Geometric Model by A. Harry Wheeler, Trihedral Angles
In this plastic model, a transparent tetrahedron has isosceles triangles for side faces. Inside it is a white triangle with one edge on the base and two on other faces. A paper tag readsL 2TRIA. Another tag reads: A.Harry Wheeler.
George Wentworth used two such figures in a theorem defining two equal trihedral angles in terms of the face angles on the faces surrounding the trihedral angle.
For a related pattern, dated February 2, 1945, see 1979.0102.109.
Compare 1979.0102.206 and 1979.0102.207.
George A. Wentworth (with David Eugene Smith), Plane and Solid Geometry, Boston: Ginn and Company, 1913, pp. 312-313.