"samsloan" writes:
I believe, but I am not certain, that books written more than 50 years
ago have passed into the public domain.

Why do you state that these books, that were written betwen 1947 and
1953, are not in the public domain?

It's much more complicated than that. Basically any book written
after 1923 is likely to be in copyright forever. There was a lawsuit
a few years ago to fix this situation but the Supreme Court screwed it
up, so we're stuck with it now.