The growing importance of the study of Sound has been shown in many ways during the last few years and most particularly in its applications to military intelligence. Since the classical experiments of Tyndall in 1872 and following years, there is no very definite record of open–air experiments until L. V. King in 1919 performed some experiments for the Canadian Government on fog horns.

A new era of investigation has now been opened up by the realisation of the importance of observation by sound during the late war. The distant gun was located very effectively on most of the Army fronts, and towards the latter end of .the war the aeroplane, invisible at night, was being located by sound also.

The urgency of the problem to be solved resulted in the development of new and effective apparatus which is now available for peace applications as they arise. New microphones and new electrical accessories, particularly the new thermionic valve, have given acoustical research a new interest and have led to the hope of our being able to produce standards, thus bringing sound into line with the other branches of physics.

If I were to take my title literally, my task would be light, and this paper would end here. For there is not, nor has there been for some six years, a Panel of the Aeronautical Research Committee on Scale Effect. It would be unfair to cast the responsibility for this error on our Secretary, as I could have changed the title when I replied to his letter asking me to read a paper before you. But as it did not seriously misrepresent the facts, and was less cumbersome than any alternative I could think of, I let it stand.

The Panel to whose work I am permitted to draw your attention is the Design Panel of the Aerodynamics Sub–Committee. It has been my privilege to be Chairman of this Panel for the last year or more. It may not be out of place to mention that the justification for its title is that it deals with the part of the Sub–Committee's work which most directly concerns the design of aeroplanes.