Periscopes for Rear Vision

This paper discusses some of the optical problems associated with the conventional rear view mirror, convex mirrors, combinations of plane mirrors, and periscopes. Two kinds of periscopes are described in some detail. The first is called a view finder and the second a folded telescope. The first presents an image inside the automobile on which the driver must focus his eyes. The second presents an image which seems to lie far away so that the driver can look into it without changing the focus of his eyes. Finally, an unconventional system is described built of parallel cylindrical lenses and mirrors and operating as a unit magnification telescope. Models of the latter system have been successfully installed in a variety of automobiles.