The Collaborative International Dictionary
Alethoscope \A*leth"o*scope\, n. [Gr. ? true + ? to view.] An instrument for viewing pictures by means of a lens, so as to present them in their natural proportions and relations.
Wiktionary
n. An instrument for viewing pictures by means of a lens, so as to present them in their natural proportions and relations.
Wikipedia
An alethoscope (Greek true+view) is an instrument for viewing pictures with a lens to enlarge and show them with natural relations and proportions. The alethoscope was invented by Carlo Ponti in 1860 and patented in 1861. It was used to view photographs that were colored, perforated and mounted on a curved frame. The alethoscope showed day-and-night effects whether viewing it against the light or reflect the light by two side mirrors. It is the larger version of a megalethoscope.