A dioptra is a surveying instrument dating back to the ancient Hellenistic civilization, since the 3rd century BCE. This article focuses on the cultural aspects of the Hellenistic age for the historical aspects see Hellenistic period.
Attached to a stand, the dioptra was a sighting tube or, alternatively, a rod with a sight at both ends. Fitted with protractors, it could be used to measure angles. In Geometry, a protractor is a circular or semicircular tool for measuring an Angle or a Circle. The Angles is a modern English word for a Germanic-speaking people who took their name from the cultural ancestral region of Angeln, a modern district located in It was used by Greek astronomers; both Euclid and Geminus refer to the dioptra in their astronomical works. Greek astronomy is the Astronomy of those who wrote in the Greek language in Classical antiquity. Euclid ( Greek:.) fl 300 BC also known as Euclid of Alexandria, is often referred to as the Father of Geometry Geminus (Γεμῖνος of Rhodes, was a Greek Astronomer and Mathematician, who flourished in the 1st century BC. By the time of Ptolemy, (2nd century AD) it was obsolete as an astronomical instrument, having been replaced by the armillary sphere. Claudius Ptolemaeus ( Greek: Klaúdios Ptolemaîos; after 83 &ndash ca The 2nd century is the period from 101 to 200 in accordance with the Julian calendar in the Christian / Common Era. It continued in use as an effective surveying tool. Surveying is the technique and science of accurately determining the terrestrial or three-dimensional space Position of points and the distances and angles between Adapted to surveying, the dioptra is similar to the theodolite, or surveyor's transit, which dates to the sixteenth century. A theodolite ( is an instrument for measuring both horizontal and vertical Angles as used in Triangulation networks It is a more accurate version of the groma. Definition The Groma or gruma (altered from Greek gnomon γνόμων "indicator" possibly through Etruscan was
The dioptra may have been sophisticated enough, for example, to construct a tunnel through two opposite points in a mountain. It may have been a factor in building the Eupalinian aqueduct, "one of the greatest engineering achievements of ancient times," a tunnel 1,036 meters (4,000 feet) long, excavated through Mount Kastro on the Greek island of Samos, in the sixth century BC. The Tunnel of Eupalinos or Eupalinian aqueduct (in Greek gr ''Efpalinion orygma'' Ευπαλίνιον όρυγμα is a tunnel of 1036 m length in Samos, Samos (Σάμος is a Greek island in the North Aegean Sea, south of Chios, north of Patmos and the Dodecanese, and off Scholars disagree whether the dioptra was available that early.
An entire book about the construction and surveying usage of the dioptra is credited to Hero of Alexandria (also known as Heron; a brief description of the book is available online; see Lahanas link, below). Hero (or Heron) of Alexandria ( Ήρων ο Αλεξανδρεύς) (c Hero was "one of history’s most ingenious engineers and applied mathematicians. An engineer is a person professionally engaged in a field of Engineering. A mathematician is a person whose primary area of study and research is the field of Mathematics. "
The theodolite is superior to the dioptra because it has a compass and telescopic lens, two inventions unavailable to Hero. A compass, magnetic compass or mariner's compass is a navigational instrument for determining direction relative to the earth's Magnetic poles It consists An optical telescope is a Telescope which is used to gather and focus light mainly from the visible part of the Electromagnetic spectrum
The dioptra was used extensively on aqueduct building projects. An aqueduct is an artificial channel that is constructed to convey water from one location to another Screw turns on several different parts of the instrument made it easy to calibrate for very precise measurements