The subject of full-scale aeroplane experiments is one which I am sure is of interest to all concerned in aeronautical engineering. The interest of the present paper would be increased if it were possible to include in it detailed descriptions of actual experiments, numerical results, and a discussion of their bearing on design. It will be realised that this is impossible. With so much to choose from each of a number of experiments would deserve fully the time which I have to divide among them all, and a paper with this title can only be a survey of the whole field, dealing with certain general questions of importance.

An instrument to indicate whether, under all conditions, the path of the aeroplane is a straight line or whether it is turning to the right or left, is much required. It is well known that when flying in a cloud or at night, and no fixed object is visible, even the most experienced pilot may, without realising it, be flying on a sharp curve. If, however, the angle of banking is great the muscular reaction of his body will have to be increased to counteract the increased force acting on it. This will tell him that his course is not straight, but there is nothing to show whether he is on a right-hand or left-hand turn. If he tries to straighten his course he is just as likely to increase the curvature as to straighten out.

To anyone who has made a careful study of aeronautics and its possibilities in the commercial world it is evident that South America offers unusual opportunities for development by aircraft, and of all South American countries Peru, on account of its climate, its rich natural resources, its geographical position and its peculiar topographical configairation, is almost ideal. To fully appreciate the significance of this remark it is necessary to have a very clear conception of all those factors which go to make aerial transport a commercial possibility.

This war has been fought with machines made of wood, a most unsatisfactory material from a constructional point of view. Wood warps and cracks; is unsuitable for tropical climates; splinters easily in a crash; is liable to transfix the aviators; is non-homogeneous; uncertain in strength and weight; weakens rapidly when exposed to moisture; and is not produced in any quantity in this country.

Since I was asked in September last to read this lecture conditions ha\c •so chang-ed that it has, been necessary totally to re-cast and re-write what I then proposed to say. A large amount of information as to the lactual achiexe- ments of airships has been published and also perhaps an even larger amount of speculation as to their future possibilities. What will, therefore, probably Tdc of interest to a technical society such as this is a general outline of tlie ships as they exist at the stage to which they have been developed during the war.

In order to make clear the various matters which inlluence the lift and behaviour of an airship, I have introduced a small amount of aerostatics which will appear obvious and unnecessary to many, but may help others to the understanding of the more interesting points treated later.

The extent of the detail which I have been allowed to include in the lecture, although such matters have not been published before, leaves the Society with .a very deep debt of gratitude to the Admiralty.