first editions

I'm looking for first editions of some books published in the early 1900's. After searching the Internet, I'm wondering how I can tell if these are authentic. Do I look at price, some type of marking or stamp, or is there someone in Louisville or on the Internet that would know?

More modern books will say "First Edition" on the publishing info page. Older books won't say anything: they didn't know if there would be a second edition or not. If a book says nothing about edition - or more likely, 'printing' - it probably is a first, and, often likely, 'only,' edition. If it's a book that became famous, and there's no 'second or third or fourth printing' note, it is likely first edition. I'd go to the UL or Bellarmine library and show it to the head librarian.