The Chromatone CT-312 Keyboard
http://www.youtube.com/watch?v=h2VfxvnofAo&feature=relatedThe keyboard is called a “Janko” keyboard, and it was invented in 1882 by Paul von Janko. Check out the following link to see a picture gallery of several models (many of which are pianos, not MIDI keyboards)
http://squeezehead.com/uniform-keyboard/