1. The basis for the lecture is a large number of individual reports from aircraft constructors which in general are not published. However, the authors feel that they wish to refer to the standard work on the subject, viz. K. D. RAITHBY, A Comparison of Predicted and Achieved Fatigue Lives of Aircraft Structures. 1961 I.C.A.F. Symposium Proceedings, p. 249, Pergamon Press, 1963.