ago, I admitted in print that I had never been able to find the source of the quotation. At once, dozens of letters arrived giving me the precise reference. So please, Gentle Readers, cease and desist from here on in. I now know.
_{from The Nightfall Effect, The Magazine of Fantasy and Science Fiction, March 1976}

As already noted in the question, the quotation is from Emerson’s essay Nature. The complete reference is “Nature. Boston: James Munroe and Company. 1836.” The essay is available online and has a Wikipedia entry.