There are several places to locate scanned books on Internet. One of my favorite places is at the FamilySearch Family History Archive. They have many family genealogies and histories. Where do they get those books and periodicals? Primarily from the FamilySearch Family History Library, the Houston Public Library, Mid-Continent Public Library, Allen County Public Library, the BYU Harold B. Lee Library, the Church of Jesus Christ of Latter-day Saints Church History Library and the BYU Hawaii Joseph F. Smith Library.
By clicking on the link, you can perform a search by surname, author or title ... or you can browse the collection or perform an advanced search.
Another way to see if books have been scanned, is by checking the Family History Library Catalog. Click on surname and enter your surname of interest. On some of the entries that you see, there may be links to view a digital version. Click and you will be shown information about the book or publication. On the left side of the web page you will see a list of pages and information pertaining to the book, along with information on the printing version. By clicking that, the book will eventually appear in PDF format that can be saved to your computer for future reading and reference.
Check these options for searching often. As of a few days ago there were 60,144 items at the FamilySearch Family History Archives. New books and publications are being added frequently. It's another good thing for genealogists!