camera lucida

‖ [ L. camera chamber + L. lucidus, lucida, lucid, light. ] (Opt.) An instrument which by means of a prism of a peculiar form, or an arrangement of mirrors, causes an apparent image of an external object or objects to appear as if projected upon a plane surface, as of paper or canvas, so that the outlines may conveniently traced. It is generally used with the microscope. [ 1913 Webster ]