Stereoscope
2 of the 7 encyclopedias on this shelf carry an entry for Stereoscope. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a simple and once the Caspian and Aral seas, between the popular optical contrivance, by which two slightly dissimilar pictures of an object are fused into one image, having the actual appearance of relief. A reflecting form of the stereoscope was invented by Professor Wheatstone in 1838. Subsequently Sir David Brewster invented the refracting or lenticular stereoscope, based on the refractive properties of semidouble convex lenses; and this instrument, of which there are numerous forms came into general use. Convex lenses magnify the pictures besides producing a stereoscopic effect. Photography greatly assists the stereoscope in providing perfectly accurate right-andleft monocular views, which are taken simultaneously sly on a plate in a twin camera. Several modifications of the re- Cyc-Vol. IX flecting stereoscope are distinguished by the names pseudoscope, iconoscope, telestereoscope, and polistereoscope, the last being an apparatus which serves the purposes of all the others.
Aiton's Encyclopedia (1910)
an optical instrument used in the examination of double photographic pictures made for the purpose. It was invented by Wheatstone in 1838. The original instrument was based on two mirrors, which have been replaced, however, by two refracting lenses. With the aid of this instrument two photographic pictures, a left hand and a right hand view, are examined at the same time, one by each eye, so that they make an impression of one picture. In this way a picture may be made to stand out more clearly. Surfaces appear in relief instead of flat, and relative distances are shown up better than by the examination of a single photograph, however clear it may be.