Heliotrope (instrument)

The heliotrope is an instrument that uses a mirror to reflect sunlight over great distances to mark the positions of participants in a land survey.

The heliotrope was invented in 1821 by the German mathematician Carl Friedrich Gauss.

[5] Surveyors used the heliotrope as a specialized form of survey target; it was employed during large triangulation surveys where, because of the great distance between stations (usually twenty miles or more), a regular target would be indistinct or invisible.

A. Colonna of the United States Coast and Geodetic Survey from Mount Shasta, a distance of 192 miles (309 km).

The inventor of the heliograph, a similar instrument specialized for signaling, was inspired by observing the use of heliotropes in the survey of India.