I have been deeply appreciative of the action of the Council in inviting me to deliver this lecture. No one could be otherwise. The Wilbur Wright. Lectureship has been illustrious in the qualifications of the thirty speakers who have been my predecessors on this platform ; but it is illustrious also in itself, in the manner of its founding, and in the manner in which the Royal Aeronautical Society has carried it on in an unbroken series through two wars and the years between.

Many problems arise in stress analysis which are not reasonably susceptible to mathematical treatment. Recourse may then be had to experimental methods. One of the most useful of these is the photoelastic method. This method is based upon the fact that transparent materials when stressed undergo changes in their optical properties which can be measured and related to the applied stress.

Flight is the most 'perfect and unconstrained form of animal motion; it is also the most widespread, since it offers the most favourable conditions of survival in the struggle for existence. Animal species losing the power of flight, are an easy prey for their enemies, and speedily become extinct.

Man, having achieved the power of mechanical flight by technical skill, has now introduced the art of flying in his own struggle for existence, as abundantly proved by the history of the past thirty years. Research, and not engineering research alone, has stood in the forefront of this development: filling the rôle of the advanced reconnaissance unit in development, experimentation, and the tactical application of the power of flight.

Man, aircraft-borne, now flies higher (record altitude 17,000 m.), faster (speed record 755 km./h.), and farther (long-range distance record over 12,000 km.), than any other animal. This raises a query as to the effect of flight on the human organism.

The object of this paper is to contribute one step toward the knowledge of the stresses in the neighbourhood of openings in monocoque aircraft fuselages by developing a procedure for the calculation of the stresses in spaced-curved rings used for reinforcing the edges of openings. The general appearance of such an opening is shown in the perspective view of Fig. 1. The procedure presented here presupposes a knowledge of the forces which act upon the ring. These forces depend upon the relative distortions of the reinforcing ring and of the rest of the fuselage, and the exact determination of their magnitude under different conditions of loading of the fuselage presents great difficulties.

Modern research in experimental aerodynamics is largely concerned with the effects of the boundary layer. Interpretation of experimental results would be greatly assisted by the knowledge of the position and extent of the transition region and of the separation points. Frequently this has to be obtained, and it can only be done by the use of an elaborated technique involving hot-wires or total head creepers with complicated traversing gear, so that the work takes on the character of a major research.

In addition to the usual aerodynamic and structural problems the seaplane designer has a number of problems to solve which are associated with the behaviour of the seaplane on the water. The operation of a seaplane on the water is well known and in these days accepted as a matter of course. However, behind these apparently easy operations there lies a background of continued effort and development.