Ellipsograph made by James Nasmyth

Ellipsograph made by James Nasmyth

In this instrument, which was formerly the property of James Nasmyth, the trammels are at right angles to each other but lie in different planes, each parallel to the plane of the paper on which the ellipses are drawn. The trammels are adjustable to various heights and can turn about their axes so as to accommodate themselves to the varying inclination of the describing bar, whose upper portion passes through a sliding-piece which is constrained to move in a circle of adjustable radius. This describing bar is free to move up and down relatively to the trammels and to the sliding-piece, and its downward pressure keeps the pencil in continuous contact with the paper.