This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
A plane is tangent to a sphere, when it touches the sphere in only one point. A plane perpendicular to a radius at its outer extremity is tangent to the sphere, Fig. 83.
Fig. 83. Plane Tangent to Sphere.
Fig. 84. Large Circle.
Fig. 85. Small Circle.
An inscribed polyedron is a polyedron whose vertices lie in the surface of the sphere.
A circumscribed polyedron is a polyedron whose faces are tangent to a sphere.
A great circle is the intersection of the spherical surface and a plane passing through the center of a sphere, Fig. 84.
A small circle is the intersection of the spherical surface and a plane which does not pass through the center, Fig. 85.