1. J. Willard Gibbs, The Scientific Papers of J. Willard Gibbs, Dover Publications, Inc., New York, (1961), p. 219.
2. Dirk J. Struik, Lectures on Classical Differential Geometry, Addison Wesley Press, Inc., (1950).
3. C.S. Smith and L. Guttman, Trans. AIME, 197 (1953) 81.
4. R. T. DeHoff, Trans. Met. Soc. AIME, 239 (1967) 617.
5. Hans Giger, Proceedings, Second International Congress for Stereology, Springer Verlag, In Press.