Many of Wikipedia’s citations are from books, and to check the book citation against the article requires that you hunt down the book. But now the Internet Archive is making the process easier.
Now, thanks to a new initiative by the Internet Archive, you can click the name of the book and see a two-page preview of the cited work, so long as the citation specifies a page number. You can also borrow a digital copy of the book, so long as no else has checked it out, for two weeks—much the same way you’d borrow a book from your local library.