France, paralysed during many years of a cruel occupation, has been unable to maintain a sustained technical effort, comparable with that of England.

Nevertheless, the work of French engineers was never discontinued. In difficult and sometimes dramatic circumstances, more often than not with only restricted facilities, their work of research continued, stubbornly and in silence.

The theme of flutter has not often been the subject of lectures before this Society, but the earliest of these was given as long ago as 1929 by my friend and former colleague Dr. R. A. Frazer. At that time a secure foundation for flutter theory had been laid and the principal methods for flutter prevention were already known. However, both theory and practice have developed much since 1929 and flutter has become of greater relative importance.

As stated in the introduction to Section 6.5 the practically important case of an open section tube with no St. Venant torsional stiffness (see Fig. 38) will be treated as the limiting case of the open tube with J as J→0. It will be shown that the stress system g1h1over the open tube degenerates into a stress system gгhг which is statically equivalent to the torque TBS about the shear centre. This stress system is for a uniform cylindrical tube with no J identical to the Wagner-Kappus torsion-bending stress system in open tubes.