The first part of the paper deals with the action of light in deteriorating the strength of doped and undoped linen aeroplane fabric. Sunlight is shown to be the only serious agent. A curve is giver showing the change in rate of loss of strength throughout the year, the effect being very great in summer and practically negligible in winter. A comparison of the weathering properties of German and British material is given. Experiments are described which indicate the loss of strength is due to the action of ozone formed by ultra-violet liglit, the :distribution of the destructive power in the spectrum corresponding very welLwith a photo-electric theory of the formation of ozone proposed F. A. Lindemann. The efhciency of dyes and pigments as protective agents is shown to be excellent, but the latter are to be preferred on account of their effect in improving the tautness given by the dope.

The second part of the paper deals with tautness and its measurement, the more important methods are discussed, and a standard one proposed l)y which The tautness can be expressed directly as a tension. A description of the standard frames and the system of rneasurement of tautness at high humidities at presc'nt used at the R.A.E. is given. A theory to account for the tautening effect of dope is suggested.

It is quite impossible in the scope of a single paper to deal with more than a small part of the vast subject of aeroplane design. What I have attempted, therefore, is to work out a few points which seem worthy of particular attention, and thence to suggest what would appear to be the best practice.

It is probable that what I have done has been done already by most people who have been engaged on designing work for the last few years, and probably done more fully and more accurately.

The rigging of aeroplanes, although not a subject necessitating extensive research work or particular scientific knowledge, is of paramount importance, in view of its effect on the safety, reliability, and performance of machines.

The mechanical principles involved are well known to the engineer, and their application rests to a great extent on experience.

In a word, practicability governs both construction and erection.

The subject of air navigation has been chosen because with the ending- of the Wiar this becomes the most important of the unsohed problems relating to aviation. It is unsolved mainly, I think, because the actual operations of the war, apart from certain individual efforts of great merit, did not reach the point at which really long flights were made. Had the activity of the Wiar continued there is little doubt that long distance air navigation would have been impelled to as high a degree of actual achievement as was attained by other branches of the new science of aeronautics.

In the early days of the war the desirabilitv of reducing the weight of aeroplane engines to a minimum, consistent with reliability and efficiency, very soon led designers to consider the advisability of using alloys considerably lighter than cast iron or steel for all possible parts of aero engines. Aluminium alloy crank cases had been used for some years in connection with motor car engines, and it was natural, therefore, that such alloys should come into use for the crank cases of aeroplane engines. Alloys of aluminium suitable for this purpose can be made, having a specific gravity not more than three, and having an ultimate breaking strength very nearly equal to that of cast iron. It was only necessary, therefore, to overcome foundry difficulties in order that such alloys should be generally used.

The strength of wooden struts consisting of a parallel centre portion with ends of conical taper is considered rnathematically. It is shown that the best results are obtained when the parallel portion is half the total length of the strut, and when the taper of the ends is such that the end diameter is half the central diameter. Such a strut is 12% lighter than a simple parallel strut of the same length and strength, and only 1% heavier than the ideal strut of the best possible gradual taper. A simple formula for design is given.

The authors suggest that struts of this pattern might be adopted, for manufacture reasons, in many parts of an aeroplane in which solid wooden struts are used, especially if of circular section. They can then be turned in the ordinary lathe.

At frequent intervals in the past the subject of the passage from model to full scale has received fairly thorough treatment at the hands of the members of this Society, and although a considerable mass of further material of extreme practical importance has since then accumulated, I do not propose to present it to you this evening. Those who are particularly interested in the data will find the greater part of it discussed in the Reports and Memoranda of the Advisory Committee for Aeronautics. I intend instead to devote this evening to a study of the question from a more theoretical standpoint, and in doing so I make no apology.

In venturing to enter this arena of the aviation world I am fully aware that I am guilty of no small amount of temerity, because in comparison with many of my audience I am a very raw recruit, both as an aviator and as a medical officer in the R.A.F. I can only plead in excuse for accepting the kind invitation of your Secretary to address you this evening- that I have done a good deal of hard thinking on the subject in the time at my disposal and have obtained some experimental results which appeared of interest to others qualified to judge; and further, it is only by free ventilation apd discussion of one's ideas that progress can be obtained in such a new field of science as aviation.

Information relating- to weather and climate has always attracted the attention of the inhabitants of all countries, as is shown by the number of popular sayings which relate to the weather and its ciranges in civilised countries, and by the general identification of atmospheric phenomena with gods and demons among savage races.

The question of whether it is possible to construct very large aeroplanes equal or superior in efficiency to the smaller aeroplanes already in existence is a subject that must be occupying the minds of people connected with aeronautics.

The subject has been considered by various aeronautical engineers and scientists in the pages of the ROYAL AËRONAUTICAL JOURNAL and elsewhere.

A few of the statements of conclusions arrived at are quoted from the AËRONAUTICAL JOURNAL of 1917 in an appendix.

In England there is no doubt that the late Colonel Cody was the pioneer of the large aeroplane, as although his plane would be considered to be of moderate dimensions to-day, yet it was large in relation to its contemporaries.

May I say how glad I am to have this opportunity of speaking to you on a subject to which I, and others, have devoted so much time and thought. Not that any of us have ever begrudged this time or labour. Far from it. I myself, after twelve years as a student of aeronautics, cannot look back on any period when, even for a moment, I have wearied in my task. And indeed the more I study this subject the more convinced I am h*^w well worth while it is for us, now, to devote all the time we can to this question of commercial aeronautics. It is a subject which is something much more than purely commercial. It is not only national but also Imperial. It is something even more than both of these; it is a question which affects the development, happiness, and peace of the entire world. When, with the growing speed of aerial transport, we shall be able to dine in New York one evening and in London the next; when no part of the earth—surface, however remote, is more than a week's journey from London by air, then I think we may say that the coming of this aerial age will do more for the world than any other invention or discovery man has ever made.