Sun Compass

The Union Observatory Sun Compass, South Africa, 1943, solid brass instrument in custom made wooden box with handle and fixing screw, number 46, 180 x 185 x 160mm. The Union Sun Compass: an item of scientific Africana by Professor Cornelis Plug. During warfare in the Western Desert, navigation by prismatic compass became a major challenge as there is little topological feature from which to take bearings, hence an urgent need to develop a reliable solar compass for the harsh environmental conditions. In 1940 the Union Observatory was directed by Prof. W H van den Bos and he was ably assisted by W S Finsen (MSc, later DSc and observatory director). Finsen relates in his journal that one afternoon in early 1940, a major and a lieutenant from the SAACR approached him with a wooden model of a solar compass they had unsuccessfully been attempting to develop for desert navigation. They asked for his help. He immediately warmed to the idea and between himself and van den Bos they designed and developed the Observatory Solar Compass very quickly. The instrument worked on different principles to most other compasses. It had a sliding lens that moved along a date scale which allowed the focused beam of sunlight to be projected onto a frosted cellulose target screen that swiveled to the hour calibration after being adjusted to the latitude. This compass had several advantages over other designs. It was not necessary to know latitude or longitude to set it. Also, adjusting it to another bearing whilst on the move was possible. It was equally as easy to reset to the original bearing after a deviation for obstacles on the route, like a sand dune or ravine, also whilst on the move. Lastly it was 'soldier proof' and compact being constructed sturdily from solid brass and its moving parts were all closely engineered to prevent the ingestion of sand and dust. Only 128 of the instruments were made. Every squadron of the SAACR was equipped with one. The SAACR used the Observatory compass to great effect and had a proud record in the desert campaign.

Interesting link:
http://samilitaryhistory.org/vol024mn.html

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