The Public Domain by James Boyle
Go to the Library of Congress.
This is an astounding repository of material-not just books and periodicals, but pictures, films, and music. The vast majority of this material, perhaps as much as 95 percent in the case of books, is commercially unavailable.
The process happens comparatively quickly. Estimates suggest that a mere twenty-eight years after publication 85 percent of the works are no longer being commercially produced. (We know that when U.S. copyright required renewal after twenty-eight years, about 85 percent of all copyright holders did not bother to renew. This is a reasonable, if rough, guide to commercial viability.)
Yet because the copyright term is now so long, in many cases extending well over a century, most of twentieth-century culture is still under copyright- copyrighted but unavailable.
Much of this, in other words, is lost culture. No one is reprinting the books, screening the films, or playing the songs. No one is allowed to.
J-Walk points out there’s a free PDF version.