The importance of healthy relations between the sporting and the scientific sides of gliding is very great; and the fact increases the responsibility of my task this evening as well as the honour that the Council of the Aeronautical Society have done me in asking me to undertake it. The history of gliding on the continent shows that at times when financial or other difficulties have given cause for anxiety, some development suggested on the scientific side has rekindled enthusiasm and given the movement a new vitality. Change is as essentially connected with a healthy sport as with a living organism. Nobody can visit the Wasserkuppe without being impressed by the zeal which prevails there; it is almost religious in its fervour, and although some of the neophytes of the hierarchy may be mere gymnasts fired with the team spirit, its bishops and its missionaries are inspired by their determination to advance knowledge.

The position to which aircraft construction has proceeded is due in a large measure to the intense metallurgical investigations of recent years. Amongst the materials that have arisen out of this are the light alloys of aluminium, and in particular, that known by the general name “duralumin.” This alloy plays the part of main structural material in many of our present-day aircraft. The object of this paper is to give a brief general account of duralumin with reference to aircraft construction.

During the last few years the use of the Diesel engine for aircraft has become important; it has advantages and some disadvantages when compared with the petrol engine, and what we are directly concerned with is overcoming, or at least reducing, the disadvantages. The most obvious of these is the relatively high weight-power ratio of the engine, but it is to be hoped that this will be overcome as rapidly as it was in the development of the petrol engine. In any case, the unfavourable weight-power ratio of the compression-ignition engine is, for long flights, offset by the weight of fuel required to be carried.

When this instrument is in its observing position the visible horizon is reflected at three points vertically downwards into a telescope. The portions of the horizon observed are facing the observer and lie 60° to his right and left. The images of the visible horizon appear as three straight lines in the field of view intersecting at about 60°. The observation consists in bringing the image of the celestial object into a certain point defined by the configuration of the horizon-lines. It is of no consequence whether all the rays after the downward reflection are again reflected into a horizontal direction, and whether this occurs before or after the rays enter the object-glass. It will be shown below how the observer is enabled to keep the error of inclination so small that its effect on the result, of second order, can be neglected.

A great deal of interest has recently been taken in the subject of rocket propulsion, undoubtedly in the main due to the rather extravagant hopes, raised by Professor Goddard (I) in 1919, that a projectile might actually be sent into interplanetary space. Esnault-Pelterie (2) and Hermann Oberth (3) have more recently reaffirmed this possibility. Experiments by the late Max Valier, Reinhold Tilling, Darwin Lyon, Goddard himself and others have sustained the attention given to the matter. Prof. Richardson's article on jet propulsion (AERONAUTICAL JOURNAL, Jan., 1931) should be referred to. Mr. David Lasser's recent book (4) gives a fair general view of the subject, and the author's paper to the Society of Engineers (May 2nd, 1932) may also be of interest.