As with most great minds of the 19th century, MT put down thoughts on an enormous range of topics. I am continually surprized at some of the things to be found in the Notebooks, Letters and Autobiography. You may be able to find an answer to your query in "The science fiction of Mark Twain" / edited by David by David Ketterer. Hamden, Conn. : Archon Books, 1984. Also try "What is man? and other essays" UC Press. Cheers, Rhio H. Barnhart Head, Music Department Library University of California, Davis