In the words of Google,
"
It turns out that not all the world's information is already on the Internet".
To address this, Google have started to index extracts from books - often
including the cover blurbs, which are a readily available approximate
summary of the contents.
The books included in this initial batch number about 7000, and include
both fiction and non-fiction books. See what shows up for
windmill
or
watermill.
Some of the books it shows up are expected, such as
Devices and Desires
by PD James, others are a surprise, such as
The Complete War of the Worlds
relating the furore this 1938 radio broadcast caused.