The geometrical shapes in Fig. 1 recently came into the Greenslade Collection. The semi‐triangular pieces of wood looked like slices from a pie, each 22.5° in angular width. They were tied together with a thin leather band tacked around their curved surfaces. What is this apparatus?

1.
Henry Crew and Robert R. Tatnall, A Laboratory Manual of Physics, for Use in High Schools (The Macmillan Company, New York, 1902), pp. 5–6.
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