1. Bobrovnikov, N.: 1941, Perkins Observatory Contribution, No.15.
2. Bobrovnikov, N.: 1942, Perkins Observatory Contribution, No. 16.
3. Bobrovnikov, N.: 1943, Perkins Observatory Contribution, No. 19.
4. Delsemme, A. H.: 1987, Symposium on the Diversity and Similarity of Comets, ESA SP-278, pp. 19?30.
5. Kidger, M. R.: 1996, Earth, Moon and Planets 73, 15 (Paper I)