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 but one pair of screws,
acting upon one set of inclined wings, a slight retrograde horizontal
movement would be produced in addition to the vertical movement, as
the current of blast from the screw would react upon the screw itself
with a force greater than that with which it would impinge upon the
wings, where a part of the blast will inevitably be wasted. But there
being two pairs of screws, acting in opposite directions, they will
neutralise each other's horizontal movement, while combining in the
production of vertical movement. So, at least, reasons our inventor;
but however ingenious this expedient, its efficiency may well be
doubted, when we remember the immense amount of resistance, offered by
the surface of the balloons, which would have to be overcome.

'To obtain lateral movement, the action of one pair of screws is
suspended, leaving the other pair in motion: the ship, according to
the calculation of M. Pétin, will immediately describe a curve, and
turn.

'Such is the air-ship constructed by M. Pétin; but, unhappily for the
demonstration of his views, the French government, either from fear of
accident, or from some other motive, has interdicted its ascension;
and the vessel which, three months ago, was ready--crew, captain, and