It has never been tried with power, and it is doubtful whether it would be successful as a sustaining surface for flying machines, for the same reasons that caused failure with the box-like formation of the Voison Machine. THE DELTOID.--The deltoid is the simplest, and the most easily constructed of all the kites. It is usually made from stiff cardboard, A-shaped in outline, as shown in Figs. 44 and 45, and bent along a central line, as at A, forming two wings, each of which is a right-angled triangle. _Fig. 44. and 45. Deltoid Formation._ The peculiarity of this formation is, that it has remarkable stability when used as a kite, with either end foremost. If a small weight is placed at the pointed end, and it is projected through the air, it will fly straight, and is but little affected by cross currents. THE DUNNE FLYING MACHINE.--A top view of this biplane is shown in Fig. 46. The A-shaped disposition of the planes, gives it good lateral stability, but it has the disadvantage under which all aeroplanes labor, that the entire body of the machine must move on a fore and aft vertical plan in order to ascend or descend. _Fig. 46. The Dunne Bi-plane._ This is a true deltoid formation, as the angle of incidence of the planes is so disposed that when the planes are horizontal from end to end, the inclination is such as to make it similar to the deltoid kite referred to. ROTATING KITE.--A type of kite unlike the others illustrated is a rotating structure, which gives great stability, due to the gyroscopic action on the supporting surfaces. Fig. 47 shows a side view with the top in section. The supporting surface is umbrella-shaped. In fact, the ordinary umbrella will answer if not dished too much. An angularly-bent piece of wire A, provided with loops B, B, at the ends, serve as bearings for the handle of the umbrella. At the bend of the wire loop C, the cord D is attached. The lower side of the umbrella top has cup-shaped pockets E, near the margin, so arranged that their open ends project in the same direction, and the wind catching them rotates the circular plane. _Fig. 47. Rotable Umbrella Kite._ KITE PRINCIPLES.--A careful study of the examples here given, will impress the novice with one important fact, which, in its effect has a more important bearing on successful flight, than all the bird study and speculations concerning its mysteries. This fact, in essence, is, that the angle of the kite is the great factor in flight next to the power necessary to hold it. Aside from this, the comparison between kites and aeroplanes is of no practical value. Disregarding the element of momentum, the drift of a machine against a wind, is the same, dynamically, as a plane at rest with the wind moving past it. But there is this pronounced difference: The cord which supports the kite holds it so that the power is in one direction only.