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.

The Wright brothers made careful observation of the flight of birds, and fourd their observations A'aluable. It is interesting to consider the resemblance and differences of the manufactured aeroplane and the living bird. The resemblance may be simply the result of copying the bird, or it may be that similar designs have been arrived at independently by birds and men. The wings of both are roughly the same shape : of wide span, and narrow in the direction in which the bird flies ; both have concave wings with thick leading edges. In many aeroplanes hollow spars arc used like bones and like the quills of the feathers of birds. We copy plants also in this respect, for they too have learnt the economy of material in the use of hollow spars. The bodies of airships {iresimilar in shape to the bodies of swimming animals, with the greatest width towards the head. The bodies of birds are of similar form.

The essential points of any anemometer are that it should be correctly calibrated and should read accurately over the whole range through which it is to be used, and that the calibration should not alter with time. The actual calibration of an anemometer by a direct comparison of its readings with its rate of movement through the air is a matter of very great difficulty, and the various methods by which it has been done will be considered later, but when it has once been cairied out for one anemometer all others can be easily calibrated from that one by comparison.

That vertical currents or components of air-motion having a velocity of several meters per second occasionally occur in the lowest tow kilometers of the atmosphere is an observed fact, but we are far as yet from compleate knowledge as to the conditions which produces such motion

I suggest, however, that wave-motion proper, that is low-velocity, periodic oscillations of pressure or temperaturem whether transmitted from a distant source of disturbance, or occurring under the continuous interaction of two horizontal currents of air can be ruled from any list of hypothetical causes of important vertical motion.

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.

The following table is the result of a series of tests carried out at East London College (University of London) on various methods of mounting flexible steel cables, in cable ends.

The specimens were kindly supplied by Messrs. T. W. K. Clarke and Co.

Cables Nos. 1 and 3 were fixed in the following manner. The ends were knotted and tinned, then inserted in sockets or cable ends, and solder run in.