The Megalethoscope was patented in in the early 1860s by the Swiss born optician and photographer Carlo Ponti (1823-1893). Ponti spent the last forty years of his life in Venice.
A Megalethoscope-slide consists of an albumen photograph, the back of the photo is painted; well-placed holes are made in the print, and layers of painted tissue paper are mounted in a canvas-wrapped wooden frame that measures approximately 11 1/2 x 15 1/2 x 1 inches. If the top of the Megalethoscope is lifted, light is reflected off of the photo, the viewer sees a beautiful landscape or city-scape and when the top is closed and light is shown through the back of the photo, the photograph is transformed into a sensuous, darkened yet colorful scene. (It’s elaborately expanded photography and perhaps an early form of animation. A Megalethoscope-photo-slide transcends the temporal limitations of a single photograph, more than a mirror with a memory, this is a photo of the past, present, and future.)
Information and “an advertisement from the early 1860’s that illustrates the then-revolutionary capabilities of Megalethoscope technology,” from the Cooper Hewitt, Smithsonian Design Museum, is here: cooperhewitt.org
A pair of blog posts (archived by the Internet Archive) from the George Eastman House blog: “Megalethoscope Slides” and “Megalethoscope Madness.”
A video, “Curators from George Eastman House demonstrate the Megalethoscope” is here.
Princeton University has a wondrous Megalethoscope, the viewing machine rests on a lion with wings.
The J. Paul Getty Museum has a beautiful, if slightly less ornate Megalethoscope.
Just a JPEG not a GIF of the entire object: