The title of this paper does not immediately suggest aeronautics, but the connection is very intimate, as the laws of similitude constitute the theory of the use of models. Aeronautics, or rather, aerodynamics, is almost entirely an experimental science at present, and a glance backwards thiough time will show how much of the fundamental data of the subject is derived from experiments on models. We have, in the first place, Langley's researches, which showed that sufficient lift could be obtained to make models fly with such light engines as he was able to construct. The development of the petrol motor removed the greater part of the engine difficulty, and with that out of the way, Langley's figures for model planes, modified by Lilienthal's experiments on cambered models, provided the initial information from which the earliest flying machines were constructed.

Sir John, Ladies and Gentlemen,—When, a few days ago, I had finished the notes for this evening, I rather wondered which portion of me, if any, you would kindly allow, to leave this room. You will, I am afraid, tell me it is not a lecture on Military Aviation at all, that—but I will not take the words out of your mouth. My excuse is that the words "military" and "aviation" are each so large and lead in such innumerable directions. It is difficult to obtain a correct perspective of the combination. I must rely upon the usual hope of the diffident speaker and say how desirous I am that my efforts may at all events lead to a brilliant and illuminating discussion.

Anyone who is worth his salt is fired with the desire to add to the sum of human knowledge. That is one of the basic principles of our lives. For all such there is a vast field of useful work in the science of Aeronautics, provided they have sufficient determination and grit. It is to these I am speaking to-night, and it is my sole purpose to endeavour to direct interest in research Work by showing how easy it is to construct simple apparatus with little money. I propose afterwards to describe a few diverse experimental researches made with such an apparatus. Needless to say, it will be a real pleasure to me to give any assistance or advice I can to all who may decide to instal such apparatus. The greater the number of experimenters at work, the faster will our knowledge proceed, and so long as the work is done it matters little whether it is you or I who do it.

The general name "airscrew" will be used throughout for the organ of propulsion of aircraft.

When the airscrew is in front of the main lifting surfaces it is called a tractor, when behind them a propeller.

When it turns clockwise, as seen by an observer standing in the blast (i.e., behind the aircraft) it is called right-handed and, when anti-clockwise, left-handed. Airscrews are thus classified as :— Propellers or Tractors. Right-handed or Left-handed.