The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



an instrument for drawing plane curves of the second order—parabolas. Its operation is based on plotting the points of the parabola in a rectangular coordinate system. Figure 1 is a schematic representation of a simple parabolograph and of its mode of operation. The instrument consists of a guide, represented by the x-axis; a rod that can slide along the guide but remains parallel to the y-axis; and a pair of rigidly connected and mutually perpendicular straightedges that can rotate about O. A shows the position of a fixed pin on the rod, and B the corresponding position of a sliding pen on straightedge 2. As the rod slides along the guide, it forces the joined straightedges to rotate about O. Then the pen rotates about O and slides along straightedge 2. The curve traced by the pen is a parabola. Parabolographs enable us to draw parabolas without the use of french curves.


Figure 1. Schematic of a parabolograph: O is the axis of rotation; A and B are the points of connection between the straightedges 1 and 2 and the rod 4; 3 is the guide; χ and y are the coordinate axes of the plane

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.