1. Beckers, J. M.: 1964, ?A Study of the Fine Structures in the Solar Chromosphere?. Thesis. AFCRL- Environmental Research Paper No. 49.
2. Beckers, J. M.: 1966, The Fine Structure of the Solar Atmosphere (ed. by K. O. Kiepenheuer), Franz Steiner Verlag, Wiesbaden, p. 80.
3. Beckers, J. M.: 1968, Solar Phys. 3, 367.
4. Bhavilai, R., Norton, D. G., and Giovanelli, R. G.: 1965, Astrophys. J. 141, 274.
5. Bray, R. J.: 1968, Solar Phys. 5, 323.