A couple notes for the technically inclined:
1. the years are pulled from field 260c (or if that doesn't exist or is unparseable, from field 008). Years in non-western calendars are often not converted correctly.
2. There are obviously books from before 1770, but they aren't included.
3. By "books", I mean items in the LC's recently-released retrospective (to 2014) "Books all" MARC files. http://www.loc.gov/cds/products/product.php?productID=5. Not the serial, map, etc. files: the total number is just over 10 million items.