Geometry
c. 1900
Keystone View Company American, 1892-1963
New York City
Text printed on reverse of stereocard:
No. 43 – (34224) Geometry Unit – The Sphere
A sphere can be circumscribed about any given tetrahedron.
Corollary: Through four points not in the same plane one spherical surface, and only one, can be passed.
Corollary: The four perpendiculars erected at the centers of the faces of the tetrahedron meet at a point.
Gelatin silver print, stereo