I’ve had a couple of these antique magic lantern chromotropes in the shop over time, and will always grab them when I come across them as I think they’re wonderful, magical feeling things, with the crank rotating the two painted glass slides in opposite directions to produce optical effects. Inventive analog wonder! This is larger than the size one typically sees, with a brass turn handle, and I believe it is a fairly early one, maybe 3rd rather than 4th quarter 19th c. It was also personalized, with the initials RD (I believe) blocked out in graphite at the top right corner on one side.  

Good condition, works great. There’s just a little bit of loss to the black paint on the glass but 7 3/4” l nit including handle (9 1/2 w/handle) x 4 1/16” x 5/8 thick.