Having had time to read the text of the patent properly it does seem that Gameswat is right and The Convicts is a working model and not Matthewson's lost machine. I'm afraid I was sucked in by the similarity to the appearance of the front of the working model and the drawing by Mathewson's step grandson. Still don't know where I got the photo from, I'm afraid.
American, British, French or German? We want to know about it.