1. Giacconi, R., Gursky, H., Paolini, F., and Rossi, B., Phys. Rev., L, 9, 439. (1962).
2. Friedman, H., Liége conference on “Astronomy from Space Vehicles” (1964).
3. Giacconi, R., Gursky, H., Waters, J., Clark, G., and Rossi, B., Nature, 204, 981 (1964).
4. Oda, M., Applied Optics (to be published).