Thanks for that. I was unaware of the extent of the recordings. It sort of
fires the imagination, although you may be correct, perhaps not a single one
has come down to us.
WRT wire recorders, I had previously thought that they had only been made
practical after the invention of the vacuum tube (i.e., after Twain's
death). But (via Google search term "wire recording") Valdemar Poulsen
seems to have made a more-or-less working wire recorder as early as 1899 and
tried to market it for a few years. "Telegraphone" (?) Anyway, these were
_cylinders wrapped with wire_ (as opposed to the later wire on spools),
although they could put sound on metal disks as well, as you say.
Cripes - you'd think that _one_ of these different types of Twain recording
would manage to have survived, wouldn't you? But maybe not ... our own
magnetic tapes, hard disks, and ordinary plastic CDs/DVDs don't have any
greater survival value (except, of course, that of sheer quantity).