Along the garden path and up the stairs
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.
[3] The
origin of the word is unknown. The first part of the
Neo-Latin theo-delitus might stem from the
Greek θεᾶσθαι, "to behold or look attentively upon"
[4] The second part is often attributed to an unscholarly variation of the Greek word:
δῆλος, meaning "evident" or "clear".
[5][6] Other Neo-Latin or Greek derivations have been suggested as well as an English origin from "the
alidade".
[7]
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.
[3] Martin Waldseemüller, a
topographer and
cartographer made the device in that year
[8] calling it the
polimetrum.
[9] 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].
[10] Possibly the first instrument approximating to a true theodolite was the built by
Josua Habemel in 1576, complete with compass and tripod.
[8] The 1728
Cyclopaedia compares "
graphometer" to "half-theodolite".
[11] 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.
[12]
The first instrument to combine the essential features of the modern theodolite was built in 1725 by
Jonathan Sisson.
[12] 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.
Jesse Ramsden's Great Theodolite of 1787
A theodolite of 1851, showing the open construction, and the altitude and azimuth scales whic