Mirror hypsometer
The mirror hypsometer was a device for measuring the height of trees in forestry, which was used until the 1930s. Its inventor, the Hessian forester Martin Faustmann , first presented the measuring instrument in 1856.
description
Faustmann's mirror hypsometer consisted of a rectangular, thin wooden board measuring 18 by 8.2 centimeters, to which a few additional parts were attached. The device was so compact that the forester could carry it in his jacket pocket along with a notebook and inch measure. The additional parts were only unfolded for measurement.
The main components of the device were:
- a two-part visor ( diopter ) made of brass with a peephole and horizontally stretched horse hair,
- a height scale, printed on paper,
- a narrow observation mirror (2.5 cm) on a hinge,
- a slide with a distance scale and
- a plumb bob attached to it from a silk thread with a lead weight.
The slider could be used to change the suspension point of the plumb bob depending on the distance from the tree to be measured. According to Faustmann, the mirror hypsometer delivered optimal results when the forester aimed at the tree from a distance that roughly corresponded to the height of the tree.
To protect against moisture, the height scale was coated with varnish and the slide was soaked in linseed oil .
function
Before measuring with the mirror hypsometer, only one variable needs to be known, namely the distance from the observation point to the tree, the so-called base line . You can pace them or measure them with a length measuring device (cord, tape measure).
The slide of the mirror hypsometer is pulled out according to the distance, lets the plumb bob on its thread in front of the height scale and aims at the tree top. As soon as the plumb line has finished its pendulum movement, you can read the tree height on the scale via the mirror. To make the scale easier to read, the numbers are written in mirror writing.
Mathematical basics
The mirror hypsometer is based on the principle of similar triangles ( congruence theorem ). The plumb bob divides a right-angled triangle on the board. Its angles are the same as the angles of the triangle that is formed from the tree trunk and the observation point.
According to this principle, so-called measuring boards were already in use as altimeters before the mirror hypsometer - a kind of vertically positioned measuring table .
history
The fundamental innovation of Faustmann was a movable mirror . As a result, the forester was able to observe the plumb bob and the scale at the same time when aiming at the tree top.
Until then, the forester either needed an assistant to read the tree height, or he had to hold the plumb line and turn the device over to read it. If he did not use a tripod, vibrations could lead to incalculable measurement errors. The mirror made the tripod dispensable.
As early as May 1854, Martin Faustmann had described the folding mirror in the Allgemeine Forst- und Jagdzeitung as a useful "improvement on the tree height gauges".
In the December 1856 edition he formulated the requirements for a device for measuring tree height. It should be inexpensive, convenient to transport and easy to use, and it should show the tree height with sufficient accuracy (one to two percent) without cumbersome calculations. Angle instruments such as theodolite and mirror sextant were more accurate, but because of their cumbersome handling and high costs, they did not gain acceptance in the forest. Instead, so-called measuring boards were used. Faustmann described his further development as "a measuring board in its perfection".
The device was foldable so that the forester could easily take it with him to the district in a small box or case. The special advantage of the mirror hypsometer compared to the Weise altimeter, which was created at the same time, was that the tree height could be read directly without having to make trigonometric calculations.
Martin Faustmann saw the limits of his measuring instrument where, for example, great accuracy was required when leveling paths. On the other hand, the mirror hypsometer is well suited to quickly determining the gradient of a short distance or a mountain wall. In order to determine the elevation angle, a task that rarely occurs in practice, a trigonometric table was supplied with the measuring instrument.
Faustmann also saw a didactic benefit in his invention. Thanks to the movable slide, it is "preferably suitable for making the theory of this type of height measurement clear".
Manufacturer and further development
The mirror hypsometer was already available after the first publication in the Allgemeine Forst- und Jagdzeitung. Martin Faustmann had a first edition of his measuring instruments produced. He later made the devices himself together with his wife Sophie. He initially sold them for two guilders and 24 kreuzers (= one and a half thalers) with a case, instructions for use and an angle plate.
After Martin Faustmann's death in 1876, his widow continued to sell the mirror hypsometer.
The devices were later also built by other manufacturers. Hartmann & Braun in Frankfurt added a foldable connection that supported the mirror.
The mirror hypsometer was used not only in Europe, but also in Australia and the USA. There the instrument was offered by Keuffel & Esser in New York in a more robust version: with a metal frame, an additional handle and a silver-plated, engraved scale.
literature
- Kurt Schäfer: Martin Faustmann, a life for the forest . In: Babenhausen then and now . tape 28 . Heimat- und Geschichtsverein Babenhausen eV, 2000, ISSN 0174-3929 .
- Martin Faustmann: The mirror hypsometer. A new instrument for measuring heights . In: Allgemeine Forst- und Jagd-Zeitung . December 1856, p. 440–447 ( plumbbob.de [PDF; 200 kB ] Copy by Wolfgang Rücker from October 2009).
- Martin Faustmann: An improvement on the tree height gauges . In: Allgemeine Forst- und Jagd-Zeitung . May 1854, p. 165–166 ( plumbbob.de [PDF] copy by Wolfgang Rücker from October 2009).
Web link with illustration
Individual evidence
- ↑ Julia Ellen Rogers: The tree book , New York 1906, quoted from Wolfgang Rücker: Wolfs Senklot News 2009-04, PDF 2.7 MB , p. 55
- ↑ Martin Faustmann: The mirror hypsometer. A new instrument for measuring heights . In: Allgemeine Forst- und Jagd-Zeitung . December 1856, p. 440 ( plumbbob.de [PDF; 200 kB ] Copy by Wolfgang Rücker from October 2009).
- ↑ Kurt Schäfer: Martin Faustmann, a life for the forest . In: Babenhausen then and now . tape 28 . Heimat- und Geschichtsverein Babenhausen eV, 2000, ISSN 0174-3929 , p. 21-22 .
- ↑ www.plumbbob.de collector side
- ↑ Wolfgang Rücker: Wolfs Senklot News 2009-04, PDF 2.7 MB , pp. 56–58