The orologist was invented in 1873 by Franz Schrader to facilitate the Cartographie mountainous regions by carrying out “ reviews ”.
It acted to combine an instrument which would automatically plot the drawing of the mountains in the shape of a perigraphic draft planes .
The principle of the apparatus is to graphically defer displacements of a sight tube on a circular plate to directly record the Azimut and the Height of the point concerned. It comprises:
- mobile glasses at the same time around a vertical axis and a horizontal pivot connected to this axis,
- a horizontal arm which follows the glasses in its rotation around the vertical axis,
- a vertical sector interdependent of the glasses in its rotation around the horizontal pivot, connected to a small rule sliding along the horizontal arm.
The observer traces initially the Horizon of the point of observation, while making carry out with the glasses regulated with horizontal complete rotation. It aims then the principal points of the landscape observed and records, by crosses, their position on the disc (they are the points numbered on the review). It can outline, by combined movements - horizontal and vertical - glasses, remarkable elements of the relief (edges or watersheds).
The observer supplements then the mechanical draft “ ”, by complements added “ by a show of hands, while placing the secondary details in the middle of the network of the broad outlines, and by giving to the tops indicated by crosses their characteristic profile ”. A very trained observer, like Schrader, could produce a review in approximately three hours.
These discs were used then for the realization of the topographic charts, according to the traditional methods of the Topographie. The advantage of the review produced with the orologist on the traditional notebooks of ground is that one found there at the same time the indications of azimuth and height of the principal points, and figuration of the forms of the relief.
Schrader produced approximately 160 reviews that it used for the realization of the chart to the 1/40 000 of the Massif of Mount-Lost and for that of the chart of the the central Pyrenees to the 1/100 000.
Schrader tried without much success to market the orologist. The instrument, although very effective between the hands of a skilful observer and excel draftsman was considered to be difficult to handle. Moreover, the use of photography in topography, as of the end of the 19th century made lose of its interest to the drawing carried out directly on the ground.
Sources and references
External bonds
- the orologist constuit by Balbreck groin
- the principle of the review. Page “Schrader” on the site of the University of Pau and the Countries of Adour
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