Stereoscope

(ster'e-os-kōp.) [ From Gr. stereos, solid, and skopeo, I examine.] No picture can give an exact representation of a solid; for the eyes to a certain extent look round the solid body, each of them seeing more of one side than the other; and the two pictures in the eyes not being absolutely the same. This may be easily proved, by placing a small cylinder of any kind on a table, and marking by dots, ., the width of the part seen by each eye when the other is closed, the head being kept in the same position. The S. has been invented to meet this peculiarity of vision. The most common form of instrument consists of a small box, in the back of which is placed an oblong slide, containing two photographic pictures of the same object, taken in two slightly different positions of the camera obscura. (See PHOTOGRAPHY.) These pictures are both seen at once, each by the eye which corresponds to it by means oftwo small tubes, containing lenses adjusted to the circumstances of and the distance between the eyes of the observer. The result is that the eyes combine the two pictures, and the object appears to stand out in relief, in other words, to po e solidity; they are viewed by transmitted light if they are transparent, and by reflected light if opaque. See PSEUDOSCOPE. [s. 856]