Area of Sphere
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“It is found that the cord covering the curved surface is twice as long as the one covering the flat surface. So the area of the entire curved surface of a sphere is equal to the area of the surface of 4 circles like the one measured.” -Foster, 1921
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SpheresSource
Ellsworth D. Foster ed. The American Educator (vol. 1) (Chicago, IL: Ralph Durham Company, 1921)
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