The underside appears to read
PAT.NOV
1875
... possibly even "NOV1" --
so if you have to time to spend on it, look through the US Patent Office website
for November 1875 patents (you might get lucky with November 1st) and see if
it shows up there.
The site is a little tricky to use when searching for older patents, but after a few hours
you get the hang of it...
