1. Arturo Uccelli,Leonardo da Vinci (New York: Reynal and Co., 1956).
2. S.P. Timoshenko,History of Strength of Materials (New York: McGraw-Hill, 1953).
3. sections 1503 and 936;I. Todhunter,1886
4. P. Ludwik,Elemente der Technologischen Mechanik (Berlin: Junius Springer, 1909).
5. T.E. Stanton and R.G.D. Batson,Proceedings of the Institute of Civil Engineers, 192 (211) (1920), p. 67.