Perspective Ruler
From Inventions
Has no specific name.
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Inventor
Grellier de Serviere
Historic Period
1719
Description
Ruler with cursors and plumb bob designed, as states the inventor, for "drawing a plan in perspective precisely without recurring to the ordinary rules, which are difficult and time-consuming" ("Moyen facile de tirer exactement un plan géometrale en perspective, sans avoir recours aux régles ordinaires, qui son longues et embarassantes", p. 150). The device consists of a ruler mounted horizontally at the centre of a drawing board on which slide two cursors. The plan drawing is positioned below the ruler, while the sheet of drawing paper is placed above it. On the blank sheet, the artist first traces the horizon line with the position of the principal point and the distance point. At these vanishing points are fixed two hooks with plumb bobs sliding in them. One end of the string passing through the distance point is tied to one of the cursors. The string passing through the principal point has two plumb bobs instead, and also slides along a slot in the other cursor. The artist first moves the principal point cursor until the plumb bob falls on a significant point on the plan drawing. Below the line serving as ground line, the string reproduces an orthogonal projection of the point in question. Above the ruler, instead, the same string indicates the line converging at the principal point, on which the perspective image of the point is found. Having noted the distance between the point on the plan and the ruler, and transferred it to the ruler itself toward the other cursor, the artist moves the latter as far as the distance measured. The string converging at the distance point thus intersects the other wire, indicating the perspective position of the point in question.
Bibliographical Resources
Grellier de Serviere. Recueil d'ouvrages curieuses de mathematique et de mecanique ou Description du cabinet de monsieur Grellier de Serviere, Lyon, 1719, p. 150, tav. 88, fig. 127.
Author of the entry: Filippo Camerota
