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 Wright brothers made careful observation of the flight of birds, and fourd their observations A'aluable. It is interesting to consider the resemblance and differences of the manufactured aeroplane and the living bird. The resemblance may be simply the result of copying the bird, or it may be that similar designs have been arrived at independently by birds and men. The wings of both are roughly the same shape : of wide span, and narrow in the direction in which the bird flies ; both have concave wings with thick leading edges. In many aeroplanes hollow spars arc used like bones and like the quills of the feathers of birds. We copy plants also in this respect, for they too have learnt the economy of material in the use of hollow spars. The bodies of airships {iresimilar in shape to the bodies of swimming animals, with the greatest width towards the head. The bodies of birds are of similar form.

The essential points of any anemometer are that it should be correctly calibrated and should read accurately over the whole range through which it is to be used, and that the calibration should not alter with time. The actual calibration of an anemometer by a direct comparison of its readings with its rate of movement through the air is a matter of very great difficulty, and the various methods by which it has been done will be considered later, but when it has once been cairied out for one anemometer all others can be easily calibrated from that one by comparison.