Library of Congress wrote an article about their project to mass digitize brittle books.
Almost 60,000 are available now and more are scanned every day. These books are in the public domain and come with no restrictions on their use. Feel free to harvest, index, investigate, and re-use.
Congratulations are due to Deanna Marcum, Mike Handy, Aaron Chaletzky, and many others of the Library, Doron Weber of the Sloan Foundation, and the scanners and engineers of the Internet Archive.