The subject defined by the title of this paper is one which cannot be covered completely in the time at my disposal. I propose therefore to confine my remarks to-night almost entirely to the aerodynamic aspects of the problem and to put before you some possible advantages that may be gained by substituting a variable pitch airscrew for the normal fixed pitch airscrew, and in certain cases to compare the results with those given by the introduction of a variable gear airscrew. The mechanical side of the problem is a subject complete in itself and will not be dealt with here.

The petrol engine has become so firmly established as the motive power for aircraft, automobiles and small vessels that a short while ago it would have seemed almost impossible that its supremacy could be challenged. It is no exaggeration to say that it was the petrol engine which made aircraft possible, while on the road, despite the fact that the steam engine is fundamentally more suited for traction work, the petrol engine has practically ousted its rival from the field. Even for the heaviest vehicle, where, owing to cheap coal, the lower running cost at one time gave the steam vehicle an advantage, the petrol engine is nearly universal, while at sea, for launches and small craft, the steam engine has practically disappeared.

“ The last thing I purposed to speak of, is, Those several Qualities of Timber or of Trunks, by which they are fitted for Mechanical Use.…. The Visible Causes whereof are observable. Partly in the Structure of the several Parts; sc. the Insertions, Sap-Vessels and Aer-Vessels; as to the Number, Size or Position of any of them. And partly, in the Nature of the Parts; I mean such as is manifest to sense. According to our clear and distinct observing of all which Causes, we may understand, Wherefore any Wood is made use of for any certain purpose. And also, wherein fitly to apply it to further Use.”

Three great drawbacks of modern aeroplanes, from a safety point of view, are their tendency to stall, their high landing speed, and their low gliding angle.

The use of wing-tip slots for preventing lateral instability is well known, but they do not materially reduce the landing speed. Moreover, they cannot be used along the whole span without making the wing unstable. The best length of wing-tip slot for securing stability and maintaining the lift coefficient is about 40 per cent, of the semi-span.

In the year 1884 the annual meeting of the Aeronautical Society was held in the rooms of the Society of Arts on the 2nd July. In those days the Society held one meeting only each year, and there were usually three or four papers read. On this occasion, the chairman was Mr. James Glaisher, F.R.S., and in his opening address he referred to the little progress which had been made during the past year, but drew consolation from the fact that there were still many earnest workers actively employed who were working more persistently and more perseveringly than ever. He also stressed the importance of experiment, stating that although the experimenter might not succeed, he could not make any experiment without increasing our knowledge in the way we desire it to be increased.