When your Secretary, shortly before Easter, wrote to ask me to give the Wilbur Wright Lecture he made me give him a title before writing the lecture. I therefore had to think of one which would fit any lecture I might conceivably want to give, so that when I came back after Easter I should be able to pick out one of those subjects connected with aeronautics with which I have been specially concerned, and discuss the results arrived at. When, however, I came to sit down to write the lecture itself it struck me that it might be more interesting to a general audience if I followed the line which is perhaps most obviously indicated by my title, and directed my remarks towards tracing and comparing some of the principal lines of argument which have been used in aeronautical research, without going particularly deeply into the results.

It is only within the last few decades that it has been possible to conceive of a flying machine operating on the flapping system which would be consistent with mechanical principles. The development of gliding or “ wedge ” flight through the medium of the screw-propelled aeroplane has largely contributed to this result, but it must not be overlooked that as far back as 1899 Prof. Maurice Fitzgerald (Trans. Roy. Soc., Vol. LXIV., p. 420, and also (A) Vol. LXXXIII., p. 72, 1909) and Rayleigh (Manchester Lit. and Phil. Soc., Vol. XLIV., Pt. 2, No. 5, pp. 1-26—see Appendix III. hereto) enunciated certain of the most important factors of the problem. Whether the mechanical action should be the same as that of a bird is a matter for discussion, but anyway it is certain that a moving surface having a periodic vertical motion and a periodic change of “ attitude ” can efficiently produce lift and propulsion. The success of several rotary feathering lifting wheels (e.g., Clarkson's and Pichou's, concerning the latter see “ L'Aerophile,” March 1st, 1912) in producing appreciable lifts per horse-power is significant, but it is probable that the inventors have not sufficiently realised :—