The Library of the University of Michigan is the only Google Books partner which has added link to the books in its OPAC Mirlyn:
http://mirlyn.lib.umich.edu/

Go to "Advanced search" and fill in the words (anywhere):

Includes both image files and keyword searchable text

Using the year filter 1400-1864 there are today 13093 books in the catalog which could be viewed freely outside the US. German books: 1259.

See also
http://archiv.twoday.net/search?q=umich+and+google