No one denies that speed is an essential to air travel. It seemed curious to me that air liners were operating at speeds varying from 100 to 150 miles an hour, and some months ago I set out to find a logical basis for determining the most economical speed of flight. I did not expect to arrive at an exact solution; but, rather to my surprise, I satisfied myself that I could give a general answer to most of the problems that interested me. I ventured to submit my calculations in a short memorandum to the Aeronautical Research Committee, and I had the privilege of meeting a sub-committee with whom I discussed my ideas. It was suggested that some further calculations on the same lines would be of interest, and it was proposed by Mr. Tizard, the Chairman of the main committee, that I should send a communication on the subject to the Aeronautical Society. The paper that I am reading to-night is the result of this suggestion.

Major Green in his paper has given prominence to a subject which is now becoming of wide interest and great commercial importance. A method of assessing the economic value of speed is very desirable and Major Green has attempted to do this by means of an index figure.

I would like to put forward a method which, whilst it does not provide a datum or index figure, offers a ready method of comparing two or more machines, taking into account those features of the aircraft which are of economic importance. It must be accepted that the geographical and political features of different routes, time-tables, and other such extra-to-aircraft items could be included in any method of comparison without the use of an empiric formula, the relative importance of whose terms would be largely a matter of opinion. Further, this method is based not on subsidy earning but profit earning capacity.

Snow falls in a great variety of forms, depending on a large number of conditions affecting the crystallisation of the moisture in the atmosphere. The forms may even vary from place to place or from time to time in one storm.

The character of snow as a medium for transportation depends not only on the form of its constituent crystals, but on the nature of the ground on which they fall, the depth of the total covering, the previous history of the underlying layers, and of course on the history of the last fall and the atmospheric temperature of the moment. Considering the characteristics for the purpose of aircraft operation, it is sufficient to make the broad classifications shown in Table I (page 504).

If the man in the street is asked his opinion of the future of aviation, he will almost invariably reply, “ Everyone will have an aeroplane on his roof and go straight up like this.” Whereupon he will go through the traditional motion of the spiral staircase joke.

The expert pilot or technician of to-day, overhearing this remark, smiles in a superior way. In his mind are two contrasting pictures : That of a city over which whirligigs are springing up from adjacent roof tops; and that of the vast empty spaces of even the busiest airport as he knows it.

In the stressing of aeroplane wing spars account must be taken of end load, particularly when this end load is compressive. When the end load is continuous over each bay the strength of the spars may be calculated by what is known as the Berry method. It may happen, however, that owing to drag loads the end load may vary in the different portions of a bay, and in such circumstances it is customary to average out the various end loads and to regard this average load as acting over the whole bay. This practice is based on an investigation by Miss Cave-Browne-Cave in which the stability of a strut was considered, having regard to different compressive loads acting over each of the two portions into which the strut was divided. Miss Cave, who dealt only with compressive loads whose lines of action were parallel, found that the failing load for the whole strut was very approximately equal to the arithmetic mean of the two compressive loads which in combination produced instability failure.