st limits of his desires in either
direction, whatever may be the size of his Balloon. Now a resistance
equal to many pounds is attainable by an inclined plane of even
moderate dimensions when propelled even with moderate velocity; and
being readily governed by the mere inclination of the impinging plane
at the will and by the hand of the aerial voyager, it will be in his
power to vary the level of his machine with very considerable nicety;
enabling him to approach the surface of the earth, or in a gentle
curve to sweep away from its occasional irregularities, and proceed to
a very considerable elevation without interrupting the progress of his
course, and, what is of more importance, without sacrificing any part
of his resources in gas or ballast, upon the preservation of which the
duration of his career so entirely depends. These properties of the
rudder it is not possible to display in the present exhibition, owing
to the confined nature of the course which it is necessary to pursue;
but they were sufficiently tested in the preliminary experiments at
Willis's Rooms, where the space being larger, a circular motion was
conferred upon the machine by connecting it with a fixed centre round
which it was thus made to revolve, without the necessity of confining
it to the one level.

The rate of motion which the Balloon thus equipped is capable of
accomplishing varies according to the circumstances of its propulsion.
When the Archimedean Screw precedes, the velocity is less than when
it is made to follow, owing to the reaction of the air in the former
instance against the car, the under surface of the balloon, and other
obstacles, by which its progress is retarded. Again, when the cord
upon which it travels is most tense and free from vibration, the rate
is found to be considerably accelerated, compared with what it is when
the contrary conditions prevail. But chiefly is its speed affected
by the proper _ballasting_ of the machine itself, upon which,
depends the friction it encounters from the cord on which it travels.
Under ordinary circumstances it proceeds at a rate of about four miles
an hour, but when the conditions alluded to have been most favourable,
it has accomplished a velocity of not less than five; and there is no
doubt that were it altogether free from restraint, as it would be in
the open air, with a hand to guide it, its progress would be upwards
of six miles an hour.

Having now, I trust, sufficiently expl