Perhaps nothing reveals the weakness of a flying boat and its equipment with more rapidity and certainty than a cruise which involves a prolonged absence from organised bases.

Relatively few have had this unique experience, and unhappily no designers of air craft in this country. Words alone cannot conjure up the atmosphere, the petty anxieties, the continual working against time, the struggle in rain and rolling swells, the idiosyncrasies of motor boats, the enthusiasm of crews snatching food when they can get it, and a thousand ills that flying boats are heir to. But it is an exhilarating life that takes a firm hold of all that fall beneath its influence.

In Part I. of this paper the theoretical stress analysis was given for a hexagonal braced tubular structure, supported at one end and subjected at the other to a system of longitudinal forces, giving no resultant load and no resultant couple. This tube had no bracing members in the planes of the bulkheads.

Among the various applications of meteorology to the practical requirements of everyday life, the observation of fog, as a meteorological element, has. been associated primarily, in the past, with locomotion on land and with navigation on the sea. The first scale of fog intensity used by meteorological observers in this country was, in fact, based on the effect of different degrees of atmospheric obscurity on navigation. The scale was drawn up in 1903 as the result of an investigation into the conditions of formation of London fogs, and subsequently modified by the Meteorological Office, in conjunction with the Admiralty and Trinity House (see Table I.). It included five specifications of fog intensity ranging from a clear atmosphere free from fog or mist, represented by “ of,” to a thick fog, denoted by “ sf.”

Within the last twelve years, while the importance of fog as an obstruction to road and rail transport and to shipping has in no way diminished, the reporting and forecasting of fog has assumed a new significance in relation to air navigation.

Perhaps I had better begin my story by giving you a very brief resume of my flight outwards to Cape Town. The flight was made possible by the very enterprising support of the Argus South African Newspapers, who purchased the Moth for me. When the flight was completed the machine was given to me ; hence the possibility of my returning, in a purely private sense, as I have done this year.

Racing airscrews differ essentially from Service or commercial types by reason of the extreme values of engine horse-power, revolutions and forward speed which enter into the specified requirements.

These three variables, associated with the condition that the thrust–horsepower shall be a maximum, determine the airscrew completely, but the exceptional values which they assume for racing aircraft have various important reactions on the efficiency obtainable.

Thus high power and revolutions, especially the latter, have a distinctly detrimental effect, whereas high forward speed contributes to a large extent to restore the position.

I propose to examine very briefly the relative importance of these factors and to indicate how they influenced the process of selection and design in the particular conditions of last year's race.

Let us first consider a typical power curve (Fig. I). As it is not permissible at this stage to publish actual figures in detail I have made use of relative scales which should be sufficient for our purpose.

In the Wilbur Wright lectures we commemorate, and pay our tribute to, that pioneer work upon which the art of flying is founded and it is only now that carrying our minds back to those early days we see how thorough were the methods which led to success. The work of Lilienthal in gliding with curved wings—brought to an untimely end through lack of control—had shown that the secret of success was to be found in free flight experiment. Then came the great contribution of the Wrights, who discarded Lilienthal's acrobatic control and carrying through the whole modern programme of wind tunnel research, detail design and construction, found out by practical flying that essential feature of control which has been used in practically every aeroplane that has been flown.

In the original Wright aeroplane, as in all its successors of fixed wing area, the only means used for varying the lift was by alteration of the angle of incidence or of the camber of the wing either by warping or by the equivalent use of ailerons.

Aero engines, whether in Service or Civil use, work under very different conditions from engines used in mechanical transport. It is absolutely necessary that a high standard of reliability should be constantly maintained, although long periods of full-throttle, or nearly full-throttle running militate against this, especially when it is considered that the weight of these engines has to be cut •down in every possible manner.

When Trans-Arctic transportation becomes common, when air routes take full advantage of great circle courses, when we travel from New York to New Guinea via Point Barrow, Alaska, from Chicago to China almost hitting the North Pole on the way, and from San Francisco to Moscow via Spitsbergen, then, and then only, will those concerned with aerial transportation realise the facilities the Arctic affords the aerial navigator.

The Air Mail route from Cairo to Baghdad is now securely established. Seven years ago the major portion of it, from Transjordan to Iraq, was no more than a project in certain far-seeing minds. The maps of this region between Amman in Transjordan and Ramadi, a little market town on the Euphrates, 65 miles west of Baghdad, were until 1921 painfully reticent. The countries of Egypt, Palestine, and to some extent Transjordan, had been fairly accurately mapped for some time, and were flown over extensively during the war by ourselves and the Germans. The landmarks are generally speaking abundant, and from the navigational point of view they therefore present no outstanding difficulties.