Semielliptical trammel

This semielliptical trammel made in brass was used to draw an ellipse. It was made in London around 1775.

The semielliptical trammel consists of a T-shaped base, into which are sunk two grooves at right-angles to each other. The base has pins on the underside, to prevent it slipping. It has a long bar, with a pen at one end, running through two sliding heads attached to wheels which run in the grooves. The pen is restrained on the end of the bar, and thus draws an ellipse. This instrument is signed 'Adams London' on the wheel.

An ellipse is one of the curves which is of some importance to draughtsmen, used, for instance, in the design of bridges or arches, and by architects when drawing or setting out ceilings or stairs. Being a conic section, the figure was known to the Greeks, but it was not until the Renaissance that the desire to draw a circle in perspective with accuracy gave the impetus to the invention of the earliest devices which could depict ellipses. Albrecht Durer invented a form of semielliptical trammel in about 1540, and examples appear in cases of drawing instruments dating from about 1600 onwards.

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