1. Quartz and Silice, F 77792 Nemours.
2. Fuji screens G4, Kasei Optonix Ltd, Minato-ku, Tokyo 105.
3. B.C. Grabmaier, Siemens R&D, München, private communication.
4. J. Dexpert, M. Chareyre, CNRS Bellevue, F 92 Meudon, private communication.
5. On the Use of X‐Ray Screens in Mammography