1. Whipple, F. L.; 1963, On the structure of the cometary nucleus. In “The Solar System”, vol. 4, ed. B. M. Middleburst and G. P. Kuiper, Univ. Chicago Press, pp. 639–664.
2. Laplace, P. S., 1813, “Exposition du systeme du Monde”, 4th edition, Paris, p. 130.
3. Hirn, G. A., 1889, “Constitution de llespace celeste”, Gauthier-Vi11ars, Paris.
4. Swings, P., 1948, Le spectre de la comete d’Encke, 1947c. Ann. Astrophys., 11, pp. 124–136.
5. Krezak, L., 1981, The lifetimes and disappearance of periodic comets. Bull. Astron. Inst. Czech., 32, pp. 321–339.