1. Babcock, H. W.: 1958,Astrophys. J. Suppl. Ser. 3, No. 30.
2. Bandyopadhyay, P.: 1968,Phys. Rev. 173, 1483.
3. Bandyopadhyay, P.: 1970,Nuovo Cimento, to be published.
4. Bandyopadhyay, P. and Chaudhuri, P. Ray: 1970,Nuovo Cimento, to be published.
5. Chaudhuri, P. Ray: 1969a,Nuovo Cimento 64A, 528.