omniscope

Century Dictionary and Cyclopedia

1. n. An improved periscope designed to be used in the conning-tower of a submarine boat. It consists of a brass tube projecting 8 inches above the sighting-hood, carrying five prisms with lenses. Four of these, used as finders, cover each a field of 21¼ degrees of the horizon, giving images of diminished size. The fifth looks only ahead, and covers a field of 2° 40′ , and presents the image in its true size without distortion. Eyepieces and a direct-vision prism are provided within the conning-tower. Two horizontal hair-lines on the lens of the direct-vision prism act as a range-finder, the space between representing the height of a man at 300 yards.