Model Illustrating Finding the Area of a Circle, Ross Surface Form #14

This is one of the models of plane figures (surface forms) designed by William Wallace Ross, a school superintendent and mathematics teacher in Fremont, Ohio. The flat wooden disc can be arranged as a circle which is divided into six wedges that are hinged together along the perimeter. These may be rearranged to form what the model calls a “rhomboid.”
One side of the model has four paper stickers and the other has six. One of them reads: AREA OF CIRCLE.
Ross, like A. H. Kennedy before him, argued that a circle could be considered as the most general case of a polygon with area equal to the sum of the area of triangles, with height equal to the radius of an inscribed circle, and with sides equal to the sides of the polygons. In other words, the area of the regular polygon equaled half the perimeter of the polygon times the radius of the inscribed circle, and the area of a circle half the circumference of the circle times the radius.
For further information about Ross models, including references, see 1985.0112.191. Closely related models are 1985.0112.200, 1985.0112.201, and 1985.0112.202. Kennedy’s version of this model is 2005.0054.01.
Currently not on view
Object Name
geometric model
date made
ca 1895
Ross, W. W.
Physical Description
metal (hinges material)
wood (overall material)
overall: 1 cm x 15 cm x 15 cm; 13/32 in x 5 29/32 in x 5 29/32 in
place made
United States: Ohio, Fremont
ID Number
catalog number
accession number
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Arithmetic Teaching
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of Wesleyan University
Additional Media

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