Geometrical pen with 12 changeable gear wheels by W.F. Stanley, London, 1876.

This is an example of the geometric pen invented by Signor J. B. Suardi and improved by Mr Stanley in 1866. Such a pen is capable of drawing innumerable ornamental geometrical figures.

It consists of an epicyclic train of three wheels, the middle one being fixed to the bridge frame which supports the instrument. The wheels are carried by a slotted bar which can rotate about the centre of the fixed wheel. The third wheel carries a crank arm underneath, to which a connecting rod may be fitted at various eccentricities. This rod slides through a sleeve fixed to the arm carrying the wheels and bears the drawing-point, which can be adjusted to any position on the rod.

Twelve wheels are provided, with 120, 96, 72, 60, 48, 36, &c., teeth, and are interchangeable on all three axes. The addition of the connecting rod and its connections, a means of raising the drawing-point, and the means of placing the figure produced in exact position, are due to Stanley.