On the last occasion I had the honour of attending a meeting of this Society the members were expressing their admiration of the great work done by the late Wilbur Wright. This consisted in first studying the known suggested theories governing the physical laws of flight, and then, after much patient labour, embodying the result of his reflections in the form of an aerial apparatus. Then at great personal risk, with his brother's aid, testing his apparatus as a glider until he was satisfied that a practical machine driven by power could be made; which he successfully accomplished and piloted with results well known to this Society.

To-night we have to consider many theories governing a different kind of law and suggest means by which they can be reduced to practical regulations. We have not the same opportunities as the physicists, no official laboratories or opportunities for making experimental tests, and have to leave this to the cumbersome machinery of the administrative authorities of the governing political powers.

The subject of my paper is the airship of to-morrow, and if I look at it rather from the point of view of military requirements, you must bear in mind that it is these requirements which have made it what it is. Commercial needs and even Naval needs have played a very small part hitherto in its development, though they may be expected to exert considerable influence on its progress in future.

Looking back over the past few years, we find an extraordinary prejudice against airships in this country, fostered in the most amazing manner by the Press, both lay and technical. This did not begin to dissipate until the autumn of 1912, just over a year ago.

As late as October, 1912, the “Times” wrote a leading article on the folly of spending money on airships, taking as its text the accident to “Gamma” after the manœuvres of that year.

In this lecture, which the Council of the Aeronautical Society, through Mr. Griffith Brewer, have done me the great honour to ask me to deliver before you, I propose to consider the rôle of speed or fast flying in aeroplanes.

As soon as aeroplanes were able to fly, the next preoccupation of designers was to make them fly as fast as possible. In order to stimulate constructors, Mr. James Gordon-Bennett created his International Aviation Cup, destined to consecrate every year the fastest flying machine. This contest, held yearly since 1909, will give us a valuable basis to examine the lessons which aviation has been able to draw from pure speed.

As far as the writer is aware, Mr. Horace Darwin was the first to call attention to the fact that there is an essential difference in action between a spring-controlled and a gravity-controlled air speed indicator on an aeroplane.

This fact was put forward in the Wilbur Wright lecture of last year and the conclusion then reached was definitely in favour of the use of the gravity type, as being more useful to a pilot on a steeply banked turn.

Since that date, however, the discovery has been made that this type fails to give warning of “ stalling ” in straight flight (the very purpose for which the instrument is installed) and equally fails under the conditions of a banked turn.

The writer believes that he has the priority in this discovery, and therefore takes the present opportunity of publishing the following formal proof of the scientific theorem involved.

In the previous contribution and in the reply to the discussion justice was not done to several points.

It was made clear that a circulation of air was established round the airscrew at standstill, creating a certain velocity before the airscrew disc in such a way as to modify fundamentally the thrust on the blades. But it was not explicitly stated that at full speed (of the aeroplane) this component of velocity was ignored altogether and each blade was assumed to be attacking “ still ” air.

This does not mean that the air was still until the blade actually drew level with it, for, if the analogy with lifting surfaces holds, we know that at a distance of twice the chord width in front of the blade the air is appreciably disturbed, and this disturbance may be by no means negligible even at four or five times the chord's width in front of the instantaneous position of the blade.