Before I left for Yosemite, I finished The Difference Engine by Doron Swade, a curator at the Science Museum in London and head of a team that built a version of the Difference Engine #2 in the 90's.

There are two parts of the book - the main section of the book details Babbage's quest to build the Difference Engine and design of the Analytical Engine. The second, smaller section, is about the quest to build a version of the Engine in time for Babbage's bicentennial. Both parts are quite interesting. I had read about Babbage and his engines before but learned a few new things from this book. For example, I didn't know that a Swedish printer named Georg Scheutz was inspired by Babbage's design and succeeded where Babbage failed and built a version of a difference engine of his own design within Babbage's lifetime. Sadly, it was a commercial failure and didn't lead to anything more than Babbage's work.