A Petoscope is an optoelectronic device for detecting small, distant objects such as flying aircraft. The design, as described in 1936, consisted of an instrument with two parallel light paths. In each path was a collimating objective lens, a screen marked with many small, alternating opaque and transparent squares in a chequerboard pattern, and a second concentrating lens focused on a photocell. The two screens were inverted with respect to each other. This caused a small object in the instrument's field of view to produce differing signals in the two photocells, while a large object affected both light paths equally. The difference between the two signals was amplified and used to raise an alarm. At the beginning of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, the device was adapted for use in

proximity fuse A proximity fuze (or fuse) is a Fuze (munitions), fuze that detonates an Explosive material, explosive device automatically when the distance to the target becomes smaller than a predetermined value. Proximity fuzes are designed for targets such ...

s for bombs. The inventor was Alan S. Fitzgerald of Wynnewood, Pennsylvania, U.S.A., a Research Associate in Electrical Engineering at

Swarthmore College Swarthmore College ( , ) is a Private college, private Liberal arts colleges in the United States, liberal arts college in Swarthmore, Pennsylvania. Founded in 1864, with its first classes held in 1869, Swarthmore is one of the earliest coeduca ...

.Persifor Frazer, in ''Journal of the Franklin Institute'', Franklin Institute (Philadelphia, Pa.), 1936

References

{{reflist Optoelectronics