The eighteenth century saw the invention of many drawing devices used by architects and artists.

The "graphic pen," invented by Giovanni Battista Suardi in 1752, is an instrument for mechanically plotting many different types of curves such as circles, ellipses, and cycloids.

The copy in our Museum is a graphic pen modified by Felice Gori, a machine craftsman at the Museo di Fisica e Storia Naturale of Florence. It is fairly similar to the one illustrated by the famous English instrument-maker George Adams.

The pen, placed on a sheet of drawing paper, is composed of three curved supports at the center of which is attached a vertical shaft. A mobile horizontal arm (designated by the letter "A") is hinged to the shaft. It carries a groove along its length and is held by a diagonal tie-rod. A train of gear wheels can be mounted by means of cursors fitted with pegs in the groove. On the axle of the outermost gear wheel is attached a second mobile arm (designated by the letter "B") fitted with a writing tip. To the vertical shaft is fixed a gear wheel that meshes with those on arm "A." As a result, the rotation of "A" generates a simultaneous rotation of "B" around its axis. The motion of the writing tip is thus the sum of two rotations. By mounting gear wheels of different diameters on the instrument, by changing the number of wheels, and by changing the length of arm "B," one can generate an extremely large number of different curves.