As Nate says, it's a complicated question.
> are Sax Rohmer's books in the public domain?
Sax Rohmer (Arthur Henry Sarsfield Ward) died 1 June 1959, so his books come out of copyright in Canada (a life+50 country) on 1 January 2010. They won't come out of copyright in England nor most of Europe (life+70 countries) until 1 January 2030. It looks like 20 or so of his books are already out of copyright in the USA, by virtue of the fact that they were published in 1923 or before.
> How about Arthur Conan Doyle
Sir Arthur Ignatius Conan Doyle died 7 July 1930, so his books are out of copyright in Canada and most of the world. There are, however, a half-dozen or so books still in copyright in the USA.
> Edgar Allen Poe or even H. G. Wells
Edgar Allan Poe died October 7, 1849 and Herbert George Wells died 13 August 1946, making their books out of copyright in Canada, but still in copyright in England and most of Europe. Those books published before 1923 in the USA are no longer in copyright.
If you're in the USA, you can trust that books posted at Project Gutenberg (
www.gutenberg.org) are not under copyright in the USA. Books found in the library here at MobileRead are copyright free in the USA or Canada -- or the authors have released them under a copyright (such as a Creative Commons license) that allows them to be freely distributed.