Sure there are the printed on paper kind of book, but the industry has changed to handheld's and online. They can be a great source for doing research and locating books. A couple areas for you to check for the books you seek.
The first would be your Public Library. Sure you need to have a library card, but once you get it you are able to download E books off their website. Check your local library to see if they have the books you are looking for. Checking the library where your ancestors lived can be a hit and miss proposition when it comes to gaining access. Most libraries do not allow you to see their books without a library card. Does not hurt to look.
The second place would be Google Books. I have found many books complete on this website that will help you in your search. Click on the Books section and type in the subject. Some books are complete, but many are just short clips.
The third and final one is Family Search. This is my favorite by far. It gets you access to eight different libraries across the country. The best part is the database keeps growing. Books are fully scanned and you can turn the pages. Saving copies is also easy. Only thing I don't like is that the search feature can be a little difficult. Less words the better.
Good luck in your hunt. As always comments are welcome.