I learned about Butler and his letter from George Dyson's book, "Darwin among the Machines: The Evolution of Global Intelligence" -- it's a very entertaining ac

I learned about Butler and his letter from George Dyson's book, "Darwin among the Machines: The Evolution of Global Intelligence" -- it's a very entertaining account. Butler was quite a character. (If I recall correctly I learned about Dyson's book from a postscript to Neal Stephenson's "Quicksilver.")