a rupture of equilibrium around the central fulcrum, and thereby changing the upward movement of the balloons into an oblique forward movement.  In other words, the ship being raised into the air—­to the stratum immediately above the region of storms—­and maintained there by the ascensional force of the balloons, and being forced onward by the screws, the four anterior wings are to be opened, the four posterior ones remaining closed.  The forepart of the ship being now relieved from the downward pressure of the air, caused by the upward movement of the balloons, this pressure still acting on the posterior wings, its equilibrium is destroyed; the forepart rises, the hindpart dips, thus changing the direction of the ship’s course, by converting its vertical into an oblique movement, which is to carry it onward upon a plane inclined slightly upward.

’This operation is to be followed by its converse.  The four posterior wings are to be opened, and the four anterior ones closed; the vessel now dips in the opposite direction, and moves forward on a plane inclined slightly downward; and so on.  Thus, by alternately opening and shutting the two sets of lateral wings, M. Petin proposes to make his ship sail forward on a series of inclined planes, upwards and downwards.  He takes care to assure us, however, that the requisite degree of inclination will be so slight as to be imperceptible to his passengers; and instances, in corroboration of this opinion, the beds of rivers, where a very slight degree of inclination suffices to produce a rapid current.

’In order to determine perpendicular movement, the central wings—­which, according to M. Petin, when placed in an oblique position, will constitute the fulcrum—­are to be brought into an upright position, thus offering no resistance to the air; the two pairs of screws are then made to turn in opposite directions with great velocity, forcing powerful convergent currents of air upon the two sets of lateral wings, maintained in oblique and opposite positions.  The force of these currents, being decomposed by the resistance of the wings, is thus changed into a perpendicular pressure, acting upwards or downwards according to the position of the wings; by means of which the aeronaut hopes to be enabled to ascend or descend without losing either gas or ballast.

’This decomposition of the force of the currents produced by the screws, is analogous to that effected by the sails of a ship sailing across the wind; where, the sails being inclined at an angle of 45 degrees to the course of the wind, the ship is impelled onwards in a direction at right angles to that of the wind:  the only difference in the two cases being this—­namely, that in the sails of the ship, the axis of inclination, represented by the mast, is vertical, creating horizontal movement; while, in the wings of the air-ship, the axis of inclination—­the pivot on which they turn—­is horizontal, creating vertical movement.  Were there