Camera Lucida

(kăm'e-rah loose-dah.) [L., light chamber.] (Opt.) A small instrument depending on internal reflection. It consists of a small four-sided gla prism, and serves for taking an outline of any object. The eye must be so held that you look with the upper half of the pupil into the prism, and with the lower half outside the prism at the pencil and paper on which the image seen in the prism appears to lie. [s. 133]