Danfries Triangualtion Instrument - 1597

A triangulation instrument is a form of surveying instrument often recommended for range-finding by gunners as well as for land surveying. It was alleged to be a convenient way to apply the principle of triangulation, and works by forming a triangle with the arms of the instrument similar to the triangle on the ground. One arm can be considered equivalent to the base-line on the ground, while a second arm, with sights, pivots at one end, and a third, also with sights, pivots on a mount that slides on the base-line arm. Each arm is marked with the same linear scale. The distance between the pivoted arms is set to a scaled equivalent of the base-line on the ground. Sightings on the target are taken with either pivoted arm at respective ends of the base-line. The lengths of either arm to their point of intersection give the equivalent distances to the target at the known scale.

As indicated below, a number of authors devised Triangulation Instruments and published books about the instruments in the late 16th and early 17th centuries. The instruments weren't very practical for most surveying purposes, however. So the instruments are very rare and were probably little used.

Very few Triangulation Instruments were made originally, and I only see a few in Museum holdings, auction results, and private collections. Triangulation Instruments are pretty cool instruments, but weren't very practical. Given the rarity, the few Triangulation Instruments that survived have been mostly snapped up by European museums and large private collectors. If one does pop up for sale, it will likely be offered at auction by Christies. It won't be cheap.

There are very Triangulation Instruments, and even fewer pics of them that aren't under copyright protection. The materials below provide a good taste of what Triangulation Instruments looked like.