On the last occasion on which I had the honour of reading a paper before this (Society 1 took as my subject the shape of stability, of bodies falling through the air. 1 endeavoured to show that if you wish to make an apparatus which will descend in perfect equilibrium you must do something more than give it lifting surfaces with the usual dihedral angle; that it is, in fact, necessary to extend this plan and form them with an upward angle in all directions from an approximately central point, thus making them take a form like the surface of an inverted cone.

To-night I want to ask you to look at stability from another point of view. A flying body, to be of practical value, must have, in addition to equilibrium of buoyancy, another equilibrium, viz., that of progression, i.e., it must have a strong tendency to proceed with the same point of its framework always to the fore.

When we examine the numerous designs that have been proposed for power- driven aëroplanes it is most apparent that the designer, in most cases, has lost sight of the all-important subject of the efficiency of the different parts.

The aeroplanes are often quite large enough to give the required “ lift,” but the “ drift “ is enormous, the propellers are usually far too small in diameter, and the motor is so poorly cooled and adjusted, that it is not capable of giving anything like its rated power.

Any one of these faults is sufficient to make a failure of a possible success, but when they are combined, as they usually are, the machine is hopeless. I have just seen in Paris a machine glaringly wrong even in the most elemental principles, yet the builder had spent a large sum of money for a costly motor and its accessories.

The particular design of flying machine about to be described was the outcome of attempts by the writer to obtain an aëroplane model of high efficiency and of very strong construction.

For more than a century past the problem of human flight by means of heavier-than-air machines appears to have exercised a strong fascination on the minds of French inventors and engineers, and since November, 1906, as the result of Santos Dumont's classic experiments, and more recently the longer successful flights of Henri Farman and Léon Delagrange, even the general public has become interested in the subject, and has at last been taught to realise that dynamic flight is not only a possibility, but a fact, and that with each day which passes the success already attained is being steadily carried another step forward towards the evolution of the eventual type of perfected machine.

If we except the performances of the Brothers Wright in America, it is admitted that France has led, and is still leading, the aeronautical progress of the world, and it is not difficult to understand why this should be the case.

The earliest attempts at flights by man have been by extended wings in imitation of those of bats or birds, all of which have ended with failure, or fatal accidents.

The bird-wing type for supporting a man and mechanism in air must extend at least 60 feet from end to end, and be very light and strong, for carrying the weight—an impracticable construction. All this is fully explained in a paper read by me in 1866 at the first meeting of the Aeronautical Society of Great Britain, of which I was the pioneer.

Perceiving that a single pair of far- extended wings was impossible for man flight, I evaded lateral extension by placing a system of five aëroplanes, or webs, above each other. The upper one slightly in advance.

Within the limits of the present article it would be impracticable to deal adequately with exhaustive constructional details, or, in fact, many points bearing particularly upon the gist of this subject. Suffice it, then, to briefly refer to those facts by which the fundamental laws upon which is evolved the future complex and impressive airship of the near future is based, the lessons of Nature containing those laws, and which, in these modern days, are certainly insufficiently studied, and how man can reproduce these selfsame teachings by his methods culminating in the long-cherished, but by no means apocryphal and abortive, subjugation of the wide realms of the air.

The flying and soaring of all natural volant creatures is simply explained on well-known mechanical principles, and the majestic air-craft of the future will, in short, embody those principles intealia by the ingenuity of man.

In a paper published in the Journal of the Aëronautical Society of Italy, p. 267 (1906), I explained some interesting points regarding certain constructional technical advantages, dynamic and economic, special to the systems of dirigibles, which have a cylindrical form of great length, a very much reduced midship section, and a minimum distance between the point of action of the ascensional force and the axis of the car, of which the “ Zeppelin ” shows, in practice, a very successful example.

Mr. Laboccetta, in his paper, in the same Journal, page 2, 1907, when comparing certain types of dirigibles, pointed out the influence of the co-efficients of resistance to forward movement, the value of extended forms, the importance of fair shapes and lifting power, and showed the advantages of the extended shape in certain cases.