I saw a copy of this at Worldcon and am still thinking about it:
My understanding, based on what Ridge says, is that this “paperback” edition first came out in 1889 a couple months after the first editon hardcover, and I think it may have been sold on the newsstands. If I remember correctly, however, the copy I saw in Denver was dated 1890, so it was probably a later printing. What an unbelievably cool steampunk cover. Even cooler, the byline on the book uses the pseudonym “Edmund Boisgilbert, M. D.” And did I say, it’s a paperback from the 1800s!