page_title: Theodolite
section_title: Historical background
hierarchical_section_title: Theodolite / History / Historical background
caption_attribution_description: English: The first of the three foot theodelites manufactured by Jesse Ramsden. Image published in "An Account of the Trigonometrical Operation, Whereby the Distance between the Meridians of the Royal Observatories of Greenwich and Paris Has Been Determined. By Major-General William Roy" (January 1, 1790). Now available at archive.org. The illustration is from Plate III. (The plates are at the end of the bound volume but Plate III is at page 202 of the PDF file.) The full text description is on true pages 135-160 corresponding to pages 28-53 of the PDF file
context_page_description: A theodolite is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but they are also used extensively for building and infrastructure construction, and some specialized applications such as meteorology and rocket launching.
  It consists of a moveable telescope mounted so it can rotate around horizontal and vertical axes and provide angular readouts. These indicate the orientation of the telescope, and are used to relate the first point sighted through the telescope to subsequent sightings of other points from the same theodolite position. These angles can be measured with accuracies down to microradians or seconds of arc. From these readings a plan can be drawn, or objects can be positioned in accordance with an existing plan. The modern theodolite has evolved into what is known as a total station where angles and distances are measured electronically, and are read directly to computer memory.
context_section_description: Prior to the theodolite, instruments such as the groma, geometric square and the dioptra, and various other graduated circles (see circumferentor) and semicircles (see graphometer) were used to obtain either vertical or horizontal angle measurements. Over time their functions were combined into a single instrument that could measure both angles simultaneously. 
  The first occurrence of the word "theodolite" is found in the surveying textbook A geometric practice named Pantometria (1571) by Leonard Digges. The origin of the word is unknown. The first part of the New Latin theo-delitus might stem from the Greek θεᾶσθαι, "to behold or look attentively upon" The second part is often attributed to an unscholarly variation of the Greek word: δῆλος, meaning "evident" or "clear", Other New-latin or Greek derivations have been suggested as well as an English origin from "the alidade" 
  The early forerunners of the theodolite were sometimes azimuth instruments for measuring horizontal angles, while others had an altazimuth mount for measuring horizontal and vertical angles. Gregorius Reisch illustrated an altazimuth instrument in the appendix of his 1512 book Margarita Philosophica. Martin Waldseemüller, a topographer and cartographer made the device in that year calling it the polimetrum.In Digges's book of 1571, the term "theodolite" was applied to an instrument for measuring horizontal angles only, but he also described an instrument that measured both altitude and azimuth which he called a topographicall instrument  [sic]. Possibly the first instrument approximating to a true theodolite was the built by Joshua Habemel in 1576, complete with compass and tripod. The 1728 Cyclopaedia compares "graphometer" to "half-theodolite". As late as the 19th century, the instrument for measuring horizontal angles only was called a simple theodolite and the altazimuth instrument, the plain theodolite. 
  The first instrument to combine the essential features of the modern theodolite was built in 1725 by Jonathan Sisson. This instrument had an altazimuth mount with a sighting telescope. The base plate had spirit levels, compass and adjusting screws. The circles were read with a vernier scale.
caption: Jesse Ramsden's Great Theodolite of 1787
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