Whoops, I'd meant to post this for its release on July 1st. I read and reviewed the first edition of this book when it came out 2 years ago.
The book originally detailed the work of steampunk artists displayed at an exhibition at The Museum of History of Science at the University of Oxford, UK. For the second edition, the author has followed how Steampunk has grown as a movement, adding more artist profiles and more than fifty new photos. They've also changed the cover art, which you can see below in a side-by-side comparison.