1. Aeronautical and miscellaneous notebook (ca. 1799-1826) of Sir George Cayley, Cambridge, England, 1933.
2. 2von Karman, T., Aerodynamics, McGraw-Hill, New York, 1963.
3. 4Maxwell, C., Scientific Papers, Vol.2, 1869, Dover Publications, New York, 1952, pp.175-177.
4. LVIII. The limits of economy of material in frame-structures