This photo viewer is called Graphoscope. It was used in the bourgeois living rooms to look at photographs in their finest details. This one was probably part of a series proposed to visitors of a world fair in Paris (the one of 1889 or that of 1900? To be determined). It was made from blackened wood and made simple The facade is beautifully engraved with floral motifs and the words "Souvenir de Paris" This graphoscope allowed me to discover in this photo of the Notre Dame cathedral the ghost of a man pushing a handcart in the middle of the street The ghost effect being obviously the consequence of a very long exposure time.