During the past year the question as to the relative advantages of monoplane and biplane types has been brought very much to the fore owing to the unfortunate accidents that have occurred—the accidents in this country being all on the monoplane type of machine. In the present paper a comparison has been made of the stresses set up in the various parts of the two types, so that conclusions might be drawn as to the limits, if any, between which each type was most suitable. A further note is included giving a short comparison as to their respective aerodynamical qualities, so that the whole survey might be as complete as'possible.

Devices thus spoken of are for the most part not concerned with stability of aircraft in the strict sense, they mostly pay no heed to the rotational energy stored in the aeroplane's mass, or the oscillation due thereto, or to their decrement, but, still, they strive in a vague way after one of the following :— (a) Its safety in the air. (b) Its staying truly on its path. (c) Its steadiness as a gun-platform or view-platform, and as such are worthy of review.

This small addition to the evening's programme has been made possible by the courtesy of Mr. Mervyn O'Gorman, who has cut out a portion of his lecture in order to make room for me. You, as scientific people, will realise that this is just about as generous a thing as a man can do, and I can assure Mr. O'Gorman that I am proportionately grateful.

The title of Mr. O'Gorman's lecture has suggested to me that perhaps after all the simplest and most readily comprehensible way of describing this machine is to present it in its aspect of a combination of a number of stability devices. This lecture will therefore be more qualitative than quantitative.