Davis-Quadrant

Davis-Quadrant

Davis-Quadrant (engl. Back-staff), das älteste Spiegelinstrument zur Beobachtung von Sonnenhöhen auf See, erfunden von Davis (berühmter Seefahrer, 1550–1605, nach dem die Davis-Straße benannt ist), besteht aus zwei sich zu 90° ergänzenden Sektoren; auf dem Kreisbogen jedes Sektors ist ein Diopter verschiebbar, und im Scheitel ist eine Auffangplatte (später Spiegel) mit Spalte angebracht. Der Beobachter dreht der Sonne den Rücken zu, visiert mit dem einen Diopter durch die Spalte der Auffangplatte den Meereshorizont und dreht gleichzeitig das andre Diopter so weit, bis es ein Sonnenbildchen auf die Auffangplatte entwirft. Die Ablesung der Stellung der beiden Diopter ergibt sodann die Sonnenhöhe.


http://www.zeno.org/Meyers-1905. 1905–1909.

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