1. Chapman, S., , J., Bartels, , Geomagnetism, Oxford, 1940,
2. Benkova, N., , J., Kalinin, , Ten-day review of cosmic data, , No. 125–128, Leningrad, 1941,
3. Gnevishev, M., , , Bulletin de l'Observatoire Central à Poulkovo, , , 16, , 2 , 36–44, Leningrad, ( 1938, ).
4. Figenson, M., , Poulkovo Observatory Circular, , No. 30, 68-87 Leningrad, 1940,