Dioptra

It is in the Dioptra a universal geodetic instrument, which can be considered as early predecessor of the theodolite. The invention of the theodolite in the 16th century had been suggested by the description of Dioptra at Heron of Alexandria.

A Dioptra consists of a vertical cylinder supporting a rotatable disc axially, which is labeled with a graduation. On this disc a horizontal rail ( alidade ) is rotatably mounted, which is provided at both ends with attachments, in the viewing slots have been inserted (the " rear sight "). With the help of these slots can be a target precise targeting.

On its underside, the disc with a semi-circular, toothed and also graduated plate is connected. This whole previously described upper part of the Dioptra turn rests on a disc which is rotatable for yourself and adjustable by screws. Heron of Alexandria mentioned in connection with the Dioptra a tunnel balance - a two-meter long horizontal bar, carrying two interconnected water tank.

It can be measured and determine both horizontal and vertical angles with this device.

There is a relationship to Peilscheibe.

The Dioptra can be used for various tasks of the field measurement and astronomy.

Is first described the Dioptra at Heron of Alexandria. When this lived, Invented can only very imprecisely, most probably in the 1st century AD was the Dioptra but much earlier: The Almagest mentions a (not preserved ) description by Hipparchus.

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