Radius of the Earth Measurements

 

Spherical Excess

For a triangle on a plane, the sum of the interior angels is 180°.  For a triangle on a sphere, the sum of the interior angles must be more than 180°.  The amount over 180° is called “spherical excess”.

 

 

 

 

Overview of several different measurements circa 1906:

History of the Determination of the Figure of the Earth from Arc Measurements