Submission of a "working model" of an invention which a patent was
applied for was a requirement of US law & patent office regulation in
the 1870's.

http://en.wikipedia.org/wiki/Patent_model

Clemens' first two patents would have fallen under this requirement.
(The 1883 Memory Builder / history game would not have). Does that mean
that hand-crafted "working models" of his adjustable elastic strap and
scrap-book might still be banging around somewhere?

DDD