on the small scale; while on the grand scale we have the axes of the earth and all celestial orbs as examples. A smooth thin stone thrown through the air keeps its plane of rotation nearly constant even when a high wind is blowing, the slight rotation in its own plane keeping it therein.

From experiments given in a former paper; ^* it was shown that when very oblique planes are moved through the air with the anterior edge only slightly elevated, there is not then much power wasted in driving a mass of air before them in a horizontal direction, and more than this there is a considerably less mass of air forced downwards, the inertia and elasticity of the air tending to impart great upward pressure unto the plane.

In a second paper^† it was endeavoured to show how very thin planes could be preserved at a certain small angle, by letting them form the tensile radii of a large wheel, the circumference of which forms the basis or skeleton thereof.

If planes were made to travel in a rectilinear direction instead of in a circle, then, provided they could be kept in that line, the theoretical conditions for flight would be attained; for all the particles of the plane, by their direction and momentum, would contribute to the result; but as practical difficulties appear to be in the way, it becomes a matter of interest to enquire if the greater part of the weight of a wheel could not be so placed at its circumference as to obtain all the advantages of the rectilinear motion of the planes, while the weight absolutely necessary at the circumference of the wheel can at the same time be utilized as actually affording the best of all means of preserving it in its position of equilibrium after the manner of a gyroscope.

To effect this a wheel was constructed about thirty inches in diameter having a metal rim and with a light axis supported in the centre by tensile radii; the radii being nearly horizontal by construction there is little air be displaced, and the resistance to the circular motion of the wheel is nearly reduced to the mere rubbing friction of the atmosphere; a great velocity can therefore be imparted to the wheel. When the axis is waxed it can be so rapidly rotated by the hands that, notwithstanding its weighing half a pound, the wheel rises for a short time off the floor, and the same if weighted; a considerably slower speed will however keep it in its plane of rotation, thereby proving that a lighter rim can be used. In large wheels paper tubing would be unequalled for rigidity and strength. A small wheel on the same principle was therefore constructed with a cane in place of a metal rim which manifested great buoyancy when rotated.

In order to prevent the framework or car which carries the wheel from rotating, I have attached another tension wheel thereto, with the opposite

edges of its planes or radii elevated, and as this requires to be turned in an opposite direction, therefore the car is kept from rotating. In the model there is a crank in each of the axes and at the same height, and each crank is connected by a rod to a vertical pedal common to both; in this manner both wheels are compelled to rotate with the same speed but in opposite directions; it then follows that by turning only one of the cranks by the hand the whole apparatus would by reaction be guided in azimuth when required. In order to apply any power or force we must have a basis or part which acts as a fulcrum wherein action and reaction can have full sway. In birds and all flying creatures each wing is paired with another.

In the working compartment of this model the attempt has been made to so arrange the parts as to utilize the immense force which the human form is so eminently capable of exerting. The machinery is reduced to the simplest form, namely the two perpendicular winches between which manual power can be exerted in a sitting posture. These winches are merely U shaped bends in the prolonged axes of the tension wheels. Let us consider the power that can be exerted by the pull stroke. It is considered that, in rowing, manual power is applied in a very advantageous manner: the feet are firmly planted and the arms and shoulders react from them. It will be seen by the model that the feet can be placed on the nearly vertical pedal; great force could therefore be exerted by the legs alone: in fact great force can be exerted by the human form between two cranks in almost every part of the revolution when they go round in opposite directions. It is not expected that full manual power can be exerted continuously, as it is found that most work is done when there is a short period of rest, as in rowing; but it might be expedient to exert full power at some particular part of the revolution, hence the present arrangement whereby the feet or hands can be used either together or alone, thus avoiding dead points and allowing of the hands being used for steering. That far more power can be exerted by the legs than by the arms is easily proved by the fact of the weight of the body being raised for a whole day long in scaling mountains, whereas if the arms were to be used in pulling the body up under a ladder or an inclined rope, a few minutes would lead to exhaustion; and even if the power of the arms alone were used in any other mechanical arrangement, it would still be fatiguing. The arms working however between two vertical cranks allows of power being exerted in four ways; 1st., in pulling from the front, as in rowing; 2nd., in pushing in the opposite direction or forwards; 3rd., in pulling the cranks nearer to the body laterally; and 4th., in the reverse direction or pushing laterally outwards; and as this possibility of change is really important from its allowing one set of muscles to rest whilst others are operating, an account of a simple arrangement for varying

the method of working the feet may not be undesirable. If the broad pedal have the middle portion removed, and another pedal be inserted and made to work loosely on the same fulcrum, a double or rather quadruple pedal is formed; the top of this middle pedal is also connected by rods to the vertical axes of the tension wheels but by additional cranks placed on the opposite sides of the centres. In this manner the feet can reciprocate with one another as in walking or similar to their action in bicycles, and in a great variety of ways reciprocate with the arms.

This is all the machinery absolutely necessary for the purpose of elevation, and, as before remarked, the extra power required for progression and steering is comparatively small and can easily be applied as shown in the drawing, fig. 5, in which the axis of the upper tension wheel passes through the tubular axis of the lower one, and the framework or car is placed below; a horizontal axis is also shown as receiving motion by bevelled wheels, thus turning the vertical tension wheel, the vanes of which are set to about 20° and act as a screw propeller; while an expanding and completely adjustable fan in the rear acts as an auxiliary in steering, for it must be borne in mind that the sectional area of the machine is very small and in fact approaches to that of discs progressing edgeways.

A bird in full speed sailing through still air may be likened to the keel of a ship cutting through the water; the permanency of its direction must be very great. This persistency of its direction is, I think, made use of for buoyant purposes in high winds in a way that appears hitherto to have been overlooked. For instance a bird, in two parts of its evolutions, is travelling transversely to the direction of the wind, and when in these positions it can often be observed to elevate the tip of that wing on which the wind first impinges, while at the same time the other wing is slightly depressed. The under surface of the wings thus receive the wind, which is thus transformed into an elevating force; it is clear that a very long sweep can be thus made, for there is no head wind to impede the bird, but only the ordinary resistance of still air to be overcome. In wheeling in the air, it may also be observed that, as soon as the tip is brought down from the elevated position to the horizontal, the bird commences flapping its wings. Every current of air can thus be utilized by the bird, which does not appear to fly long directly against the wind, but it wheels and tacks to prevent fatigue. In fact, many sea-birds appear to fly with greater ease and swiftness when a stiff breeze is blowing, and it may be observed that they keep continually on the wing in gales, but rest much in calms as they sooner tire. When a bird has been elevated whilst sailing transversely to the wind as alluded to above, and also possibly when sailing a short time against the wind, it can then,