This brass device is a patent model for a “new and improved instrument for drawing curves and figures approximating in form ovals” (U.S. Patent 22910, February 8, 1859). An oval shape, the ellipse is one of the four conic sections, the others being the circle, the parabola, and the hyperbola. Ellipses are important curves used in the mathematical sciences. For example, the planets follow elliptical orbits around the sun. Ellipses are required in surveying, engineering, architectural, and machine drawings for two main reasons. First, any circle viewed at an angle will appear to be an ellipse. Second, ellipses were common architectural elements, often used in ceilings, staircases, and windows, and needed to be rendered accurately in drawings. For this reason, several drawing devices that produce ellipses, called ellipsographs or elliptographs, were developed and patented in the late 19th and early 20th centuries.
Developed by Thomas William and William Joslin of Fishersville, Connecticut, in the 1850s, this invention consists of a circular disc that freely moves along the slot in the base of the model as it rotates. The base of the steel arm is fixed while the point fits by means of a pin into one of several holes in the disc which are at various distances from the center. The shape and movement of the arm is reminiscent of an hour hand on a clock. Attached to the bottom of the disc is an armature that can be set in various positions and has an attachment for a pencil. As the disc is rotated by hand, the arm is constrained to move side to side. This in turn forces the disc to move in a perpendicular direction along the slot. Finally, the pencil arm below the disc will move in an elliptical path. By changing the connection point of the arm on the disc as well as the distance of pencil is from the center of the disc, ellipses of different sizes and eccentricities can be produced.
The Smithsonian also owns the 1852 patent model of a machine for making cordage designed by William Joslin (U.S. Patent 8825).
This model was transferred to the Smithsonian from the U.S. Patent Office in the early 20th century along with several other patent models.
U.S. Patents, Google Patents.
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