[This is a fast-access FAQ excerpt.]
The original version of this joke was apparently by Mark Twain,
and can be found at [...].
[You can read the joke at http://www.mantex.co.uk/samples/spell.htm.
Recent research has cast doubt on Mark Twain's authorship of
this joke. See more.]
elaborate version, by Dolton Edwards (probably a pseudonym), which
gives no credit to Twain, was published in the science fiction
magazine Astounding in 1946 and can be found at [...].
[For the text of this article, ask Google.]
Various other versions are in circulation.